KRas4b–Calmodulin\nInteraction with Membrane\nSurfaces: Role of Headgroup, Acyl Chain, and Electrostatics

KRas4b is a small plasma membrane-bound G-protein that\nregulates\nsignal transduction pathways. The interaction of KRas4b with the plasma\nmembrane is governed by both its basic C-terminus, which is farnesylated\nand methylated, and the lipid composition of the membrane itself.\nThe signaling activity of KRas4b is intricately related to its interaction\nwith various binding partners at the plasma membrane, underlining\nthe critical role played by the lipid environment. The calcium-binding\nprotein calmodulin binds farnesylated KRas4b and plays an important\nrole in the dynamic spatial cycle of KRas4b trafficking in the cell.\nWe utilize Biolayer Interferometry to assay the role of lipid headgroup,\nchain length, and electrostatics in the dissociation kinetics of fully\npost-translationally modified KRas4b from Nanodisc bilayers with defined\nlipid compositions. Our results suggest that calmodulin promotes the\ndissociation of KRas4b from an anionic membrane, with a comparatively\nslower displacement of KRas4b from PIP2 relative to PS containing\nbilayers. In addition to this headgroup dependence, KRas4b dissociation\nappears to be slower from Nanodiscs wherein the lipid composition\ncontains mismatched, unsaturated acyl chains as compared to lipids\nwith a matched acyl chain length. These findings contribute to understanding\nthe role of the lipid composition in the binding of KRas4b and release\nfrom lipid bilayers, showing that the overall charge of the bilayer,\nthe identity of the headgroups present, and the length and saturation\nof the acyl chains play key roles in KRas4b release from the membrane,\npotentially providing insights in targeting Ras-membrane interactions\nfor therapeutic interventions.