Compositions and methods for improved adeno-associated viral gene therapy

Abstract

Provided herein are targeting agents, such as recombinant adeno-associated virus (AAV) capsid proteins, that contain an artificial peptide insert, as well as AAV particles containing such capsid proteins and methods of administering such AAV particles to a subject, e.g., so as to express a transgene of interest.

Description

[0001]ATTORNEY DOCKET NO.: 51772-005WO3 PATENT COMPOSITIONS AND METHODS FOR IMPROVED ADENO-ASSOCIATED VIRAL GENE THERAPY SEQUENCE LISITING The instant application contains a Sequence Listing which has been submitted electronically in XML format and is hereby incorporated in its entirety. Said XML copy, created on March 27, 2025, is named “51772-005WO3_Sequence_Listing_3_27_25.xml” and is 470,048 bytes in size. BACKGROUND Recombinant vectors derived from adeno-associated viruses (AAVs) have become a prevalent modality in gene therapy due, at least in part, to the remarkable safety profile of this non-pathogenic virus, as well as its potential to achieve transgene expression in a variety of tissues. Intramuscularly or intravenously administered AAV vectors have been explored as a vehicle for the delivery of various transgenes, including therapeutic and prophylactic proteins. Despite early successes in proof-of-concept studies, the clinical development of intramuscularly or intravenously administered AAV vectors has largely been limited as a result of insufficient potency, as the transduction efficiency that natural AAV serotypes exhibit – particularly for muscle cells – is often too low to achieve adequate levels of therapeutic or prophylactic protein secretion to the serum. Accordingly, there remains a need for AAV vectors that effectuate enhanced transduction activity, whether provided intramuscularly, intravenously, or by way of another route of administration. SUMMARY OF THE INVENTION The present invention addresses the limitations of adeno associated viruses (AAVs) used in gene therapy. Historically, these vectors have been hindered by insufficient transduction efficiency, leading to inadequate levels of transgene expression. To address this, the current disclosure describes the discovery and optimization of peptide inserts that, upon incorporation into an AAV capsid protein, enhance transduction efficiency, tropism, and biodistribution in targeted tissue. Also described herein are exemplary processes for incorporating peptide inserts of the invention into an AAV capsid protein, producing recombinant AAV particles containing peptide inserts disclosed herein, and administering recombinant AAV particles to a patient in need thereof through various routes described herein. Peptide inserts of the invention may have a core motif of three amino acids (e.g., MPR). A surprising benefit of the MPR motif is that MPR-containing peptides can confer a transduction advantage when inserted into AAV capsid proteins. This effect is observed regardless of the peptide insert’s length, provided that the MPR core motif sequence is present within the inserted peptide. Additionally, described herein is the discovery that the position of the core MPR motif within the peptide sequence is flexible, allowing for frame-shifting capabilities. This flexibility means that the MPR motif can be positioned at various frames within the peptide sequence while maintaining its transduction-enhancing properties. Thus, MPR-containing peptides can confer enhanced transduction or tropism, regardless of the peptide’s length or the exact positioning of the MPR motif sequence within the peptide. In addition to being incorporated into AAV capsid proteins, peptide inserts of the invention can also be incorporated into other viral proteins. Furthermore, peptide inserts of the invention can be used as ATTORNEY DOCKET NO.: 51772-005WO3 PATENT targeting agents for various drug delivery systems. Non-limiting examples of drug delivery systems are lipid nanoparticles (LNPs), exosomes, and liposomes. Peptide inserts used as targeting agents (e.g., attached to an LNP) may have increased transduction efficiency and tropism in target cells (e.g., muscle cells or cells of the nervous system). In a first aspect, the disclosure features a targeting agent comprising an artificial peptide insert, wherein the peptide insert comprises a contiguous methionine-proline-arginine (MPR) tripeptide segment. In some embodiments, the targeting agent comprises an artificial peptide insert that is conjugated, either covalently or noncovalently, to a lipid nanoparticle (LNP), liposome, lipoplex, exosome, or vesicle. In some embodiments, the targeting agent comprises an artificial peptide insert that is incorporated into an AAV capsid protein. In some embodiments, the peptide insert has a length of at least 4 amino acids, optionally wherein the length is 4-40 amino acids, optionally wherein the length is 4-35 amino acids, optionally wherein the length is 4-30 amino acids, optionally wherein the length is 4-25 amino acids, optionally wherein the length is 4-20 amino acids, optionally wherein the length is 4-15 amino acids, optionally wherein the length is 4-10 amino acids. In some embodiments, the peptide insert has a length of 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In some embodiments, the peptide insert has a length of at least 5 amino acids, optionally wherein the length is 5-40 amino acids, optionally wherein the length is 5-35 amino acids, optionally wherein the length is 5-30 amino acids, optionally wherein the length is 5-25 amino acids, optionally wherein the length is 5-20 amino acids, optionally wherein the length is 5-15 amino acids, optionally wherein the length is 5-10 amino acids. In some embodiments, the peptide insert has a length of 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In some embodiments, the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids. In some embodiments, the peptide insert has a length of 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In some embodiments, the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids. In some embodiments, the peptide insert has a length of 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In some embodiments, the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally ATTORNEY DOCKET NO.: 51772-005WO3 PATENT wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids. In some embodiments, the peptide insert has a length of 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In some embodiments, the MPR tripeptide segment appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between. In some embodiments, the MPR tripeptide segment appears at frame 1 of the peptide insert. In some embodiments, the MPR tripeptide segment appears at frame 2 of the peptide insert and the peptide insert has a length of at least 4 amino acids, optionally wherein the length is 4-40 amino acids, optionally wherein the length is 4-35 amino acids, optionally wherein the length is 4-30 amino acids, optionally wherein the length is 4-25 amino acids, optionally wherein the length is 4-20 amino acids, optionally wherein the length is 4-15 amino acids, optionally wherein the length is 4-10 amino acids. In some embodiments, the MPR tripeptide segment appears at frame 3 of the peptide insert and the peptide insert has a length of at least 5 amino acids, optionally wherein the length is 5-40 amino acids, optionally wherein the length is 5-35 amino acids, optionally wherein the length is 5-30 amino acids, optionally wherein the length is 5-25 amino acids, optionally wherein the length is 5-20 amino acids, optionally wherein the length is 5-15 amino acids, optionally wherein the length is 5-10 amino acids. In some embodiments, the MPR tripeptide segment appears at frame 4 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids. In some embodiments, the MPR tripeptide segment appears at frame 5 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids. In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of IMPR (SEQ ID NO: 512). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of AMPR (SEQ ID NO: 513). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of FMPR (SEQ ID NO: 514). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of MMPR (SEQ ID NO: 515). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of QMPR (SEQ ID NO: 516). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of YMPR (SEQ ID NO: 517). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of MPRT (SEQ ID NO: 518). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of MPRY (SEQ ID NO: 519). In another aspect, the disclosure ATTORNEY DOCKET NO.: 51772-005WO3 PATENT features a peptide insert comprising an amino acid sequence of MPRQ (SEQ ID NO: 520). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of MPRS (SEQ ID NO: 521). In some embodiments of the foregoing aspects, the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 1 of the peptide insert. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 5 amino acids, optionally wherein the length is 5-40 amino acids, optionally wherein the length is 5-35 amino acids, optionally wherein the length is 5-30 amino acids, optionally wherein the length is 5-25 amino acids, optionally wherein the length is 5-20 amino acids, optionally wherein the length is 5-15 amino acids, optionally wherein the length is 5-10 amino acids. In some embodiments, the peptide insert has a length of 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids. In some embodiments, the peptide insert has a length of 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids. In some embodiments, the peptide insert has a length of 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids. In some embodiments, the peptide insert has a length of 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. ATTORNEY DOCKET NO.: 51772-005WO3 PATENT In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of IMPRT (SEQ ID NO: 490). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of AMPRY (SEQ ID NO: 522). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of MPRTA (SEQ ID NO: 523). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of MPRYG (SEQ ID NO: 524). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of MPRQP (SEQ ID NO: 525). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of MPRTP (SEQ ID NO: 526). In some embodiments of the foregoing aspects, the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 1 of the peptide insert. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids. In some embodiments, the peptide insert has a length of 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids. In some embodiments, the peptide insert has a length of 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids. In some embodiments, the peptide insert has a length of 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 9 amino acids, optionally wherein the length is 9-40 amino acids, optionally wherein the length is 9-35 amino acids, optionally wherein the length is 9-30 amino acids, optionally wherein the length is 9-25 amino acids, optionally wherein the ATTORNEY DOCKET NO.: 51772-005WO3 PATENT length is 9-20 amino acids, optionally wherein the length is 9-15 amino acids, optionally wherein the length is 9-10 amino acids. In some embodiments, the peptide insert has a length of 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of IMPRTA (SEQ ID NO: 527). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of AMPRYG (SEQ ID NO: 528). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of MPRTAG (SEQ ID NO: 493). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of MPRYGG (SEQ ID NO: 529). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of MPRQPG (SEQ ID NO: 530). In another aspect, the disclosure features a peptide insert comprising an amino acid sequence of MPRTPG (SEQ ID NO: 531). In some embodiments of the foregoing aspects, the amino acid sequence appears at the first permissible frame, last permissible frame, or any frame in between. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 1 of the peptide insert. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids. In some embodiments, the peptide insert has a length of 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids. In some embodiments, the peptide insert has a length of 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 9 amino acids, optionally wherein the length is 9-40 amino acids, optionally wherein the length is 9-35 amino acids, optionally wherein the length is 9-30 amino acids, optionally wherein the length is 9-25 amino acids, optionally wherein the length is 9-20 amino acids, optionally wherein the length is 9-15 amino acids, optionally wherein the length is 9-10 amino acids. In some embodiments, the peptide insert has a length of 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. ATTORNEY DOCKET NO.: 51772-005WO3 PATENT In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 10 amino acids, optionally wherein the length is 10-40 amino acids, optionally wherein the length is 10-35 amino acids, optionally wherein the length is 10-30 amino acids, optionally wherein the length is 10-25 amino acids, optionally wherein the length is 10-20 amino acids, optionally wherein the length is 10-15 amino acids. In some embodiments, the peptide insert has a length of 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In another aspect, the disclosure features a recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (I): (X1)MPR(X2)(X3)(X4), wherein each of (X1), (X2), (X3), and (X4), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala. In some embodiments, (X1) represents Phe, Leu, Ile, Met, or Gln. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, or Ala. In some embodiments, (X1) represents Tyr, Ile, Met, Ser, or Ala. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro. In some embodiments, (X2) represents Tyr, Ser, Thr, Gln, or Asp. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Phe, Tyr, Ser, Thr, Asn, or Gln. In some embodiments, (X2) represents Tyr or Thr. In some embodiments, (X3) represents Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro. In some embodiments, (X3) represents Ile, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala or Pro. In some embodiments, (X3) represents Val, Lys, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Gly, Ala, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In another aspect, the disclosure features a recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (II): IMPR(X2)(X3)(X4), wherein each of (X2), (X3), and (X4), independently, represents any naturally occurring amino acid. ATTORNEY DOCKET NO.: 51772-005WO3 PATENT In some embodiments, (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro. In some embodiments, (X2) represents Tyr, Ser, Thr, Gln, or Asp. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Tyr or Thr. In some embodiments, (X3) represents Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro. In some embodiments, (X3) represents Ile, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala or Pro. In some embodiments, (X3) represents Val, Lys, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala, Gly, or Pro. In some embodiments, (X3) represents Ala or Gly. In some embodiments, (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Gly, Ala, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In another aspect, the disclosure features a recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (III): AMPR(X2)(X3)(X4), wherein each of (X2), (X3), and (X4), independently, represents any naturally occurring amino acid. In some embodiments, (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro. In some embodiments, (X2) represents Tyr, Ser, Thr, Gln, or Asp. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Tyr or Thr. In some embodiments, (X3) represents Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro. In some embodiments, (X3) represents Ile, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala or Pro. In some embodiments, (X3) represents Val, Lys, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala, Gly, or Pro. In some embodiments, (X3) represents Ala or Gly. In some embodiments, (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Gly, Ala, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In another aspect, the disclosure features a recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (IV): (X1)MPRT(X3)(X4), wherein each of (X1), (X3), and (X4), independently, represents any naturally occurring amino acid. ATTORNEY DOCKET NO.: 51772-005WO3 PATENT In some embodiments, (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala. In some embodiments, (X1) represents Phe, Leu, Ile, Met, or Gln. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, or Ala. In some embodiments, (X3) represents Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro. In some embodiments, (X3) represents Ile, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala or Pro. In some embodiments, (X3) represents Val, Lys, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Gly, Ala, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In another aspect, the disclosure features a recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (V): (X1)MPRY(X3)(X4), wherein each of (X1), (X3), and (X4), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala. In some embodiments, (X1) represents Phe, Leu, Ile, Met, or Gln. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, or Ala. In some embodiments, (X1) represents Tyr, Ile, Met, Ser, or Ala. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X3) represents Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro. In some embodiments, (X3) represents Ile, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala or Pro. In some embodiments, (X3) represents Val, Lys, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala, Gly, or Pro. In some embodiments, (X3) represents Ala or Gly. In some embodiments, (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Gly, Ala, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In another aspect, the disclosure features a recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (VI): (X1)MPR(X2)A(X4), wherein each of (X1), (X2), and (X4), independently, represents any naturally occurring amino acid. ATTORNEY DOCKET NO.: 51772-005WO3 PATENT In some embodiments, (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala. In some embodiments, (X1) represents Phe, Leu, Ile, Met, or Gln. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, or Ala. In some embodiments, (X1) represents Tyr, Ile, Met, Ser, or Ala. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro. In some embodiments, (X2) represents Tyr, Ser, Thr, Gln, or Asp. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Tyr or Thr. In some embodiments, (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Gly, Ala, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In another aspect, the disclosure features a recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (VII): (X1)MPR(X2)G(X4), wherein each of (X1), (X2), and (X4), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala. In some embodiments, (X1) represents Phe, Leu, Ile, Met, or Gln. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, or Ala. In some embodiments, (X1) represents Tyr, Ile, Met, Ser, or Ala. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro. In some embodiments, (X2) represents Tyr, Ser, Thr, Gln, or Asp. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Tyr or Thr. In some embodiments, (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Gly, Ala, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. ATTORNEY DOCKET NO.: 51772-005WO3 PATENT In another aspect, the disclosure features a recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (VIII): (X1)MPR(X2)(X3)G, wherein each of (X1), (X2), and (X3), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly. (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala. (X1) represents Phe, Leu, Ile, Met, or Gln. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, or Ala. In some embodiments, (X1) represents Tyr, Ile, Met, Ser, or Ala. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro. In some embodiments, (X2) represents Tyr, Ser, Thr, Gln, or Asp. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Tyr or Thr. In some embodiments, (X3) represents Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro. In some embodiments, (X3) represents Ile, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala or Pro. In some embodiments, (X3) represents Val, Lys, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala, Gly, or Pro. In some embodiments, (X3) represents Ala or Gly. In another aspect, the disclosure features a recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (IX): (X1)MPR(X2)(Nonpolar1)G, wherein (Nonpolar1) represents any amino acid having a nonpolar, neutral side chain, and wherein each of (X1) and (X2), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Val, Asn, His, Lys, or Gly. In some embodiments, (X1) represents Lys, Met, Leu, Gln, Tyr, Phe, Thr, Ile, and Ala. In some embodiments, (X1) represents Tyr, Ser, Ala, Ile, or Met. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Val, Asn, His, Gly, or Trp. In some embodiments, (X2) represents Gln, Phe, Tyr, Thr, Ser, or Asn. In some embodiments, (X2) represents Tyr or Thr. In some embodiments, (Nonpolar1) represents Phe, Met, Leu, Ala, Ile, Val, Gly, and Pro. In some embodiments, (Nonpolar1) represents Ala, Val, Ile, Gly, or Pro. In some embodiments, (Nonpolar1) represents Ala, Gly, or Pro. In some embodiments, (Nonpolar1) represents Ala or Gly. In another aspect, the disclosure features a recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (X): (X1)M(X2)(X3)(X4)(X5)(X6), wherein (X2) represents an amino acid selected from the group consisting of Pro and Ser, and wherein each of (X1), (X3), (X4), (X5), and (X6), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, ATTORNEY DOCKET NO.: 51772-005WO3 PATENT Ser, Ala, Ile, Val, Asn, His, Lys, or Gly. In some embodiments, (X1) represents Lys, Met, Leu, Gln, Tyr, Phe, Thr, Ile, and Ala. In some embodiments, (X1) represents Tyr, Ser, Ala, Ile, or Met. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Pro. In some embodiments, (X2) represents Ser. In some embodiments, (X3) represents Val, His, or Arg. In some embodiments, (X3) represents Arg. In some embodiments, (X4) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X4) represents Gln, Phe, Tyr, Thr, Ser, or Asn. In some embodiments, (X4) represents Tyr or Thr. In some embodiments, (X5) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X5) represents Ala, Gly, or Pro. In some embodiments, (X5) represents Ala or Gly. In some embodiments, (X6) represents Pro, Lys, Ala, Arg, Ser, Gly, Val, Leu, Gln, Thr, Ile, Met, and Asn. In some embodiments, (X6) represents Gly or Ala. In some embodiments, (X6) represents Gly or Pro. In some embodiments, (X6) represents Gly. In another aspect, the disclosure features a recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (XI): (X1)M(X2)(X3)(X4)(X5)G, wherein (X2) represents an amino acid selected from the group consisting of Pro and Ser, and wherein each of (X1), (X3), (X4), and (X5), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Val, Asn, His, Lys, or Gly. In some embodiments, (X1) represents Lys, Met, Leu, Gln, Tyr, Phe, Thr, Ile, and Ala. In some embodiments, (X1) represents Tyr, Ser, Ala, Ile, or Met. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Pro. In some embodiments, (X2) represents Ser. In some embodiments, (X3) represents Val, His, or Arg. In some embodiments, (X3) represents Arg. In some embodiments, (X4) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X4) represents Gln, Phe, Tyr, Thr, Ser, or Asn. In some embodiments, (X4) represents Tyr or Thr. In some embodiments, (X5) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X5) represents Ala, Gly, or Pro. In some embodiments, (X5) represents Ala or Gly. In another aspect, the disclosure features a recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (XII): (X1)M(X2)(X3)(X4)(Nonpolar1)G, wherein (X2) represents an amino acid selected from the group consisting of Pro and Ser, (Nonpolar1) represents any amino acid having a nonpolar, neutral side chain, and each of (X1), (X3), and (X4), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, ATTORNEY DOCKET NO.: 51772-005WO3 PATENT Ser, Ala, Ile, Val, Asn, His, Lys, or Gly. In some embodiments, (X1) represents Lys, Met, Leu, Gln, Tyr, Phe, Thr, Ile, and Ala. In some embodiments, (X1) represents Tyr, Ser, Ala, Ile, or Met. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Pro. In some embodiments, (X2) represents Ser. In some embodiments, (X3) represents Val, His, or Arg. In some embodiments, (X3) represents Arg. In some embodiments, (X4) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X4) represents Gln, Phe, Tyr, Thr, Ser, or Asn. In some embodiments, (X4) represents Tyr or Thr. In some embodiments, (Nonpolar1) represents Phe, Met, Leu, Ala, Ile, Val, Gly, and Pro. In some embodiments, (Nonpolar1) represents Ala, Val, Ile, Gly, or Pro. In some embodiments, (Nonpolar1) represents Ala, Gly, or Pro. In some embodiments, (Nonpolar1) represents Ala or Gly. In another aspect, the disclosure features a recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (XIII): In some embodiments, a peptide insert of the invention has an amino acid sequence represented by Formula (XIII): (X1)M(X2)(X3)(X4)(Nonpolar1)(Nonpolar2), wherein (X2) represents an amino acid selected from the group consisting of Pro and Ser, each of (Nonpolar1) and (Nonpolar2), independently, represents any amino acid listed in Table 1, above, as having a nonpolar, neutral side chain, and each of (X1), (X3), and (X4), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Val, Asn, His, Lys, or Gly. In some embodiments, (X1) represents Lys, Met, Leu, Gln, Tyr, Phe, Thr, Ile, and Ala. In some embodiments, (X1) represents Tyr, Ser, Ala, Ile, or Met. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Pro. In some embodiments, (X2) represents Ser. In some embodiments, (X3) represents Val, His, or Arg. In some embodiments, (X3) represents Arg. In some embodiments, (X4) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X4) represents Gln, Phe, Tyr, Thr, Ser, or Asn. In some embodiments, (X4) represents Tyr or Thr. In some embodiments, (Nonpolar1) represents Phe, Met, Leu, Ala, Ile, Val, Gly, and Pro. In some embodiments, (Nonpolar1) represents Ala, Val, Ile, Gly, or Pro. In some embodiments, (Nonpolar1) represents Ala, Gly, or Pro. In some embodiments, (Nonpolar1) represents Ala or Gly. In some embodiments, (Nonpolar2) represents Met, Leu, Gly, Ala, or Pro. In some embodiments, (Nonpolar2) represents Gly or Ala. In some embodiments, (Nonpolar2) represents Gly or Pro. In some embodiments, (Nonpolar2) represents Gly. In some embodiments of the foregoing aspects, the amino acid sequence appears at the first permissible frame, last permissible frame, or any frame in between. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 1 of the peptide insert. ATTORNEY DOCKET NO.: 51772-005WO3 PATENT In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids. In some embodiments, the peptide insert has a length of 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 9 amino acids, optionally wherein the length is 9-40 amino acids, optionally wherein the length is 9-35 amino acids, optionally wherein the length is 9-30 amino acids, optionally wherein the length is 9-25 amino acids, optionally wherein the length is 9-20 amino acids, optionally wherein the length is 9-15 amino acids, optionally wherein the length is 9-10 amino acids. In some embodiments, the peptide insert has a length of 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 10 amino acids, optionally wherein the length is 10-40 amino acids, optionally wherein the length is 10-35 amino acids, optionally wherein the length is 10-30 amino acids, optionally wherein the length is 10-25 amino acids, optionally wherein the length is 10-20 amino acids, optionally wherein the length is 10-15 amino acids. In some embodiments, the peptide insert has a length of 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In some embodiments of the foregoing aspects, the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 11 amino acids, optionally wherein the length is 11-40 amino acids, optionally wherein the length is 11-35 amino acids, optionally wherein the length is 11-30 amino acids, optionally wherein the length is 11-25 amino acids, optionally wherein the length is 11-20 amino acids, optionally wherein the length is 11-15 amino acids. In some embodiments, the peptide insert has a length of 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 amino acids. In some embodiments of the foregoing aspects, the peptide insert is incorporated into a wild-type AAV capsid protein. In some embodiments, the wild-type AAV capsid protein is a capsid protein that occurs naturally in an AAV serotype selected from the group consisting of AAV1, AAV2, AAV3, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV10, AAVrh10, or AAVrh74. In some embodiments, the wild-type AAV capsid protein is a capsid protein that occurs naturally in AAV9. In some embodiments, the wild-type AAV capsid protein is a VP1, VP2, or VP3 capsid protein. In some embodiments, the wild-type AAV capsid protein is a VP1 capsid protein. In some embodiments, the peptide insert is incorporated into the wild-type AAV capsid protein between a pair of consecutive amino acid residues that are located within a variable region (VR) selected from the group consisting of VR-I, VR-II, VR-III, VR-IV, VR-V, VR-VI, VR-VII, VR-VIII, and VR-IX. In some embodiments, the peptide insert is incorporated into the wild-type AAV capsid protein between a pair of ATTORNEY DOCKET NO.: 51772-005WO3 PATENT consecutive amino acid residues that are located within VR-VIII. In some embodiments, the pair of consecutive amino acid residues is selected from the group consisting of (a) amino acids 581 and 582, (b) amino acids 582 and 583, (c) amino acids 583 and 584, (d) amino acids 584 and 585, (e) amino acids 585 and 586, (f) amino acids 586 and 587, (g) amino acids 587 and 588, (h) amino acids 588 and 589, (i) amino acids 589 and 590, (j) amino acids 590 and 591, (k) amino acids 591 and 592, or (l) amino acids 592 and 593, wherein the amino acids are numbered relative to the amino acid sequence of wild-type AAV9 VP1 (SEQ ID NO: 492). In a further aspect, the disclosure features an AAV particle comprising any of the AAV capsid proteins of any one of the foregoing aspects or embodiments of the disclosure. In some embodiments, the AAV capsid protein encapsulates an AAV genome comprising, in the 5’-to-3’ direction: a) a first inverted terminal repeat (ITR); b) a transgene of interest; and c) a second ITR. In some embodiments, the AAV genome further comprises, between the first ITR and the transgene, one or more transcription regulatory elements that modulate expression of the transgene. In a further aspect, the disclosure features a method of expressing a transgene in a subject, the method comprising administering to the subject the AAV particle of any of the foregoing aspects or embodiments of the disclosure. In some embodiments, the AAV particle is administered to the subject by way of intramuscular, intrahepatic, intravenous, intrathecal, intracerebroventricular, intracisternal, intrastriatal, intracerebral, intracerebrospinal, intracranial, intracortical, intradermal, transdermal, parenteral, intranasal, subcutaneous, percutaneous, intratracheal, intraocular, or intravascular administration. In some embodiments, the AAV particle is administered to the subject by way of intramuscular administration. In some embodiments, the subject is a mammal. In some embodiments, the subject is a human. In a further aspect, the disclosure features a kit comprising the AAV particle of any of the foregoing aspects or embodiments of the disclosure and a package insert, wherein the package insert instructs a user of the kit to administer the AAV particle to a subject in accordance with the method of any one of the above aspects or embodiments of the disclosure. BRIEF DESCRIPTION OF THE FIGURES FIG.1 is a graph showing the sequence logo of the FMPRTPG (SEQ ID NO: 38) motif discovered in the initial stringent data analysis (as is described in the working examples, below). In brief, 506 unique peptides were subjected to clustering analysis using available web tools and this distinct peptide family with the FMPRTPG (SEQ ID NO: 38) motif was discovered. The experiments were performed as described in Example 1, below. FIG.2A is a chart showing tabulated results for the QMPRTPG (SEQ ID NO: 75) saturation mutagenesis library screen. Single site saturation mutagenesis on an MPR-family member was scored for in vitro HEK293 cell transduction activity. The relative transduction activity of every variant in the library was quantified and normalized to its abundance in the AAV input library. The results are presented in this ATTORNEY DOCKET NO.: 51772-005WO3 PATENT chart and are relative to the in vitro HEK293 activity organized by the positional substitutions made in each variant. The experiments were performed as described in Example 5, below. FIG.2B is a bar graph showing in vitro HEK293 cell transduction activity score. The scoring of replicates of the base sequence that were each encoded by unique synonymous codons (variants encoding QMPRTPG (SEQ ID NO: 75)) was compared to the scoring of variants that contain a STOP codon. The experiments were performed as described in Example 5, below. FIGS.3A-3C are a series of graphs showing the comparison of AAV9 and MPR2 capsids for intramuscularly administered AAV in mice measuring the following in vivo: (FIG.3A) serum [glucagon-like peptide-1 (GLP-1)] pM, (FIG.3B) relative mRNA level from muscle, and (FIG.3C) relative mRNA level from liver. The MPR2 capsid enhanced serum production of the reporter protein across a wide range of doses (Figure 3A). Local enhancement at the muscle injection site was pronounced, particularly at higher doses, for MPR2 (Figure 3B). Rag mice were dosed intramuscularly with MPR2 and AAV9 (each encapsulating identical cytomegalovirus-GLP-1-fragment crystallizable (CMV-GLP-1-Fc) reporter constructs). Fourteen days later, serum was collected from a terminal bleed for GLP-1-Fc reporter protein determination, and from the muscle and liver for reporter mRNA quantification. The experiments were performed as described in Example 6, below. FIG.3A abbreviations: GLP-1; glucagon-like peptide-1. FIGS.4A-4C are a series of bar graphs showing the comparison of AAV9 and MPR3 capsids for intramuscular AAV in mice at 2E9 GC / mouse measuring the following: (FIG.4A) serum GLP-1-Fc, (FIG. 4B) GLP-1-Fc mRNA from muscle, and (FIG.4C) GLP-1-Fc mRNA from liver. The MPR3 capsid enhanced serum production of the reporter protein 40-fold (FIG.4A). Local enhancement at the muscle injection site for MPR3 was 21-fold (vs AAV9, FIG.4B). MPR3 transduction of liver was nearly equal to AAV9 (FIG.4C), demonstrating superior muscle versus liver specificity. Rag mice were dosed at 2E9 GC / mouse intramuscularly with MPR3 and AAV9 (each encapsulating identical cytomegalovirus-GLP-1- fragment crystallizable (CMV-GLP-1-Fc) reporter constructs). Fourteen days later, serum was collected from a terminal bleed for GLP-1-Fc reporter protein determination, and from the muscle and liver for reporter mRNA quantification. The experiments were performed as described in Example 6, below. FIG. 4A abbreviations: GLP-1-Fc; glucagon-like peptide-1-fragment crystallizable. FIGS.5A-5C are a series of graphs showing the transduction activity as normalized to AAV9 in HEK293 cells for the following constructs: (FIG.5A) MPR-containing peptides of different length, (FIG. 5B) MPR-containing peptides with MPR at different frame positions of the base sequence IMPRTAG (SEQ ID NO: 46), and (FIG.5C) MPR-containing peptides with MPR at different frame positions of the base sequence AMPRYGG (SEQ ID NO: 5). FIG.5A includes IMPRT (SEQ ID NO: 490), IMPRA (SEQ ID NO: 491), IMPRG (SEQ ID NO: 492), MPRTAG (SEQ ID NO: 493), IMPRTAG (SEQ ID NO: 46), GIMPRTAG (SEQ ID NO: 494), and GIMPRTAA (SEQ ID NO: 495). FIG.5B includes MPRITAG (SEQ ID NO: 482), IMPRTAG (SEQ ID NO: 46), ITMPRAG (SEQ ID NO: 483), ITAMPRG (SEQ ID NO: 484), and ITAGMPR (SEQ ID NO: 485). FIG.5C includes MPRAYGG (SEQ ID NO: 486), AMPRYGG (SEQ ID NO: 5), AYMPRGG (SEQ ID NO: 487), AYGMPRG (SEQ ID NO: 488), and AYGGMPR (SEQ ID NO: 489). FIGS.5A-5C abbreviations: WT; wild type. The experiments were performed as described in Example 7, below. DEFINITIONS ATTORNEY DOCKET NO.: 51772-005WO3 PATENT As used herein, the term “about” refers to a value that is within 10% above or below the value being described. For example, “about 100 pounds” as used in the context of weight described herein includes quantities that are within 10% above or below 100 lbs. Additionally, when used in the context of a list of numerical quantities, it is to be understood that the term “about,” when preceding a list of numerical quantities, applies to each individual quantity recited in the list. Throughout the specification and claims, the word “comprise,” or variations such as “comprises” or “comprising,” will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. As used herein, “activity” refers to the functionality or effectiveness of a molecule or system. For example, “transduction activity” refers to the effectiveness of transferring genetic material into a cell with the aid of a viral vector, such as using the methods described herein. As used herein, the term “endogenous” describes a molecule (e.g., a polypeptide, nucleic acid, or cofactor) that is found naturally in a particular organism (e.g., a human) or in a particular location within an organism (e.g., an organ, a tissue, or a cell, such as a human cell). As used herein, the term “exogenous” describes a molecule (e.g., a polypeptide, nucleic acid, or cofactor) that is not found naturally in a particular organism (e.g., a human) or in a particular location within an organism (e.g., an organ, a tissue, or a cell, such as a human cell). Exogenous materials include those that are provided from an external source to an organism or to cultured matter extracted therefrom. As used herein, the term "genetically modified" or "transformed" or "transfected" or "transduced" by exogenous DNA (e.g., via a recombinant virus) refers to when such DNA has been introduced inside the cell. The presence of the exogenous DNA results in permanent or transient genetic change. The transforming DNA may or may not be integrated (covalently linked) into the genome of the cell. A "clone" is a population of cells derived from a single cell or common ancestor by mitosis. A "cell line" is a clone of a primary cell that is capable of stable growth in vitro for many generations. As used herein, the term “level” refers to a level of a molecule, for example, a protein or nucleic acid, as compared to a reference. The reference may be any useful reference, as defined herein. By a “decreased level” and an “increased level” of a protein is meant a decrease or increase in protein level, as compared to a reference. A level of a protein may be expressed in mass / vol (e.g., g / dL, mg / mL, μg / mL, or ng / mL) or percentage relative to total protein in a sample. As used herein, the “length” of a nucleic acid refers to the linear size of the nucleic acid as assessed by measuring the quantity of nucleotides from the 5’ to the 3’ end of the nucleic acid. Exemplary molecular biology techniques that may be used to determine the length of a nucleic acid of interest are known in the art. As used herein, the “frame” of a peptide refers to the position at which a designated amino acid sequence (e.g., MPR) commences, consistent with the use of “frame” in Example 7. As a non-limiting example, if a peptide contains the amino acid sequence “MPR” and it is said that the “MPR” amino acid sequence appears at frame 1, then there is a methionine at position 1 of the peptide, proline at position 2 of the peptide, and arginine at position 3 of the peptide. As used herein, “first permissible frame” refers to the earliest position within the peptide that can accommodate the amino acid sequence, and “last permissible frame” refers to the last frame that can accommodate the amino acid sequence, based on the ATTORNEY