Modulation of structured polypeptide specificity

A peptide ligand specific for human Kallikrein comprising a polypeptide comprising three reactive groups, separated by two loop sequences, and a molecular scaffold which forms covalent bonds with the reactive groups of the polypeptide such that two polypeptide loops are formed on the molecular scaffold, wherein the loops of the peptide ligand comprise five amino acids and wherein the polypeptide comprises the motif Grx1x2x3x4x5Grx6x7x8x9x10Gr, wherein x1 and x9 are independently any amino acid, x2 is tryptophan or phenylalanine, x3 is proline or azetidine carboxylic acid, x4 is alanine or tyrosine, x5 is arginine, N-methyl arginine, homoarginine, or guanidylphenylalanine, x6 is tyrosine, leucine or alanine, x7 is histidine, x8 is glutamine or threonine, x10 is leucine, and Gr represents cysteine;

• and wherein the peptide bond between x6 and x7 is replaced by ΨCH2NH.