Max Planck Institute for Dynamics and Self-Organization -- Department for Nonlinear Dynamics and Network Dynamics Group
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MPI Kolloquium

Wednesday, 16.11.2005 17 c.t.

Fusion Mechanism of Model Membranes: Computer Simulation and Self-Consistent Field Calculations

by Prof. Markus Müller
from Uni Göttingen

Contact person: Theo Geisel

Location

Seminarraum Haus 2, 4. Stock (Bunsenstr.)

Abstract

Membrane fusion is a fundamental biological process of importance in fertilization, synaptic release, intracellular traffic, and viral infection, but its basic mechanism is not well understood. We have carried out computer simulations of the fusion of tense apposed bilayers formed by amphiphilic molecules within the framework of a coarse-grained lattice model. The fusion pathway differs from the usual stalk mechanism. Stalks do form between the apposed bilayers, but rather than expand radially to form an axial-symmetric hemifusion diaphragm, they promote the nucleation of small holes in their vicinity. Then, the stalk encircles a hole in one bilayer creating a diaphragm which ruptures to complete the fusion pore, or a second hole forms in the other bilayer, and the stalk aligns and encircles them both to complete fusion. Both pathways give rise to mixing between both leaves of the bilayer and allow for transient leakage. Self-consistent field calculations have be used to explored the role of lipid architecture and tension, and to calculate free energy barriers along the fusion path. We find that (i) successful fusion is found to be severely limited by the architecture of the lipids and that (ii) any mechanism which affects even modestly the line tension of a hole in a membrane affects greatly the ability of that membrane to undergo fusion.

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