DOCKET NO.: 51772-005WO3 PATENT length of the peptide and the length of the amino acid sequence. For example, for a 7-residue peptide and a 3-residue amino acid sequence (e.g., “MPR”), the last permissible frame would be frame 5 (i.e., in which a methionine is present at position 5 of the peptide, proline at position 6 of the peptide, and arginine at position 7 of the peptide). As used herein, the terms “nucleic acid molecule,” “nucleic acid,” and “polynucleotide” are used interchangeably and refer to polymers of nucleotides of any length. Examples of polynucleotides are DNA polynucleotides and RNA polynucleotides. All nucleic acid sequences herein are written in the 5’-to-3’ direction and are to be construed accordingly. As used herein, the term "polynucleotide" refers to a polymeric form of nucleotides of any length, including deoxyribonucleotides or ribonucleotides, or analogs thereof. A polynucleotide may comprise modified nucleotides, such as methylated nucleotides and nucleotide analogs, and may be interrupted by non- nucleotide components. If present, modifications to the nucleotide structure may be imparted before or after assembly of the polymer. The term polynucleotide, as used herein, refers interchangeably to double- and single- stranded molecules. Unless otherwise specified or required, any embodiment herein that comprises a polynucleotide encompasses both the double-stranded form and each of two complementary single-stranded forms known or predicted to make up the double-stranded form. A nucleic acid molecule, e.g., a nucleic acid molecule in a vector (e.g., an expression vector, a viral vector) may be introduced into a host cell. As used herein, the term “host cell” refers to not only to the particular cell(s) into which the nucleic acid molecule has been introduced, but also to the progeny or potential progeny of such a cell. A host cell may be a “producer cell,” which refers to cells involved in ex vivo amplifying and manufacturing of a viral product. Many suitable producer cells are known to those skilled in the art; producer cells may be prokaryotic cells (e.g., E. coli) or eukaryotic cells (e.g., yeast cells, insect cells, plant cells, mammalian cells). Representative producer cells include, without limitation, A549, WEHI, 3T3, 10T1 / 2, BHK, MDCK, COS 1, COS 7, BSC 1, BSC 40, BMT 10, VERO, WI38, HeLa, 293 cells, Saos, C2C12, L cells, HT1080, HepG2 and primary fibroblast, hepatocyte and myoblast cells derived from mammals including human, monkey, mouse, rat, rabbit, and hamster. A host cell may be a “target cell,” which refers to cells in a human or animal, for example muscle cells, that may be targeted for a therapeutic purpose, such as treating a genetic disorder described herein. Methods for introducing nucleic acid molecules into host cells are well known in the art and include, without limitation, calcium phosphate precipitation, electroporation, heat shock, lipofection, microinjection, and viral -mediated nucleic acid transfer (e.g., transduction). As used herein, the term “codon” refers to any group of three consecutive nucleotide bases in a given messenger RNA molecule, or coding strand of DNA, that specifies a particular amino acid or a starting or stopping signal for translation. The term codon also refers to base triplets in a DNA strand. As used herein, the terms "polypeptide," "peptide," and "protein" are used interchangeably herein to refer to polymers of amino acids of any length. The terms also encompass an amino acid polymer that has been modified; for example, disulfide bond formation, glycosylation, lipidation, phosphorylation, or conjugation with a labeling component. Polypeptides such as therapeutic proteins, when discussed in the context of delivering a gene product to a mammalian subject, and compositions therefor, refer to the respective intact polypeptide, or any fragment or genetically engineered derivative thereof, which retains the desired biochemical function of the intact protein. Similarly, references to nucleic acids encoding ATTORNEY DOCKET NO.: 51772-005WO3 PATENT therapeutic proteins, and other such nucleic acids for use in delivery of a gene product to a mammalian subject (which may be referred to as "transgenes" to be delivered to a recipient cell), include polynucleotides encoding the intact polypeptide or any fragment or genetically engineered derivative possessing the desired biochemical function. As used herein, the term “gene” refers to a region of DNA that encodes a protein. A gene may include regulatory regions and a protein-coding region. In some embodiments, a gene may include two or more introns and three or more exons, wherein each intron forms an intervening sequence between two exons. The term "gene" refers to a polynucleotide that performs a function of some kind in the cell. For example, a gene may contain an open reading frame that is capable of encoding a gene product. One example of a gene product is a protein, which is transcribed and translated from the gene. Another example of a gene product is an RNA, e.g., a functional RNA product, e.g., an aptamer, an interfering RNA, a ribosomal RNA (rRNA), a transfer RNA (tRNA), a non-coding RNA (ncRNA), a guide RNA for nucleases, etc., which is transcribed but not translated. As used herein, the term “transgene” refers to a recombinant nucleic acid (e.g., DNA or cDNA) encoding a gene product. The gene product may be an RNA, peptide, or protein. In addition to the coding region for the gene product, the transgene may include or be operably linked to one or more elements to facilitate or enhance expression, such as a promoter, enhancer(s), destabilizing domain(s), response element(s), reporter element(s), insulator element(s), polyadenylation signal(s) and / or other functional elements. Embodiments may utilize any known suitable promoter, enhancer(s), destabilizing domain(s), response element(s), reporter element(s), insulator element(s), polyadenylation signal(s), and / or other functional elements. As used herein, the term “gene expression” or “transgene expression” refers to the process by which a nucleic acid is transcribed from a nucleic acid molecule, and often, translated into a peptide or protein. The process may include transcription, post-transcriptional control, post-transcriptional modification, translation, post-translational control, post translational modification, or any combination thereof. Reference to a measurement of “gene expression” may refer to measurement of the product of transcription (e.g., RNA or mRNA), the product of translation (e.g., peptides or proteins). The term "gene expression product" or "gene product" is a molecule resulting from expression of a particular gene, as defined above. Gene expression products include, e.g., a polypeptide, an aptamer, an interfering RNA, a messenger RNA (mRNA), an rRNA, a tRNA, a non-coding RNA (ncRNA), and the like. In some embodiments, gene products include active polypeptide product or inhibitory RNA from a transcribed gene. In some embodiments, the transgene is operably linked to expression control sequences. As used herein, the term “wild-type” or “non-mutant” form of a gene refers to a nucleic acid that encodes a protein associated with normal or non-pathogenic activity (e.g., a protein lacking a mutation). In some embodiments, the wild-type gene may serve as a reference to compare a variant gene that is associated with a genetic disorder, e.g., as described in Table 4 herein. As used herein, the term “variant” or “mutant” refers to any gene with a change in sequence, such that the sequence is not identical to that of the wild-type gene and results in an altered form of the gene. A mutation may be selected from the group including a single nucleotide point mutation that results in a premature termination codon, a single nucleotide insertion, a single nucleotide deletion, the insertion of two or more contiguous nucleotides, the deletion of two or more contiguous nucleotides, the duplication of ATTORNEY DOCKET NO.: 51772-005WO3 PATENT a contiguous region within a gene (e.g., an exon), or the deletion of a contiguous region within a gene. A mutated gene may include a single mutation, or multiple mutations. A mutation may occur in any region of the gene. Gene mutations include the substitution, insertion, or deletion of a single base in DNA or the substitution, insertion, deletion, or rearrangement of multiple bases or larger sections of genes or chromosomes, including repeat expansions. As used herein, the terms “conservative mutation,” “conservative substitution,” and “conservative amino acid substitution” refer to a substitution of one or more amino acids for one or more different amino acids that exhibit similar physicochemical properties, such as polarity, electrostatic charge, and steric volume. These properties are summarized for each of the twenty naturally-occurring amino acids in Table 1, below. Table 1. Representative physicochemical properties of naturally-occurring amino acids †based on volume in A3: 50-100 is small, 100-150 is intermediate, 150-200 is large, and >200 is bulky ATTORNEY DOCKET NO.: 51772-005WO3 PATENT From this table it is appreciated that the conservative amino acid families include (i) G, A, V, L and I; (ii) D and E; (iii) C, S and T; (iv) H, K and R; (v) N and Q; and (vi) F, Y and W. A conservative mutation or substitution is therefore one that substitutes one amino acid for a member of the same amino acid family (e.g., a substitution of Ser for Thr or Lys for Arg). “Percent (%) sequence identity,” with respect to a reference polynucleotide or polypeptide sequence, is defined as the percentage of nucleic acids or amino acids in a candidate sequence that are identical to the nucleic acids or amino acids in the reference polynucleotide or polypeptide sequence, after aligning the sequences and introducing gaps, if necessary, to achieve the maximum percent sequence identity. Alignment for purposes of determining percent nucleic acid or amino acid sequence identity may be achieved in various ways that are within the capabilities of one of skill in the art, for example, using publicly available computer software such as BLAST, BLAST-2, or Megalign software. Those skilled in the art may determine appropriate parameters for aligning sequences, including any algorithms needed to achieve maximal alignment over the full length of the sequences being compared. For example, percent sequence identity values may be generated using the sequence comparison computer program BLAST. As an illustration, the percent sequence identity of a given nucleic acid or amino acid sequence, A, to, with, or against a given nucleic acid or amino acid sequence, B, (which may alternatively be phrased as a given nucleic acid or amino acid sequence, A that has a certain percent sequence identity to, with, or against a given nucleic acid or amino acid sequence, B) is calculated as follows: 100 multiplied by (the fraction X / Y) where X is the number of nucleotides or amino acids scored as identical matches by a sequence alignment program (e.g., BLAST) in that program’s alignment of A and B, and where Y is the total number of nucleic acids in B. It will be appreciated that where the length of nucleic acid or amino acid sequence A is not equal to the length of nucleic acid or amino acid sequence B, the percent sequence identity of A to B will not equal the percent sequence identity of B to A. “Percent (%) sequence complementarity” with respect to a reference polynucleotide sequence is defined as the percentage of nucleic acids in a candidate sequence that are complementary to the nucleic acids in the reference polynucleotide sequence, after aligning the sequences and introducing gaps, if necessary, to achieve the maximum percent sequence complementarity. A given nucleotide is considered to be “complementary” to a reference nucleotide as described herein if the two nucleotides form canonical Watson-Crick base pairs. For the avoidance of doubt, Watson-Crick base pairs in the context of the present disclosure include adenine-thymine, adenine-uracil, and cytosine-guanine base pairs. A proper Watson-Crick base pair is referred to in this context as a “match,” while each unpaired nucleotide, and each incorrectly paired nucleotide, is referred to as a “mismatch.” Alignment for purposes of determining percent nucleic acid sequence complementarity may be achieved in various ways that are within the capabilities of one of skill in the art, for example, using publicly available computer software such as BLAST, BLAST-2, or Megalign software. Those skilled in the art may determine appropriate parameters for aligning sequences, including any algorithms needed to achieve maximal complementarity over the full length of the sequences being compared. As an illustration, the percent sequence complementarity of a given nucleic acid sequence, A, to a given nucleic acid sequence, B, (which may alternatively be ATTORNEY DOCKET NO.: 51772-005WO3 PATENT phrased as a given nucleic acid sequence, A that has a certain percent complementarity to a given nucleic acid sequence, B) is calculated as follows: 100 multiplied by (the fraction X / Y) where X is the number of complementary base pairs in an alignment (e.g., as executed by computer software, such as BLAST) in that program’s alignment of A and B, and where Y is the total number of nucleic acids in B. It will be appreciated that where the length of nucleic acid sequence A is not equal to the length of nucleic acid sequence B, the percent sequence complementarity of A to B will not equal the percent sequence complementarity of B to A. As used herein, a query nucleic acid sequence is considered to be “completely complementary” to a reference nucleic acid sequence if the query nucleic acid sequence has 100% sequence complementarity to the reference nucleic acid sequence. As used herein, the term “functional,” with respect to a gene, refers to a functional gene product, for example, a functional protein. A gene product is functional if it fulfills its normal (wild-type) functions. Disruption of the gene prevents expression of a functional factor encoded by the gene and contains an insertion, deletion, or substitution of one or more bases in a sequence encoded by the gene and / or a promoter and / or an operator that is necessary for expression of the gene in the animal. As used herein, the term “plasmid” refers to an extrachromosomal circular double stranded DNA molecule into which additional DNA segments may be ligated. A plasmid is a type of vector, a nucleic acid molecule capable of transporting another nucleic acid to which it has been linked. Certain plasmids are capable of autonomous replication in a host cell into which they are introduced (e.g., bacterial plasmids having a bacterial origin of replication and episomal mammalian plasmids). Other vectors (e.g., non- episomal mammalian vectors) may be integrated into the genome of a host cell upon introduction into the host cell, and thereby are replicated along with the host genome. Certain plasmids are capable of directing the expression of genes to which they are operably linked. As used herein, the term “promoter” refers to a recognition site on DNA that is bound by an RNA polymerase. The polymerase drives transcription of the transgene. Exemplary promoters suitable for use with the compositions and methods described herein are described, for example, in Sandelin et al., Nature Reviews Genetics 8:424 (2007), the disclosure of which is incorporated herein by reference as it pertains to nucleic acid regulatory elements. Additionally, the term “promoter” may refer to a synthetic promoter, which are regulatory DNA sequences that do not occur naturally in biological systems. Synthetic promoters contain parts of naturally occurring promoters combined with polynucleotide sequences that do not occur in nature and may be optimized to express recombinant DNA using a variety of transgenes, vectors, and target cell types. The term “promoter,” as used herein, refers to a region within the regulatory region of a gene that enables initiation of the transcription of a gene into a messenger RNA, wherein transcription is initiated with the binding of an RNA polymerase on or nearby the promoter. As used herein, the term “operably linked” in the context of a nucleic acid refers to a nucleic acid that is placed into a structural or functional relationship with another nucleic acid. For example, one segment of DNA may be operably linked to another segment of DNA if they are positioned relative to one another on the same contiguous DNA molecule and have a structural or functional relationship, such as a promoter or enhancer that is positioned relative to a coding region so as to facilitate transcription of the coding region. In other examples, the operably linked nucleic acids are not contiguous, but are positioned ATTORNEY DOCKET NO.: 51772-005WO3 PATENT in such a way that they have a functional relationship with each other as nucleic acids or as proteins that are expressed by them. Enhancers, for example, do not have to be contiguous. Linking may be accomplished by ligation at convenient restriction sites or by using synthetic oligonucleotide adaptors or linkers. For example, a promoter is operably linked to a transcribable polynucleotide molecule if the promoter modulates transcription of the transcribable polynucleotide molecule of interest in a cell. Additionally, two portions of a transcription regulatory element are operably linked to one another if they are joined such that the transcription-activating functionality of one portion is not adversely affected by the presence of the other portion. Two transcription regulatory elements may be operably linked to one another by way of a linker nucleic acid (e.g., an intervening non-coding nucleic acid) or may be operably linked to one another with no intervening nucleotides present. The term “operably linked” may also refer to a first molecule joined to a second molecule, wherein the molecules are so arranged that the first molecule affects the function of the second molecule. The two molecules may or may not be part of a single contiguous molecule and may or may not be adjacent. A vector containing a nucleic acid molecule may have one or more elements for expression operably linked to such a nucleic acid molecule, and further may include sequences such as those encoding a selectable marker (e.g., an antibiotic resistance gene), and / or those that may be used in purification of a polypeptide (e.g., 6xHis tag). Elements for expression include nucleic acid sequences that direct and regulate expression of nucleic acid coding sequences. One example of an expression element is a promoter sequence. Expression elements also may include one or more introns, enhancer sequences, response elements, or inducible elements that modulate expression of a nucleic acid molecule. Expression elements may be of bacterial, yeast, insect, mammalian, or viral origin and vectors may contain a combination of expression elements from different origins. As used herein, operably linked means that elements for expression are positioned in a vector relative to a coding sequence in such a way as to direct or regulate expression of the coding sequence. Vectors, including expression vectors, are commercially available or may be produced by recombinant technology. As used herein, the term “regulatory element” or “regulatory sequence” refers to a nucleic acid that controls, at least in part, the transcription of a gene of interest. Transcription regulatory elements may include promoters, enhancers, and other nucleic acids (e.g., polyadenylation signals) that control or help to control gene transcription. Examples of transcription regulatory elements are described, for example, in Goeddel, Gene Expression Technology: Methods in Enzymology 185 (Academic Press, San Diego, CA, 1990). As used herein, the term “vector” includes a nucleic acid vector, e.g., a DNA vector, such as a plasmid, an RNA vector, virus, or other suitable replicon (e.g., viral vector). A variety of vectors have been developed for the delivery of polynucleotides encoding exogenous proteins into a prokaryotic or eukaryotic cell. Examples of such expression vectors are disclosed in, e.g., WO 1994 / 011026; incorporated herein by reference as it pertains to vectors suitable for the expression of a gene of interest. Expression vectors suitable for use with the compositions and methods described herein contain a polynucleotide sequence as well as, e.g., additional sequence elements used for the expression of proteins and / or the integration of these polynucleotide sequences into the genome of a mammalian cell. Certain vectors that may be used for the expression of transgenes as described herein include plasmids that contain regulatory sequences, such as promoter and enhancer regions, which direct gene ATTORNEY DOCKET NO.: 51772-005WO3 PATENT transcription. Other useful vectors for expression of a transgenes contain polynucleotide sequences that enhance the rate of translation of these genes or improve the stability or nuclear export of the mRNA that results from gene transcription. These sequence elements include, e.g., 5’ and 3’ untranslated regions, an internal ribosomal entry site (IRES), and polyadenylation signal site in order to direct efficient transcription of the gene carried on the expression vector. The expression vectors suitable for use with the compositions and methods described herein may also contain a polynucleotide encoding a marker for selection of cells that contain such a vector. Examples of a suitable marker are genes that encode resistance to antibiotics, such as ampicillin, chloramphenicol, kanamycin, nourseothricin, or zeocin. As used herein, the terms "AAV viral particle" refer to a viral particle composed of at least one AAV capsid protein and an encapsidated AAV polynucleotide. The term “particle” as used herein, refers to any suitable sized particles for delivery of the engineered AAV capsid system components described herein. Suitable sizes include macro-, micro-, and nano-sized particles. In some embodiments, any of the of the engineered AAV capsid system components (e.g., polypeptides such as peptide inserts, polynucleotides, vectors and combinations thereof described herein) may be attached to, coupled to, integrated with, otherwise associated with one or more particles or component thereof as described herein. The particles described herein may then be administered to a cell or organism by an appropriate route and / or technique. In some embodiments, particle delivery may be selected and be advantageous for delivery of the polynucleotide or vector components. It will be appreciated that in embodiments, particle delivery may also be advantageous for other engineered capsid system molecules and formulations described elsewhere herein. The term "rAAV" is an abbreviation that refers to recombinant AAV vectors. "Recombinant," as applied to a polynucleotide, means that the polynucleotide is the product of various combinations of cloning, restriction or ligation steps, and other procedures that result in a construct that is distinct from a polynucleotide found in nature. The term "rAAV vector” refers to a polynucleotide, such as a nucleic acid genome, within an AAV viral particle. The terms include replicates of the original polynucleotide construct and progeny of the original virus construct. If an AAV particle comprises a heterologous polynucleotide (i.e., a polynucleotide other than a wild-type AAV genome, e.g., a transgene to be delivered to a target cell, an RNAi agent or CRISPR agent to be delivered to a target cell, etc.), it is typically referred to as a "recombinant AAV (rAAV) virion" or an "rAAV viral particle" or an “rAAV particle.” In general, the heterologous polynucleotide is flanked by at least one, and generally by two, AAV ITRs. Recombinant AAV polynucleotides also encompass polynucleotides encoding rAAV (e.g., a single stranded polynucleotide encoding rAAV (ss-rAAV); a double stranded polynucleotide encoding rAAV (ds-rAAV), e.g., plasmids encoding rAAV; and the like). Unless otherwise indicated, the viral vectors of the invention are recombinant, as they contain heterologous nucleic acids. As used herein, the terms “adeno-associated virus” and “AAV” include, but are not limited to, AAV type 1, AAV type 2, AAV type 3 (including types 3A and 3B), AAV type 4, AAV type 5, AAV type 6, AAV type 7, AAV type 8, AAV type 9, AAV type 10, AAV type 11, AAV type 12, AAV type 13, snake AAV, avian AAV, bovine AAV, canine AAV, equine AAV, ovine AAV, goat AAV, shrimp AAV, and any other AAV now known or later discovered. See, e.g., Fields et al. Virology, 4thed. Lippincott-Raven Publishers, Philadelphia, 1996. Additional AAV serotypes and clades have been identified recently. (See, e.g., Gao et al. J. Virol.78:6381 (2004); Moris et al. Virol.33:375 (2004). The genomic sequences of various ATTORNEY DOCKET NO.: 51772-005WO3 PATENT serotypes of AAV, as well as the sequences of the native inverted terminal repeats (ITRs), Rep proteins, and capsid subunits are known in the art. Such sequences may be found in the literature or in public databases such as GenBank. See, e.g., GenBank Accession Numbers NC—002077, NC—001401, NC— 001729, NC—001863, NC—001829, NC—001862, NC—000883, NC—001701, NC—001510, NC— 006152, NC—006261, AF063497, U89790, AF043303, AF028705, AF028704, J02275, J01901, J02275, X01457, AF288061, AH009962, AY028226, AY028223, AY631966, AX753250, EU285562, NC—001358, NC—001540, AF513851, AF513852 and AY530579; the disclosures of which are incorporated by reference herein for teaching AAV nucleic acid and amino acid sequences. See also, e.g., Bantel-Schaal et al. J. Virol.73:939 (1999); Chiorini et al. J. Virol.71:6823 (1997); Chiorini et al. J. Virol.73:1309 (1999); Gao et al. Proc. Nat. Acad. Sci. USA 99:11854 (2002); Moris et al. Virol.33:375 (2004); Muramatsu et al. Virol.221:208 (1996); Ruffing et al. J. Gen. Virol.75:3385 (1994); Rutledge et al. J. Virol.72:309 (1998); Schmidt et al. J. Virol.82:8911 (2008); Shade et al. J. Virol.58:921 (1986); Srivastava et al. J. Virol. 45:555 (1983); Xiao et al. J. Virol.73:3994 (1999); WO 00 / 28061, WO 99 / 61601, WO 98 / 11244; and US 6,156,303; the disclosures of which are incorporated by reference herein for teaching AAV nucleic acid and amino acid sequences. From a structural perspective, AAV is a nonpathogenic parvovirus composed of a 4.7 kb single- stranded DNA genome within a non-enveloped, icosahedral capsid. The genome contains three open reading frames (ORF) flanked by inverted terminal repeats (ITR) that function as the viral origin of replication and packaging signal. The Rep ORF encodes four nonstructural proteins that play roles in viral replication, transcriptional regulation, site-specific integration, and virion assembly. The Cap ORF encodes three structural proteins (VP 1-3) that assemble to form a 60-mer viral capsid. Finally, an ORF present as an alternate reading frame within the Cap gene produces the assembly-activating protein (AAP), a viral protein that localizes AAV capsid proteins to the nucleolus and functions in the capsid assembly process. There are several naturally occurring ("wild-type") serotypes and over 100 known variants of AAV, each of which differs in amino acid sequence, particularly within the hypervariable regions of the capsid proteins, and thus in their gene delivery properties. No AAV has been associated with any human disease, making recombinant AAV attractive for clinical applications. The genomic sequences of various serotypes of AAV, as well as the sequences of the native terminal repeats (TRs), Rep proteins, and capsid subunits, are known in the art. Such sequences may be found in the literature or in public databases such as GenBank. See, e.g., GenBank Accession Numbers NC_002077.1 (AAV1), AF063497.1 (AAV1), NC_001401.2 (AAV2), AF043303.1 (AAV2), J01901.1 (AAV2), U48704.1 (AAV3A), NC_001729.1 (AAV3A), AF028705.1 (AAV3B), NC .001829.1 (AAV4), U89790.1 (AAV4), NC_006152.1 (AA5), AF085716.1 (AAV-5), AF028704.1 (AAV6), NC 006260.1 (AAV7), AF513851.1 (AAV7), AF513852.1 (AAV8) NC 006261.1 (AAV-8), AY530579.1 (AAV9), AAT46337 (AAV10) and AAO88208 (AAVrh10); the disclosures of which are incorporated by reference herein for teaching AAV nucleic acid and amino acid sequences. See also, e.g., Srivistava et al. (1983) J. Virology 45:555; Chiorini et al. (1998) J. Virology 71:6823; Chiorini et al. (1999) J. Virology 73: 1309; Bantel-Schaal et al. (1999) J. Virology 73:939; Xiao et al. (1999) J. Virology 73:3994; Muramatsu et al. (1996) Virology 221:208; Shade et al. (1986) J. Virol.58:921; Gao et al. (2002) Proc. Nat. Acad. Sci. USA 99: 11854; Moris et al. (2004) Virology 33:375-383; international patent publications WO 00 / 28061, WO 99 / 61601, WO 98 / 11244; and U.S. Pat. No.6,156,303. ATTORNEY DOCKET NO.: 51772-005WO3 PATENT The sequences of naturally existing Cap (capsid) proteins associated with AAV serotypes are known in the art and include those disclosed herein as AAV1, AAV2, AAV3, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV10, AAVrh10, and AAVrh74. The terms "variant AAV capsid protein" or "AAV variant” refer to an AAV capsid protein comprising an amino acid sequence that includes at least one modification or substitution (including deletion, insertion, point mutation, etc.) relative to a naturally existing or "wild- type" AAV capsid protein sequence, e.g., as set forth in Table 3 herein. A variant AAV capsid protein may have about 80% identity or more to the amino acid sequence of a wild-type capsid protein, for example, 85% identity or more, 90% identity or more, or 95% identity or more to the amino acid sequence of the wild-type capsid protein, for example, 98% or 99% identity to the wild-type capsid protein. A variant AAV capsid protein may not be a wild-type capsid protein. As used herein, the term "packaging" refers to a series of intracellular events that result in the assembly and encapsidation of an AAV particle. AAV “Rep” and “Cap” genes refer to polynucleotide sequences encoding replication and encapsidation proteins of adeno-associated virus. AAV Rep and Cap are referred to herein as AAV “packaging genes”. “Rep proteins” are proteins which fill capsids with a polynucleotide molecule (e.g., viral DNA) into a capsid. In addition, a Rep protein may enable nucleic acid molecule replication, transcriptional regulation of a nucleic acid molecule, and / or site-specific integration (e.g., chromosomal integration) of a nucleic acid molecule. The Rep protein may be from any parvovirus. As one of skill in the art will appreciate, in some parvovirus family virus species, a Rep protein is referred to as a “non-structural (NS) protein”. As used herein, a Rep protein may refer to a NS protein. As used herein, a Rep protein may refer to an AAV Rep protein, which have been found in all AAV serotypes examined to date, and a synthetic Rep protein. For example, in some embodiments, an AAV Rep protein (e.g., AAV Rep40, AAV Rep52, AAV Rep68, and AAV Rep78) is a capsid protein having an amino acid sequence derived from a particular AAV serotype, for example AAV type 1, AAV type 2, AAV type 3 (including types 3A and 3B), AAV type 4, AAV type 5, AAV type 6, AAV type 7, AAV type 8, AAV type 9, AAV type 10, AAV type 11, AAV type 12, AAV type 13, avian AAV, bovine AAV, canine AAV, goat AAV, snake AAV, equine AAV, and ovine AAV. Alternatively, for example, as used herein, a Rep protein may include a synthetic Rep protein. Any suitable Rep protein may be used. As used herein, the term “viral capsid protein” refers to a capsid protein composing a proteinaceous shell. Such a proteinaceous shell is generally composed of one or more viral capsid proteins and when assembled is capable of being loaded with one or more polynucleotide molecules. A viral capsid protein described herein may, for example, be a viral protein VP1, VP2, or VP3. Further, a viral capsid protein described herein may refer to a synthetic protein or a viral capsid protein from Parvoviridae (e.g., an AAV). A “viral capsid protein” as used herein refers to any of the AAV capsid proteins that are components of AAV viral particles. As used herein, the term “same capsid species” refers to a population of capsids having the same defined stoichiometry of viral capsid protein components, which may include one or more of VP1, VP2, and VP3. As used herein, the terms “viral protein 1” and “VP1” refer to any capsid protein that is a component of a capsid, for example, a parvovirus (e.g., AAV) capsid particle. As used herein, a VP1 may possess a surface binding site that interacts with one or more molecules on the surface of a cell to initiate ATTORNEY DOCKET NO.: 51772-005WO3 PATENT the process of cell entry (e.g., endocytic entry and receptor-mediated fusion). As used herein, a VP1 may self-assemble into a structure consisting of VP1, VP2, and / or VP3 molecules. VP1 may exhibit self- binding properties and self-assemble around the exterior of a respective VP1-containing capsid. As used herein, a VP1 may be synthetic or a VP1 derived from Parvoviridae (e.g., an AAV). For example, a VP1 derived from an AAV may be a VP1 derived from AAV type 1, AAV type 2, AAV type 3, AAV type 4, AAV type 5, AAV type 6, AAV type 7, AAV type 8, AAV type 9, AAV type 10, AAV type 11, AAV type 12, AAV type 13, avian AAV, bovine AAV, canine AAV, goat AAV, snake AAV, equine AAV, ovine AAV, goat AAV, shrimp AAV, or any other AAV now known and later discovered. As used herein, the terms “viral protein 2” and “VP2” refer to any capsid protein that is a component of a capsid, for example, a parvovirus (e.g., AAV) capsid particle. As used herein, a VP2 may facilitate capsid entry into a host cell, for example, by mediating associations with and exit from the endoplasmic reticulum of a host cell and by facilitating the entry of a nucleic acid molecule into a host cell nucleus. As used herein, a VP2 may self-assemble into a structure consisting of VP1, VP2, and / or VP3 molecules. VP2 may self-assemble within the interior of a respective VP2-containing capsid. As used herein, a VP2 may be synthetic or a VP2 derived from Parvoviridae (e.g., an AAV). For example, a VP2 derived from an AAV may be a VP2 derived from AAV type 1, AAV type 2, AAV type 3, AAV type 4, AAV type 5, AAV type 6, AAV type 7, AAV type 8, AAV type 9, AAV type 10, AAV type 11, AAV type 12, AAV type 13, avian AAV, bovine AAV, canine AAV, goat AAV, snake AAV, equine AAV, ovine AAV, goat AAV, shrimp AAV, or any other AAV now known and later discovered. As used herein, the terms “viral protein 3” and “VP3” refer to any capsid protein that is a component of a capsid, for example, a parvovirus (e.g., AAV) capsid particle. As used herein, a VP3 may facilitate capsid entry into a host cell, for example, by mediating associations with and exit from the endoplasmic reticulum of a host cell and by facilitating the entry of a nucleic acid molecule into a host cell nucleus. As used herein, a VP3 may self-assemble into a structure consisting of VP1, VP2, and / or VP3 molecules. VP3 may self-assemble within the interior of a respective VP3-containing capsid. As used herein, a VP3 may be synthetic or a VP3 derived from Parvoviridae (e.g., an AAV). For example, a VP3 derived from an AAV may be a VP3 derived from AAV type 1, AAV type 2, AAV type 3, AAV type 4, AAV type 5, AAV type 6, AAV type 7, AAV type 8, AAV type 9, AAV type 10, AAV type 11, AAV type 12, AAV type 13, avian AAV, bovine AAV, canine AAV, goat AAV, snake AAV, equine AAV, ovine AAV, goat AAV, shrimp AAV, or any other AAV now known and later discovered. As used herein, the terms “encapsidation,” “encapsulating,” “encapsidate,” and the like refer to non-enzymatically driven encasing of nucleic acid molecules in a capsid shell. Thus, when a suitable population of viral capsid proteins (e.g., VP1, VP2, and / or VP3) and conditions are combined with a nucleic acid molecule, the nucleic acid molecule may be encapsidated by the capsid to form an assembled capsid particle packaged with one or more nucleic acid molecules. The encapsidation process may occur simultaneously with capsid assembly or after capsid assembly is complete. An “ITR” is a palindromic nucleic acid, e.g., an inverted terminal repeat, that is about 120 nucleotides to about 250 nucleotides in length and capable of forming a hairpin. The term “ITR” includes the site of the viral genome replication that may be recognized and bound by a parvoviral protein (e.g., Rep78 / 68). An ITR may be from any AAV, with serotype 2 being preferred. An ITR includes a replication protein binding element (RBE) and a terminal resolution sequence (TRS). The term “ITR” does not ATTORNEY DOCKET NO.: 51772-005WO3 PATENT require a wild-type parvoviral ITR (e.g., a wild-type nucleic acid sequence may be altered by insertion, deletion, truncation, or missense mutations), as long as the ITR functions to mediate virus packaging, replication, integration, and / or provirus rescue, and the like. The “5’ ITR” is intended to mean the parvoviral ITR located at the 5’ boundary of the nucleic acid molecule; and the term “3’ ITR” is intended to mean the parvoviral ITR located at the 3’ boundary of the nucleic acid molecule. As used herein, the term "helper virus" for AAV refers to a virus that allows AAV (e.g., wild-type AAV) to be replicated and packaged by a mammalian cell. A variety of such helper viruses for AAV are known in the art, including adenoviruses, herpesviruses, and poxviruses such as vaccinia. The adenoviruses encompass a number of different subgroups, although Adenovirus type 5 of subgroup C is most commonly used. Numerous adenoviruses of human, non-human mammalian and avian origin are known and available from depositories such as the ATCC. Viruses of the herpes family include, for example, herpes simplex viruses (HSV) and Epstein-Barr viruses (EBV), as well as cytomegaloviruses (CMV) and pseudorabies viruses (PRV); which are also available from depositories such as ATCC. As used herein, the term "helper virus functions" refers to functions encoded in a helper virus genome which allow AAV replication and packaging (in conjunction with other requirements for replication and packaging described herein). As described herein, "helper virus function" may be provided in a number of ways, including by providing helper virus or providing, for example, polynucleotide sequences encoding the requisite function(s) to a producer cell in trans. For example, a plasmid or other expression vector comprising nucleotide sequences encoding one or more adenoviral proteins is transfected into a producer cell along with an rAAV vector. The terminology "infectious" virus or viral particle is one that comprises a competently assembled viral capsid and is capable of delivering a polynucleotide component into a cell for which the viral species is tropic. The term does not necessarily imply any replication capacity of the virus. Assays for counting infectious viral particles are described elsewhere in this disclosure and in the art. Viral infectivity may be expressed as the ratio of infectious viral particles to total viral particles. Methods of determining the ratio of infectious viral particle to total viral particle are known in the art. See, e.g., Grainger et al. (2005) Mol. Ther.11: S337 (describing a TCID50 infectious titer assay); and Zolotukhin et al. (1999) Gene Ther.6:973. As used herein, the term “targeting agent” refers to a peptide or compound (e.g., a peptide insert of an invention) that localizes a virus (e.g., an AAV) or non-viral delivery vehicle (e.g., lipid nanoparticle (LNP), liposome, lipoplex, exosome, or vesicle) to specific cell types (e.g., muscle cells or neural cells). A virus comprising a targeting agent may have changes in tropism relative to a naturally occurring viral particle, as described herein. As used herein, the term "tropism" refers to the preferential targeting by a virus (e.g., an AAV) of cells of a particular host species or of particular cell types within a host species. For example, a virus that may infect cells of the heart, lung, liver, and muscle has a broader (i.e., increased) tropism relative to a virus that may infect only lung and muscle cells. Changes in tropism can also manifest as more subtle shift in cell-type preference generally or in cell-type preference in the context of a particular route of administration. Tropism may also include the dependence of a virus