▎ 摘　　要

NOVELTY - A polypeptide is new. USE - The polypeptide is useful in kit or apparatus for conjugating two molecules or components, and purifying or isolating a molecule or component (all claimed), preferably antigen e.g. an antigen associated with disease e.g. infection, an autoimmune disease, allergy or cancer. ADVANTAGE - The polypeptide has excellent solubility, stability, binding affinity and specificity. DETAILED DESCRIPTION - A polypeptide is new. The polypeptide comprises (i) an amino acid sequence of SEQ ID NO: 1, (ii) a portion of (i) comprising an amino acid sequence of SEQ ID NO: 2, (iii) an amino acid sequence with at least 80% sequence identity to a sequence of SEQ ID NO: 1, or (iv) a portion of (iii) comprising an amino acid sequence with at least 80% sequence identity to a sequence of SEQ ID NO: 2. The amino acid sequence (iii), comprises a lysine at position 9, a glutamic acid at position 70 and two or more of glutamic acid at position 4, aspartic acid at position 11, threonine at position 13, aspartic acid at position 47, threonine at position 59, isoleucine at position 69, proline at position 75, serine at position 87, arginine at position 89, and aspartic acid at position 92 in SEQ ID NO: 1, and if the amino acid sequence comprises proline at position 75, the polypeptide further comprises one or more amino acid residues chosen from aspartic acid at position 7, threonine at position 9, aspartic acid at position 43, threonine at position 55, isoleucine at position 65, proline at position 71, arginine at position 85, and aspartic acid at position 88, and the specified amino acid residues are at positions equivalent to the positions in SEQ ID NO: 1. The amino acid sequence (iv) comprises a lysine at position 5, a glutamic acid at position 66 and one or more of aspartic acid at position 7, threonine at position 9, aspartic acid at position 43, threonine at position 55, isoleucine at position 65, proline at position 71, serine at position 83, arginine at position 85, and aspartic acid at position 88, where if the amino acid sequence comprises proline at position 71, the amino acid sequence further comprises one or more amino acid residues chosen from aspartic acid at position 7, threonine at position 9, aspartic acid at position 43, threonine at position 55, isoleucine at position 65, serine at position 83, arginine at position 85, and aspartic acid at position 88, and the specified amino acid residues are at positions equivalent to the positions in SEQ ID NO: 2, and the polypeptide is capable of spontaneously forming an isopeptide bond with a peptide comprising an amino acid sequence of SEQ ID NO: 3, where the isopeptide bond forms between the asparagine residue at position 17 of SEQ ID NO: 3 and the lysine residue at position 9 of SEQ ID NO: 1 or position 5 of SEQ ID NO: 2. INDEPENDENT CLAIMS are included for the following: recombinant or synthetic polypeptide comprising a peptide or polypeptide linked to a polypeptide; nucleic acid molecule comprising a nucleotide sequence which encodes the polypeptide or recombinant polypeptide; vector comprising the nucleic acid molecule; cell comprising the nucleic acid molecule or vector; process for producing or expressing the polypeptide or recombinant polypeptide involves transforming or transfecting a host cell with a vector, culturing the host cell under conditions which allow expression of polypeptide, and optionally isolating the polypeptide; use of a polypeptide to conjugate two molecules or components via an isopeptide bond, where the molecules or components conjugated via an isopeptide bond, comprise a first molecule or component comprising a polypeptide, and a second molecule or component comprising a peptide chosen from (i) a peptide comprising an amino acid sequence of SEQ ID NOs: 3-5 or 17, and (ii) a peptide comprising an amino acid sequence with at least 80% sequence identity to a sequence of SEQ ID NOs: 3-5 or 17, where the peptide is capable of spontaneously forming an isopeptide bond with a polypeptide comprising an amino acid sequence of SEQ ID NO: 1, and the isopeptide bond forms between the asparagine residue at position 17 of SEQ ID NOs: 3, 4, 5 or 17 and the lysine residue at position 9 of SEQ ID NO: 1; process for conjugating two molecules or components via an isopeptide bond involves providing a first molecule or component comprising a polypeptide, providing a second molecule or component comprising a peptide chosen from (i) a peptide comprising amino acid sequences of SEQ ID NOs: 3-5 or 17, and (ii) a peptide comprising an amino acid sequence with at least 80% sequence identity to SEQ ID NOs: 3-5 or 17, and contacting first and second molecules or components under conditions that enable the spontaneous formation of an isopeptide bond between the polypeptide and peptide, and conjugating the first molecule or component to second molecule or component via an isopeptide bond to form a complex, where the amino acid sequence comprises an asparagine residue at position 17 and optionally comprises a threonine residue at position 5, an aspartic acid residue at position 10 and a glycine residue at position 11, the peptide is capable of spontaneously forming an isopeptide bond with a polypeptide comprising an amino acid sequence of SEQ ID NO: 1, the isopeptide bond forms between the asparagine residue at position 17 of SEQ ID NOs: 3, 4, 5 or 17 and the lysine residue at position 9 of SEQ ID NO: 1; kit (K1) comprising the polypeptide, optionally conjugated or fused to a molecule or component, a peptide, optionally conjugated or fused to a molecule or component, and/or a nucleic acid molecule, preferably a vector, encoding a polypeptide; process for purifying or isolating a molecule or component comprising a peptide having an amino acid sequence with at least 80% sequence identity to SEQ ID NOs: 3-5 or 17, involves providing a solid substrate on which a polypeptide is immobilized, providing a sample comprising molecule or component, contacting the solid substrate with the sample under conditions that enable peptide to selectively bind to polypeptide, forming a non-covalent complex between polypeptide immobilized on the solid substrate and molecule or component comprising peptide, washing the solid substrate with a buffer, separating the molecule or component comprising the peptide from the polypeptide immobilized on the solid substrate; use of a polypeptide to purify or isolate a molecule or component comprising the peptide having SEQ ID NOs: 3-5 or 17; apparatus comprising a solid substrate on which a polypeptide is immobilized; and kit (K2) comprising the polypeptide and a unit means for immobilizing the polypeptide on a solid substrate. Sequences not defined here may be found at ftp://ftp.wipo.int/pub/published_pct_sequences/publication.