Control of Influenza Virus Binding by Target Membrane Composition

Despite the availability of a vaccine for more than six decades, influenza infection remains a major cause of morbidity and mortality and a global health threat. Infectivity depends on viral hemagglutinin recognizing sialic acid in the host cell membrane to initiate endocytosis and deliver the viral RNA. We have investigated how the lipid composition of target membranes modulates viral binding by visualizing the interaction of fluorescently labeled virions with synthetic planar lipid bilayers in a microfluidic device. In comparative studies of membranes supplemented with seven different sterol analogues, ketocholesterol (K-chol) outperformed other sterol variants in enhancing viral capture. Membranes containing 10 mol % K-chol showed a 35% increase in viral binding when compared to 10 mol % cholesterol membranes and a 60% enhancement when compared to sterol-free membranes. FRAP measurements demonstrated that K-chol decreased lipid lateral diffusion constants by a factor of two, confirming that K-chol is differentially altering membrane behavior. Both heightened viral capture and diminished lipid diffusion rates were nonlinearly dependent on K-chol concentration. In addition, at a constant mol % sterol, K-chol-containing membranes showed a much greater sensitivity to GD1A concentration, saturating binding at 4-fold lower mol % GD1A than membranes containing an equimolar amount of cholesterol. These data are compatible with virus-membrane contact involving a multivalent interaction that is highly sensitive to membrane organization and lipid mobility. Therefore, membrane sterol composition modulates influenza virus-receptor binding in a manner closely correlated to nanoscale organization and dynamics. The resulting changes to receptor sensitivity may be important in controlling permissiveness to infection.