K-Ras, a molecular switch that regulates cell growth, apoptosis and metabolism, is activated when it undergoes a conformation change upon binding GTP and is deactivated following the hydrolysis of GTP to GDP. Hydrolysis of GTP in water is accelerated by coordination to K-Ras, where GTP adopts a high-energy conformation approaching the transition state. The G12A mutation reduces intrinsic K-Ras GTP hydrolysis by an unexplained mechanism. Here, crystal structures of G12A K-Ras in complex with GDP, GTP, GTPγS and GppNHp, and of Q61A K-Ras in complex with GDP, are reported. In the G12A K-Ras–GTP complex, the switch I region undergoes a significant reorganization such that the Tyr32 side chain points towards the GTP-binding pocket and forms a hydrogen bond to the GTP γ-phosphate, effectively stabilizing GTP in its precatalytic state, increasing the activation energy required to reach the transition state and contributing to the reduced intrinsic GTPase activity of G12A K-Ras mutants.
Keywords: K-Ras; G12A K-Ras; Q61A K-Ras; GTP hydrolysis; precatalytic state; cell growth regulation; cancer cell regulation; apoptosis.
Supporting information
Portable Document Format (PDF) file https://doi.org/10.1107/S2059798317015418/dw5182sup1.pdf |
PDB references: G12A K-Ras–GTP, 5vpi; G12A K-Ras–GppNHp, 5vpy; G12A K-Ras–GTPγS, 5vpz; G12A K-Ras–GDP, 5vp7; G12A K-Ras–GDP, EDTA-treated, 5vq0; Q61A K-Ras–GDP, 5vq1; WT K-Ras–GTP, 5vq2; WT K-Ras–GTPγS, 5vq6; WT K-Ras–GDP, EDTA-treated, 5vq8; WT K-Ras–GDP, 5w22