Patent ID: 7351690

Claim:
A method of determining the specific residues binding to a target of interest, such residues being within a known parent polypeptide that binds to the target of interest, comprising the steps of: (a) providing a known parent polypeptide with a known primary structure, such primary structure consisting of n residues where n is 3 to about 20 amino acid residues, which parent polypeptide binds to a target of interest; (b) constructing a first peptide of the formula R 1 —Z—R 2 , wherein R 1 comprises from 2 to n residues, such residues being the same as residues in the parent polypeptide and in the same order as residues in the parent polypeptide primary structure, provided that any proline residue in the two residue positions immediately adjacent the amino-terminus side of Z is substituted with glycine, alanine, serine, 2-aminoisobutyric acid (Aib), 1-amino, 1-cyclopentane carboxylic acid, or dehydroalanine, and any cysteine residue in R 1 is S-protected or substituted with glycine, alanine, serine, 2-aminoisobutyric acid, 1-amino, 1-cyclopentane carboxylic acid, or dehydroalanine; Z is an amino acid residue providing both a nitrogen atom (N) and a sulfur atom (S) for metal ion complexation; R 2 comprises from 0 to n−2 residues, such residues being the same as residues in the parent polypeptide and in the same order as residues in the parent polypeptide primary structure, provided that any cysteine residue is S-protected or substituted with glycine, alanine, serine, 2-aminoisobutyric acid, 1-amino, 1-cyclopentane carboxylic acid, or dehydroalanine, and forming with R 1 a sequence in the same order as in the parent polypeptide primary structure with Z either inserted between two adjacent residues corresponding to two adjacent residues in such primary structure or substituting for a single residue corresponding to a single residue in such primary structure, and wherein the residues comprising R 1 —Z—R 2 are equal to either n or n+1; (c) complexing the first peptide of the formula R 1 —Z—R 2 to a rhenium (Re) or technetium (Tc) metal ion, thereby forming a first R 1 —Z—R 2 metallopeptide; (d) screening the first R 1 —Z—R 2 metallopeptide for binding to the target of interest; (e) repeating steps (b) through (d), wherein the resulting R 1 —Z—R 2 metallopeptide differs in at least either R 1 or R 2 ; and (f) selecting the R 1 —Z—R 2 metallopeptide exhibiting decreased binding to the target of interest as compared to the binding of the parent polypeptide to the target of interest, whereby at least one residue of the sequence binding to the metal ion of such R 1 —Z—R 2 metallopeptide is identified as the specific residues of the parent polypeptide binding to the target of interest.