ROLE OF TARGET MEMBRANE-STRUCTURE IN FUSION WITH INFLUENZA-VIRUS - EFFECT OF MODULATING ERYTHROCYTE TRANSBILAYER PHOSPHOLIPID DISTRIBUTION

To study the role of the target membrane in influenza virus fusion we chose erythrocyte membranes whose phospholipid arrangement can readily be modified. The phospholipids of normal erythrocytes are arranged as ymmetrically across the plasma membrane, phosphatidylcholine (PC) and sphingomyelin are predominantly on the outer surface, whereas others s uch as phosphatidylserine (PS) and phosphatidylethanolamine (PE) are p redominantly restricted to the inner leaflet. However, erythrocytes ca n be lyzed and resealed under conditions where the asymmetric distribu tion of phospholipids is lost or retained. Low pH-induced fusion of th e A/PR 8 strain of influenza virus, monitored spectrofluorometrically by the octadecylrhodamine dequenching assay, was more rapid with lipid -symmetric erythrocyte ghosts than with lipid-asymmetric ghosts or int act erythrocytes. Neither conversion of PS in the lipid-symmetric ghos t membrane to PE by means of the enzyme PS decarboxylaze, nor incorpor ation of spin-labeled phospholipid analogs with PS, PC or PE headgroup s into the outer leaflet of lipid-asymmetric erythrocytes altered rate s or extents of fusion of A/PR 8 with the modified target. These resul ts indicate that effects on influenza virus fusion are not associated with any particular phospholipid headgroup, but rather related to the packing characteristics of the target membrane.