Detection and separation of individual rare earth elements with a new lanmodulin ortholog and variants thereof

Abstract

Provided are proteins and peptides suitable for binding lanthanide ions and / or actinide ions. Proteins of the present disclosure may contain or be one of the following sequences: X1-X2-G-X3-X4-X5-L-X6-X7-X8-NKD-X9-D-X10-X11-X12-EI-X13-E-X14-I-X15-X16-G-X17-X18-X19-F-X20-AINPD-X21-D-X22-TLE-X23-X24-ET-X25-GRL-X26-X27-X28-DWA-X29-X30-NKDGD-X31-TLE-X32-DE-X33-L-X34-X35-X36-R-X37-RF-X38-X39-AD-X40-NKDGKLT-X41-X42-ELD-X43-X44-AGQ-X45-X46-X47-X48-X49-I-X50-K (SEQ ID NO:1), where X1 = any residue; X2 = T or S; X3 = any residue; X4 = E or D; X5 = any hydrophobic residue; X6 = R, S, K, or A; X7 = any residue; X8 = any hydrophobic residue; X9 = any residue; X10 = D, N, S, or Q; X11 = S or T; X12 = any hydrophobic residue; X13 = any residue; X14 = any hydrophobic residue; X15 = any residue; X16 = A, W, or L; X17 = S, T, A, Q, or V; X18 = Q, D, E, or K; X19 = any hydrophobic or polar residue; X20 = any residue; X21 = K, H, or G; X22 = K or T; X23 = P, K, A, or S; X24 = P, A, N, D, or G; X25 = K, N, or E; X26 = S or T; X27 = D, E, P, A, or K; X28 = any residue; X29 = any residue; X30 = any hydrophobic residue; X31 = K, Q, or E; X32 = any hydrophobic residue; X33 = F, W, or Y; X34 = S, A, or T; X35 = any hydrophobic residue; X36 = any hydrophobic residue; X37 = any residue; X38 = E, K, A, or N; X39 = any residue; X40 = K, A, or P; X41 = A, V, or E; X42 = K, A, Q, or E; X43 = A, S, or T; X44 = K, P, E, or A; X45 = any residue; X46 = any hydrophobic residue; X47 = any hydrophobic residue; X48 = K, V, or L; X49 = any hydrophobic residue; X50 = any hydrophobic residue. Also provided are methods of using any one of the proteins or peptides, methods of making any one of the proteins or peptides, and kits.

Description

Attorney Docket No.: 074339.00321 DETECTION AND SEPARATION OF INDIVIDUAL RARE EARTH ELEMENTS WITH A NEW LANMODULIN ORTHOLOG AND VARIANTS THEREOF CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No.63 / 635,348, filed on April 17, 2024, the disclosure of which is hereby incorporated by reference. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] This invention was made with government support under Grant Nos. DE- AC52-07NA27344 and DE-AC02-07CH11358 awarded by the Department of Energy and under Grant No. GM119707 awarded by the National Institutes of Health. The Government has certain rights in the invention. SEQUENCE LISTING

[0003] The instant application contains a Sequence Listing which has been submitted electronically in XML format and is hereby incorporated by reference in its entirety. Said XML copy, created on April 17, 2025, is named “074339_00321_ST26.xml”, and is 110,174 bytes in size. BACKGROUND OF THE DISCLOSURE

[0004] Rare earth elements (REs), including the 15 lanthanides (Ln), are indispensable for advanced technologies ranging from electric vehicle batteries and permanent magnets to medical imaging agents, owing to their unique optical and magnetic properties. As a result of the physicochemical similarity and miniscule differences in ionic radius between adjacent LnIIIions, their separation and purification is intrinsically challenging. Conventional hydrometallurgical solvent extraction relies on extractants with low selectivities among REs, thus necessitating multi-stage processes with high energy consumption. Despite many recent, creative advances—including preorganized-type ligands, tug-of-war and precipitation-based extraction schemes, kinetic separation methods, and functionalized inorganic materials—achieving high intra-RE selectivity remains difficult.

[0005] Nature provides a promising alternative: lanmodulins (LanMs), small proteins that have evolved exceptional lanthanide-binding properties. The first characterized LanM, from Methylobacterium (Methylorubrum) extorquens AM1 (Mex-LanM), undergoes large, cooperative conformational changes upon binding REs to its EF hands. It boasts picomolar affinity, favorable adsorption / desorption kinetics, and >1011-fold selectivity for certain REsover other metals, as determined by radiotracer studies. However, it displays comparatively modest selectivity among REs—in part because its multiple binding sites can form heterometallic (mixed-metal) complexes. Whereas Mex-LanM is strictly monomeric, an ortholog from Hansschlegelia quercus (Hans-LanM) dimerizes in a manner sensitive to ionic radius of the bound REs, driven in part by a hydrogen-bonding network spanning the dimer interface involving an Arg residue from one protomer interacting with two RE-ligating carboxylate residues and a third carboxylate, all in EF-hand 3 (EF3) of the other protomer. Hans-LanM exhibits enhanced intra-RE selectivity relative to Mex-LanM – achieving high- purity, single-stage Nd / Dy separation when immobilized in a column, but requiring elution with stepped concentrations of a competing small-molecule chelator. As Hans-LanM was not competent to dimerize when immobilized, however, we could not demonstrate that this improved separation efficiency was tied to dimerization.

[0006] Apart from protein / peptide-based and bioinspired recovery and separations, the high affinity and selectivity of bioligands can be exploited for detection of lanthanides in complex milieux, such as in environmental samples (e.g., acid mine drainage) and bacterial isolates, which could be used as feedstocks and passive accumulators, respectively, of valuable REs. Indeed, LanMs have inspired our group and others to develop such biosensors. For example, the LanM-based FRET sensor LaMP1 was used to interrogate RE transport and trafficking mechanisms in LnIII-utilizing bacteria. These bacteria favor only a subset of REs (generally the lightest lanthanides LREs, LaIII-NdIII), which selectively activate LnIII- dependent enzymes. LaMP1 was expressed in the cytosol of a methylotrophic bacterium and provided the first demonstration that LREs are taken up into the cytosol despite LanM and the enzymes known to utilize lanthanide ions being periplasmic, and that cytosolic uptake falls off sharply beyond NdIII. The mechanism of RE discrimination is proposed to include a periplasmic sorting pathway, in which LanM participates, that helps control cytosolic entry of LnIIIions for lanthanoenzyme activation. Unfortunately, the sensors developed to date exhibit largely indistinguishable responses to all REs, and the LaMP1 sensor is restricted to cytosolic applications because its two fluorescent proteins hinder export to the periplasm. The pH sensitivity of the YFP fluorophore also limits its use at low pH values, which are most relevant to industrial feedstocks. To overcome these challenges, we developed a Trp- containing LanM that has high enough affinity and selectivity to sensitize Tb luminescence in acid mine drainage, but its signal was low. Therefore, more robust biosensors are needed.SUMMARY OF THE DISCLOSURE

[0007] The present disclosure provides proteins that bind rare earth metal ions (e.g., heavy rare earth element ions (HRE ions)). Also provided are devices and kits comprising a protein of the present disclosure. Also provided are methods of using the proteins and devices.

[0008] In an aspect, the present disclosure provides proteins that bind metal ions (e.g., lanthanide ions and / or actinide ions). Other metal-binding proteins are disclosed in WO2020051274, WO2023004333, WO2024155330, and WO2025064730, which are incorporated herein by reference. As used throughout, the term “metal” refers to metal ions.

[0009] A protein of the present disclosure may comprise the following sequence: X1-X2-G-X3-X4-X5-L-X6-X7-X8-NKD-X9-D-X10-X11-X12-EI-X13-E-X14-I-X15-X16-G-X17-X18- X19-F-X20-AINPD-X21-D-X22-TLE-X23-X24-ET-X25-GRL-X26-X27-X28-DWA-X29-X30- NKDGD-X31-TLE-X32-DE-X33-L-X34-X35-X36-R-X37-RF-X38-X39-AD-X40-NKDGKLT-X41- X42-ELD-X43-X44-AGQ-X45-X46-X47-X48-X49-I-X50-K (SEQ ID NO:1), where X1= any residue (e.g., L); X2= T or S; X3= any residue (e.g., A or K); X4= E or D; X5= any hydrophobic residue (e.g., V, I, A, Y, or F); X6= R, S, K, or A; X7= any residue (e.g., Q); X8= any hydrophobic residue (e.g., V, I, A, or Y); X9= any residue (e.g., G); X10= D, N, S, or Q; X11= S or T; X12= any hydrophobic residue (e.g., V, I, F, or L); X13= any residue (e.g., P); X14= any hydrophobic residue (e.g., V, I, or A); X15= any residue (e.g., D); X16= A, W, or L; X17= S, T, A, Q, or V; X18= Q, D, E, or K; X19= any hydrophobic or polar residue (e.g., L, V, M, or T); X20= any residue (e.g., H);X21= K, H, or G; X22= K or T; X23= P, K, A, or S; X24= P, A, N, D, or G; X25= K, N, or E; X26= S or T; X27= D, E, P, A, or K; X28= any residue (e.g., K); X29= any residue (e.g., K); X30= any hydrophobic residue (e.g., V, I, A, or L); X31= K, Q, or E; X32= any hydrophobic residue (e.g., V, I, M, or L); X33= F, W, or Y; X34= S, A, or T; X35= any hydrophobic residue (e.g., V, I, or L); X36= any hydrophobic residue (e.g., L, A, or V); X37= any residue (e.g., A); X38= E, K, A, or N; X39= any residue (e.g., A); X40= K, A, or P; X41= A, V, or E; X42= K, A, Q, or E; X43= A, S, or T; X44= K, P, E, or A; X45= any residue (e.g., S); X46= any hydrophobic residue (e.g., V, F, or L); X47= any hydrophobic residue (e.g., V, I, or L); X48= K, V, or L; X49= any hydrophobic residue (e.g., V, M, or L); X50= any hydrophobic residue (e.g., A, M, or V). In various examples, a metal-binding protein of the present disclosure has at least 70% (e.g., at least 70%, at least 71%, at least 72%, at least 73%, at least 74%, at least 75%, at least 76%, at least 77%, at least 78%, at least 79%, at least 80%, at least 81%, at least 82%, at least 83%, at least 84%, at least 85%, at least 86%, at least 87%, at least 88%, at least 89%, at least 90%,at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or least 99%) identity to SEQ ID NO:1. In various examples, a protein of the present disclosure may be affixed or disposed on a substrate. A protein of the present disclosure may further comprise a signal peptide. The signal peptide may be cleaved prior to using a protein of the present disclosure. A signal peptide has the following sequence: MTRSLTRLAAAAGLASLVSIGMASSAFA (SEQ ID NO:2). In various examples, any protein of the present disclosure may have a methionine residue present at the N-terminus.

[0010] In various examples, a rare earth element binding protein comprises one or more metal-binding or metal coordination motifs. Such a protein may comprise up to 4 EF hand motifs (e.g., a first EF hand motif, a second EF hand motif, a third EF hand motif, and a fourth EF hand motif), each EF hand motif comprising 11, 12, or 13 amino acid residues and each EF hand motif is separated by 12 or 13 amino acid residues, where each residue is a canonical residue and at least one amino acid residue is a hydrophobic amino acid residue. When the EF hand motif has 12 amino acid residues, two or more metal-binding or metal coordination motifs may have the following sequence: N-X1-D-G-D-X2-T-L-E-X3-X4-E (SEQ ID NO:89), where X1may be any amino acid but at least one X1residue in the protein is a proline, X2may be any amino acid, X3may be any amino acid, X4may be any amino acid where at least one X4residue in the protein is an aspartate, and X3and / or X4is a proline in at least one metal-binding or metal coordination motif. In various examples, the metal- binding or metal coordination motif has the following sequence: NKDGDQTLEIPE (SEQ ID NO:90), NPDGDTTLEPDE (SEQ ID NO:91), or NKDGDQTLELDE (SEQ ID NO:92). Additionally, such proteins may be concatenated (connected in series), either with or without linkers (including but not limited to peptides) between each protein.

[0011] In an aspect, the present disclosure provides various methods of using the proteins and / or devices of the present disclosure. A method of the present disclosure may be for binding one or more lanthanides and / or actinides or for detecting and / or quantifying the amount of one or more lanthanides and / or actinides.

[0012] A method of using a protein and / or device of the present disclosure may be a method for binding one or more rare earth metal ions (e.g., lanthanides and / or actinides) in a sample. Metal ions may simply be described as metals. Binding may occur by contacting the sample with one or more proteins and / or devices of the present disclosure. The method may be performed on various types of samples. Examples of samples include, but are not limited to drinking water, wastewater, ground water, ash ponds, aqueous extract from contaminated soil, drainage (e.g., mine drainage, such as, for example, acidic mine drainage) or leachate(e.g., electronic waste leachate or leachate of an ore leachate). In various other examples, the sample is a solid sample. The method may be applied to samples over a variety of pH values (e.g., 3 to 8, including all 0.01 pH values and ranges therebetween).

[0013] In an aspect, the present disclosure provides kits. The kits may comprise a protein of the present disclosure. The kit may further comprise instructions for use. Additionally, a kit may comprise a substate, instructions and materials to conjugate or otherwise attach the protein to the substrate.

[0014] In an aspect, the present disclosure provides methods of making a protein of the present disclosure. A protein may be made by methods known in the art, such as by ligation, solid phase peptide synthesis (SPPS), or expression in a bacterial cell. BRIEF DESCRIPTION OF THE FIGURES

[0015] For a fuller understanding of the nature and objects of the disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying figures.

[0016] Figure 1. Strong dimerization, helical apoprotein, and large differences in Kd,appvalues in Al-LanM. (A) Comparison of amino acid sequences of Hans-, Xan-, and Al- LanMs (signal peptides removed). The underlined sequences indicate EF-hands 1-4. Residues in blue and red are involved in hydrophobic and hydrogen-bonding interactions, respectively, at the Hans-LanM dimer interface (and also see Al-LanM structure below). Hans-LanM is SEQ ID NO:100, Xan-LanM is SEQ ID NO:3, and Al-LanM is SEQ ID NO:4. (B) Dimerization behavior of apo- and metal-bound Al-LanM. Protein (250 µM, 300 µL, 3 equiv. LnIIIions, pH 7.0) was applied to an analytical S75 column (24 mL). The CaIIsample was run in buffer containing 5 mM CaII. (C) Conformational changes in Al-LanM (10 µM) monitored by CD spectroscopy (20 °C). Spectra of apo- and TbIII-bound (2 equiv.) protein at pH 5.0. (D) Comparison of binding affinities of Al-LanM for Gd, Tb, and Dy at pH 7.0. The lower intensities for the Dy titrations likely reflect quenching of the Trp excited state via energy transfer. (E) Comparison of Kd,appvalues of Hans-LanM (pH 5.0, 15 µM) and Al-LanM (pH 5.0 and 7.0, 2 μM) plotted versus ionic radius (CN=9). Results for Hans-LanM with LaIII, NdIII, and DyIIIare reproduced from Mattocks et al. Other values are shown in Tables 1-2.

[0017] Figure 2. Al-LanM is bright and robust, enabling individual RE sensing in vitro and in vivo. (A) In vitro time-resolved emission spectra of 5 µM LanMs with two equivalents of Tb at pH 5.0. The distinctive emission bands of Tb are shown. (B) Sensitized luminescence studies using 5 µM Al-LanM and Al-Y100W in the presence of 2 equiv. Tb. (C)Time-resolved emission spectra of 10 µM Al-Y100W in AMD with addition of 5-25 ppb Tb. (D) Standard curve generated from the average emission at 544-546 nm for 10 µM Al- Y100W and 543-547 nm for 10 µM Mex-T90W, including the regression lines and equations. (E) Time-resolved emission intensities of E. coli expressing various LanM sensors. Sensors were expressed with periplasmic signal sequences in E. coli HST08, and buffer-washed cells were treated with TbCl3for 30 min prior to assay. (F) Emission intensities for an analogous experiment as (E), but with Al-LanM expressed without the signal sequence, resulting in its localization to the cytosol. Conditions: 280 nm excitation, 100 µs delay, and 1000 µs collection.

[0018] Figure 3. Al-LanM’s preferential dimerization with LREs improves separation performance. (A) Comparison of Nd / Dy separation factors for various LanMs, in-solution (orange bars, left in each series) and on-column (green bars, right in each series). Statistical significance was determined using one-way ANOVA with Bonferroni post-test for each group (in-solution and on-column). *p <0.05 vs. on-column Al-LanM; **p <0.01 vs. in- solution Al-H60A. Sample sizes were as follows: in-solution – n = 3 for Al-LanM, H60A, and Hans-LanM; n = 2 for the rest. On-column – n = 6 for Al-LanM and H60A; n = 3 for the rest. (B) Comparison of Dy / Lu separation factors for various LanMs, in-solution (yellow bars, left in each series) and on-column (light blue bars, right in each series). One-way ANOVA with Bonferroni post-test was used for each in-solution or on-column group (*p <0.05, **p <0.01, vs. on-column Al-LanM); n = 2 for in-solution samples, n = 3 for on-column samples. (C) X- ray crystal structure of NdIII-Al-LanM. The hydrogen-bonding network connecting EF2 of each protomer via N63, an ordered water molecule, H60, and a sulfate ion is illustrated. Nd ions are depicted as cyan spheres, Ca ions as green spheres, with chain A colored light purple and chain B dark purple. (D) The intrahelical hydrogen bonding between backbone carbonyl of E99 and side chain of S102 on helix ⍺2. (E) SEC-MALS traces for apo (black), Nd (red), and Dy (blue) Al-LanMs at pH 3.3.

[0019] Figure 4. Separation of RE pairs using column-immobilized Al-LanM and Al- S102T. (A) Nd / Dy separation: A 95:5 mixture of Nd (0.38 mM) and Dy (0.02 mM) was fed into an agarose-Al-LanM column (0.6 mL) at pH 3.0. Dy was desorbed at pH 2.3, with a pH 1.5 step to desorb Nd. (B) Gd / Dy separation: A 1:1 mixture of Gd (0.2 mM) and Dy (0.2 mM) was fed into an agarose-Al-S102T column at pH 3.0. A pH step from 2.2 (Dy) to 1.5 (Gd) was employed.

[0020] Figure 5. (A) Size exclusion chromatography of 20 μM Xan-LanM in the presence of 4.0 equivalents of LaIIIor DyIII. A sharp peak at a retention volume of ~12.0 mLindicates a dimeric species for both conditions with an apparent molecular weight of ~29.1 kDa. Buffer: 30 mM MOPS, 100 mM KCl, 5% glycerol, pH 7.0. (B) Size exclusion chromatography of 400 μM Xan-LanM in the absence of lanthanides. A peak at a retention volume of ~14.0 mL suggests a monomeric species with an apparent molecular weight of ~14.2 kDa. Buffer: 30 mM MOPS, 100 mM KCl, 5% glycerol, pH 7.0.

[0021] Figure 6. Conformational change of 10 µM Al-LanM monitored using CD spectroscopy. Spectra of apoprotein and protein in the presence of 2 equiv. TbIIIpH 7.0.

[0022] Figure 7. Conformational change of 10 µM Xan-LanM monitored using CD spectroscopy. Spectra of apoprotein and protein in the presence of 2 equiv. TbIII, at (A) pH 5.0 and (B) pH 7.0.

[0023] Figure 8. (A) Temperature-dependent CD spectra of 20 µM Al-LanM with 2 equiv. of LaIIIor DyIIIwere obtained at pH 5.0. The ellipticity values of Al-LanM from 218 to 222 nm from the CD experiments were averaged and plotted against temperature. The helical structure of the apoprotein unfolds at lower temperature (between 40 and 50 °C) than the protein in the presence of LaIIIor DyIII. (B) Comparison of CD spectra at pH 5.0 for apo-Al- LanM (20 µM) at 20 °C (red) and 60 °C (light blue), and apo-Hans-LanM (15 µM) at 20 °C (black). Only at approximately 60 °C do apo-Al-LanM’s helices mostly unfold and the CD spectrum resembles that of apo-Hans-LanM.

[0024] Figure 9. Chelator-buffered titrations of 2 µM Al-LanM with RE ions at pH 5. (A) Representative steady-state emission spectra of Trp fluorescence in Al-LanM were displayed in response to the concentration of free YIIIions. (B) Intensities at 335 nm were plotted against the concentration of free LnIIIions. Excitation: 280 nm. Buffer: 20 mM acetate, 100 mM KCl, 10 mM chelators, 0-10 mM LnIII, pH 5.0. The intensity of the blank solution was subtracted from the spectra. Uncertainties were determined from three independent replicates. We were unable to determine the Kd,appvalues for NdIII- and EuIII-Al- LanM using this method. Fluorescence response to NdIIIwas outside the detectable range using EGTA as chelator, and we observed energy transfer from Trp to EuIII. Attempts to measure time-resolved emissions for EuIII-bound Al-LanM were unsuccessful due to interference from the high concentrations of EuIII-EGTA present (up to 10 mM).

[0025] Figure 10. Comparison of Hans-LanM Kd,app for TbIIIat pH 5.0 determined by circular dichroism (CD) and fluorescence (FL) spectroscopy. Conditions: 15 µM protein (CD), 2 µM protein (FL), 20 °C, 20 mM acetate, 100 mM KCl, 10 mM EGTA, 0-10 mM TbIII, pH 5.0. Uncertainties were determined from two independent replicates.

[0026] Figure 11. Al-LanM (20 µM) was titrated with EuIIIat pH 5.0 and the emission spectra were collected with an excitation wavelength of 394 nm (direct excitation of EuIII). The intensity at 617 nm was plotted against the number of Eu equivalents added. Binding of EuIIIto protein enhances fluorescence intensity, so this experiment assesses binding stoichiometry, roughly 2.75 equiv. under these conditions.

[0027] Figure 12. Chelator-buffered titrations of 2 µM Xan-LanM with RE ions. Intensities at 335 nm were plotted against the concentration of free LnIIIions. Excitation: 280 nm. Buffer: 20 mM acetate, 100 mM KCl, 10 mM chelators, 0-10 mM LnIII, pH 5.0. The intensity of the blank solution was subtracted from the spectra. Uncertainties were determined from three independent replicates.

[0028] Figure 13. Comparison of Kd,app values of Xan- and Al-LanMs at pH 5.0. The Kd,appvalues were determined using Hill fitting from Figure 9 and Figure 12 and plotted against the ionic radius (CN = 9).

[0029] Figure 14. To investigate whether dimer equilibria contribute to the differences in apparent Kds observed for Al-LanM, titrations were carried out with (A) GdIII- EGTA and (B) DyIII-EGTA at 20 µM protein concentrations. The values in Table 1 show only minor differences, suggesting that Al-LanM may be mostly dimerized in the presence of some HREs even at 2 µM proteinThis is consistent with the SEC analysis (Figure 1B) and is distinct from Hans-LanM.

[0030] Figure 15. Unbuffered titration of 2 µM Al-LanM with CaII, followed by steady-state Trp fluorescence (intensities at 335 nm). Excitation: 280 nm. Buffer: 20 mM acetate, 100 mM KCl, pH 5.0. The intensity of the blank solution was subtracted from the spectra. Uncertainties were determined from three independent replicates. The first three points were omitted from the Hill fitting. The parameters can be found in Table 1. The apparent Kdcould not be determined as the fluorescence intensity increase did not saturate at the highest concentration of CaIItested, and therefore a minimum value (>5 mM) is reported.

[0031] Figure 16. Sensitized luminescence studies as a function of pH, using Hans- LanM (5 µM) in the presence of 2 equiv. EuIII, TbIII, and DyIII, or 20 µM protein in the presence of 2 equiv. SmIII. Excitation 280 nm, delay 100 µs, collection 1000 µs (plate reader). Note the different y-axis scales for each panel.

[0032] Figure 17. Sensitized luminescence studies as a function of pH, using Xan- LanM (5 µM) in the presence of 2 equiv. EuIII, TbIII, and DyIII, or 20 µM protein in the presence of 2 equiv. SmIII. Excitation 280 nm, delay 100 µs, collection 1000 µs (plate reader).Note the different y-axis scales for each panel, as well as the better performance at low pH (pH < 5) than for Hans-LanM.

[0033] Figure 18. EGTA-buffered titrations of 2 µM Al-Y100W with SmIIIand DyIII. Unlike wild-type Al-LanM, where a gradual sigmoidal increase was observed, Sm titration of this variant showed a decrease in intensity at low free Sm concentration, followed by an increase, which may reflect the environments of the two Trp residues near EF2 and EF3 being differentially affected by metal ion binding. Uncertainties were determined from two independent replicates.

[0034] Figure 19. In vitro time-resolved emission spectra of LanMs in the presence of 2 equiv. each lanthanide ion at pH 5.0, obtained on the plate reader. The distinctive emission bands of each lanthanide are shown. (A) 20 µM Sm2-LanMs; (B) 5 µM Eu2-LanMs; (C) 5 µM Tb2-LanMs; (D) Dy2-LanMs. Conditions: 280 nm excitation, 100 µs delay, and 1000 µs collection. As Hans-LanM and Xan-LanM have similar emission intensities at pH 5.0 (Figure 16, Figure 17), the full spectra of Xan-LanM are omitted here for sake of clarity.

[0035] Figure 20. Sensitized luminescence studies as a function of pH, using Mex- T90W (5 µM) in the presence of 2 equiv. EuIII, TbIII, and DyIII, or 20 µM protein in the presence of 2 equiv. SmIII. Excitation 280 nm, delay 100 µs, collection 1000 µs (plate reader).

[0036] Figure 21. Sensitized luminescence studies as a function of pH, using Al- LanM (5 µM) in the presence of 2 equiv. EuIII, TbIII, and DyIII, or 20 µM protein in the presence of 2 equiv. SmIII. Excitation 280 nm, delay 100 µs, collection 1000 µs (plate reader).

[0037] Figure 22. Estimation of the number of coordinated solvent molecules (q) in EuIII2-Al-LanM. Phosphorescence decay of EuIII2-Al-LanM complex at various D2O mole fraction was recorded with excitation at 394 nm and emission collected at 617 nm. The lifetime constant (^^) was determined by single exponential fitting of the decay curves at each D2O mole fraction. The 1 / ^^ value of EuIII2-Al-LanM complex at 100% D2O was extrapolated from the trendline and used to hydration number (q) according to the equation outlined in the Experimental section. The calculated q value is 0.25.

[0038] Figure 23. Sensitized luminescence studies as a function of pH, using Al- Y100W (5 µM) in the presence of 2 equiv. EuIII, TbIII, and DyIII, or 20 µM protein in the presence of 2 equiv. SmIII. Excitation 280 nm, delay 100 µs, collection 1000 µs (plate reader).

[0039] Figure 24. Sensitized luminescence studies as a function of pH, using Hans- R100K (5 µM) in the presence of 2 equiv. Tb. Excitation 280 nm, delay 100 µs, collection 1000 µs (plate reader). The Hans-R100K variant exhibited a stronger signal at lower pH values (compare to Figure 16). Therefore, we opted to use the Hans-R100K instead of wild-type Hans-LanM for studying sensitization of NIR-emitting lanthanides. See Mattocks et al. (Nature 2023) for more characterization of this variant.

[0040] Figure 25. Steady-state emission spectra of NdIII-bound LanM sensors. (A) 5 µM NdIII2-Mex-T90W. (B) 5 µM NdIII2-Hans-R100K. (C) 5 µM NdIII2-Xan-LanM. Excitation at 280 nm.

[0041] Figure 26. Steady-state emission spectra of YbIII-bound LanM sensors. (A) 5 µM YbIII2-Mex-T90W. (B) 5 µM YbIII2-Hans-R100K. (C) 5 µM YbIII2-Xan-LanM. Excitation at 280 nm.

[0042] Figure 27. Sensitization of NdIIIfluorescence by LanM proteins. Plots of emission intensity at 1059-1061 nm vs. pH. (A) 5 µM NdIII2-Mex-T90W. (B) 5 µM NdIII2- Hans-R100K. (C) 5 µM NdIII2-Xan-LanM. Excitation at 280 nm. Three independent measurements were conducted to show uncertainties.

[0043] Figure 28. Sensitization of YbIIIfluorescence by LanM proteins. Plots of emission intensity at 979-981 nm vs. pH. (A) 5 µM YbIII2-Mex-T90W. (B) 5 µM YbIII2-Hans- R100K. (C) 5 µM YbIII2-Xan-LanM. Excitation at 280 nm. Three independent measurements were conducted to show uncertainties.

[0044] Figure 29. Analysis of LanM sensor expression in E. coli using SDS-PAGE. The same growth conditions as those used for the detection of lanthanide ions in E. coli were applied here. Plus and minus signs denote pre- and post-rhamnose induction, respectively. LanMs targeted to the periplasm contain additional signal sequences, resulting in a higher molecular weight prior to secretion and cleavage of the signal peptide, compared to the LanMs targeted to the cytoplasm. The molecular weights of Al-LanM with and without the signal sequence are 14,857 Da and 12,177 Da, respectively. Post-rhamnose induction samples showed overexpression bands at ~12 kDa across all samples, indicating secretion, cleavage of the signal peptides, and correct localization to the periplasm. Faint bands at ~15 kDa were observed in post-induction samples of periplasmically targeted LanMs, indicating a small amount of uncleaved signal peptide.

[0045] Figure 30. Representative emission spectra of Al-Y100W in E. coli periplasm in response to different extracellular concentrations of TbIII.

