CRYSTAL-STRUCTURE OF THE SH2 DOMAIN FROM THE ADAPTER PROTEIN SHC - A MODEL FOR PEPTIDE BINDING BASED ON X-RAY AND NMR DATA

Src homology 2 domains (SH2) are protein modules found within a wide v ariety of cytoplasmic signalling molecules that bind with high affinit y to phosphotyrosyl (pY)-containing protein sequences. We report here the crystal structure of the SH2 domain from the adaptor protein SHC ( She), which has been refined by restrained least-squares methods to an X-factor of 17.3% to 2.7 Angstrom. The overall She architecture is es sentially similar to that determined in other SH2 domains but it shows significant differences in a number of loops, thus providing a molecu lar surface With no obvious secondary pocket. Based on the knowledge o f the crystal structure of the protein a model for a low affinity She- bound peptide has been generated from nuclear magnetic resonance data in solution using transferred nuclear Overhauser enhancements as intra molecular distance restraints. The model shows that the tyrosine moiet y binds She in a rather similar way to that observed for other SH2-pep tide complexes, but that the residue in position +3 does not seem to m ake specific contact with the protein. An intermolecular crystallograp hic interaction occurs between the pY-binding site and the C-terminal residues of a symmetry-related molecule. This crystal packing interact ion suggests how inhibitory regulation could play a role in SHC activi ty.