Human fibronectin type III protein scaffold

Abstract

Protein scaffolds and scaffold libraries based on fibronectin type III (FN3) domains with alternative binding surface designs, isolated nucleic acids encoding the protein scaffolds, vectors, host cells, methods for making them, and their use as therapeutic molecules for the treatment and diagnosis of diseases and disorders.

Description

[Technical field]

[0001] Related Applications This application claims priority to U.S. Provisional Application No. 63 / 203,343, filed July 19, 2021, which is incorporated by reference in its entirety.

[0002] The present disclosure relates to fibronectin type III (FN3) domain molecules and methods of making and using such molecules. [Background technology]

[0003] Monoclonal antibodies are the most widely used type of therapeutic protein when high affinity and specificity for target molecules are desired. However, non-antibody proteins, commonly referred to as protein scaffolds, that have relatively well-defined three-dimensional structures that can be engineered to bind desired target molecules, may have advantages over traditional antibodies due to their small size, lack of disulfide bonds, high stability, and ability to be expressed in prokaryotic hosts. These scaffolds usually contain one or more regions that are suitable for specific or random sequence mutations, and such sequence randomization is often carried out to produce libraries of proteins from which desired products are selected. Novel purification methods are easily applied; scaffolds are easily conjugated to drugs / toxins, efficiently penetrate tissues, and are formatted into multispecific binders (Non-Patent Document 1; Non-Patent Document 2).

[0004] One such protein scaffold is the fibronectin type III (FN3) domain, which has been identified in many proteins and has a characteristic tertiary structure with six loops connected by seven beta strands. Three loops, particularly the FG, BC, and DE loops, are structurally similar to the complementarity determining regions (CDRs) of antibodies. These loops have been randomized to generate libraries of FN3 domain scaffolds that successfully select specific binders for many different targets while retaining important biophysical properties (Non-Patent Document 3; Non-Patent Document 4; Non-Patent Document 5; Non-Patent Document 6; Non-Patent Document 7; Non-Patent Document 8; Non-Patent Document 9). [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Binz and Pluckthun, Curr Opin Biotechnol, 16, 459-469, 2005 [Non-Patent Document 2] Skerra, J Mal Recognit, 13, pp. 167-187, 2000. [Non-Patent Document 3] Getmanov et al., Chem Biol, 13, 549-556, 2006 [Non-Patent Document 4] Hackel et al., J Mol Biol, 381, 1238-1252, 2008 [Non-Patent Document 5] Karatan et al., Chem Biol, 11, 835-844, 2004 [Non-Patent Document 6] Koide et al., J Mol Biol, 284, pp. 1141-1151, 1998 [Non-Patent Document 7] Koide et al., Proc Natl Acad Sci US A, 104, pp. 6632-6637, 2007 [Non-Patent Document 8] Parker et al., Protein Eng Des Sel, 18, pp. 435-444, 2005 [Non-Patent Document 9] Xu et al., Chemistry & Biology, 9, 933-942, 2002 Summary of the Invention [Problem to be solved by the invention]

[0006] There is a need for alternative binding domains that can bind to target molecules, thereby facilitating delivery of therapeutics, such as oligonucleotide-based therapeutics, or can be used as targeting moieties with direct therapeutic effect. The present disclosure provides such improved proteins. [Means for solving the problem]

[0007] In some embodiments, a library is provided comprising a plurality of fibronectin type III module (FN3) domains (polypeptides), the library having a diversified C-CD-DF-FG-G alternative surface comprising a diversified C beta chain, a CD loop, a D beta chain, an F beta chain, an FG loop and a G beta chain, wherein the polypeptide comprises an amino acid sequence at least 80%, 85%, 90%, or 95% identical to the amino acid sequence of SEQ ID NO: 44; wherein the plurality of polypeptides comprises at least one mutated amino acid residue in one or more of the C beta chain, the CD loop, the D beta chain, the F beta chain, the FG loop, and the G beta chain, or each thereof, when compared to SEQ ID NO: 24, to form an FN3 domain library having a diversified C-CD-DF-FG-G alternative surface.

[0008] In some embodiments, methods of producing the libraries described herein are provided.

[0009] In some embodiments, a method for generating a library of human fibronectin type III (FN3) domains is provided, wherein the library comprises a diversified C-CD-DF-FG-G alternative surface comprising one or more of a diversified C beta strand, a CD loop, a D beta strand, a F beta strand, a FG loop, and a G beta strand, or each of them, comprising: providing a reference FN3 domain polypeptide having an amino acid sequence at least 80, 85, or 90% identical to the amino acid sequence of SEQ ID NO: 44; and introducing diversity into the reference FN3 domain polypeptide by mutating at least one residue in any one of the following domains: the C beta strand, the CD loop, the F beta strand, the FG loop, and the G beta strand residues to form a human FN3 domain library having a diversified C-CD-DF-FG-G alternative surface.

[0010] In some embodiments, a library produced by the methods described herein is provided.

[0011] In some embodiments, a method is provided for obtaining a protein scaffold comprising a human fibronectin type III module (FN3) domain having a diversified C-CD-DF-FG-G alternative surface that specifically binds to a target molecule, the method comprising contacting or panning a library with the target molecule and isolating a protein scaffold that specifically binds to the target molecule with a predetermined affinity.

[0012] In some embodiments, a method is provided for obtaining a polypeptide comprising a fibronectin type III module (FN3) domain having a diversified C-CD-DF-FG-G alternative surface that binds or specifically binds to a target molecule, the method comprising contacting or panning (screening) a library disclosed herein with the target molecule and isolating polypeptides that bind or specifically bind to the target molecule. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The term "fibronectin type III (FN3) domain" (FN3 domain) as used herein refers to a domain that occurs frequently in proteins including fibronectin, tenascin, intracellular cytoskeletal proteins, cytokine receptors and prokaryotic enzymes (Bork and Doolittle, Proc Nat Acad Sci USA 89:8990-8994, 1992; Meinke et al., J Bacteriol 175:1910-1918, 1993; Watanabe et al., J Biol Chem 265:15659-15665, 1990). Exemplary FN3 domains are the 15 different FN3 domains present in human tenascin-C, the 15 different FN3 domains present in human fibronectin (FN), and non-natural synthetic FN3 domains, such as those described in U.S. Pat. No. 8,278,419. Individual FN3 domains are referred to by domain number and protein name, eg, the third FN3 domain of tenascin (TN3), or the tenth FN3 domain of fibronectin (FN10).

[0014] The term "alternative surface" as used herein refers to a surface on the side of an FN3 domain that comprises one or more beta strands and one or more loops.In some embodiments, the alternative surface is a C-CD-DF-FG-G surface formed by amino acids in the C beta strand, the CD loop, the D beta strand, the F beta strand, the FG loop, and the G beta strand.In some embodiments, the alternative surface comprises diversified C beta strand, the CD loop, the D beta strand, the F beta strand, the FG loop, and the G beta strand.

[0015] The term "biological sample" refers to blood, tissue, bone marrow, sputum, and the like.

[0016] The term "diagnostic reagent" refers to any substance used to analyze a biological sample, whether or not the substance is distributed as a single substance or in combination with other substances in a diagnostic kit.

[0017] The terms "substituting" or "substituted" or "mutating" or "mutated" as used herein refer to altering, deleting, or inserting one or more amino acids or nucleotides in a polypeptide or polynucleotide sequence to generate a variant of that sequence.

[0018] The terms "randomizing" or "randomized" or "diversified" or "diversifying" as used herein refer to making at least one substitution, insertion or deletion in a polynucleotide or polypeptide sequence.

[0019] The term "variant" as used herein refers to a polypeptide or polynucleotide that differs from a reference polypeptide or polynucleotide by one or more modifications, such as a substitution, insertion or deletion.

[0020] The term "specifically binds" or "specific binding" as used herein refers to a binding -6 M or less, e.g., about 1×10 -7 M or less, approximately 1 x 10 -8 M or less, approximately 1 x 10 -9 M or less, about 1×10 -10 M or less, approximately 1 x 10 -11 M or less, approximately 1 x 10 -12 M or less, or about 1 x 10 -13This refers to the ability of the FN3 domain described herein to bind to a given antigen with a dissociation constant (KD) of M or less. Typically, the FN3 domain binds to a given antigen (i.e., human PSMA) with a KD that is at least 10-fold less than the KD for a non-specific antigen (e.g., BSA or casein) as measured by surface plasmon resonance using, for example, a Proteon Instrument (BioRad). However, an isolated FN3 domain that specifically binds to human PSMA may have cross-reactivity to other related antigens, for example, to the same given antigen from other species (homologues), such as Macaca Fascicularis (cynomolgus monkey, cyno) or Pan troglodytes (chimpanzee).