[0046] Figure 31. Analysis of protein expression and localization by SDS-PAGE. Lane 1: Pre-induction (whole cell); Lane 2: Post-induction (whole cell, 0.2% rhamnose, 4 h). Symbols: +, induced with 0.2% rhamnose; −, no induction; SP, spheroplast; PE, periplasmic extract. The SP and PE preparation methods followed those described previously. Briefly, after induction (with the negative group remaining uninduced), E. coli (HST08) cellsexpressing periplasmic Xan-LanM and Mex-LanM were grown for an additional 4 and 24 h before being harvested at each time point. The cell paste was resuspended in 40 mL / g of 30 mM Tris, 1 mM EDTA, and 20% sucrose (pH 7.4) and stirred at room temperature for 20 min. After centrifugation at 9,000 ×g for 10 min at 4 °C, the supernatant was discarded, and the cell pellet was resuspended in 20 mL of cold 5 mM MgSO4 per g of the original cell paste. This mixture was stirred for 20 min at 4 °C and centrifuged again at 9,000 × g for 10 min at 4 °C. The resulting supernatant (PE) was recovered, and 0.05 volumes of 1.0 M Tris (pH 7.4) and solid NaCl were added to a final concentration of 100 mM. The spheroplast fraction (SP) was also collected for gel analysis. (A) No notable overexpression band is observed in the post-induction periplasmic extract for Xan-LanM. A band just below 17 kDa that is more intense in the samples with rhamnose induction may correspond to overexpressed Xan-LanM (with the signal peptide) that cannot be transported to the periplasm due to insolubility. (B) In contrast, a distinct, darker band around 12 kDa (red box) is visible in the post-induction extract for Mex-T90W. This band appears at both the 4-h and 24-h time points in the presence of rhamnose (orange arrows). The bands observed near 10 kDa, slightly lower than the Mex-T90W band, appear to correspond to an endogenous E. coli periplasmic protein, as they are present in samples without rhamnose induction (blue arrows). These results indicate that Xan-LanM is not transported to the periplasm in this system, while Mex-T90W shows detectable overexpression and transport under the same conditions.

[0047] Figure 32. (A) Representative emission spectra of Al-Y100W in E. coli periplasm in response to different extracellular concentrations of EuIII. (B) Plot of sensor emission intensities against exogenous EuIIIconcentrations. Excitation: 280 nm, 100 μs delay, 1000 µs collection. Cell density: OD600nm= 0.6. The signal above background is very low for the EuIIIsamples; for example, it is possible that reduction of EuIIIto EuIIis occurring, or perhaps smaller REs (TbIII, DyIII) are more efficiently taken up into the periplasm of E. coli than is EuIII.

[0048] Figure 33. (A) Representative emission spectra of Al-Y100W in E. coli periplasm in response to different extracellular concentrations of DyIII. (B) Plot of sensor emission intensities against exogenous DyIIIconcentrations. Excitation: 280 nm, 100 μs delay, 1000 µs collection. Cell density: OD600nm = 0.6.

[0049] Figure 34. Al-LanM was expressed in E. coli without the signal sequence, resulting in its localization to the cytosolic space. The emission intensities were plotted against Eu concentrations. Only the 5 μM EuIIIsample shows a significant difference between cyto-Al-LanM response and the vector control by Student’s t-test (p < 0.05).

[0050] Figure 35. Schematic representation of the separation process using a spin- concentrator system. The initial mixture containing Al-LanM was treated with equal concentrations of a pair of REs (2 equiv. each RE for most experiments; 3 equiv. for optimized experiments at pH 7.0). After centrifugation, an RE that exhibits higher affinity for Al-LanM will tend to remain in the retentate, bound to Al-LanM. Conversely, another RE with weaker affinity will partition to the retentate. The separation factors obtained using this spin-concentrator system will be referred to as in-solution SFs.

[0051] Figure 36. To assess the optimal RE1-to-RE2ratio for efficient separation, we conducted a competition assay between Eu and Dy with Al-LanM. Figure 21 shows that Eu luminescence is ~3-fold higher than Dy luminescence when bound to Al-LanM. The large fold difference in signal intensity between Eu and Dy suggests strongly favored binding of Eu. Al-LanM (20 µM) at pH 3.3 (Buffer 2H) was treated with equimolar Eu and Dy (0.5, 1, 2, 3, or 4 equiv. each). The Trp residue (W84) was excited at 280 nm and the intrinsic emission wavelengths of Eu (617-619 nm) and Dy (574 – 576 nm) were monitored. Al-LanM showed a linear response until 2:2 equivalents. Therefore, the 2:2 equivalents of RE1:RE2 were used for separation experiments at pH 3.3.

[0052] Figure 37. In-solution separation factors (SF) and distribution coefficients (D) for RE1 / RE2 using Al-LanM at varying protein concentrations and pH levels. The SF is represented by bars, with yellow and blue colors indicating 2 µM and 10 µM protein used for the separation, respectively. Distribution coefficients for light RE1 (DRE1, black squares) and RE2 (DRE2, red circles) are also provided. (A) At pH 3.0, the SF for Nd / Dy is higher at 10 µM than at 2 µM, which is associated with larger DNd at 10 µM. At pH 3.3, the SF for Nd / Dy is significantly improved. (B) At pH 3.3, the SFs for Sm / Dy at 2 µM and 10 µM Al-LanM were 16.7 and 23.4, respectively, again driven by an increase in DSm but not DDy. At pH 7.0, the SFs for 2 µM and 10 µM Al-LanM were similar to each other and to the values at pH 3.3. Interestingly, at pH 7.0, the SF with 10 µM was not higher than with 2 µM. Both DSm and DDywere reduced at 10 µM protein compared to 2 µM protein. In summary, a 10 μM protein concentration resulted in better SFs than 2 μM, particularly at lower pH. The improved SFs at 10 µM were driven by increase in DLRE, perhaps suggesting that LRE-selective dimerization may contribute to separations under these conditions. At pH 3.0, the competitive binding of H+to the binding sites likely lowered the affinity for light REs, resulting in low SFs. Although the pH 7.0 condition also showed a large in vitro luminescence difference between LRE-Al-LanM and HRE-Al-LanM (Figure 2B and Figure 21), SFs at pH 7.0 were lower than at pH 3.3, which might mean a site far from the Trp (e.g., EF1) is contributing to bindingunder these conditions and negatively impacting selectivity. Alternatively, tighter dimerization at pH 7 for all REs and the use of protein concentrations above Kdimermay be contributing factors to lower selectivity.

[0053] Figure 38. In-solution separation factors of Al-LanM for RE pairs under optimized conditions (pH 3.3, 10 µM protein).

[0054] Figure 39. X-ray crystal structure of one protomer of NdIII-Al-LanM, depicting the positions of the 22 amino acids that differ from both Xan-LanM and Hans-LanM (in gold). Cyan spheres: NdIII, green sphere: CaII. Below the figure, a sequence alignment of these three LanMs is shown, with the corresponding 22 differing amino acids highlighted. Hans-LanM is SEQ ID NO:100, Xan-LanM is SEQ ID NO:3, and Al-LanM is SEQ ID NO:4.

[0055] Figure 40. Chelator-buffered titrations of 2 µM Al-LanM with RE ions at pH 7.0. Intensities at 335 nm were plotted against the concentration of free LnIIIions. Excitation: 280 nm. Buffer: 20 mM acetate, 100 mM KCl, 10 mM chelators (EGTA for La, Pr, EDDS for Sm – Dy), 0-10 mM LnIII, pH 7.0. The intensity of the blank solution was subtracted from the spectra. Uncertainties were determined from three independent replicates. The Kd,app values obtained from the fit are shown in Table 3.

[0056] Figure 41. Chelator-buffered titrations of 2 µM Al-LanM variants with RE ions at pH 7.0. Intensities at 335 nm were plotted against the concentration of free LnIIIions. Variants tested are: (A) H60A, (B) H60N, (C) S102A, and (D) S102T. Excitation: 280 nm. Buffer: 20 mM acetate, 100 mM KCl, 10 mM chelators (EGTA for La, EDDS for Dy), 0-10 mM LnIII, pH 7.0. The intensity of the blank solution was subtracted from the spectra. Uncertainties were determined from three independent replicates. The Kd,app values obtained from the fit are shown in Table 3.

[0057] Figure 42. Comparison of Tb luminescence intensity between Al-LanM and H60X (5 µM) incubated with 2 equiv. Tb at various pH conditions. Excitation 280 nm, delay 100 µs, collection 1000 µs (plate reader).

[0058] Figure 43. Determination of the oligomeric state of Tb-Al-LanM at pH 3.3. (A) Size-exclusion chromatogram of analytical S75 for Tb3-Al-LanM (250 µM, 300 µL). The apparent MW is calculated as 15.0 kDa. (B) UV-Vis spectrum of the SEC fraction peak at 13.74 mL, with the protein concentration determined as 17 µM. (C) Time-resolved emission spectrum of the SEC fraction sample. Excitation: 280 nm, 100-1000 µs scan. (D) Standard curve of 17 µM Al-LanM at pH 3.3 with increasing Tb concentration to determine protein- bound Tb in the SEC sample. At least 6.7 µM TbIIIis bound to 17 µM Al-LanM following theSEC experiment. Note that this Tb luminescence assay method can sensitize metals bound at EF2 / EF3, but not at EF1.

[0059] Figure 44. Gd / Dy separation using Al-LanM columns (A) A 1:1 mixture of Gd (0.2 mM) and Dy (0.2 mM) was fed into an Al-LanM column (0.6 mL) at pH 3.0. Dy was desorbed at pH 2.2, with a pH 1.5 step to desorb Gd. (B) Similar Dy / Gd separation experiment with the Al-H60A column (0.6 mL).

[0060] Figure 45. Details of metal coordination in EF3 of NdIII-Al-LanM and its extended hydrogen bonding interactions with Arg105 from the adjacent monomer. Cyan sphere: NdIII.

[0061] Figure 46. Detailed view of the metal coordination in EF4 of chains A and B in NdIII-Al-LanM, as well as EF4 in LaIII-Hans-LanM (PDB: 8DQ2). Green sphere: Ca; purple sphere: Na; red spheres: water molecules.

[0062] Figure 47. Investigation of the structural changes in (A) EF2 inactivated 1 and (C) EF2 inactivated 2 proteins upon NaCl treatment by monitoring changes in Trp emission. Instead of the metal-buffered solution, pH 5.0 (Buffer 2E) was used. Although they responded differently to the addition of NaCl in terms of signal changes, both were saturated at 20 mM NaCl. Determination of the binding stoichiometry of (B) EF2 inactivated 1 and (D) EF2 inactivated 2 using Eu luminescence. It was found that both have a 1-1.5 equivalent binding stoichiometry.

[0063] Figure 48. (A) Sm-EGTA-buffered, (B) Dy-EGTA-buffered, (C) Y-EGTA- buffered titrations of 2 µM EF2 inactivated 1 protein. The metal-EGTA-buffered solutions contain 20 mM NaCl. Note that the final intensity of the Sm titration is different from that of the main phases of the Dy and Y titrations, likely due to energy transfer from the Trp residue to the Sm.

[0064] Figure 49. Sensitized luminescence studies using EF2 inactivated 1 protein (5 µM) in the presence of 2 equiv. Tb and comparison to the wt-Al-LanM and Y100W. Excitation 280 nm, delay 100 µs, collection 1000 µs.

[0065] Figure 50. (A) 5 µM of EF2 inactivated 1 (B) 5 µM of EF2 inactivated 2 proteins were treated with equimolar Eu and Dy, but in different numbers of equivalents. The Trp residue (W84) was excited at 280 nm and the intrinsic emission wavelengths of Eu (617– 619 nm) and Dy (574–576 nm) were monitored. Conditions where Eu:Dy = 1:1 at pH 3.3 and Eu:Dy = 2:2 at pH 4.0 exhibited the largest fold change between the Eu and Dy signals, suggesting optimal separation conditions for these proteins.

[0066] Figure 51. The emission intensity of 1 equiv. Dy(III)-bound EF2 inactivated proteins with varying equiv. of Y(III). The intensities were determined by summing the signals between 565 and 585 nm. Buffer: 20 mM glycine, 20 mM NaCl, 100 mM KCl, pH 3.3. Excitation: 280 nm, 100 μs delay, 1000 µs collection. The ~25% decrease in intensity with 1 equiv. Y(III), and requirement for 4 equiv. Y(III) to decrease intensity by 50% suggests that Dy is preferred by 3- to 4-fold over Y (in line with Kddeterminations above, Table 16).

[0067] Figure 52. SEC-MALS traces for TD2-TD7 (A-F). Protein at a concentration of 2 mg / mL was incubated with 4 equiv. LaIIIin Buffer B (30 mM MOPS, 100 mM KCl, pH 7.0) and injected to a Wyatt SEC-MALS instrument equipped with a Superdex 200 increase 10 / 300 GL column run at 0.8 mL / min.

[0068] Figure 53. SEC-MALS traces for apoproteins of TD4 (A) and TD9 (B).

[0069] Figure 54. SEC-MALS traces for TD 8-TD10 illustrating that self-dimerized proteins predominate, at least at 1 mg / mL protein. A) 2 mg / mL TD9 was incubated with 6 equiv. LaIII. Note that in this case, the protein was not previously run on an S75 column and, at this protein concentration, ~20% of the protein is aggregated (peak eluted at 8-11 min). TD8 (B), TD9 (C), and TD10 (D) at concentrations of 1 mg / mL were metalated with 6 equiv. TbIII, run on an S75 column to remove aggregate, and then applied to the SEC-MALS column. Flow rate: 0.8 mL / min.

[0070] Figure 55. Assessment of Tb luminescence of fractions from SEC-MALS characterization of TD8, TD9, and TD10, compared to Al-LanM run under the same conditions.

[0071] Figure 56. pH dependence of TbIIIbinding to Al-LanM fused tandem dimer (2.5 μM, 10 μM Tb). Wild-type Al-LanM data (5 μM, 10 μM Tb) is shown for reference.

[0072] Figure 57. Spectrofluorometric titrations of Al-LanM fused tandem dimers with EuIII. See text for instrument settings and conditions. A) Spectrofluorometric spectra from a representative titration. B) Stoichiometry of TD8, TD9, and TD10 at pH 7.0. C) Stoichiometry of TD8, TD9, and TD10 at pH 3.3. DETAILED DESCRIPTION OF THE DISCLOSURE

[0073] Although claimed subject matter will be described in terms of certain examples, other examples, including examples that do not provide all of the benefits and features set forth herein, are also within the scope of this disclosure. Various structural,logical, process step, and electronic changes may be made without departing from the scope of the disclosure.

[0074] As used herein, unless otherwise indicated, “about”, “substantially”, or “the like”, when used in connection with a measurable variable (such as, for example, a parameter, an amount, a temporal duration, or the like) or a list of alternatives, is meant to encompass variations of and from the specified value including, but not limited to, those within experimental error (which can be determined by, e.g., a given data set, an art accepted standard, etc. and / or with, e.g., a given confidence interval (e.g.90%, 95%, or more confidence interval from the mean), such as, for example, variations of + / -10% or less, + / -5% or less, + / -1% or less, and + / -0.1% or less of and from the specified value), insofar such variations in a variable and / or variations in the alternatives are appropriate to perform in the instant disclosure. As used herein, the term “about” may mean that the amount or value in question is the exact value or a value that provides equivalent results or effects as recited in the claims or taught herein. That is, it is understood that amounts, sizes, compositions, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and / or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error, or the like, or other factors known to those of skill in the art such that equivalent results or effects are obtained. In general, an amount, size, composition, parameter, or other quantity or characteristic, or alternative is “about” or “the like,” whether or not expressly stated to be such. It is understood that where “about,” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

[0075] Ranges of values are disclosed herein. The ranges set out a lower limit value and an upper limit value. Unless otherwise stated, the ranges include the lower limit value, the upper limit value, and all values between the lower limit value and the upper limit value, including, but not limited to, all values to the magnitude of the smallest value (either the lower limit value or the upper limit value) of a range. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a numerical range of “0.1% to 5%” should be interpreted to include not only the explicitly recited values of 0.1% to 5%, but also, unless otherwise stated, include individual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5% to 1.1%; 0.5% to 2.4%; 0.5% to 3.2%, and 0.5% to4.4%, and other possible sub-ranges) within the indicated range. It is also understood (as presented above) that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. Ranges can be expressed herein as from “about” one particular value, and / or to “about” another particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about, it will be understood that the particular value forms a further disclosure. For example, if the value “about 10” is disclosed, then “10” is also disclosed.

[0076] The articles “a” and “an” are used in this disclosure to refer to one or more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element.

[0077] As used herein, unless otherwise stated or indicated, “s” refers to second(s), “min” refers to minute(s), and “h” refers to hour(s).

[0078] As used herein, unless otherwise stated, the term “group” refers to a chemical entity that is monovalent (i.e., has one terminus that can be covalently bonded to other chemical species), divalent, or polyvalent (i.e., has two or more termini that can be covalently bonded to other chemical species). The term “group” also includes radicals (e.g., monovalent and multivalent, such as, for example, divalent, trivalent, and the like, radicals). Illustrative examples of groups include: .be referred to herein by either their commonly known three letter symbols or by the one-letter symbols recommended by the IUPAC-IUB Biochemical Nomenclature Commission. Throughout the disclosure, amino acid residues may simply be referred to as “residues.”

[0080] Examples of hydrophobic amino acid and hydrophobic amino acid residues include, but are not limited to, glycine, alanine, valine, leucine, isoleucine, proline, cysteine, phenylalanine, methionine, tyrosine, and tryptophan.

[0081] The present disclosure provides proteins that bind rare earth metal ions (e.g., heavy rare earth element ions (HRE ions)). Also provided are devices and kits comprising a protein of the present disclosure. Also provided are methods of using the proteins and devices.

[0082] In an aspect, the present disclosure provides proteins that bind metal ions (e.g., lanthanide ions and / or actinide ions). Other metal-binding proteins are disclosed in WO2020051274, WO2023004333, WO2024155330, and WO2025064730, which are incorporated herein by reference. As used throughout, the term “metal” refers to metal ions.

[0083] A protein of the present disclosure may be of various lengths. For example, a protein of the present disclosure has 50 to 175 amino acid residues, including all integer amino acid values and ranges therebetween (e.g., 55 to 150 amino acid residues). For example, the protein has a molecular weight of around 6 kDa to 14 kDa, including all 0.1 Da values and ranges therebetween (e.g., ~12 kDa). A protein of the present disclosure comprises at least one segment where one or more rare earth metal ions can bind. In various examples, the protein of the present disclosure may be conjugated to form an intramolecular dimer. For example, an intramolecular dimer of the present disclosure has 50 to 350 amino acid residues, including all integer amino acid values and ranges therebetween (e.g., 55 to 300 amino acid residues). For example, the protein has a molecular weight of around 6 kDa to 28 kDa, including all 0.1 Da values and ranges therebetween (e.g., ~24 kDa).

[0084] A protein of the present disclosure may comprise the following sequence: X1-X2-G-X3-X4-X5-L-X6-X7-X8-NKD-X9-D-X10-X11-X12-EI-X13-E-X14-I-X15-X16-G-X17-X18- X19-F-X20-AINPD-X21-D-X22-TLE-X23-X24-ET-X25-GRL-X26-X27-X28-DWA-X29-X30- NKDGD-X31-TLE-X32-DE-X33-L-X34-X35-X36-R-X37-RF-X38-X39-AD-X40-NKDGKLT-X41- X42-ELD-X43-X44-AGQ-X45-X46-X47-X48-X49-I-X50-K (SEQ ID NO:1), where X1= any residue (e.g., L); X2= T or S; X3= any residue (e.g., A or K); X4= E or D; X5= any hydrophobic residue (e.g., V, I, A, Y, or F); X6= R, S, K, or A; X7= any residue (e.g., Q); X8= any hydrophobic residue (e.g., V, I, A, or Y); X9= any residue (e.g., G); X10= D, N, S, or Q; X11= S or T; X12= any hydrophobic residue (e.g., V, I, F, or L); X13= any residue (e.g., P); X14= any hydrophobic residue (e.g., V, I, or A);X15= any residue (e.g., D); X16= A, W, or L; X17= S, T, A, Q, or V; X18= Q, D, E, or K; X19= any hydrophobic or polar residue (e.g., L, V, M, or T); X20= any residue (e.g., H); X21= K, H, or G; X22= K or T; X23= P, K, A, or S; X24= P, A, N, D, or G; X25= K, N, or E; X26= S or T; X27= D, E, P, A, or K; X28= any residue (e.g., K); X29= any residue (e.g., K); X30= any hydrophobic residue (e.g., V, I, A, or L); X31= K, Q, or E; X32= any hydrophobic residue (e.g., V, I, M, or L); X33= F, W, or Y; X34= S, A, or T; X35= any hydrophobic residue (e.g., V, I, or L); X36= any hydrophobic residue (e.g., L, A, or V); X37= any residue (e.g., A); X38= E, K, A, or N; X39= any residue (e.g., A); X40= K, A, or P; X41= A, V, or E; X42= K, A, Q, or E; X43= A, S, or T; X44= K, P, E, or A; X45= any residue (e.g., S); X46= any hydrophobic residue (e.g., V, F, or L); X47= any hydrophobic residue (e.g., V, I, or L); X48= K, V, or L;X49= any hydrophobic residue (e.g., V, M, or L); X50= any hydrophobic residue (e.g., A, M, or V). In various examples, a metal-binding protein of the present disclosure has at least 70% (e.g., at least 70%, at least 71%, at least 72%, at least 73%, at least 74%, at least 75%, at least 76%, at least 77%, at least 78%, at least 79%, at least 80%, at least 81%, at least 82%, at least 83%, at least 84%, at least 85%, at least 86%, at least 87%, at least 88%, at least 89%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or least 99%) identity to SEQ ID NO:1. In various examples, a protein of the present disclosure may be affixed or disposed on a substrate. A protein of the present disclosure may further comprise a signal peptide. The signal peptide may be cleaved prior to using a protein of the present disclosure. A signal peptide has the following sequence: MTRSLTRLAAAAGLASLVSIGMASSAFA (SEQ ID NO:2). In various examples, any protein of the present disclosure may have a methionine residue present at the N-terminus.

[0085] In various examples, a rare earth element (e.g., heavy rare earth element) binding protein of the present disclosure is affixed or disposed on a substrate or encapsulated by or in a substrate. Various substrates may be used. Non-limiting examples of substrates include, but are not limited to, a bead (e.g., agarose, silica, polymeric resin, or the like), a membrane, a hydrogel, a protein-based material, a porous framework (e.g., MOF), a cell surface, and others known in the art.

[0086] In various examples, a protein of the present disclosure has a residue suitable for immobilization onto the substrate. The residue may be part of a large sequence comprising 2 to 13 amino acid residues. For example, the residue comprises a functional group that chemically reacts with another functional group on the substrate such that the residue (and thus protein) is covalently attached to the substrate. For example, the substrate may comprise a maleimide group or a succinimide group that can react with a nucleophilic group, such as the thiol of a cysteine or amine of a lysine or ornithine or a nucleophilic atom of a non-canonical amino acid. Other suitable chemistries (e.g., Click chemistry, SpyTag / SpyCatcher, and the like) are known in the art and may be used. For example, the substrate may be a resin or bead comprising a functional group that can react with the residue of the metal-binding protein. For example, the functional group may be a maleimide, alkyne, or azide. In various examples, the protein comprises the following sequence: GSGC (SEQ ID NO:62), GSGHHWGSTGSGC (SEQ ID NO:86), or GAGHHWGSTGSGC (SEQ ID NO:87), which can be used to conjugate the protein to a substrate.

[0087] In various examples, a rare earth element binding protein comprises one or more metal-binding or metal coordination motifs. Such a protein may comprise up to 4 EF hand motifs (e.g., a first EF hand motif, a second EF hand motif, a third EF hand motif, and a fourth EF hand motif), each EF hand motif comprising 11, 12, or 13 amino acid residues and each EF hand motif is separated by 12 or 13 amino acid residues, where each residue is a canonical residue and at least one amino acid residue is a hydrophobic amino acid residue. When the EF hand motif has 12 amino acid residues, two or more metal-binding or metal coordination motifs may have the following sequence: N-X1-D-G-D-X2-T-L-E-X3-X4-E (SEQ ID NO:89), where X1may be any amino acid but at least one X1residue in the protein is a proline, X2may be any amino acid, X3may be any amino acid, X4may be any amino acid where at least one X4residue in the protein is an aspartate, and X3and / or X4is a proline in at least one metal-binding or metal coordination motif. In various examples, the metal- binding or metal coordination motif has the following sequence: NKDGDQTLEIPE (SEQ ID NO:90), NPDGDTTLEPDE (SEQ ID NO:91), or NKDGDQTLELDE (SEQ ID NO:92). Additionally, such proteins may be concatenated (connected in series), either with or without linkers (including but not limited to peptides) between each protein.

[0088] A protein of the present disclosure may be or comprise the following sequence: >Xan-LanM LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:3); >Al-LanM LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:4); >Al-LanM(Y100W) (also referred to as Al-Y100W) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EWLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:5); >Al-LanM(H60A) (also referred to as Al-H60A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:6); >Al-LanM(H60N) (also referred to as Al-H60N) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:7); >Al-LanM(S102A) (also referred to as Al-S102A)LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:8); >Al-LanM(S102T) (also referred to as Al-S102T) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:9); >Al-LanM-GSGC LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:10); >Al-LanM(S102T)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:11); >Al-LanM(H60A)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:12); >Al-LanM-12mer-Cys (12mer-Cys underlined) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGHHWGSTG SGC (SEQ ID NO:13); >Xan-LanM GSGC (GSGC is SEQ ID NO:62) LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK GSGC (SEQ ID NO:14); >Al-LanM(H60N)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:36); >Al-LanM(S102A)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:37); >Xan-LanM with native signal peptide (underlined) MKRRMISLGV VAAVSLAATG SAFALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:93); >Al-LanM with native signal peptide (underlined) MTRSLTRLAA AAGLASLVSI GMASSAFALT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVK (SEQ ID NO:94); >Mal-Xan-LanMMKIKTGARIL ALSALTTMMF SASALAMLTG KEFLRKYNKD KDSTVEIVEA IDLGTKVFKA INPDKDKTLE AAETKGRLSD EDWAQFNKDG DKTLELDEWL IIVRKRFNDA DANKDGKLTE AELDAPAGQQ LILLIAK (SEQ ID NO:95); >Mal-Al-LanM MKIKTGARIL ALSALTTMMF SASALALTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:96); >Mal-Al-LanM(Y100W) MKIKTGARIL ALSALTTMMF SASALALTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEWLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:97); >Al-LanM EF2 inactivated 1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAIDKNKDG KLTPNETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:84); >Al-LanM EF2 inactivated 2 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAIDKNKDG KLTPNETEGR LTKKDWAKIN KDGDQSLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:85).

[0089] In various examples, a protein of the present disclosure may be concatenated with the same or different metal-binding protein of the present disclosure. The proteins may be concatenated or otherwise conjugated through a linker group (e.g., Protein1-X-Protein2, where Protein1and Protein2are proteins of the present disclosure, which may be the same or different, and X is a linker group). Various linker groups may be used. In various examples, the linker group is a peptide comprising 5 to 48 amino acid residues. In various other examples, the linker group is an aliphatic group or a poly(ethylene)glycol group or other suitable carbon-based linker groups. Examples of peptide linker groups include, but are not limited to, GGSGGSGGSGGSGGSGGS (SEQ ID NO:15), GGSGGSGGSGGSGGSGGSGGSGGSGGSGG (SEQ ID NO:16), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:17), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:18), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:19), or GSGGSGAEAAAKEAAAKAGGSGGSAEAAAKEAAAKAGSGGSG (SEQ ID NO:20).

[0090] Examples of concatenated proteins (which may be referred to as tandem peptides) include, but are not limited to, >TD1 – Xan-LanM tandem dimer (18-aa GGS linker)ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:20); >TD2 – Xan-LanM tandem dimer (30-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SALTGKEFLR KYNKDKDSTV EIVEAIDLGT KVFKAINPDK DKTLEAAETK GRLSDEDWAQ FNKDGDKTLE LDEWLIIVRK RFNDADANKD GKLTEAELDA PAGQQLILLI AK (SEQ ID NO:21); >TD3 – Xan-LanM tandem dimer (36-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSALT GKEFLRKYNK DKDSTVEIVE AIDLGTKVFK AINPDKDKTL EAAETKGRLS DEDWAQFNKD GDKTLELDEW LIIVRKRFND ADANKDGKLT EAELDAPAGQ QLILLIAK (SEQ ID NO:22); >TD4 – Xan-LanM tandem dimer (42-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:23); >TD5 – Xan-LanM tandem dimer (48-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:24); >TD6 – Xan-LanM tandem dimer (42-aa EAAAK linker) (EAAAK is SEQ ID NO:88) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGSGGSGAEA AAKEAAAKAG GSGGSAEAAA KEAAAKAGSG GSGALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:25); >TD7 – Hans-LanM tandem dimer (42-aa GGS linker) ASGADALKAL NKDNDDSLEI AEVIHAGATT FTAINPDGDT TLESGETKGR LTEKDWARAN KDGDQTLEMD EWLKILRTRF KRADANKDGK LTAAELDSKA GQGVLVMIMK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSASGADALK ALNKDNDDSL EIAEVIHAGA TTFTAINPDG DTTLESGETK GRLTEKDWAR ANKDGDQTLE MDEWLKILRT RFKRADANKD GKLTAAELDS KAGQGVLVMI MK (SEQ ID NO:26);>TD8 – Al-LanM tandem dimer (36-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:27); >TD9 – Al-LanM tandem dimer (42-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VK (SEQ ID NO:28); >TD10 – Al-LanM tandem dimer (48-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVK (SEQ ID NO:29); >TD9-GSGC (also called TD9-Cys-1) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:30); >TD9-12mer-Cys (also called TD9-Cys-2) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:31); >TD9(H60A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:38); >TD9(H60A)-Cys-2 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETEGRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:39); >TD9(H60N)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFNAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:40); >TD9(S102A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLALVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:41); >TD9(S102T)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLTLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:42).

