Cold co-extraction of hemagglutinin and matrix M1 protein from influenza virus A by a combination of non-ionic detergents allows for visualization of the raft-like nature of the virus envelope.

Membrane solubilization with a mixture of cold non-ionic detergents has been applied to isolate detergent-resistant membranes from intact virus A lipid bilayer. Association of the viral envelope glycoproteins and M1 into a raft lipid-protein complex was verified via detergent insolubility experiments, and the M1:HA stoichiometry of the proposed supramolecular complex was estimated via amino acid analysis. Electron microscopy and dynamic light scattering data revealed that these lipid-protein rafts form unilamellar vesicles with HA spikes on their surfaces similar to influenza virus virions. Together, our data suggest that the cold co-extraction technique visualizes the raft-like nature of the viral envelope and demonstrates the interaction of matrix M1 protein with the envelope.