Membrane insertion mechanism of the caveolae coat protein Cavin1

Abstract

Caveolae are small plasma membrane invaginations, important for control of membrane tension, signaling cascades and lipid sorting. The caveolae coat protein Cavin1 is essential for shaping such high curvature membrane structures. Yet, a mechanistic understanding of how Cavin1 assembles at the membrane interface is lacking. Here, we used model membranes combined with biophysical dissection and computational modelling to show that Cavin1 inserts into membranes. We establish that initial PI(4,5)P2-dependent membrane adsorption of the trimeric helical region 1 (HR1) of Cavin1 mediates the subsequent partial separation and membrane insertion of the individual helices. Insertion kinetics of the HR1 is further enhanced by the presence of flanking negatively charged disordered regions, which was found important for the co-assembly of Cavin1 with Caveolin1 in living cells. We propose that this intricate mechanism potentiates membrane curvature generation and facilitates dynamic rounds of assembly and disassembly of Cavin1 at the membrane. Significance statementCaveolae are cholesterol enriched membrane invaginations coupled to severe muscle and lipid disorders. Their formation is dependent on assembly of the protein Cavin1 at the lipid membrane interface driving membrane curvature. In this work, we dissect the mechanism for how Cavin1 binds and inserts into membranes using a combination of biochemical and biophysical characterization as well as computational modelling. The proposed model for membrane assembly potentiates dynamic switching between shielded and exposed hydrophobic helices used for membrane insertion and clarifies how Cavin1 can drive membrane curvature and the formation of caveolae.