on particular types of cell surface molecules of the host. For example, some viruses may infect only cells with surface glycosaminoglycans, while other viruses may infect only cells with sialic acid (such dependencies may be tested using various cells lines deficient in particular classes of molecules as potential host cells for viral infection). In some ATTORNEY DOCKET NO.: 51772-005WO3 PATENT cases, the tropism of a virus describes the virus's relative preferences. For example, a first virus may be able to infect all cell types but is much more successful in infecting those cells with surface glycosaminoglycans. A second virus may be considered to have a similar (or identical) tropism as the first virus if the second virus also prefers the same characteristics (e.g., the second virus is also more successful in infecting those cells with surface glycosaminoglycans), even if the absolute transduction efficiencies are not similar. For example, the second virus might be more efficient than the first virus at infecting every given cell type tested, but if the relative preferences are similar (or identical), the second virus may still be considered to have a similar (or identical) tropism as the first virus. In some embodiments, the tropism of a viral particle comprising a subject variant AAV capsid protein is not altered relative to a naturally occurring viral particle. In some embodiments, the tropism of a viral particle comprising a subject variant AAV capsid protein is expanded (i.e., broadened) relative to a naturally occurring viral particle. In some embodiments, the tropism of a viral particle comprising a subject variant AAV capsid protein is reduced relative to a naturally occurring viral particle. As used herein, the term "heterologous" means derived from a genotypically distinct entity from that of the rest of the entity to which it is being compared. For example, a polynucleotide introduced by genetic engineering techniques into a plasmid or vector derived from a different species is a heterologous polynucleotide. A promoter removed from its native coding sequence and operatively linked to a coding sequence with which it is not naturally found linked is a heterologous promoter. Thus, for example, an rAAV that includes a heterologous nucleic acid sequence encoding a heterologous gene product is an rAAV that includes a polynucleotide not normally included in a naturally-occurring, wild-type AAV, and the encoded heterologous gene product is a gene product not normally encoded by a naturally-occurring, wild-type AAV. As used herein, the term “hybridize” refers to the formation of a stable duplex of nucleic acids by way of annealing mediated by inter-strand hydrogen bonding, for example, according to Watson-Crick base pairing. The nucleic acids of the duplex may be, for example, at least 50% complementary to one another. The “stable duplex” formed upon the hybridization of one nucleic acid to another is a duplex structure that is not denatured by a stringent wash. Exemplary stringent wash conditions are known in the art and include temperatures of about 5° C less than the melting temperature of an individual strand of the duplex and low concentrations of monovalent salts, such as monovalent salt concentrations. The complementarity of the nucleic acids of the duplex may be low overall but there may be segments of the nucleic acid that are contiguous and fully complementary to an equal-length segment of the target that, in the duplex form, allow for hybridizing across the target’s length. As used herein, the phrases “specifically binds” and “binds” refer to a binding reaction which is determinative of the presence of a particular molecule, in a heterogeneous population of ions, salts, small molecules, and / or proteins that is recognized. A variety of assay formats may be used to determine the affinity of a ligand for a specific protein. For example, solid-phase ELISA assays are routinely used to identify ligands that specifically bind a target protein. See, e.g., Harlow & Lane, Antibodies, A Laboratory Manual, Cold Spring Harbor Press, New York (1988) and Harlow & Lane, Using Antibodies, A Laboratory Manual, Cold Spring Harbor Press, New York (1999), for a description of assay formats and conditions that may be used to determine specific protein binding. ATTORNEY DOCKET NO.: 51772-005WO3 PATENT As used herein, the terms “subject” and “patient” refer to an animal (e.g., a mammal, such as a human). As used herein, the terms “administering,” “administration,” and the like refer to directly giving a patient an agent, for example, a therapeutic agent (e.g., a pharmaceutical composition including a viral vector including a nucleic acid sequence encoding a transgene operably linked to a promoter), by any effective route. Exemplary routes of administration are described herein and include systemic administration routes, such as intravenous injection, as well as routes of administration directly to muscle cells. As used herein, the term “dose” refers to the quantity of a therapeutic agent, such as a viral vector described herein, that is administered to a subject at a particular instant for the treatment of a disorder, such as to treat or ameliorate one or more symptoms of a disorder described herein. A therapeutic agent as described herein may be administered in a single dose or in multiple doses over the course of a treatment period, as defined herein. In each case, therapeutic agent may be administered using one or more unit dosage forms of therapeutic agent, a term that refers to a one or more discrete compositions containing a therapeutic agent that collectively constitute a single dose of the agent. As used herein, the terms “effective amount,” “therapeutically effective amount,” and a “sufficient amount” of composition, vector construct, or viral vector described herein refer to a quantity sufficient to, when administered to the subject, including a mammal, for example a human, effect beneficial or desired results, including clinical results, and, as such, an “effective amount” or synonym thereto depends upon the context in which it is being applied. For example, in the context of treating a disease, it is an amount of the composition, vector construct, or viral vector sufficient to achieve a treatment response as compared to the response obtained without administration of the composition, vector construct, or viral vector. The amount of a given composition described herein that will correspond to such an amount will vary depending upon various factors, such as the given agent, the pharmaceutical formulation, the route of administration, the type of disease or disorder, the identity of the subject (e.g., age, sex, weight) or host being treated, and the like, but may nevertheless be routinely determined by one skilled in the art. Also, as used herein, a “therapeutically effective amount” of a composition, vector construct, or viral vector of the present disclosure is an amount which results in a beneficial or desired result in a subject as compared to a control. As defined herein, a therapeutically effective amount of a composition, vector construct, or viral vector of the present disclosure may be readily determined by one of ordinary skill by routine methods known in the art. Dosage regime may be adjusted to provide the optimum therapeutic response. In the practice of the methods of the present invention, an “effective amount” of any one of the compounds or a combination of any of the compounds or a pharmaceutically acceptable salt thereof, is administered via any of the usual and acceptable methods known in the art, either singly or in combination. As used herein, the term “pharmaceutically acceptable” refers to those compounds, materials, compositions and / or dosage forms, which are suitable for contact with the tissues of a subject, such as a mammal (e.g., a human) without excessive toxicity, irritation, allergic response, and other problem complications commensurate with a reasonable benefit / risk ratio. As used herein, the term “pharmaceutical composition” refers to a mixture containing a therapeutic agent, such as a nucleic acid or vector described herein, optionally in combination with one or ATTORNEY DOCKET NO.: 51772-005WO3 PATENT more pharmaceutically acceptable excipients, diluents, and / or carriers, to be administered to a subject, such as a mammal, e.g., a human, in order to prevent, treat or control a particular disease or condition affecting or that may affect the subject. As used herein, the term “sample” refers to a specimen (e.g., blood, blood component (e.g., serum or plasma), urine, saliva, amniotic fluid, cerebrospinal fluid, tissue (e.g., placental, or dermal), pancreatic fluid, chorionic villus sample, and cells) isolated from a subject. As used herein, “treat”, “treatment”, or “treating” in reference to a disease or condition, refer to an approach for obtaining beneficial or desired results, e.g., clinical results. Beneficial or desired results may include, but are not limited to, alleviation or amelioration of one or more symptoms or conditions; diminishment of extent of disease or condition; stabilized (i.e., not worsening) state of disease, disorder, or condition; preventing spread of disease or condition; delay or slowing the progress of the disease or condition; amelioration or palliation of the disease or condition; and remission (whether partial or total), whether detectable or undetectable. “Ameliorating” or “palliating” a disease or condition means that the extent and / or undesirable clinical manifestations of the disease, disorder, or condition are lessened and / or time course of the progression is slowed or lengthened, as compared to the extent or time course in the absence of treatment. “Treatment” may also mean prolonging survival as compared to expected survival if not receiving treatment. Those in need of treatment include those already with the condition or disorder, as well as those prone to have the condition or disorder or those in which the condition or disorder is to be prevented. As used herein, the term “therapeutic protein” refers to (i) a protein whose deficiency or lack of activity is associated with a disorder (e.g., a genetic disorder, for example, a loss-of-function disorder recited in Table 4), as well as (ii) a protein that is not necessarily deficient in a patient, but whose supplementation would nonetheless have a beneficial effect on the patient. DETAILED DESCRIPTION Recombinant vectors derived from adeno-associated viruses (AAVs) are widely used in gene therapy, but have historically been hindered by insufficient transduction efficiency, resulting in levels of transgene expression that fall short of that required for robust therapeutic or prophylactic activity. This problem is directly addressed by the present invention, which provides peptide inserts that, upon incorporation into an AAV capsid protein, engender unexpected improvements in various important parameters, including transduction efficiency, tropism, and residence time in desired tissue. Using the compositions and methods disclosed herein, one may incorporate a peptide insert of the invention into AAV capsid protein, such as an existing, wild-type AAV capsid protein (e.g., VP1, VP2, VP3) associated with any known AAV serotype (e.g., AAV, AAV1, AAV2, AAV3, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV10, AAVrh10, AAVrh74). AAV capsids of the invention may, in turn, be used to encapsulate an AAV nucleic acid vector (e.g., encoding a therapeutic or prophylactic transgene of interest), thereby producing a viral particle. Viral particles described herein may be administered to patients by any of a variety of routes of administration, including intramuscular delivery, among an array of others described herein. Peptide inserts of the invention may have a core motif of three amino acids (e.g., MPR). A surprising benefit of the MPR motif is that MPR-containing peptides can confer a transduction advantage ATTORNEY DOCKET NO.: 51772-005WO3 PATENT when inserted into AAV capsid proteins. This effect is observed regardless of the peptide insert’s length, provided that the MPR core motif sequence is present within the inserted peptide. Additionally, described herein is the discovery that the position of the core MPR motif within the peptide sequence is flexible, allowing for frame-shifting capabilities. This flexibility means that the MPR motif can be positioned at various frames within the peptide sequence while maintaining its transduction-enhancing properties. Thus, MPR-containing peptides can confer enhanced transduction or tropism, regardless of the peptide’s length or the exact positioning of the MPR motif sequence within the peptide. Described in more detail below is the discovery and optimization (including in vivo AAV activity, muscle versus liver specificity, and vector manufacturability) of a number of capsid peptide inserts. Also described below are exemplary processes for incorporating peptide inserts of the invention into an AAV capsid protein, as well as methods of producing recombinant AAV particles containing peptide inserts disclosed herein and methods of administering the same to a patient in need thereof. In addition to being incorporated into AAV capsid proteins, peptide inserts of the invention can also be incorporated into other viral proteins. Furthermore, peptide inserts of the invention can be used as targeting agents for various drug delivery systems. Non-limiting examples of drug delivery systems are lipid nanoparticles (LNPs), exosomes, liposomes, lipoplexes, and vesicles. Peptide inserts used as targeting agents (e.g., attached to an LNP) may have increased transduction efficiency and tropism in target cells (e.g., muscle cells or cells of the nervous system). Peptide Inserts The peptide inserts of the invention are amino acid sequences that may be inserted into any one or more AAV capsid proteins, such as a wild-type AAV capsid protein known in the art. In addition to AAV capsid proteins, peptide inserts of the invention may also be incorporated into other viruses or attached to lipid nanoparticles, as described herein. In some embodiments, the peptide inserts may be of various length, e.g., 4 amino acids, 5 amino acids, 6 amino acids, 7 amino acids, 8 amino acids, 9 amino acids, 10 amino acids, 11 amino acids, 12 amino acids, 13 amino acids, 14 amino acids, 15 amino acids, 16 amino acids, 17 amino acids, 18 amino acids, 19 amino acids, 20 amino acids, 21 amino acids, 22 amino acids, 23 amino acids, 24 amino acids, 25 amino acids, 26 amino acids, 27 amino acids, 28 amino acids, 29 amino acids, 30 amino acids, 31 amino acids, 32 amino acids, 33 amino acids, 34 amino acids, 35 amino acids, 36 amino acids, 37 amino acids, 38 amino acids, 39 amino acids, or 40 amino acids, or more. In some embodiments, the peptide inserts may contain a core MPR motif. In some embodiments, the MPR motif may be at various frame positions, e.g., frame 1, frame 2, frame 3, frame 4, or frame 5, among others. An AAV capsid protein of the invention may, in turn, encapsulate a viral vector (e.g., an AAV vector), thereby furnishing a recombinant AAV particle. In some embodiments, an engineered AAV capsid of the invention containing one or more of the peptide inserts may direct or redirect AAVs to novel cellular receptors, resulting in enhanced transduction activity from intramuscular or other direct tissue routes of administration. Peptide inserts described herein may enhance muscle transduction and muscle-specificity when delivered intramuscularly or intravenously in vivo. In some embodiments, a peptide insert of the invention comprises an amino acid sequence of IMPR (SEQ ID NO: 512). In some embodiments, a peptide insert of the invention comprises an amino ATTORNEY DOCKET NO.: 51772-005WO3 PATENT acid sequence of AMPR (SEQ ID NO: 513). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of FMPR (SEQ ID NO: 514). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of MMPR (SEQ ID NO: 515). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of QMPR (SEQ ID NO: 516). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of YMPR (SEQ ID NO: 517). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of MPRT (SEQ ID NO: 518). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of MPRY (SEQ ID NO: 519). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of MPRQ (SEQ ID NO: 520). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of MPRS (SEQ ID NO: 521). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of IMPRT (SEQ ID NO: 490). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of AMPRY (SEQ ID NO: 522). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of MPRTA (SEQ ID NO: 523). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of MPRYG (SEQ ID NO: 524). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of MPRQP (SEQ ID NO: 525). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of MPRTP (SEQ ID NO: 526). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of IMPRTA (SEQ ID NO: 527). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of AMPRYG (SEQ ID NO: 528). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of MPRTAG (SEQ ID NO: 493). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of MPRYGG (SEQ ID NO: 529). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of MPRQPG (SEQ ID NO: 530). In some embodiments, a peptide insert of the invention comprises an amino acid sequence of MPRTPG (SEQ ID NO: 531). In some embodiments, a peptide insert of the invention has an amino acid sequence represented by Formula (I): (X1)MPR(X2)(X3)(X4) Formula (I) wherein each of (X1), (X2), (X3), and (X4), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala. In some embodiments, (X1) represents Phe, Leu, Ile, Met, or Gln. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, or Ala. In some embodiments, (X1) represents Tyr, Ile, Met, Ser, or Ala. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro. In some embodiments, (X2) represents Tyr, Ser, Thr, Gln, or Asp. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Phe, Tyr, Ser, Thr, Asn, or Gln. In some embodiments, (X2) represents Tyr or Thr. In some embodiments, (X3) represents ATTORNEY DOCKET NO.: 51772-005WO3 PATENT Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro. In some embodiments, (X3) represents Ile, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala or Pro. In some embodiments, (X3) represents Ala or Gly. In some embodiments, (X3) represents Val, Lys, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Gly, Ala, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, a peptide insert of the invention has an amino acid sequence represented by Formula (II): IMPR(X2)(X3)(X4) Formula (II) wherein each of (X2), (X3), and (X4), independently, represents any naturally occurring amino acid. In some embodiments, (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro. In some embodiments, (X2) represents Tyr, Ser, Thr, Gln, or Asp. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Phe, Tyr, Ser, Thr, Asn, or Gln. In some embodiments, (X2) represents Tyr or Thr. In some embodiments, (X3) represents Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro. In some embodiments, (X3) represents Ile, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala or Pro. In some embodiments, (X3) represents Ala or Gly. In some embodiments, (X3) represents Val, Lys, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Gly, Ala, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, a peptide insert of the invention has an amino acid sequence represented by Formula (III): AMPR(X2)(X3)(X4) Formula (III) wherein each of (X2), (X3), and (X4), independently, represents any naturally occurring amino acid. In some embodiments, (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro. In some embodiments, (X2) represents Tyr, Ser, Thr, Gln, or Asp. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Phe, Tyr, Ser, Thr, Asn, or Gln. In some embodiments, (X2) represents Tyr or Thr. In some embodiments, (X3) represents Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro. In some embodiments, (X3) represents Ile, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala or Pro. In some embodiments, (X3) represents Ala or Gly. In some embodiments, (X3) represents Val, Lys, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Gly, Ala, or Pro. In some embodiments, (X4) represents Gly or Ala. In ATTORNEY DOCKET NO.: 51772-005WO3 PATENT some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, a peptide insert of the invention has an amino acid sequence represented by Formula (IV): (X1)MPRT(X3)(X4) Formula (IV) wherein each of (X1), (X3), and (X4), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala. In some embodiments, (X1) represents Phe, Leu, Ile, Met, or Gln. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, or Ala. In some embodiments, (X1) represents Tyr, Ile, Met, Ser, or Ala. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X3) represents Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro. In some embodiments, (X3) represents Ile, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala or Pro. In some embodiments, (X3) represents Ala or Gly. In some embodiments, (X3) represents Val, Lys, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Gly, Ala, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, a peptide insert of the invention has an amino acid sequence represented by Formula (V): (X1)MPRY(X3)(X4) Formula (V) wherein each of (X1), (X3), and (X4), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala. In some embodiments, (X1) represents Phe, Leu, Ile, Met, or Gln. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, or Ala. In some embodiments, (X1) represents Tyr, Ile, Met, Ser, or Ala. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X3) represents Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro. In some embodiments, (X3) represents Ile, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala or Pro. In some embodiments, (X3) represents Ala or Gly. In some embodiments, (X3) represents Val, Lys, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Gly, Ala, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. ATTORNEY DOCKET NO.: 51772-005WO3 PATENT In some embodiments, a peptide insert of the invention has an amino acid sequence represented by Formula (VI): (X1)MPR(X2)A(X4) Formula (VI) wherein each of (X1), (X2), and (X4), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala. In some embodiments, (X1) represents Phe, Leu, Ile, Met, or Gln. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, or Ala. In some embodiments, (X1) represents Tyr, Ile, Met, Ser, or Ala. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro. In some embodiments, (X2) represents Tyr, Ser, Thr, Gln, or Asp. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Phe, Tyr, Ser, Thr, Asn, or Gln. In some embodiments, (X2) represents Tyr or Thr. In some embodiments, (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Gly, Ala, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, a peptide insert of the invention has an amino acid sequence represented by Formula (VII): (X1)MPR(X2)G(X4) Formula (VII) wherein each of (X1), (X2), and (X4), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala. In some embodiments, (X1) represents Phe, Leu, Ile, Met, or Gln. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, or Ala. In some embodiments, (X1) represents Tyr, Ile, Met, Ser, or Ala. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro. In some embodiments, (X2) represents Tyr, Ser, Thr, Gln, or Asp. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Phe, Tyr, Ser, Thr, Asn, or Gln. In some embodiments, (X2) represents Tyr or Thr. In some embodiments, (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro. In some embodiments, (X4) represents Ser, Gly, Ala, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. In some embodiments, (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro. In some embodiments, (X4) represents Gly or Ala. In some embodiments, (X4) represents Gly or Pro. In some embodiments, (X4) represents Gly. ATTORNEY DOCKET NO.: 51772-005WO3 PATENT In some embodiments, a peptide insert of the invention has an amino acid sequence represented by Formula (VIII): (X1)MPR(X2)(X3)G Formula (VIII) wherein each of (X1), (X2), and (X3), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala. In some embodiments, (X1) represents Phe, Leu, Ile, Met, or Gln. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, Ala, or Gly. In some embodiments, (X1) represents Phe, Leu, Ile, Met, Gln, or Ala. In some embodiments, (X1) represents Tyr, Ile, Met, Ser, or Ala. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro. In some embodiments, (X2) represents Tyr, Ser, Thr, Gln, or Asp. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro. In some embodiments, (X2) represents Ser, Thr, or Gln. In some embodiments, (X2) represents Phe, Tyr, Ser, Thr, Asn, or Gln. In some embodiments, (X2) represents Tyr or Thr. In some embodiments, (X3) represents Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro. In some embodiments, (X3) represents Ile, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala or Pro. In some embodiments, (X3) represents Ala or Gly. In some embodiments, (X3) represents Val, Lys, Ala, Gly, or Pro. In some embodiments, (X3) represents Ala, Gly, or Pro. In some embodiments, a peptide insert of the invention has an amino acid sequence represented by Formula (IX): (X1)MPR(X2)(Nonpolar1)G Formula (IX) wherein (Nonpolar1) represents any amino acid listed in Table 1, above, as having a nonpolar, neutral side chain, and wherein each of (X1) and (X2), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Val, Asn, His, Lys, or Gly. In some embodiments, (X1) represents Lys, Met, Leu, Gln, Tyr, Phe, Thr, Ile, and Ala. In some embodiments, (X1) represents Tyr, Ser, Ala, Ile, or Met. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X2) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Val, Asn, His, Gly, or Trp. In some embodiments, (X2) represents Gln, Phe, Tyr, Thr, Ser, or Asn. In some embodiments, (X2) represents Tyr or Thr. In some embodiments, (Nonpolar1) represents Phe, Met, Leu, Ala, Ile, Val, Gly, and Pro. In some embodiments, (Nonpolar1) represents Ala, Val, Ile, Gly, or Pro. In some embodiments, (Nonpolar1) represents Ala, Gly, or Pro. In some embodiments, (Nonpolar1) represents Ala or Gly. In some embodiments, a peptide insert of the invention has an amino acid sequence represented by Formula (X): (X1)M(X2)(X3)(X4)(X5)(X6) Formula (X) ATTORNEY DOCKET NO.: 51772-005WO3 PATENT wherein (X2) represents an amino acid selected from the group consisting of Pro and Ser, and wherein each of (X1), (X3), (X4), (X5), and (X6), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Val, Asn, His, Lys, or Gly. In some embodiments, (X1) represents Lys, Met, Leu, Gln, Tyr, Phe, Thr, Ile, and Ala. In some embodiments, (X1) represents Tyr, Ser, Ala, Ile, or Met. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Pro. In some embodiments, (X2) represents Ser. In some embodiments, (X3) represents Val, His, or Arg. In some embodiments, (X3) represents Arg. In some embodiments, (X4) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X4) represents Gln, Phe, Tyr, Thr, Ser, or Asn. In some embodiments, (X4) represents Tyr or Thr. In some embodiments, (X5) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X5) represents Ala, Gly, or Pro. In some embodiments, (X5) represents Ala or Gly. In some embodiments, (X6) represents Pro, Lys, Ala, Arg, Ser, Gly, Val, Leu, Gln, Thr, Ile, Met, and Asn. In some embodiments, (X6) represents Gly or Ala. In some embodiments, (X6) represents Gly or Pro. In some embodiments, (X6) represents Gly. In some embodiments, a peptide insert of the invention has an amino acid sequence represented by Formula (XI): (X1)M(X2)(X3)(X4)(X5)G Formula (XI) wherein (X2) represents an amino acid selected from the group consisting of Pro and Ser, and wherein each of (X1), (X3), (X4), and (X5), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Val, Asn, His, Lys, or Gly. In some embodiments, (X1) represents Lys, Met, Leu, Gln, Tyr, Phe, Thr, Ile, and Ala. In some embodiments, (X1) represents Tyr, Ser, Ala, Ile, or Met. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Pro. In some embodiments, (X2) represents Ser. In some embodiments, (X3) represents Val, His, or Arg. In some embodiments, (X3) represents Arg. In some embodiments, (X4) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X4) represents Gln, Phe, Tyr, Thr, Ser, or Asn. In some embodiments, (X4) represents Tyr or Thr. In some embodiments, (X5) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X5) represents Ala, Gly, or Pro. In some embodiments, (X5) represents Ala or Gly. In some embodiments, a peptide insert of the invention has an amino acid sequence represented by Formula (XII): (X1)M(X2)(X3)(X4)(Nonpolar1)G Formula (XII) wherein (X2) represents an amino acid selected from the group consisting of Pro and Ser, (Nonpolar1) represents any amino acid listed in Table 1, above, as having a nonpolar, neutral side chain, and each of (X1), (X3), and (X4), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, ATTORNEY DOCKET NO.: 51772-005WO3 PATENT Gly, Trp, or Pro. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Val, Asn, His, Lys, or Gly. In some embodiments, (X1) represents Lys, Met, Leu, Gln, Tyr, Phe, Thr, Ile, and Ala. In some embodiments, (X1) represents Tyr, Ser, Ala, Ile, or Met. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Pro. In some embodiments, (X2) represents Ser. In some embodiments, (X3) represents Val, His, or Arg. In some embodiments, (X3) represents Arg. In some embodiments, (X4) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X4) represents Gln, Phe, Tyr, Thr, Ser, or Asn. In some embodiments, (X4) represents Tyr or Thr. In some embodiments, (Nonpolar1) represents Phe, Met, Leu, Ala, Ile, Val, Gly, and Pro. In some embodiments, (Nonpolar1) represents Ala, Val, Ile, Gly, or Pro. In some embodiments, (Nonpolar1) represents Ala, Gly, or Pro. In some embodiments, (Nonpolar1) represents Ala or Gly. In some embodiments, a peptide insert of the invention has an amino acid sequence represented by Formula (XIII): (X1)M(X2)(X3)(X4)(Nonpolar1)(Nonpolar2) Formula (XIII) wherein (X2) represents an amino acid selected from the group consisting of Pro and Ser, each of (Nonpolar1) and (Nonpolar2), independently, represents any amino acid listed in Table 1, above, as having a nonpolar, neutral side chain, and each of (X1), (X3), and (X4), independently, represents any naturally occurring amino acid. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Val, Asn, His, Lys, or Gly. In some embodiments, (X1) represents Lys, Met, Leu, Gln, Tyr, Phe, Thr, Ile, and Ala. In some embodiments, (X1) represents Tyr, Ser, Ala, Ile, or Met. In some embodiments, (X1) represents Ala or Ile. In some embodiments, (X2) represents Pro. In some embodiments, (X2) represents Ser. In some embodiments, (X3) represents Val, His, or Arg. In some embodiments, (X3) represents Arg. In some embodiments, (X4) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro. In some embodiments, (X4) represents Gln, Phe, Tyr, Thr, Ser, or Asn. In some embodiments, (X4) represents Tyr or Thr. In some embodiments, (Nonpolar1) represents Phe, Met, Leu, Ala, Ile, Val, Gly, and Pro. In some embodiments, (Nonpolar1) represents Ala, Val, Ile, Gly, or Pro. In some embodiments, (Nonpolar1) represents Ala, Gly, or Pro. In some embodiments, (Nonpolar1) represents Ala or Gly. In some embodiments, (Nonpolar2) represents Met, Leu, Gly, Ala, or Pro. In some embodiments, (Nonpolar2) represents Gly or Ala. In some embodiments, (Nonpolar2) represents Gly or Pro. In some embodiments, (Nonpolar2) represents Gly. Amino acid sequences may appear at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between. Table 2 illustrates exemplary peptide inserts of the invention. Table 2. Exemplary Peptide Inserts ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT AAV Capsid Proteins The peptide inserts of the invention may be incorporated into any one or more AAV capsid proteins that are known in the art. AAV capsid proteins compose the exterior, non-nucleic acid portion of the viral particle and are encoded by the AAV Cap gene. The Cap gene encodes three viral coat proteins, VP1, VP2 and VP3, which are required for particle assembly. The sequences of naturally existing capsid proteins associated with AAV serotypes are known in the art and include those disclosed herein as AAV1, AAV2, AAV3, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV10, AAVrh10, and AAVrh74. Table 3 illustrates several, non-limiting examples of naturally occurring AAV capsid proteins. Table 3. Capsid Proteins of AAV Serotypes ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT In some embodiments, a peptide insert of the invention may be incorporated into a variant AAV capsid protein, such as a variant of any of the capsid protein sequence recited in Table 3, above. For example, an AAV peptide insert of the invention may be incorporated into an amino acid sequence having at least, e.g., 85% identity to the amino acid sequence of any one of SEQ ID NOs: 496-511 (e.g., at least 85% identity, 87% identity, 88% identity, 89% identity, 90% identity, 91% identity, 92% identity, 93% identity, 94% identity, 95% identity, 96% identity, 97% identity, 98% identity, 99% identity, or 100% identity to any one of SEQ ID NOs: 496-511). Peptide inserts of the invention may be incorporated at one of several different sites within an AAV Cap gene. Peptide inserts may be incorporated in any one or more of nine variable loop regions on the surface of the AAV capsid, for example, VR-I, VR-II, VR-III, VR-IV, VR-V, VR-VI, VR-VII, VR-VIII, and VR-IX. In preferred embodiments, peptides of the invention may be inserted between any amino acids of VR-VIII (e.g., of AAV9), for example, between amino acids 581 and 582, amino acids 582 and 583, amino acids 583 and 584, amino acids 584 and 585, amino acids 585 and 586, amino acids 586 and 587, amino acids 587 and 588, amino acids 588 and 589, amino acids 589 and 590, amino acids 590 and 591, amino acids 591 and 592, or amino acids 592 and 593, with numbering of amino acids with respect to VP1 (DiMattia et al., Journal of Virology 86:12 (2012), the disclosure of which is incorporated herein by reference). Methods of Screening for Optimized AAV Capsid Variants Various processes may be used to characterize and further refine AAV capsid variants containing peptide inserts. For example, such variants may be screened to identify optimized AAV capsid variants with the use of library-based approaches. Generally, an AAV capsid library may be generated by expressing engineered capsid variants, each containing a peptide insert of the invention, in an appropriate AAV producer cell line. ATTORNEY DOCKET NO.: 51772-005WO3 PATENT After first-round administration, one or more engineered AAV viral particles having an engineered capsid variant may then be used to form a filtered AAV capsid library. Desirable AAV viral particles may be identified by measuring the mRNA expression of the capsid variants and determining which variants are highly expressed in the desired cell type(s) as compared to non-desired cells type(s). Those that are highly expressed in the desired cell, tissue, and / or organ type are the desired AAV capsid variant particles. The recombinant AAV capsid variant particles identified from the first round may then be administered to various non-human animals. In some embodiments, the animals used in the second round of selection and identification are not the same as those animals used for first round selection and identification. Similar to round 1, after administration the top expressing variants in the desired cell, tissue, and / or organ type(s) may be identified by measuring viral mRNA expression in the cells. Administration at each round may be systemic. The top variants, or optimized capsid variants, identified after round two may then be optionally barcoded and optionally pooled. In some embodiments, optimized capsid variants from the second round may then be administered to a non-human primate to identify the top cell-specific variant(s), particularly if the end use for the top variant is in humans. In some embodiments, the method of generating an AAV capsid variant may include the steps of: (a) expressing a vector system described herein that contains an engineered AAV capsid polynucleotide in a cell to produce engineered AAV virus particle capsid variants; (b) harvesting the engineered AAV virus particle capsid variants produced in step (a); (c) administering engineered AAV virus particle capsid variants to one or more first subjects, wherein the engineered AAV virus particle capsid variants are produced by expressing an engineered AAV capsid variant vector or system thereof in a cell and harvesting the engineered AAV virus particle capsid variants produced by the cell; and (d) identifying one or more engineered AAV capsid variants produced at a significantly high level by one or more specific cells or specific cell types in the one or more first subjects. The method may further include the steps of: (e) administering some or all engineered AAV capsid variant particles identified in step (d) to one or more second subjects; and (f) identifying one or more optimized AAV capsid variant particles produced at a significantly high level in one or more specific cells or specific cell types in the one or more second subjects. The cell in step (a) may be a prokaryotic cell or a eukaryotic cell. In some embodiments, the administration in step (c), step (e), or both is systemic. In some embodiments, one or more first subjects, one or more second subjects, or both, are non-human mammals. In some embodiments, one or more first subjects, one or more second subjects, or both, are each independently selected from the group consisting of: a wild-type non-human mammal, a humanized non-human mammal, a disease-specific non-human mammal model, and a non-human primate. AAV Vectors for Nucleic Acid Delivery Nucleic acids encoding optimized capsid variants containing the peptide inserts of the invention may be incorporated into an AAV particle in order to facilitate introduction into a target cell of interest. AAV particles useful in conjunction with the compositions and methods described herein include those derived from a variety of AAV serotypes, including AAV 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, rh10, rh74, and others. Construction and use of AAV vectors and AAV proteins of different serotypes are described, for example, in Chao et al., Mol. Ther.2:619-623 (2000); Davidson et al., Proc. Natl. Acad. Sci. USA 97:3428-3432 ATTORNEY DOCKET NO.: 51772-005WO3 PATENT (2000); Xiao et al., J. Virol.72:2224-2232 (1998); Halbert et al., J. Virol.74:1524-1532 (2000); Halbert et al., J. Virol.75:6615-6624 (2001); and Auricchio et al., Hum. Molec. Genet.10:3075-3081 (2001), the disclosures of each of which are incorporated herein by reference as they pertain to AAV vectors for gene delivery. Also useful in conjunction with the compositions and methods described herein are pseudotyped AAV vectors. Pseudotyped vectors include AAV vectors of a given serotype (e.g., AAV9) pseudotyped with a capsid gene derived from a serotype other than the given serotype (e.g., AAV1, AAV2, AAV3, AAV4, AAV5, AAV6, AAV7, AAV8, etc.). For example, a representative pseudotyped vector is an AAV2 vector encoding a therapeutic protein pseudotyped with a capsid gene derived from AAV serotype 8 or AAV serotype 9. For example, a representative pseudotyped vector is an AAV8 vector encoding a therapeutic protein pseudotyped with a capsid gene derived from AAV serotype 2. Techniques involving the construction and use of pseudotyped AAV particles are known in the art and are described, for example, in Duan et al., J. Virol.75:7662-7671 (2001); Halbert et al., J. Virol.74:1524-1532 (2000); Zolotukhin et al., Methods, 28:158-167 (2002); and Auricchio et al., Hum. Molec. Genet., 10:3075-3081 (2001). AAV Particle Production AAV particles of the invention, containing one or more of the optimized AAV capsid proteins described herein, may be manufactured from producer cells. There are various approaches to producing AAV particles, often differing based on how the adenovirus helper factors are provided to a producer cell. As non-limiting examples, in some embodiments, a method of producing AAV particles may include introducing, into cell lines that stably harbor AAV replication- and capsid-encoding polynucleotides, adenovirus helper factors and the target AAV genome (containing, e.g., a transgene of interest). In some embodiments, a method of producing AAV particles includes co-transfection of an appropriate producing cell line with three vectors (e.g., plasmid vectors): (1) an AAV genome that contains a transgene of interest between two ITRs; (2) a vector that carries the AAV Rep-Cap encoding polynucleotides; and (3) a vector containing helper polynucleotides. The construction of AAV particles has been described, e.g., in US Patent Nos.5,173,414; 5,139,941; 5,863,541; 5,869,305; 6,057,152; and 6,376,237; as well as in Rabinowitz et al., J. Virol. 