Membrane lipids drive formation of KRAS4b-RAF1 RBDCRD nanoclusters on the membrane

Area of Science:

• Molecular biology
• Cell signaling
• Biophysics

Background:

• The oncogene RAS is critical in cell signaling, but its precise role in initiating MAPK cascades at the plasma membrane is not fully understood.
• Existing structural and spatial data from advanced microscopy techniques highlight the need for detailed molecular mechanisms of RAS-mediated signaling, particularly protein-protein and protein-lipid interactions.

Purpose of the Study:

• To investigate the molecular mechanisms of KRAS4b and RAF1 interactions on a lipid bilayer.
• To elucidate how these interactions contribute to the formation of signaling nanoclusters and the activation of MAP kinase pathways.

Main Methods:

• Utilized single-molecule experimental techniques and nuclear magnetic resonance (NMR) spectroscopy.
• Employed the computational Machine-Learned Modeling Infrastructure (MuMMI) for long-timescale simulations with atomic detail on a lipid bilayer.
• Combined in vitro and computational approaches for comprehensive analysis.

Main Results:

• Observed that RBDCRD binding significantly alters KRAS4b lateral diffusion on the lipid bilayer, leading to larger and less mobile clusters.
• Demonstrated that hydrophobic residues in the CRD region of RAS penetrate the lipid bilayer upon membrane binding, stabilizing complexes via β-strand elongation.
• Identified cooperative interactions between lipids, KRAS4b, and RAF1.

Conclusions:

• KRAS4b and RAF1 form membrane-associated nanoclusters through cooperative lipid and protein interactions.
• These nanoclusters, stabilized by hydrophobic interactions and β-strand elongation, are proposed as essential for initiating MAP kinase signal activation.
• The findings provide a molecular basis for RAS-driven signaling and offer potential targets for therapeutic strategies.