Influenza viruses select ordered lipid domains during budding from the plasma membrane

During the budding of enveloped viruses from the plasma membrane, the lipid s are not randomly incorporated into the envelope, but virions seem to have a lipid composition different from the host membrane. Here, we have analyz ed Lipid assemblies in three different viruses: fowl plague virus (FPV) fro m the influenza virus family, vesicular stomatitis virus (VSV), and Semliki Forest virus (SFV). Analysis of detergent extractability of proteins, chol esterol, phosphoglycerolipids, and sphingomyelin in virions showed that FPV contains high amounts of detergent-insoluble complexes, whereas such compl exes are largely absent from VSV or SFV. Cholesterol depletion from the vir al envelope by methyl-beta-cyclodextrin results in increased solubility of sphingomyelin and of the glycoproteins in the FPV envelope. This biochemica l behavior suggest that so-called raft-lipid domains are selectively incorp orated into the influenza virus envelope. The "fluidity" of the FPV envelop e, as measured by the fluorescence polarization of diphenylhexatriene, was significantly lower than compared with VSV or SFV. Furthermore, influenza v irus hemagglutinin incorporated into the envelope of recombinant VSV was la rgely detergent-soluble, indicating the depletion of raft-lipid assemblies from this membrane. The results provide a model for lipid selectivity durin g virus budding and support the view of lipid rafts as cholesterol-dependen t, ordered domains in biological membranes.