[0021] The term "target molecule" as used herein refers to a protein, peptide, carbohydrate, lipid, etc., that bears an antigen or epitope recognized by an FN3 domain. A target molecule may be naturally occurring or non-naturally occurring.

[0022] The term "epitope" as used herein refers to the part of an antigen that FN3 domain specifically binds to. Epitopes usually consist of chemically active (such as polar, non-polar or hydrophobic) surface groups of moieties such as amino acids or polysaccharide side chains, and may have specific three-dimensional structural characteristics, as well as specific charge characteristics. Epitopes are composed of contiguous and / or discontinuous amino acids that form a conformational space unit. For discontinuous epitopes, amino acids from different parts of the linear sequence of an antigen come into close proximity in three-dimensional space through folding of the protein molecule.

[0023] The term "library" refers to a collection of variants. A library is composed of variants of a polypeptide or polynucleotide.

[0024] The term "stability" as used herein refers to the ability of a molecule to remain folded under physiological conditions so as to retain at least one of its normal functional activities, e.g., binding to a given antigen.

[0025] "Tencon" as used herein refers to a synthetic fibronectin type III (FN3) domain having the sequence described in US Patent Application Publication No. 2010 / 0216708.

[0026] The term "tenascin-C" as used herein refers to human tenascin-C having the sequence shown in GenBank Acc. No. NP_002151. Tenascin-C has 15 tandem FN3 domains.

[0027] "Cancer cells" or "tumor cells" as used herein refer to cancerous, precancerous or transformed cells, either in vivo, ex vivo and in tissue culture, that have spontaneous or induced phenotypic changes that do not necessarily involve the incorporation of new genetic material. Transformation may occur from infection with a transforming virus and incorporation of new genomic nucleic acid, or from the incorporation of exogenous nucleic acid, but transformation may also occur spontaneously or following exposure to carcinogens, thereby mutating endogenous genes. Transformation / cancer is exemplified, for example, by morphological changes, cellular immortalization, abnormal growth control, lesion formation, proliferation, malignancy, tumor-specific marker levels, invasiveness, tumor growth or suppression, etc. in suitable animal hosts, such as nude mice, in vitro, in vivo and ex vivo (Freshney, Culture of Animal Cells: A Manual of Basic Technique (3rd ed. 1994)).

[0028] "Inhibit growth" (e.g., with reference to cells such as tumor cells) refers to a measurable decrease in cell growth in vitro or in vivo when contacted with a therapeutic agent or combination of therapeutic agents or drugs, as compared to the growth of the same cells grown in appropriate control conditions known to those of skill in the art. Inhibition of cell growth in vitro or in vivo may be at least about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 99%, or 100%. Inhibition of cell growth may occur by various mechanisms, for example, by apoptosis, necrosis, or by inhibition of cell proliferation, or lysis of the cells.

[0029] The term "vector" refers to a polynucleotide that can be replicated in a biological system or can be transferred between such systems. Vector polynucleotides usually contain elements such as origins of replication, polyadenylation signals, or selection markers that function to facilitate the replication or maintenance of these polynucleotides in biological systems. Examples of such biological systems include cells, viruses, animals, plants, and biological systems reconstituted using biological components capable of replicating vectors. The polynucleotides that comprise vectors may be DNA or RNA molecules, or hybrids thereof.

[0030] The term "expression vector" refers to a vector that is utilized in a biological system or in a reconstituted biological system to direct the translation of a polypeptide encoded by a polynucleotide sequence present in the expression vector.

[0031] The term "polynucleotide" refers to a molecule comprising a chain of nucleotides covalently linked by a sugar-phosphate backbone or other equivalent covalent chemistry. Double- and single-stranded DNA and RNA are typical examples of polynucleotides.

[0032] The term "polypeptide" or "protein" refers to a molecule containing at least two amino acid residues linked by a peptide bond to form a polypeptide. Small polypeptides of less than about 50 amino acids are referred to as "peptides."

[0033] The term "in combination with" as used herein means that two or more therapeutic agents can be administered to a subject together in a mixture, simultaneously as a single agent, or sequentially as a single agent in any order.

[0034] The term "heterologous" means that the described polypeptide is derived from a different cell type or a different species and is not naturally occurring.

[0035] The present embodiment provides FN3 domains that specifically bind target molecules, and thus can be widely used in therapeutic and diagnostic applications. FN3 polypeptides have domains that include one or more beta strands and one or more loops, which can be randomized to generate protein scaffolds and select protein scaffolds that specifically bind target molecules with high affinity. The published FN3-based domain libraries were generated by diversifying the upper or lower loops, which are regions structurally similar to the CDRs in antibody variable chains, to provide curved binding surfaces. In contrast, high affinity binding molecules can be selected from the FN3 domain libraries provided herein that exhibit concave interaction surfaces that are generated by randomizing alternative surfaces as provided herein based on a reference sequence. This can be done, for example, to increase the number of epitopes and targets for which high affinity binding protein scaffolds are selected. In some embodiments, polynucleotides encoding the protein domains or their complementary nucleic acids, vectors, host cells, and methods of making and using them are provided. The present embodiment also provides a method of making a library of FN3 domains as provided herein, and the libraries made as described above.

[0036] Fibronectin type III domain Fibronectin type III (FN3) domains (or modules) are prototypical repeat domains that were first identified in fibronectin and are now known to be present in a variety of animal protein families, including cell surface receptors, extracellular matrix proteins, enzymes, and muscle proteins. Structurally, FN3 domains have a topology very similar to that of immunoglobulin-like domains, except for the lack of disulfide bonds. As is known in the art, naturally occurring FN3 domains have a beta sandwich structure with seven beta strands, designated A, B, C, D, E, F, and G, connected by six loops, designated AB, BC, CD, DE, EF, and FG loops (Bork and Doolittle, Proc Natl Acad Sci USA 89, pp. 8990-8992, 1992; U.S. Patent No. 6,673,901). Three loops, BC, DE, FG loops, exist at the top of the FN3 domain, and three, AB, CD, and EF loops, exist at the bottom of the domain. The conformation of FN3 domains is highly conserved, whereas the similarity between different domains at the amino acid level is very low. FN3 domains may be naturally occurring or non-naturally occurring. Exemplary non-naturally occurring FN3 domains are consensus FN3 domains that are designed based on the alignment of selected FN3 domains present in a certain protein, incorporating the most conserved (high frequency) amino acids at each position to generate non-naturally occurring FN3 domains. For example, non-naturally occurring FN3 domains are designed based on the consensus sequence of 15 FN3 domains from human tenascin-C, or based on the consensus sequence of 15 FN3 domains from human fibronectin. These non-naturally occurring FN3 domains retain the typical topology of FN3 domains, and can show improved properties, such as improved stability, when compared to wild-type FN3 domains.Exemplary non-naturally occurring FN3 domains are the Tencon and Fibcon domains described in US Patent Application Publication Nos. 2010 / 0216708 and 2010 / 0255056. However, improvements in binding molecules are still needed.

[0037] The amino acid residues that define each loop and each beta strand are shown in Table 1 for the FN3 scaffold described herein. The residues shown below for each domain / region can be determined for another sequence by aligning two sequences, one being the reference sequence of SEQ ID NO: 44 and the other being the query sequence. For example, Blastp (available from NBCI) can be used to align the two sequences using default settings.

[0038] [Table 1]

[0039] Variability in the FN3 domain to create libraries or alternative sequences can be in one or more of the following regions: C beta strand, CD loop, D beta strand, F beta strand, FG loop and G beta strand, which are referred to as "C-CD-DF-FG-G alternative surfaces."

[0040] This alternative surface can be diversified based on consensus sequences and mutated residues at specific positions to generate a library of polypeptides that can be used to bind target moieties, such as cell surface proteins or receptors or other target molecules. In some embodiments, the library comprises a polypeptide sequence similar to SEQ ID NO:44: [ka]

[0041] wherein each X is independently any amino acid. In some embodiments, each X is independently any amino acid except methionine or cysteine.

