Interaction of Sendai virus proteins with the cytoplasmic surface of erythrocyte membranes following viral envelope fusion.

Radiolabeled Sendai virus was allowed to fuse with human erythrocytes and inside out vesicles were prepared from the erythrocyte membranes. Viral proteins incorporated into inside out vesicles were released from the membrane following treatment with various agents which perturb protein structure. Disruption products were analyzed by sucrose gradient centrifugation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis to identify the viral proteins. The results indicated that 6 M guanidine, 40 mM lithium diiodosalicylate (pH 11-13), and 4 M potassium thiocyanate removed viral nucleocapsid and M proteins from the vesicles. Urea (6.0 M) and 5 mM p-chloromercuribenzenesulfonate removed only viral nucleocapsid proteins. KCl (1.0 or 0.1 M), 5 or 0.5 mM sodium phosphate, 10 mM EDTA (pH 10), 10 mM lithium diiodosalicylate, 1 M urea, 0.5 mM ATP, or freeze-thaw cycles did not release any viral proteins. By contrast, treatment of inside out vesicles with Triton X-100 solubilizes the lipid bilayer, releasing viral integral membrane glycoproteins and leaving viral nucleocapsids intact. Nucleocapsids isolated from virions do not adsorb nonspecifically to control inside out vesicles. These data imply that Sendai viral nucleocapsid and M proteins interact extensively with the cytoplasmic surface of infected cell membranes, in the manner of peripheral membrane proteins, whereas the glycoproteins, HN and F1, behave as integral membrane proteins.