Peptide library and use thereof

A method for producing a peptide that binds to a target molecule, wherein the target molecule is not an endogenous target of SPINK2 selected from trypsin or acrosin, the method comprising the following steps (i) to (iii):

• (i) contacting a plurality of peptides with the target molecule, wherein each of the plurality of peptides has an amino acid sequence with at least 80% sequence identity to SEQ ID NO:15, wherein each peptide comprises an amino acid sequence comprising SEQ ID NO:1 wherein X can be any amino acid except Cys, and wherein each peptide is conjugated at
• (a) its amino terminus to an amino acid sequence encoded by the nucleic acid sequence from the 1st base guanine or the 4th base cytosine to the 42nd base thymine of SEQ ID NO:14, and
• (b) its carboxyl terminus to an amino acid sequence encoded by the nucleic acid sequence from the 94th base guanine to the 189th base cytosine in SEQ ID NO:14;
• and
• (ii) recovering a peptide that binds to the target molecule;
• and
• (iii) preparing, by chemical synthesis, gene recombination, or in vitro translation, a peptide that binds to the target molecule, wherein said peptide corresponds to the peptide recovered in step (ii).

A method for determining whether or not a peptide binds to a target molecule, wherein the target molecule is not an endogenous target of SPINK2 selected from trypsin or acrosin, the method comprising the following steps (i) and (ii):

• (i) contacting a plurality of peptides with the target molecule, wherein each of the plurality of peptides has an amino acid sequence with at least 80% sequence identity to SEQ ID NO:15, wherein each peptide comprises an amino acid sequence comprising SEQ ID NO:1 wherein X can be any amino acid except Cys, and wherein each peptide is conjugated at
• (a) its amino terminus to an amino acid sequence encoded by the nucleic acid sequence from the 1st base guanine or the 4th base cytosine to the 42nd base thymine of SEQ ID NO:14, and
• (b) its carboxyl terminus to an amino acid sequence encoded by the nucleic acid sequence from the 94th base guanine to the 189th base cytosine in SEQ ID NO:14;
• and
• (ii) determining that a peptide is positive for binding when the peptide binds to the target molecule;
• and
• (iii) preparing, by chemical synthesis, gene recombination, or in vitro translation, a peptide that binds to the target molecule, wherein said peptide corresponds to the peptide recovered in step (ii).