[0042] In some embodiments, the leading methionine of SEQ ID NO:44 can be removed. Thus, in some embodiments, the library comprises SEQ ID NO:74: LSPPSNLRVTDVTSTSVTLSWKPPAPITGYXVXYXEXXXXGEWKXVXVPGSETSYTVTGLKPGTEYXFXVXAVNGAXXGXPSQXVXVTT (SEQ ID NO: 74) wherein each X is independently any amino acid. In some embodiments, each X is independently any amino acid except methionine or cysteine.

[0043] The alternative surfaces that can be described herein in the FN3 domains are encoded by non-contiguous stretches of amino acids in each FN3 domain. For example, the C-CD-DF-FG-G surface is formed by amino acid residues 29-37, 38-43, 44-50, 65-74, 75-80, and 81-90 of SEQ ID NO: 44, e.g., as shown in Table 2. In some embodiments, the C-CD-DF-FG-G surface comprises amino acid residues 29-37, 38-43, 44-50, 65-74, 75-80, and 81-90 of SEQ ID NO: 44.

[0044] In some embodiments, a polypeptide is provided herein, wherein the polypeptide comprises the amino acid sequence of SEQ ID NO: 44, wherein each X in SEQ ID NO: 44 is independently any amino acid. In some embodiments, each X in SEQ ID NO: 44 is independently any amino acid except methionine or cysteine.

[0045] In some embodiments, a polypeptide is provided herein, wherein the polypeptide comprises the amino acid sequence of SEQ ID NO: 74, wherein each X in SEQ ID NO: 74 is independently any amino acid. In some embodiments, each X in SEQ ID NO: 74 is independently any amino acid except methionine or cysteine.

[0046] Protein scaffolds based on alternative surface randomization In some embodiments, an isolated protein scaffold is provided comprising an FN3 domain comprising an alternative surface, wherein the alternative surface has at least one amino acid substitution in a region of the C-CD-DF-FG-G alternative surface that forms the alternative surface.

[0047] In some embodiments, the library contains a protein or proteins that are at least or about 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to the amino acid sequence of SEQ ID NO:44.

[0048] In some embodiments, the FN3 domain comprises an amino acid sequence that is at least, or about, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to the amino acid sequence of SEQ ID NO:24.

[0049] In some embodiments, the FN3 domain comprises the amino acid sequence of SEQ ID NO:24. MLSPPSNLRVTDVTSTSVTLSWKPPAPITGYIVEYREKDGSGEWKEVTVPGSETSYTVTGLKPGTEYEFRVRAVNGAGEGPPSQSVTVTT (SEQ ID NO: 24)

[0050] In some embodiments, the FN3 domain comprises an amino acid sequence having one or more substitutions at positions 32, 34, 36, 38, 39, 40, 41, 46, 48, 68, 70, 72, 78, 79, 81, 85, and / or 87 of SEQ ID NO: 24. These positions correspond to domains, as shown in Table 2 below, that can be mutated to create a new FN3 polypeptide or library of polypeptides.

[0051] In some embodiments, the protein scaffold or library comprises a C-CD-DF-FG-G alternative surface formed by a C beta strand, a CD loop, a D beta strand, an F beta strand, an FG loop, and a G beta strand. In some embodiments, the protein scaffold or library comprises a C-CD-DF-FG-G alternative surface comprising a C beta strand, a CD loop, a D beta strand, an F beta strand, an FG loop, and a G beta strand. In some embodiments, the protein scaffold or library comprises a C-CD-DF-FG-G alternative surface comprising diversified C beta strands, CD loops, D beta strands, F beta strands, FG loops, and / or beta strands.

[0052] In some embodiments, the C beta strand, CD loop, D beta strand, F beta strand, FG loop, or G beta strand forming the C-CD-DF-FG-G alternative surface comprises certain amino acid sequences as shown in Table 2 and in SEQ ID NOs: 45-48.

[0053] [Table 2]

[0054] wherein each X is independently any amino acid. In some embodiments, each X is independently any amino acid except methionine or cysteine.

[0055] In some embodiments, the FN3 domain comprises a C beta chain having the amino acid sequence TGYXVXYXE (SEQ ID NO: 45) with substitutions at one, two, or three residues, where each X is independently any amino acid except methionine or cysteine.

[0056] In some embodiments, the FN3 domain comprises a CD loop having an amino acid sequence of XXXXGE (SEQ ID NO: 46) with substitutions at 1, 2, 3, or 4 residues, where each X is independently any amino acid except methionine or cysteine.

[0057] In some embodiments, the FN3 domain comprises a D beta chain having the amino acid sequence WKXVXVP (SEQ ID NO: 47) with substitutions at one or two residues, where each X is independently any amino acid except methionine or cysteine.

[0058] In some embodiments, the FN3 domain comprises an F beta chain having the amino acid sequence TEYXFXVXAV (SEQ ID NO: 48) with substitutions at one, two, or three residues, where each X is independently any amino acid except methionine or cysteine.

[0059] In some embodiments, the FN3 domain comprises an FG loop having the amino acid sequence NGAXXG (SEQ ID NO:49) with substitutions at one or two residues, where each X is independently any amino acid except methionine or cysteine.

[0060] In some embodiments, the FN3 domain comprises an F beta chain having the amino acid sequence XPSQXVXVTT (SEQ ID NO:50) with substitutions at one, two, or three residues, where each X is independently any amino acid except methionine or cysteine.

[0061] In some embodiments, a library comprises a plurality of polypeptides comprising the sequences of TGYXVXYXE (SEQ ID NO:45), XXXXGE (SEQ ID NO:46), WKXVXVP (SEQ ID NO:47), TEYXFXVXAV (SEQ ID NO:48), NGAXXG (SEQ ID NO:49), and XPSQXVXVTT (SEQ ID NO:50), where each X is independently any amino acid except methionine or cysteine.

[0062] In some embodiments, the library comprises a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:1.

[0063] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:2.

[0064] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:3.

[0065] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:4.

[0066] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:5.

[0067] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:6.

[0068] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:7.

[0069] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:8.

[0070] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:9.

[0071] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:10.

[0072] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:11.

[0073] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:12.

[0074] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:13.

[0075] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:14.

[0076] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:15.

[0077] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:16.

[0078] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:17.

[0079] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:18.

[0080] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:19.

[0081] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:20.

[0082] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:21.

[0083] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:22.

[0084] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:23.

[0085] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:24.

[0086] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:25.

[0087] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:26.

[0088] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:27.

[0089] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:28.

[0090] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:29.

[0091] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:30.

[0092] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:31.

[0093] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:32.

[0094] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:33.

[0095] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:34.

[0096] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:35.

[0097] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:36.

[0098] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:37.

[0099] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:38.

[0100] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:39.

[0101] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:40.

[0102] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:41.

[0103] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:42.

[0104] In some embodiments, the library contains a polypeptide or multiple polypeptides comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to the sequence of SEQ ID NO:43.

[0105] In some embodiments, polypeptide is provided herein.In some embodiments, polypeptide comprises at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical amino acid sequence or identical to the sequence selected from the group consisting of SEQ ID NO:1, 2, 3, 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, 40, 41, 42 and 43. In some embodiments, a pharmaceutical composition comprising the polypeptide is provided.

[0106] In some embodiments, the resulting FN3 domain based on the consensus or reference sequence provided herein can be further modified at residues present outside or within alternative surfaces such as those provided herein, for example, to improve stability, reduce immunogenicity, enhance binding affinity, on-rate, off-rate, half-life, solubility, or any other suitable property. In one way to achieve this goal, scaffold proteins can be optionally produced by a process of analysis of parent sequences and various conceptual engineered products using three-dimensional models of the parent and engineered sequences. Three-dimensional models are generally available and are familiar to those skilled in the art. Computer programs are available that can illustrate and display the likely three-dimensional conformation of selected candidate sequences and also measure possible immunogenicity (e.g., Immunofilter program, Xencor, Inc., Monrovia, Calif.). Examination of these displays allows analysis of the likely role of residues in the function of the candidate sequence, for example, residues that affect the stability of the scaffold protein or the ability of the candidate scaffold protein to bind its target molecule. In this manner, residues can be selected and combined from the parent and reference sequences to achieve desired properties, such as improved scaffold stability. Alternatively, or in addition to the above procedures, other suitable engineering methods can be used, as known in the art.

