The Ras-RasGAP Complex: Structural Basis for GTPase Activation and Its Loss in Oncogenic Ras Mutants

TLDR

Arginine‑789 of GAP‑334 inserts into Ras’s active site to neutralize transition‑state charges, while GAP‑334 stabilizes Ras switch II, enabling catalytic participation of glutamine‑61. High‑resolution (2.5 Å) crystal structure of the H‑Ras–GAP‑334 complex reveals a mixed hydrophilic/hydrophobic interface sensitive to salts and lipids, supports an associative phosphoryl‑transfer mechanism, and explains how G12 and Q61 mutations activate Ras by positioning these residues near GAP‑334’s arginine‑789.

Abstract

The three-dimensional structure of the complex between human H-Ras bound to guanosine diphosphate and the guanosine triphosphatase (GTPase)–activating domain of the human GTPase-activating protein p120 GAP (GAP-334) in the presence of aluminum fluoride was solved at a resolution of 2.5 angstroms. The structure shows the partly hydrophilic and partly hydrophobic nature of the communication between the two molecules, which explains the sensitivity of the interaction toward both salts and lipids. An arginine side chain (arginine-789) of GAP-334 is supplied into the active site of Ras to neutralize developing charges in the transition state. The switch II region of Ras is stabilized by GAP-334, thus allowing glutamine-61 of Ras, mutation of which activates the oncogenic potential, to participate in catalysis. The structural arrangement in the active site is consistent with a mostly associative mechanism of phosphoryl transfer and provides an explanation for the activation of Ras by glycine-12 and glutamine-61 mutations. Glycine-12 in the transition state mimic is within van der Waals distance of both arginine-789 of GAP-334 and glutamine-61 of Ras, and even its mutation to alanine would disturb the arrangements of residues in the transition state.