Biochemical and Structural Analysis of Common Cancer-Associated KRAS Mutations

TLDR

KRAS mutations are the most common genetic abnormalities in cancer, and their distribution across tumor types and differential therapeutic responses imply that distinct KRAS variants possess unique biochemical behaviors. The study aimed to explain clinical differences and identify therapeutic strategies by biochemically characterizing the most common KRAS mutants for substrate binding, GTPase activity, and RAF interaction. The authors performed kinetic assays of mutant KRAS proteins and solved high‑resolution X‑ray structures of GDP‑bound G12V, G12R, and Q61L to reveal structural insights. KRAS G13D exhibited markedly faster nucleotide exchange, attributable to altered electrostatic charge in the active site, and the combined biochemical and structural data suggest that specific KRAS isoforms preferentially signal through RAF, guiding targeted therapy selection.

Abstract

KRAS mutations are the most common genetic abnormalities in cancer, but the distribution of specific mutations across cancers and the differential responses of patients with specific KRAS mutations in therapeutic clinical trials suggest that different KRAS mutations have unique biochemical behaviors. To further explain these high-level clinical differences and to explore potential therapeutic strategies for specific KRAS isoforms, we characterized the most common KRAS mutants biochemically for substrate binding kinetics, intrinsic and GTPase-activating protein (GAP)-stimulated GTPase activities, and interactions with the RAS effector, RAF kinase. Of note, KRAS G13D shows rapid nucleotide exchange kinetics compared with other mutants analyzed. This property can be explained by changes in the electrostatic charge distribution of the active site induced by the G13D mutation as shown by X-ray crystallography. High-resolution X-ray structures are also provided for the GDP-bound forms of KRAS G12V, G12R, and Q61L and reveal additional insight. Overall, the structural data and measurements, obtained herein, indicate that measurable biochemical properties provide clues for identifying KRAS-driven tumors that preferentially signal through RAF.Biochemical profiling and subclassification of KRAS-driven cancers will enable the rational selection of therapies targeting specific KRAS isoforms or specific RAS effectors.