CONTROL OF BACULOVIRUS GP64-INDUCED SYNCYTIUM FORMATION BY MEMBRANE LIPID-COMPOSITION

We have investigated the effects of membrane lipid composition on biol ogical membrane fusion triggered by low pH and mediated by the baculov irus envelope glycoprotein gp64. Lysolipids, either added exogenously or produced in situ by phospholipase A2 treatment of cell membranes, r eversibly inhibited syncytium formation. Lysolipids also decreased the baculovirus infection rate. In contrast, oleic and arachidonic acids and mono-olein promoted cell-cell fusion. Membrane lipid composition a ffected pH-independent processes which followed the low-pH-induced cha nge in fusion protein conformation. Inhibition and promotion of membra ne fusion by a number of lipids could not be explained by mere binding or incorporation into membranes, but rather was correlated with the e ffective molecular shape of exogenous lipids. Our data are consistent with the hypothesis that membrane fusion proceeds through highly bent membrane intermediates (stalks) having a net negative curvature. Conse quently, inverted cone-shaped lysolipids inhibit and cone-shaped cis-u nsaturated fatty acids promote stalk formation and, ultimately, membra ne fusion.