[0107] Desirable physical properties of FN3 domains include high thermostability and reversibility of thermal folding and unfolding. Several methods have been applied to increase the apparent thermostability of proteins and enzymes, including rational design based on comparison with highly similar thermostable sequences, design to stabilize disulfide bridges, mutations to increase alpha-helical propensity, engineering salt bridges, modifying the surface charge of the protein, directed evolution, and constructing consensus sequences (Lehmann and Wyss, Curr Opin Biotechnol, 12, pp. 371-375, 2001). High thermostability may increase the yield of expressed proteins, improve solubility or activity, reduce immunogenicity, and minimize the need for a cold chain in production.

[0108] Residues that can be substituted to improve any property of the FN3 domain can be determined by making the substitution and assaying for the desired property of the scaffold.

[0109] In terms of loss of stability, i.e., "denaturing" a protein or "denaturation" refers to a process in which some or all of the three-dimensional conformation that confers the functional properties of the protein is lost with a concomitant loss of activity and / or solubility. Forces that are disrupted during denaturation include intramolecular bonds, such as electrostatic forces, hydrophobic forces, van der Waals forces, hydrogen bonds, and disulfides. Protein denaturation is caused by forces applied to the protein or a solution containing the protein, such as mechanical forces (e.g., compression or shear forces), thermal stress, osmotic stress, changes in pH, electric or magnetic fields, ionizing radiation, ultraviolet radiation, and dehydration, as well as by chemical denaturants.

[0110] Measurements of protein stability and protein instability can be considered as the same or different aspects of protein integrity. Proteins are sensitive or "unstable" to denaturation caused by heat, ultraviolet or ionizing radiation, changes in ambient osmolality and pH when in liquid solution, mechanical shear forces imposed by small pore filtration, ultraviolet irradiation, ionizing radiation such as by gamma irradiation, chemical or thermal dehydration, or any other action or force that can cause protein structure collapse. Molecular stability can be determined using standard methods. For example, molecular stability can be determined using standard methods by measuring the thermal melting ("TM") temperature, which is the temperature in degrees Celsius (°C) at which one-half of the molecule becomes unfolded. Typically, the higher the TM, the more stable the molecule. In addition to heat, the chemical environment also changes the ability of a protein to maintain a particular three-dimensional structure.

[0111] In some embodiments, the FN3 domain exhibits increased stability of at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95% or more compared to the same domain before engineering as measured by increased TM.

[0112] Similarly, chemical denaturation can be measured by a variety of methods. Chemical denaturants include guanidine hydrochloride, guanidine thiocyanate, urea, acetone, organic solvents (DMF, benzene, acetonitrile), salts (ammonium sulfate, lithium bromide, lithium chloride, sodium bromide, calcium chloride, sodium chloride); reducing agents (e.g., hydrides such as dithiothreitol, beta-mercaptoethanol, dinitrothiobenzene, and sodium borohydride), non-ionic and ionic detergents, acids (e.g., hydrochloric acid (HCl), acetic acid (CH3COOH), acetic acid halides), hydrophobic molecules (e.g., phospholipids), and target denaturants. Quantification of the extent of denaturation can depend on the loss of functional properties, such as the ability to bind target molecules, or on physicochemical properties, such as the tendency to aggregate, exposure of residues previously inaccessible to the solvent, or the disruption or formation of disulfide bonds.

[0113] In some embodiments, the polypeptides exhibit at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95% or more increased stability compared to the same scaffold prior to engineering as measured by using guanidine hydrochloride as a chemical denaturant. Increased stability can be measured as a function of the decrease in tryptophan fluorescence upon treatment with increasing concentrations of guanidine hydrochloride using well known methods.

[0114] The FN3 domain described herein can be produced as a monomer, dimer, or multimer, for example, as a means of increasing the valency and thus the avidity of target molecule binding, or to produce a bispecific or multispecific scaffold that simultaneously binds two or more different target molecules.Dimers and multimers can be produced by linking monospecific, bispecific, or multispecific protein scaffolds, for example, by including an amino acid linker, such as a linker that contains polyglycine, glycine and serine, or alanine and proline. The use of naturally occurring as well as artificial peptide linkers to join polypeptides into novel linked fusion polypeptides is well known in the literature (Hallewell et al., J Biol Chem 264, 5260-5268, 1989; Alfthan et al., Protein Eng. 8, 725-731, 995; Robinson & Sauer, Biochemistry 35, 109-116, 1996; U.S. Patent No. 5,856,456).

[0115] The FN3 domain is used as a bispecific molecule, where a first alternative surface in the domain has specificity for a first target molecule and a second alternative surface in the same domain has specificity for a second target molecule.

[0116] The FN3 domain may incorporate other subunits, for example, via covalent interactions. All or part of an antibody constant region may be attached to the FN3 domain to confer antibody-like properties, particularly properties associated with the Fe region, such as complement activity, half-life, etc. For example, Fe effector functions such as Clq binding, complement-dependent cytotoxicity (CDC), Fe receptor binding, antibody-dependent cell-mediated cytotoxicity (ADCC), phagocytosis, downregulation of cell surface receptors (e.g., B cell receptor; BCR), etc., can be provided and / or controlled by modifying residues in Fe involved in these activities (for review; see Strohl, Curr Opin Biotechnol. 20, 685-691, 2009).

[0117] Additional moieties such as toxin conjugates, albumin or albumin binders, polyethylene glycol (PEG) molecules such as PEG5000 or PEG20,000, fatty acids and fatty acid esters of different chain lengths, such as laurate, myristic acid, stearate, arachidic acid, behenic acid, oleic acid, arachidonic acid, octanedioic acid, tetradecanediic acid, octadecanedioic acid, docosanedioic acid, etc., polylysine, octane, carbohydrates (dextran, cellulose, oligosaccharides or polysaccharides) are incorporated into or conjugated to the FN3 domain for desired properties. These moieties may be direct fusions with protein coding sequences, or produced by standard cloning and expression techniques. Alternatively, well-known chemical coupling methods may be used to combine moieties for recombinantly producing the FN3 domains described herein. In some embodiments, FN3 is conjugated to nucleic acid molecules such as antisense molecules, siRNAs, PMOs, etc.

[0118] The FN3 domains incorporating additional moieties are compared for functionality by several well-known assays.For example, the altered FN3 domain properties resulting from the incorporation of Fc domains and / or Fc domain variants are assayed in Fc receptor binding assays using soluble forms of receptors such as FcyRI, FcyRII, FcyRIII or FcRn receptors, or using well-known cell-based assays such as measuring ADCC or CDC, or evaluating the pharmacokinetic properties of protein scaffolds in in vivo models.

[0119] Generation and production of FN3 domain proteins In some embodiments, a method is provided for making a library of FN3 domains that comprise alternative surfaces, wherein the alternative surfaces have at least one amino acid substitution when compared with reference FN3 domains as provided herein.In some embodiments, the method includes: providing a polynucleotide that codes for a reference FN3 domain; randomizing the alternative surfaces to generate a library of the polynucleotide sequences of the reference FN3 domain; translating the library in vitro or expressing the library in a host.

[0120] In some embodiments, a method is provided for generating a library of FN3 polypeptides having a diversified C-CD-DF-FG-G alternative surface formed by a C beta strand, a CD loop, a D beta strand, an F beta strand, an FG loop, or a G beta strand, the method comprising: providing a reference FN3 domain polypeptide having an amino acid sequence at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to the amino acid sequence of SEQ ID NO: 44; and introducing diversity into the consensus FN3 domain polypeptide by mutating at least one residue in the C beta strand, the CD loop, the D beta strand, the F beta strand, the FG loop, or the G beta strand to form an FN3 domain library having a diversified C-CD-DF-FG-G alternative surface.

[0121] In some embodiments, a method is provided for generating a library of FN3 polypeptides having diversified C-CD-DF-FG-G alternative surfaces comprising diversified C beta strands, CD loops, D beta strands, F beta strands, FG loops, or G beta strands, the method comprising: providing a reference FN3 domain polypeptide having an amino acid sequence at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to the amino acid sequence of SEQ ID NO: 44; and introducing diversity into the consensus FN3 domain polypeptide by mutating at least one residue in the C beta strand, CD loop, D beta strand, F beta strand, FG loop, or G beta strand to form an FN3 domain library having diversified C-CD-DF-FG-G alternative surfaces.