[0091] In various examples, a protein of the present disclosure can be further modified to comprise fluorescent groups or FRET pairs. In various examples, the FRET pairs may be peptide-based FRET pairs. In various examples, the FRET pair may be mNeonGreen (MVSKGEEDNMASLPATHELHIFGSINGVDFDMVGQGTGNPNDGYEELNLKSTKGD LQFSPWILVPHIGYGFHQYLPYPDGMSPFQAAMVDGSGYQVHRTMQFEDGASLTVN YRYTYEGSHIKGEAQVKGTGFPADGPVMTNSLTAADWCRSKKTYPNDKTIISTFKW SYTTGNGKRYRSTARTTYTFAKPMAANYLKNQPMYVFRKTELKHSKTELNFKEWQ KAFTDVMGMDELYK (SEQ ID NO:32)) and mScarlet (MVSKGEAVIKEFMRFKVHMEGSMNGHEFEIEGEGEGRPYEGTQTAKLKVTKGGPL PFSWDILSPQFMYGSRAFIKHPADIPDYYKQSFPEGFKWERVMNFEDGGAVTVTQDT SLEDGTLIYKVKLRGTNFPPDGPVMQKKTMGWEASTERLYPEDGVLKGDIKMALRL KDGGRYLADFKTTYKAKKPVQMPGAYNVDRKLDITSHNEDYTVVEQYERSEGRHS TGGMDELYK (SEQ ID NO:33)). Other FRET pairs are known in the art and may be used. For example, the FRET pair may be ECFP(Δ11) (MVSKGEELFTGVVPILVELDGDVNGHRFSVSGEGEGDATYGKLTLKFICTTGKLPVP WPTLVTTLTWGVQCFSRYPDHMKQHDFFKSAMPEGYVQERTIFFKDDGNYKTRAE VKFEGDTLVNRIELKGIDFKEDGNILGHKLEYNYISHNVYITADKQKNGIKAHFKIRHNIEDGSVQLADHYQQNTPIGDGPVLLPDNHYLSTQSALSKDPNEKRDHMVLLEFVTA A (SEQ ID NO:98)) and citrine (MVSKGEELFTGVVPILVELDGDVNGHKFSVSGEGEGDATYGKLTLKFICTTGKLPVP WPTLVTTFGYGLMCFARYPDHMKQHDFFKSAMPEGYVQERTIFFKDDGNYKTRAE VKFEGDTLVNRIELKGIDFKEDGNILGHKLEYNYNSHNVYIMADKQKNGIKVNFKIR HNIEDGSVQLADHYQQNTPIGDGPVLLPDNHYLSYQSALSKDPNEKRDHMVLLEFV TAAGITLGMDELYK (SEQ ID NO:99)). Small molecule FRET pairs, such as Cy3 and Cy5, appended to protein via conjugation chemistry known in the art, may also be used. Non- limiting examples of proteins comprising a FRET pair comprise or have the following sequence: >TD9-FRET1 MVSKGEEDNM ASLPATHELH IFGSINGVDF DMVGQGTGNP NDGYEELNLK STKGDLQFSP WILVPHIGYG FHQYLPYPDG MSPFQAAMVD GSGYQVHRTM QFEDGASLTV NYRYTYEGSH IKGEAQVKGT GFPADGPVMT NSLTAADWCR SKKTYPNDKT IISTFKWSYT TGNGKRYRST ARTTYTFAKP MAANYLKNQP MYVFRKTELK HSKTELNFKE WQKAFTDVMG MDELYKLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVKGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVKMV SKGEAVIKEF MRFKVHMEGS MNGHEFEIEG EGEGRPYEGT QTAKLKVTKG GPLPFSWDIL SPQFMYGSRA FIKHPADIPD YYKQSFPEGF KWERVMNFED GGAVTVTQDT SLEDGTLIYK VKLRGTNFPP DGPVMQKKTM GWEASTERLY PEDGVLKGDI KMALRLKDGG RYLADFKTTY KAKKPVQMPG AYNVDRKLDI TSHNEDYTVV EQYERSEGRH STGGMDELYK (SEQ ID NO:34) or >TD9-FRET2 MVSKGEAVIK EFMRFKVHME GSMNGHEFEI EGEGEGRPYE GTQTAKLKVT KGGPLPFSWD ILSPQFMYGS RAFIKHPADI PDYYKQSFPE GFKWERVMNF EDGGAVTVTQ DTSLEDGTLI YKVKLRGTNF PPDGPVMQKK TMGWEASTER LYPEDGVLKG DIKMALRLKD GGRYLADFKT TYKAKKPVQM PGAYNVDRKL DITSHNEDYT VVEQYERSEG RHSTGGMDEL YKLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSLTGAEF LAQYNKDGDQ TLEIPEAIDL GTKTFHAINP DGDTTLEPDE TEGRLTKKDW AKINKDGDQT LELDEYLSLV RARFNAADKN KDGKLTAKEL DSKAGQSLLK LIVKMVSKGE EDNMASLPAT HELHIFGSIN GVDFDMVGQG TGNPNDGYEE LNLKSTKGDL QFSPWILVPH IGYGFHQYLP YPDGMSPFQA AMVDGSGYQV HRTMQFEDGA SLTVNYRYTY EGSHIKGEAQ VKGTGFPADG PVMTNSLTAA DWCRSKKTYP NDKTIISTFK WSYTTGNGKR YRSTARTTYT FAKPMAANYL KNQPMYVFRK TELKHSKTEL NFKEWQKAFT DVMGMDELYK (SEQ ID NO:35).

[0092] In an aspect, the present disclosure provides various methods of using the proteins and / or devices of the present disclosure. A method of the present disclosure may befor binding one or more lanthanides and / or actinides or for detecting and / or quantifying the amount of one or more lanthanides and / or actinides.

[0093] A method of using a protein and / or device of the present disclosure may be a method for binding one or more rare earth metal ions (e.g., lanthanides and / or actinides) in a sample. Metal ions may simply be described as metals. Binding may occur by contacting the sample with one or more proteins and / or devices of the present disclosure. The method may be performed on various types of samples. Examples of samples include, but are not limited to drinking water, wastewater, ground water, ash ponds, aqueous extract from contaminated soil, drainage (e.g., mine drainage, such as, for example, acidic mine drainage) or leachate (e.g., electronic waste leachate or leachate of an ore leachate). In various other examples, the sample is a solid sample. The method may be applied to samples over a variety of pH values (e.g., 3 to 8, including all 0.01 pH values and ranges therebetween).

[0094] Various lanthanides (e.g., lanthanide ions) and / or actinides (e.g., actinide ions) may be bound by a protein and / or device. Examples of lanthanide ions and actinide ions that may be bound include, but are not limited to, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, Ac, Th, U, Np, Pu, Am, Cm, Bk, Cf and various ions thereof. In various examples, any lanthanide ion or any actinide ion is bound. For example, the lanthanide is chosen from Pr, Nd, Sm, Eu, Gd, Tb, Dy, Tm, Yb, and Lu, and ions thereof. In various examples, the lanthanide is Pr, Nd, Tb, Dy, or an ion thereof; or Sm, Eu, Gd, or an ion thereof; or Tm, Yb, Lu, or an ion thereof; or Am, Cm, or an ion thereof. In various examples, the lanthanide or actinide ions are trivalent, for example Nd(III) or Ac(III). In various examples, the actinide ions are tetravalent, for example Th(IV), U(IV), or Bk(IV). The concentration of the lanthanide and / or actinides in the sample may be less than 100 ppm (e.g., less than 90, 80, 70, 60, 50, 40, 30, 20, 10, 1, 0.1, or 0.05 ppm). The apparent Kd values of the protein can range between 100 fM and 1 nM at pH 7.0, or lanthanide ions can bind at least 4-fold tighter than lanthanide ion binding to Hans-LanM at pH 5.0.

[0095] In various examples, the one or more lanthanides and / or actinides bound to the one or more proteins and / or devices may be isolated from the proteins and / or devices and recovered. The lanthanides and / or actinides may be unbound by lowering the pH below ~3 or by adding a chelator (e.g., citrate, EDTA, EGTA, malonate, or the like). In various embodiments, if one or more different lanthanides and / or actinides are bound to the one or more proteins or devices, the one or more different lanthanides and / or actinides may be sequentially dissociated from the proteins. As an illustrative example, if both Dy and Nd are bound, one species of metal can be selectively dissociated, while the other metal remainsbound. For example, one metal can be dissociated via contacting with a chelator, while the other metal is dissociated via adjustment of the pH. As another example, one metal can be dissociated via adjustment of the pH, while the other metal is dissociated via adjustment of the pH to a lower value. The one or more proteins and / or devices may be reused after the one or more lanthanides are unbound and separated.

[0096] Various lanthanides (e.g., lanthanide ions) and / or actinides (e.g., actinide ions) may be bound by a protein and / or device. For example, the lanthanide ion is any lanthanide ion, or the actinide ion is any actinide ion. The bound lanthanides and / or actinides may be the same or different. The concentration of the lanthanide and / or actinide in the sample may be less than 1 ppm, or less than 100 ppb, or less than 50 ppb, or less than 10 ppb.

[0097] In an aspect, the present disclosure provides kits. The kits may comprise a protein of the present disclosure. The kit may further comprise instructions for use. Additionally, a kit may comprise a substate, instructions and materials to conjugate or otherwise attach the protein to the substrate.

[0098] In an aspect, the present disclosure provides methods of making a protein of the present disclosure. A protein may be made by methods known in the art, such as by ligation, solid phase peptide synthesis (SPPS), or expression in a bacterial cell.

[0099] The steps of the method described in the various embodiments and examples disclosed herein are sufficient to carry out the methods of the present invention. Thus, in an embodiment, the method consists essentially of a combination of the steps of the methods disclosed herein. In another embodiment, the method consists of such steps.

[0100] The following Statements provide various examples of the present disclosure. Statement 1. A rare earth element binding protein comprising the following sequence: X1-X2-G-X3-X4-X5-L-X6-X7-X8-NKD-X9-D-X10-X11-X12-EI-X13-E-X14-I-X15-X16-G-X17-X18- X19-F-X20-AINPD-X21-D-X22-TLE-X23-X24-ET-X25-GRL-X26-X27-X28-DWA-X29-X30- NKDGD-X31-TLE-X32-DE-X33-L-X34-X35-X36-R-X37-RF-X38-X39-AD-X40-NKDGKLT-X41- X42-ELD-X43-X44-AGQ-X45-X46-X47-X48-X49-I-X50-K (SEQ ID NO:1), wherein X1= any residue; X2= T or S; X3= any residue; X4= E or D; X5= any hydrophobic residue; X6= R, S, K, or A; X7= any residue; X8= any hydrophobic residue; X9= any residue; X10= D, N, S, or Q; X11= S or T; X12= any hydrophobic residue; X13= any hydrophobic residue; X15= any residue; X16= A, W, or L; X17= S, T, A, D, E, or K; X19= any hydrophobic or polar residue; X20= any residue; X21= K or T; X23= P, K, A, or S; X24= P, A, N, D, or G; X25= K, N, or E; X26=D, E, P, A, or K; X28= any residue; X29= any residue; X30= any hydrophobic residue; X31= K, Q, or E; X32= any hydrophobic residue; X33= F, W, or Y; X34= S, A, or T; X35= any hydrophobic residue; X36= any hydrophobic residue; X37= any residue; X38= E, K, A, or N; X39= any residue; X40= K, A, or P; X41= A, V, or E; X42= K, A, Q, or E; X43= A, S, or T; X44= K, P, E, or A; X45= any residue; X46= any hydrophobic residue; X47= any hydrophobic residue; X48= K, V, or L; X49= any hydrophobic residue; X50= any hydrophobic residue; wherein the rare earth element binding protein is optionally disposed or affixed to a substrate or encapsulated by or in the substrate and wherein when the rare earth element binding protein is LTGAEFLAQYNKDGDQTLEIPEAIDLGTKTFHAINPDGDTTLEPDETEGRLTKKDWA KINKDGDQTLELDEYLSLVRARFNAADKNKDGKLTAKELDSKAGQSLLKLIVK (SEQ ID NO:4), then the rare earth element binding protein is disposed or affixed to a substrate or encapsulated by or in the substrate and the rare earth element binding protein does not have the following sequence: LTGKEFLRKYNKDKDSTVEIVEAIDLGTKVFKAINPDKDKTLEAAETKGRLSDEDWA QFNKDGDKTLELDEWLIIVRKRFNDADANKDGKLTEAELDAPAGQQLILLIAK (SEQ ID NO:3) or ASGADALKALNKDNDDSLEIAEVIHAGATTFTAINPDGDTTLESGETKGRLTEKDWA RANKDGDQTLEMDEWLKILRTRFKRADANKDGKLTAAELDSKAGQGVLVMIMK (SEQ ID NO:100). Statement 2. A rare earth element binding protein according to Statement 1, wherein X1= L; X3= A or K; X5= V, I, A, Y, or F; X6= R, S, K, or A; X7= Q; X8= V, I, A, or Y; X9= G; X12= V, I, F, or L; X13= P; X14= V, I, or A; X15= D; X19= L, V, M, or T; X20= H, N, or A; X28= K; X29= K; X30= V, I, A, or L; X32= V, I, M, or L; X35= V, I, or L; X36= L, A, or V; X37= A; X39= A; X45= S; X46= V, F, or L; X47= V, I, or L; X49= V, M, or L; and / or X50= A, M, or V. Statement 3. A rare earth element binding protein according to Statement 1 or Statement 2, wherein the protein is disposed or affixed to the substrate or encapsulated by or in the substrate. Statement 4. A rare earth element binding protein according to Statement 3, wherein the substrate is a bead, a membrane, a hydrogel, a protein-based material, a cell surface, or a porous framework.Statement 5. A rare earth element binding protein according to Statement 3, wherein the protein further comprises a linker group. Statement 6. A rare earth element binding protein according to Statement 5, wherein the linker group is conjugated to a protein, wherein the protein is or comprises SEQ ID NO:1. Statement 7. A rare earth element binding protein according to Statement 5, wherein the linker group is a peptide. Statement 8. A rare earth element binding protein according to any one of Statements 5–7, wherein the linker group has the following sequence: GGSGGSGGSGGSGGSGGS (SEQ ID NO:15), GGSGGSGGSGGSGGSGGSGGSGGSGGSGG (SEQ ID NO:16), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:17), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:18), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:19), or GSGGSGAEAAAKEAAAKAGGSGGSAEAAAKEAAAKAGSGGSG (SEQ ID NO:20). Statement 9. A rare earth element binding protein according to any one of the preceding Statements, further comprising a fluorescence resonance energy transfer pair. Statement 10. A rare earth element binding protein according to any one of the preceding Statements, wherein the protein comprises or has the following sequence: >Al-LanM LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:4); >Al-LanM(Y100W) (also referred to as Al-Y100W) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EWLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:5); >Al-LanM(H60A) (also referred to as Al-H60A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:6); >Al-LanM(H60N) (also referred to as Al-H60N) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:7); >Al-LanM(S102A) (also referred to as Al-S102A)LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:8); >Al-LanM(S102T) (also referred to as Al-S102T) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:9); >Al-LanM-GSGC LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:10); >Al-LanM(S102T)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:11); >Al-LanM(H60A)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:12); >Al-LanM-12mer-Cys (12mer-Cys underlined) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGHHWGSTG SGC (SEQ ID NO:13); >Xan-LanM GSGC (GSGC is SEQ ID NO:62) LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK GSGC (SEQ ID NO:14); >Al-LanM(H60N)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:36); >Al-LanM(S102A)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:37); >Xan-LanM with native signal peptide (underlined) MKRRMISLGV VAAVSLAATG SAFALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:93); >Al-LanM with native signal peptide (underlined) MTRSLTRLAA AAGLASLVSI GMASSAFALT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVK (SEQ ID NO:94); >Mal-Xan-LanMMKIKTGARIL ALSALTTMMF SASALAMLTG KEFLRKYNKD KDSTVEIVEA IDLGTKVFKA INPDKDKTLE AAETKGRLSD EDWAQFNKDG DKTLELDEWL IIVRKRFNDA DANKDGKLTE AELDAPAGQQ LILLIAK (SEQ ID NO:95); >Mal-Al-LanM MKIKTGARIL ALSALTTMMF SASALALTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:96); >Mal-Al-LanM(Y100W) MKIKTGARIL ALSALTTMMF SASALALTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEWLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:97); >Al-LanM EF2 inactivated 1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAIDKNKDG KLTPNETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:84); >Al-LanM EF2 inactivated 2 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAIDKNKDG KLTPNETEGR LTKKDWAKIN KDGDQSLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:85); >TD1 – Xan-LanM tandem dimer (18-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:20); >TD2 – Xan-LanM tandem dimer (30-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SALTGKEFLR KYNKDKDSTV EIVEAIDLGT KVFKAINPDK DKTLEAAETK GRLSDEDWAQ FNKDGDKTLE LDEWLIIVRK RFNDADANKD GKLTEAELDA PAGQQLILLI AK (SEQ ID NO:21); >TD3 – Xan-LanM tandem dimer (36-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSALT GKEFLRKYNK DKDSTVEIVE AIDLGTKVFK AINPDKDKTL EAAETKGRLS DEDWAQFNKD GDKTLELDEW LIIVRKRFND ADANKDGKLT EAELDAPAGQ QLILLIAK (SEQ ID NO:22); >TD4 – Xan-LanM tandem dimer (42-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:23);>TD5 – Xan-LanM tandem dimer (48-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:24); >TD6 – Xan-LanM tandem dimer (42-aa EAAAK linker) (EAAAK is SEQ ID NO:88) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGSGGSGAEA AAKEAAAKAG GSGGSAEAAA KEAAAKAGSG GSGALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:25); >TD7 – Hans-LanM tandem dimer (42-aa GGS linker) ASGADALKAL NKDNDDSLEI AEVIHAGATT FTAINPDGDT TLESGETKGR LTEKDWARAN KDGDQTLEMD EWLKILRTRF KRADANKDGK LTAAELDSKA GQGVLVMIMK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSASGADALK ALNKDNDDSL EIAEVIHAGA TTFTAINPDG DTTLESGETK GRLTEKDWAR ANKDGDQTLE MDEWLKILRT RFKRADANKD GKLTAAELDS KAGQGVLVMI MK (SEQ ID NO:26); >TD8 – Al-LanM tandem dimer (36-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:27); >TD9 – Al-LanM tandem dimer (42-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VK (SEQ ID NO:28); >TD10 – Al-LanM tandem dimer (48-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVK (SEQ ID NO:29); >TD9-GSGC (also called TD9-Cys-1) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETEGRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:30); >TD9-12mer-Cys (also called TD9-Cys-2) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:31); >TD9(H60A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:38); >TD9(H60A)-Cys-2 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:39); >TD9(H60N)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFNAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:40); >TD9(S102A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLALVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:41); >TD9(S102T)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLTLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:42); >TD9-FRET1 MVSKGEEDNM ASLPATHELH IFGSINGVDF DMVGQGTGNP NDGYEELNLK STKGDLQFSP WILVPHIGYG FHQYLPYPDG MSPFQAAMVD GSGYQVHRTMQFEDGASLTV NYRYTYEGSH IKGEAQVKGT GFPADGPVMT NSLTAADWCR SKKTYPNDKT IISTFKWSYT TGNGKRYRST ARTTYTFAKP MAANYLKNQP MYVFRKTELK HSKTELNFKE WQKAFTDVMG MDELYKLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVKGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVKMV SKGEAVIKEF MRFKVHMEGS MNGHEFEIEG EGEGRPYEGT QTAKLKVTKG GPLPFSWDIL SPQFMYGSRA FIKHPADIPD YYKQSFPEGF KWERVMNFED GGAVTVTQDT SLEDGTLIYK VKLRGTNFPP DGPVMQKKTM GWEASTERLY PEDGVLKGDI KMALRLKDGG RYLADFKTTY KAKKPVQMPG AYNVDRKLDI TSHNEDYTVV EQYERSEGRH STGGMDELYK (SEQ ID NO:34) or >TD9-FRET2 MVSKGEAVIK EFMRFKVHME GSMNGHEFEI EGEGEGRPYE GTQTAKLKVT KGGPLPFSWD ILSPQFMYGS RAFIKHPADI PDYYKQSFPE GFKWERVMNF EDGGAVTVTQ DTSLEDGTLI YKVKLRGTNF PPDGPVMQKK TMGWEASTER LYPEDGVLKG DIKMALRLKD GGRYLADFKT TYKAKKPVQM PGAYNVDRKL DITSHNEDYT VVEQYERSEG RHSTGGMDEL YKLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSLTGAEF LAQYNKDGDQ TLEIPEAIDL GTKTFHAINP DGDTTLEPDE TEGRLTKKDW AKINKDGDQT LELDEYLSLV RARFNAADKN KDGKLTAKEL DSKAGQSLLK LIVKMVSKGE EDNMASLPAT HELHIFGSIN GVDFDMVGQG TGNPNDGYEE LNLKSTKGDL QFSPWILVPH IGYGFHQYLP YPDGMSPFQA AMVDGSGYQV HRTMQFEDGA SLTVNYRYTY EGSHIKGEAQ VKGTGFPADG PVMTNSLTAA DWCRSKKTYP NDKTIISTFK WSYTTGNGKR YRSTARTTYT FAKPMAANYL KNQPMYVFRK TELKHSKTEL NFKEWQKAFT DVMGMDELYK (SEQ ID NO:35). Statement 11. A rare earth element binding protein according to any one of the preceding Statements, wherein the protein is or comprises the following sequence: >Al-LanM(H60A) (also referred to as Al-H60A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:6); >Al-LanM(H60N) (also referred to as Al-H60N) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:7); >Al-LanM(S102T) (also referred to as Al-S102T) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:9); >Al-LanM-GSGCLTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:10); >Al-LanM(S102T)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:11); >TD9 – Al-LanM tandem dimer (42-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VK (SEQ ID NO:28); >TD9-GSGC (also called TD9-Cys-1) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:30); >TD9-12mer-Cys (also called TD9-Cys-2) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:31). Statement 12. A rare earth element binding protein comprising one or more metal-binding or metal-coordination motifs, wherein at least one of the metal-binding or metal coordination motifs has the following sequence: N-X1-D-G-D-X2-T-L-E-X3-X4-E (SEQ ID NO:89), wherein X1is any amino acid, X2is any amino acid, X3is any amino acid, X4is any amino acid, wherein when there is more than one metal-binding or metal-coordination motif, at least one X1is a proline, at least one X4residue in the protein is an aspartate, and X3and / or X4is a proline. Statement 13. A rare earth element binding protein according to Statement 12, wherein at least one of the metal-binding or metal coordination motifs has the following sequence: NKDGDQTLEIPE (SEQ ID NO:90), NPDGDTTLEPDE (SEQ ID NO:91), or NKDGDQTLELDE (SEQ ID NO:92).Statement 14. A rare earth element binding protein according to Statement 12 or Statement 13, wherein the protein is disposed or affixed to the substrate or encapsulated by or in the substrate. Statement 15. A rare earth element binding protein according to Statement 14, wherein the substrate is a bead, a membrane, a hydrogel, a protein-based material, a cell surface, or a porous framework. Statement 16. A rare earth element binding protein according to any one of Statements 12– 15, wherein the protein comprises the following sequence: >Al-LanM LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:4); >Al-LanM(Y100W) (also referred to as Al-Y100W) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EWLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:5); >Al-LanM(H60A) (also referred to as Al-H60A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:6); >Al-LanM(H60N) (also referred to as Al-H60N) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:7); >Al-LanM(S102A) (also referred to as Al-S102A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:8); >Al-LanM(S102T) (also referred to as Al-S102T) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:9); >Al-LanM-GSGC LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:10); >Al-LanM(S102T)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:11); >Al-LanM(H60A)-GSGC (GSGC is SEQ ID NO:62)LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:12); >Al-LanM-12mer-Cys (12mer-Cys underlined) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGHHWGSTG SGC (SEQ ID NO:13); >Xan-LanM GSGC (GSGC is SEQ ID NO:62) LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK GSGC (SEQ ID NO:14); >Al-LanM(H60N)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:36); >Al-LanM(S102A)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:37); >Xan-LanM with native signal peptide (underlined) MKRRMISLGV VAAVSLAATG SAFALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:93); >Al-LanM with native signal peptide (underlined) MTRSLTRLAA AAGLASLVSI GMASSAFALT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVK (SEQ ID NO:94); >Mal-Xan-LanM MKIKTGARIL ALSALTTMMF SASALAMLTG KEFLRKYNKD KDSTVEIVEA IDLGTKVFKA INPDKDKTLE AAETKGRLSD EDWAQFNKDG DKTLELDEWL IIVRKRFNDA DANKDGKLTE AELDAPAGQQ LILLIAK (SEQ ID NO:95); >Mal-Al-LanM MKIKTGARIL ALSALTTMMF SASALALTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:96); >Mal-Al-LanM(Y100W) MKIKTGARIL ALSALTTMMF SASALALTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEWLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:97); >Al-LanM EF2 inactivated 1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAIDKNKDG KLTPNETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:84); >Al-LanM EF2 inactivated 2LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAIDKNKDG KLTPNETEGR LTKKDWAKIN KDGDQSLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:85); >TD1 – Xan-LanM tandem dimer (18-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:20); >TD2 – Xan-LanM tandem dimer (30-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SALTGKEFLR KYNKDKDSTV EIVEAIDLGT KVFKAINPDK DKTLEAAETK GRLSDEDWAQ FNKDGDKTLE LDEWLIIVRK RFNDADANKD GKLTEAELDA PAGQQLILLI AK (SEQ ID NO:21); >TD3 – Xan-LanM tandem dimer (36-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSALT GKEFLRKYNK DKDSTVEIVE AIDLGTKVFK AINPDKDKTL EAAETKGRLS DEDWAQFNKD GDKTLELDEW LIIVRKRFND ADANKDGKLT EAELDAPAGQ QLILLIAK (SEQ ID NO:22); >TD4 – Xan-LanM tandem dimer (42-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:23); >TD5 – Xan-LanM tandem dimer (48-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:24); >TD6 – Xan-LanM tandem dimer (42-aa EAAAK linker) (EAAAK is SEQ ID NO:88) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGSGGSGAEA AAKEAAAKAG GSGGSAEAAA KEAAAKAGSG GSGALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:25); >TD7 – Hans-LanM tandem dimer (42-aa GGS linker) ASGADALKAL NKDNDDSLEI AEVIHAGATT FTAINPDGDT TLESGETKGR LTEKDWARAN KDGDQTLEMD EWLKILRTRF KRADANKDGK LTAAELDSKAGQGVLVMIMK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSASGADALK ALNKDNDDSL EIAEVIHAGA TTFTAINPDG DTTLESGETK GRLTEKDWAR ANKDGDQTLE MDEWLKILRT RFKRADANKD GKLTAAELDS KAGQGVLVMI MK (SEQ ID NO:26); >TD8 – Al-LanM tandem dimer (36-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:27); >TD9 – Al-LanM tandem dimer (42-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VK (SEQ ID NO:28); >TD10 – Al-LanM tandem dimer (48-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVK (SEQ ID NO:29); >TD9-GSGC (also called TD9-Cys-1) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:30); >TD9-12mer-Cys (also called TD9-Cys-2) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:31); >TD9(H60A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:38); >TD9(H60A)-Cys-2LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:39); >TD9(H60N)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFNAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:40); >TD9(S102A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLALVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:41); >TD9(S102T)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLTLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:42); >TD9-FRET1 MVSKGEEDNM ASLPATHELH IFGSINGVDF DMVGQGTGNP NDGYEELNLK STKGDLQFSP WILVPHIGYG FHQYLPYPDG MSPFQAAMVD GSGYQVHRTM QFEDGASLTV NYRYTYEGSH IKGEAQVKGT GFPADGPVMT NSLTAADWCR SKKTYPNDKT IISTFKWSYT TGNGKRYRST ARTTYTFAKP MAANYLKNQP MYVFRKTELK HSKTELNFKE WQKAFTDVMG MDELYKLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVKGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVKMV SKGEAVIKEF MRFKVHMEGS MNGHEFEIEG EGEGRPYEGT QTAKLKVTKG GPLPFSWDIL SPQFMYGSRA FIKHPADIPD YYKQSFPEGF KWERVMNFED GGAVTVTQDT SLEDGTLIYK VKLRGTNFPP DGPVMQKKTM GWEASTERLY PEDGVLKGDI KMALRLKDGG RYLADFKTTY KAKKPVQMPG AYNVDRKLDI TSHNEDYTVV EQYERSEGRH STGGMDELYK (SEQ ID NO:34) or >TD9-FRET2 MVSKGEAVIK EFMRFKVHME GSMNGHEFEI EGEGEGRPYE GTQTAKLKVT KGGPLPFSWD ILSPQFMYGS RAFIKHPADI PDYYKQSFPE GFKWERVMNF EDGGAVTVTQ DTSLEDGTLI YKVKLRGTNF PPDGPVMQKK TMGWEASTER LYPEDGVLKG DIKMALRLKD GGRYLADFKT TYKAKKPVQM PGAYNVDRKLDITSHNEDYT VVEQYERSEG RHSTGGMDEL YKLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSLTGAEF LAQYNKDGDQ TLEIPEAIDL GTKTFHAINP DGDTTLEPDE TEGRLTKKDW AKINKDGDQT LELDEYLSLV RARFNAADKN KDGKLTAKEL DSKAGQSLLK LIVKMVSKGE EDNMASLPAT HELHIFGSIN GVDFDMVGQG TGNPNDGYEE LNLKSTKGDL QFSPWILVPH IGYGFHQYLP YPDGMSPFQA AMVDGSGYQV HRTMQFEDGA SLTVNYRYTY EGSHIKGEAQ VKGTGFPADG PVMTNSLTAA DWCRSKKTYP NDKTIISTFK WSYTTGNGKR YRSTARTTYT FAKPMAANYL KNQPMYVFRK TELKHSKTEL NFKEWQKAFT DVMGMDELYK (SEQ ID NO:35). 17. The rare earth element binding protein according to claim 16, wherein the protein is or comprises the following sequence: >Al-LanM(H60A) (also referred to as Al-H60A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:6); >Al-LanM(H60N) (also referred to as Al-H60N) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:7); >Al-LanM(S102T) (also referred to as Al-S102T) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:9); >Al-LanM-GSGC LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:10); >Al-LanM(S102T)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:11); >TD9 – Al-LanM tandem dimer (42-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VK (SEQ ID NO:28); >TD9-GSGC (also called TD9-Cys-1) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSGGSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:30); >TD9-12mer-Cys (also called TD9-Cys-2) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:31). Statement 18. A rare earth element binding protein having the following structure: Protein1-X-Protein2, wherein X is a linker group and Protein1and Protein2are the same or different. Statement 19. A rare earth element binding protein according to claim 18, wherein Protein1and / or Protein2independently comprise the following sequence: X1-X2-G-X3-X4-X5-L-X6-X7-X8-NKD-X9-D-X10-X11-X12-EI-X13-E-X14-I-X15-X16-G-X17-X18- X19-F-X20-AINPD-X21-D-X22-TLE-X23-X24-ET-X25-GRL-X26-X27-X28-DWA-X29-X30- NKDGD-X31-TLE-X32-DE-X33-L-X34-X35-X36-R-X37-RF-X38-X39-AD-X40-NKDGKLT-X41- X42-ELD-X43-X44-AGQ-X45-X46-X47-X48-X49-I-X50-K (SEQ ID NO:1), wherein X1= any residue; X2= T or S; X3= any residue; X4= E or D; X5= any hydrophobic residue; X6= R, S, K, or A; X7= any residue; X8= any hydrophobic residue; X9= any residue; X10= D, N, S, or Q; X11= S or T; X12= any hydrophobic residue; X13= any residue; X14= any hydrophobic residue; X15= any residue; X16= A, W, or L; X17= S, T, A, Q, or V; X18= Q, D, E, or K; X19= any hydrophobic or polar residue; X20= any residue; X21= K, H, or G; X22= K or T; X23= P, K, A, or S; X24= P, A, N, D, or G; X25= K, N, or E; X26= S or T; X27= D, E, P, A, or K; X28= any residue; X29= any residue; X30= any hydrophobic residue; X31= K, Q, or E; X32= any hydrophobic residue; X33= F, W, or Y; X34= S, A, or T; X35= any hydrophobic residue; X36= any hydrophobic residue; X37= any residue; X38= E, K, A, or N; X39= any residue; X40= K, A, or P; X41= A, V, or E; X42= K, A, Q, or E; X43= A, S, or T; X44= K, P, E, or A; X45= any residue; X46= any hydrophobic residue; X47= any hydrophobic residue; X48= K, V, or L; X49= any hydrophobic residue; X50= any hydrophobic residue. Statement 20. A rare earth element binding protein according to Statement 19, wherein X1= L; X3= A or K; X5= V, I, A, Y, or F; X6= R, S, K, or A; X7= Q; X8= V, I, A, or Y; X9= G; X12= V, I, F, or L; X13= P; X14= V, I, or A; X15= D; X19= L, V, M, or T; X20= H; X28= K; X29= K; X30= V, I, A, or L; X32= V, I, M, or L; X35= V, I, or L; X36= L, A, or V;X37= A; X39= A; X45= S; X46= V, F, or L; X47= V, I, or L; X49= V, M, or L; and / or X50= A, M, or V. Statement 21. A rare earth element binding protein according to any one of Statements 18– 20, wherein the protein is disposed or affixed to the substrate or encapsulated by or in the substrate. Statement 22. A rare earth element binding protein according to Statement 21, wherein the substrate is a bead, a membrane, a hydrogel, a protein-based material, a cell surface, or a porous framework. Statement 23. A rare earth element binding protein according to any one of Statements 18– 22, wherein the linker group is a peptide. Statement 24. A rare earth element binding protein according to any one of Statements 18– 23, wherein the linker group has the following sequence: GGSGGSGGSGGSGGSGGS (SEQ ID NO:15), GGSGGSGGSGGSGGSGGSGGSGGSGGSGG (SEQ ID NO:16), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:17), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:18), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:19), or GSGGSGAEAAAKEAAAKAGGSGGSAEAAAKEAAAKAGSGGSG (SEQ ID NO:20). Statement 25. A rare earth element binding protein according to any one of Statements 18– 24, wherein the protein comprises or has the following sequence: >TD1 – Xan-LanM tandem dimer (18-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:20); >TD2 – Xan-LanM tandem dimer (30-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SALTGKEFLR KYNKDKDSTV EIVEAIDLGT KVFKAINPDK DKTLEAAETK GRLSDEDWAQ FNKDGDKTLE LDEWLIIVRK RFNDADANKD GKLTEAELDA PAGQQLILLI AK (SEQ ID NO:21); >TD3 – Xan-LanM tandem dimer (36-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAPAGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSALT GKEFLRKYNK DKDSTVEIVE AIDLGTKVFK AINPDKDKTL EAAETKGRLS DEDWAQFNKD GDKTLELDEW LIIVRKRFND ADANKDGKLT EAELDAPAGQ QLILLIAK (SEQ ID NO:22); >TD4 – Xan-LanM tandem dimer (42-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:23); >TD5 – Xan-LanM tandem dimer (48-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:24); >TD6 – Xan-LanM tandem dimer (42-aa EAAAK linker) (EAAAK is SEQ ID NO:88) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGSGGSGAEA AAKEAAAKAG GSGGSAEAAA KEAAAKAGSG GSGALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:25); >TD7 – Hans-LanM tandem dimer (42-aa GGS linker) ASGADALKAL NKDNDDSLEI AEVIHAGATT FTAINPDGDT TLESGETKGR LTEKDWARAN KDGDQTLEMD EWLKILRTRF KRADANKDGK LTAAELDSKA GQGVLVMIMK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSASGADALK ALNKDNDDSL EIAEVIHAGA TTFTAINPDG DTTLESGETK GRLTEKDWAR ANKDGDQTLE MDEWLKILRT RFKRADANKD GKLTAAELDS KAGQGVLVMI MK (SEQ ID NO:26); >TD8 – Al-LanM tandem dimer (36-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:27); >TD9 – Al-LanM tandem dimer (42-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VK (SEQ ID NO:28); >TD10 – Al-LanM tandem dimer (48-aa GGS linker)LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVK (SEQ ID NO:29); >TD9-GSGC (also called TD9-Cys-1) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:30); >TD9-12mer-Cys (also called TD9-Cys-2) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:31); >TD9(H60A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:38); >TD9(H60A)-Cys-2 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:39); >TD9(H60N)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFNAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:40); >TD9(S102A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETEGRLTKKDWAK INKDGDQTLE LDEYLALVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:41); or >TD9(S102T)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLTLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:42). Statement 26. A rare earth element binding protein, wherein the rare earth element binding protein comprises or has the following sequence: LTGAEFLAQYNKDGDQTLEIPEAIDLGTKTFHAINPDGDTTLEPDETEGRLTKKDWA KINKDGDQTLELDEYLSLVRARFNAADKNKDGKLTAKELDSKAGQSLLKLIVK (SEQ ID NO:4), or a sequence having at least 80%, at least 81%, at least 82%, at least 83%, at least 84%, at least 85%, at least 86%, at least 87%, at least 88%, at least 89%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or least 99% identity thereto, wherein when the rare earth element binding protein is SEQ ID NO:4, the rare earth element binding protein disposed or affixed to a substrate or encapsulated by or in the substrate, and the rare earth element binding protein is not LTGKEFLRKYNKDKDSTVEIVEAIDLGTKVFKAINPDKDKTLEAAETKGRLSDEDWAID NO:3) or ASGADALKALNKDNDDSLEIAEVIHAGATTFTAINPDGDTTLESGETKGRLTEKDWA RANKDGDQTLEMDEWLKILRTRFKRADANKDGKLTAAELDSKAGQGVLVMIMK (SEQ ID NO:100). Statement 27. A rare earth element binding protein according to Statement 26, wherein the protein is disposed or affixed to the substrate or encapsulated by or in the substrate. Statement 28. A rare earth element binding protein according to Statement 26 or Statement 27, wherein the substrate is a bead, a membrane, a hydrogel, a protein-based material, a cell surface, or a porous framework. Statement 29. A rare earth element binding protein according to any one of Statements 26– 28, wherein the protein further comprises a linker group. Statement 30. A rare earth element binding protein according to Statement 29, wherein the linker group is conjugated to a protein, wherein the protein is or comprises SEQ ID NO:1.Statement 31. A rare earth element binding protein according to Statement 29 or Statement 30, wherein the linker group is a peptide. Statement 32. A rare earth element binding protein according to any one of Statements 29– 31, wherein the linker group has the following sequence: GGSGGSGGSGGSGGSGGS (SEQ ID NO:15), GGSGGSGGSGGSGGSGGSGGSGGSGGSGG (SEQ ID NO:16), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:17), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:18), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:19), or GSGGSGAEAAAKEAAAKAGGSGGSAEAAAKEAAAKAGSGGSG (SEQ ID NO:20). Statement 33. A rare earth element binding protein according to any one of Statements 26– 32, further comprising a fluorescence resonance energy transfer pair. Statement 34. A rare earth element binding protein according to any one of Statements 26– 33, wherein the protein comprises or has the following sequence: >Al-LanM LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:4); >Al-LanM(Y100W) (also referred to as Al-Y100W) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EWLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:5); >Al-LanM(H60A) (also referred to as Al-H60A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:6); >Al-LanM(H60N) (also referred to as Al-H60N) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:7); >Al-LanM(S102A) (also referred to as Al-S102A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:8); >Al-LanM(S102T) (also referred to as Al-S102T) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:9);>Al-LanM-GSGC LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:10); >Al-LanM(S102T)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:11); >Al-LanM(H60A)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:12); >Al-LanM-12mer-Cys (12mer-Cys underlined) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGHHWGSTG SGC (SEQ ID NO:13); >Xan-LanM GSGC (GSGC is SEQ ID NO:62) LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK GSGC (SEQ ID NO:14); >Al-LanM(H60N)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:36); >Al-LanM(S102A)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:37); >Xan-LanM with native signal peptide (underlined) MKRRMISLGV VAAVSLAATG SAFALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:93); >Al-LanM with native signal peptide (underlined) MTRSLTRLAA AAGLASLVSI GMASSAFALT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVK (SEQ ID NO:94); >Mal-Xan-LanM MKIKTGARIL ALSALTTMMF SASALAMLTG KEFLRKYNKD KDSTVEIVEA IDLGTKVFKA INPDKDKTLE AAETKGRLSD EDWAQFNKDG DKTLELDEWL IIVRKRFNDA DANKDGKLTE AELDAPAGQQ LILLIAK (SEQ ID NO:95); >Mal-Al-LanM MKIKTGARIL ALSALTTMMF SASALALTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:96); >Mal-Al-LanM(Y100W)MKIKTGARIL ALSALTTMMF SASALALTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEWLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:97); >Al-LanM EF2 inactivated 1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAIDKNKDG KLTPNETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:84); >Al-LanM EF2 inactivated 2 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAIDKNKDG KLTPNETEGR LTKKDWAKIN KDGDQSLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:85); >TD1 – Xan-LanM tandem dimer (18-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:20); >TD2 – Xan-LanM tandem dimer (30-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SALTGKEFLR KYNKDKDSTV EIVEAIDLGT KVFKAINPDK DKTLEAAETK GRLSDEDWAQ FNKDGDKTLE LDEWLIIVRK RFNDADANKD GKLTEAELDA PAGQQLILLI AK (SEQ ID NO:21); >TD3 – Xan-LanM tandem dimer (36-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSALT GKEFLRKYNK DKDSTVEIVE AIDLGTKVFK AINPDKDKTL EAAETKGRLS DEDWAQFNKD GDKTLELDEW LIIVRKRFND ADANKDGKLT EAELDAPAGQ QLILLIAK (SEQ ID NO:22); >TD4 – Xan-LanM tandem dimer (42-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:23); >TD5 – Xan-LanM tandem dimer (48-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:24); >TD6 – Xan-LanM tandem dimer (42-aa EAAAK linker) (EAAAK is SEQ ID NO:88)ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGSGGSGAEA AAKEAAAKAG GSGGSAEAAA KEAAAKAGSG GSGALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:25); >TD7 – Hans-LanM tandem dimer (42-aa GGS linker) ASGADALKAL NKDNDDSLEI AEVIHAGATT FTAINPDGDT TLESGETKGR LTEKDWARAN KDGDQTLEMD EWLKILRTRF KRADANKDGK LTAAELDSKA GQGVLVMIMK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSASGADALK ALNKDNDDSL EIAEVIHAGA TTFTAINPDG DTTLESGETK GRLTEKDWAR ANKDGDQTLE MDEWLKILRT RFKRADANKD GKLTAAELDS KAGQGVLVMI MK (SEQ ID NO:26); >TD8 – Al-LanM tandem dimer (36-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:27); >TD9 – Al-LanM tandem dimer (42-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VK (SEQ ID NO:28); >TD10 – Al-LanM tandem dimer (48-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVK (SEQ ID NO:29); >TD9-GSGC (also called TD9-Cys-1) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:30); >TD9-12mer-Cys (also called TD9-Cys-2) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETEGRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:31); >TD9(H60A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:38); >TD9(H60A)-Cys-2 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:39); >TD9(H60N)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFNAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:40); >TD9(S102A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLALVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:41); >TD9(S102T)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLTLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:42); >TD9-FRET1 MVSKGEEDNM ASLPATHELH IFGSINGVDF DMVGQGTGNP NDGYEELNLK STKGDLQFSP WILVPHIGYG FHQYLPYPDG MSPFQAAMVD GSGYQVHRTM QFEDGASLTV NYRYTYEGSH IKGEAQVKGT GFPADGPVMT NSLTAADWCR SKKTYPNDKT IISTFKWSYT TGNGKRYRST ARTTYTFAKP MAANYLKNQP MYVFRKTELK HSKTELNFKE WQKAFTDVMG MDELYKLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVKGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVKMVSKGEAVIKEF MRFKVHMEGS MNGHEFEIEG EGEGRPYEGT QTAKLKVTKG GPLPFSWDIL SPQFMYGSRA FIKHPADIPD YYKQSFPEGF KWERVMNFED GGAVTVTQDT SLEDGTLIYK VKLRGTNFPP DGPVMQKKTM GWEASTERLY PEDGVLKGDI KMALRLKDGG RYLADFKTTY KAKKPVQMPG AYNVDRKLDI TSHNEDYTVV EQYERSEGRH STGGMDELYK (SEQ ID NO:34) or >TD9-FRET2 MVSKGEAVIK EFMRFKVHME GSMNGHEFEI EGEGEGRPYE GTQTAKLKVT KGGPLPFSWD ILSPQFMYGS RAFIKHPADI PDYYKQSFPE GFKWERVMNF EDGGAVTVTQ DTSLEDGTLI YKVKLRGTNF PPDGPVMQKK TMGWEASTER LYPEDGVLKG DIKMALRLKD GGRYLADFKT TYKAKKPVQM PGAYNVDRKL DITSHNEDYT VVEQYERSEG RHSTGGMDEL YKLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSLTGAEF LAQYNKDGDQ TLEIPEAIDL GTKTFHAINP DGDTTLEPDE TEGRLTKKDW AKINKDGDQT LELDEYLSLV RARFNAADKN KDGKLTAKEL DSKAGQSLLK LIVKMVSKGE EDNMASLPAT HELHIFGSIN GVDFDMVGQG TGNPNDGYEE LNLKSTKGDL QFSPWILVPH IGYGFHQYLP YPDGMSPFQA AMVDGSGYQV HRTMQFEDGA SLTVNYRYTY EGSHIKGEAQ VKGTGFPADG PVMTNSLTAA DWCRSKKTYP NDKTIISTFK WSYTTGNGKR YRSTARTTYT FAKPMAANYL KNQPMYVFRK TELKHSKTEL NFKEWQKAFT DVMGMDELYK (SEQ ID NO:35). Statement 35. A rare earth element binding protein according to any one of Statements 26– 334, wherein the protein is or comprises the following sequence: >Al-LanM(H60A) (also referred to as Al-H60A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:6); >Al-LanM(H60N) (also referred to as Al-H60N) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:7); >Al-LanM(S102T) (also referred to as Al-S102T) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:9); >Al-LanM-GSGC LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:10); >Al-LanM(S102T)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:11); >TD9 – Al-LanM tandem dimer (42-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKAGQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VK (SEQ ID NO:28); >TD9-GSGC (also called TD9-Cys-1) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:30); >TD9-12mer-Cys (also called TD9-Cys-2) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:31). Statement 36. A device comprising the rare earth element binding protein according to any one of the preceding Statements. Statement 37. A device according to Statement 36, wherein the device is a filter, membrane, sensor, handheld detector, plate reader, fluorimeter, biosensor, or in-line monitor. Statement 38. A kit comprising the rare earth element binding protein according to any one of Statements 1–35 or materials to prepare a device comprising the rare earth element binding protein according to any one of Statements 1–35. Statement 39. A method for rare earth element ions to a protein comprising contacting one or more rare earth element binding protein according to any one of Statements 1–35 with a sample comprising or suspected of comprising rare earth element ions and one or more of the rare earth element ions binds to the one or more rare earth element binding protein according to any one of Statements 1–35. Statement 40. A method according to Statement 39, wherein the rare earth element ions are chosen from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, Ac, Th, U, Np, Pu, Am, Cm, Bk, Cf, and Es, and any combination thereof. Statement 41. A method according to Statement 39 or Statement 40, wherein the sample is drinking water, wastewater, ground water, process water, ash ponds, aqueous extract from contaminated soil, drainage, leachate, aqueous extract or leachate from a solid waste, or a solid sample.Statement 42. A method according to any one of Statements 39–41, further comprising isolating the one or more rare earth element binding proteins having one or more rare earth element ions bound thereto. Statement 43. A method according to Statement 42, wherein the one or more rare earth element ions are separated individually from the one or more rare earth element binding proteins.

