Membrane fusion

Although catalyzed by different proteins, the energy barriers for lipid bil ayer fusion in exocytosis, viral fusion, and trafficking seem to be the sam e as those for the fusion of protein-free phospholipid membranes. To minimi ze this energy, fusion will proceed through a minimal number of lipid molec ules, probably localized in bent non-bilayer intermediates. Experiments on phospholipid bilayer membrane fusion show the pathway of contact, hemifusio n, flickering fusion pore formation, and fusion pore enlargement caused by swelling of the vesicle. Lipid curvature determines the barriers to hemifus ion and fusion pore formation, while swelling-induced membrane tension driv es fusion pore enlargement. Experiments on viral protein-induced cell-cell fusion and exocytosis show the same pathway with the same fundamental effec ts of lipid curvature and membrane tension. Thus while proteins control the se reactions, lipid energetics determine the basic reaction scheme for memb rane fusion. Published by Elsevier Science B.V.