Why does the Ras switch "break" by oncogenic mutations?

Area of Science:

• Biochemistry
• Molecular Biology
• Computational Biology

Background:

• RasGAP complex structure elucidation links protein structure to cancer-causing mutations.
• Gln 61 mutations in RasGAP are known to destroy GTPase activity, leading to cellular "ON" states and cancer.
• The precise mechanism by which Gln 61 mutations drive oncogenesis remains unclear.

Purpose of the Study:

• To elucidate the role of Gln 61 in the RasGAP complex's GTPase reaction.
• To understand the molecular basis for Gln 61's critical function in cancer.
• To investigate the impact of Gln 61 mutations on the catalytic activity and stability of the RasGAP complex.

Main Methods:

• Computer simulations of the GTPase reaction involving Ras, RasGAP, and their mutants.
• Analysis of activation energies and energy contributions associated with Gln 61 mutations.
• Investigation of the transition state (TS) interactions and active site configuration.

Main Results:

• Simulations accurately reproduced observed changes in activation energies due to Gln 61 mutations.
• Gln 61 does not directly interact chemically, electrostatically, or sterically with the transition state.
• Oncogenic Gln 61 mutations disrupt the preorganized catalytic configuration of the RasGAP active site, causing significant loss of transition state stabilization.

Conclusions:

• Gln 61's function is allosteric, maintaining the active site's catalytic configuration.
• The disruption of this configuration by mutations leads to reduced transition state stabilization and oncogenesis.
• Findings have broader implications for understanding signal transduction proteins and related diseases.