[0122] In the method of making the library described herein, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, or 17 residues in any one of the C beta chain, the CD loop, the D beta chain, the F beta chain, the FG loop, or the G beta chain of SEQ ID NO: 44 can be mutated or modified. In some embodiments, the mutation is a substitution, insertion, or deletion.

[0123] In some embodiments, libraries are provided that are produced by the methods provided herein. The generation of scaffold proteins, FN3 domains (polypeptides or modules) is accomplished, for example, at the nucleic acid level. Libraries of FN3 domains with substitution codons at one or more specific residues can be synthesized, for example, using standard PCR cloning methods, or chemical gene synthesis according to the methods described in U.S. Pat. Nos. 6,521,427 and 6,670,127. Codons can be randomized using well-known methods, for example, using degenerate oligonucleotides that match the designed diversity, or using Kunkel mutagenesis (Kunkel et al., Methods Enzymol. 154, 367-382, 1987).

[0124] The library can be randomized at the selected codon using a random or defined set of amino acids. For example, variants in the library with random substitutions can be generated using the NNK codon, which codes for all 20 naturally occurring amino acids. In another diversification scheme, the DVK codon can be used to code for the amino acids Ala, Trp, Tyr, Lys, Thr, Asn, Lys, Ser, Arg, Asp, Glu, Gly, and Cys. Alternatively, the NNS codon can be used to generate all 20 amino acid residues, while simultaneously reducing the frequency of stop codons. The codon designation follows the well-known IUB code. In some embodiments, diversification is performed without methionine and / or cysteine ​​as options at the mutated residue.

[0125] FN3 domains, as any other protein, are prone to various physical and / or chemical instabilities, which negatively impact downstream processing. For example, physical and chemical instabilities can lead to aggregation, degradation, reduced product yield, loss of potency, increased immunogenicity potential, molecular heterogeneity, and loss of activity. Thus, the presence of possible instability-inducing residues and recognition sequences is minimized during library design. For example, surface-exposed methionine and tryptophan can be oxidized under storage conditions, potentially causing loss of potency of the protein scaffold. The presence of asparagine, in addition to contributing to the well-known N-glycosylation recognition site (NXS / T), can also be deamidated if followed by glycine, potentially resulting in heterogeneity (Robinson, Proc Natl Acad Sci US A, 99, pp. 5283-5288, 2002). Thus, some or all of these amino acids are omitted or not omitted from the mixture used to randomize the selected positions. Additionally, cysteines and prolines are omitted to minimize disulfide bridge formation and disruption of beta sheets.

[0126] Libraries of FN3 domains with biased amino acid distribution at the positions to be diversified can be synthesized, for example, using Slonomics® technology (http: / / www_sloning_com). This technology uses a library of pre-made double-stranded triplets that serve as generic building blocks sufficient for thousands of gene synthesis processes. The triplet library represents all possible sequence combinations required to construct any desired DNA molecule.

[0127] The synthesis of oligonucleotides with selected nucleotide "degeneracy" at a particular position is well known in the art, for example, the TRIM approach (Knappek et al., J Mal Biol 296, 57-86, 1999; Garrard & Renner, Gene 128, 103-109, 1993). Such a set of nucleotides with a particular codon set can be synthesized using commercially available nucleotide or nucleoside reagents and equipment.

[0128] Use standard cloning and expression techniques to clone the library into vectors, or to synthesize double-stranded cDNA cassettes of the library, or to express or translate the library in vitro.For example, use cis display to ligate the DNA fragments encoding scaffold proteins to the DNA fragments encoding RepA to generate a pool of protein-DNA complexes formed after in vitro translation, where each protein is stably linked to the DNA that encodes it (US Pat. No. 7,842,476; Odegrip et al., Proc Natl Acad Sci USA 101, 2806-2810, 2004). Other methods can be used, such as ribosome display (Hanes and Pluckthun, Proc Natl Acad Sci USA, 94, 4937-4942, 1997), mRNA display (Roberts and Szostak, Proc Natl Acad Sci USA, 94, 12297-12302, 1997), or other cell-free systems (US Pat. No. 5,643,768). The library of protein scaffolds is expressed, for example, as a fusion protein displayed on the surface of any suitable bacteriophage. Methods for displaying fusion polypeptides on the surface of bacteriophage are well known (U.S. Patent Application Publication No. 2011 / 0118144; WO 2009 / 085462; U.S. Patent No. 6,969,108; U.S. Patent No. 6,172,197; U.S. Patent No. 5,223,409; U.S. Patent No. 6,582,915; U.S. Patent No. 6,472,147).

[0129] screening Screening a library of engineered protein FN3 domains or FN3 domain variants for specific binding to a target molecule can be accomplished, for example, by producing a library using cis-display as described in the Examples and Odegrip et al., Proc Natl Acad Sci US 101, 2806-2810, 2004, and assaying the library for specific binding to the target molecule by any method known in the art. Exemplary well-known methods that can be used are ELISA, sandwich immunoassays, and competitive and noncompetitive assays (see, for example, Ausubel et al., 1994, Current Protocols in Molecular Biology, Vol. 1, John Wiley & Sons, Inc., New York). FN3 domains can bind human or other mammalian proteins with a wide range of affinities (KD). Typically, FN3 domains bind human or other mammalian proteins with a KD of about 10 as determined by surface plasmon resonance or Kinexa methods as performed by those skilled in the art. -7 M, 10 -8 M, 10 -9 M, 10 -10 M, 10 -11 M, 10 -12 M, 10 -13 M, 10 -14 M or 10 -15The FN3 domain can bind to the target protein with a KD equal to or less than M. The affinity of the FN3 domain for the antigen can be experimentally determined using any suitable method. (See, for example, Berzofsky et al., "Antibody-Antigen Interactions," In Fundamental Immunology, Paul, WE, Raven Press: New York, NY (1984); Kuby, Janis Immunology, WH Freeman and Company: New York, NY (1992); and the methods described herein). The measured affinity of a particular FN3 domain-antigen interaction may vary when measured under various conditions (e.g., osmolarity, pH). Therefore, the measurement of affinity and other antigen binding parameters (e.g., KD, Kon, Koff) is preferably performed using standardized solutions of protein scaffold and antigen, and standardized buffers such as those described herein. Other screening methods are also described in U.S. Patent No. 7,842,476 and U.S. Patent No. 8,679,781, each of which is incorporated herein by reference in its entirety.

[0130] Nucleic Acid Molecules and Vectors The present disclosure provides nucleic acids encoding FN3 as isolated polynucleotides or as part of an expression vector or as part of a linear DNA sequence used for in vitro transcription / translation, prokaryotic, eukaryotic or filamentous phage expression, secretion and / or display of the composition or directed mutagen. Although certain exemplary polynucleotides are disclosed herein, other polynucleotides that encode the protein scaffolds and libraries of protein scaffolds disclosed herein are also within the scope, taking into account the degeneracy of the genetic code or codon choice in a given expression system.

[0131] The polynucleotides disclosed herein can be produced by chemical synthesis, such as solid-phase polynucleotide synthesis on an automated polynucleotide synthesizer, and assembled into complete single-stranded or double-stranded molecules.Alternatively, the polynucleotides disclosed herein can be produced by other techniques, such as PCR, followed by routine cloning.Techniques for producing or obtaining polynucleotides of a given known sequence are well known in the art.

[0132] The polynucleotides disclosed herein may include at least one non-coding sequence, such as a promoter or enhancer sequence, an intron, a polyadenylation signal, a cis sequence that promotes RepA binding. The polynucleotide sequence may also include additional sequences that code for additional amino acids, such as a marker or tag sequence, such as a histidine tag or an HA tag, for example, to facilitate protein purification or detection, a signal sequence, a fusion protein partner, such as RepA, a bacteriophage coat protein, such as Fe or pIX or pIII. An exemplary polynucleotide includes sequences for the Tac promoter, sequences that code for the FN3 domain library and repA, cis elements, and a bacterial origin of replication (ori). Another exemplary polynucleotide includes a pelB or ompA signal sequence, a pIII or pIX bacteriophage coat protein, an FN3 domain, and a polyA site.

