Influenza Binding Avidity Governed by Sterol-Dependent Ganglioside Dynamics

Abstract

Influenza virions attach to host membranes by binding cell-surface glycans containing sialic acid, initiating the viral life cycle and infecting cells. While the primary determinant of viral binding is thought to be the glycan chemical structure, single interactions between a viral hemagglutinin binding site and a sialic acid are weak, so binding specificity is presumed to occur via multivalent interactions. Here, we show that target membrane composition can alter influenza binding while total receptor content is held constant. We hypothesize that this effect occurs by changing the spatial distribution of target receptors. Viral binding was quantitated by monitoring individual viruses binding to synthetic supported lipid bilayers using fluorescence microscopy. Adding cholesterol to target bilayers increased binding in a dose-dependent manner. Furthermore, membranes containing 5-cholesten-3-one, an oxidized variant of cholesterol, displayed significantly higher binding avidity compared to membranes supplemented with an equal amount of cholesterol. When sterol mole fractions were held constant, viral target receptor concentration and binding exhibited a sigmoidal relationship, confirming the multivalent nature of virus receptor binding. The cooperativity required for binding established the potential for local receptor concentration to regulate membrane binding affinity. To develop a physical model for sterol-induced changes in the lateral organization of GD1a receptors, we performed coarse grained molecular dynamics simulations of target lipid bilayers. Irrespective of sterol content, GD1a receptors showed strong tendencies to self-associate. The inclusion of cholesterol in membranes increased pairwise receptor contacts, suggesting that sterol addition stabilized target receptor clustering. This observation supports the hypothesis that sterols can modulate membrane nanoscale organization and thus alter viral binding avidity, illuminating a previously underappreciated mechanism by which target membrane context can influence influenza infectivity.