76:791-801 (2002) and Bowles et al., J. Virol.77:423-432 (2003), the disclosures of each of which are incorporated herein by reference as they pertain to AAV vectors for gene delivery. The engineered AAV vectors and systems thereof described herein may be produced by any of these methods. Cell-based Vector Amplification and Expression Vectors may be designed for expression of one or more elements of the optimized AAV capsid system in a suitable producer cell. In some embodiments, the suitable producer cell is a eukaryotic cell. Suitable producer cells include, but are not limited to, insect cells and mammalian cells. The vectors may be viral-based or non-viral based. In some embodiments, the vector is a baculovirus vector or expression vector and may be suitable for expression of polynucleotides and / or proteins in insect cells. Baculovirus vectors available for expression of proteins in cultured insect cells (e.g., SF9 cells) include the pAc series (Smith, et al., 1983. ATTORNEY DOCKET NO.: 51772-005WO3 PATENT Mol. Cell. Biol.3: 2156-2165) and the pVL series (Lucklow and Summers, 1989. Virology 170: 31-39). rAAV (recombinant adeno-associated viral) vectors are preferably produced in insect cells, e.g., Spodoptera frugiperda S19 insect cells, grown in serum-free suspension culture. Serum-free insect cells may be purchased from commercial vendors, e.g., Sigma Aldrich (EX-CELL 405). In some embodiments, the vector is a mammalian expression vector. In some embodiments, the mammalian expression vector is capable of expressing one or more polynucleotides and / or polypeptides in a mammalian cell. Examples of mammalian expression vectors include, but are not limited to, pCDM8 (Seed, 1987. Nature 329: 840) and pMT2PC (Kaufman, et al., 1987. EMBO J.6: 187-195). The mammalian expression vector may include one or more suitable regulatory elements capable of controlling expression of the one or more polynucleotides and / or proteins in the mammalian cell. For example, commonly used promoters are derived from polyoma, adenovirus 2, cytomegalovirus, simian virus 40, and others disclosed herein and known in the art. More detail on suitable regulatory elements is described elsewhere herein. For other suitable expression vectors and vector systems for both prokaryotic and eukaryotic cells see, e.g., Chapters 16 and 17 of Sambrook, et al, MOLECULAR CLONING: A LABORATORY MANUAL.2nd ed., Cold Spring Harbor Laboratory, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1989. In some embodiments, the recombinant mammalian expression vector is capable of directing expression of the nucleic acid preferentially in a particular cell type (e.g., tissue-specific regulatory elements are used to express the nucleic acid). Tissue-specific regulatory elements are known in the art. Non-limiting examples of suitable tissue-specific promoters include the albumin promoter (liver-specific; Pinkert, et al, 1987. Genes Dev.1: 268-277) and muscle-specific promoters (Skopenkova, et al, 2021. Acta Naturae 13:47-58). Developmentally-regulated promoters are also encompassed, e.g., the murine hox promoters (Kessel and Gruss, 1990. Science 249: 374-379) and the a-fetoprotein promoter (Campes and Tilghman, 1989. Genes Dev.3: 537-546). With regards to these eukaryotic vectors, mention is made of U.S. Patent 6,750,059, the contents of which are incorporated by reference herein in their entirety. Other embodiments may utilize viral vectors, with regards to which mention is made of U.S. Patent application 13 / 092,085, the contents of which are incorporated by reference herein in their entirety. Tissue-specific regulatory elements are known in the art and in this regard, mention is made of U.S. Patent 7,776,321, the contents of which are incorporated by reference herein in their entirety. In some embodiments, a regulatory element may be operably linked to one or more elements of an optimized AAV capsid system so as to drive expression of the one or more elements of the optimized AAV capsid system described herein. Methods for the Delivery of Exogenous Nucleic Acids to Host Cells The vector or vector components described herein may be delivered into a host cell, such as a producer cell or a target cell, by any suitable method. Suitable methods of the invention include, but are not limited to, those described below. Techniques that may be used to introduce a polynucleotide, such as codon-optimized DNA or RNA (e.g., mRNA, tRNA, siRNA, miRNA, shRNA, chemically modified RNA) into a mammalian cell are well known in the art. For example, electroporation may be used to permeabilize mammalian cells (e.g., human target cells) by the application of an electrostatic potential to the cell of interest. Mammalian cells, ATTORNEY DOCKET NO.: 51772-005WO3 PATENT such as human cells, subjected to an external electric field in this manner are subsequently predisposed to the uptake of exogenous nucleic acids. Electroporation of mammalian cells is described in detail, e.g., in Chu et al., Nucleic Acids Research 15:1311 (1987), the disclosure of which is incorporated herein by reference. A similar technique, NucleofectionTM, utilizes an applied electric field in order to stimulate the uptake of exogenous polynucleotides into the nucleus of a eukaryotic cell. NucleofectionTMand protocols useful for performing this technique are described in detail, e.g., in Distler et al., Experimental Dermatology 14:315 (2005), as well as in US 2010 / 0317114, the disclosures of each of which are incorporated herein by reference. Additional techniques useful for the transfection of target cells are the squeeze-poration methodology. This technique induces the rapid mechanical deformation of cells in order to stimulate the uptake of exogenous DNA through membranous pores that form in response to the applied stress. This technology is advantageous in that a vector is not required for delivery of nucleic acids into a cell, such as a human target cell. Squeeze-poration is described in detail, e.g., in Sharei et al., Journal of Visualized Experiments 81:e50980 (2013), the disclosure of which is incorporated herein by reference. Lipofection represents another technique useful for transfection of target cells. This method involves the loading of nucleic acids into a liposome, which often presents cationic functional groups, such as quaternary or protonated amines, towards the liposome exterior. This promotes electrostatic interactions between the liposome and a cell due to the anionic nature of the cell membrane, which ultimately leads to uptake of the exogenous nucleic acids, for example, by direct fusion of the liposome with the cell membrane or by endocytosis of the complex. Lipofection is described in detail, for example, in US 7,442,386, the disclosure of which is incorporated herein by reference. Similar techniques that exploit ionic interactions with the cell membrane to provoke the uptake of foreign nucleic acids are contacting a cell with a cationic polymer-nucleic acid complex. Exemplary cationic molecules that associate with polynucleotides so as to impart a positive charge favorable for interaction with the cell membrane are activated dendrimers (described, e.g., in Dennig, Topics in Current Chemistry 228:227 (2003), the disclosure of which is incorporated herein by reference) polyethylenimine, and diethylaminoethyl (DEAE)-dextran, the use of which as a transfection agent is described in detail, for example, in Gulick et al., Current Protocols in Molecular Biology 40:I:9.2:9.2.1 (1997), the disclosure of which is incorporated herein by reference. Magnetic beads are another tool that may be used to transfect target cells in a mild and efficient manner, as this methodology utilizes an applied magnetic field in order to direct the uptake of nucleic acids. This technology is described in detail, for example, in US 2010 / 0227406, the disclosure of which is incorporated herein by reference. Another useful tool for inducing the uptake of exogenous nucleic acids by target cells is laserfection, also called optical transfection, a technique that involves exposing a cell to electromagnetic radiation of a particular wavelength in order to gently permeabilize the cells and allow polynucleotides to penetrate the cell membrane. The bioactivity of this technique is similar to, and in some cases found superior to, electroporation. Impalefection is another technique that may be used to deliver genetic material to target cells. It relies on the use of nanomaterials, such as carbon nanofibers, carbon nanotubes, and nanowires. Needle-like nanostructures are synthesized perpendicular to the surface of a substrate. DNA containing the gene, intended for intracellular delivery, is attached to the nanostructure surface. A chip with arrays of ATTORNEY DOCKET NO.: 51772-005WO3 PATENT these needles is then pressed against cells or tissue. Cells that are impaled by nanostructures may express the delivered gene(s). An example of this technique is described in Shalek et al., PNAS 107: 1870 (2010), the disclosure of which is incorporated herein by reference. Magnetofection may also be used to deliver nucleic acids to target cells. The magnetofection principle is to associate nucleic acids with cationic magnetic nanoparticles. The magnetic nanoparticles are made of iron oxide, which is fully biodegradable, and coated with specific cationic proprietary molecules varying upon the applications. Their association with the gene vectors (DNA, siRNA, viral vector, etc.) is achieved by salt-induced colloidal aggregation and electrostatic interaction. The magnetic particles are then concentrated on the target cells by the influence of an external magnetic field generated by magnets. This technique is described in detail in Scherer et al., Gene Therapy 9:102 (2002), the disclosure of which is incorporated herein by reference. Another useful tool for inducing the uptake of exogenous nucleic acids by target cells is sonoporation, a technique that involves the use of sound (typically ultrasonic frequencies) for modifying the permeability of the cell plasma membrane permeabilize the cells and allow polynucleotides to penetrate the cell membrane. This technique is described in detail, e.g., in Rhodes et al., Methods in Cell Biology 82:309 (2007), the disclosure of which is incorporated herein by reference. Microvesicles represent another potential vehicle that may be used to modify the genome of a target cell according to the methods described herein. For example, microvesicles that have been induced by the co-overexpression of the glycoprotein VSV-G with, e.g., a genome-modifying protein, such as a nuclease, may be used to efficiently deliver proteins into a cell that subsequently catalyze the site- specific cleavage of an endogenous polynucleotide sequence so as to prepare the genome of the cell for the covalent incorporation of a polynucleotide of interest, such as a gene or regulatory sequence. The use of such vesicles, also referred to as Gesicles, for the genetic modification of eukaryotic cells is described in detail, e.g., in Quinn et al., Genetic Modification of Target Cells by Direct Delivery of Active Protein [abstract]. In: Methylation changes in early embryonic genes in cancer [abstract], in: Proceedings of the 18th Annual Meeting of the American Society of Gene and Cell Therapy; 2015 May 13, Abstract No.122. Cell-free Vector and Polynucleotide Expression The AAV capsid proteins of the invention may be incorporated into a vector or suitable polynucleotide in a cell-free in vitro system. In other words, AAV capsid proteins may be transcribed and optionally translated in vitro. In vitro transcription / translation systems and appropriate vectors are generally known in the art and commercially available. Generally, in vitro transcription and in vitro translation systems replicate the processes of RNA and protein synthesis, respectively, outside of the cellular environment. Vectors and suitable polynucleotides for in vitro transcription may include T7, SP6, T3, promoter regulatory sequences that may be recognized and acted upon by an appropriate polymerase to transcribe the polynucleotide or vector. In vitro translation may be stand-alone (e.g., translation of a purified polyribonucleotide) or linked / coupled to transcription. In some embodiments, the cell-free (or in vitro) translation system may include extracts from rabbit reticulocytes, wheat germ, and / or E. cob. The extracts may include various macromolecular components that are needed for translation of exogenous RNA (e.g., 70S or 80S ribosomes, tRNAs, aminoacyl-tRNA, synthetases, initiation, elongation factors, termination factors, etc.). ATTORNEY DOCKET NO.: 51772-005WO3 PATENT Other components may be included or added during the translation reaction, including but not limited to, amino acids, energy sources (ATP, GTP), energy regenerating systems (creatine phosphate and creatine phosphokinase (eukaryotic systems)) (phosphoenol pyruvate and pyruvate kinase for bacterial systems), and other co-factors (Mg2+, K+, etc.). As previously mentioned, in vitro translation may be based on RNA or DNA starting material. Some translation systems may utilize an RNA template as starting material (e.g., reticulocyte lysates and wheat germ extracts). Some translation systems may utilize a DNA template as a starting material (e.g., E cob-based systems). In these systems transcription and translation are coupled and DNA is first transcribed into RNA, which is subsequently translated. Suitable standard and coupled cell-free translation systems are generally known in the art and are commercially available. Selectable Markers and Tags Selectable markers and tags may be used in conjunction with cell-based and cell-free vector amplification and expression. One or more of the engineered polynucleotides of the present invention (e.g., an optimized AAV capsid polynucleotide) may be operably linked, fused to, or otherwise modified to include a polynucleotide that encodes a selectable marker or tag, which may be a polynucleotide or polypeptide. In some embodiments, the polypeptide encoding a polypeptide selectable marker may be incorporated in the engineered polynucleotide of the present invention (e.g., an optimized AAV capsid polynucleotide) such that the selectable marker polypeptide, when translated, is inserted between two amino acids between the N- and C- terminus of an engineered polypeptide (e.g., an optimized AAV capsid polypeptide). It will be appreciated that the polynucleotide encoding such selectable markers or tags may be incorporated into a polynucleotide encoding one or more components of the engineered AAV capsid system described herein in an appropriate manner to allow expression of the selectable marker or tag. Such techniques and methods are described elsewhere herein and will be instantly appreciated by one of ordinary skill in the art in view of this disclosure. Many such selectable markers and tags are generally known in the art and are intended to be within the scope of this disclosure. Suitable selectable markers and tags include, but are not limited to, affinity tags, such as chitin binding protein (CBP), maltose binding protein (MBP), glutathione-S-transferase (GST), poly(His) tag; solubilization tags such as thioredoxin (TRX) and poly(NANP), MBP, and GST; chromatography tags such as those consisting of polyanionic amino acids, such as FLAG-tag; epitope tags such as V5-tag, Myc-tag, HA-tag and NE-tag; protein tags that may allow specific enzymatic modification (such as biotinylation by biotin ligase) or chemical modification (such as reaction with FlAsH-EDT2 for fluorescence imaging), DNA and / or RNA segments that contain restriction enzyme or other enzyme cleavage sites; DNA segments that encode products that provide resistance against otherwise toxic compounds including antibiotics, such as, spectinomycin, ampicillin, kanamycin, tetracycline, Basta, neomycin phosphotransferase II (NEO), hygromycin phosphotransferase (HPT)) and the like; DNA and / or RNA segments that encode products that are otherwise lacking in the recipient cell (e.g., tRNA genes, auxotrophic markers); DNA and / or RNA segments that encode products which may be readily identified (e.g., phenotypic markers such as b-galactosidase, GUS; fluorescent proteins such as green fluorescent protein (GFP), cyan (CFP), yellow (YFP), red (RFP), luciferase, and cell surface proteins); polynucleotides that may generate one or more new primer sites for PCR (e.g., the juxtaposition of two ATTORNEY DOCKET NO.: 51772-005WO3 PATENT DNA sequences not previously juxtaposed), DNA sequences not acted upon or acted upon by a restriction endonuclease or other DNA modifying enzyme, chemical, etc.; epitope tags (e.g. GFP, FLAG- and His-tags), and, DNA sequences that make a molecular barcode or unique molecular identifier (UMI), DNA sequences required for a specific modification (e.g., methylation) that allows its identification. Other suitable markers will be appreciated by those of skill in the art. Selectable markers and tags may be operably linked to one or more components of the optimized AAV capsid system or other compositions and / or systems described herein via suitable linker. The vector or vector system may include one or more polynucleotides encoding one or more targeting moieties. In some embodiments, the targeting moiety encoding polynucleotides may be included in the vector or vector system, such as a viral vector system, such that they are expressed within and / or on the virus particle(s) produced such that the virus particles may be targeted to specific cells, tissues, organs, etc. In some embodiments, the targeting moiety encoding polynucleotides may be included in the vector or vector system such that the engineered polynucleotide(s) of the present invention (e.g., an optimized AAV capsid polynucleotide(s)) and / or products expressed therefrom include the targeting moiety and may be targeted to specific cells, tissues, organs, etc. In some embodiments, such as non- viral carriers, the targeting moiety may be attached to the carrier (e.g., polymer, lipid, inorganic molecule etc.) and may be capable of targeting the carrier and any attached or associated engineered polypeptides of the present invention, or other compositions of the present invention described herein, to specific cells, tissues, organs, etc. In some embodiments, the specific cells are muscle cells. Non-AAV Viral Vectors for Nucleic Acid Delivery The peptide inserts of the invention may be incorporated into a non-AAV viral particle for nucleic acid delivery. Viral genomes provide a rich source of vectors that can be used for the efficient delivery of a transgene of interest into a host cell (e.g., a muscle cell or neural cell). Viral genomes are particularly useful vectors for gene delivery because the polynucleotides contained within such genomes are typically incorporated into the genome of a target cell by generalized or specialized transduction. These processes occur as part of the natural viral replication cycle and do not require added proteins or reagents to induce gene integration. Examples of viral vectors that may be used in conjunction with the compositions and methods described herein are AAV, retrovirus, adenovirus (e.g., Ad5, Ad26, Ad34, Ad35, and Ad48), parvovirus (e.g., adeno-associated viruses), coronavirus, negative strand RNA viruses such as orthomyxovirus (e.g., influenza virus), rhabdovirus (e.g., rabies and vesicular stomatitis virus), paramyxovirus (e.g. measles and Sendai), positive strand RNA viruses, such as picornavirus and alphavirus, and double stranded DNA viruses including adenovirus, herpesvirus (e.g., Herpes Simplex virus types 1 and 2, Epstein-Barr virus, cytomegalovirus), and poxvirus (e.g., vaccinia, modified vaccinia Ankara (MVA), fowlpox and canarypox). Other viruses that may be used in conjunction with the compositions and methods described herein include Norwalk virus, togavirus, flavivirus, reoviruses, papovavirus, hepadnavirus, and hepatitis virus, for example. Examples of retroviruses include avian leukosis-sarcoma, mammalian C-type, B-type viruses, D-type viruses, HTLV-BLV group, lentivirus, spumavirus (Coffin, J. M., Retroviridae: The viruses and their replication, In Fundamental Virology, Third Edition, B. N. Fields, et al., Eds., Lippincott-Raven Publishers, Philadelphia, 1996). Other examples include murine leukemia viruses, murine sarcoma viruses, mouse mammary tumor virus, bovine leukemia ATTORNEY DOCKET NO.: 51772-005WO3 PATENT virus, feline leukemia virus, feline sarcoma virus, avian leukemia virus, human T-cell leukemia virus, baboon endogenous virus, Gibbon ape leukemia virus, Mason Pfizer monkey virus, simian immunodeficiency virus, simian sarcoma virus, Rous sarcoma virus and lentiviruses. Other examples of vectors are described, for example, in US Patent No.5,801,030, the disclosure of which is incorporated herein by reference as it pertains to viral vectors for use in gene therapy. Lipid Nanoparticles (LNPs) The peptide inserts of the invention may be attached (e.g., covalently or non-covalently) to lipid nanoparticles (LNPs) to enhance targeting of specific cell types, e.g. muscle cells or neural cells. These LNPs, modifications thereof, and pharmaceutical compositions thereof are useful for the methods of treatment described herein. The term “lipid nanoparticle” or “LNP” refers to a transfer or delivery vehicle including one or more lipids (e.g., cationic lipids, non-cationic lipids, and polyethylene glycol (PEG)-modified lipids). LNPs are nanoparticles composed of lipids. LNPs are generally spherical and have an average diameter ranging from 10 to 1000 nm. Examples of suitable lipids include, for example, the phosphatidyl compounds (e.g., phosphatidylglycerol, phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, sphingolipids, cerebrosides, and gangliosides). Examples of suitable lipids also include, for example, triglycerides, diglycerides, monoglycerides, fatty acids, steroids, and waxes. LNPs may contain a cationic lipid, or a lipid species with a net positive charge at a selected pH (e.g., physiological pH), to encapsulate and / or enhance the delivery of a therapeutic product into the target cells. LNPs can deliver a variety of therapeutic agents such as small molecules, mRNA, mRNA vaccines, mRNA therapeutics, proteins, nucleoside-modified messenger RNA (modRNA), nucleic acids, and small interfering RNA (siRNA) drugs, among others. LNPs may comprise an ionizable lipid (e.g., an ionizable amino lipid), a sterol or other structural lipid, a non-cationic helper lipid or phospholipid, and a PEG-modified lipid. Emulsifiers or surfactants stabilize lipid cores. Emulsifiers are used to stabilize lipid dispersion and they prevent particle agglomeration. In some embodiments, a payload is formulated as a solid LNP (SLN), which can be spherical with an average diameter between 10 to 1000 nm and has only one phospholipid layer. SLNs possess a solid lipid core matrix that can solubilize lipophilic molecules and can be stabilized with surfactants and / or emulsifiers. A payload can be embedded in the interior of an SLN. SLNs may have targeting compounds bound to their exterior surface such as antibodies, cell-targeting peptides, and drug molecules, among others. The relative amounts of the lipids and the payload in an LNP composition of the present disclosure can be optimized according to considerations of efficacy and tolerability. LNPs are carriers that provide a biocompatible and biodegradable delivery system for a payload. Nanostructured lipid carriers (NLCs) are modified SLNs that retain the characteristics of the SLN, improve drug stability and loading capacity, and prevent drug leakage. Polymer nanoparticles (PNPs) are a key component of drug delivery. These nanoparticles can effectively direct drug delivery to specific targets and improve drug stability and controlled drug release. Lipid–polymer nanoparticles (PLNs), a new type of carrier that combines liposomes and polymers, may also be employed. These nanoparticles possess the complementary advantages of PNPs and liposomes. A PLN is composed of a core–shell structure; the polymer core provides a stable structure, and the phospholipid shell offers good biocompatibility. As such, ATTORNEY DOCKET NO.: 51772-005WO3 PATENT the two components increase the drug encapsulation efficiency rate, facilitate surface modification, and prevent leakage of water-soluble drugs. Lipid components of LNPs, such as phospholipids (for example, phosphatidylcholine and phosphatidylethanolamine), cholesterol, or polyethylene glycol (PEG)-functionalized lipids (PEG-lipids) can help improve LNP properties, such as particle stability, delivery efficacy, tolerability, and biodistribution. Phosphatidylcholine derivatives can help destabilize endosomal membranes and facilitate endosomal escape of LNPs. Molecular shape and configuration of cholesterol derivatives can impact LNP delivery efficacy and biodistribution, for example, some cholesterol derivatives can affect the selectivity for the type of liver cell. PEG-lipids enable targeted delivery through conjugation of specific ligands to LNPs and help prevent clearance by renal filtration. Organ selectivity can vary based on the relative proportions of the lipid components and administration routes. Intravenous administration may lead to accumulation of LNPs in the liver and lymph nodes. Biodistribution of LNPs is affected by the chemical composition, proportions of the individual components, shape, size, molecular geometry, and surface properties of the LNP. LNPs can be used to deliver therapeutic products intramuscularly, and LNPs help protect the therapeutic products from degradation before cellular uptake and endosomal escape into their cytoplasmic target compartment. In some embodiments, an LNP of the present disclosure is administered intramuscularly. In some embodiments, an LNP of the present disclosure is administered intravenously. LNPs, in some embodiments, include one or more ionic lipids, such as non-cationic lipids (e.g., neutral, or anionic, or zwitterionic lipids); one or more conjugated lipids (such as PEG-conjugated lipids or lipids conjugated to polymers described in Table 5 of International Patent Publication No. WO2019 / 217941; incorporated herein by reference in its entirety); and / or one or more sterols (e.g., cholesterol). Lipids that can be used in nanoparticle formations (e.g., LNPs) include, for example those described in Table 4 of International Patent Publication No. WO2019 / 217941, which is incorporated by reference—e.g., a lipid-containing nanoparticle can include one or more of the lipids in Table 4 of International Patent Publication No. WO2019 / 217941. LNPs can include additional elements, such as polymers, such as the polymers described in Table 5 of International Patent Publication No. WO2019 / 217941, incorporated by reference. In some embodiments, conjugated lipids, when present, can include one or more of PEG-diacylglycerol (DAG) (such as 1-(monomethoxy-polyethyleneglycol)-2,3- dimyristoylglycerol (PEG-DMG)), PEG-dialkyloxypropyl (DAA), PEG-phospholipid, PEG- ceramide (Cer), a pegylated phosphatidylethanoloamine (PEG-PE), PEG succinate diacylglycerol (PEGS-DAG) (such as 4-0-(2',3'-di(tetradecanoyloxy)propyl-1-0-(w- methoxy(polyethoxy)ethyl) butanedioate (PEG-S-DMG)), PEG dialkoxypropylcarbam, and N- (carbonyl-methoxypoly ethylene glycol 2000)-1,2-distearoyl-sn- glycero-3-phosphoethanolamine sodium salt, among others. In some embodiments, sterols that can be incorporated into LNPs include one or more of cholesterol or cholesterol derivatives, such as those in WO2009 / 127060 or US2010 / 0130588, which are incorporated by reference. In some embodiments, a composition described herein is provided in an LNP that includes an ionizable lipid. In some embodiments, an ionizable lipid may be a cationic lipid, an ionizable cationic lipid, e.g., a cationic lipid that can exist in a positively charged or neutral form depending on pH, or an amine- containing lipid that can be readily protonated. In some embodiments, the cationic lipid is a lipid capable of being positively charged, e.g., under physiological conditions. Exemplary cationic lipids include one or more amine group(s) which bear the positive charge. In some embodiments, the lipid particle includes a ATTORNEY DOCKET NO.: 51772-005WO3 PATENT cationic lipid in formulation with one or more of neutral lipids, ionizable amine-containing lipids, biodegradable alkyne lipids, steroids, phospholipids including polyunsaturated lipids, structural lipids (e.g., sterols), PEG, cholesterol, and polymer conjugated lipids. In some embodiments, the cationic lipid may be an ionizable cationic lipid. In some embodiments, the LNP may include a targeting moiety, e.g., coated with a targeting agent. In some embodiments, the LNP formulation is biodegradable. In some embodiments, the LNP can include a PEG or a conjugated lipid molecule. Generally, these are used to inhibit aggregation of LNPs and / or provide steric stabilization. Exemplary conjugated lipids include, but are not limited to, PEG-lipid conjugates, polyoxazoline (POZ)-lipid conjugates, polyamide-lipid conjugates (such as ATTA-lipid conjugates), cationic-polymer lipid (CPL) conjugates, and mixtures thereof. In some embodiments, the conjugated lipid molecule is a PEG-lipid conjugate, for example, a (methoxy polyethylene glycol)-conjugated lipid. In some embodiments, one or more additional compounds can also be included. Those compounds can be administered separately, or the additional compounds can be included in the LNPs of the disclosure. Without limitations, other additional compounds can be selected from the group consisting of small or large organic or inorganic molecules, monosaccharides, disaccharides, trisaccharides, oligosaccharides, polysaccharides, peptides, proteins, peptide analogs and derivatives thereof, peptidomimetics, nucleic acids, nucleic acid analogs and derivatives, an extract made from biological materials, or any combinations thereof. An LNP may optionally include one or more coatings. In some embodiments, an LNP may be formulated in a capsule, film, or tablet having a coating. A capsule, film, or tablet including a composition described herein may have any useful size, tensile strength, hardness, or density. In some embodiments, the LNP formulations can be engineered to alter the surface properties of particles so that the LNPs can penetrate the mucosal barrier. The LNP engineered to penetrate mucus can comprise a polymeric material (i.e., a polymeric core) and / or a polymer-vitamin conjugate and / or a tri- block co-polymer. The polymeric material can include, but is not limited to, polyamines, polyethers, polyamides, polyesters, polycarbamates, polyureas, polycarbonates, poly(styrenes), polyimides, polysulfones, polyurethanes, polyacetylenes, polyethylenes, polyethyeneimines, polyisocyanates, polyacrylates, polymethacrylates, polyacrylonitriles, and polyarylates. LNPs engineered to penetrate mucus can also include surface altering agents such as, but not limited to, polynucleotides, anionic proteins (e.g., bovine serum albumin), surfactants (e.g., cationic surfactants such as for example dimethyldioctadecyl-ammonium bromide), sugars or sugar derivatives (e.g., cyclodextrin), nucleic acids, polymers (e.g., heparin, polyethylene glycol and poloxamer), mucolytic agents (e.g., N-acetylcysteine, mugwort, bromelain, papain, clerodendrum, acetylcysteine, bromhexine, carbocisteine, eprazinone, mesna, ambroxol, sobrerol, domiodol, letosteine, stepronin, tiopronin, gelsolin, thymosin β4 dornase alfa, neltenexine, erdosteine), and various DNases including rhDNase. Methods of Treatment The methods and compositions of the disclosure may be used to treat any disease with a genetic association. In some embodiments, an AAV particle of the invention containing an AAV vector and one or more of the optimized AAV capsid proteins described herein may be delivered to a subject in need thereof, as a therapy for one or more diseases. In some embodiments, the disease to be treated is a ATTORNEY DOCKET NO.: 51772-005WO3 PATENT genetic or epigenetic disease. In some embodiments, the therapy is gene therapy. In some embodiments, the disease to be treated is not a genetic or epigenetic disease. In some embodiments, compositions of the invention may be incorporated into a pharmaceutical composition or pharmaceutical formulation and may be administered to a subject via any of the routes of administration described herein. In some embodiments, an AAV particle or pharmaceutical composition described herein may be delivered to a subject in need thereof as a treatment or prevention (or as a part of a treatment or prevention) of a disease. The specific disease to be treated and / or prevented by delivery of an AAV particle or pharmaceutical composition described herein may be dependent on the cargo coupled to, attached to, contained in, or otherwise associated with the AAV particle or pharmaceutical composition. Genetic diseases that may be treated by administering an AAV particle or pharmaceutical composition of the invention are discussed in greater detail below. Other diseases that may be treated by administering an AAV particle or pharmaceutical composition of the invention, include, but are not limited to, any of the following: Acinetobacter infections, actinomycosis, African sleeping sickness, AIDS / HIV, amoebiasis, Anaplasmosis, Angiostrongyliasis, Anisakiasis, Anthrax, Arcanobacterium haemolyticum infection, Argentine hemorrhagic fever, Ascariasis, Aspergillosis, Astrovirus infection, Babesiosis, Bacterial meningitis, Bacterial pneumonia, Bacterial vaginosis, Bacteroides infection, balantidiasis, Bartonellosis, Baylisascaris infection, BK virus infection, Black Piedra, Blastocytosis, Blastomycosis, Bolivian hemorrhagic fever, Botulism, Brazilian hemorrhagic fever, brucellosis, Bubonic plague, Burkholderia infection, buruli ulcer, calicivirus invention, campylobacteriosis, cancer, Candidiasis, Capillariasis, Carrion’s disease, Cat-scratch disease, cellulitis, Chagas Disease, Chancroid, Chickenpox, Chikungunya, Chlamydia, Chlamydia pneumoniae, Cholera, Chromoblastomycosis, Chytridiomycosis, Clonorchiasis, Clostridium difficile colitis, Coccidioidomycosis, Colorado tick fever, rhinovirus / coronavirus infection (common cold), Creutzfeldt-Jakob disease, Crimean-congo hemorrhagic fever, Cryptococcosis, Cryptosporidiosis, Cutaneous larva migrans (CLM), cyclosporiasis, cysticercosis, cytomegalovirus infection, Dengue fever, Desmodesmus infection, Dientamoebiasis, Diphtheria, Diphyllobothriasis, Dracunculiasis, Ebola, Echinococcosis, Ehrlichiosis, Enterobiasis, Enterococcus infection, Enterovirus infection, Epidemic typhus, Erythema Infectiosum, Exanthem subitum, Fascioliasis, Fasciolopsiasis, fatal familial insomnia, filariasis, Clostridium perfringens infection, Fusobacterium infection, Gas gangrene (clostridial myonecrosis), geotrichosis, Gerstmann-Straussler-Scheinker syndrome, Giardiasis, Glanders, Gnathostomiasis, Gonorrhea, Granuloma inguinale, Group A streptococcal infection, Group B streptococcal infection, Haemophilus influenzae infection, Hand, foot, and mouth disease, hantavirus pulmonary syndrome, heartland virus disease, helicobacter pylori infection, hemorrhagic fever with renal syndrome, Hendra virus infection, Hepatitis (all groups A, B, C, D, E), herpes simplex, histoplasmosis, hookworm infection, human bocavirus infection, human ewingii ehrlichiosis, Human granulocytic anaplasmosis, human metapneumovirus infection, human monocytic ehrlichiosis, human papilloma virus, Hymenolepiasis, Epstein-Barr infection, mononucleosis, influenza, isosporiasis, Kawasaki disease, Kingella kingae infection, Kuru, Lassa fever, Legionellosis (Legionnaires disease and Potomac Fever), Leishmaniasis, Leprosy, Leptospirosis, Listeriosis, Lyme disease, lymphatic filariasis, lymphocytic choriomeningitis, Malaria, Marburg hemorrhagic fever, measles, Middle East respiratory syndrome, Melioidosis, meningitis, Meningococcal disease, Metagonimiasis, Microsporidosis, Molluscum contagiosum, Monkeypox, Mumps, Murine typhus, Mycoplasma pneumonia, Mycoplasma genitalium ATTORNEY DOCKET NO.: 51772-005WO3 PATENT infection, Mycetoma, Myiasis, Conjunctivitis, Nipah virus infection, Norovirus, Variant Creutzfeldt-Jakob disease, Nocardiosis, Onchocerciasis, Opisthorchiasis, Paracoccidioidomycosis, Paragonimiasis, Pasteurellosis, Pediculosisi capitis, Pediculosis corporis, Pediculosis pubis, pelvic inflammatory disease, pertussis, plague, pneumococcal infection, pneumocystis pneumonia, pneumonia, poliomyelitis, prevotella infection, primary amoebic meningoencephalitis, progressive multifocal leukoencephalopathy, Psittacosis, Q fever, rabies, relapsing fever, respiratory syncytial virus infection, rhinovirus infection, rickettsial infection, Rickettsialpox, Rift Valley Fever, Rocky Mountain Spotted Fever, Rotavirus infection, Rubella, Salmonellosis, SARS, Scabies, Scarlet fever, Schistosomiasis, sepsis, Shigellosis, Shingles, Smallpox, Sporotrichosis, Staphylococcal infection (including methicillin-resistant Staphylococcus aureus or MRSA), strongyloidiasis, subacute sclerosing panencephalitis, Syphilis, Taeniasis, tetanus, Trichophyton species infection, Toxocariasis, Toxoplasmosis, Trachoma, Trichinosis, Trichiniasis, Tuberculosis, Tularemia, Typhoid Fever, Typhus Fever, Ureaplasma urealyticum infection, Valley fever, Venezuelan equine encephalitis, Venezuelan hemorrhagic fever, Vibrio species infection, Viral pneumonia, West Nile Fever, White Piedra, Yersinia pseudotuberculosis, Yersiniosis, Yellow fever, Zeaspora, Zika fever, Zygomycosis and combinations thereof. Some other diseases and disorders that may be treated using an AAV particle or pharmaceutical composition of the present disclosure include, but are not limited to, muscle diseases of infectious or non- infectious origin, endocrine diseases (e.g., Type I and Type II diabetes, gestational diabetes, hypoglycemia, glucagonoma, goiter, hyperthyroidism, hypothyroidism, thyroiditis, thyroid cancer, thyroid hormone resistance, parathyroid gland disorders, osteoporosis, osteitis deformans, rickets, osteomalacia, hypopituitarism, pituitary tumors, etc.), skin conditions of infections and non-infectious origin, eye diseases of infectious or non-infectious origin, gastrointestinal disorders of infectious or non-infectious origin, cardiovascular diseases of infectious or non-infectious origin, brain and neuron diseases of infectious or non-infectious origin, nervous system diseases of infectious or non-infectious origin, bone diseases of infectious or non-infectious origin, reproductive system diseases of infectious or non- infectious origin, renal system diseases of infectious or non-infectious origin, blood diseases of infectious or non-infectious origin, lymphatic system diseases of infectious or non-infectious origin, immune system diseases of infectious or non-infectious origin, and mental-illnesses of infectious or non-infectious origin, among others. In some embodiments, the disease is a muscle disease or disorder, neuromuscular disease or disorder, a musculoskeletal disease or disorder, a muscular dystrophy, or a cardiomyopathy. In some embodiments, the disease or disorder may be selected from any one or more of the following categories: (a) a muscle disease; (b) a muscular dystrophy; (c) a neuromuscular disease; (d) a musculoskeletal disease; (e) a cardiomyopathy; (f) an expanded repeat disease; (g) a dominant negative disease; (h) a sugar or glycogen storage disease; (i) a viral, bacterial, or fungal disease; ATTORNEY