[0101] The following examples are presented to illustrate the present disclosure. They are not intended to be limiting in any matter. EXAMPLE 1

[0102] This example provides a description of proteins and peptides of the present disclosure and uses thereof.

[0103] Biomolecular recovery, detection, and separation of rare earth elements (REs) has accelerated since the discovery of the lanmodulin (LanM) proteins. While exceptional at total RE recovery, prior LanMs, like most ligands, exhibited limited ability to differentiate REs, for both detection and separation applications. Described are dimerizing LanMs (Al- LanM from Ancylobacter lacus and Xan-LanM from Xanthobacter flavus) that address these two major challenges in RE research. First, these proteins’ abilities to sensitize luminescence of specific REs enable their use as biosensors for the valuable heavy RE, terbium, in addition to other, specific REs. Furthermore, Al-LanM’s separation factors (SFs) far outperform prior LanMs, e.g., SF(Nd / Lu) >1200 vs. <100 for prior LanMs, and Al-LanM’s SFs were improved through structure-guided mutagenesis. Over the range of 11 elements between Nd and Lu, Al- LanM’s average SF for adjacent REs is 2.1, whereas SFs for many small-molecule separation systems are <2 even when aided by competing ligands. Immobilized Al-LanM performs high- purity separations of Nd / Dy and even challenging near-adjacent Gd / Dy (98% Gd, 92% Dy purity) with just a single pH step. However, Al-LanM’s SFs in solution are even higher, establishing that dimerization amplifies RE discrimination.

[0104] Greater apoprotein helicity and inter-RE affinity differences in Al-LanM. It was initially sought to develop a LanM ortholog that could sensitize the intrinsic luminescence of multiple individual lanthanide ions. Proteins with >50% sequence identity to Hans-LanM were identified as promising candidates for two reasons:, (1) in proteins with EF hands similar to Hans-LanM’s, which feature Asn in the first position and Glu in the ninth position and have been shown to possess no coordinated solvent molecules, the bound LnIIIions are predicted to have no solvent molecules in the first coordination sphere, which should enhance luminescence lifetimes by minimizing solvent-based quenching, and (2) proteins similar to Hans-LanM may share its native tryptophan residue(s) near EF hands 2 and 3, which could serve as luminescence sensitizers. Furthermore, these proteins featured conservation of the pattern of residues (Arg100 and three carboxylates in EF-hand 3) forming the interfacial hydrogen-bonding network associated with RE-sensitive dimerization in Hans- LanM.

[0105] Xan-LanM (59% sequence identity with Hans-LanM) was expressed recombinantly in E. coli without a signal sequence and found predominantly localized in the cell pellet. Purification of the protein from inclusion bodies gave similar yields to previously characterized LanMs. Despite favorable in-vitro sensing performance (vide infra), Xan- LanM’s low in-cell solubility spurred identification of Al-LanM, a highly soluble ortholog sharing 69% sequence identity with Xan-LanM and 65% sequence identity with Hans-LanM (Figure 1A).

[0106] Analytical size-exclusion chromatography (SEC) was used to investigate the tertiary and quaternary structures of Al-LanM (Figure 1B) and Xan-LanM (Figure 5). Previous work has shown that the apo forms of Mex- and Hans-LanMs migrate at anomalously large apparent molecular weights (MWs), indicative of substantial disorder. Whereas both Xan- and Al-LanMs eluted at slightly higher apparent MWs (14 and 19 kDa, respectively) than the ~12 kDa expected for a monomer, these values are smaller than for the previously characterized LanMs, suggesting more ordered (yet still partly disordered) apoproteins. In the presence of 5 mM CaII, Al-LanM’s apparent MW decreased to 16 kDa, suggesting a more globular monomeric structure. Upon binding with LaIII, NdIII, and DyIIIions, however, Al- and Xan-LanMs eluted at apparent MWs of ~30 kDa, consistent with dimerization. This result differs from Hans-LanM, which dimerizes tightly with LaIII(dimerization Kd, Kdimer <0.4 μM) but not with DyIII(Kdimer = 60 μM) under similar conditions.

[0107] Circular dichroism (CD) spectroscopy has been employed to measure the changes in secondary structure, particularly a large increase in α-helical content, associated with LnIIIion binding in Mex- and Hans-LanMs. The CD spectra of Al-LanM (Figure 1C, Figure 6) and Xan-LanM (Figure 7) showed only minor changes between apo- and TbIII- bound states, indicating that the apoproteins contain α-helical structure at room temperature. This secondary structure of the apoprotein can be disrupted by increasing temperature (Figure 8). The CD results are consistent with the SEC data indicating greater order for theapoproteins relative to previously characterized LanMs. However, the SEC studies above also showed that CaIIbinding partially compacts the protein structure relative to the apo state, whereas Trp fluorescence studies below show that CaII- and LnIII-bound structures are distinct. Together, these data indicate that, while more ordered than the archetypal LanMs, apo-Al-LanM must still be disordered relative to the LnIII-bound state.

[0108] Because metal binding yields minimal changes in the CD signal, metal- dependent changes in intrinsic fluorescence of a Trp residue (W84 in Al-LanM, Figure 9) in the vicinity of EF-hands 2 and 3 were instead followed to determine apparent dissociation constants (Kd,app) for REs for these EF hands. A similar response is seen in Hans-LanM and yields similar Kd,appto CD experiments (Figure 10). It is noted that this method does not necessarily report on EF1, which is distant from W84, but stoichiometric titration followed by direct excitation of EuIIIluminescence indicates binding of ~3 equiv. (presumably EF1-3) at pH 5.0 (Figure 11). The overall trend in Kd,app values for both Xan- and Al-LanMs is similar to that of Hans-LanM, but 4- to 10-fold tighter (Figure 1D, Tables 1-2, Figure 12- 13). Their Kd,app values also exhibited steeper dependence on radius (greater intra-RE selectivity) than Hans-LanM, which itself was greater than Mex-LanM. The only exception is for the Tb / Dy pair of Hans-LanM, which likely reflects the protein concentration being on the order of Kdimer for DyIII. In the case of Al-LanM, studies at 10-fold higher protein concentration (20 μM) yielded similar Kd,appvalues for GdIIIand DyIII, suggesting that Kdimer<2 μM even for these HREs, >30-fold tighter than Hans-LanM (Table 1, Figure 14). Notably, at pH 7.0, the trend in Kd,appvalues among the LREs (La-Pr) is different than at pH 5.0 (Figure 1D, Table 3). Although a Kd,app for Ce (and Eu) was not determined due to photoelectron-based Trp fluorescence quenching, the equivalence of La and Pr Kd,appvalues means that Ce should bind equally tightly or tighter than those metals; either way this represents a selectivity plateau shifted to lighter REs (around Ce) relative to selectivity at pH 5.0 (around Pr), and relative to the prototypal Mex-LanM (around Nd-Sm). Al-LanM’s 5-fold selectivity for DyIIIover YIII, which have nearly identical ionic radii, was notable relative to Mex-LanM and many small-molecule chelators. The protein also exhibits weaker response to CaII(Kd,app>5 mM) than Hans-LanM (60 μM) and even Mex-LanM (1.4 mM) (Table 1, Figure 15). Overall, Al-LanM exhibits tighter RE binding and dimerization than Hans-LanM, greater RE / CaIIselectivity, and greater intra-RE selectivity in (at least) the Pr-Tb range than previously characterized LanMs, presaging better separation performance (vide infra).

[0109] Sensing of six luminescent REs in vitro. The presence of two Trp residues and a coordination sphere saturated with protein residues (q ~0; no coordinated watermolecules to vibrationally quench the luminescence signal) in Hans-LanM suggested that this protein and perhaps other dimerizing LanMs might be especially robust sensitizers for lanthanides. Therefore, the luminescence signals of Tb (the lanthanide with generally the longest luminescence lifetime) was compared for Hans-, Xan-, and Al-LanMs with Mex- LanM T90W (hereafter, Mex-T90W), which has been shown to sensitize Tb luminescence well enough to detect Tb directly in acid mine drainage (AMD) at pH 3.3. All sensors sensitized Tb via excitation of Trp at 280 nm, displaying distinctive emission bands including the maximum at 545 nm (Figure 2A). Mex-T90W produced the weakest signal due to quenching effects from water molecules in its first coordination sphere (q = 1.4). Hans- and Xan-LanM, which both contain two intrinsic Trp residues, exhibited the strongest luminescence (Figure 16C, 17C). Al-LanM, in which one of the Trp residues present in the other two dimerizing LanMs is replaced by a Tyr residue (Y100), demonstrated slightly lower intensity. This observation led to positing that replacing Y100 with Trp in Al-LanM would increase emission intensity; indeed, Al-Y100W showed a ~35% higher intensity than the wild-type Al-LanM, matching that of Hans-LanM (Figure 2A). This substitution had little effect on binding affinity (Figure 18, Table 4). Expanding the analysis to metal ions with shorter lifetimes that are more sensitive to water coordination— Sm, Eu, and Dy—the expected distinct emission bands were observed using the same Trp excitation: 560, 600, and 640 nm for Sm; 590 and 620 nm for Eu; and 575 nm for Dy, using Hans-LanM, Xan-LanM, Al-LanM, and Al-Y100W (Figure 19). Mex-T90W was only able to sensitize Eu luminescence, underscoring the necessity of excluding water molecules from the first coordination sphere in sensor development.

[0110] The luminescence signals can be used to report on the stability of metal- protein complexes at a range of pH values. Al-LanM bound with Tb displayed high luminescence from pH 3.3 to 7.0, yet it still maintained considerable intensity at pH 3.0 (Figure 2B). By contrast, the luminescence of Tb-bound Hans-LanM and Mex-T90W decreased sharply below pH 5.0 and 4.0, respectively, and were completely quenched at pH 3.0 (Figure 16C, 20C). Al-LanM detected Sm, Eu, Tb, and Dy at pH 3.0, whereas Mex- T90W and Hans-LanM were restricted to Eu and Sm detection, respectively (Figures 16, 20, 21). The exceptional stability of Al-LanM’s luminescence signals under acidic conditions likely reflects both a strong binding affinity and a low hydration number (q = 0.25) (Figure 22).

[0111] Unlike wt Al-LanM, Y100W exhibits a reduction in fluorescence intensity above pH 5.5 for the HREs, Tb and Dy, but not LREs, Sm and Eu (Figure 2C, Figure 23).Coupled with the similar stability of the wt- and Y100W forms of Al-LanM (Figure 18), the pH-dependent differences in luminescence at high pH might suggest that the native W84 may primarily be reporting on EF3 while W100, adjacent to EF2, reports on that EF hand, an observation that may be useful in selectively probing metal occupancy in individual EF hands. Furthermore, this pattern suggests that HRE binding to EF2 specifically is compromised (or, more likely, the conformation of the loop is altered) at elevated pH.

[0112] Additionally, the ability of a representative subset of these proteins to sensitize two near-infrared (NIR)-emitting lanthanide ions, NdIIIand YbIII, was investigated. Hans- LanM (R100K) (hereafter, Hans-R100K, see Figure 24 for more information) and Xan- LanM were able to sensitize Nd and Yb above pH 4.0, whereas the performance of Mex- T90W was much weaker (Figure 25-26). At pH 3.0, only Xan-LanM maintained significant intensity for Nd (Figure 27-28). None of the sensors sensitized Yb at pH 3.0, likely due to relatively weak binding of the heaviest REs (Figure 1D). Similar to the findings with the visible-emitting lanthanides, where Xan-LanM exhibited the brightest signal, it is anticipated that Al-LanM and Al-Y100W would also effectively sensitize Nd and Yb. Therefore, dimerizing LanM proteins such as Xan-LanM can sensitize luminescence of six individual visible- and NIR-emitting lanthanides down to pH 4.0.

[0113] The stronger performance of Al-LanM and Al-Y100W than Mex-T90W led to the testing of the ability of the Al-Y100W sensor to quantify lanthanide ions in AMD. The source used had pH 3.27, 2.93 ppb (0.02 μM) Tb, 3.56 ppb (0.02 µM) Eu, 18.9 ppb (0.12 µM) Dy, and 300 ppm non-REs, such as Mg, Al, and Mn. We compared the performance of Al-Y100W side to side with that of Mex-T90W, using 10 µM of each protein. The proteins’ responses were calibrated by spiking the AMD with 0–25 ppb Tb and determining the regression line (Figure 2D), from which the Tb concentration was calculated. Compared to Mex-T90W, the slope of the calibration curve for Al-Y100W was ~20 times higher, reflecting the much stronger luminescence signal from tighter binding and exclusion of water. Both sensors gave values similar to the Tb concentration determined by ICP-MS (2.93 ppb), but Al-Y100W’s (2.76 ± 0.20 ppb vs.6.21 ± 1.04 ppb for Mex-T90W) yielded better agreement and smaller uncertainty, in line with its higher signal-to-noise. Efforts to detect Eu and Dy in this solution were unsuccessful because of interference from the strong Tb signal. Overall, Al-LanM(Y100W) improved performance of LanM-based Tb sensing by 20-fold.

