SOLUTION STRUCTURE OF GAP SH(3) DOMAIN BY H-1-NMR AND SPATIAL ARRANGEMENT OF ESSENTIAL RAS SIGNALING-INVOLVED SEQUENCE

Src homology 3 (SH3) domains are found in numerous cytoplasmic protein s involved in intracellular signal transduction. We used 2-D H-1 NMR t o determine the structure of the SH3 domain of the guanosine triphosph atase-activating protein (GAP), an essential component of the Ras sign aling pathway. The structure of the GAP SH3 domain (275-350) was found to be a compact beta-barrel made of six antiparallel beta-strands arr anged in two roughly perpendicular beta-sheets with the acidic residue s located at the surface of the protein. The Trp317, Trp319, Thr321 an d Leu323 residues belonging to the sequence (317-326), which was shown to be essential for Ras signaling, formed two nearby lipophilic bulge s followed by a hydrophilic domain (Arg324-Asp326). These structural d ata could be used to characterize the still unidentified downstream co mponents of GAP, which are involved in Ras signaling, and to rationall y design inhibitors of this pathway.