DOCKET NO.: 51772-005WO3 PATENT (j) a progeroid disease; (k) an autoimmune disease; (l) a cancer; (m) a neurodegenerative disease; (n) a lysosomal storage disease; or (o) any combination thereof. Using an AAV particle or pharmaceutical composition of the invention, a variety of disorders of the central nervous system (CNS) may be treated. The following is a non-limiting list of genes associated with CNS-associated disorders that may be expressed using an AAV vector of the invention: neuronal apoptosis inhibitory protein (NAIP), nerve growth factor (NGF), glial-derived growth factor (GDNF), brain- derived growth factor (BDNF), ciliary neurotrophic factor (CNTF), tyrosine hydroxylase (TH), GTP- cyclohydrolase (GTPCH), aspartoacylase (ASPA), superoxide dismutase type 1 (SOD1), and amino acid decorboxylase (AADC), among others. For example, a useful transgene in the treatment of Parkinson’s disease (PD) encodes TH, which is a rate limiting enzyme in the synthesis of dopamine. A transgene encoding GTPCH, which generates the TH cofactor tetrahydrobiopterin, may also be used in the treatment of PD. A transgene encoding GDNF, BDNF, or AADC, which facilitates conversion of L-Dopa to dopamine (DA), may also be used for the treatment of PD. For the treatment of ALS, a useful transgene may encode: GDNF, BDNF, or CNTF. Also, for the treatment of ALS, a useful transgene may encode a functional RNA, e.g., shRNA, miRNA, that inhibits the expression of SOD1. For the treatment of ischemia, a useful transgene may encode NAIP or NGF. A transgene encoding Beta-glucuronidase (GUS) may be useful for the treatment of certain lysosomal storage diseases (e.g., Mucopolysaccharidosis type VII (MPS VII)). A transgene encoding a prodrug activation gene, e.g., HSV-Thymidine kinase which converts ganciclovir to a toxic nucleotide which disrupts DNA synthesis and leads to cell death, may be useful for treating certain cancers, e.g., when administered in combination with the prodrug. A transgene encoding an endogenous opioid, such a β-endorphin may be useful for treating pain. Other examples of transgenes that may be expressed using the AAV vectors of the invention will be apparent to the skilled artisan (See, e.g., Costantini L C, et al., Gene Therapy (2000) 7, 93-109). The AAV vectors described herein may include a polynucleotide encoding a therapeutic protein useful for the treatment of a genetic disorder. In some embodiments, the therapeutic transgene (e.g., a transgene encoding a therapeutic protein) may encode a polypeptide, a short peptide fragment, or a full- length protein. In some embodiments of the disclosure, the transgene contained within the AAV vector encodes a therapeutic RNA molecule that inhibits the expression of an endogenous gene of interest. Such inhibitory nucleic acids may specifically bind (e.g., hybridizes to) at least a portion of a target nucleic acid, such as a target RNA, pre-mRNA, or mRNA, and inhibit its expression or activity. In some embodiments, the inhibitory nucleic acid is complementary to a protein coding region or non-coding region (e.g., 5’UTR, 3’UTR, intron, etc.). In some embodiments, the inhibitory nucleic acid is complementary to a wild-type nucleic acid or a naturally occurring variant thereof. In some embodiments, the inhibitory nucleic acid is single stranded or double-stranded. In some embodiments, the inhibitory nucleic acid is an interfering RNA molecule, such as short interfering RNA (siRNA), short hairpin RNA (shRNA), microRNA (miRNA), or double-stranded RNA (dsRNA). ATTORNEY DOCKET NO.: 51772-005WO3 PATENT The following table provides a list of exemplary transgenes of the invention and their corresponding associated diseases which may be treated or prevented by administering an AAV particle or pharmaceutical composition of the invention. Table 4. Exemplary transgenes of the invention and associated diseases ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT In some embodiments, a subject treated by administering an AAV particle or pharmaceutical composition described herein is a mammal such as a mouse, a rat, or a primate (e.g., monkey, chimpanzee, or human). In some embodiments, the subject is a primate. In some embodiments, the subject is a non-human primate. In some embodiments, the subject is a human. Pharmaceutical Compositions Pharmaceutical compositions of the present disclosure may include a vehicle for administration into a patient, such as a human patient suffering from a disorder or disease, as described herein. The pharmaceutical composition described herein may be prepared using methods known in the art. For example, pharmaceutical compositions may be prepared using, e.g., physiologically acceptable carriers, excipients or stabilizers (Remington's Pharmaceutical Sciences 16th edition, Osol, A. Ed. (1980); incorporated herein by reference), and in a desired form, e.g., in the form of lyophilized formulations or aqueous solutions. Pharmaceutical compositions may be prepared in water suitably mixed with one or more excipients, carriers, or diluents. Dispersions may also be prepared in glycerol, liquid polyethylene glycols, and mixtures thereof and in oils. Under ordinary conditions of storage and use, these preparations may contain a preservative to prevent the growth of microorganisms. The pharmaceutical forms suitable for injectable use include sterile aqueous solutions or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersions (described in US 5,466,468, the disclosure of which is incorporated herein by reference). In any case the formulation may be sterile and may be fluid to the extent that easy syringability exists. Formulations may be stable under the conditions ATTORNEY DOCKET NO.: 51772-005WO3 PATENT of manufacture and storage and may be preserved against the contaminating action of microorganisms, such as bacteria and fungi. The carrier may be a solvent or dispersion medium containing, for example, water, ethanol, polyol (e.g., glycerol, propylene glycol, and liquid polyethylene glycol, and the like), suitable mixtures thereof, and / or vegetable oils. Proper fluidity may be maintained, for example, by the use of a coating, such as lecithin, by the maintenance of the required particle size in the case of dispersion and by the use of surfactants. The prevention of the action of microorganisms may be brought about by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, sorbic acid, thimerosal, and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars or sodium chloride. Prolonged absorption of the injectable compositions may be brought about by the use in the compositions of agents delaying absorption, for example, aluminum monostearate and gelatin. For example, a pharmaceutical composition of the present disclosure may be suitably buffered, if necessary, and the liquid diluent first rendered isotonic with sufficient saline or glucose. These particular aqueous solutions are especially suitable for administration by a route selected from intramuscular, intrahepatic, intravenous, intrathecal, intracerebroventricular, intraparenchymal, intracisternal, intraocular (e.g., intravitreal), intraventricular, intralumbar, intrahippocampal, intrastriatal (putamen and / or caudate), intracerebral, intracerebrospinal, intracranial, intracortical, intradermal, transdermal, parenteral, intranasal, subcutaneous, percutaneous, intratracheal, intraperitoneal, intraarterial, intraputaminal, intramidbrain, intra cisterna magna, intra substantia nigra, intra ventral tegmental area, intrathalamic, intravascular, inhalation, perfusion, lavage, and / or oral administration. In this connection, sterile aqueous media that may be employed will be known to those of skill in the art in light of the present disclosure. For example, one dosage may be dissolved in 1 ml of isotonic NaCl solution and either added to 1000 ml of hypodermoclysis fluid or injected at the proposed site of infusion. Some variation in dosage will necessarily occur depending on the condition of the subject being treated. The person responsible for administration will, in any event, determine the appropriate dose for the individual subject. Moreover, for human administration, preparations may meet sterility, pyrogenicity, general safety, and purity standards as required by FDA Office of Biologics standards. A pharmaceutical composition containing, for example, an AAV viral particle described herein, typically includes a pharmaceutically acceptable diluent or carrier. A pharmaceutical composition may include (e.g., consist of), e.g., a sterile saline solution and a nucleic acid. The sterile saline is typically a pharmaceutical grade saline. A pharmaceutical composition may include (e.g., consist of), e.g., sterile water and a nucleic acid. The sterile water is typically a pharmaceutical grade water. A pharmaceutical composition may include (e.g., consist of), e.g., phosphate-buffered saline (PBS) and a nucleic acid. The sterile PBS is typically a pharmaceutical grade PBS. In certain embodiments, pharmaceutical compositions include one or more AAV viral particles described herein and one or more excipients. In certain embodiments, excipients are selected from water, salt solutions, alcohol, polyethylene glycols, gelatin, lactose, amylase, magnesium stearate, talc, silicic acid, viscous paraffin, hydroxymethylcellulose, and polyvinylpyrrolidone. In certain embodiments, AAV viral particles described herein may be mixed with pharmaceutically acceptable active and / or inert substances for the preparation of pharmaceutical compositions or formulations. Compositions and ATTORNEY DOCKET NO.: 51772-005WO3 PATENT methods for the formulation of pharmaceutical compositions depend on a number of criteria, including, but not limited to, route of administration, extent of disease, or dose to be administered. In certain embodiments, pharmaceutical compositions including an AAV viral particle described herein encompass any pharmaceutically acceptable salts or esters. Accordingly, for example, the disclosure is also drawn to pharmaceutically acceptable salts of inhibitors. Suitable pharmaceutically acceptable salts include, but are not limited to, sodium and potassium salts. In certain embodiments, pharmaceutical compositions include a delivery system. Examples of delivery systems include, but are not limited to, liposomes and emulsions. Certain delivery systems are useful for preparing certain pharmaceutical compositions including those including hydrophobic compounds. In certain embodiments, certain organic solvents such as dimethylsulfoxide are used. Lipid moieties have been used in nucleic acid therapies in a variety of methods. In certain such methods, the AAV capsid proteins of the invention may be introduced into preformed liposomes or lipoplexes made of mixtures of cationic lipids and neutral lipids. In certain methods, DNA complexes with mono- or poly- cationic lipids are formed without the presence of a neutral lipid. In certain embodiments, a lipid moiety is selected to increase distribution of a pharmaceutical agent to a particular cell or tissue. In certain embodiments, a lipid moiety is selected to increase distribution of a pharmaceutical agent to fat tissue. In certain embodiments, a lipid moiety is selected to increase distribution of a pharmaceutical agent to muscle tissue. In certain embodiments, pharmaceutical compositions include one or more tissue-specific delivery molecules designed to deliver the one or more pharmaceutical agents of the present invention to specific tissues or cell types. For example, in certain embodiments, pharmaceutical compositions include liposomes coated with a tissue-specific antibody. In certain embodiments, pharmaceutical compositions include a co-solvent system. Certain of such co-solvent systems include, for example, benzyl alcohol, a nonpolar surfactant, a water-miscible organic polymer, and an aqueous phase. In certain embodiments, such co-solvent systems are used for hydrophobic compounds. A non-limiting example of such a co-solvent system is the VPD co-solvent system, which is a solution of absolute ethanol including 3% w / v benzyl alcohol, 8% w / v of the nonpolar surfactant Polysorbate 80™ and 65% w / v polyethylene glycol 300. The proportions of such co-solvent systems may be varied considerably without significantly altering their solubility and toxicity characteristics. Furthermore, the identity of co-solvent components may be varied: for example, other surfactants may be used instead of Polysorbate 80™; the fraction size of polyethylene glycol may be varied; other biocompatible polymers may replace polyethylene glycol, e.g., polyvinyl pyrrolidone; and other sugars or polysaccharides may substitute for dextrose. In certain embodiments, pharmaceutical compositions are prepared for oral administration. In certain embodiments, pharmaceutical compositions are prepared for buccal administration. In certain embodiments, a pharmaceutical composition is prepared for administration by injection (e.g., intramuscular, intraocular (e.g., intravitreal), intravenous, subcutaneous, intrathalamic, intrathecal, intracerebroventricular, etc.). In certain of such embodiments, a pharmaceutical composition includes a carrier and is formulated in aqueous solution, such as water or physiologically compatible buffers such as Hanks's solution, Ringer's solution, or physiological saline buffer. In certain embodiments, other ingredients are included (e.g., ingredients that aid in solubility or serve as preservatives). In certain ATTORNEY DOCKET NO.: 51772-005WO3 PATENT embodiments, injectable suspensions are prepared using appropriate liquid carriers, suspending agents and the like. Certain pharmaceutical compositions for injection are presented in unit dosage form, e.g., in ampoules or in multi-dose containers. Certain pharmaceutical compositions for injection are suspensions, solutions or emulsions in oily or aqueous vehicles, and may contain formulatory agents such as suspending, stabilizing and / or dispersing agents. Certain solvents suitable for use in pharmaceutical compositions for injection include, but are not limited to, lipophilic solvents and fatty oils, such as sesame oil, synthetic fatty acid esters, such as ethyl oleate or triglycerides, and liposomes. In some embodiments, the AAV compositions are formulated to reduce aggregation of AAV particles in the composition, particularly where high AAV concentrations are present. Methods for reducing aggregation of AAVs are well known in the art and include, for example, addition of surfactants, pH adjustment, salt concentration adjustment, etc. (See, e.g., Wright F R, et al., Molecular Therapy (2005) 12, 171-178, the contents of which are incorporated herein by reference.). Formulation of pharmaceutically acceptable excipients and carrier solutions is well-known to those of skill in the art, as is the development of suitable dosing and treatment regimens for using the particular compositions described herein in a variety of treatment regimens. Typically, these formulations may contain at least about 0.1% of the active ingredient or more, although the percentage of the active ingredient(s) may, of course, be varied and may conveniently be between about 1 or 2% and about 70% or 80% or more of the weight or volume of the total formulation. Naturally, the amount of active ingredient in each therapeutically useful composition may be prepared in such a way that a suitable dosage will be obtained in any given unit dose of the compound. Factors such as solubility, bioavailability, biological half-life, route of administration, product shelf life, as well as other pharmacological considerations will be contemplated by one skilled in the art of preparing such pharmaceutical formulations, and as such, a variety of dosages and treatment regimens may be desirable. The pharmaceutical forms suitable for injectable use include sterile aqueous solutions or dispersions for the extemporaneous preparation of sterile injectable solutions or dispersions. Dispersions may also be prepared in glycerol, liquid polyethylene glycols, and mixtures thereof and in oils. Under ordinary conditions of storage and use, these preparations contain a preservative to prevent the growth of microorganisms. In many cases the form is sterile and fluid to the extent that easy syringability exists. It must be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms, such as bacteria and fungi. The carrier may be a solvent or dispersion medium containing, for example, water, ethanol, polyol (e.g., glycerol, propylene glycol, and liquid polyethylene glycol, and the like), suitable mixtures thereof, and / or vegetable oils. Proper fluidity may be maintained, for example, by using a coating, such as lecithin, by the maintenance of the required particle size in the case of dispersion and by using surfactants. For administration of an injectable aqueous solution, for example, the solution may be suitably buffered, if necessary, and the liquid diluent first rendered isotonic with sufficient saline or glucose. In this connection, a sterile aqueous medium that may be employed will be known to those of skill in the art. For example, one dosage may be dissolved in 1 ml of isotonic NaCl solution and either added to 1000 ml of hypodermoclysis fluid or injected at the proposed site of infusion, (see for example, “Remington's Pharmaceutical Sciences” 15th Edition, pages 1035-1038 and 1570-1580). Some variation in dosage will necessarily occur depending on the condition ATTORNEY DOCKET NO.: 51772-005WO3 PATENT of the host. The person responsible for administration will, in any event, determine the appropriate dose for the individual host. Sterile injectable solutions are prepared by incorporating the active AAV in the required amount in the appropriate solvent with various of the other ingredients enumerated herein, as required, followed by filtered sterilization. Generally, dispersions are prepared by incorporating the various sterilized active ingredients into a sterile vehicle which contains the basic dispersion medium and the required other ingredients from those enumerated above. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum-drying and freeze-drying techniques which yield a powder of the active ingredient plus any additional desired ingredient from a previously sterile-filtered solution thereof. The agents, compositions, and / or systems described herein may, in some embodiments, be assembled into pharmaceutical or diagnostic or research kits to facilitate their use in therapeutic, diagnostic or research applications. A kit may include one or more containers housing the components of the invention and instructions for use. Kits for research purposes may contain the components in appropriate concentrations or quantities for running various experiments. Routes of Administration The AAV viral particle or pharmaceutical composition of the present disclosure, containing a transgene described herein may be administered to a patient (e.g., a human patient) by a variety of routes of administration. Administration of an effective dose of the AAV particle or pharmaceutical composition may be by exemplary routes of administration standard in the art, including, but not limited to, systemic (e.g., by intravenous), local (e.g., intracortical), and direct injection (e.g., delivery to a particular muscle or other tissue). The route of administration may vary, for example, with the onset and severity of disease, and may include, e.g., intramuscular, intrahepatic, intravenous, intrathecal, intracerebroventricular, intracisternal, intrastriatal (putamen and / or caudate), intracerebral, intracerebrospinal, intracranial, intracortical, intraparenchymal, intradermal, transdermal, parenteral, intranasal, subcutaneous, percutaneous, intratracheal, intraocular (e.g., intravitreal), intraventricular, intralumbar, intraperitoneal, intraarterial, intravascular, inhalation, perfusion, lavage, and / or oral administration. Intravascular administration may include delivery into the vasculature of a patient. In some embodiments, the administration is into a vessel considered to be a vein (intravenous), and in some administration, the administration is into a vessel considered to be an artery (intraarterial). Veins include, but are not limited to, the internal jugular vein, a peripheral vein, a coronary vein, a hepatic vein, the portal vein, great saphenous vein, the pulmonary vein, superior vena cava, inferior vena cava, a gastric vein, a splenic vein, inferior mesenteric vein, superior mesenteric vein, cephalic vein, and / or femoral vein. Arteries include, but are not limited to, coronary artery, pulmonary artery, brachial artery, internal carotid artery, aortic arch, femoral artery, peripheral artery, and / or ciliary artery. It is contemplated that delivery may be through or to an arteriole or capillary. Administration may be performed by intrathecal injection with or without Trendelenberg tilting. In some cases, the AAV viral particle or pharmaceutical composition may be administered, e.g., in a single administration. Treatment regimens may vary, and often depend on disease severity and the age, weight, and sex of the patient. Treatment may include administration of viral particles or other agents described herein ATTORNEY DOCKET NO.: 51772-005WO3 PATENT as useful for the introduction of a transgene into a target cell in various unit doses. Each unit dose will ordinarily contain a predetermined quantity of the therapeutic composition. Kits The compositions described herein, such as an AAV viral particle or pharmaceutical composition of the present disclosure may be provided in a kit. In some embodiments, the kit may include an AAV viral particle as described herein. In some embodiments, the kit may include a pharmaceutical composition as described herein. The kit may include a package insert that instructs a user of the kit, such as a physician of skill in the art, to perform any one of the methods of treatment described herein. The kit may optionally include a syringe or other device for administering the AAV viral particle or pharmaceutical composition of the present disclosure. In some embodiments, the kit may include one or more additional therapeutic agents. EXAMPLES Example 1. Discovery of the MPR peptide family Objective This Example describes the results of a series of experiments undertaken to discover and characterize a family of 7-mer peptide inserts that may be incorporated into an AAV capsid protein (such as AAV9, among others) in order to enhance transduction, particularly of muscle cells. Materials and Methods Peptide insert AAV library A large, randomized library of 7-mer peptide inserts was constructed for incorporation into the AAV9 VP1 capsid protein. Briefly, a library oligo was generated by solid phase synthesis. The method avoided the introduction of Cys and stop codons. The redundancy at the nucleic acid level (due to synonymous codons) that is often introduced using degenerate base approaches was also avoided with our approach. Standard techniques were used to preserve the diversity of the library through oversampling at all stages of library construction, propagation, and vector production. The library oligo between the codons for amino acids 588 and 589 (corresponding to AAV9 VP1 numbering) was cloned in the AAV9 Cap gene, which was situated between inverted terminal repeats (ITRs) in the library plasmid. The library of Cap variants was driven by a CMV promoter and contained a fragment of Rep upstream of the Cap ORF to ensure proper Cap VP ratios. After sequence-verifying the correct assembly of the Cap9 variant library, the library plasmid was transfected along with an adenovirus helper plasmid and a plasmid containing a full-length copy of Rep2. The plasmid library was then converted to a vector library in which each AAV9 peptide insertion capsid variant packaged its own genome. This linkage between genotype and phenotype was essential for capsid directed evolution since it allowed for the tracking and propagation of the most successful variants through rounds of selection. ATTORNEY DOCKET NO.: 51772-005WO3 PATENT Primary capsid library screen The unbiased AAV9 peptide insert capsid library was subjected to several rounds of selection to identify the ability to infect muscle cells. Next generation sequencing (NGS)-based scoring was performed on the screen output, and clustering of the resulting peptide sequences revealed distinct peptide insert families. Results Subjecting the top 506 hit peptides from the primary screen to clustering analysis led to the discovery of the peptide family of the invention (Figure 1). This family of peptides generally has the amino acid consensus motif xMPRxxx, where x is any amino acid. Of the 506 unique peptides, those with sequences having a core MPR motif, or a structurally similar variant thereof, are shown in Table 5. Table 5. Round 2 enrichment score ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT Conclusion The above results describe a library-based approach and further analysis to discover the peptide family of the invention. Example 2. In vitro validation of MPR variant family capsid activity in HEK293 cells Objective This Example describes the results of experiments undertaken to validate the activity of certain MPR-family peptides in vitro. Materials and Methods Exemplary MPR-family peptides were sourced from the primary screen results, and additional peptides were inferred from consensus alignments of the primary hits. Individual lab scale vector preps of MPR-presenting capsids using a luciferase reporter were produced. The titer of the vector preps was quantified to assess the intrinsic manufacturability of the capsids. Capsid yield is frequently compromised by peptide insertion engineering, impacting cost-of-goods for gene therapy products. Assessment of this property of various engineered variants can thus be relevant to variant selection. In addition to titer, the relative transduction activity of each variant was evaluated compared to AAV9 using transduction of HEK293 cells. Results Table 6 presents a summary of HEK293 cell transduction activity and production yields, both normalized to the AAV9 comparator. Table 6. Summary of HEK293 cell transduction activity and production yields ATTORNEY DOCKET NO.: 51772-005WO3 PATENT Conclusion The above results demonstrated that many capsid variants with a peptide insert of the invention successfully enhanced the transduction of human-kidney-origin HEK293 cells relative to AAV9 (up to 86- fold) while retaining acceptable production yields. Example 3. In vitro confirmation of cross-species potential of MPR variant capsids in human and mouse muscle cells Objective This Example describes the results of experiments undertaken to confirm the cross-species potential of MPR-family peptides in vitro. Materials and Methods To confirm the potential of these capsids for cross-species intramuscular AAV activity, several MPR-motif-containing capsid variants were generated. The transduction activity of each of MPR variant and AAV9 vectors was determined using a luciferase reporter in primary muscle cell cultures derived from human and mouse. Results All tested MPR variants exhibited broad enhancement over AAV9 in transduction of primary muscle cell cultures from human and mouse origin (Table 7). Table 7. In vitro transduction activity in muscle cells ATTORNEY DOCKET NO.: 51772-005WO3 PATENT Conclusion The above results demonstrated the potential of capsid variants with a peptide insert of the invention for cross-species intramuscularly administered AAV activity. Example 4. In vitro discovery of MPR-family sequences using an AAV library Objective Based on the peptides in Example 1, this Example describes the results of experiments undertaken in vitro to expand on the primary screen and discover additional family peptides. Materials and Methods To further characterize the MPR motif and discover exemplary insert sequences with intramuscular AAV potential, the data filters for the clustering analysis in Example 1 were relaxed, generating an additional 355 MPR-family peptides (shown in Table 8). Table 8. Primary screen MPR-family members ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT Example 5. In vitro saturation mutagenesis to define and expand upon the discovered MPR motif Objective This Example describes the results of a series of experiments undertaken in vitro to discover and characterize an MPR-family peptide sequence starting from a single MPR-family member. Materials and Methods To further explore and define the MPR-motif, a single-site saturation mutagenesis library (all possible single amino acid changes to the starting sequence) was cloned starting with a single representative MPR-family member, (QMPRTPG, SEQ ID NO: 75, Table 6). QMPRTPG (SEQ ID NO: 75) was near the consensus sequence for the MPR motif discovered in the primary screen and had an excellent in vitro activity and production yield profile (Table 6). The QMPRTPG (SEQ ID NO: 75) single site saturation library was cloned into the same capsid library format as the original primary screen (Cap9 variant genes encoded between AAV2 ITRs with a CMV promoter). An AAV library was then generated in which each of 147 capsid insert variants (20 amino acids + 1 stop codon per position at 7 positions) packaged its own genome. Due to the NNK oligo diversification strategy, many peptide sequences within this library were encoded by several synonymous DNA sequences. In these cases, the transduction score was averaged across all synonymous versions. The AAV library was used to transduce HEK293 cells. Three days post-transduction, mRNA was collected from the cells, and deep sequencing of the capsid variant cDNAs was used to quantify the relative transduction activity of each variant in the library, normalized to its abundance in the AAV input library (Figure 2A). Results Quantification of the relative transduction activity of capsid variants in HEK293 cells is presented in Figure 2A, with the relative in vitro HEK293 activity organized by the positional substitutions made in each variant. The substitution of a stop codon at any position within the 7-mer resulted in background-level scoring in the assay (Figure 2B). In contrast, the base sequence (QMPRTPG, SEQ ID NO: 75), which is known to have 26-fold enhancement over AAV9 for HEK293 cell transduction in vitro (Table 6), received one of the highest scores in the library. Furthermore, the base sequence QMPRTPG (SEQ ID NO: 75) was encoded several times within the library using synonymous codons, and these independent measurements of its activity showed high correlation (Figure 2B). Taken together these results validated the approach for scoring relative activities of MPR-family variants in a high throughput, NGS-driven library assay. The pattern of activity scores in the saturation mutagenesis experiment clearly defined the essential elements of the MPR motif. Consistent with the high conservation of MPR at positions 2, 3, and 4 in the discovered motif, any substitution away from this MPR trio at those positions resulted in drastic loss of activity (Figure 2A). The motif was more flexible at positions 1, 5, 6, and 7, with some substitutions at these positions exceeding the activity of the base sequence. ATTORNEY DOCKET NO.: 51772-005WO3 PATENT Conclusion This results in this Example demonstrate the use of a single-site mutagenesis library in further characterization of the MPR motif. Example 6. In vivo validation of MPR variant capsid activity in mice Objective This Example describes the results of experiments undertaken to validate the activity of MPR- family peptides in vivo. Materials and Methods To test the in vivo potential of MPR-family members, an MPR-motif-containing capsid variant (IMPRTAG (SEQ ID NO: 46), herein referred to as MPR2) was compared to AAV9 vectors for intramuscular AAV activity in mice. MPR2 and AAV9 (each encapsulating identical CMV-GLP-1-Fc reporter constructs) were dosed into Rag mice at several doses intramuscularly. Fourteen days later, serum was collected from a terminal bleed for GLP-1-Fc reporter protein determination (Figure 3A). Muscle (Figure 3B) and liver (Figure 3C) were collected for reporter mRNA quantification. Next, an additional MPR-family variant (AMPRYGG (SEQ ID NO: 5), herein referred to as MPR3) was evaluated for intramuscular AAV in mice. MPR3 and AAV9 (each encapsulating identical CMV-GLP- 1-Fc reporter constructs) were dosed into Rag mice at 2E9 GC / mouse intramuscularly. Fourteen days later, serum was collected from a terminal bleed for GLP-1-Fc reporter protein determination (Figure 4A). Muscle (Figure 4B) and liver (Figure 4C) were collected for reporter mRNA quantification. Results MPR2 reporter protein determination and mRNA quantification are shown in Figure 3A, Figure 3B, and Figure 3C. The MPR2 capsid enhanced serum production of the reporter protein across a wide range of doses (Figure 3A). Local enhancement at the muscle injection site was pronounced, particularly at higher doses, for MPR2 (Figure 3B). The lower serum protein enhancement relative to muscle mRNA enhancement may be partially explained by partially reduced liver targeting by MPR2 (Figure 3C), another clinically beneficial attribute. MPR3 reporter protein determination and mRNA quantification are shown in Figure 4A, Figure 4B, and Figure 4C. The MPR3 capsid enhanced serum production of the reporter protein 40-fold (Figure 4A). Local enhancement at the muscle injection site for MPR3 was 21-fold (vs AAV9, Figure 4B). MPR3 transduction of liver was approximately equal to AAV9 (Figure 4C), demonstrating superior muscle specificity compared to liver. ATTORNEY DOCKET NO.: 51772-005WO3 PATENT Conclusion This results in this Example established the intramuscular AAV potential for the MPR-family. Furthermore, the in vivo results were consistent with in vitro transduction comparisons on primary muscle cells. Example 7. Further defining the MPR motif Objective This Example describes experiments designed to define how positioning of the MPR core sequence within an insert of variable overall length relates to enhanced transduction activity in the AAV capsid context. Materials and Methods A series of AAV9-based constructs to encode the insertion of various peptides between positions 588 and 589 of VP1 was prepared. The inserted sequences all contained the core MPR amino acid motif. Recombinant AAV vectors with these constructs and a wild-type AAV9 control were generated, all packaging a firefly luciferase reporter. In vitro activity as compared to the wild-type AAV9 was assessed by titering the recombinant vectors and performing transductions on HEK293 cells. Recombinant vector was added to the culture medium of HEK293 cells at specified concentrations, and luciferase activity was measured with standard techniques 3 days post transduction. Results In one series of constructs, the length of the MPR-containing peptide was varied, keeping the MPR motif in the original position of the insert sequence, with MPR occurring at positions 2, 3, and 4 of the insert peptide. The base sequence for this exercise was IMPRTAG (SEQ ID NO: 46), a 7 amino acid insert known to confer high transduction activity relative to AAV9 both in vivo and in vitro. The originally discovered 7-mer (IMPRTAG, SEQ ID NO: 46) had the highest transduction activity, nearly 100x AAV9 (Figure 5A). Shortening the length to 5 or 6 amino acids reduced the overall transduction activity, though the shorter MPR inserts still provided a transduction advantage relative to AAV9. Similarly, extending the insert peptide to 8 amino acids reduced but did not eliminate the transduction advantage relative to AAV9 (Figure 5A). In the next series of constructs, the positioning of the MPR core sequence within 7-mer insert peptides was varied. The first model for this was the same 7-mer peptide as in Figure 5A (IMPRTAG, SEQ ID NO: 46). Again, maximum transduction activity was observed for the originally discovered peptide, with MPR in the 2ndframe. Similar to Figure 5A, IMPRTAG (SEQ ID NO: 46) conferred nearly 100-fold transduction advantage over AAV9 (Figure 5B). Moving MPR to other frames (frames 1, 3, 4, and 5) reduced but did not eliminate the transduction advantage over wild-type AAV9 (Figure 5B). This exercise was repeated with a different base sequence, AMPRYGG (SEQ ID NO: 5), also known to confer excellent in vivo and in vitro transduction activity to AAV9. Again, MPR in frame 2, as displayed in the originally discovered MPR motif, conferred the largest transduction advantage relative to wild-type AAV9 (Figure 5C). As with the base sequence in Figure 5B, there was reduced but not ATTORNEY DOCKET NO.: 51772-005WO3 PATENT eliminated transduction advantage when moving the MPR sequence into different frames within the context of the surrounding sequence. Conclusion MPR-containing peptides of multiple lengths can confer a transduction advantage when inserted into AAV capsids. MPR-containing peptides can confer transduction advantage to AAV capsids regardless of the exact positioning of the MPR core motif sequence within the inserted peptide. Example 8. Screening diverse MPR peptide sequences in vivo to improve low dose intramuscular AAV gene transfer Objective This Example describes the in vivo screen of two libraries of diverse MPR variants of AAV9. The objective of the screen was to discover MPR-variants that can confer higher in vivo gene transfer from intramuscular delivery. Materials and Methods Two collections of MPR insert sequences (‘MUL library’ and ‘MNA library’) between amino acids 588 and 589 in the AAV9 backbone was cloned as before (see Example 1) in a construct that places the capsid variant gene and promoter between the AAV ITR packaging sequences. The MPR insert sequences were sourced from our primary screen and derivatives of the MPR-family peptides discovered therein. Standard techniques were used with this DNA variant library to generate a vector library in which each capsid variant packages the gene variant encoding it. The vector library was purified by affinity chromatography using commercial AAV9 affinity resin. Approximately 1E10 vector genome copies of the library in 10ul were injected into five identical Rag mice. Three weeks after library injection, muscle tissue was collected for RNA extraction and RT-PCR of the capsid gene variable region. The capsid variable region in the injected AAV library was also amplified by PCR. The PCR products were subjected to Illumina next generation sequencing and the NGS data were processed via a custom analysis pipeline that 1) estimates the relative abundance of each variant in the injected AAV library and in each of the 5 mRNA libraries from the mouse replicates, 2) calculates an enrichment score for each variant considering the change in abundance between injected library and AAV capsid transcripts in each mouse. Variants not detected in muscle mRNA were assumed to either have low intramuscular AAV activity or to have been insufficiently abundant in the injected library to be assessed with this method. Results The tables below list in vivo IM-AAV activities (the log2(muscle enrichment) or ‘log2ME’) for the MPR variant library experiments in mice. For reference, the IM-AAV activity score for the insert sequence IMPRTAG, an insert known to confer enhanced muscle gene transfer in mice from IM-delivery, is highlighted in each results table. These results clearly demonstrate enhanced IM-AAV activity for many MPR family members. ATTORNEY DOCKET NO.: 51772-005WO3 PATENT Table 9. MUL library ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT Table 10. MNA library ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT ATTORNEY DOCKET NO.: 51772-005WO3 PATENT OTHER EMBODIMENTS All publications, patents, and patent applications mentioned in this specification are incorporated herein by reference to the same extent as if each independent publication or patent application was specifically and individually indicated to be incorporated by reference. While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations described herein following, in general, the principles described herein and including such departures from the invention that come within known or customary practice within the art to which the invention pertains and may be applied to the essential features hereinbefore set forth, and follows in the scope of the claims. Other embodiments are within the claims.