[0114] Sensing RE uptake in E. coli. Aiming to sense individual REs in both the cytosol and periplasm of cells, we initially assessed the localization of our LanM sensor constructs in E. coli. For periplasmic localization, the proteins were expressed fused to asignal sequence derived from the maltose binding protein, which was omitted for cytosolic localization. A vector encoding a random sequence of 100 amino acids was used as control. A 30-min incubation with Tb at room temperature was sufficient to achieve signal saturation, and sensor compartmentalization in vivo was verified by SDS-PAGE analysis (Figure 29).

[0115] The periplasmic LanMs effectively sensitized the luminescence of externally added Tb in a concentration-dependent manner (Figure 2E, Figure 30). Al-LanM and Al- Y100W were the most effective in detecting Tb, with Al-Y100W producing the strongest luminescence signal, >25-fold higher than the control. The sensor was saturated at 5 µM Tb added and even showed a clear response to 1 µM Tb, the lowest concentration tested (Figure 2E). Contrary to the in vitro results, signals from Mex-T90W and Hans-LanM in the cell were much lower, likely due to their lower affinities for Tb than Al-LanM. Despite its promising in vitro performance, Xan-LanM displayed little difference from the vector control, consistent with its poor solubility upon overexpression (vide supra, Figure 31). Thus, although Al-LanM is a slightly weaker sensitizer of TbIIIthan Xan-LanM, its superior solubility during expression is advantageous overall in E. coli studies.

[0116] The periplasmic Al-LanM-based sensors, especially Al-Y100W, sensitized both Eu and Dy (Figure 32-33). Despite having ~40 times longer luminescence lifetimes to Dy (for the fully aquated complex), the Eu signal was only ~2-fold above background, whereas the Dy signal was ~40-fold above background. This surprising result deserves further investigation.

[0117] When Al-LanM was employed as a cytosolic sensor in E. coli, little difference in Eu and Tb luminescence intensity was observed compared to the vector control (Figure 2F, Figure 34). This result suggests minimal or no cytosolic uptake of Tb and Eu under these conditions. It was concluded that Tb and Eu can enter the E. coli periplasm even at low micromolar extracellular concentrations, but uptake into the cytosol is poor.

[0118] Dimerization-dependent separation factors in Al-LanM. Given Al-LanM’s large Kd,appdifference among REs, its capacity for intra-RE separation was examined. We first employed a spin-concentrator system to separate REs bound to Al-LanM from unbound REs (Figure 35). The metal contents of the retentate and filtrate were measured by ICP-MS, from which distribution coefficients (DM) and separation factors (SFM1 / M2) were calculated.

[0119] Separation efficiency was optimized by assessing the impact of metal stoichiometry, protein concentrations, and pH on SFs. pH-dependent luminescence results (Figure 2B) had suggested a large difference in apparent Kds for Al-LanM’s LRE and HRE complexes at pH 3.0–3.7 and pH 6.0–7.0. Using Eu and Dy luminescence, it was determinedthat a ratio of 2:2:1 RE1:RE2:protein was optimal for in-solution HRE / LRE separation (Figure 36). Separation of RE pairs with 2 µM and 10 μM protein concentrations were tested at pH 3.0, 3.3, and 7.0, showing that 10 µM protein and pH 3.3 are optimal for suppressing HRE binding while retaining strong LRE binding (Figure 37, Table 5-6). Under the optimized conditions, SFNd / Dy was 38.4 ± 0.5 and SFDy / Lu was 32.4 ± 0.6, totaling SFNd / Lu ~1200 (Figure 3A,B, Figure 38 for data on other RE pairs). These values far outperform previously characterized, column-immobilized Mex-LanM (SFNd / Lu = 45) and other dimerizing LanMs in solution (SFNd / Dy6.1 ± 1.5 for Hans-LanM, 18.1 ± 0.8 for Xan-LanM) (Table 7) and even some industrial chelators (Table 8).

[0120] There are only 22 residues in Al-LanM that differ from either Hans-LanM or Xan-LanM (Figure 1A, Figure 39), making Al-LanM’s much stronger separation performance particularly surprising. In order to obtain insight into the importance of these variations for Al-LanM’s better separations, the structure of the protein in complex with NdIIIwas determined, to 0.99 Å resolution. Overall, the structure is very similar to that of LaIII- Hans-LanM (RMSD 0.564 Å), with 10-coordinate NdIIIbound to EF1-EF3, a CaIIion instead of NaIin EF4, and interfacial hydrogen-bonding networks between the D3, E9, and D11 residues of EF3 (Asp90, Glu96, and Asp98) of one protomer and Arg105 (analogous to critical Arg100 in Hans-LanM) of the other (Figure 45). Two salient, unique features of the Al-LanM structure were probed further.

[0121] First, His60 is part of a water-mediated hydrogen-bonding network that links the EF2s of each protomer (Figure 4C). Because the structure change at pH~6 evident in luminescence studies of Y100W (near EF2) (Figure 2B) aligns with a typical histidine pKa, it was hypothesized that protonation of this residue might be associated with this effect. This residue was substituted with Ala (H60A) or Asn (H60N), the latter of which might be able to retain hydrogen bonding. Interestingly, both substitutions increased affinity by ~2-fold for LaIIIand slightly less for DyIII, compared to WT, at pH 7.0 (Table 3); the LaIII-H60N Kd,app of 300 fM is the tightest achieved to date with a LanM, by an order of magnitude. Both variants muted the wild-type’s pH-dependent luminescence profile around pH 7 (Figure 42), indicating the potential involvement of His60 protonation in disrupting the HRE complexes at circumneutral pH. Finally, both variants showed ~25% higher in-solution SFs for Nd / Dy and 10% higher for Dy / Lu at pH 3.3 (Figure 3A,B, Table 9).

[0122] Second, Al-LanM features an intrahelical hydrogen bond between the sidechain of Ser102 and the backbone carbonyl of Glu99, the final (E12) coordinating residue in EF3 (Figure 3D). Typically, i→i–3 hydrogen bonding bends the downstream α-helix and,in this case, may affect the position of Arg105. It is postulated that small RE-dependent differences in Glu99 position could be tied to S102 and R105 orientation and therefore to the dimer interface. Therefore, S102 was substituted with Ala (S102A) to remove the hydrogen bond, predicted to decrease selectivity, and with a more conservative Thr (S102T). The S102A variant exhibited a ~40% reduction in binding affinity for both LaIIIand DyIII, whereas S102T showed no significant change in affinity, relative to the WT (Table 3). Neither variant significantly affected Nd / Dy and Dy / Lu separations in solution (Table 9). These studies suggest that the S102 locus similarly impacts both LREs and HREs, whereas H60 variants differentially affect LREs and HREs.

[0123] The strong separation performance in solution prompted us to immobilize Al- LanMs both for scalability and comparison to previous work. The proteins were conjugated to maleimide-functionalized agarose beads and packed into a column, analogously to previous work. Wild-type Al-LanM immobilized to comparable density as prior LanMs and exhibited slightly higher binding stoichiometry at pH 3.0, 2.6 equiv. Nd, compared to 2.3 equiv. for Mex-LanM and 2.1 equiv. for Hans-R100K. A 0.6-mL column was equilibrated with binary solutions of Nd / Dy and Dy / Lu to characterize D and SF values of immobilized Al-LanM, its variants, and Xan-LanM. Under these conditions, the on-column SF of Al-LanM for Nd / Dy was 14.7 ± 2.9, nearly 3-fold lower than in solution (Figure 4A). This reduction upon immobilization was also observed for the Al-LanM variants and Xan-LanM. Notably, although the H60A variant showed an increased SF for Nd / Dy in solution, this enhancement was not retained on-column. By contrast, the S102T variant displayed an on-column SF of 18.5 ± 1.7, a 25% increase relative to the wild-type protein. Al-LanM also exhibited an on- column SF of 47.3 ± 6.3 for Dy / Lu, which was higher (p value = 0.051) than its in-solution SF; however, the H60A and S102T variants showed on-column SFs comparable to in- solution values (Figure 4B).

[0124] It is hypothesized that the higher SFs in solution for Nd / Dy but not Dy / Lu reflected dimers being able to form selectively with Nd in solution but not on column, where immobilization forces the protein to be monomeric. Experiments at pH 7 had shown that Al- LanM is a tight dimer for all investigated REs (Figure 1B), so dimerization was investigated at the pH 3.3 condition used for optimal in-solution separations. SEC-MALS analyses performed on apo-, Nd-, and Dy-Al-LanM yielded molecular weights of 11, 20, and 13 kDa, respectively (Figure 4E), indicating that Nd-Al-LanM predominantly exists as a dimer, whereas Dy- and apo-Al-LanM remain largely monomeric. In a parallel experiment, luminescence confirmed that a significant amount of Tb was retained by Al-LanM underthese conditions (Figure 43). It was concluded that the ~3-fold and 4-fold enhancements of Nd / Dy SFs by wt- and H60X Al-LanMs in solution arise from the proteins’ ability to dimerize selectively in the presence of LREs, whereas Dy / Lu separations are only minimally affected, or perhaps slightly enhanced, by immobilization because dimerization is unfavorable for both Dy- and Lu-bound protein even in solution.

[0125] One-step separation of near-adjacent lanthanides. Heavy RE separations are more challenging than LRE separations due to HRE’s smaller differences in ionic radius; e.g., the near-adjacent ions GdIIIand DyIIIdiffer by only 0.024 Å (CN=9). Although Al- LanM’s on-column SFs are lower than those in solution, they still outperform previous LanMs. As a result, immobilized Al-LanM was tested to determine if it could efficiently separate the LRE / HRE pair Nd / Dy, which is important for permanent magnet recycling. Indeed, immobilized Al-LanM enabled one-step separation of a 95:5 Nd:Dy mixture (mimicking electronic waste feed), achieving 96.8% Dy purity (93.1% yield) and 99.7% Nd purity (99.8% yield) using a single pH step: pH 2.3 to desorb Dy and pH 1.5 to recover Nd (Figure 4A). By contrast, to obtain similar levels of purity, the Mex-LanM column required two stages and the Hans-R100K column needed three different malonate concentrations for Dy elution, followed by acid desorption for Nd. Encouraged by this performance, separation of a more challenging RE pair: mixtures of 50:50 Gd:Dy (near-adjacent REs) was attempted. For the Gd / Dy separation using a single pH step, 88.2% Dy purity (97.0% yield) and 97.5% Gd purity (85.5% yield) were obtained (Figure 44). As suggested by its improved on-column SFNd / Dyversus wild-type, S102T performs even better; 92.2% Dy purity (98.1% yield) and 98.2% Gd purity (91.1% yield) were obtained (Figure 4B). It is anticipated that a longer column would achieve baseline separation of Gd / Dy (and even for Tb / Dy, of particular value for permanent magnet recycling) with little additional optimization.

[0126] Al-LanM utilizes all levels of protein structure, primary to quaternary, to derive selectivity between LnIIIions. Previously characterized LanMs have also leveraged primary, secondary, and tertiary structure differences for RE / non-RE and RE / RE selectivity; while Hans-LanM was the first lanmodulin to be shown to undergo RE-sensitive dimerization, we were unable to leverage that quaternary structure change for separations, as we now can with Al-LanM.

[0127] As a dimer, but also even as a monomer, Al-LanM disfavors HREs more strongly than Mex- and Hans-LanMs. As one example, although Al-LanM’s SFs are muted relative to the single-RE Kd,appvalues, the protein does appear to exploit cooperativity to disfavor mixed metal complexes to a greater extent than previously characterized LanMs.Whereas Mex-LanM’s selectivity plateau is Nd / Sm, Al-LanM’s selectivity peak being at or near Ce means that almost all REs are on the same side of the peak, so that binding of a disfavored RE is less easily stabilized by co-binding of a favored one. This effect can be seen from Mex-LanM, where the stability (normalized to 1 for La / La) of a heterocomplex of metals on different sides of its selectivity plateau like Nd / Dy (4) is closer to that of Nd / Nd (9) than a heterocomplex of metals on the same side, like Gd / Er (0.35), is to Gd / Gd (1.5). Greater selectivity within a monomer could be amplified by dimerization. Furthermore, it is possible that, once affinity differences between adjacent REs become large enough, mixed metal complexes are increasingly disfavored and metal-binding cooperativity becomes beneficial in terms of amplifying separation factors.

[0128] These observations do not necessarily explain why Al-LanM performs better than other dimerizing LanMs, however (or why the variants improve SFs). One possible contributor may be that a partially folded apo state removes the need for metal binding to induce helix formation (as is the case for Mex- and Hans-LanM), which might have kinetic and entropic advantages for “favored” LnIIIions.

[0129] Using the Al-LanM sensor, it was demonstrated that E. coli can readily uptake Eu, Tb, and Dy from low micromolar extracellular concentrations into the periplasm but not the cytosol. Periplasmic uptake of LnIIIions by E. coli has been reported, examined by fixation and TEM analysis. Earlier studies have suggested cytosolic RE uptake in E. coli, although generally at millimolar extracellular concentrations, at which point the inner membrane may be compromised; likely, E. coli lacks a mechanism for cytosolic import of free REs. The significant luminescence of Sm, Eu, Tb, and Dy complexes in vitro also expedited optimization of Al-LanM for RE separation, traditionally performed using ICP-MS, and pointed to the surprising importance of His60 and its variants that displayed enhanced SFs.

[0130] Al-LanM’s average SF for adjacent REs across the whole Nd-Lu range is >2, whereas most single-ligand liquid-liquid extraction SFs are <2 (Table 12). Al-LanM exhibits a similar selectivity trend and similar SFs to the recently reported “octadecyl acyclopa” (certainly after factoring out the contribution from the lactate hold-back ligand), which itself has some of the best SFs between adjacent REs among reverse-size selective extractants (a category into which LanMs fall). Importantly, unlike previous LanMs, Al-LanM enables robust separations without requiring competing chelators, which tend to complicate processes because of the need to remove them for multiple cycles and because they may hinder downstream processing into an oxide. Continuing efforts to immobilize a functional dimerwill examine whether dimerization’s beneficial effect on Al-LanM’s selectivity in solution can be leveraged chromatographically. The partial folding of this apoprotein may be particularly advantageous, potentially suppressing aggregation and enhancing stability of a tandem dimer.

[0131] General considerations. Chemical reagents were obtained from Millipore Sigma unless otherwise noted. All lanthanide(III) (LnIII) chloride salts were at a minimum purity of 99.9% rare earth metal content. Stock solutions of LnIIIions were prepared by dissolution in 1 M HCl to achieve ~0.5 M solution and their concentration was determined by inductively coupled plasma mass spectrometry (ICP-MS) analysis on a Thermo Scientific iCAP RQ instrument with He in KED mode, in the Laboratory for Isotopes and Metals in the Environment (LIME) at the Pennsylvania State University. E. coli strains, BL21 (DE3) (for recombinant protein expression) and HST08 (for in-vivo metal sensing), were obtained from New England Biolabs and Takara Bio USA, respectively. Plasmids for expression and purification of proteins (pET29b-based vectors) were obtained from Twist Bioscience and pD871 plasmids for in vivo sensing were obtained from ATUM. Anion exchange column chromatography was performed using Q Sepharose Fast Flow resin obtained from Millipore Sigma. Automated protein chromatography was carried out on a GE Healthcare Biosciences Akta Pure fast protein liquid chromatography (FPLC) system using either a HiLoad Superdex 75 pg 16 / 600 column for preparative scale or a Superdex 75 pg Increase 10 / 300 GL column for analytical scale. The luminescence emission spectra of metal ions were obtained using a Horiba Fluorolog-QM fluorometer equipped with a double monochromator on the excitation arm and single monochromator on the emission arm. NIR emission spectra were obtained using a Horiba Jobin-Yvon NanoLog spectrofluorometer with a 450 W xenon source and a Symphony II InGaAs array detector. A quartz cuvette with 10 mm × 2 mm dimensions (Starna Cells, Inc.) was used. Luminescence analysis using 96-well plates was carried out on a BioTek Synergy H1 microplate reader.

[0132] Expression and purification of Xanthobacter flavus LanM (Xan-LanM). Expression of Xan-LanM was carried out as described for Al-LanM below, but using pET29b-Xan-LanM (Table 13). The protein was purified from the soluble fraction of the lysate as described for Hans-LanM, yielding 10 mg / L culture. Protein concentrations were determined by UV-visible spectroscopy using ε280nm= 12490 M−1cm−1, calculated using the ExPASy ProtParam tool.

[0133] Because the majority of the overexpressed protein was present in the insoluble fraction of the lysate, the protein was purified from inclusion bodies. Briefly, the cell pellet(3.5 g) was resuspended in 200 mL of 50 mM sodium phosphate buffer (NaPi), containing 8 mM urea, at pH 7.0. The suspension was stirred for 1 h to ensure complete solubilization. Then, the solution was added dropwise to 1.2 L of Buffer A (50 mM Tris, 10 mM KCl, 1 mM EDTA, 5% glycerol, pH 8.0) while stirring. After ~2 h of stirring, 50 mL of Q-sepharose resin, pre-equilibrated with Buffer A, was added and stirred for 1 h. The resin was then loaded into a column (2.5 × 15 cm, height ~10 cm) and washed with Buffer A for 2 column volumes (CV). The bound protein was eluted using 250 mM KCl in Buffer A over a total volume of 400 mL. Only Xan-LanM was bound to the resin; therefore, the eluent contained Xan-LanM with high purity. To buffer exchange into the storage buffer and remove trace impurities, the size exclusion chromatography and dialysis were performed as described in the Al-LanM purification section (vide infra). The protocol yielded 80 mg Xan-LanM per L culture.

[0134] Expression and purification of Ancylobacter lacus LanM (Al-LanM). pET29b-Al-LanM was transformed into competent E. coli BL21 (DE3) cells by heat shock. After transformation, cells were recovered in LB at 37°C with 200 rpm shaking for 1 h and then streaked onto an LB plate containing 1.5% agar and 50 μg / mL kanamycin (Km50). A single colony was used to inoculate 50 mL of LB broth supplemented with Km (LB / Km50) and cells were grown for ~16 h at 37°C with shaking at 200 rpm. This overnight culture was diluted into 2 L of LB / Km50 in a 6-L flask to achieve an optical density at 600 nm (OD600nm) of 0.05 and incubated at 37°C with shaking at 170 rpm. At OD600nm = 0.6-0.8, protein expression was induced by addition of isopropyl β-D-1-thiogalactopyranoside (IPTG, Oakwood Chemical) to a final concentration of 0.2 mM. After 3 h, cells were harvested by centrifugation at 7,000 ×g for 8 min. The cell paste (5 g / L culture) was stored at -80°C.

[0135] The cell paste from the 2-L culture was thawed on ice and resuspended at 5 mL / g in Buffer A, supplemented with two Roche Complete mini protease inhibitor tablets, 2 U / mL DNase, and 0.25 mM phenylmethanesulfonyl fluoride (PMSF). The resuspended cells were lysed by sonication for 10 min at 50% amplitude with a pulse cycle of 3 s on and 7 s off. The lysate was centrifuged at 40,000 ×g for 40 min at 4°C. The soluble fraction of the lysate was applied to a 15-mL Q Sepharose FF column that had been pre-equilibrated with Buffer A. The column was washed with Buffer A for 2 CV and eluted with an 80 × 80 mL gradient of 10-600 mM KCl in Buffer A. Fractions (5 mL) containing Al-LanM were collected and pooled based on SDS-PAGE gel analysis. The protein eluted from the column at ~300 – 550 mM KCl. The selected fractions were concentrated to <5 mL using an Amicon®Ultra 10-kDa centrifugal filtration device and further purified using size-exclusion chromatography on anFPLC using a HiLoad Superdex 75 pg 16 / 600 column. The column was run at 1.0 mL / min in Buffer B (30 mM MOPS, 100 mM KCl, 5 mM CaCl2, 5% glycerol, pH 7.0). The FPLC fractions containing Al-LanM eluted at 72-82 mL and were placed into a dialysis cassette (Thermo Scientific 10 kDa MWCO, 12 mL capacity) and dialyzed against 500 mL Buffer C (30 mM MOPS, 100 mM KCl, 5% glycerol, pH 7.0) containing 10 g / L Chelex-100, for 16 h. The protein concentration was determined by UV-visible spectroscopy using ε280nm= 8480 M−1cm−1, obtained via the ExPASy ProtParam tool. The purification procedure yielded 60 mg Al-LanM per L culture.

[0136] For the Y100W variant, the same expression and purification protocol was used. Protein concentrations were determined by UV-visible spectroscopy using ε280nm= 12490 M−1cm−1. The protocol yielded 40 mg protein per L culture.

[0137] Dimerization behavior studied by size exclusion chromatography. Proteins were diluted to a concentration of 250 µM (300 µL) in Buffer C. Lanthanide stock solutions of 75 mM were prepared in the same buffer. For each addition, protein samples were treated with 1 µL of the metal stock, corresponding to 1 equivalent of metal, with gentle mixing. In total, 3 µL of the metal stock was added, yielding 3 equiv. of metal. The apparent MW of the metal-bound proteins was then determined by their retention time during size exclusion chromatography on FPLC using a Superdex 75 pg Increase 10 / 300 GL column (0.8 mL / min), previously calibrated as described, and Buffer C. Additionally, the size of CaII-bound Al- LanM was assessed by injecting apo-Al-LanM into the same SEC column but using Buffer B.

[0138] Main peak retention times and corresponding apparent MWs are as follows (Figure 1A): La-bound at 11.71 min (30.8 kDa), Nd-bound at 11.75 min (30.3 kDa), Dy- bound at 11.78 min (30.0 kDa), apo at 13.05 min (19.2 kDa), and Ca-bound at 13.49 min (16.4 kDa).

[0139] Circular dichroism spectroscopy. The secondary structure of the protein was analyzed using circular dichroism spectroscopy with a Jasco J-1500 CD spectrometer. Proteins were diluted to a concentration of 10 µM in buffers at pH 5.0 (20 mM acetate, 100 mM KCl – Buffer D) and pH 7.0 (30 mM MOPS, 100 mM KCl – Buffer E). To prepare the metal-bound proteins, 2 equivalents of Tb were added to the protein samples. Both apo and holo proteins were scanned from 195 nm to 255 nm using the following settings: 1 nm bandwidth, 0.5 nm data pitch, a scan rate of 50 nm / min, and 4 s average time. Temperature- dependent CD studies were conducted with 20 µM protein diluted in Buffer D. For the metal- bound protein, 2 equiv. of lanthanides were added, and the solution was incubated for 30 min at room temperature. To prevent evaporation during the measurement, the cuvette cellscontaining the samples were tightly capped. CD spectra were obtained every 2°C from 16 to 90°C with 1°C / min increase. The resulting ellipticity values at 218 to 222 nm were averaged and plotted against temperature.

[0140] Determination of apparent Kdvalues using fluorescence spectroscopy. Chelator-buffered titrations. The fluorescence intensity changes of Trp residues in Al- and Xan-LanM at different free metal concentrations were monitored to determine the dissociation constants (Kds). DTPA or EGTA-buffered LnIIIsolutions were prepared as described in previous studies. Briefly, the metal-chelator equivalence point was first determined using the xylenol orange competition assay. With the equivalence point of each metal and chelator stock solution known, both Low and High chelator-buffered metal solutions were prepared as follows: The Low contained 20 mM acetate, 100 mM KCl, and 10 mM chelator at pH 5.0; the High contained 20 mM acetate, 100 mM KCl, and 10 mM Ln- chelator at pH 5.0. DTPA was used for La, Ce and Pr ions, whereas EGTA was used for the other RE ions. For titrations at pH 7.0, EGTA was used as the metal-chelating agent for La and Ce while EDDS was used for Sm and Dy. The metal-EDDS equivalence point was determined by CD spectroscopy, following our previously reported protocol. Proteins were diluted into each of the Low and High metal-buffered solutions to a final concentration of 2 µM unless otherwise noted. The protein-supplemented Low and High solutions were mixed (200 µL) in various ratios to achieve a broad range of free metal concentrations. The prepared samples were incubated at room temperature for ~16 hours prior to measurement to ensure equilibrium. An NMR tube cap was placed on the cuvette holder to raise the solution’s height for measurement. There was no difference in readings between cuvettes with 200 µL supported by the NMR tube cap and the 500 µL volume. Steady-state emission scans were performed with 280 nm excitation, excitation slit width 2 nm / 2 nm / 2 nm (Entrance slit / Central slit / Exit slit; hereafter, En / Ctr / Ex), emission slit width 2 nm / 2 nm (En / Ex), and an integration time of 0.1 s. Changes in fluorescence intensity at 335 nm were plotted against the determined free metal concentration. The data points were fitted to the Hill equation to determine the apparent dissociation constants (Kd,apps) and the Hill coefficients (n).

[0141] CaIItitration. Al-LanM’s weak response to CaIIallowed us to measure the Kd,app for CaIIby direct titration monitored by spectrofluorometry. Al-LanM was diluted to 2 µM (500 µL) in Buffer D (pH 5.0). CaCl2stock solutions were prepared at 100 µM, 1 mM, 10 mM, or 100 mM in the same buffer, or at 1 M in water. To achieve the desired final concentrations (0.1 to 20 mM), volumes ranging from 0.5 to 2.5 µL of the CaCl2solutions were added to the protein solution. The total volume change of the solution did not exceed5%. Steady-state emission scans were acquired with 280 nm excitation, excitation slit width 2 nm / 2 nm / 2 nm (En / Ctr / Ex), scanning 300-400 nm emission, with emission slit width 2 nm / 2 nm (En / Ex), and an integration time of 0.1 s. Changes in emission intensity at 335 nm were plotted against the total CaIIconcentration and fitted to the Hill equation.

[0142] EuIIIluminescence for stoichiometry determination. The metal-binding stoichiometries of LanM proteins were determined by monitoring fluorescence emission of the directly excited EuIIIion in the presence of protein. The protein (20 μM in 500 μL Buffer D, pH 5.0) was titrated with 1 µL additions of a 2.5 mM EuIIIstock solution. Titration was continued until a total of 4 equiv. of EuIIIwas added. Under these conditions, emission intensity of unbound EuIIIis negligible. Steady-state emission scans were performed with 394 nm excitation, excitation slit width 5 nm / 5 nm / 5 nm (En / Ctr / Ex), emission slit width 5 nm / 5 nm (En / Ex). The integration time was set to 0.5 s and spectra were recorded over the range of 560 nm to 650 nm.

[0143] In vitro characterization of sensors. Plate reader. Mex-T90W, Hans-LanM, Hans-R100K, Xan-LanM, Al-LanM, and Al-Y100W were diluted to 5 µM or 20 µM in each of the following buffers: 30 mM MOPS, 100 mM KCl, pH 7.0 (Buffer E); 20 mM MES, 100 mM KCl, pH 6.3 (Buffer F); 20 mM MES, 100 mM KCl, pH 6.0 (Buffer G); 20 mM MES, 100 mM KCl, pH 5.7 (Buffer H); 20 mM acetate, 100 mM KCl, pH 5.0 (Buffer I); 20 mM acetate, 100 mM KCl, pH 4.0 (Buffer J); 20 mM glycine, 100 mM KCl, pH 3.7 (Buffer K); 20 mM glycine, 100 mM KCl, pH 3.3 (Buffer L); or 20 mM glycine, 100 mM KCl, pH 3.0 (Buffer M). EuCl3, TbCl3, and DyCl3stock solutions (2 mM) and SmCl3(8 mM) were made fresh each day in Buffer I. Each sample consisted of 100 μL protein solution (5 µM for EuIII, TbIII, and DyIIIand 20 µM for SmIII) in Greiner BioOne 96-well black flat bottom plates. Two equivalents of the appropriate lanthanide ion were added to each sample and incubated for 30 min at room temperature. Time-resolved luminescence emission spectra were obtained from 500 to 650 nm (1 nm increments) using a BioTek Synergy H1 microplate reader with the following instrument settings: 280 nm excitation, 100 µs delay, and 1000 µs collection time. A gain of 140 was applied for Sm, Eu, and Dy measurements, while a gain of 100 was used for Tb. For control groups, spectra of the lanthanide ion without protein were obtained using the same experimental settings. Emission intensities were averaged at 640-645 nm for Sm, 617-619 nm for Eu, 544-546 nm for Tb, and 574-576 nm for Dy. Uncertainties were determined from three independent replicates.

[0144] NIR spectroscopy. Sensor proteins (Mex-T90W, Hans-R100K, and Xan- LanM) were diluted to 5 µM in 500 µL of pH 7.0, 5.0, 4.0 and pH 3.0 buffer solutions(Buffer E, Buffer I, Buffer J, and Buffer M). NdCl3 and YbCl3 stock solutions (10 mM) were made fresh each day in Buffer I. Two equivalents of each lanthanide ion were added to each protein sample and incubated for 30 min at room temperature. The pre-mixed sample was transferred to a 10 mm × 2 mm quartz cuvette (Starna Cells, Inc.). NIR emission spectra were obtained using a Horiba Jobin-Yvon NanoLog spectrofluorometer with a 450 W xenon source and a Symphony II InGaAs array detector. Sensor proteins were excited at 280 nm using an excitation slit width of 10 nm and an emission slit width of 20 nm. Emission was collected from 750 nm to 1500 nm, using a 20 s integration time with a high sensitivity. For control groups, spectra of protein samples without metals were obtained using the same experimental settings. Emission intensities were averaged from three independent replicates at 1059-1061 nm for Nd and 979-981 nm for Yb.

