Arf GTPase activates the WAVE Regulatory Complex through a novel binding site

Abstract

Crosstalk between Rho- and Arf-family GTPases plays an important role in linking actin cytoskeletal remodeling to membrane protrusion, organelle structure, and vesicle trafficking. The central actin regulator, WAVE Regulatory Complex (WRC), is a converging point of Rac1 (a Rho-family GTPase) and Arf signaling in many processes, but how Arf promotes WRC activation is unknown. Here we reconstituted a direct interaction between Arf and WRC. This interaction can be greatly enhanced by Rac1 binding to the D site of the WRC. Arf1 binds to a newly identified conserved surface on Sra1 located between the D site and the WH2 helix of WAVE1, which can drive WRC activation using a mechanism distinct from that of Rac1. Mutating Arf binding site abolishes Arf1-WRC interaction, disrupts Arf1-mediated WRC activation, and impairs lamellipodia morphology. This work uncovers a new mechanism underlying WRC activation and provides a mechanistic foundation for studying how WRC-mediated actin polymerization links Arf and Rac signaling in the cell.