STRUCTURE OF THE WW DOMAIN OF A KINASE-ASSOCIATED PROTEIN COMPLEXED WITH A PROLINE-RICH PEPTIDE

THE WW domain is a new protein module with two highly conserved trypto phans that binds proline-rich peptide motifs in vitro. It is present i n a number of signalling and regulatory proteins, often in several cop ies(1-3). Here we investigate the solution structure of the WW domain of human YAP65 (for Yes kinase-associated protein) in complex with pro line-rich peptides containing the core motif PPxY (ref. 4). The struct ure of the domain with the bound peptide GTPPPPYTVG is a slightly curv ed, three-stranded, antiparallel beta-sheet. Two prolines pack against the first tryptophan, forming a hydrophobic buckle on the convex side of the sheet. The concave side has three exposed hydrophobic residues (tyrosine, tryptophan and leucine) which form the binding site for th e ligand, A non-conserved isoleucine in the amino-terminal flanking re gion covers a hydrophobic patch and stabilizes the WW domain of human YAP65 irt vitro. The structure of the WW domain differs from that of t he SH3 domain and reveals a new design for a protein module that uses stacked aromatic surface residues to arrange a binding site for prolin e-rich peptides.