[0145] Determination of coordinated solvent molecules (q) in EuIII2-Al-LanM. Al- LanM (20 µM) was prepared in Buffer E (pH 7.0). EuIIIwas introduced to the solution by adding EuCl3(10 mM stock in pH 7.0 Buffer E) to achieve a final EuIIIconcentration of 40 µM in a total volume of 1 mL. The solution was lyophilized for 16 h and resuspended in 1 mL of D2O (99.8%, TCI America). Lyophilization was repeated once more to ensure the complete removal of residual H2O. The final lyophilized sample was resuspended in 1 mL of D2O. A separate 20 µM Eu2-Al-LanM sample was prepared in Buffer E (H2O). To create samples with varying D2O content, the EuIII2-Al-LanM in D2O and H2O samples were mixed in appropriate ratios to produce solutions with 0%, 25%, 50%, and 75% D2O. Phosphorescence decay measurements were conducted using a Fluorolog-QM fluorometer. The excitation wavelength was set to 394 nm, with emission detection at 617 nm with 2000 shots. The decay acquisition started at 13 µs and ended at 2500 µs. Lifetime constant (^^) was determined using a One-To-Four exponentials fit with the following equation in FelixFL (1.0.26.0) Powerfit-10 software (Horiba Scientific): ே ^^^^^^

[0146] Then, ^^ and ^^−1fraction of D2O, and ^^−1in 100%D2O was determined from the q can be calculated using the equation: ^^ ൌ 1.11^^^ ି^ െ ି^ୌమ^ ^^ୈమ^ െ 0.31 ^ 0.45^^^ୌ ^ 0.99^^^ୌ ^ 0.0075^^^ୀେ^ୌ^where ^^ୌି^మ^and ^^ୈି^మ^are the inverses of lifetime constants in 100% H2O and 100% D2O, respectively. The terms nOH, nNH, and nO=CNHrepresent the number of alcoholic O−H oscillators coordinated to the EuIII, the number of amine N−H oscillators coordinated to theEuIII, and the number of N−H oscillators where amide oxygen atom is coordinated to the EuIII, respectively. Assuming the coordination sphere of Al-LanM resembles that of Hans- LanM, contribution from contribution nOH and nNH are negligible (nOH and nNH = 0), while three N-H groups from nO=CNHare assumed due to the amide O coordination of 1stAsn side chain and 7thThr backbone (nO=CNH = 3).

[0147] Quantification of lanthanides in AMD using LanMs. Sensor proteins (Mex- T90W and Al-Y100W) were diluted to 10 µM in 100 µL of AMD (pH 3.27) in Greiner Bio- One 96-well black flat-bottom plates. TbIIImetal stock solutions (1 ppm, 6.29 µM) were prepared through serial dilutions from 10 mM and 100 µM TbCl3 in Buffer L (pH 3.3). To achieve the desired final concentrations (5-25 ppb), volumes ranging from 0.5 to 2.5 µL of the 1 ppm Tb solutions were added to the protein solutions. Time-resolved emission spectra were obtained using the settings mentioned above for Tb, except a gain of 140 was used. Emission intensities, averaged from three independent replicates at 544-546 nm, were fitted to a linear regression to obtain the slope and y-intercept. The value of the y-intercept divided by the slope yielded the concentration of Tb.

[0148] In vivo sensing in E. coli. Cell growth. Chemically competent E. coli HST08 cells were transformed with pD871-control (control vector containing 300 random bases), pD871-mal-Mex-T90W, pD871-mal-Hans-LanM, pD871-mal-Xan-LanM, pD871-mal-Al- LanM sensor, pD871-mal-Al-Y100W, and pD871-Al-LanM (see Table 14, Table 15). These were then plated on LB-agar plates containing 50 µg / mL kanamycin (Km) and grown at 37℃. A single colony from these plates was used to inoculate 7 mL of LB (50 µg / mL Km in all growth media), and this culture was grown for ~16 h at 37 ℃ with shaking at 200 rpm. This culture was used to inoculate new 7 mL LB (100-fold dilution) and grown under the same conditions. After 2 h growth, L-(+)-rhamnose monohydrate (>98% purity, TCI) was added to a final concentration of 0.2%. After an additional 4 h of incubation (OD600nm~1.0), the cells were centrifuged at 3000 ×g for 7 min and washed twice with 20 mM acetate, 20 mM MES, 100 mM NaCl, 100 mM KCl, 0.2% glucose, pH 6.0. After pelleting the second time, the cells were resuspended in the same washing buffer to achieve a final cell density of OD600nm= 0.6 and kept on ice until the measurement.

[0149] In vivo sensing in E. coli. Fluorescence assay. From each cell suspension, 100 µL were transferred to Greiner BioOne 96-well black flat bottom plates. Stock solutions of EuCl3, TbCl3, and DyCl3 were prepared at 100 µM and 1 mM in the same buffer. Cells were exogenously treated with lanthanide ions at concentrations ranging from 1 µM to 40 µM (with volumes of lanthanide stock solutions ranging from 0.5 µL to 4 µL) and were incubatedat room temperature for 30 min prior to measurements. Time-resolved emission spectra from 500 nm to 650 nm were recorded using a BioTek Synergy H1 microplate reader, employing the same instrument settings as those used in in-vitro characterization. Emission intensities were averaged at 544-546 nm for Tb. For Eu and Dy, due to the relatively low signal-to-noise ratio compared to Tb, emission intensities were determined by summing the signals across 610-630 nm and 565-585 nm, respectively. Uncertainties were determined from three independent replicates.

[0150] Eu / Dy competition assay. Al-LanM was diluted to 20 µM in Buffer L (pH 3.3) and mixed with final concentrations of 10 µM, 20 µM, 40 µM, 60 µM, and 80 µM Eu and an equimolar concentration of Dy in a total volume of 100 µL. The mixtures were prepared in the 96-well black flat-bottom plates. Control samples lacking protein were prepared under the same conditions. After incubation for 30 min at room temperature, time- resolved luminescence emission spectra were recorded from 500 to 650 nm (1 nm increments) using the microplate reader. Instrument settings were configured as follows: 280 nm excitation, 100 µs delay, and 1000 µs collection time, 140 gain. Emission intensities were averaged over the following wavelength ranges: 617-619 nm for Eu and 574-576 nm for Dy. Uncertainties were calculated from three independent replicates.

[0151] Solution-based separation of lanthanide ion pairs using Al-LanM and its variants by filtration. Solutions of Al-LanM LanM and its variants (or Hans-LanM) with a concentration of 10 µM, unless otherwise noted, were prepared in a total volume of 10 mL using a pH 3.0 (Buffer M), pH 3.3 (Buffer L), 4.0 (Buffer 2J), 5.0 (Buffer I), 6.0 (Buffer G), and pH 7.0 (Buffer E). These solutions were then treated with 2 equiv., unless otherwise noted, each of two RE ions and mixed for 30 min at room temperature. Subsequently, they were concentrated to the final volume of ~500 µL using Amicon®Ultra 10-kDa centrifugal filtration device at 4000 ×g, with the retentate being resuspended every 10 min to ensure homogeneous protein concentration throughout the solution. The volume of retentate was measured using a pipette with an accuracy of two significant figures. For ICP-MS sample preparation, 50 µL of retentate and 500 µL of flow through were transferred to 4.95 mL and 4.50 mL of 2% HNO3solutions, respectively, to achieve 100- and 10-fold dilutions. The metal ion concentrations were determined by ICP-MS. The reported ppb values were converted to µg / mL, then multiplied by the dilution factor and measured volumes of retentate and flowthrough to obtain the weight (µg) of metals present in each solution (Mret and MFT). The weight of each metal was used to calculate distribution coefficients, from whichseparation factors were determined. The numbers of replicates are shown in the figure legends. Distribution coefficient: ^^ ൌ ெ^^^ெಷ^Separation ^^^^^ೃಶభ

[0152] NdIII-Al-LanM X-ray and structure determination. Sample preparation. Al-LanM3 equiv. of NdIIIand exchanged into 30 mM MOPS, 50 mM KCl, pH 7 by SEC. The corresponding fractions were collected and further concentrated to 20 mg / mL (1.6 mM). Crystals were obtained by using the sitting drop vapor diffusion method, in which 1 μL of protein solution (20 mg / mL) was mixed with 1 μL 200 mM ammonium sulfate and 30% (w / v) PEG 4000 in a 24-well plate from Hampton Research (cat. no. HR1-002) at room temperature. Long rod-shaped crystals appeared within five days. Crystals suitable for data collection were mounted on rayon loops, soaked briefly in a cryoprotectant solution consisting of the well solution supplemented with perfluoropolyether oil from Hampton Research (cat. no. HR2-814), and flash frozen in liquid N2.

[0153] Data collection. Diffraction datasets were collected at the Brookhaven National laboratory (BNL) 17-ID-2 FMX beamline and processed with the HKL2000 package. NdIII-loaded Al-LanM crystallized in the P21 space group with 2 monomers in the ASU. The structure was solved using the single-wavelength anomalous diffraction (SAD) method. Using a dataset collected at 12.7 keV (0.97934 Å), HySS identified four NdIIIsites that were subsequently used to obtain phases in phenix.autosol. The initial figure of merit (FOM) and Bayesian CC was 0.827 and 0.75, respectively. An initial model was generated with phenix.autobuild with subsequent rounds of manual modification and refinement in Coot and phenix.refine. In the final stages of model refinement and anisotropic displacement parameters (ADP) were refined for all NdIIIsites. The final model afforded an Rwork / Rfree of 0.1356 / 0.1435. The final model consists of residues 28-138, six NdIIIions, two CaIIions, one SO42−ion and 438 water molecules (Table 28). Of the residues modeled, 100% are in allowed or preferred regions as indicated by Ramachandran statistical analysis. Model validation was performed with the Molprobity server. Figures were prepared using the PyMOL molecular graphics software package (Schrödinger, LLC).

[0154] Table 28. Data collection and refinement statistics for the X-ray structures of NdIII-Al-LanM. Statistics for the highest resolution shell are shown in parentheses. NdResolution range38.19 – 0.99(1.03 – 0.99) Space group P 21

[0155] SEC-MALS to determine oligomeric states of Al-LanM at pH 3.3. The Nd- Al-LanM samples used in this study were the same as those previously prepared for X-ray crystallography, with metal contents verified by ICP-MS. The Dy-Al-LanM sample was prepared by addition of 3 equiv. of Dy to Al-LanM and subjected to SEC using 30 mM MOPS, 50 mM KCl, pH 7.0. The apoprotein sample was loaded to the analytical FPLC column in the same buffer, without any metal or chelator addition. Subsequently, the samples were subjected to SEC to exchange their buffer solutions with Buffer L (pH 3.3). Therelevant SEC fractions were collected and concentrated to 3 mg / mL (250 µM). Then, 120 µL of each sample was centrifuged at 20,000 ×g for 30 minutes at 4 °C to remove any potential aggregates. After centrifugation, 105 µL of the supernatant was transferred to a new 1.5 mL tube. SEC-MALS experiments were performed using an Agilent 1260 Infinity II HPLC system equipped with an autosampler and fraction collector. Before use, the system was equilibrated for 5 h with Buffer L. Calibration was performed using bovine serum albumin (monomer MW: 66 kDa) in the same buffer, followed by normalization and alignment of the MALS and refractive index detectors. The sample (95 µL) was injected into the SEC-MALS system (Wyatt Technology) at a flow rate of 0.8 mL / min. The elution was carried out on a Wyatt SEC hydrophilic column with 5-μm silica beads, a pore size of 100 Å, and dimensions of 7.8 × 300 mm. Molar mass analysis of eluted peaks was conducted using Wyatt Technology’s DAWN MALS and Optilab refractive index detectors. Data were analyzed using the ASTRA software (Wyatt).

[0156] To provide evidence that Dy-Al-LanM at pH 3.3 is monomeric rather than an apoprotein, we performed SEC using Tb3-Al-LanM (250 µM, 300 µL) in a pH 3.3 elution buffer (Buffer L). Tb was used as a surrogate for Dy, as Tb is adjacent to Dy in the lanthanide series and it is expected to exhibit similar dimerization behavior and affinity but with significantly higher luminescence intensity. The elution profile was monitored at 260 and 280 nm. The apparent molecular weight of the fraction corresponding to the SEC peak at 13.74 mL was estimated based on calibration standards, yielding a value of 15.0 kDa. This fraction was collected and its UV-visible spectrum was obtained, with the protein concentration determined to be 17 µM based on absorbance at 280 nm. To assess TbIIIcoordination, a time- resolved emission spectrum was recorded for the SEC fraction. Excitation was performed at 280 nm, and emission spectra were collected over a time delay of 100-1000 µs. To quantify the amount of TbIIIbound to Al-LanM in the SEC fraction, a luminescence-based assay was performed. Tb luminescence spectra of 17 µM Al-LanM at pH 3.3 were recorded with increasing TbIIIconcentrations. The first six data points were used to generate a standard curve, which yielded an equation for Tb quantification.

[0157] Determination of Nd binding capacity for immobilized LanM. For immobilization, LanMs were expressed and purified with two different C-terminal linkers: GSGC (SEQ ID NO: 32) and GSGHHWGSTGSGC (SEQ ID NO:86) (12mer-Cys, derived from the SNAC tag). We confirmed that LanMs immobilized with different linkers showed no difference in binding properties as well as separation efficiency. The specific linker used for LanM is specified in each method section. LanM-Cys constructs were immobilized ontomaleimide-functionalized agarose beads using our established protocols. The immobilization capacity of LanM was determined by measuring the LanM concentrations before and after the immobilization process using a NanoDrop spectrophotometer at 280 nm, with an extinction coefficient of 8480 M−1cm−1.

[0158] Econo-Column glass chromatography columns (Bio-Rad; 5 cm ^ 0.5 cm) were filled with MilliQ water (18.2 MΩ cm-1) and loaded gravimetrically with Al-LanM-GSGC- microbeads (GSGC is SEQ ID NO:62) Columns (0.6-1.0 mL) were washed with 25 mM HCl, MilliQ water, and conditioned with DI water before conducting RE breakthrough experiments. Nd stock solution was prepared by dissolving NdCl3 salts in 1 mM HCl and further diluted into pH 3.0 HCl for the final concentration of 0.4 mM. The Nd solutions were pumped at 0.5 mL / min and the column effluent was collected in aliquots of 1 bed volume. A washing step with 5 bed volumes of MilliQ water was included before performing desorption experiments. Nd desorption was achieved by eluting with a 25 mM HCl solution.

[0159] Column RE separation experiments. Econo-Column glass chromatography columns (Bio-Rad; 5 cm ^ 0.5 cm) were filled with MilliQ water (18.2 MΩ cm-1), and LanM- Cys-microbeads (5 mM) were added gravimetrically to a final volume of 0.6 mL (height = 3 cm). Al-LanM-12mer-Cys, H60A-GSGC (GSGC is SEQ ID NO:62), and S102T-GSGC (GSGC is SEQ ID NO:62) were used for this study; Al-LanM-GSGC (GSGC is SEQ ID NO:62) yields similar results to the Al-LanM-12mer-Cys. Columns were washed with 25 mM HCl, MilliQ water, and conditioned with DI water before conducting RE separation experiments. RE stock solutions were prepared by dissolving individual RE chloride salts in 1 mM HCl. The stock solutions were diluted in 1 mM HCl to achieve the desired final concentrations (Nd:Dy pair = 0.38 mM:0.02 mM; Gd:Dy pair = 0.2 mM:0.2 mM). The RE solutions were pumped at 0.15 mL / min unless otherwise specified and the column effluent was collected in 0.6 mL aliquots. A washing step with 5 bed volumes of MilliQ water was included before performing desorption experiments. Desorption of weakly bound REs (Dy) was achieved by solutions at pH 2.2 or 2.3, while more tightly bound REs (Nd, Gd) were desorbed by subsequent pH 1.5 solution. The metal ion concentrations were determined by ICP-MS.

[0160] For the RE pair separation experiments, the metal ion purity and yield are defined as: ^^ ^^^^^^^^^^^^ோா^where CRE1and CRE2areand RE2, respectively, and^^^^1 ^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^ோா^ൌ ^^^^^^^^^^ ^^^^1 ^^^^^^^^^^^^

[0161] Table 1. Apparent Kdvalues for Xan- and Al-LanM complexes with REs, determined using chelator-buffered titrations and monitored by Trp fluorescence emission. Values represent mean(SD) from 3 replicates. Conditions: 2 µM protein, 20 ℃, 20 mM acetate, 100 mM KCl, pH 5.0. Xan-LanM Al-LanM 20 µM Al-LanM Metal Kd,app(pM) n Kd,app(pM) n Kd,app(pM) ntitrations and monitored by CD spectroscopy. Values for LaIII, NdIII, and DyIIIwere previously reported. Others were determined herein. Conditions: 15 µM protein, 20 ℃, 20 mM acetate, 100 mM KCl, pH 5.0. Metal ion Kd,app (pM)n Δ[Θ] (deg cm2 dmol-1 × 10-3)LaIII68(7) 1.8(6) -728(57)was used for the chelator-buffered La titration, whereas EDDS was used for other RE ions. The values were derived from the plots presented in Figure 40-41. Conditions: 2 µM protein, 20℃, 20 mM MOPS, 100 mM KCl, pH 7.0. WT-Al-LanM H60A H60N S102A S102T 7

[0164] Table 4. Apparent Kds and n for Al-Y100W at pH 5.0. Conditions: 2 µM protein, 20℃, 20 mM acetate, 100 mM KCl, pH 5.0. Metal ion Kd, app(pM) n Sm 52(8) 1.4(2) Dy 358(52) 1.9(5)

[0165] Table 5. Distribution coefficients and SFs from spin-concentrator separations using 2 µM Al-LanM.2:2:1 = RE1:RE2:Al-LanM was used unless otherwise indicated. pH DM1DM2SF Dy / Y 4.0 3.8 0.57 6.62

[0166] Table 6. Distribution coefficients and SFs from spin-concentrator separations using 10 µM Al-LanM.2:2:1 = RE1:RE2:Al-LanM was used unless otherwise indicated. pH DM1DM2SF Dy / Y 3.3 3.5 0.53 6.61 a3:3:1

[0167] Table 7. Distribution coefficients and SFs from spin-concentrator separations using 10 µM, Hans-LanM and Xan-LanM.2:2:1 = RE1:RE2:LanM was used.

[0168] Table 8. Separation factors for Al-LanM-based binary separations, compared to common industrial ligands (DEHPA and PC88A) and selected newer ligands. See Table 12 for additional comparisons. ND: not determined. Al-LanM Mex-LanM Hans-LanM DEHPA PC88A31Also in-solution on-column on-column noteworthy Nd / Sm1.7a1.0 1.5 4.9 (Sm / Nd) 2.0 7.5,322.5,33934) )

[0169] Table 9. Comparison of in-solution SFs for Al-LanM and its variants under optimized conditions (10 µM protein, pH 3.3, 2:2:1 = RE1:RE2:protein). WT-Al-LanM H60A H60N S102A S102T Nd / Dy 38.4 ± 0.5 47.5 ± 1.9 48.1 ± 2.6 37.6 ± 6.8 38.8 ± 3.0 Dy / Lu 32.4 ± 0.6 35.8 ± 0.9 35.4 ± 0.2 31.2 ± 3.6 34.0 ± 1.7

[0170] Table 10. Comparison of separation factors for Nd / Dy between in-solution (pH 3.3) and on-column (pH 5.0) conditions. ND: not determined. In-solution On-column Al-LanM 384 ± 05 147 ± 29

[0171] Table 11. Comparison of separation factors for Dy / Lu between in-solution (pH 3.3) and on-column (pH 5.0) conditions. ND: not determined. In-solution On-columnXan-LanM ND 11.9 ± 3.4 Hans-LanM ND 8.2 ± 2.1 ent RE pairs from Nd to Lu.Comparison of average SFs for adjacent RE pairs within certain indicated ranges (denoted with dashes, e.g., Nd-Lu). A slash indicates a binary separation (e.g., Nd / Dy). SFs for adjacent RE pairs earlier than Nd are not collected here. The calculated average SF for each adjacent RE pair (e.g., Nd / Sm, Sm / Eu, Eu / Gd, … Yb / Lu) is presented as a geometric mean ((ABCD…)1 / n). To acknowledge any particularly high SFs in each system, these values are listed in the footnote separately. Note that in some of the systems described below, the aqueous phase includes a “hold-back reagent” such as lactate or HDEHP in order to improve SFs. Ligand Separation method RE range Calculated collected average SF for d nt RE irsystem with 0.1 M DMDODGA in n-dodecane with 10 vol % 1-octanol. (SF for Sm / Nd = 18.03)c3 M HCl, 0.1 M ligand in isoparaffinic C11−C13 hydrocarbon (Isopar L) mixed with 30 vol % isotridecanol (Exxal 13)d0.5 mM of each LnIII, 0.9 M HNO3, BLPhen 1 in 1,2-dichloroethane. (SF for Nd / Sm = 7.5)e250 µM NdIII, 250 µM DyIII, and 4 mM G-macropa (L / M = 8) in 10 mM HCO3−. Selective Dy2(HCO3)3precipitation. [Nd-G-macropa]+is soluble in aqueous solution. Only Nd / Dy separation reported.f0.01 mM each of LnIII. pH 4.0, 1 mM macropa 0.05 M sodium lactate / 1 M NaNO3. Synergistic separation system with HDEHP in o-xylene. (SFs for Sm / Nd = 106.2 and Eu / Sm = 6.7)g39.5 mM NdIII, 39.5 mM DyIII, and 79 mM H31 in 1.5 M HCl. Selective Nd^1 complex precipitation.h0.0025 M mixed LnIIIsolution and 5-fold excess ligand relative to metal in 8 M HNO3 / toluene solution. LRE- selective precipitation.i1.0 g of HEHAEP / SiO2-P mixed with 5 mM REs at pH 2.0, 3.0, and 5.0. Desorption by HCl, HNO3, and H2SO4.j0.1-12 mM ODA in 1,1,2,2-tetrachloroethane (TCE) and 0.2 M NaCl / 50 mM sodium lactate buffer. Synergistic separation system with lactate. (SF for Nd / Dy = ~215)

[0173] Table 13. DNA sequences of constructs used in this study for protein expression and purification. Sequences were inserted into pET29b(+) between NdeI and XhoI. Amino acid substitutions are underlined. Construct DNA sequence insert SEQ ID NO: Xan-LanM CTCACAGGTAAAGAGTTTCTCCGGAAATATAATAAAGATAAGGACAGT ACCGTCGAGATCGTCGAAGCGATCGATTTGGGTACCAAAGTTTTTAAGAATGCGGCCGATAAAAACAAAGATGGTAAACTCACAGCGAAGGAACTG GACTCTAAGGCGGGCCAGTCGTTATTGAAACTCATAGTAAAATAA Al-LanM TTGACTGGAGCAGAATTTCTGGCACAGTATAATAAAGATGGCGATCAGg. For E. coli, these sequences were inserted into pD871 vector. The signal peptide (underlined) from E. coli maltose binding protein was added so that proteins would be exported to the periplasm. The Y100W mutation is bolded. DNA name Sequence SEQ ID NOTGGCCATTCTGGCGGTCCTCCAGTTCCCCCA TATTTTCTCGCGATCGAACAGTTCCCCAACG TACGAACGATCGGTACGATGACGCGAGCGCGTTGGCCCTGACCGGTGCCGAG TTTCTGGCACAGTACAACAAAGACGGCGATC AGACCCTGGAAATCCCGGAAGCGATCGATCTStrain / Plasmid Relevant genotype strainspET-29b Xan-LanM- KmR, IPTG-inducible expression, cytosolic Xan-LanM- GSGC GSGC GSGC expression ET 29b Al H60A KmRIPTG-ind ibl x r i n t li Al-H60A-

[0176] This example provides a description of proteins and peptides of the present disclosure and uses thereof.

[0177] The separation factors shown above are strong but not as large as would be expected based on the biochemical characterization with individual REs. On potential reason for this suboptimal efficiency is that, although EF3 (at the dimer interface) may be largely driving the selectivity, the ability of EF2 to bind a different RE that what is bound at EF3 (mixed complex formation) is negatively impacting the SF. Therefore, inactivation of EF2 was attempted. Inactivating an EF hand in a way such that the adjacent EF hand is not compromised in structure, affinity, and selectivity is not trivial. EF2 was substituted with an EF4-like EF-hand with the intention that it will bind calcium (as observed in the Al-LanM x- ray structure) or sodium (as observed in some of the Hans-LanM x-ray structures). While not the most atom-economical solution, it is hoped that success here might serve as the starting point for high-performance, more minimal binders. This work demonstrates that EF hands can be grafted in different parts of the protein (as long as consideration is given to retaining interactions outside the immediate coordination sphere, such as the hydrophobic residue at the 8thposition of the EF hand and its importance in packing with the adjacent EF hand, or hydrogen bonds in which loop residues are involved). It also demonstrates that EF4 of Al-LanM is not suited for REE binding, even when it is substituted into the EF2 region of the protein. EF2 inactivated 1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAIDKNKDG KLTPNETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:84) EF2 inactivated 2 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAIDKNKDG KLTPNETEGR LTKKDWAKIN KDGDQSLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:85)

[0178] Table 16. Apparent Kds and n for Sm-, Dy-, and Y- EF2 inactivated 1 complexes. See Figure 48 for raw data. The smaller differences between these Kds vs. the wild-type protein might reflect the loss of the cooperativity effect that may disfavor binding of two heavy REs relative to two light REs, or it might reflect Na+being relatively large (coupled with the Pro residue at the 10thposition) such that binding of the smaller, heavy REEs becomes more favored in the variants at the expense of light RE binding. Metal Kd, app(pM) n Sm 57 0.7inactivated 1 protein at pH 4.0. EF2-inactivated 1 (10 µM monomer, 10 mL) was treated with 2.0 equiv. of each lanthanide ion. Mass (µg) of RE, measured by ICP-MS, in the retentate, flow through (FT), and total yield with theoretical recovery rate (in parenthesis) are shown. The total weight of metal added (theoretical, based on stock concentrations): 17.8 µg Y; 28.9 µg Nd; 30.1 µg Sm; 31.5 µg Gd; 32.5 µg Dy. Lower recovery rates for Sm and Gd likely reflect errors in the stock concentration. Y Nd Sm Gd Dy ratio(RE / RE ) ratio(ret / ft) SF Y / Dy retentate 3.6 17.2 4.7 Dy: 1.4 5.7 2.9 7.5 6.9

[0180] Table 18. Separation of RE pairs with 10 µM EF2-inactivated 2 protein at pH 4.0. EF2-inactivated 2 (10 µM monomer, 10 mL) was treated with 2.0 equiv. of each lanthanide ion. Mass (µg) of RE, measured by ICP-MS, in the retentate, flow through (FT), and total yield with theoretical recovery rate (in parenthesis) are shown. The total weight of metal added (theoretical, based on stock concentrations): 17.8 µg Y; 28.9 µg Nd; 30.1 µg Sm; 31.5 µg Gd; 32.5 µg Dy. Lower recovery rates for Sm and Gd likely reflect errors in the stock concentration. Y Nd Sm Gd Dy ratio(RE / RE ) ratio(ret / ft) SF retentate 3.7 17.6 4.8 Dy: 1.4 5.82.98.1 7.6two pH conditions. EF2-inactivated 1 (10 µM monomer, 10 mL) was treated with 1.0 equiv. of each lanthanide ion. Mass (µg) of RE, measured by ICP-MS, in the retentate, flow through (FT), and total yield with theoretical recovery rate (in parentheses) are shown. The total weight of metal added (theoretical, based on stock concentrations): 15.0 µg Sm; 16.3 µg Dy. Sm Dy ratio(Sm / Dy) ratio(ret / ft) SF pH 3.3 .0 8

[0008] ab e 0. Separa on o pa rs w 0 µ - nac vated 2 protein at two pH conditions. EF2-inactivated 2 (10 µM monomer, 10 mL) was treated with 1.0 equiv. of each lanthanide ion. Mass (µg) of RE, measured by ICP-MS, in the retentate, flow through(FT), and total yield with theoretical recovery rate (in parentheses) are shown. The total weight of metal added (theoretical, based on stock concentrations): 15.0 µg Sm; 16.3 µg Dy. Sm Dy ratio(Sm / Dy) ratio(ret / ft) SF pH 3.3 D 122 4 2 .6 .3ed 1 protein at pH 3.3. EF2-inactivated 1 (10 µM monomer, 10 mL) was treated with 1.0 equiv. of each lanthanide ion. Mass (µg) of RE, measured by ICP-MS, in the retentate, flow through (FT), and total yield with theoretical recovery rate (in parenthesis) are shown. The total weight of metal added (theoretical, based on stock concentrations): 8.9 µg Y; 16.3 µg Dy. Y Dy ratio(Sm / Dy) ratio(ret / ft) SF Y / Dy retentate 2.3 9.3 4.1 Dy: 2.1 5.2F2-inactivated 2 protein at pH 3.3. EF2-inactivated 1 (10 µM monomer, 10 mL) was treated with 1.0 equiv. of each lanthanide ion. Mass (µg) of RE, measured by ICP-MS, in the retentate, flow through (FT), and total yield with theoretical recovery rate (in parenthesis) are shown. The total weight of metal added (theoretical, based on stock concentrations): 8.9 µg Y; 16.3 µg Dy. Y Dy ratio(Sm / Dy) ratio(ret / ft) SF Y / Dy retentate 24 100 42 Dy: 21 49in apparently inactivating the EF hand and reducing overall RE-binding stoichiometry, and they also retained rather tight RE binding at the remaining site (presumably EF3 at low pH), but this came at the expense of RE / RE selectivity. The Kd difference between Y and Dy only decreased slightly. (It might be interesting in the future to see if the Ho Kdis decreased by even a greater degree than Dy and Y, given that the Sm Kd is increased and the overall trend is flattening of the selectivity trend.) However, the results of separation experiments are not improved, even for Dy / Y, eventhough a direct Y / Dy competition experiment monitored by luminescence seems to be consistent with Kddeterminations indicating ~4-fold tighter binding of Dy, and despite observation of ~1 equiv. total binding during the separation so “incorrect” sites are likely not being occupied (Figure 51, Table 21, Table 22).

[0186] These observations might be due to: 1) loss of communication / cooperativity between EF2 and EF3, resulting in less selectivity in EF3, 2) Na+binding to EF2, altering the selectivity of EF3 because of its relatively large size or coordination, therefore biasing EF3 to smaller ions, 3) possibly loss of metal-dependent dimerization, if that is the main driver of cooperativity, or some combination of these. There may also be more trivial contributing factors, related to high protein concentrations at the end of the separation experiment, such that EF1 may have some binding, or higher NaCl concentrations might be needed at low pH for this type of experiment.

