The Self‐Association of the KRAS4b Protein is Altered by Lipid‐Bilayer Composition and Electrostatics

AbstractKRAS is a peripheral membrane protein that regulates multiple signaling pathways, and is mutated in ≈30 % of cancers. Transient self‐association of KRAS is essential for activation of the downstream effector RAF and oncogenicity. The presence of anionic phosphatidylserine (PS) lipids in the membrane was shown to promote KRAS self‐assembly, however, the structural mechanisms remain elusive. Here, we employed nanodisc bilayers of defined lipid compositions, and probed the impact of PS concentration on KRAS self‐association. Paramagnetic NMR experiments demonstrated the existence of two transient dimer conformations involving alternate electrostatic contacts between R135 and either D153 or E168 on the “α4/5‐α4/5” interface, and revealed that lipid composition and salt modulate their dynamic equilibrium. These dimer interfaces were validated by charge‐reversal mutants. This plasticity demonstrates how the dynamic KRAS dimerization interface responds to the environment, and likely extends to the assembly of other signaling complexes on the membrane.