Claims

ATTORNEY DOCKET NO.: 51772-005WO3 PATENT What is claimed is: CLAIMS 1. A recombinant adeno-associated virus (AAV) capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises a contiguous methionine-proline-arginine (MPR) tripeptide segment.

2. The recombinant AAV capsid protein of claim 1, wherein the peptide insert has a length of at least 4 amino acids, optionally wherein the length is 4-40 amino acids, optionally wherein the length is 4- 35 amino acids, optionally wherein the length is 4-30 amino acids, optionally wherein the length is 4-25 amino acids, optionally wherein the length is 4-20 amino acids, optionally wherein the length is 4-15 amino acids, optionally wherein the length is 4-10 amino acids.

3. The recombinant AAV capsid protein of claim 1, wherein the peptide insert has a length of at least 5 amino acids, optionally wherein the length is 5-40 amino acids, optionally wherein the length is 5- 35 amino acids, optionally wherein the length is 5-30 amino acids, optionally wherein the length is 5-25 amino acids, optionally wherein the length is 5-20 amino acids, optionally wherein the length is 5-15 amino acids, optionally wherein the length is 5-10 amino acids.

4. The recombinant AAV capsid protein of claim 1, wherein the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6- 35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.

5. The recombinant AAV capsid protein of claim 1, wherein the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7- 35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

6. The recombinant AAV capsid protein of claim 1, wherein the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8- 35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

7. The AAV capsid protein of any one of claims 1-6, wherein the MPR tripeptide segment appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

8. The AAV capsid protein of claim 7, wherein the MPR tripeptide segment appears at frame 1 of the peptide insert.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 9. The AAV capsid protein of claim 7, wherein the MPR tripeptide segment appears at frame 2 of the peptide insert and the peptide insert has a length of at least 4 amino acids, optionally wherein the length is 4-40 amino acids, optionally wherein the length is 4-35 amino acids, optionally wherein the length is 4-30 amino acids, optionally wherein the length is 4-25 amino acids, optionally wherein the length is 4-20 amino acids, optionally wherein the length is 4-15 amino acids, optionally wherein the length is 4-10 amino acids.

10. The AAV capsid protein of claim 7, wherein the MPR tripeptide segment appears at frame 3 of the peptide insert and the peptide insert has a length of at least 5 amino acids, optionally wherein the length is 5-40 amino acids, optionally wherein the length is 5-35 amino acids, optionally wherein the length is 5-30 amino acids, optionally wherein the length is 5-25 amino acids, optionally wherein the length is 5-20 amino acids, optionally wherein the length is 5-15 amino acids, optionally wherein the length is 5-10 amino acids.

11. The AAV capsid protein of claim 7, wherein the MPR tripeptide segment appears at frame 4 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.

12. The AAV capsid protein of claim 7, wherein the MPR tripeptide segment appears at frame 5 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

13. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of IMPR (SEQ ID NO: 512).

14. The AAV capsid protein of claim 13, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

15. The AAV capsid protein of claim 14, wherein the amino acid sequence appears at frame 1 of the peptide insert.

16. The AAV capsid protein of claim 14, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 5 amino acids, optionally wherein the length is 5-40 amino acids, optionally wherein the length is 5-35 amino acids, optionally wherein the length is 5-30 amino acids, optionally wherein the length is 5-25 amino acids, optionally wherein the length is 5-20 amino acids, optionally wherein the length is 5-15 amino acids, optionally wherein the length is 5-10 amino acids.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 17. The AAV capsid protein of claim 14, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.

18. The AAV capsid protein of claim 14, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

19. The AAV capsid protein of claim 14, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

20. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of AMPR (SEQ ID NO: 513).

21. The AAV capsid protein of claim 20, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

22. The AAV capsid protein of claim 21, wherein the amino acid sequence appears at frame 1 of the peptide insert.

23. The AAV capsid protein of claim 21, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 5 amino acids, optionally wherein the length is 5-40 amino acids, optionally wherein the length is 5-35 amino acids, optionally wherein the length is 5-30 amino acids, optionally wherein the length is 5-25 amino acids, optionally wherein the length is 5-20 amino acids, optionally wherein the length is 5-15 amino acids, optionally wherein the length is 5-10 amino acids.

24. The AAV capsid protein of claim 21, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 25. The AAV capsid protein of claim 21, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

26. The AAV capsid protein of claim 21, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

27. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of FMPR (SEQ ID NO: 514).

28. The AAV capsid protein of claim 27, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

29. The AAV capsid protein of claim 28, wherein the amino acid sequence appears at frame 1 of the peptide insert.

30. The AAV capsid protein of claim 28, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 5 amino acids, optionally wherein the length is 5-40 amino acids, optionally wherein the length is 5-35 amino acids, optionally wherein the length is 5-30 amino acids, optionally wherein the length is 5-25 amino acids, optionally wherein the length is 5-20 amino acids, optionally wherein the length is 5-15 amino acids, optionally wherein the length is 5-10 amino acids.

31. The AAV capsid protein of claim 28, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.

32. The AAV capsid protein of claim 28, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 33. The AAV capsid protein of claim 28, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

34. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of MMPR (SEQ ID NO: 515).

35. The AAV capsid protein of claim 34, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

36. The AAV capsid protein of claim 35, wherein the amino acid sequence appears at frame 1 of the peptide insert.

37. The AAV capsid protein of claim 35, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 5 amino acids, optionally wherein the length is 5-40 amino acids, optionally wherein the length is 5-35 amino acids, optionally wherein the length is 5-30 amino acids, optionally wherein the length is 5-25 amino acids, optionally wherein the length is 5-20 amino acids, optionally wherein the length is 5-15 amino acids, optionally wherein the length is 5-10 amino acids.

38. The AAV capsid protein of claim 35, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.

39. The AAV capsid protein of claim 35, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

40. The AAV capsid protein of claim 35, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 41. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of QMPR (SEQ ID NO: 516).

42. The AAV capsid protein of claim 41, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

43. The AAV capsid protein of claim 42, wherein the amino acid sequence appears at frame 1 of the peptide insert.

44. The AAV capsid protein of claim 42, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 5 amino acids, optionally wherein the length is 5-40 amino acids, optionally wherein the length is 5-35 amino acids, optionally wherein the length is 5-30 amino acids, optionally wherein the length is 5-25 amino acids, optionally wherein the length is 5-20 amino acids, optionally wherein the length is 5-15 amino acids, optionally wherein the length is 5-10 amino acids.

45. The AAV capsid protein of claim 42, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.

46. The AAV capsid protein of claim 42, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

47. The AAV capsid protein of claim 42, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

48. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of YMPR (SEQ ID NO: 517).

49. The AAV capsid protein of claim 48, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 50. The AAV capsid protein of claim 49, wherein the amino acid sequence appears at frame 1 of the peptide insert.

51. The AAV capsid protein of claim 49, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 5 amino acids, optionally wherein the length is 5-40 amino acids, optionally wherein the length is 5-35 amino acids, optionally wherein the length is 5-30 amino acids, optionally wherein the length is 5-25 amino acids, optionally wherein the length is 5-20 amino acids, optionally wherein the length is 5-15 amino acids, optionally wherein the length is 5-10 amino acids.

52. The AAV capsid protein of claim 49, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.

53. The AAV capsid protein of claim 49, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

54. The AAV capsid protein of claim 49, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

55. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of MPRT (SEQ ID NO: 518).

56. The AAV capsid protein of claim 55, wherein the amino acid sequence appears at the first permissible frame, last permissible frame, or any frame in between.

