Figure 2.

An unusual conformation for the FLVR arginine of p120RasGAP C-SH2. A, crystal structure of phosphopeptide-bound p120RasGAP C-SH2 showing the FLVR arginine Arg³⁷⁷, Asp³⁸⁰, and Tyr³⁸⁹ and p190RhoGAP pTyr¹⁰⁸⁷. B, crystal structure of apo p120RasGAP C-SH2. C, crystal structure of phosphopeptide-bound p120RasGAP N-SH2 (PDB code 2PXC) (39) showing the equivalent residues and phosphotyrosine. D, superposition of FLVR motif arginines from 592 Dali-aligned SH2 domains. E, crystal structure of Src family kinase Fyn (PDB code 4U1P) shows residue BC1 (Glu⁵³) caps helix αB.