Cholesterol-Induced Membrane Organization Promotes Influenza Virus Binding

Abstract

The influenza virus attaches to a cell surface by binding sialic-acid containing receptors with the viral ligand hemagglutinin. Stable viral binding requires more than one viral ligand- host receptor interaction to simultaneously occur. Thus, binding can be modulated by the spatial distribution of target receptors in the host membrane. We show that membrane sterols critically control viral attachment and propose that sterols alter the nanoscale clustering of viral receptors to facilitate binding. Using single virus fluorescence microscopy, we demonstrated that viral binding is dependent on the cholesterol content of the target membrane. Fluorescently labeled viral particles preferentially bound synthetic membranes supplemented with increasing amounts of cholesterol (0-40 mol%). Other sterols exhibited a similar effect on binding, independent of their ability to support liquid-liquid phase separation. To develop a molecular explanation for cholesterol's effect, we ran a series of course grained molecular dynamics simulations of lipid bilayers containing the viral receptor, disialoganglioside GD1a. While simulated GD1a molecules self-associated independent of cholesterol, the dissociation rate between pairs of GD1a molecules was a function of bilayer cholesterol concentration. Additionally, cholesterol increased the order parameter of simulated GD1a lipid tails. We suggest that, by preordering the viral receptor in its monomeric state, cholesterol lowers the entropic penalty of receptor association. This in turn promotes the formation of GD1a multimers and increases the influenza virus binding avidity of the lipid bilayer. Our findings assign a critical role to the host cellular membrane in viral infectivity and reveal sterol-dependent membrane organization not associated with phase separation.