57. The AAV capsid protein of claim 56, wherein the amino acid sequence appears at frame 1 of the peptide insert.

58. The AAV capsid protein of claim 56, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 5 amino acids, optionally wherein the length is 5-40 amino acids, optionally wherein the length is 5-35 amino acids, optionally wherein the length is 5-30 amino acids, optionally wherein the length is 5-25 amino acids, optionally wherein theATTORNEY DOCKET NO.: 51772-005WO3 PATENT length is 5-20 amino acids, optionally wherein the length is 5-15 amino acids, optionally wherein the length is 5-10 amino acids.

59. The AAV capsid protein of claim 56, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.

60. The AAV capsid protein of claim 56, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

61. The AAV capsid protein of claim 56, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

62. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of MPRY (SEQ ID NO: 519).

63. The AAV capsid protein of claim 62, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

64. The AAV capsid protein of claim 63, wherein the amino acid sequence appears at frame 1 of the peptide insert.

65. The AAV capsid protein of claim 63, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 5 amino acids, optionally wherein the length is 5-40 amino acids, optionally wherein the length is 5-35 amino acids, optionally wherein the length is 5-30 amino acids, optionally wherein the length is 5-25 amino acids, optionally wherein the length is 5-20 amino acids, optionally wherein the length is 5-15 amino acids, optionally wherein the length is 5-10 amino acids.

66. The AAV capsid protein of claim 63, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein theATTORNEY DOCKET NO.: 51772-005WO3 PATENT length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.

67. The AAV capsid protein of claim 63, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

68. The AAV capsid protein of claim 63, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

69. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of MPRQ (SEQ ID NO: 520).

70. The AAV capsid protein of claim 69, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

71. The AAV capsid protein of claim 70, wherein the amino acid sequence appears at frame 1 of the peptide insert.

72. The AAV capsid protein of claim 70, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 5 amino acids, optionally wherein the length is 5-40 amino acids, optionally wherein the length is 5-35 amino acids, optionally wherein the length is 5-30 amino acids, optionally wherein the length is 5-25 amino acids, optionally wherein the length is 5-20 amino acids, optionally wherein the length is 5-15 amino acids, optionally wherein the length is 5-10 amino acids.

73. The AAV capsid protein of claim 70, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.

74. The AAV capsid protein of claim 70, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein theATTORNEY DOCKET NO.: 51772-005WO3 PATENT length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

75. The AAV capsid protein of claim 70, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

76. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of MPRS (SEQ ID NO: 521).

77. The AAV capsid protein of claim 76, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

78. The AAV capsid protein of claim 77, wherein the amino acid sequence appears at frame 1 of the peptide insert.

79. The AAV capsid protein of claim 77, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 5 amino acids, optionally wherein the length is 5-40 amino acids, optionally wherein the length is 5-35 amino acids, optionally wherein the length is 5-30 amino acids, optionally wherein the length is 5-25 amino acids, optionally wherein the length is 5-20 amino acids, optionally wherein the length is 5-15 amino acids, optionally wherein the length is 5-10 amino acids.

80. The AAV capsid protein of claim 77, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.

81. The AAV capsid protein of claim 77, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 82. The AAV capsid protein of claim 77, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

83. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of IMPRT (SEQ ID NO: 490).

84. The AAV capsid protein of claim 83, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

85. The AAV capsid protein of claim 84, wherein the amino acid sequence appears at frame 1 of the peptide insert.

86. The AAV capsid protein of claim 84, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.

87. The AAV capsid protein of claim 84, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

88. The AAV capsid protein of claim 84, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

89. The AAV capsid protein of claim 84, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 9 amino acids, optionally wherein the length is 9-40 amino acids, optionally wherein the length is 9-35 amino acids, optionally wherein the length is 9-30 amino acids, optionally wherein the length is 9-25 amino acids, optionally wherein the length is 9-20 amino acids, optionally wherein the length is 9-15 amino acids, optionally wherein the length is 9-10 amino acids.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 90. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of AMPRY (SEQ ID NO: 522).

91. The AAV capsid protein of claim 90, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

92. The AAV capsid protein of claim 91, wherein the amino acid sequence appears at frame 1 of the peptide insert.

93. The AAV capsid protein of claim 91, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.

94. The AAV capsid protein of claim 91, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

95. The AAV capsid protein of claim 91, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

96. The AAV capsid protein of claim 91, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 9 amino acids, optionally wherein the length is 9-40 amino acids, optionally wherein the length is 9-35 amino acids, optionally wherein the length is 9-30 amino acids, optionally wherein the length is 9-25 amino acids, optionally wherein the length is 9-20 amino acids, optionally wherein the length is 9-15 amino acids, optionally wherein the length is 9-10 amino acids.

97. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of MPRTA (SEQ ID NO: 523).

98. The AAV capsid protein of claim 97, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 99. The AAV capsid protein of claim 98, wherein the amino acid sequence appears at frame 1 of the peptide insert.

100. The AAV capsid protein of claim 98, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.

101. The AAV capsid protein of claim 98, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

102. The AAV capsid protein of claim 98, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

103. The AAV capsid protein of claim 98, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 9 amino acids, optionally wherein the length is 9-40 amino acids, optionally wherein the length is 9-35 amino acids, optionally wherein the length is 9-30 amino acids, optionally wherein the length is 9-25 amino acids, optionally wherein the length is 9-20 amino acids, optionally wherein the length is 9-15 amino acids, optionally wherein the length is 9-10 amino acids.

104. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of MPRYG (SEQ ID NO: 524).

105. The AAV capsid protein of claim 104, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

106. The AAV capsid protein of claim 105, wherein the amino acid sequence appears at frame 1 of the peptide insert.

107. The AAV capsid protein of claim 105, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein theATTORNEY DOCKET NO.: 51772-005WO3 PATENT length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.

108. The AAV capsid protein of claim 105, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

109. The AAV capsid protein of claim 105, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

110. The AAV capsid protein of claim 105, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 9 amino acids, optionally wherein the length is 9-40 amino acids, optionally wherein the length is 9-35 amino acids, optionally wherein the length is 9-30 amino acids, optionally wherein the length is 9-25 amino acids, optionally wherein the length is 9-20 amino acids, optionally wherein the length is 9-15 amino acids, optionally wherein the length is 9-10 amino acids.

111. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of MPRQP (SEQ ID NO: 525).

112. The AAV capsid protein of claim 111, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

113. The AAV capsid protein of claim 112, wherein the amino acid sequence appears at frame 1 of the peptide insert.

114. The AAV capsid protein of claim 112, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.

115. The AAV capsid protein of claim 112, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein theATTORNEY DOCKET NO.: 51772-005WO3 PATENT length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

116. The AAV capsid protein of claim 112, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

117. The AAV capsid protein of claim 112, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 9 amino acids, optionally wherein the length is 9-40 amino acids, optionally wherein the length is 9-35 amino acids, optionally wherein the length is 9-30 amino acids, optionally wherein the length is 9-25 amino acids, optionally wherein the length is 9-20 amino acids, optionally wherein the length is 9-15 amino acids, optionally wherein the length is 9-10 amino acids.

118. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of MPRTP (SEQ ID NO: 526).

119. The AAV capsid protein of claim 118, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

120. The AAV capsid protein of claim 119, wherein the amino acid sequence appears at frame 1 of the peptide insert.

121. The AAV capsid protein of claim 119, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 6 amino acids, optionally wherein the length is 6-40 amino acids, optionally wherein the length is 6-35 amino acids, optionally wherein the length is 6-30 amino acids, optionally wherein the length is 6-25 amino acids, optionally wherein the length is 6-20 amino acids, optionally wherein the length is 6-15 amino acids, optionally wherein the length is 6-10 amino acids.

122. The AAV capsid protein of claim 119, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 123. The AAV capsid protein of claim 119, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

124. The AAV capsid protein of claim 119, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 9 amino acids, optionally wherein the length is 9-40 amino acids, optionally wherein the length is 9-35 amino acids, optionally wherein the length is 9-30 amino acids, optionally wherein the length is 9-25 amino acids, optionally wherein the length is 9-20 amino acids, optionally wherein the length is 9-15 amino acids, optionally wherein the length is 9-10 amino acids.

125. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of IMPRTA (SEQ ID NO: 527).

126. The AAV capsid protein of claim 125, wherein the amino acid sequence appears at the first permissible frame, last permissible frame, or any frame in between.

127. The AAV capsid protein of claim 126, wherein the amino acid sequence appears at frame 1 of the peptide insert.

128. The AAV capsid protein of claim 126, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

129. The AAV capsid protein of claim 126, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

130. The AAV capsid protein of claim 126, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 9 amino acids, optionally wherein the length is 9-40 amino acids, optionally wherein the length is 9-35 amino acids, optionally wherein the length is 9-30 amino acids, optionally wherein the length is 9-25 amino acids, optionally wherein the length is 9-20 amino acids, optionally wherein the length is 9-15 amino acids, optionally wherein the length is 9-10 amino acids.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 131. The AAV capsid protein of claim 126, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 10 amino acids, optionally wherein the length is 10-40 amino acids, optionally wherein the length is 10-35 amino acids, optionally wherein the length is 10-30 amino acids, optionally wherein the length is 10-25 amino acids, optionally wherein the length is 10-20 amino acids, optionally wherein the length is 10-15 amino acids.

132. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of AMPRYG (SEQ ID NO: 528).

133. The AAV capsid protein of claim 132, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

134. The AAV capsid protein of claim 133, wherein the amino acid sequence appears at frame 1 of the peptide insert.

135. The AAV capsid protein of claim 133, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

136. The AAV capsid protein of claim 133, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

137. The AAV capsid protein of claim 133, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 9 amino acids, optionally wherein the length is 9-40 amino acids, optionally wherein the length is 9-35 amino acids, optionally wherein the length is 9-30 amino acids, optionally wherein the length is 9-25 amino acids, optionally wherein the length is 9-20 amino acids, optionally wherein the length is 9-15 amino acids, optionally wherein the length is 9-10 amino acids.

138. The AAV capsid protein of claim 133, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 10 amino acids, optionally wherein the length is 10-40 amino acids, optionally wherein the length is 10-35 amino acids, optionally wherein the length is 10-30 amino acids, optionally wherein the length is 10-25 amino acids, optionally wherein the length is 10-20 amino acids, optionally wherein the length is 10-15 amino acids.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 139. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of MPRTAG (SEQ ID NO: 493).

140. The AAV capsid protein of claim 139, wherein the amino acid sequence appears at the first permissible frame, last permissible frame, or any frame in between.

141. The AAV capsid protein of claim 140, wherein the amino acid sequence appears at frame 1 of the peptide insert.

142. The AAV capsid protein of claim 140, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

143. The AAV capsid protein of claim 140, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

144. The AAV capsid protein of claim 140, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 9 amino acids, optionally wherein the length is 9-40 amino acids, optionally wherein the length is 9-35 amino acids, optionally wherein the length is 9-30 amino acids, optionally wherein the length is 9-25 amino acids, optionally wherein the length is 9-20 amino acids, optionally wherein the length is 9-15 amino acids, optionally wherein the length is 9-10 amino acids.

145. The AAV capsid protein of claim 140, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 10 amino acids, optionally wherein the length is 10-40 amino acids, optionally wherein the length is 10-35 amino acids, optionally wherein the length is 10-30 amino acids, optionally wherein the length is 10-25 amino acids, optionally wherein the length is 10-20 amino acids, optionally wherein the length is 10-15 amino acids.

146. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of MPRYGG (SEQ ID NO: 529).

147. The AAV capsid protein of claim 146, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

148. The AAV capsid protein of claim 147, wherein the amino acid sequence appears at frame 1 of the peptide insert.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 149. The AAV capsid protein of claim 147, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

150. The AAV capsid protein of claim 147, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

151. The AAV capsid protein of claim 147, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 9 amino acids, optionally wherein the length is 9-40 amino acids, optionally wherein the length is 9-35 amino acids, optionally wherein the length is 9-30 amino acids, optionally wherein the length is 9-25 amino acids, optionally wherein the length is 9-20 amino acids, optionally wherein the length is 9-15 amino acids, optionally wherein the length is 9-10 amino acids.

152. The AAV capsid protein of claim 147, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 10 amino acids, optionally wherein the length is 10-40 amino acids, optionally wherein the length is 10-35 amino acids, optionally wherein the length is 10-30 amino acids, optionally wherein the length is 10-25 amino acids, optionally wherein the length is 10-20 amino acids, optionally wherein the length is 10-15 amino acids.

153. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of MPRQPG (SEQ ID NO: 530).

154. The AAV capsid protein of claim 153, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

155. The AAV capsid protein of claim 154, wherein the amino acid sequence appears at frame 1 of the peptide insert.

156. The AAV capsid protein of claim 154, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 157. The AAV capsid protein of claim 154, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

158. The AAV capsid protein of claim 154, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 9 amino acids, optionally wherein the length is 9-40 amino acids, optionally wherein the length is 9-35 amino acids, optionally wherein the length is 9-30 amino acids, optionally wherein the length is 9-25 amino acids, optionally wherein the length is 9-20 amino acids, optionally wherein the length is 9-15 amino acids, optionally wherein the length is 9-10 amino acids.

159. The AAV capsid protein of claim 154, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 10 amino acids, optionally wherein the length is 10-40 amino acids, optionally wherein the length is 10-35 amino acids, optionally wherein the length is 10-30 amino acids, optionally wherein the length is 10-25 amino acids, optionally wherein the length is 10-20 amino acids, optionally wherein the length is 10-15 amino acids.

160. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence of MPRTPG (SEQ ID NO: 531).

161. The AAV capsid protein of claim 160, wherein the amino acid sequence appears at the first permissible frame of the peptide insert, last permissible frame of the peptide insert, or any frame in between.

162. The AAV capsid protein of claim 161, wherein the amino acid sequence appears at frame 1 of the peptide insert.

163. The AAV capsid protein of claim 161, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 7 amino acids, optionally wherein the length is 7-40 amino acids, optionally wherein the length is 7-35 amino acids, optionally wherein the length is 7-30 amino acids, optionally wherein the length is 7-25 amino acids, optionally wherein the length is 7-20 amino acids, optionally wherein the length is 7-15 amino acids, optionally wherein the length is 7-10 amino acids.

164. The AAV capsid protein of claim 161, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 165. The AAV capsid protein of claim 161, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 9 amino acids, optionally wherein the length is 9-40 amino acids, optionally wherein the length is 9-35 amino acids, optionally wherein the length is 9-30 amino acids, optionally wherein the length is 9-25 amino acids, optionally wherein the length is 9-20 amino acids, optionally wherein the length is 9-15 amino acids, optionally wherein the length is 9-10 amino acids.

166. The AAV capsid protein of claim 161, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 10 amino acids, optionally wherein the length is 10-40 amino acids, optionally wherein the length is 10-35 amino acids, optionally wherein the length is 10-30 amino acids, optionally wherein the length is 10-25 amino acids, optionally wherein the length is 10-20 amino acids, optionally wherein the length is 10-15 amino acids.

167. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (I): (X1)MPR(X2)(X3)(X4) Formula (I) wherein each of (X1), (X2), (X3), and (X4), independently, represents any naturally occurring amino acid.

168. The recombinant AAV capsid protein of claim 167, wherein (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly.

169. The recombinant AAV capsid protein of claim 168, wherein (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala.

170. The recombinant AAV capsid protein of claim 169, wherein (X1) represents Phe, Leu, Ile, Met, or Gln.

171. The recombinant AAV capsid protein of claim 168, wherein (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, Ala, or Gly.

172. The recombinant AAV capsid protein of claim 171, wherein (X1) represents Phe, Leu, Ile, Met, Gln, or Ala.

173. The recombinant AAV capsid protein of claim 168, wherein (X1) represents Tyr, Ile, Met, Ser, or Ala.

174. The recombinant AAV capsid protein of claim 173, wherein (X1) represents Ala or Ile.

175. The recombinant AAV capsid protein of any one of claims 167-174, wherein (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro.

176. The recombinant AAV capsid protein of claim 175, wherein (X2) represents Tyr, Ser, Thr, Gln, or Asp.

177. The recombinant AAV capsid protein of claim 176, wherein (X2) represents Ser, Thr, or Gln.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 178. The recombinant AAV capsid protein of claim 175, wherein (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro.

179. The recombinant AAV capsid protein of claim 178, wherein (X2) represents Ser, Thr, or Gln.

180. The recombinant AAV capsid protein of claim 175, wherein (X2) represents Phe, Tyr, Ser, Thr, Asn, or Gln.

181. The recombinant AAV capsid protein of claim 180, wherein (X2) represents Tyr or Thr.

182. The recombinant AAV capsid protein of any one of claims 167-174, wherein (X3) represents Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro.

183. The recombinant AAV capsid protein of claim 182, wherein (X3) represents Ile, Ala, Gly, or Pro.

184. The recombinant AAV capsid protein of claim 183, wherein (X3) represents Ala or Pro.

185. The recombinant AAV capsid protein of claim 183, wherein (X3) represents Ala or Gly.

186. The recombinant AAV capsid protein of claim 182, wherein (X3) represents Val, Lys, Ala, Gly, or Pro.

187. The recombinant AAV capsid protein of claim 186, wherein (X3) represents Ala, Gly, or Pro.

188. The recombinant AAV capsid protein of any one of claims 167-187, wherein (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro.

189. The recombinant AAV capsid protein of claim 187, wherein (X4) represents Ser, Gly, Ala, or Pro.

190. The recombinant AAV capsid protein of claim 188, wherein (X4) represents Gly or Ala.

191. The recombinant AAV capsid protein of claim 187, wherein (X4) represents Gly or Pro.

192. The recombinant AAV capsid protein of claim 191, wherein (X4) represents Gly.

193. The recombinant AAV capsid protein of any one of claims 167-187, wherein (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro.

194. The recombinant AAV capsid protein of claim 193, wherein (X4) represents Gly or Ala.

195. The recombinant AAV capsid protein of claim 193, wherein (X4) represents Gly or Pro.

196. The recombinant AAV capsid protein of claim 195, wherein (X4) represents Gly.

197. A recombinant AAV capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (II): IMPR(X2)(X3)(X4)ATTORNEY DOCKET NO.: 51772-005WO3 PATENT Formula (II) wherein each of (X2), (X3), and (X4), independently, represents any naturally occurring amino acid.

198. The recombinant AAV capsid protein of claim 197, wherein (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro.

199. The recombinant AAV capsid protein of claim 198, wherein (X2) represents Tyr, Ser, Thr, Gln, or Asp.

200. The recombinant AAV capsid protein of claim 199, wherein (X2) represents Ser, Thr, or Gln.

201. The recombinant AAV capsid protein of claim 198, wherein (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro.

202. The recombinant AAV capsid protein of claim 201, wherein (X2) represents Ser, Thr, or Gln.

203. The recombinant AAV capsid protein of claim 201, wherein (X2) represents Tyr or Thr.

204. The recombinant AAV capsid protein of any one of claims 197-203, wherein (X3) represents Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro.

205. The recombinant AAV capsid protein of claim 204, wherein (X3) represents Ile, Ala, Gly, or Pro.

206. The recombinant AAV capsid protein of claim 205, wherein (X3) represents Ala or Pro.

207. The recombinant AAV capsid protein of claim 204, wherein (X3) represents Val, Lys, Ala, Gly, or Pro.

208. The recombinant AAV capsid protein of claim 207, wherein (X3) represents Ala, Gly, or Pro.

209. The recombinant AAV capsid protein of claim 208, wherein (X3) represents Ala or Gly.

210. The recombinant AAV capsid protein of any one of claims 197-209, wherein (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro.

211. The recombinant AAV capsid protein of claim 210, wherein (X4) represents Ser, Gly, Ala, or Pro.

212. The recombinant AAV capsid protein of claim 211, wherein (X4) represents Gly or Ala.

213. The recombinant AAV capsid protein of claim 210, wherein (X4) represents Gly or Pro.

214. The recombinant AAV capsid protein of claim 213, wherein (X4) represents Gly.

215. The recombinant AAV capsid protein of any one of claims 197-214, wherein (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro.

216. The recombinant AAV capsid protein of claim 215, wherein (X4) represents Gly or Ala.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 217. The recombinant AAV capsid protein of claim 215, wherein (X4) represents Gly or Pro.

218. The recombinant AAV capsid protein of claim 215, wherein (X4) represents Gly.

219. A recombinant adeno-associated virus (AAV) capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (III): AMPR(X2)(X3)(X4) Formula (III) wherein each of (X2), (X3), and (X4), independently, represents any naturally occurring amino acid.

220. The recombinant AAV capsid protein of claim 219, wherein (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro.

221. The recombinant AAV capsid protein of claim 220, wherein (X2) represents Tyr, Ser, Thr, Gln, or Asp.

222. The recombinant AAV capsid protein of claim 221, wherein (X2) represents Ser, Thr, or Gln.

223. The recombinant AAV capsid protein of claim 220, wherein (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro.

224. The recombinant AAV capsid protein of claim 223, wherein (X2) represents Ser, Thr, or Gln.

225. The recombinant AAV capsid protein of claim 223, wherein (X2) represents Tyr or Thr.

226. The recombinant AAV capsid protein of any one of claims 219-225, wherein (X3) represents Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro.

227. The recombinant AAV capsid protein of claim 226, wherein (X3) represents Ile, Ala, Gly, or Pro.

228. The recombinant AAV capsid protein of claim 227, wherein (X3) represents Ala or Pro.

229. The recombinant AAV capsid protein of claim 226, wherein (X3) represents Val, Lys, Ala, Gly, or Pro.

230. The recombinant AAV capsid protein of claim 229, wherein (X3) represents Ala, Gly, or Pro.

231. The recombinant AAV capsid protein of claim 230, wherein (X3) represents Ala or Gly.

232. The recombinant AAV capsid protein of any one of claims 219-231, wherein (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro.

233. The recombinant AAV capsid protein of claim 232, wherein (X4) represents Ser, Gly, Ala, or Pro.

234. The recombinant AAV capsid protein of claim 233, wherein (X4) represents Gly or Ala.

235. The recombinant AAV capsid protein of claim 233, wherein (X4) represents Gly or Pro.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 236. The recombinant AAV capsid protein of claim 233, wherein (X4) represents Gly.

237. The recombinant AAV capsid protein of any one of claims 219-231, wherein (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro.

238. The recombinant AAV capsid protein of claim 237, wherein (X4) represents Gly or Ala.

239. The recombinant AAV capsid protein of claim 237, wherein (X4) represents Gly or Pro.

240. The recombinant AAV capsid protein of claim 237, wherein (X4) represents Gly.

241. A recombinant adeno-associated virus (AAV) capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (IV): (X1)MPRT(X3)(X4) Formula (IV) wherein each of (X1), (X3), and (X4), independently, represents any naturally occurring amino acid.

242. The recombinant AAV capsid protein of claim 241, wherein (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly.

243. The recombinant AAV capsid protein of claim 242, wherein (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala.

244. The recombinant AAV capsid protein of claim 243, wherein (X1) represents Phe, Leu, Ile, Met, or Gln.

245. The recombinant AAV capsid protein of claim 242, wherein (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, Ala, or Gly.

246. The recombinant AAV capsid protein of claim 245, wherein (X1) represents Phe, Leu, Ile, Met, Gln, or Ala.

247. The recombinant AAV capsid protein of claim 242, wherein (X1) represents Tyr, Ile, Met, Ser, or Ala.

248. The recombinant AAV capsid protein of claim 247, wherein (X1) represents Ala or Ile.

249. The recombinant AAV capsid protein of any one of claims 241-248, wherein (X3) represents Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro.

250. The recombinant AAV capsid protein of claim 249, wherein (X3) represents Ile, Ala, Gly, or Pro.

251. The recombinant AAV capsid protein of claim 250, wherein (X3) represents Ala or Pro.

252. The recombinant AAV capsid protein of claim 249, wherein (X3) represents Val, Lys, Ala, Gly, or Pro.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 253. The recombinant AAV capsid protein of claim 252, wherein (X3) represents Ala, Gly, or Pro.

254. The recombinant AAV capsid protein of claim 253, wherein (X3) represents Ala or Gly.

255. The recombinant AAV capsid protein of any one of claims 241-254, wherein (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro.

256. The recombinant AAV capsid protein of claim 255, wherein (X4) represents Ser, Gly, Ala, or Pro.

257. The recombinant AAV capsid protein of claim 256, wherein (X4) represents Gly or Ala.

258. The recombinant AAV capsid protein of claim 255, wherein (X4) represents Gly or Pro.

259. The recombinant AAV capsid protein of claim 258, wherein (X4) represents Gly.

260. The recombinant AAV capsid protein of any one of claims 241-254, wherein (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro.

261. The recombinant AAV capsid protein of claim 260, wherein (X4) represents Gly or Ala.

262. The recombinant AAV capsid protein of claim 260, wherein (X4) represents Gly or Pro.

263. The recombinant AAV capsid protein of claim 260, wherein (X4) represents Gly.

264. A recombinant adeno-associated virus (AAV) capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (V): (X1)MPRY(X3)(X4) Formula (V) wherein each of (X1), (X3), and (X4), independently, represents any naturally occurring amino acid.

265. The recombinant AAV capsid protein of claim 264, wherein (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly.

266. The recombinant AAV capsid protein of claim 265, wherein (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala.

267. The recombinant AAV capsid protein of claim 266, wherein (X1) represents Phe, Leu, Ile, Met, or Gln.

268. The recombinant AAV capsid protein of claim 265, wherein (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, Ala, or Gly.

269. The recombinant AAV capsid protein of claim 268, wherein (X1) represents Phe, Leu, Ile, Met, Gln, or Ala.

270. The recombinant AAV capsid protein of claim 265, wherein (X1) represents Tyr, Ile, Met, Ser, or Ala.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 271. The recombinant AAV capsid protein of claim 270, wherein (X1) represents Ala or Ile.

272. The recombinant AAV capsid protein of any one of claims 264-271, wherein (X3) represents Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro.

273. The recombinant AAV capsid protein of claim 272, wherein (X3) represents Ile, Ala, Gly, or Pro.

274. The recombinant AAV capsid protein of claim 273, wherein (X3) represents Ala or Pro.

275. The recombinant AAV capsid protein of claim 272, wherein (X3) represents Val, Lys, Ala, Gly, or Pro.

276. The recombinant AAV capsid protein of claim 275, wherein (X3) represents Ala, Gly, or Pro.

277. The recombinant AAV capsid protein of claim 276, wherein (X3) represents Ala or Gly.

278. The recombinant AAV capsid protein of any one of claims 264-277, wherein (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro.

279. The recombinant AAV capsid protein of claim 278, wherein (X4) represents Ser, Gly, Ala, or Pro.

280. The recombinant AAV capsid protein of claim 279, wherein (X4) represents Gly or Ala.

281. The recombinant AAV capsid protein of claim 278, wherein (X4) represents Gly or Pro.

282. The recombinant AAV capsid protein of claim 281, wherein (X4) represents Gly.

283. The recombinant AAV capsid protein of any one of claims 264-277, wherein (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro.

284. The recombinant AAV capsid protein of claim 283, wherein (X4) represents Gly or Ala.

285. The recombinant AAV capsid protein of claim 283, wherein (X4) represents Gly or Pro.

286. The recombinant AAV capsid protein of claim 283, wherein (X4) represents Gly.

287. A recombinant adeno-associated virus (AAV) capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (VI): (X1)MPR(X2)A(X4) Formula (VI) wherein each of (X1), (X2), and (X4), independently, represents any naturally occurring amino acid.

288. The recombinant AAV capsid protein of claim 287, wherein (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly.

289. The recombinant AAV capsid protein of claim 288, wherein (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 290. The recombinant AAV capsid protein of claim 289, wherein (X1) represents Phe, Leu, Ile, Met, or Gln.

291. The recombinant AAV capsid protein of claim 288, wherein (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, Ala, or Gly.

292. The recombinant AAV capsid protein of claim 291, wherein (X1) represents Phe, Leu, Ile, Met, Gln, or Ala.

293. The recombinant AAV capsid protein of claim 288, wherein (X1) represents Tyr, Ile, Met, Ser, or Ala.

294. The recombinant AAV capsid protein of claim 293, wherein (X1) represents Ala or Ile.

295. The recombinant AAV capsid protein of any one of claims 287-294, wherein (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro.

296. The recombinant AAV capsid protein of claim 295, wherein (X2) represents Tyr, Ser, Thr, Gln, or Asp.

297. The recombinant AAV capsid protein of claim 296, wherein (X2) represents Ser, Thr, or Gln.

298. The recombinant AAV capsid protein of claim 295, wherein (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro.

299. The recombinant AAV capsid protein of claim 298, wherein (X2) represents Ser, Thr, or Gln.

300. The recombinant AAV capsid protein of claim 298, wherein (X2) represents Tyr or Thr.

301. The recombinant AAV capsid protein of any one of claims 287-300, wherein (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro.

302. The recombinant AAV capsid protein of claim 301, wherein (X4) represents Ser, Gly, Ala, or Pro.

303. The recombinant AAV capsid protein of claim 302, wherein (X4) represents Gly or Ala.

304. The recombinant AAV capsid protein of claim 301, wherein (X4) represents Gly or Pro.

305. The recombinant AAV capsid protein of claim 304, wherein (X4) represents Gly.

306. The recombinant AAV capsid protein of any one of claims 287-300, wherein (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro.

307. The recombinant AAV capsid protein of claim 306, wherein (X4) represents Gly or Ala.

308. The recombinant AAV capsid protein of claim 306, wherein (X4) represents Gly or Pro.

309. The recombinant AAV capsid protein of claim 306, wherein (X4) represents Gly.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 310. A recombinant adeno-associated virus (AAV) capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (VII): (X1)MPR(X2)G(X4) Formula (VII) wherein each of (X1), (X2), and (X4), independently, represents any naturally occurring amino acid.

311. The recombinant AAV capsid protein of claim 310, wherein (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly.

312. The recombinant AAV capsid protein of claim 311, wherein (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala.

313. The recombinant AAV capsid protein of claim 312, wherein (X1) represents Phe, Leu, Ile, Met, or Gln.

314. The recombinant AAV capsid protein of claim 311, wherein (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, or Gly.