[0133] Another embodiment is a vector comprising at least one polynucleotide disclosed herein. Such vectors may be plasmid vectors, viral vectors, vectors for baculovirus expression, transposon-based vectors or any other vectors suitable for introducing polynucleotides into a given organism or genetic background by any means. Such vectors may be expression vectors that contain nucleic acid sequence elements that can control, regulate, cause or enable the expression of the polypeptide encoded by such vector. Such elements may include transcription enhancer binding sites, RNA polymerase initiation sites, ribosome binding sites and other sites that facilitate the expression of the encoded polypeptide in a given expression system. Such expression systems may be cell-based or cell-free systems well known in the art.

[0134] Host Cell Selection or Engineering The FN3 domains disclosed herein are optionally produced by cell lines, mixed cell lines, immortalized cells or clonal populations of immortalized cells, as is well known in the art.See, for example, Ausubel et al., Current Protocols in Molecular Biology, John Wiley & Sons, Inc., NY, NY (1987-2001); Sambrook et al., Molecular Cloning: A Laboratory Manual, 2nd ed., Cold Spring Harbor, NY (1989); Harlow and Lane, Antibodies, A Laboratory Manual, Cold Spring Harbor, NY (1989); Colligan et al., Current Protocols in Immunology, John Wiley & Sons, Inc., NY (1994-2001); Colligan et al., Current Protocols in Protein Science, John Wiley & Sons, NY, NY, (1997-2001).

[0135] The host cell selected for expression may be of mammalian origin or is selected from COS-1, COS-7, HEK293, BHK21, CHO, BSC-1, Hep G2, 653, SP2 / 0, 293, HeLa, myeloma, lymphoma, yeast, insect or plant cells, or any derivative, immortalized or transformed cell thereof. Alternatively, the host cell is selected from a species or organism that is unable to glycosylate polypeptides, such as BL21, BL21(DE3), BL21-GOLD(DE3), XL1-Blue, JM109, HMS1 74, HMS1 74(DE3), and any of the naturally occurring or engineered strains of E. coli spp., Klebsiella spp., or Pseudomonas spp.

[0136] Use of FN3 domain The compositions of FN3 domain (module) based molecules described herein and generated by any of the above methods are used to diagnose, monitor, regulate, treat, alleviate, help prevent the occurrence of, or reduce the symptoms of human diseases or specific pathologies in cells, tissues, organs, fluids, or generally in a host. Purpose-specific engineered FN3 domains are used to treat immune-mediated or immune deficiency diseases, metabolic diseases, cardiovascular disorders or diseases; malignant diseases; neurological disorders or diseases; infections such as bacterial, viral or parasitic infections; or other known or specific related conditions, including swelling, pain, and tissue necrosis or fibrosis.

[0137] Such methods can include administering an effective amount of a composition or pharmaceutical composition comprising at least one FN3 domain that specifically binds a target molecule to a cell, tissue, organ, animal, or patient in need of such modulation, treatment, amelioration, prevention, or reduction in symptoms, effects, or mechanisms. An effective amount can include an amount of about 0.001-500 mg / kg per single (e.g., bolus), multiple, or continuous administration, or can achieve a serum concentration of 0.01-5000 μg / ml per single, multiple, or continuous administration, or any effective range or value therein, as performed and determined using known methods, as described herein or known in the relevant art.

[0138] The FN3 polypeptide can be linked to another therapeutic agent to facilitate delivery of the therapeutic agent. Thus, the FN3 polypeptide can be used to deliver a therapeutic agent to a cell expressing a target to which the FN3 polypeptide binds, such as CD71.

[0139] Pharmaceutical Compositions Comprising FN3 Domain-Based Proteins The FN3 domain that specifically binds the target molecule, whether modified or unmodified, is a monomer, dimer, or multimer, or is single, double, or multispecific, can be isolated and purified to the extent required for commercial use by using separation procedures well known in the art for capture, immobilization, division, or precipitation.Also, they are conjugated with nucleic acid molecule or other therapeutic agent.In some embodiments, the nucleic acid molecule is siRNA or antisense molecule.

[0140] For therapeutic use, the FN3 domain that specifically binds a target molecule is prepared as a pharmaceutical composition containing an effective amount of the FN3 domain as an active ingredient in a pharma- ceutically acceptable carrier. The term "carrier" refers to a diluent, adjuvant, excipient, or vehicle with which the active compound is administered. Such vehicles may be liquids such as water and oils, including those of petroleum, animal, vegetable, or synthetic origin, such as peanut oil, soybean oil, mineral oil, sesame oil, and the like. For example, 0.4% saline and 0.3% glycine can be used. These solutions are sterile and generally free of particulate matter. They are sterilized by conventional, well-known sterilization techniques (e.g., filtration). The compositions may contain pharma-ceutically acceptable auxiliary substances as necessary to approximate physiological conditions, such as pH adjusting and buffering agents, stabilizers, thickeners, lubricants, and coloring agents. The concentration of the drug in such pharmaceutical formulations can vary over a wide range, i.e., from less than about 0.5%, usually at or at least about 1% by weight, up to as much as 15 or 20% by weight, and is selected primarily based on the required dose, liquid volume, viscosity, etc., according to the particular mode of administration selected. Suitable vehicles and formulations, including other human proteins, e.g., human serum albumin, are described, for example, in Remington: The Science and Practice of Pharmacy, 21st Edition, Troy, DB, Lipincott Williams and Wilkins, Philadelphia, PA 2006, Part 5, Pharmaceutical Manufacturing, pp. 691-1092. See especially pp. 958-989.

[0141] Modes of administration for therapeutic use of FN3 domains that specifically bind target molecules may be any suitable route of delivery of an agent to a host, such as parenteral, e.g., intradermal, intramuscular, intraperitoneal, intravenous or subcutaneous, pulmonary; transmucosal (oral, intranasal, intravaginal, rectal); using formulations in tablets, capsules, solutions, powders, gels, particles; and contained in syringes, implantable devices, osmotic pumps, cartridges, micropumps; or other means recognized by those of skill in the art as are well known in the art. Site-specific administration is achieved, for example, by intra-articular, intrabronchial, intraperitoneal, intracapsular, intrachondral, intracavity, intrathecal, intracerebellar, intraventricular, intracolonic, intracervical, intragastric, intrahepatic, intracardiac, intraosseous, intrapelvic, intrapericardial, intraperitoneal, intrapleural, intraprostatic, intrapulmonary, intrarectal, intrarenal, intraretinal, intraspinal, intrasynovial, intrathoracic, intrauterine, intravascular, intravesical, intralesional, vaginal, rectal, buccal, sublingual, intranasal, or transdermal delivery.

[0142] Enumeration of embodiments Embodiments described herein also include, but are not limited to, the following:

[0143] Having described the embodiments in general terms, certain specific embodiments are further disclosed in the following examples, which should not be construed as limiting the scope of the claims.

[0144] 1. A library comprising a plurality of fibronectin type III module (FN3) domains (polypeptides) having a diversified C-CD-DF-FG-G alternative surface, including a diversified C beta strand, a CD loop, a D beta strand, an F beta strand, an FG loop and a G beta strand, the polypeptides comprising: MLSPPSNLRVTDVTSTSVTLSWKPPAPITGYXVXYXEXXXXGEWKXVXVPGSETSYTVTGLKPGTEYXFXVXAVNGAXXGXPSQXVXVTT (SEQ ID NO: 44) or an amino acid sequence at least 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identical to the amino acid sequence of SEQ ID NO:44, and each X is independently any amino acid.

[0145] 2. The library of embodiment 1, wherein each X is independently any amino acid except methionine or cysteine.

[0146] 3. The library of embodiment 1 or 2, wherein the polypeptide comprises at least one mutated amino acid residue in one or more of the C beta strand, the CD loop, the D beta strand, the F beta strand, the FG loop, or the G beta strand, or each thereof, when compared to SEQ ID NO: 24, to form an FN3 domain library having a diversified C-CD-DF-FG-G alternative surface.

[0147] 4. The library of any one of embodiments 1-3, wherein the plurality of polypeptides has one or more mutations (e.g., substitutions, insertions, or deletions) at positions corresponding to positions 32, 34, 36, 38, 39, 40, 41, 46, 48, 68, 70, 72, 78, 79, 81, 85, and / or 87 of SEQ ID NO:24.