[0187] Along the lines of the above discussion, it is also possible that binding of a smaller ion like Li+at EF2 in the EF2-inactivated proteins might shift selectivity of EF3 to a lesser extent. If similar effects on Trp fluorescence are observed as with sodium, the ion is binding but the ion is smaller so it might force the loop to contract and favor HREs to a lesser extent (see legend for Table 16). It is even possible that Sm Kd will be enhanced and HRE Kds may be negatively impacted. It is possible the Pro could counteract this, but this will be investigated as well. Incidentally, the ability to graft EF4 into EF2 gives insight into selective recognition of lower valent alkali and / or alkaline earth metal ions. EXAMPLE 3

[0188] This example provides a description of proteins and peptides of the present disclosure and uses thereof.

[0189] Overview. Previous work has shown the enhanced intra-RE selectivity and separation performance of Hans-LanM and other LanM orthologs (e.g., Xan-LanM and Al- LanM) that dimerize in a RE-dependent manner. However, the current immobilization strategy results in LanM monomers that cannot dimerize (as evidenced by differences in selectivity trend on-column vs. in-solution). It is hypothesized that the on-column dimerization of LanM would further enhance its separation performance, which can be achieved by tethering two LanM protomers capable of dimerization in a single polypeptide chain, with a polypeptide linker in between. Polypeptide linkers of different lengths, comprising several repeating units (GlyGlySer), either fully flexible or interspersed with helical GluAlaAlaAlaLys (SEQ ID NO:88) units, were designed and used to fuse threedifferent dimerizing LanMs: Hans-LanM, Xan-LanM, and Al-LanM. Ability of these “tandem dimer” proteins to self-dimerize (form intramolecular rather than intermolecular dimers) was evaluated in solution, suggesting that certain Al-LanM tandem dimers could self- dimerize with little aggregation in solution and behaved similarly in terms of affinity and pH dependence to wild-type Al-LanM (without linkers). In-solution separation performance of one tandem dimer, in particular – TD9, with a 42-residue GlyGlySer linker – was similar or better than the wild-type Al-LanM, suggesting the potential for on-column dimerization, which is predicted to improve the on-column RE separation performance especially in the Nd-Dy range.

[0190] Composition, expression, and purification of tandem dimers (TD) TD1- TD10. The genes encoding TD 1-10, codon-optimized for expression in E.coli, were purchased from Twist Bioscience already inserted into pET-29b(+) using the restriction sites Ndel / Xhol. The general features of these proteins (LanM protein used, number of amino acids in the linker between LanM monomers, amino acids comprising the linkers, and whether experimental results supported the TD’s ability to form a “self-dimer”) are shown in Table 23. Complete amino acid sequences of constructs used in this study are listed in Table 24.

[0191] Table 23. General features of the LanM tandem dimer (TD) proteins studied herein. ND: not determined. TD LanM linker length amino acids of linker self-dimerized TD 1 X n L nM 18 Gl S r ND

[0192] Table 24. Amino acid sequences of the LanM tandem dimers (linker sequences are underlined, immobilization tag sequences are in double underline).SEQ ID Protein sequence NO: ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS 20 GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS 21 GGSGGSGGSG GSGGSGGSGG SALTGKEFLR KYNKDKDSTV EIVEAIDLGT KVFKAINPDK DKTLEAAETK GRLSDEDWAQ FNKDGDKTLE LDEWLIIVRK RFNDADANKD GKLTEAELDA PAGQQLILLI AK ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS 22 GGSGGSGGSG GSGGSGGSGG SGGSGGSALT GKEFLRKYNK DKDSTVEIVE AIDLGTKVFK AINPDKDKTL EAAETKGRLS DEDWAQFNKD GDKTLELDEW LIIVRKRFND ADANKDGKLT EAELDAPAGQ QLILLIAK ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSALTGKEF LRKYNKDKDS TVEIVEAIDL 23 GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS 24 GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGSGGSGAEA 25 AAKEAAAKAG GSGGSAEAAA KEAAAKAGSG GSGALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK ASGADALKAL NKDNDDSLEI AEVIHAGATT FTAINPDGDT TLESGETKGR LTEKDWARAN KDGDQTLEMD EWLKILRTRF KRADANKDGK LTAAELDSKA GQGVLVMIMK GGSGGSGGSG 26 GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSASGADALK ALNKDNDDSL EIAEVIHAGA TTFTAINPDG DTTLESGETK GRLTEKDWAR ANKDGDQTLE MDEWLKILRT RFKRADANKD GKLTAAELDS KAGQGVLVMI MK LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG 27 GSGGSGGSGG SGGSGGSGGS GGSGGSLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG 28 GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VK LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG 29 GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVKLTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG 30 GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGCa Q Sepharose FF column and subsequently a HiLoad Superdex 75 pg 16 / 600 column, using the same protocol as Al-LanM. With the size-exclusion chromatography, tandem dimers eluted at 56-70 mL and dialyzed against Buffer A (30 mM MOPS, 100 mM KCl, 5% glycerol, pH 7.0) after centrifugation. Calculated by the ExPASy ProtParam tool, ε280nm of TD1-TD6 is 24980 M-1cm-1, ε280nm of TD7 is 22000 M-1cm-1, and ε280nm of TD8-TD10 is 16960 M-1cm-1. Purification yielded 2-7 mg for TD2-TD7 per liter culture, whereas TD8- TD10 exhibited a purification yield of 26-47 mg per liter culture, suggesting that Al-LanM- based tandem dimers are more stable than those of Hans-LanM and Xan-LanM, perhaps due to the solubility and helical nature of the Al-LanM apoprotein. TD1 was designed as a negative control likely to be unable to self-dimerize because of the very short linker; TD1 was not purified or characterized once it was demonstrated that even TD2 failed to self- dimerize.

[0194] SEC-MALS. It was hypothesized that functional tandem dimers could be determined using size exclusion chromatography – multi angle light scattering (SEC-MALS). An apoprotein that is well behaved (e.g., does not aggregate significantly) would elute at a similar retention time (~20 min under the conditions shown below) to the Hans- or Al-LanM dimers, with a molecular weight of ~25 kDa, depending on the length of the linker. Addition of a lanthanide ion that causes dimerization in the wild-type LanMs, such as LaIII, would yield a complex with a molecular weight of ~25 kDa that would suggest intramolecular interaction of the LanM protomers (self-dimerization). However, if the protein cannot self- dimerize but instead protomers dimerize intermolecularly (e.g., if the linker is too short), the molecular weight would be ~50 kDa or form even higher molecular weight aggregates.

[0195] Figure 52 shows SEC-MALS analysis of TD2-TD7. TD2 (A), TD5 (D), TD6 (E), and TD7 (F) do not show significant peaks in the UV spectrum around 20 min, and refractive index measurements suggest the formation of species that elute much earlier with molecular weights of 50 kDa or higher, suggesting aggregation. TD3 (B) and TD4 (C)yielded minor UV feature at ~21 min with MALS suggesting ~20 kDa, suggesting self- dimerization given that Al-LanM dimer elutes at ~20-21 min under these conditions. However, even for these two constructs, most of the protein formed higher molecular weight oligomers. TD1 was not tested once the poor performance of TD2 was known. Whether self- dimerization was observed for these constructs is shown in Table 23. These data suggest that neither Hans- nor Xan-LanM is suitable for creating a functional tandem dimer.

[0196] To see whether the aggregation of these tandem dimers was related to addition of metal ions, the apo proteins TD4 and TD9 were prepared and subjected to SEC-MALS analysis at a concentration of 2 mg / mL in Buffer C (30 mM MOPS, 100 mM KCl, 1 mM EDTA, pH 7.0) (Figure 53). Apo-TD4 appeared largely as an aggregate (140 kDa) whereas TD9 primarily appeared as a species just below 30 kDa, matching the molecular weight of the protein. This result suggestive of much less aggregation led us to investigate Al-LanM-based tandem dimers.

[0197] Because linker lengths of 36 and 42 seemed to perform best (see TD3, TD4), this length (in addition to 48 residues) was used for Al-LanM-based constructs. TD8, TD9, and TD10 (500 µM) were metalated with 6 equiv. LaIIIor TbIIIin Buffer B and run through a Superdex 75 pg Increase 10 / 300 GL column (0.8 mL / min flowrate) to remove minor amounts of aggregate. Fractions containing the tandem dimer were concentrated to 1 mg / mL (TbIII- TD8, -TD9, -TD10, Figure 54B-D) and applied to SEC-MALS. In Figure 54A, LaIII-TD9 (6 equiv. La) was prepared at 2 mg / mL and loaded directly onto SEC-MALS without the prior S75 column. One-minute fractions were collected in the range of 16-27 min. For reference, Al-LanM dimer elutes at ~20-21 min under these conditions. The results in Figure 54 show that, at 2 mg / mL TD9 protein, although multiple peaks are present, the major peaks correspond to molar masses of ~30 kDa. At 1 mg / mL, all three proteins exhibit a major peak at 19-20 mL and a minor peak at 18-19 mL, both of which have masses of ~25-30 kDa, suggesting that these proteins are less prone to aggregation. The RE binding of these fractions was assessed through TbIIIluminescence using a BioTek Synergy H1 microplate reader with the following settings: 100 μL sample, λex: 280 nm, λem: 500-650 nm (1 nm increments), 100 μs delay, 1000 μs collection time, and 140 gain (Figure 55). All three proteins exhibited Tb luminescence corresponding to the major peaks in the SEC-MALS runs, which coincided with the elution volume for the Tb-Al-LanM dimer (~21 min). Therefore, we conclude that, at 1 mg / mL, TD8, TD9, and TD10 effectively self-dimerize in the presence of lanthanide ions (Table 23).

[0198] pH dependence of RE binding. To investigate whether the self-dimers that appear to form have similar properties to the wild-type protein dimer, TD8, TD9, and TD10 were diluted in buffer with 100 mM KCl and 20 mM buffer (pH 6.3, 6.0: MES; pH 5.7, 5.0, 4.0: acetate; pH 3.7, 3.3, 3.0: glycine; or 30 mM MOPS for pH 7.0). TD8, TD9, and TD10 (2.5 μM) were metalated with TbIII(10 μM) and incubated for 30 min at room temperature. TbIIIluminescence was monitored in 100 μL of each sample using a plate reader with the following settings: λex: 280 nm, λem: 500-650 nm (1 nm increments), 100 μs delay, 1000 μs collection time, 100 gain (Figure 56). Uncertainties were determined by triplicate measurements. All three constructs exhibited a profile similar to the wild-type protein, with TD9 having somewhat higher luminescence than TD8 and TD10. The similarity in profile to the wild-type protein suggests that the affinity and structure of the tandem dimers is similar to that of the wild-type protein.

[0199] Stoichiometry of tandem dimers. Spectrofluorometric titration of TD8-TD10 (15 μM) with 0-10 equiv. EuIIIwas performed in Buffer B and Buffer D (20 mM glycine, 100 mM KCl, pH 3.3) with the following settings: λex= 394 nm (slits 5 nm), λem: 580-640 nm (slits 5 nm), integration 150-2000 μs, shots 300 nm, steps 0.5 nm. The luminescence intensity values of EuIIIat 618-620 nm were averaged and plotted against the number of EuIIIequivalents added, allowing for estimation of binding stoichiometry of TD8, TD9, and TD10 (Figure 57). TD8 and TD9 both show ~5 binding equivalents at pH 7.0 and 3.3, similar to the wild-type protein (2.75 per monomer or 5.5 per dimer at pH 7), whereas TD10 shows only ~4 at pH 7.0 and ~3 at pH 3.3. Therefore, these results support the earlier data indicating TD8 and TD9, especially, have similar properties to wild-type Al-LanM.

[0200] Separation studies. The above characterization of the Al-LanM-based tandem dimers suggested that constructs TD9 and TD8 most faithfully reproduce the properties of the wild-type Al-LanM. We sought to determine whether these proteins also perform similarly to the wild-type protein in in-solution separations. Each tandem dimer (5 μM, 10 mL) was metalated with 4 equiv. each of two lanthanide ions in Buffer D (pH 3.3) and incubated for 30 min in a Multi Tube Rotator. The protein sample was applied into a spin concentrator equipped with a 10-kDa cutoff membrane and concentrated until the final volume was about 0.5 mL. Centrifugation was performed at 4000 ×g at 20 °C with 10 min intervals. The total volume of retentate was measured and solutions in retentate and flow through were diluted into 2% nitric acid. The masses of each RE, measured by inductively coupled plasma mass spectrometry (ICP-MS), in the retentate (RT) and flow through (FT) were used to calculate distribution coefficients (D), from which the separation factors (SF) were determined. Thetheoretical masses of each metal added were: 28.85 μg NdIII, 30.07 μg SmIII, 30.39 μg EuIII, 31.45 μg GdIII, 32.50 μg DyIII. The full analysis for representative separation tests using TD8- TD10 are shown in Table 25, and the average D and SF values are summarized in Table 26. Separation factors for the wild-type Al-LanM in the analogous assay are ~40 for Nd / Dy. Therefore, TD8 and TD9 performed as well as, or better than, the wild-type protein, while TD10 performed worse. The data in Table 26 suggest that separation factors start to increase (especially once normalized for differences in ionic radius) at Eu for TD9; this might suggest that Eu / Gd is where the impact of dimerization in amplifying SFs may begin to manifest.

[0201] Table 25. Representative data for binary RE separation experiments using TD8-TD10. TD REE pair NdIIISmIIIEuIIIGdIIIDyIIID SF TD9 Nd / Sm RT 13.69 10.03 Nd: 1.19 2.38 FT 1146 1995 S 050

[0202] Table 26. Distribution coefficients (D) and separation factors (SF) from binary RE separation experiments using TD8-TD10. Uncertainties were determined by duplicate separations. TD D SF TD-9 NdIII / SmIIINdIII: 1.18 ^ 0.02 2.37 ^ 0.01III^ 1e single chain FRET-based sensor (linker sequence is underlined, TD-9 sequence is in black, mNeonGreen sequence is in double underline, and mScarlet sequence is in bold). Sensor Protein sequence MVSKGEEDNM ASLPATHELH IFGSINGVDF DMVGQGTGNP NDGYEELNLK STKGDLQFSP WILVPHIGYG FHQYLPYPDG MSPFQAAMVD GSGYQVHRTM QFEDGASLTV NYRYTYEGSH IKGEAQVKGT GFPADGPVMT NSLTAADWCR SKKTYPNDKT IISTFKWSYT TGNGKRYRST ARTTYTFAKP MAANYLKNQP MYVFRKTELK HSKTELNFKE WQKAFTDVMG MDELYKLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVKGGSG TD9- GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK FRET1 DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVKMV SKGEAVIKEF MRFKVHMEGS MNGHEFEIEG EGEGRPYEGT QTAKLKVTKG GPLPFSWDIL SPQFMYGSRA FIKHPADIPD YYKQSFPEGF KWERVMNFED GGAVTVTQDT SLEDGTLIYK VKLRGTNFPP DGPVMQKKTM GWEASTERLY PEDGVLKGDI KMALRLKDGG RYLADFKTTY KAKKPVQMPG AYNVDRKLDI TSHNEDYTVV EQYERSEGRH STGGMDELYK (SEQ ID NO:34) MVSKGEAVIK EFMRFKVHME GSMNGHEFEI EGEGEGRPYE GTQTAKLKVT KGGPLPFSWD ILSPQFMYGS RAFIKHPADI PDYYKQSFPE GFKWERVMNF EDGGAVTVTQ DTSLEDGTLI YKVKLRGTNF PPDGPVMQKK TMGWEASTER TD9- LYPEDGVLKG DIKMALRLKD GGRYLADFKT TYKAKKPVQM PGAYNVDRKL FRET2 DITSHNEDYT VVEQYERSEG RHSTGGMDEL YKLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSLTGAEF LAQYNKDGDQTLEIPEAIDL GTKTFHAINP DGDTTLEPDE TEGRLTKKDW AKINKDGDQT LELDEYLSLV RARFNAADKN KDGKLTAKEL DSKAGQSLLK LIVKMVSKGE EDNMASLPAT HELHIFGSIN GVDFDMVGQG TGNPNDGYEE LNLKSTKGDL QFSPWILVPH IGYGFHQYLP YPDGMSPFQA AMVDGSGYQV HRTMQFEDGA SLTVNYRYTY EGSHIKGEAQ VKGTGFPADG PVMTNSLTAA DWCRSKKTYP NDKTIISTFK WSYTTGNGKR YRSTARTTYT FAKPMAANYL KNQPMYVFRK TELKHSKTEL NFKEWQKAFT DVMGMDELYK (SEQ ID NO:35)

[0204] To connect two monomers of LanM, polypeptide chains of lengths ranging from 18 to 48 residues and comprising repeating units were designed to behave largely as random coils when fused between the two LanM domains. The length of the linker is important because excessive length and insufficient linker length could both lead to functional impairment. To evaluate the functionality of the constructs containing these linkers, tethering Xan-LanM monomers were tethered, which has analogous on-column separation ability to Hans-LanM but has a partially folded apo state and tighter RE binding. Constructs derived from Hans-LanM and Al-LanM were examined; overall, 10 different constructs were examined.

[0205] The first set of tandem dimers developed, TD1-TD5, were used to evaluate the effect of linker length. It was found that TD3 and TD4 (36- and 42-residue linkers) were able to self-dimerize, although they also formed substantial amounts of large oligomers. To provide more rigidity in the linker, TD6, with EAAAK (SEQ ID NO:88) units expected to form helices, was constructed, although this linker disfavored self-dimerization. Hans-LanM was fused with a glycine- and serine-rich linker (TD7), but characterization indicated that Hans-LanM is less suitable than Xan-LanM in the tandem dimer strategy, because TD7 primarily aggregated even with the same linker length as TD4.

[0206] TD8-TD10 used Al-LanM, a protein that expresses to high levels in soluble form as a monomer and also exhibits substantial helical character even as the apoprotein at room temperature, as their basis. The best-performing linkers from earlier studies were focused on, with lengths of 36, 42, or 48 residues. As shown by SEC-MALS, self-dimerized TD8, TD9, and TD10 were the dominant species in the presence of lanthanide ions, and all three exhibited a comparable trend of pH-dependent TbIIIluminescence to Al-LanM, even though the TbIIIluminescence intensity was slightly diminished; TD9 had the strongest luminescence signal of the three. The EuIIIluminescence was used to assess RE binding stoichiometry, yielding 5 equiv. EuIIIbinding for TD8 and TD9 and 4 equiv. binding for TD10. Given that Al-LanM possessed 2.75 equiv. RE binding, slightly sub-stoichiometric EuIIIbinding of tandem dimers might reflect a small portion of the proteins may aggregate rather than self-dimerize. These results led to testing the RE selectivity and separationperformance of tandem dimers. Small-scale separation tests employing spin concentrators and pairs of REs were used. TD8 and TD9 performed similarly but TD10 performed somewhat worse; the Nd / Dy separation factor for TD9 was 51.3, approximately 20% higher than wild-type Al-LanM under the same conditions. This improved performance might reflect a lesser dependence of dimerization on total protein concentration during the assay when the tandem dimer is used, since the dimers are intramolecular rather than intermolecular (as with wild-type Al-LanM). Overall, TD9’s properties appear to be optimal of the constructs tested.

[0207] These studies showed that protein identity and linker length and composition are important in concatenating LanM monomers together to make tandem dimers. It is clear from this work that there are a number of different linkers that would suffice to yield functional tandem dimers with properties similar to the wild-type Al-LanM, for example the range of 36-42 residues, but likely this range extends further on either side. However, a 42- residue GlyGlySer linker appears to be best. Similarly, while both Xan- and Al-LanM-based tandem dimers show some self-dimerization ability – suggesting that partially folding of the apoprotein is important for this property – Al-LanM performs much better. This may be related to Xan-LanM being prone to aggregation during expression, as evidenced by most of the protein being found in the insoluble fraction upon cell lysis, even though it behaves well once it is refolded from the inclusion bodies. More generally, these results also suggest that LanMs with partially pre-folded apo states may be particularly suitable for concatenation, whether or not a monomeric or dimerizing LanM is used.

[0208] The strong performance of TD9 suggests that it may perform substantially better in separations than Al-LanM itself when immobilized. Therefore, a TD9 construct with GSGC (SEQ ID NO:62) added to the C-terminus (TD9-Cys-1, analogous to previously immobilized LanMs), or other appropriate amino acid sequence prior to a Cys for immobilization (e.g., TD9-Cys-2), has been purified. If there are not steric or kinetic issues with immobilizing this larger protein, higher capacity and SFs would be expected. Because the H60A and H60N substitutions increased Nd / Dy SFs by 20-30% in solution with Al- LanM, it will be interesting to see if these substitutions similarly improve performance of TD9. With two monomers of Al-LanM combined into a single polypeptide, we can also begin to explore how to minimize the size of each monomer but still be able to leverage RE- sensitive dimerization for enhanced selectivity.

[0209] Finally, the success of TD9 suggests that single-chain FRET-based sensors could be designed that take advantage of LanM dimerization for selective response to LREEs, for example by appending mNeonGreen and mScarlet to the N- and C-termini (or C- and N-termini), respectively, of TD9 (Table 27). Such a sensor could also indicate, by magnitude of the FRET ratios in the presence of different REs, whether the structures of the LRE and HRE complexes of Al-LanM are similar.

[0210] Although the present disclosure has been described with respect to one or more particular embodiments and / or examples, it will be understood that other embodiments and / or examples of the present disclosure may be made without departing from the scope of the present disclosure.

Claims

CLAIMS:

1. A rare earth element binding protein comprising the following sequence: X1-X2-G-X3-X4-X5-L-X6-X7-X8-NKD-X9-D-X10-X11-X12-EI-X13-E-X14-I-X15-X16-G-X17-X18- X19-F-X20-AINPD-X21-D-X22-TLE-X23-X24-ET-X25-GRL-X26-X27-X28-DWA-X29-X30- NKDGD-X31-TLE-X32-DE-X33-L-X34-X35-X36-R-X37-RF-X38-X39-AD-X40-NKDGKLT-X41- X42-ELD-X43-X44-AGQ-X45-X46-X47-X48-X49-I-X50-K (SEQ ID NO:1), wherein X1= any residue; X2= T or S; X3= any residue; X4= E or D; X5= any hydrophobic residue; X6= R, S, K, or A; X7= any residue; X8= any hydrophobic residue; X9= any residue; X10= D, N, S, or Q; X11= S or T; X12= any hydrophobic residue; X13= any residue; X14= any hydrophobic residue; X15= any residue; X16= A, W, or L; X17= S, T, A, Q, or V; X18= Q, D, E, or K; X19= any hydrophobic or polar residue; X20= any residue; X21= K, H, or G; X22= K or T; X23= P, K, A, or S; X24= P, A, N, D, or G; X25= K, N, or E; X26= S or T; X27= D, E, P, A, or K;X28= any residue; X29= any residue; X30= any hydrophobic residue; X31= K, Q, or E; X32= any hydrophobic residue; X33= F, W, or Y; X34= S, A, or T; X35= any hydrophobic residue; X36= any hydrophobic residue; X37= any residue; X38= E, K, A, or N; X39= any residue; X40= K, A, or P; X41= A, V, or E; X42= K, A, Q, or E; X43= A, S, or T; X44= K, P, E, or A; X45= any residue; X46= any hydrophobic residue; X47= any hydrophobic residue; X48= K, V, or L; X49= any hydrophobic residue; X50= any hydrophobic residue; wherein the rare earth element binding protein is optionally disposed or affixed to a substrate or encapsulated by or in the substrate and wherein when the rare earth element binding protein is LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:4), then the rare earth element binding protein is disposed or affixed to a substrate or encapsulated by or in the substrate and the rare earth element binding protein does not have the following sequence: LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:3) or ASGADALKALNKDNDDSLEIAEVIHAGATTFTAINPDGDTTLESGETKGRLTEKDWARANKDGDQTLEMDEWLKILRTRFKRADANKDGKLTAAELDSKAGQGVLVMIMK (SEQ ID NO:100).

2. The rare earth element binding protein according to claim 1, wherein X1= L; X3= A or K; X5= V, I, A, Y, or F; X6= R, S, K, or A; X7= Q; X8= V, I, A, or Y; X9= G; X12= V, I, F, or L; X13= P; X14= V, I, or A; X15= D; X19= L, V, M, or T; X20= H, N, or A; X28= K; X29= K; X30= V, I, A, or L; X32= V, I, M, or L; X35= V, I, or L; X36= L, A, or V; X37= A; X39= A; X45= S; X46= V, F, or L; X47= V, I, or L; X49= V, M, or L; and / or X50= A, M, or V.

3. The rare earth element binding protein according to claim 1, wherein the protein is disposed or affixed to the substrate or encapsulated by or in the substrate.

4. The rare earth element binding protein according to claim 3, wherein the substrate is a bead, a membrane, a hydrogel, a protein-based material, a cell surface, or a porous framework.

5. The rare earth element binding protein according to claim 3, wherein the protein further comprises a linker group.

6. The rare earth element binding protein according to claim 5, wherein the linker group is conjugated to a protein, wherein the protein is or comprises SEQ ID NO:

1.

7. The rare earth element binding protein according to claim 5, wherein the linker group is a peptide.

8. The rare earth element binding protein according to claim 7, wherein the linker group has the following sequence: GGSGGSGGSGGSGGSGGS (SEQ ID NO:15), GGSGGSGGSGGSGGSGGSGGSGGSGGSGG (SEQ ID NO:16), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:17), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:18), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:19), or GSGGSGAEAAAKEAAAKAGGSGGSAEAAAKEAAAKAGSGGSG (SEQ ID NO:20).

9. The rare earth element binding protein according to claim 1, further comprising a fluorescence resonance energy transfer pair.

10. The rare earth element binding protein according to claim 1, wherein the protein comprises or has the following sequence: >Al-LanM LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:4); >Al-LanM(Y100W) (also referred to as Al-Y100W) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EWLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:5);>Al-LanM(H60A) (also referred to as Al-H60A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:6); >Al-LanM(H60N) (also referred to as Al-H60N) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:7); >Al-LanM(S102A) (also referred to as Al-S102A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:8); >Al-LanM(S102T) (also referred to as Al-S102T) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:9); >Al-LanM-GSGC LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:10); >Al-LanM(S102T)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:11); >Al-LanM(H60A)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:12); >Al-LanM-12mer-Cys (12mer-Cys underlined) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGHHWGSTG SGC (SEQ ID NO:13); >Xan-LanM GSGC (GSGC is SEQ ID NO:62) LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK GSGC (SEQ ID NO:14); >Al-LanM(H60N)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:36); >Al-LanM(S102A)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:37); >Xan-LanM with native signal peptide (underlined)MKRRMISLGV VAAVSLAATG SAFALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:93); >Al-LanM with native signal peptide (underlined) MTRSLTRLAA AAGLASLVSI GMASSAFALT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVK (SEQ ID NO:94); >Mal-Xan-LanM MKIKTGARIL ALSALTTMMF SASALAMLTG KEFLRKYNKD KDSTVEIVEA IDLGTKVFKA INPDKDKTLE AAETKGRLSD EDWAQFNKDG DKTLELDEWL IIVRKRFNDA DANKDGKLTE AELDAPAGQQ LILLIAK (SEQ ID NO:95); >Mal-Al-LanM MKIKTGARIL ALSALTTMMF SASALALTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:96); >Mal-Al-LanM(Y100W) MKIKTGARIL ALSALTTMMF SASALALTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEWLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:97); >Al-LanM EF2 inactivated 1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAIDKNKDG KLTPNETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:84); >Al-LanM EF2 inactivated 2 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAIDKNKDG KLTPNETEGR LTKKDWAKIN KDGDQSLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:85); >TD1 – Xan-LanM tandem dimer (18-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:20); >TD2 – Xan-LanM tandem dimer (30-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SALTGKEFLR KYNKDKDSTV EIVEAIDLGT KVFKAINPDK DKTLEAAETK GRLSDEDWAQ FNKDGDKTLE LDEWLIIVRK RFNDADANKD GKLTEAELDA PAGQQLILLI AK (SEQ ID NO:21); >TD3 – Xan-LanM tandem dimer (36-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSALT GKEFLRKYNK DKDSTVEIVE AIDLGTKVFK AINPDKDKTL EAAETKGRLSDEDWAQFNKD GDKTLELDEW LIIVRKRFND ADANKDGKLT EAELDAPAGQ QLILLIAK (SEQ ID NO:22); >TD4 – Xan-LanM tandem dimer (42-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:23); >TD5 – Xan-LanM tandem dimer (48-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:24); >TD6 – Xan-LanM tandem dimer (42-aa EAAAK linker) (EAAAK is SEQ ID NO:88) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGSGGSGAEA AAKEAAAKAG GSGGSAEAAA KEAAAKAGSG GSGALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:25); >TD7 – Hans-LanM tandem dimer (42-aa GGS linker) ASGADALKAL NKDNDDSLEI AEVIHAGATT FTAINPDGDT TLESGETKGR LTEKDWARAN KDGDQTLEMD EWLKILRTRF KRADANKDGK LTAAELDSKA GQGVLVMIMK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSASGADALK ALNKDNDDSL EIAEVIHAGA TTFTAINPDG DTTLESGETK GRLTEKDWAR ANKDGDQTLE MDEWLKILRT RFKRADANKD GKLTAAELDS KAGQGVLVMI MK (SEQ ID NO:26); >TD8 – Al-LanM tandem dimer (36-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:27); >TD9 – Al-LanM tandem dimer (42-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VK (SEQ ID NO:28); >TD10 – Al-LanM tandem dimer (48-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKAGQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVK (SEQ ID NO:29); >TD9-GSGC (also called TD9-Cys-1) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:30); >TD9-12mer-Cys (also called TD9-Cys-2) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:31); >TD9(H60A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:38); >TD9(H60A)-Cys-2 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:39); >TD9(H60N)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFNAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:40); >TD9(S102A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLALVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:41); >TD9(S102T)-Cys-1LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLTLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:42); >TD9-FRET1 MVSKGEEDNM ASLPATHELH IFGSINGVDF DMVGQGTGNP NDGYEELNLK STKGDLQFSP WILVPHIGYG FHQYLPYPDG MSPFQAAMVD GSGYQVHRTM QFEDGASLTV NYRYTYEGSH IKGEAQVKGT GFPADGPVMT NSLTAADWCR SKKTYPNDKT IISTFKWSYT TGNGKRYRST ARTTYTFAKP MAANYLKNQP MYVFRKTELK HSKTELNFKE WQKAFTDVMG MDELYKLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVKGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVKMV SKGEAVIKEF MRFKVHMEGS MNGHEFEIEG EGEGRPYEGT QTAKLKVTKG GPLPFSWDIL SPQFMYGSRA FIKHPADIPD YYKQSFPEGF KWERVMNFED GGAVTVTQDT SLEDGTLIYK VKLRGTNFPP DGPVMQKKTM GWEASTERLY PEDGVLKGDI KMALRLKDGG RYLADFKTTY KAKKPVQMPG AYNVDRKLDI TSHNEDYTVV EQYERSEGRH STGGMDELYK (SEQ ID NO:34) or >TD9-FRET2 MVSKGEAVIK EFMRFKVHME GSMNGHEFEI EGEGEGRPYE GTQTAKLKVT KGGPLPFSWD ILSPQFMYGS RAFIKHPADI PDYYKQSFPE GFKWERVMNF EDGGAVTVTQ DTSLEDGTLI YKVKLRGTNF PPDGPVMQKK TMGWEASTER LYPEDGVLKG DIKMALRLKD GGRYLADFKT TYKAKKPVQM PGAYNVDRKL DITSHNEDYT VVEQYERSEG RHSTGGMDEL YKLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSLTGAEF LAQYNKDGDQ TLEIPEAIDL GTKTFHAINP DGDTTLEPDE TEGRLTKKDW AKINKDGDQT LELDEYLSLV RARFNAADKN KDGKLTAKEL DSKAGQSLLK LIVKMVSKGE EDNMASLPAT HELHIFGSIN GVDFDMVGQG TGNPNDGYEE LNLKSTKGDL QFSPWILVPH IGYGFHQYLP YPDGMSPFQA AMVDGSGYQV HRTMQFEDGA SLTVNYRYTY EGSHIKGEAQ VKGTGFPADG PVMTNSLTAA DWCRSKKTYP NDKTIISTFK WSYTTGNGKR YRSTARTTYT FAKPMAANYL KNQPMYVFRK TELKHSKTEL NFKEWQKAFT DVMGMDELYK (SEQ ID NO:35).

