The arginine finger of RasGAP helps Gln-61 align the nucleophilic water in GAP-stimulated hydrolysis of GTP.
The Ras family of GTPases is a collection of molecular switches that link receptors on the plasma membrane to signaling pathways that regulate cell proliferation and differentiation. The accessory GTPase-activating proteins (GAPs) negatively regulate the cell signaling by increasing the slow intrinsic GTP to GDP hydrolysis rate of Ras. Mutants of Ras are found in 25-30% of human tumors. The most dramatic property of these mutants is their insensitivity to the negative regulatory action of GAPs. All known oncogenic mutants of Ras map to a small subset of amino acids. Gln-61 is particularly important because virtually all mutations of this residue eliminate sensitivity to GAPs. Despite its obvious importance for carcinogenesis, the role of Gln-61 in the GAP-stimulated GTPase activity of Ras has remained a mystery. Our molecular dynamics simulations of the p21ras-p120GAP-GTP complex suggest that the local structure around the catalytic region can be different from that revealed by the x-ray crystal structure. We find that the carbonyl oxygen on the backbone of the arginine finger supplied in trans by p120GAP (Arg-789) interacts with a water molecule in the active site that is forming a bridge between the NH(2) group of the Gln-61 and the gamma-phosphate of GTP. Thus, Arg-789 may play a dual role in generating the nucleophile as well as stabilizing the transition state for PO bond cleavage.
Resat
H
H
Pacific Northwest National Laboratory, Richland, WA 99352, USA. haluk.resat@pnl.gov
Straatsma
T P
TP
Dixon
D A
DA
Miller
J H
JH
D001120:Arginine / Q000737:chemistry*; D001665:Binding Sites; D016000:Cluster Analysis; D005973:Glutamine / Q000737:chemistry*; D006160:Guanosine Triphosphate / Q000737:chemistry*; D006868:Hydrolysis; D016283:Proto-Oncogene Proteins p21(ras) / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D020729:p120 GTPase Activating Protein / Q000737:chemistry*
D020729:p120 GTPase Activating Protein; D014867:Water; D005973:Glutamine; D006160:Guanosine Triphosphate; D001120:Arginine; D016283:Proto-Oncogene Proteins p21(ras)