Binding compounds and methods for identifying binding compounds

A method for determining an amino acid sequence binding motif for a phosphorylation site of a kinase, comprising:

• a) contacting the kinase with a peptide library, wherein each peptide comprises a single non-degenerate phosphorylatable amino acid in a fixed position of the peptide and wherein each peptide comprises one or more degenerate amino acids, under conditions which allow for binding of a peptide by the kinase at the phosphorylation site of the kinase;
• b) allowing the kinase to bind peptides of the peptide library having a binding site for the kinase phosphorylation site to form kinase-peptide complexes;
• c) isolating the kinase-peptide complexes from the unbound peptides;
• d) releasing the peptides from the kinase-peptide complexes;
• e) isolating the peptides previously bound to the kinase in kinase-peptide complexes;
• f) determining the amino acid sequences of the peptides isolated in (e);
• and
• g) determining an amino acid sequence motif for a binding site of the kinase based upon the relative abundance of different amino acid residues at each degenerate position within the peptides.