Binding of SV40's Viral Capsid Protein VP1 to Its Glycosphingolipid Receptor GM1 Induces Negative Membrane Curvature: A Molecular Dynamics Study.

Abstract

The binding of the pentameric capsid protein VP1 of simian virus 40 to its glycosphingolipid receptor GM1 is a key step for the entry of the virus into the host cell. Recent experimental studies have shown that the interaction of variants of soluble VP1 pentamers with giant unilamellar vesicles composed of GM1, DOPC, and cholesterol leads to the formation of tubular membrane invaginations to the inside of the vesicles, mimicking the initial steps of endocytosis. We have used coarse-grained and atomistic molecular dynamics (MD) simulations to study the interaction of VP1 with GM1/DOPC/cholesterol bilayers. In the presence of one VP1 protein, we monitor the formation of small local negative curvature and membrane thinning at the protein binding site as well as reduction of area per lipid. These membrane deformations are also observed under cholesterol-free conditions. However, here, the number of GM1 molecules attached to the VP1 binding pockets increases. The membrane curvature is slightly increased for asymmetric GM1 distribution that mimics conditions in vivo, compared to symmetric GM1 distributions which are often applied in experiments. Slightly smaller inward curvature was observed in atomistic control simulations. Binding of four VP1 proteins leads to an increase of the average intrinsic area per lipid in the protein binding leaflet. Membrane fluctuations appear to be the driving force of VP1 aggregation, as was previously shown for membrane-adhering particles because no VP1 aggregation is observed in the absence of a lipid membrane.