315. The recombinant AAV capsid protein of claim 314, wherein (X1) represents Phe, Leu, Ile, Met, Gln, or Ala.

316. The recombinant AAV capsid protein of claim 311, wherein (X1) represents Tyr, Ile, Met, Ser, or Ala.

317. The recombinant AAV capsid protein of claim 316, wherein (X1) represents Ala or Ile.

318. The recombinant AAV capsid protein of any one of claims 310-317, wherein (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro.

319. The recombinant AAV capsid protein of claim 318, wherein (X2) represents Tyr, Ser, Thr, Gln, or Asp.

320. The recombinant AAV capsid protein of claim 319, wherein (X2) represents Ser, Thr, or Gln.

321. The recombinant AAV capsid protein of claim 318, wherein (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro.

322. The recombinant AAV capsid protein of claim 321, wherein (X2) represents Ser, Thr, or Gln.

323. The recombinant AAV capsid protein of claim 321, wherein (X2) represents Tyr or Thr.

324. The recombinant AAV capsid protein of any one of claims 310-323, wherein (X4) represents Ser, Asp, Glu, Ala, Gly, or Pro.

325. The recombinant AAV capsid protein of claim 324, wherein (X4) represents Ser, Gly, Ala, or Pro.

326. The recombinant AAV capsid protein of claim 325, wherein (X4) represents Gly or Ala.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 327. The recombinant AAV capsid protein of claim 324, wherein (X4) represents Gly or Pro.

328. The recombinant AAV capsid protein of claim 327, wherein (X4) represents Gly.

329. The recombinant AAV capsid protein of any one of claims 310-323, wherein (X4) represents Met, Ser, Glu, Ala, Gly, Gln, or Pro.

330. The recombinant AAV capsid protein of claim 329, wherein (X4) represents Gly or Ala.

331. The recombinant AAV capsid protein of claim 329, wherein (X4) represents Gly or Pro.

332. The recombinant AAV capsid protein of claim 329, wherein (X4) represents Gly.

333. A recombinant adeno-associated virus (AAV) capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (VIII): (X1)MPR(X2)(X3)G Formula (VIII) wherein each of (X1), (X2), and (X3), independently, represents any naturally occurring amino acid.

334. The recombinant AAV capsid protein of claim 333, wherein (X1) represents Phe, Tyr, Leu, Ile, Val, Met, Ser, Thr, Gln, Lys, Arg, Asp, Glu, Ala, or Gly.

335. The recombinant AAV capsid protein of claim 334, wherein (X1) represents Phe, Leu, Ile, Met, Gln, Asp, or Ala.

336. The recombinant AAV capsid protein of claim 335, wherein (X1) represents Phe, Leu, Ile, Met, or Gln.

337. The recombinant AAV capsid protein of claim 334, wherein (X1) represents Phe, Leu, Ile, Met, Ser, Thr, Gln, Arg, Ala, or Gly.

338. The recombinant AAV capsid protein of claim 337, wherein (X1) represents Phe, Leu, Ile, Met, Gln, or Ala.

339. The recombinant AAV capsid protein of claim 334, wherein (X1) represents Tyr, Ile, Met, Ser, or Ala.

340. The recombinant AAV capsid protein of claim 339, wherein (X1) represents Ala or Ile.

341. The recombinant AAV capsid protein of any one of claims 333-340, wherein (X2) represents Phe, Tyr, Trp, His, Ser, Thr, Asn, Gln, Lys, Asp, or Pro.

342. The recombinant AAV capsid protein of claim 341, wherein (X2) represents Tyr, Ser, Thr, Gln, or Asp.

343. The recombinant AAV capsid protein of claim 342, wherein (X2) represents Ser, Thr, or Gln.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 344. The recombinant AAV capsid protein of claim 341, wherein (X2) represents Tyr, Trp, His, Ser, Thr, Asn, Gln, or Pro.

345. The recombinant AAV capsid protein of claim 344, wherein (X2) represents Ser, Thr, or Gln.

346. The recombinant AAV capsid protein of claim 344, wherein (X2) represents Tyr or Thr.

347. The recombinant AAV capsid protein of any one of claims 333-346, wherein (X3) represents Ile, Val, Gln, Lys, Arg, Ala, Gly, or Pro.

348. The recombinant AAV capsid protein of claim 347, wherein (X3) represents Ile, Ala, Gly, or Pro.

349. The recombinant AAV capsid protein of claim 348, wherein (X3) represents Ala or Pro.

350. The recombinant AAV capsid protein of claim 347, wherein (X3) represents Val, Lys, Ala, Gly, or Pro.

351. The recombinant AAV capsid protein of claim 350, wherein (X3) represents Ala, Gly, or Pro.

352. The recombinant AAV capsid protein of claim 351, wherein (X3) represents Ala or Gly.

353. A recombinant adeno-associated virus (AAV) capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (IX): (X1)MPR(X2)(Nonpolar1)G Formula (IX) wherein (Nonpolar1) represents any amino acid having a nonpolar, neutral side chain, and wherein each of (X1) and (X2), independently, represents any naturally occurring amino acid.

354. The recombinant AAV capsid protein of claim 353, wherein (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Val, Asn, His, Lys, or Gly.

355. The recombinant AAV capsid protein of claim 354, wherein (X1) represents Lys, Met, Leu, Gln, Tyr, Phe, Thr, Ile, and Ala.

356. The recombinant AAV capsid protein of claim 355, wherein (X1) represents Tyr, Ser, Ala, Ile, or Met.

357. The recombinant AAV capsid protein of claim 356, wherein (X1) represents Ala or Ile.

358. The recombinant AAV capsid protein of any one of claims 353-357, wherein (X2) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Val, Asn, His, Gly, or Trp.

359. The recombinant AAV capsid protein of claim 358, wherein (X2) represents Gln, Phe, Tyr, Thr, Ser, or Asn.

360. The recombinant AAV capsid protein of claim 359, wherein (X2) represents Tyr or Thr.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 361. The recombinant AAV capsid protein of any one of claims 353-360, wherein (Nonpolar1) represents Phe, Met, Leu, Ala, Ile, Val, Gly, and Pro.

362. The recombinant AAV capsid protein of claim 361, wherein (Nonpolar1) represents Ala, Val, Ile, Gly, or Pro.

363. The recombinant AAV capsid protein of claim 362, wherein (Nonpolar1) represents Ala, Gly, or Pro.

364. The recombinant AAV capsid protein of claim 363, wherein (Nonpolar1) represents Ala or Gly.

365. A recombinant adeno-associated virus (AAV) capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (X): (X1)M(X2)(X3)(X4)(X5)(X6) Formula (X) wherein (X2) represents an amino acid selected from the group consisting of Pro and Ser, and wherein each of (X1), (X3), (X4), (X5), and (X6), independently, represents any naturally occurring amino acid.

366. The recombinant AAV capsid protein of claim 365, wherein (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro.

367. The recombinant AAV capsid protein of claim 366, wherein (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Val, Asn, His, Lys, or Gly.

368. The recombinant AAV capsid protein of claim 367, wherein (X1) represents Lys, Met, Leu, Gln, Tyr, Phe, Thr, Ile, and Ala.

369. The recombinant AAV capsid protein of claim 368, wherein (X1) represents Tyr, Ser, Ala, Ile, or Met.

370. The recombinant AAV capsid protein of claim 369, wherein (X1) represents Ala or Ile.

371. The recombinant AAV capsid protein of any one of claims 365-370, wherein (X2) represents Pro.

372. The recombinant AAV capsid protein of any one of claims 365-370, wherein (X2) represents Ser.

373. The recombinant AAV capsid protein of any one of claims 365-372, wherein (X3) represents Val, His, or Arg.

374. The recombinant AAV capsid protein of claim 373, wherein (X3) represents Arg.

375. The recombinant AAV capsid protein of any one of claims 365-374, wherein (X4) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 376. The recombinant AAV capsid protein of claim 375, wherein (X4) represents Gln, Phe, Tyr, Thr, Ser, or Asn.

377. The recombinant AAV capsid protein of claim 376, wherein (X4) represents Tyr or Thr.

378. The recombinant AAV capsid protein of any one of claims 365-377, wherein (X5) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro.

379. The recombinant AAV capsid protein of claim 378, wherein (X5) represents Ala, Gly, or Pro.

380. The recombinant AAV capsid protein of claim 379, wherein (X5) represents Ala or Gly.

381. The recombinant AAV capsid protein of any one of claims 365-380, wherein (X6) represents Pro, Lys, Ala, Arg, Ser, Gly, Val, Leu, Gln, Thr, Ile, Met, and Asn.

382. The recombinant AAV capsid protein of claim 381, wherein (X6) represents Gly or Ala.

383. The recombinant AAV capsid protein of claim 381, wherein (X6) represents Gly or Pro.

384. The recombinant AAV capsid protein of claim 381, wherein (X6) represents Gly.

385. A recombinant adeno-associated virus (AAV) capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (XI): (X1)M(X2)(X3)(X4)(X5)G Formula (XI) wherein (X2) represents an amino acid selected from the group consisting of Pro and Ser, and wherein each of (X1), (X3), (X4), and (X5), independently, represents any naturally occurring amino acid.

386. The recombinant AAV capsid protein of claim 385, wherein (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro.

387. The recombinant AAV capsid protein of claim 386, wherein (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Val, Asn, His, Lys, or Gly.

388. The recombinant AAV capsid protein of claim 387, wherein (X1) represents Lys, Met, Leu, Gln, Tyr, Phe, Thr, Ile, and Ala.

389. The recombinant AAV capsid protein of claim 388, wherein (X1) represents Tyr, Ser, Ala, Ile, or Met.

390. The recombinant AAV capsid protein of claim 389, wherein (X1) represents Ala or Ile.

391. The recombinant AAV capsid protein of any one of claims 385-390, wherein (X2) represents Pro.

392. The recombinant AAV capsid protein of any one of claims 385-390, wherein (X2) represents Ser.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 393. The recombinant AAV capsid protein of any one of claims 385-392, wherein (X3) represents Val, His, or Arg.

394. The recombinant AAV capsid protein of claim 393, wherein (X3) represents Arg.

395. The recombinant AAV capsid protein of any one of claims 385-394, wherein (X4) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro.

396. The recombinant AAV capsid protein of claim 395, wherein (X4) represents Gln, Phe, Tyr, Thr, Ser, or Asn.

397. The recombinant AAV capsid protein of claim 396, wherein (X4) represents Tyr or Thr.

398. The recombinant AAV capsid protein of any one of claims 385-397, wherein (X5) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro.

399. The recombinant AAV capsid protein of claim 398, wherein (X5) represents Ala, Gly, or Pro.

400. The recombinant AAV capsid protein of claim 399, wherein (X5) represents Ala or Gly.

401. A recombinant adeno-associated virus (AAV) capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (XII): (X1)M(X2)(X3)(X4)(Nonpolar1)G Formula (XII) wherein (X2) represents an amino acid selected from the group consisting of Pro and Ser, (Nonpolar1) represents any amino acid having a nonpolar, neutral side chain, and each of (X1), (X3), and (X4), independently, represents any naturally occurring amino acid.

402. The recombinant AAV capsid protein of claim 401, wherein (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro.

403. The recombinant AAV capsid protein of claim 402, wherein (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Val, Asn, His, Lys, or Gly.

404. The recombinant AAV capsid protein of claim 403, wherein (X1) represents Lys, Met, Leu, Gln, Tyr, Phe, Thr, Ile, and Ala.

405. The recombinant AAV capsid protein of claim 404, wherein (X1) represents Tyr, Ser, Ala, Ile, or Met.

406. The recombinant AAV capsid protein of claim 405, wherein (X1) represents Ala or Ile.

407. The recombinant AAV capsid protein of any one of claims 401-406, wherein (X2) represents Pro.

408. The recombinant AAV capsid protein of any one of claims 401-406, wherein (X2) represents Ser.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 409. The recombinant AAV capsid protein of any one of claims 401-408, wherein (X3) represents Val, His, or Arg.

410. The recombinant AAV capsid protein of claim 409, wherein (X3) represents Arg.

411. The recombinant AAV capsid protein of any one of claims 401-410, wherein (X4) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro.

412. The recombinant AAV capsid protein of claim 411, wherein (X4) represents Gln, Phe, Tyr, Thr, Ser, or Asn.

413. The recombinant AAV capsid protein of claim 412, wherein (X4) represents Tyr or Thr.

414. The recombinant AAV capsid protein of any one of claims 401-410, wherein (Nonpolar1) represents Ala, Val, Ile, Gly, or Pro.

415. The recombinant AAV capsid protein of claim 414, wherein (Nonpolar1) represents Ala, Gly, or Pro.

416. The recombinant AAV capsid protein of claim 415, wherein (Nonpolar1) represents Ala or Gly.

417. A recombinant adeno-associated virus (AAV) capsid protein comprising an artificial peptide insert, wherein the peptide insert comprises an amino acid sequence represented by Formula (XIII): (X1)M(X2)(X3)(X4)(Nonpolar1)(Nonpolar2) Formula (XIII) wherein (X2) represents an amino acid selected from the group consisting of Pro and Ser, each of (Nonpolar1) and (Nonpolar2), independently, represents any amino acid having a nonpolar, neutral side chain, and each of (X1), (X3), and (X4), independently, represents any naturally occurring amino acid.

418. The recombinant AAV capsid protein of claim 417, wherein (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro.

419. The recombinant AAV capsid protein of claim 418, wherein (X1) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Val, Asn, His, Lys, or Gly.

420. The recombinant AAV capsid protein of claim 419, wherein (X1) represents Lys, Met, Leu, Gln, Tyr, Phe, Thr, Ile, and Ala.

421. The recombinant AAV capsid protein of claim 420, wherein (X1) represents Tyr, Ser, Ala, Ile, or Met.

422. The recombinant AAV capsid protein of claim 421, wherein (X1) represents Ala or Ile.

423. The recombinant AAV capsid protein of any one of claims 417-422, wherein (X2) represents Pro.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 424. The recombinant AAV capsid protein of any one of claims 417-422, wherein (X2) represents Ser.

425. The recombinant AAV capsid protein of any one of claims 417-424, wherein (X3) represents Val, His, or Arg.

426. The recombinant AAV capsid protein of claim 425, wherein (X3) represents Arg.

427. The recombinant AAV capsid protein of any one of claims 417-426, wherein (X4) represents Gln, Phe, Met, Leu, Tyr, Thr, Ser, Ala, Ile, Asp, Glu, Val, Asn, His, Arg, Lys, Gly, Trp, or Pro.

428. The recombinant AAV capsid protein of claim 427, wherein (X4) represents Gln, Phe, Tyr, Thr, Ser, or Asn.

429. The recombinant AAV capsid protein of claim 428, wherein (X4) represents Tyr or Thr.

430. The recombinant AAV capsid protein of any one of claims 417-429, wherein (Nonpolar1) represents Ala, Val, Ile, Gly, or Pro.

431. The recombinant AAV capsid protein of claim 430, wherein (Nonpolar1) represents Ala, Gly, or Pro.

432. The recombinant AAV capsid protein of claim 431, wherein (Nonpolar1) represents Ala or Gly.

433. The recombinant AAV capsid protein of any one of claims 417-432, wherein (Nonpolar2) represents Met, Leu, Gly, Ala, or Pro.

434. The recombinant AAV capsid protein of claim 433, wherein (Nonpolar2) represents Gly or Ala.

435. The recombinant AAV capsid protein of claim 433, wherein (Nonpolar2) represents Gly or Pro.

436. The recombinant AAV capsid protein of claim 433, wherein (Nonpolar2) represents Gly.

437. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353, 365, 385, 401, and 417, wherein (X1) represents Arg.

438. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353, 365, 385, 401, and 417, wherein (X1) represents Lys.

439. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353, 365, 385, 401, and 417, wherein (X1) represents Trp.

440. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353, 365, 385, 401, and 417, wherein (X1) represents Leu.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 441. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353,, 385, 401, and 417, wherein (X1) represents Tyr.

442. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353,, 385, 401, and 417, wherein (X1) represents Met.

443. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353,, 385, 401, and 417, wherein (X1) represents Thr.

444. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353,, 385, 401, and 417, wherein (X1) represents Val.

445. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353,, 385, 401, and 417, wherein (X1) represents Phe.

446. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353,, 385, 401, and 417, wherein (X1) represents Gln.

447. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353,, 385, 401, and 417, wherein (X1) represents Ala.

448. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353,, 385, 401, and 417, wherein (X1) represents Ile.

449. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353,, 385, 401, and 417, wherein (X1) represents Ser.

450. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353,, 385, 401, and 417, wherein (X1) represents His.

451. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353,, 385, 401, and 417, wherein (X1) represents Asn.

452. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353,, 385, 401, and 417, wherein (X1) represents Pro.

453. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353,, 385, 401, and 417, wherein (X1) represents Gly.

454. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353,, 385, 401, and 417, wherein (X1) represents Glu.

455. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353,, 385, 401, and 417, wherein (X1) represents Asp.

456. The recombinant AAV capsid protein of any one of claims 167, 241, 264, 287, 310, 333, 353,, 385, 401, and 417, wherein (X1) represents Cys.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 457. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents Arg.

458. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents Lys.

459. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents Trp.

460. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents Leu.

461. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents Tyr.

462. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents Met.

463. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents Thr.

464. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents Val.

465. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents Phe.

466. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents Gln.

467. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents Ala.

468. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents Ile.

469. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, 365, 385, 401, 417, and 437-456, wherein (X2) represents Ser.

470. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents His.

471. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents Asn.

472. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents Pro.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 473. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, 365, 385, 401, 417, and 437-456, wherein (X2) represents Gly.

474. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents Glu.

475. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents Asp.

476. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 287, 310, 333, 353, and 437-456, wherein (X2) represents Cys.

477. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365, 385, 401, 417, and 437-476, wherein (X3) represents Arg.

478. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365, 385, 401, 417, and 437-476, wherein (X3) represents Lys.

479. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365, 385, 401, 417, and 437-476, wherein (X3) represents Trp.

480. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365, 385, 401, 417, and 437-476, wherein (X3) represents Leu.

481. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365, 385, 401, 417, and 437-476, wherein (X3) represents Tyr.

482. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365, 385, 401, 417, and 437-476, wherein (X3) represents Met.

483. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365, 385, 401, 417, and 437-476, wherein (X3) represents Thr.

484. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365, 385, 401, 417, and 437-476, wherein (X3) represents Val.

485. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365, 385, 401, 417, and 437-476, wherein (X3) represents Phe.

486. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365, 385, 401, 417, and 437-476, wherein (X3) represents Gln.

487. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365, 385, 401, 417, and 437-476, wherein (X3) represents Ala.

488. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365, 385, 401, 417, and 437-476, wherein (X3) represents Ile.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 489. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365,, 401, 417, and 437-476, wherein (X3) represents Ser.

490. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365,, 401, 417, and 437-476, wherein (X3) represents His.

491. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365,, 401, 417, and 437-476, wherein (X3) represents Asn.

492. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365,, 401, 417, and 437-476, wherein (X3) represents Pro.

493. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365,, 401, 417, and 437-476, wherein (X3) represents Gly.

494. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365,, 401, 417, and 437-476, wherein (X3) represents Glu.

495. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365,, 401, 417, and 437-476, wherein (X3) represents Asp.

496. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 333, 365,, 401, 417, and 437-476, wherein (X3) represents Cys.

497. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310,, 385, 401, 417, and 437-496, wherein (X4) represents Arg.

498. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310,, 385, 401, 417, and 437-496, wherein (X4) represents Lys.

499. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310,, 385, 401, 417, and 437-496, wherein (X4) represents Trp.

500. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310,, 385, 401, 417, and 437-496, wherein (X4) represents Leu.

501. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310,, 385, 401, 417, and 437-496, wherein (X4) represents Tyr.

502. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310,, 385, 401, 417, and 437-496, wherein (X4) represents Met.

503. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310,, 385, 401, 417, and 437-496, wherein (X4) represents Thr.

504. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310,, 385, 401, 417, and 437-496, wherein (X4) represents Val.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 505. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310, 365, 385, 401, 417, and 437-496, wherein (X4) represents Phe.

506. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310, 365, 385, 401, 417, and 437-496, wherein (X4) represents Gln.

507. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310, 365, 385, 401, 417, and 437-496, wherein (X4) represents Ala.

508. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310, 365, 385, 401, 417, and 437-496, wherein (X4) represents Ile.

509. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310, 365, 385, 401, 417, and 437-496, wherein (X4) represents Ser.

510. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310, 365, 385, 401, 417, and 437-496, wherein (X4) represents His.

511. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310, 365, 385, 401, 417, and 437-496, wherein (X4) represents Asn.

512. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310, 365, 385, 401, 417, and 437-496, wherein (X4) represents Pro.

513. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310, 365, 385, 401, 417, and 437-496, wherein (X4) represents Gly.

514. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310, 365, 385, 401, 417, and 437-496, wherein (X4) represents Glu.

515. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310, 365, 385, 401, 417, and 437-496, wherein (X4) represents Asp.

516. The recombinant AAV capsid protein of any one of claims 167, 197, 219, 241, 264, 287, 310, 365, 385, 401, 417, and 437-496, wherein (X4) represents Cys.

517. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Arg.

518. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Lys.

519. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Trp.

520. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Leu.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 521. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Tyr.

522. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Met.

523. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Thr.

524. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Val.

525. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Phe.

526. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Gln.

527. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Ala.

528. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Ile.

529. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Ser.

530. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents His.

531. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Asn.

532. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Pro.

533. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Gly.

534. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Glu.

535. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Asp.

536. The recombinant AAV capsid protein of any one of claims 365, 385, and 437-516, wherein (X5) represents Cys.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 537. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Arg.

538. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Lys.

539. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Trp.

540. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Leu.

541. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Tyr.

542. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Met.

543. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Thr.

544. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Val.

545. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Phe.

546. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Gln.

547. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Ala.

548. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Ile.

549. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Ser.

550. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents His.

551. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Asn.

552. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Pro.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 553. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Gly.

554. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Glu.

555. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Asp.

556. The recombinant AAV capsid protein of any one of claims 365 and 437-536, wherein (X6) represents Cys.

557. The recombinant AAV capsid protein of any one of claims 353, 401, 417, and 437-556, wherein (Nonpolar1) represents Ala.

558. The recombinant AAV capsid protein of any one of claims 353, 401, 417, and 437-556, wherein (Nonpolar1) represents Val.

559. The recombinant AAV capsid protein of any one of claims 353, 401, 417, and 437-556, wherein (Nonpolar1) represents Leu.

560. The recombinant AAV capsid protein of any one of claims 353, 401, 417, and 437-556, wherein (Nonpolar1) represents Ile.

561. The recombinant AAV capsid protein of any one of claims 353, 401, 417, and 437-556, wherein (Nonpolar1) represents Met.

562. The recombinant AAV capsid protein of any one of claims 353, 401, 417, and 437-556, wherein (Nonpolar1) represents Phe.

563. The recombinant AAV capsid protein of any one of claims 353, 401, 417, and 437-556, wherein (Nonpolar1) represents Trp.

564. The recombinant AAV capsid protein of any one of claims 353, 401, 417, and 437-556, wherein (Nonpolar1) represents Pro.

565. The recombinant AAV capsid protein of any one of claims 353, 401, 417, and 437-556, wherein (Nonpolar1) represents Gly.

566. The recombinant AAV capsid protein of any one of claims 417 and 437-565, wherein (Nonpolar2) represents Ala.

567. The recombinant AAV capsid protein of any one of claims 417 and 437-565, wherein (Nonpolar2) represents Val.

568. The recombinant AAV capsid protein of any one of claims 417 and 437-565, wherein (Nonpolar2) represents Leu.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 569. The recombinant AAV capsid protein of any one of claims 417 and 437-565, wherein (Nonpolar2) represents Ile.

570. The recombinant AAV capsid protein of any one of claims 417 and 437-565, wherein (Nonpolar2) represents Met.

571. The recombinant AAV capsid protein of any one of claims 417 and 437-565, wherein (Nonpolar2) represents Phe.

572. The recombinant AAV capsid protein of any one of claims 417 and 437-565, wherein (Nonpolar2) represents Trp.

573. The recombinant AAV capsid protein of any one of claims 417 and 437-565, wherein (Nonpolar2) represents Pro.

574. The recombinant AAV capsid protein of any one of claims 417 and 437-565, wherein (Nonpolar2) represents Gly.

575. The recombinant AAV capsid protein of any one of claims 167-574, wherein the peptide wherein the amino acid sequence appears at the first permissible frame, last permissible frame, or any frame in between.

576. The AAV capsid protein of claim 575, wherein the amino acid sequence appears at frame 1 of the peptide insert.

577. The AAV capsid protein of claim 575, wherein the amino acid sequence appears at frame 2 of the peptide insert and the peptide insert has a length of at least 8 amino acids, optionally wherein the length is 8-40 amino acids, optionally wherein the length is 8-35 amino acids, optionally wherein the length is 8-30 amino acids, optionally wherein the length is 8-25 amino acids, optionally wherein the length is 8-20 amino acids, optionally wherein the length is 8-15 amino acids, optionally wherein the length is 8-10 amino acids.

578. The AAV capsid protein of claim 575, wherein the amino acid sequence appears at frame 3 of the peptide insert and the peptide insert has a length of at least 9 amino acids, optionally wherein the length is 9-40 amino acids, optionally wherein the length is 9-35 amino acids, optionally wherein the length is 9-30 amino acids, optionally wherein the length is 9-25 amino acids, optionally wherein the length is 9-20 amino acids, optionally wherein the length is 9-15 amino acids, optionally wherein the length is 9-10 amino acids.

579. The AAV capsid protein of claim 575, wherein the amino acid sequence appears at frame 4 of the peptide insert and the peptide insert has a length of at least 10 amino acids, optionally wherein the length is 10-40 amino acids, optionally wherein the length is 10-35 amino acids, optionally wherein the length is 10-30 amino acids, optionally wherein the length is 10-25 amino acids, optionally wherein the length is 10-20 amino acids, optionally wherein the length is 10-15 amino acids.ATTORNEY DOCKET NO.: 51772-005WO3 PATENT 580. The AAV capsid protein of claim 575, wherein the amino acid sequence appears at frame 5 of the peptide insert and the peptide insert has a length of at least 11 amino acids, optionally wherein the length is 11-40 amino acids, optionally wherein the length is 11-35 amino acids, optionally wherein the length is 11-30 amino acids, optionally wherein the length is 11-25 amino acids, optionally wherein the length is 11-20 amino acids, optionally wherein the length is 11-15 amino acids 581. A recombinant AAV capsid protein comprising a peptide insert having the amino acid sequence of any one of ID NOs: 1-495 and 512-531.

582. The recombinant AAV capsid protein of any one of claims 1-581, wherein the peptide insert is incorporated into a wild-type AAV capsid protein.

583. The recombinant AAV capsid protein of claim 582, wherein the wild-type AAV capsid protein is a capsid protein that occurs naturally in an AAV serotype selected from the group consisting of AAV1, AAV2, AAV3, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV10, AAVrh10, or AAVrh74.

584. The recombinant AAV capsid protein of claim 583, wherein the wild-type AAV capsid protein is a capsid protein that occurs naturally in AAV9.

585. The recombinant AAV capsid protein of any one of claims 582-584, wherein the wild-type AAV capsid protein is a VP1, VP2, or VP3 capsid protein.

586. The recombinant AAV capsid protein of claim 585, wherein the wild-type AAV capsid protein is a VP1 capsid protein.

587. The recombinant AAV capsid protein of any one of claims 582-586, wherein the peptide insert is incorporated into the wild-type AAV capsid protein between a pair of consecutive amino acid residues that are located within a variable region (VR) selected from the group consisting of VR-I, VR-II, VR-III, VR-IV, VR-V, VR-VI, VR-VII, VR-VIII, and VR-IX.

588. The recombinant AAV capsid protein of claim 587, wherein the peptide insert is incorporated into the wild-type AAV capsid protein between a pair of consecutive amino acid residues that are located within VR-VIII.

589. The recombinant AAV capsid protein of claim 588, wherein the pair of consecutive amino acid residues is selected from the group consisting of (a) amino acids 581 and 582, (b) amino acids 582 and 583, (c) amino acids 583 and 584, (d) amino acids 584 and 585, (e) amino acids 585 and 586, (f) amino acids 586 and 587, (g) amino acids 587 and 588, (h) amino acids 588 and 589, (i) amino acids 589 and 590, (j) amino acids 590 and 591, (k) amino acids 591 and 592, or (l) amino acids 592 and 593, wherein the amino acids are numbered relative to the amino acid sequence of wild-type AAV9 VP1 (SEQ ID NO: 492).

590. An AAV particle comprising the AAV capsid protein of any one of claims 1-589.

591. The AAV particle of claim 590, wherein the AAV capsid protein encapsulates an AAV genome comprising, in the 5’-to-3’ direction:ATTORNEY DOCKET NO.: 51772-005WO3 PATENT a) a first inverted terminal repeat (ITR); b) a transgene of interest; and c) a second ITR.

592. The AAV particle of claim 591, wherein the AAV genome further comprises, between the first ITR and the transgene, one or more transcription regulatory elements that modulate expression of the transgene.

593. A method of expressing a transgene in a subject, the method comprising administering to the subject the AAV particle of any one of claims 590-592.

594. The method of claim 593, wherein the AAV particle is administered to the subject by way of intramuscular, intrahepatic, intravenous, intrathecal, intracerebroventricular, intracisternal, intrastriatal, intracerebral, intracerebrospinal, intracranial, intracortical, intradermal, transdermal, parenteral, intranasal, subcutaneous, percutaneous, intratracheal, intraocular, or intravascular administration.

595. The method of claim 594, wherein the AAV particle is administered to the subject by way of intramuscular administration.

596. The method of any one of claims 593-595, wherein the subject is a mammal.

597. The method of claim 596, wherein the subject is a human.

598. A kit comprising the AAV particle of any one of claims 590-592 and a package insert, wherein the package insert instructs a user of the kit to administer the AAV particle to a subject in accordance with the method of any one of claims 593-597.

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