Conformational Dynamics Allows Sampling of an "Active-like" State by Oncogenic K-Ras-GDP

Area of Science:

• Molecular biology
• Structural biology
• Cancer research

Background:

• K-Ras GTPase mutations (G12D, G12V) are prevalent in cancer, impairing GTP hydrolysis and increasing active K-Ras-GTP.
• These mutations drive cancer progression, but distinct structural features between G12D and G12V remain unclear.

Purpose of the Study:

• To investigate the distinct structural dynamics of oncogenic K-Ras4B mutants (G12D vs. G12V) in their GDP-bound state.
• To elucidate the underlying molecular mechanisms responsible for observed conformational differences.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy
• X-ray crystallography
• Computational modeling

Main Results:

• Oncogenic K-Ras4B mutants, particularly G12V, exhibit distinct GDP-bound conformational dynamics, accessing an 'active-like' state.
• The V12 side chain's interaction with the Switch II region in K-Ras4B^G12V-GDP differentiates it from K-Ras4B^G12D-GDP.
• Crystal contacts masked these dynamics in prior X-ray studies, explaining the lack of reported structural differences.

Conclusions:

• A novel K-Ras activation mechanism involving mutation-induced conformational dynamics in the GDP-bound state is proposed.
• These findings suggest that therapeutic strategies targeting K-Ras-GTP levels may have differential efficacy depending on the specific oncogenic mutation.