[0148] 5. The library of any one of embodiments 1-4, wherein the diversified C beta chain has an amino acid sequence of TGYXVXYXE (SEQ ID NO: 45), where each X is independently any amino acid except methionine or cysteine.

[0149] 6. The library of any one of embodiments 1-5, wherein the diversified CD loop has an amino acid sequence of XXXXGE (SEQ ID NO: 46), where each X is independently any amino acid except methionine or cysteine.

[0150] 7. The library of any one of embodiments 1-6, wherein the diversified D beta chain has an amino acid sequence of WKXVXVP (SEQ ID NO: 47), where each X is independently any amino acid except methionine or cysteine.

[0151] 8. The library of any one of embodiments 1-7, wherein the diversified F beta chain has an amino acid sequence of TEYXFXVXAV (SEQ ID NO: 48), where each X is independently any amino acid except methionine or cysteine.

[0152] 9. The library of any one of embodiments 1-8, wherein the diversified FG loop has an amino acid sequence of NGAXXG (SEQ ID NO: 49), where each X is independently any amino acid except methionine or cysteine.

[0153] 10. The library of any one of embodiments 1-9, wherein the diversified G beta chain has the amino acid sequence XPSQXVXVTT (SEQ ID NO: 50), where each X is independently any amino acid except methionine or cysteine.

[0154] 11. The library of any one of embodiments 1-10, comprising an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to a sequence selected from the group consisting of SEQ ID NOs: 1, 2, 3, 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, 40, 41, 42, and 43.

[0155] 12. The diversified C beta chain has an amino acid sequence of TGYXVXYXE (SEQ ID NO:45), where each X is independently any amino acid except methionine or cysteine; the diversified CD loop has an amino acid sequence of XXXXGE (SEQ ID NO:46), where each X is independently any amino acid except methionine or cysteine; The diversified D beta chain has an amino acid sequence of WKXVXVP (SEQ ID NO:47), where each X is independently any amino acid except methionine or cysteine; The diversified F beta chain has an amino acid sequence of TEYXFXVXAV (SEQ ID NO: 48), where each X is independently any amino acid except methionine or cysteine; The diversified FG loop has an amino acid sequence of NGAXXG (SEQ ID NO:49), where each X is independently any amino acid except methionine or cysteine; The diversified G beta chain has the amino acid sequence XPSQXVXVTT (SEQ ID NO: 50), where each X is independently any amino acid except methionine or cysteine. The library of any one of embodiments 1 to 11.

[0156] 13. A method of producing a library according to any one of embodiments 1 to 12, comprising expressing a polynucleotide encoding a plurality of polypeptides.

[0157] 14. A method for generating a library of fibronectin modules of type III (FN3) domains with diversified C-CD-F-FG-G alternative surfaces comprising diversified one or more of, or each of, the C beta strand, the CD loop, the F beta strand, the FG loop and the G beta strand, comprising: providing a reference FN3 domain polypeptide having an amino acid sequence at least 80% identical to the amino acid sequence of SEQ ID NO:1, 2, 3, 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, 40, 41, 42, 43, or 44; b. Introducing diversity into a reference FN3 domain polypeptide by mutating at least one residue in the C beta strand, the CD loop region, the F beta strand region, the FG loop region, or the G beta strand region to form an FN3 domain library having a diversified C-CD-F-FG-G alternative surface. and where: The diversified C beta chain has an amino acid sequence of TGYXVXYXE (SEQ ID NO: 45), where each X is independently any amino acid except methionine or cysteine; the diversified CD loop has an amino acid sequence of XXXXGE (SEQ ID NO:46), where each X is independently any amino acid except methionine or cysteine; The diversified D beta chain has an amino acid sequence of WKXVXVP (SEQ ID NO:47), where each X is independently any amino acid except methionine or cysteine; The diversified F beta chain has an amino acid sequence of TEYXFXVXAV (SEQ ID NO: 48), where each X is independently any amino acid except methionine or cysteine; The diversified FG loop has an amino acid sequence of NGAXXG (SEQ ID NO:49), where each X is independently any amino acid except methionine or cysteine; The diversified G beta chain has the amino acid sequence XPSQXVXVTT (SEQ ID NO:50), where each X is independently any amino acid except methionine or cysteine. method.

[0158] 15. A library produced by the method of embodiment 13 or 14.

[0159] 16. A method for obtaining a polypeptide comprising a fibronectin type III module (FN3) domain having a diversified C-CD-DF-FG-G alternative surface that binds or specifically binds to a target molecule, comprising contacting a library according to any one of embodiments 1 to 12 with the target molecule and isolating a polypeptide that binds or specifically binds to the target molecule.

[0160] 17. A polypeptide having an amino acid sequence that is at least or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to or identical to a sequence selected from the group consisting of SEQ ID NOs: 1, 2, 3, 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, 40, 41, 42, and 43.

[0161] 18. Below: MLSPPSNLRVTDVTSTSVTLSWKPPAPITGYXVXYXEXXXXGEWKXVXVPGSETSYTVTGLKPGTEYXFXVXAVNGAXXGXPSQXVXVTT (SEQ ID NO: 44) wherein each X is independently any amino acid.

[0162] 19. The polypeptide of embodiment 18, wherein each X is independently any amino acid except methionine or cysteine.

[0163] 20. Below: LSPPSNLRVTDVTSTSVTLSWKPPAPITGYXVXYXEXXXXGEWKXVXVPGSETSYTVTGLKPGTEYXFXVXAVNGAXXGXPSQXVXVTT (SEQ ID NO: 74) wherein each X is independently any amino acid.

[0164] 21. The polypeptide of embodiment 20, wherein each X is independently any amino acid except methionine or cysteine.

[0165] 22. A pharmaceutical composition comprising a polypeptide according to any one of embodiments 17 to 21.

[0166] 23. A nucleic acid molecule encoding the polypeptide of embodiment 22.

[0167] 24. A plurality of nucleic acid molecules encoding a library of polypeptides of any one of embodiments 1-12.

[0168] 25. A host cell comprising the nucleic acid molecule of embodiment 24. EXAMPLES

[0169] Design of the human consensus sequence (HumCon) for the Fn3 domain The Prosite sequence database alignment of fibronectin type III domains (http: / / prosite.expasy.org / PDOC50853) was used as the starting point for generating consensus sequences. This alignment was edited to remove all sequences of non-human origin, and the resulting alignment contained 806 human sequences. The prominent residues at each of the 94 positions were used to determine candidate consensus sequences. At two positions (47 and 89), two residues were equally prominent. These were N and T at position 47 and S and V at position 89. At every other position, a single residue predominated. Due to the ambiguity at positions 47 and 89, four consensus sequences were generated (Table 3).

[0170] [Table 3]

[0171] Loop Design: Loop regions can be highly variable in both length and sequence. 806 sequences were aligned to form a consensus, and while most sequences contained residues at each of the 94 positions, some positions contained less sequence, usually due to deletions occurring in the loops. Some loops were therefore shortened to yield more stable sequences. Putative BC and CD loops were identified as regions of length variability. To test the hypothesis that these loops could be shortened, a series of deletions in these regions were designed using SEQ ID NO:2 as a scaffold sequence. The results are SEQ ID NOs:5-13, listed below in Table 4.

[0172] [Table 4]

[0173] Gene synthesis, expression and characterization Genes for 13 sequences in Tables 3 and 4 were designed with a C-terminal His tag and cloned into an expression vector under the control of a T5 promoter. Expression yields as mg / L of culture were assessed in shake flasks and melting temperatures were assessed by differential scanning calorimetry (Table 5). SDS PAGE assays were established and MW standards were used to confirm homogeneity of monomers. Several clones showed behavior consistent with dimer formation hypothesized to result from chain swapping that could be demonstrated by SDS PAGE and size exclusion chromatography.

[0174] [Table 5]

[0175] Further optimization (N-terminus, proline, pI) SEQ ID NO:2 was selected as a lead candidate to engineer for improved biophysical properties. A series of mutations were designed to 1) remove prolines from segments predicted to have beta-sheet structure based on homology modeling to other FN3 domain structures, with the goal of minimizing strand swapping; or 2) increase predicted pI values, allowing for simplified manufacturing and formulation properties. The sequences for these variants are listed in Table 6. Each of the proteins was expressed in Escherichia coli (E. coli), purified via a C-terminal His tag, and evaluated for solubility (soluble protein expression / L (E. coli)), stability (Tm by differential scanning calorimetry) and monomer homogeneity (SDS-PAGE) in comparison to the parental clone (SEQ ID NO:2) (Table 7).

