Model of Membrane Fusion: Continuous Transition to Fusion Pore with Regard of Hydrophobic and Hydration Interactions

The process of membranes fusion is theoretically considered from stage of minimal radius stalk to formation of fusion pore. It is assumed that expanding stalk transforms directly to fusion pore bypassing trilaminar structure. The energy of the intermediate states is calculated on the basis of the classical theory of elasticity of liquid crystals, adapted to lipid membranes. The trajectory of transition of stalk to pore is obtained taking into account hydrophobic and hydration interactions. Along the trajectory there is a continuous change of orientation of lipids of distal monolayers from direction along the axis of rotation, characteristic to stalk, to the direction corresponding to the fusion pore. The dependence of the energy of the intermediate states on spontaneous curvature of distal monolayers of merging membranes is obtained. It is shown that the energy barrier of transition of stalk to fusion pore decreases withpositive spontaneous curvature of distal monolayers, which is in agreement with available experimental data.