Simulations suggest a scaffolding mechanism of membrane deformation by the caveolin 8S complex

Caveolins form complexes of various sizes that deform membranes into polyhedral shapes. However, the recent structure of the 8S complex was disk-like with a flat membrane-binding surface. How can a flat complex deform membranes into nonplanar structures? Molecular dynamics simulations revealed that the 8S complex rapidly takes the form of a suction cup. Simulations on implicit membrane vesicles determined that binding is stronger when E140 gets protonated. In that case, the complex binds much more strongly to 5 and 10-nm radius vesicles. A concave membrane binding surface readily explains the membrane-deforming ability of caveolins by direct scaffolding. We propose that the 8S complex sits at the vertices of the caveolar polyhedra, rather than at the center of the polyhedral faces. Significance Caveolae are membrane invaginations that play important roles in eukaryotic cells. Crucial for their formation is the caveolin protein family, but the mechanism by which these proteins deform membranes is unclear. Molecular dynamics simulations revealed that a recently determined structure changes shape from flat to concave. With one titratable residue protonated, this structure binds more strongly to spherical membranes, thus providing a possible mechanism for the membrane-deforming ability of caveolins.