[0176] [Table 6]

[0177] [Table 7]

[0178] Library design - alanine scanning To verify the feasibility of the library design strategy, 19 mutant proteins were designed, where each variant protein encoded one alanine residue at a unique position that was intended to be part of the designed binding interface. The alanine scanning mutant sequences are listed in Table 8. Each protein was expressed in E. coli, purified via a C-terminal His tag, and characterized to ensure that the biophysical properties matched those of the parent clone (SEQ ID NO: 24). Protein variants were evaluated for solubility (soluble protein expression / L), stability (Tm by differential scanning calorimetry), and monomer homogeneity (SDS-PAGE) (Table 9).

[0179] [Table 8]

[0180] [Table 9]

[0181] Library validation by screening for specific binding to CD71 A library of HumCon variants was constructed using standard molecular biology methods, in which 17 of the positions identified by alanine mutation experiments were mutated to 18 possible amino acids (all amino acids except methionine and cysteine). This library was cloned into a CIS display vector and panned for binding to CD71 using the methods described herein. Specific binders were determined by ELISA. Library members that successfully bound to the CD71 target are listed in Table 10.

[0182] [Table 10-1] [Table 10-2]

[0183] The present examples and embodiments provided herein demonstrate that the library can be used to generate the FN3 domains provided herein and produce molecules that can bind to target proteins of interest.These results were not predictable, and therefore the library of molecules, compositions comprising the library of molecules, and methods of using the library of molecules are provided herein in an unpredictable manner.It is clear that the present embodiment can be carried out other than as specifically described in the preceding description and examples.Many modifications and variations of the present embodiment are possible in light of the above teachings, and therefore are within the scope of the appended claims.

Claims

**Claim 1** A library comprising a plurality of polypeptides comprising a fibronectin type III (FN3) domain having a diversified C-CD-D-F-FG-G alternative surface comprising a diversified C-beta strand, CD loop, D-beta strand, F-beta strand, FG loop, and G-beta strand, wherein the plurality of polypeptides are as follows: MLSPPSNLRTVDVTSSTSVTLSWKPPAPITGYXVXYXEXXXXGEWKXVXVPGSET SYTVTGLKPGTEYXFFXVAVNGAXXGXPSEQXVXVTT (SEQ ID NO: 44) comprises an amino acid sequence having at least 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity to the amino acid sequence of SEQ ID NO: 44, wherein each X is independently any amino acid, optionally, each X is independently any amino acid other than methionine or cysteine, the library. **Claim 2** The plurality of polypeptides form an FN3 domain library having a diversified C-CD-D-F-FG-G alternative surface, and one or more of the C-beta strand, CD loop, D-beta strand, F-beta strand, FG loop, or G-beta strand, or each thereof, comprises at least one mutant amino acid residue when compared to SEQ ID NO:

24. The library according to claim 1. **Claim 3** The plurality of polypeptides have one or more mutations at positions corresponding to positions 32, 34, 36, 38, 39, 40, 41, 46, 48, 68, 70, 72, 78, 79, 81, 85, and / or 87 of SEQ ID NO:

24. The library according to claim 1 or 2. **Claim 4** At least, or about, 80% identity to an amino acid sequence selected from the group consisting of SEQ ID NOs: 1, 2, 3, 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, 40, 41, 42, and 43 The library according to any one of claims 1 to 3, comprising one or more polypeptides having an amino acid sequence that is the same as, or identical to, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%.

5. The diversified C-beta strand has the amino acid sequence of TGYXVXYYXE (SEQ ID NO: 45), where X is each independently any amino acid other than methionine or cysteine; The diversified CD loop has the amino acid sequence of XXXGE (SEQ ID NO: 46), where X is each independently any amino acid other than methionine or cysteine; The diversified D-beta strand has the amino acid sequence of WKXVXV P (SEQ ID NO: 47), where X is each independently any amino acid other than methionine or cysteine; The diversified F-beta strand has the amino acid sequence of TEYXFXV XAV (SEQ ID NO: 48), where X is each independently any amino acid other than methionine or cysteine; The diversified FG loop has the amino acid sequence of NGAXXG (SEQ ID NO: 49), where X is each independently any amino acid other than methionine or cysteine; The diversified G-beta strand has the amino acid sequence XPSQX VXVTT (SEQ ID NO: 50), where X is each independently any amino acid other than methionine or cysteine, The library according to any one of claims 1 to 3.

6. A method for producing the library according to any one of claims 1 to 5, the method comprising expressing a polynucleotide encoding a plurality of polypeptides.

7. A method for generating a library of fibronectin type III (FN3) domains having a diversified C-C D-F-FG-G replacement surface comprising one or more, or each, of the diversified C-beta strand, CD loop, F-beta strand, FG loop, and G-beta strand, a. supplying a reference FN3 domain polypeptide having an amino acid sequence that is at least 80% identical to the amino acid sequence of SEQ ID NO: 1, 2, 3, 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, 40, 41, 42, 43 or 44; b. introducing diversity into the reference FN3 domain polypeptide by mutating at least one residue in the C beta strand, CD loop region, F beta strand region, FG loop region, or G beta strand region to form an FN3 domain library having a diversified C - CD - F - FG - G substitution surface; comprising: the diversified C beta strand has the amino acid sequence of TGYXVXYYXE (SEQ ID NO: 45), wherein X is independently any amino acid other than methionine or cysteine; the diversified CD loop has the amino acid sequence of XXXXGE (SEQ ID NO: 46), wherein X is independently any amino acid other than methionine or cysteine; the diversified D beta strand has the amino acid sequence of WKXVXV P (SEQ ID NO: 47), wherein X is independently any amino acid other than methionine or cysteine; the diversified F beta strand has the amino acid sequence of TEYXFXV XAV (SEQ ID NO: 48), wherein X is independently any amino acid other than methionine or cysteine; the diversified FG loop has the amino acid sequence of NGAXXG (SEQ ID NO: 49), wherein X is independently any amino acid other than methionine or cysteine; the diversified G beta strand has the amino acid sequence of XPSQXV XVTT (SEQ ID NO: 50), wherein X is independently any amino acid other than methionine or cysteine, method. [

8. ] A library produced by the method according to claim 6 or 7. [

9. ] A method for obtaining a polypeptide comprising a fibronectin type III module (FN3) domain having a diversified C - CD - D - F - FG - G substitution surface that binds or specifically binds to a target molecule, the method comprising contacting the library according to any one of claims 1 - 5 with the target molecule and isolating the polypeptide that binds or specifically binds to the target molecule.

10. A polypeptide having an amino acid sequence that is at least, or about, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% identical to, or identical to, an amino acid sequence selected from the group consisting of SEQ ID NOs: 1, 2, 3, 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, 40, 41, 42, and 43.

11. The following: MLSPPSNL RVTDVTS TS VTLSWKPPAPITGY XVXYXEX XXXXGEWK XVXVPGSETSYTVTGLKPGTEY XFXVXVAVNGAX XGXPSQXVXVTT (SEQ ID NO: 44) A polypeptide comprising the amino acid sequence of, wherein each X is independently any amino acid, Optionally, each X is independently any amino acid other than methionine or cysteine, an isolated polypeptide.

12. The following: LSPPSNL RVTDVTS TS VTLSWKPPAPITGY XVXYXEX XXXXGEWK XVXVPGSETSYTVTGLKPGTEY XFXVXVAVNGAX XGXPSQXVXVTT (SEQ ID NO: 74) A polypeptide comprising the amino acid sequence of, wherein each X is independently any amino acid, Optionally, each X is independently any amino acid other than methionine or cysteine, a polypeptide.

13. A pharmaceutical composition comprising the isolated polypeptide according to any one of Claims 10 to 12.

14. A nucleic acid molecule encoding the isolated polypeptide according to Claim 13.

15. A plurality of nucleic acid molecules encoding a library of polypeptides according to any one of Claims 1 to 5.

16. A host cell comprising the nucleic acid molecule according to Claim 15.