Avidity-driven polarity establishment via multivalent lipid-GTPase module interactions

Abstract

While Rho GTPases are indispensible regulators of cellular polarity, the mechanisms underlying their anisotropic activation at membranes have been elusive. Using the budding yeast Cdc42 GTPase module, which includes a Guanine nucleotide Exchange Factor (GEF) Cdc24 and the scaffold Bem1, we find that avidity generated via multivalent anionic lipid interactions is a critical mechanistic constituent of polarity establishment. We identify Cationic-enriched Lipid Interacting Clusters (CLICs) in Bem1 that drive the interaction of the scaffold-GEF complex with anionic lipids at the cell pole. This interaction increases lipid acyl chain ordering, thus contributing to membrane rigidity and feedback between Cdc42 and the membrane environment. Sequential mutation of the Bem1 CLIC motifs, PX domain and the PH domain of Cdc24 lead to a progressive loss of cellular polarity stemming from defective Cdc42 nanoclustering on the plasma membrane and perturbed signaling. Our work demonstrates the importance of avidity via multivalent anionic lipid interactions in the spatial control of GTPase activation.