Revealing KRas4b topology on the membrane surface

Area of Science:

• Molecular Biology
• Biophysics
• Cancer Research

Background:

• KRas4b is a small GTPase crucial for signal transduction, acting as a molecular switch.
• Oncogenic KRas4b mutations drive ~85% of Ras-driven cancers, making its membrane-bound state a therapeutic target.
• The precise conformation and membrane interaction of KRas4b remain debated, with conflicting models suggesting membrane-proximal or distal orientations.

Purpose of the Study:

• To investigate the membrane-bound conformation of KRas4b using advanced biophysical techniques.
• To elucidate the role of anionic lipids in modulating KRas4b's topology and interactions.
• To provide insights for developing targeted therapies against KRas4b-driven oncogenic signaling.

Main Methods:

• Utilized Förster Resonance Energy Transfer (FRET) measurements to determine KRas4b conformation.
• Employed a Nanodisc-based assay with fully post-translationally modified KRas4b.
• Studied KRas4b interactions with model membrane bilayers containing anionic lipids.

Main Results:

• Demonstrated an extended conformation of KRas4b relative to the membrane surface.
• Quantified FRET donor-acceptor distances, revealing conformational dynamics.
• Showed that negatively charged membrane surfaces weakly promote closer association of KRas4b with the membrane.

Conclusions:

• KRas4b adopts a predominantly extended conformation on the membrane surface.
• Anionic lipids play a significant role in determining the dynamic conformations and membrane association of KRas4b.
• Findings offer a deeper understanding of KRas4b's membrane topology, crucial for targeting oncogenic signaling pathways.