Key Oncogenic Ras Mutations Impair Limiting Proton Transfer Rates

Ras-positive cancer constitutes a major challenge for medical treatment. Hot spot residues Gly12, Gly13 and Gln61 constitute the majority of oncogenic mutations which are associated with detrimental clinical prognosis. Here we present a two-step mechanism of GTP hydrolysis of the wild type Ras.GAP complex using QM/MM free energy calculations with the finite-temperature string method. We found that the deprotonation of the catalytic water takes place via the Gln61 as a transient Brønsted base. We obtained reaction profiles for key oncogenic Ras mutants G12D and G12C, reproducing the experimentally observed loss of catalytic activity, and validating our reaction mechanism.