11. The rare earth element binding protein according to claim 10, wherein the protein is or comprises the following sequence: >Al-LanM(H60A) (also referred to as Al-H60A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:6); >Al-LanM(H60N) (also referred to as Al-H60N)LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:7); >Al-LanM(S102T) (also referred to as Al-S102T) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:9); >Al-LanM-GSGC LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:10); >Al-LanM(S102T)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:11); >TD9 – Al-LanM tandem dimer (42-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VK (SEQ ID NO:28); >TD9-GSGC (also called TD9-Cys-1) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:30); >TD9-12mer-Cys (also called TD9-Cys-2) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:31).

12. A rare earth element binding protein comprising one or more metal-binding or metal- coordination motifs, wherein at least one of the metal-binding or metal coordination motifs has the following sequence: N-X1-D-G-D-X2-T-L-E-X3-X4-E (SEQ ID NO:89), wherein X1is any amino acid, X2is any amino acid, X3is any amino acid, X4is any amino acid, wherein when there is more than one metal-binding or metal-coordination motif, at least one X1is a proline, at least one X4residue in the protein is an aspartate, and X3and / or X4is a proline.

13. The rare earth element binding protein according to claim 12, wherein at least one of the metal-binding or metal coordination motifs has the following sequence: NKDGDQTLEIPE (SEQ ID NO:90), NPDGDTTLEPDE (SEQ ID NO:91), or NKDGDQTLELDE (SEQ ID NO:92).

14. The rare earth element binding protein according to claim 12, wherein the protein is disposed or affixed to the substrate or encapsulated by or in the substrate.

15. The rare earth element binding protein according to claim 14, wherein the substrate is a bead, a membrane, a hydrogel, a protein-based material, a cell surface, or a porous framework.

16. The rare earth element binding protein according to claim 14, wherein the protein comprises the following sequence: >Al-LanM LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:4); >Al-LanM(Y100W) (also referred to as Al-Y100W) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EWLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:5); >Al-LanM(H60A) (also referred to as Al-H60A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:6); >Al-LanM(H60N) (also referred to as Al-H60N) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:7); >Al-LanM(S102A) (also referred to as Al-S102A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:8); >Al-LanM(S102T) (also referred to as Al-S102T) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:9); >Al-LanM-GSGCLTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:10); >Al-LanM(S102T)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:11); >Al-LanM(H60A)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:12); >Al-LanM-12mer-Cys (12mer-Cys underlined) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGHHWGSTG SGC (SEQ ID NO:13); >Xan-LanM GSGC (GSGC is SEQ ID NO:62) LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK GSGC (SEQ ID NO:14); >Al-LanM(H60N)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:36); >Al-LanM(S102A)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:37); >Xan-LanM with native signal peptide (underlined) MKRRMISLGV VAAVSLAATG SAFALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:93); >Al-LanM with native signal peptide (underlined) MTRSLTRLAA AAGLASLVSI GMASSAFALT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVK (SEQ ID NO:94); >Mal-Xan-LanM MKIKTGARIL ALSALTTMMF SASALAMLTG KEFLRKYNKD KDSTVEIVEA IDLGTKVFKA INPDKDKTLE AAETKGRLSD EDWAQFNKDG DKTLELDEWL IIVRKRFNDA DANKDGKLTE AELDAPAGQQ LILLIAK (SEQ ID NO:95); >Mal-Al-LanM MKIKTGARIL ALSALTTMMF SASALALTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:96); >Mal-Al-LanM(Y100W)MKIKTGARIL ALSALTTMMF SASALALTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEWLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:97); >Al-LanM EF2 inactivated 1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAIDKNKDG KLTPNETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:84); >Al-LanM EF2 inactivated 2 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAIDKNKDG KLTPNETEGR LTKKDWAKIN KDGDQSLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:85); >TD1 – Xan-LanM tandem dimer (18-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:20); >TD2 – Xan-LanM tandem dimer (30-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SALTGKEFLR KYNKDKDSTV EIVEAIDLGT KVFKAINPDK DKTLEAAETK GRLSDEDWAQ FNKDGDKTLE LDEWLIIVRK RFNDADANKD GKLTEAELDA PAGQQLILLI AK (SEQ ID NO:21); >TD3 – Xan-LanM tandem dimer (36-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSALT GKEFLRKYNK DKDSTVEIVE AIDLGTKVFK AINPDKDKTL EAAETKGRLS DEDWAQFNKD GDKTLELDEW LIIVRKRFND ADANKDGKLT EAELDAPAGQ QLILLIAK (SEQ ID NO:22); >TD4 – Xan-LanM tandem dimer (42-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:23); >TD5 – Xan-LanM tandem dimer (48-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:24); >TD6 – Xan-LanM tandem dimer (42-aa EAAAK linker) (EAAAK is SEQ ID NO:88)ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGSGGSGAEA AAKEAAAKAG GSGGSAEAAA KEAAAKAGSG GSGALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:25); >TD7 – Hans-LanM tandem dimer (42-aa GGS linker) ASGADALKAL NKDNDDSLEI AEVIHAGATT FTAINPDGDT TLESGETKGR LTEKDWARAN KDGDQTLEMD EWLKILRTRF KRADANKDGK LTAAELDSKA GQGVLVMIMK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSASGADALK ALNKDNDDSL EIAEVIHAGA TTFTAINPDG DTTLESGETK GRLTEKDWAR ANKDGDQTLE MDEWLKILRT RFKRADANKD GKLTAAELDS KAGQGVLVMI MK (SEQ ID NO:26); >TD8 – Al-LanM tandem dimer (36-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:27); >TD9 – Al-LanM tandem dimer (42-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VK (SEQ ID NO:28); >TD10 – Al-LanM tandem dimer (48-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVK (SEQ ID NO:29); >TD9-GSGC (also called TD9-Cys-1) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:30); >TD9-12mer-Cys (also called TD9-Cys-2) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETEGRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:31); >TD9(H60A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:38); >TD9(H60A)-Cys-2 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:39); >TD9(H60N)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFNAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:40); >TD9(S102A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLALVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:41); >TD9(S102T)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLTLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:42); >TD9-FRET1 MVSKGEEDNM ASLPATHELH IFGSINGVDF DMVGQGTGNP NDGYEELNLK STKGDLQFSP WILVPHIGYG FHQYLPYPDG MSPFQAAMVD GSGYQVHRTM QFEDGASLTV NYRYTYEGSH IKGEAQVKGT GFPADGPVMT NSLTAADWCR SKKTYPNDKT IISTFKWSYT TGNGKRYRST ARTTYTFAKP MAANYLKNQP MYVFRKTELK HSKTELNFKE WQKAFTDVMG MDELYKLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVKGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVKMVSKGEAVIKEF MRFKVHMEGS MNGHEFEIEG EGEGRPYEGT QTAKLKVTKG GPLPFSWDIL SPQFMYGSRA FIKHPADIPD YYKQSFPEGF KWERVMNFED GGAVTVTQDT SLEDGTLIYK VKLRGTNFPP DGPVMQKKTM GWEASTERLY PEDGVLKGDI KMALRLKDGG RYLADFKTTY KAKKPVQMPG AYNVDRKLDI TSHNEDYTVV EQYERSEGRH STGGMDELYK (SEQ ID NO:34) or >TD9-FRET2 MVSKGEAVIK EFMRFKVHME GSMNGHEFEI EGEGEGRPYE GTQTAKLKVT KGGPLPFSWD ILSPQFMYGS RAFIKHPADI PDYYKQSFPE GFKWERVMNF EDGGAVTVTQ DTSLEDGTLI YKVKLRGTNF PPDGPVMQKK TMGWEASTER LYPEDGVLKG DIKMALRLKD GGRYLADFKT TYKAKKPVQM PGAYNVDRKL DITSHNEDYT VVEQYERSEG RHSTGGMDEL YKLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSLTGAEF LAQYNKDGDQ TLEIPEAIDL GTKTFHAINP DGDTTLEPDE TEGRLTKKDW AKINKDGDQT LELDEYLSLV RARFNAADKN KDGKLTAKEL DSKAGQSLLK LIVKMVSKGE EDNMASLPAT HELHIFGSIN GVDFDMVGQG TGNPNDGYEE LNLKSTKGDL QFSPWILVPH IGYGFHQYLP YPDGMSPFQA AMVDGSGYQV HRTMQFEDGA SLTVNYRYTY EGSHIKGEAQ VKGTGFPADG PVMTNSLTAA DWCRSKKTYP NDKTIISTFK WSYTTGNGKR YRSTARTTYT FAKPMAANYL KNQPMYVFRK TELKHSKTEL NFKEWQKAFT DVMGMDELYK (SEQ ID NO:35).

17. The rare earth element binding protein according to claim 16, wherein the protein is or comprises the following sequence: >Al-LanM(H60A) (also referred to as Al-H60A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:6); >Al-LanM(H60N) (also referred to as Al-H60N) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:7); >Al-LanM(S102T) (also referred to as Al-S102T) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:9); >Al-LanM-GSGC LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:10); >Al-LanM(S102T)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:11); >TD9 – Al-LanM tandem dimer (42-aa GGS linker)LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VK (SEQ ID NO:28); >TD9-GSGC (also called TD9-Cys-1) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:30); >TD9-12mer-Cys (also called TD9-Cys-2) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:31).

18. A rare earth element binding protein having the following structure: Protein1-X-Protein2, wherein X is a linker group and Protein1and Protein2are the same or different.

19. The rare earth element binding protein according to claim 18, wherein Protein1and / or Protein2independently comprise the following sequence: X1-X2-G-X3-X4-X5-L-X6-X7-X8-NKD-X9-D-X10-X11-X12-EI-X13-E-X14-I-X15-X16-G-X17-X18- X19-F-X20-AINPD-X21-D-X22-TLE-X23-X24-ET-X25-GRL-X26-X27-X28-DWA-X29-X30- NKDGD-X31-TLE-X32-DE-X33-L-X34-X35-X36-R-X37-RF-X38-X39-AD-X40-NKDGKLT-X41- X42-ELD-X43-X44-AGQ-X45-X46-X47-X48-X49-I-X50-K (SEQ ID NO:1), wherein X1= any residue; X2= T or S; X3= any residue; X4= E or D; X5= any hydrophobic residue; X6= R, S, K, or A X7= any residue; X8= any hydrophobic residue; X9= any residue;X10= D, N, S, or Q; X11= S or T; X12= any hydrophobic residue; X13= any residue; X14= any hydrophobic residue; X15= any residue; X16= A, W, or L; X17= S, T, A, Q, or V; X18= Q, D, E, or K; X19= any hydrophobic or polar residue; X20= any residue; X21= K, H, or G; X22= K or T; X23= P, K, A, or S; X24= P, A, N, D, or G; X25= K, N, or E; X26= S or T; X27= D, E, P, A, or K; X28= any residue; X29= any residue; X30= any hydrophobic residue; X31= K, Q, or E; X32= any hydrophobic residue; X33= F, W, or Y; X34= S, A, or T; X35= any hydrophobic residue; X36= any hydrophobic residue; X37= any residue; X38= E, K, A, or N; X39= any residue; X40= K, A, or P; X41= A, V, or E; X42= K, A, Q, or E; X43= A, S, or T;X44= K, P, E, or A; X45= any residue; X46= any hydrophobic residue; X47= any hydrophobic residue; X48= K, V, or L; X49= any hydrophobic residue; X50= any hydrophobic residue.

20. The rare earth element binding protein according to claim 19, wherein X1= L; X3= A or K; X5= V, I, A, Y, or F; X6= R, S, K, or A; X7= Q; X8= V, I, A, or Y; X9= G; X12= V, I, F, or L; X13= P; X14= V, I, or A; X15= D; X19= L, V, M, or T; X20= H; X28= K; X29= K; X30= V, I, A, or L; X32= V, I, M, or L; X35= V, I, or L; X36= L, A, or V; X37= A; X39= A; X45= S; X46= V, F, or L; X47= V, I, or L; X49= V, M, or L; and / orX50= A, M, or V.

21. The rare earth element binding protein according to claim 18, wherein the protein is disposed or affixed to the substrate or encapsulated by or in the substrate.

22. The rare earth element binding protein according to claim 21, wherein the substrate is a bead, a membrane, a hydrogel, a protein-based material, a cell surface, or a porous framework.

23. The rare earth element binding protein according to claim 18, wherein the linker group is a peptide.

24. The rare earth element binding protein according to claim 23, wherein the linker group has the following sequence: GGSGGSGGSGGSGGSGGS (SEQ ID NO:15), GGSGGSGGSGGSGGSGGSGGSGGSGGSGG (SEQ ID NO:16), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:17), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:18), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:19), or GSGGSGAEAAAKEAAAKAGGSGGSAEAAAKEAAAKAGSGGSG (SEQ ID NO:20).

25. The rare earth element binding protein according to claim 18, wherein the protein comprises or has the following sequence: >TD1 – Xan-LanM tandem dimer (18-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:20); >TD2 – Xan-LanM tandem dimer (30-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SALTGKEFLR KYNKDKDSTV EIVEAIDLGT KVFKAINPDK DKTLEAAETK GRLSDEDWAQ FNKDGDKTLE LDEWLIIVRK RFNDADANKD GKLTEAELDA PAGQQLILLI AK (SEQ ID NO:21);>TD3 – Xan-LanM tandem dimer (36-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSALT GKEFLRKYNK DKDSTVEIVE AIDLGTKVFK AINPDKDKTL EAAETKGRLS DEDWAQFNKD GDKTLELDEW LIIVRKRFND ADANKDGKLT EAELDAPAGQ QLILLIAK (SEQ ID NO:22); >TD4 – Xan-LanM tandem dimer (42-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:23); >TD5 – Xan-LanM tandem dimer (48-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:24); >TD6 – Xan-LanM tandem dimer (42-aa EAAAK linker) (EAAAK is SEQ ID NO:88) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGSGGSGAEA AAKEAAAKAG GSGGSAEAAA KEAAAKAGSG GSGALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:25); >TD7 – Hans-LanM tandem dimer (42-aa GGS linker) ASGADALKAL NKDNDDSLEI AEVIHAGATT FTAINPDGDT TLESGETKGR LTEKDWARAN KDGDQTLEMD EWLKILRTRF KRADANKDGK LTAAELDSKA GQGVLVMIMK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSASGADALK ALNKDNDDSL EIAEVIHAGA TTFTAINPDG DTTLESGETK GRLTEKDWAR ANKDGDQTLE MDEWLKILRT RFKRADANKD GKLTAAELDS KAGQGVLVMI MK (SEQ ID NO:26); >TD8 – Al-LanM tandem dimer (36-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:27); >TD9 – Al-LanM tandem dimer (42-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETEGRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VK (SEQ ID NO:28); >TD10 – Al-LanM tandem dimer (48-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVK (SEQ ID NO:29); >TD9-GSGC (also called TD9-Cys-1) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:30); >TD9-12mer-Cys (also called TD9-Cys-2) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:31); >TD9(H60A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:38); >TD9(H60A)-Cys-2 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:39); >TD9(H60N)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFNAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:40); >TD9(S102A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKAGQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLALVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:41); or >TD9(S102T)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLTLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:42).

26. A rare earth element binding protein, wherein the rare earth element binding protein comprises or has the following sequence: LTGAEFLAQYNKDGDQTLEIPEAIDLGTKTFHAINPDGDTTLEPDETEGRLTKKDWA KINKDGDQTLELDEYLSLVRARFNAADKNKDGKLTAKELDSKAGQSLLKLIVK (SEQ ID NO:4), or a sequence having at least 80% identity thereto, wherein when the rare earth element binding protein is SEQ ID NO:4, the rare earth element binding protein disposed or affixed to a substrate or encapsulated by or in the substrate, and the rare earth element binding protein is not LTGKEFLRKYNKDKDSTVEIVEAIDLGTKVFKAINPDKDKTLEAAETKGRLSDEDWA QFNKDGDKTLELDEWLIIVRKRFNDADANKDGKLTEAELDAPAGQQLILLIAK (SEQ ID NO:3).

27. The rare earth element binding protein according to claim 26, wherein the protein is disposed or affixed to the substrate or encapsulated by or in the substrate.

28. The rare earth element binding protein according to claim 26, wherein the substrate is a bead, a membrane, a hydrogel, a protein-based material, a cell surface, or a porous framework.

29. The rare earth element binding protein according to claim 26, wherein the protein further comprises a linker group.

30. The rare earth element binding protein according to claim 29, wherein the linker group is conjugated to a protein, wherein the protein is or comprises SEQ ID NO:1.

31. The rare earth element binding protein according to claim 30, wherein the linker group is a peptide.

32. The rare earth element binding protein according to claim 31, wherein the linker group has the following sequence: GGSGGSGGSGGSGGSGGS (SEQ ID NO:15), GGSGGSGGSGGSGGSGGSGGSGGSGGSGG (SEQ ID NO:16), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:17), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:18), GGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGSGGS (SEQ ID NO:19), or GSGGSGAEAAAKEAAAKAGGSGGSAEAAAKEAAAKAGSGGSG (SEQ ID NO:20).

33. The rare earth element binding protein according to claim 26, further comprising a fluorescence resonance energy transfer pair.

34. The rare earth element binding protein according to claim 26, wherein the protein comprises or has the following sequence: >Al-LanM LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:4); >Al-LanM(Y100W) (also referred to as Al-Y100W) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EWLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:5); >Al-LanM(H60A) (also referred to as Al-H60A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:6); >Al-LanM(H60N) (also referred to as Al-H60N) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:7); >Al-LanM(S102A) (also referred to as Al-S102A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:8); >Al-LanM(S102T) (also referred to as Al-S102T)LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:9); >Al-LanM-GSGC LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:10); >Al-LanM(S102T)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:11); >Al-LanM(H60A)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:12); >Al-LanM-12mer-Cys (12mer-Cys underlined) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGHHWGSTG SGC (SEQ ID NO:13); >Xan-LanM GSGC (GSGC is SEQ ID NO:62) LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK GSGC (SEQ ID NO:14); >Al-LanM(H60N)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:36); >Al-LanM(S102A)-GSGC (GSGC is SEQ ID NO:62) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:37); >Xan-LanM with native signal peptide (underlined) MKRRMISLGV VAAVSLAATG SAFALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:93); >Al-LanM with native signal peptide (underlined) MTRSLTRLAA AAGLASLVSI GMASSAFALT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVK (SEQ ID NO:94); >Mal-Xan-LanM MKIKTGARIL ALSALTTMMF SASALAMLTG KEFLRKYNKD KDSTVEIVEA IDLGTKVFKA INPDKDKTLE AAETKGRLSD EDWAQFNKDG DKTLELDEWL IIVRKRFNDA DANKDGKLTE AELDAPAGQQ LILLIAK (SEQ ID NO:95); >Mal-Al-LanMMKIKTGARIL ALSALTTMMF SASALALTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:96); >Mal-Al-LanM(Y100W) MKIKTGARIL ALSALTTMMF SASALALTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEWLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:97); >Al-LanM EF2 inactivated 1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAIDKNKDG KLTPNETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:84); >Al-LanM EF2 inactivated 2 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAIDKNKDG KLTPNETEGR LTKKDWAKIN KDGDQSLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:85); >TD1 – Xan-LanM tandem dimer (18-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:20); >TD2 – Xan-LanM tandem dimer (30-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SALTGKEFLR KYNKDKDSTV EIVEAIDLGT KVFKAINPDK DKTLEAAETK GRLSDEDWAQ FNKDGDKTLE LDEWLIIVRK RFNDADANKD GKLTEAELDA PAGQQLILLI AK (SEQ ID NO:21); >TD3 – Xan-LanM tandem dimer (36-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSALT GKEFLRKYNK DKDSTVEIVE AIDLGTKVFK AINPDKDKTL EAAETKGRLS DEDWAQFNKD GDKTLELDEW LIIVRKRFND ADANKDGKLT EAELDAPAGQ QLILLIAK (SEQ ID NO:22); >TD4 – Xan-LanM tandem dimer (42-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:23); >TD5 – Xan-LanM tandem dimer (48-aa GGS linker) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSGGSGGSGGSGGSGGSA LTGKEFLRKY NKDKDSTVEI VEAIDLGTKV FKAINPDKDK TLEAAETKGR LSDEDWAQFN KDGDKTLELD EWLIIVRKRF NDADANKDGK LTEAELDAPA GQQLILLIAK (SEQ ID NO:24); >TD6 – Xan-LanM tandem dimer (42-aa EAAAK linker) (EAAAK is SEQ ID NO:88) ALTGKEFLRK YNKDKDSTVE IVEAIDLGTK VFKAINPDKD KTLEAAETKG RLSDEDWAQF NKDGDKTLEL DEWLIIVRKR FNDADANKDG KLTEAELDAP AGQQLILLIA KGSGGSGAEA AAKEAAAKAG GSGGSAEAAA KEAAAKAGSG GSGALTGKEF LRKYNKDKDS TVEIVEAIDL GTKVFKAINP DKDKTLEAAE TKGRLSDEDW AQFNKDGDKT LELDEWLIIV RKRFNDADAN KDGKLTEAEL DAPAGQQLIL LIAK (SEQ ID NO:25); >TD7 – Hans-LanM tandem dimer (42-aa GGS linker) ASGADALKAL NKDNDDSLEI AEVIHAGATT FTAINPDGDT TLESGETKGR LTEKDWARAN KDGDQTLEMD EWLKILRTRF KRADANKDGK LTAAELDSKA GQGVLVMIMK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSASGADALK ALNKDNDDSL EIAEVIHAGA TTFTAINPDG DTTLESGETK GRLTEKDWAR ANKDGDQTLE MDEWLKILRT RFKRADANKD GKLTAAELDS KAGQGVLVMI MK (SEQ ID NO:26); >TD8 – Al-LanM tandem dimer (36-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGD QTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVK (SEQ ID NO:27); >TD9 – Al-LanM tandem dimer (42-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VK (SEQ ID NO:28); >TD10 – Al-LanM tandem dimer (48-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVK (SEQ ID NO:29); >TD9-GSGC (also called TD9-Cys-1) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:30); >TD9-12mer-Cys (also called TD9-Cys-2)LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:31); >TD9(H60A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:38); >TD9(H60A)-Cys-2 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFAAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:39); >TD9(H60N)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFNAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:40); >TD9(S102A)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLALVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLALVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:41); >TD9(S102T)-Cys-1 LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLTLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:42); >TD9-FRET1 MVSKGEEDNM ASLPATHELH IFGSINGVDF DMVGQGTGNP NDGYEELNLK STKGDLQFSP WILVPHIGYG FHQYLPYPDG MSPFQAAMVD GSGYQVHRTM QFEDGASLTV NYRYTYEGSH IKGEAQVKGT GFPADGPVMT NSLTAADWCR SKKTYPNDKT IISTFKWSYT TGNGKRYRST ARTTYTFAKP MAANYLKNQP MYVFRKTELK HSKTELNFKE WQKAFTDVMG MDELYKLTGA EFLAQYNKDG DQTLEIPEAI DLGTKTFHAI NPDGDTTLEP DETEGRLTKK DWAKINKDGDQTLELDEYLS LVRARFNAAD KNKDGKLTAK ELDSKAGQSL LKLIVKGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSLT GAEFLAQYNK DGDQTLEIPE AIDLGTKTFH AINPDGDTTL EPDETEGRLT KKDWAKINKD GDQTLELDEY LSLVRARFNA ADKNKDGKLT AKELDSKAGQ SLLKLIVKMV SKGEAVIKEF MRFKVHMEGS MNGHEFEIEG EGEGRPYEGT QTAKLKVTKG GPLPFSWDIL SPQFMYGSRA FIKHPADIPD YYKQSFPEGF KWERVMNFED GGAVTVTQDT SLEDGTLIYK VKLRGTNFPP DGPVMQKKTM GWEASTERLY PEDGVLKGDI KMALRLKDGG RYLADFKTTY KAKKPVQMPG AYNVDRKLDI TSHNEDYTVV EQYERSEGRH STGGMDELYK (SEQ ID NO:34) or >TD9-FRET2 MVSKGEAVIK EFMRFKVHME GSMNGHEFEI EGEGEGRPYE GTQTAKLKVT KGGPLPFSWD ILSPQFMYGS RAFIKHPADI PDYYKQSFPE GFKWERVMNF EDGGAVTVTQ DTSLEDGTLI YKVKLRGTNF PPDGPVMQKK TMGWEASTER LYPEDGVLKG DIKMALRLKD GGRYLADFKT TYKAKKPVQM PGAYNVDRKL DITSHNEDYT VVEQYERSEG RHSTGGMDEL YKLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSGGSGGSGG SGGSLTGAEF LAQYNKDGDQ TLEIPEAIDL GTKTFHAINP DGDTTLEPDE TEGRLTKKDW AKINKDGDQT LELDEYLSLV RARFNAADKN KDGKLTAKEL DSKAGQSLLK LIVKMVSKGE EDNMASLPAT HELHIFGSIN GVDFDMVGQG TGNPNDGYEE LNLKSTKGDL QFSPWILVPH IGYGFHQYLP YPDGMSPFQA AMVDGSGYQV HRTMQFEDGA SLTVNYRYTY EGSHIKGEAQ VKGTGFPADG PVMTNSLTAA DWCRSKKTYP NDKTIISTFK WSYTTGNGKR YRSTARTTYT FAKPMAANYL KNQPMYVFRK TELKHSKTEL NFKEWQKAFT DVMGMDELYK (SEQ ID NO:35).

35. The rare earth element binding protein according to claim 26, wherein the protein is or comprises the following sequence: >Al-LanM(H60A) (also referred to as Al-H60A) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FAAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:6); >Al-LanM(H60N) (also referred to as Al-H60N) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FNAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:7); >Al-LanM(S102T) (also referred to as Al-S102T) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK (SEQ ID NO:9); >Al-LanM-GSGC LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:10); >Al-LanM(S102T)-GSGC (GSGC is SEQ ID NO:62)LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLTLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GSGC (SEQ ID NO:11); >TD9 – Al-LanM tandem dimer (42-aa GGS linker) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VK (SEQ ID NO:28); >TD9-GSGC (also called TD9-Cys-1) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGSGC (SEQ ID NO:30); >TD9-12mer-Cys (also called TD9-Cys-2) LTGAEFLAQY NKDGDQTLEI PEAIDLGTKT FHAINPDGDT TLEPDETEGR LTKKDWAKIN KDGDQTLELD EYLSLVRARF NAADKNKDGK LTAKELDSKA GQSLLKLIVK GGSGGSGGSG GSGGSGGSGG SGGSGGSGGS GGSGGSGGSG GSLTGAEFLA QYNKDGDQTL EIPEAIDLGT KTFHAINPDG DTTLEPDETE GRLTKKDWAK INKDGDQTLE LDEYLSLVRA RFNAADKNKD GKLTAKELDS KAGQSLLKLI VKGAGHHWGS TGSGC (SEQ ID NO:31).

36. A device comprising the rare earth element binding protein according to claims 1, 12, 18, or 26.

37. The device according to claim 36, wherein the device is a filter, membrane, sensor, handheld detector, plate reader, fluorimeter, biosensor, or in-line monitor.

38. A kit comprising the rare earth element binding protein according to claims 1, 12, 18, or 26 or materials to prepare a device comprising the rare earth element binding protein according to claims 1, 12, 18, or 26.

39. A method for rare earth element ions to a protein comprising contacting one or more rare earth element binding protein according to claims 1, 12, 18, or 26 with a sample comprising or suspected of comprising rare earth element ions and one or more of the rare earth element ions binds to the one or more rare earth element binding protein according to claims 1, 12, 18, or 26.

40. The method according to claim 39, wherein the rare earth element ions are chosen from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, Ac, Th, U, Np, Pu, Am, Cm, Bk, Cf, and Es, and any combination thereof.

41. The method according to claim 39, wherein the sample is drinking water, wastewater, ground water, process water, ash ponds, aqueous extract from contaminated soil, drainage, leachate, aqueous extract or leachate from a solid waste, or a solid sample.

42. The method according to claim 39, further comprising isolating the one or more rare earth element binding proteins having one or more rare earth element ions bound thereto.

43. The method according to claim 42, wherein the one or more rare earth element ions are separated individually from the one or more rare earth element binding proteins.

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