However even though two membranes are proximal, fusion will not occur unless the bilayer structure is transiently disrupted. Such disruption may result from internal components of the membrane or from the external environment.
Phospholipids can form a variety of nonlamellar lipid assemblies.
Most of these nonlamellar structures have been proposed as being involved as intermediates in membrane fusion. Cylindrical-shaped phospholipids, like phosphatidylcholine, prefers bilayer phases. In biological membranes, proteins stabilize the bilayer phases. A decrease in the membrane protein concentration would favor the non-bilayer formation. 4 - Schematic presentation of the role of lipids in the proposed mechanism of membrane fusion, via the formation of nonlamellar inverted micellar intermediates.