Emerging Insights into the Membrane Binding Domain of RAF Engaging with the Plasma Membrane and its Implication on RAF Activation

Abstract

KRAS, is a peripheral plasma membrane (PM) that functions as a molecular switch to activate MAPK signaling. The first step in the MAPK pathway is the activation of Raf by GTP bound KRAS. This signal is then propagated through the MAPK pathway that results in cell growth and proliferation. Mutations in KRAS, Raf and other constituents in the MAPK pathway result in oncogenesis. Activation of Raf by KRAS occurs only at the PM and it has been shown that Raf interacts with the PM via its cysteine rich domain (CRD), however, the mechanistic details by which Raf engages the membrane is not completely understood. Previous studies show that CRD engages the membrane via insertion of its hydrophobic loops in the PM. However, the structural basis by which this occurs and its role in orienting the Ras binding domain (RBD) of RAF to engage KRAS on the PM has not been well characterized. To investigate this mechanism, we have utilized NMR, biochemical, biophysical and cell imaging techniques to thoroughly characterize how Raf membrane binding domain interact with membranes. Our findings provide insights into how Raf engages with the membrane and the role this interaction may play in Raf activation.