Solution structure of GAP SH3 domain by 1H NMR and spatial arrangement of essential Ras signaling‐involved sequence

Src homology 3 (SH3) domains are found in numerous cytoplasmic proteins involved in intracellular signal transduction. We used 2‐D 1H NMR to determine the structure of the SH3 domain of the guanosine triphosphatase‐activating protein (GAP), an essential component of the Ras signaling pathway. The structure of the GAP SH3 domain (275‐350) was found to be a compact beta‐barrel made of six antiparallel beta‐strands arranged in two roughly perpendicular beta‐sheets with the acidic residues located at the surface of the protein. The Trp317, Trp319, Thr321 and Leu323 residues belonging to the sequence (317‐326), which was shown to be essential for Ras signaling, formed two nearby lipophilic bulges followed by a hydrophilic domain (Arg324‐Asp326). These structural data could be used to characterize the still unidentified downstream components of GAP, which are involved in Ras signaling, and to rationally design inhibitors of this pathway.