Multiple interactions between an Arf/GEF complex and charged lipids determine activation kinetics on the membrane

Abstract

Significance Small GTPases and their regulators require association to membranes to propagate actions in the cell, but our understanding of how the membrane exerts its effects has remained fragmentary. Here, we combined X-ray crystallography, coarse-grained molecular dynamics, and experimental reconstitution of the lipidated ADP ribosylation factor (Arf) GTPase and its guanine-nucleotide exchange factor, Brag2, in artificial membranes to study how this system functions on membranes. Our results reveal that the Arf/Brag2 complex interacts with multiple PIP 2 lipids, resulting in a well-defined orientation in close apposition to the membrane that explains the exceptional efficiency of activation of Arf by Brag2. Our coarse-grained model provides a structural framework to understand the assembly of Arf GTPases complexes with regulators and effectors at the surface of membranes.