Journal of Membrane Biology

, Volume 231, Issue 2, pp 101–115

Minimum Membrane Bending Energies of Fusion Pores

Article

DOI: 10.1007/s00232-009-9209-x

Cite this article as:
Jackson, M.B. J Membrane Biol (2009) 231: 101. doi:10.1007/s00232-009-9209-x

Abstract

Membranes fuse by forming highly curved intermediates, culminating in structures described as fusion pores. These hourglass-like figures that join two fusing membranes have high bending energies, which can be estimated using continuum elasticity models. Fusion pore bending energies depend strongly on shape, and the present study developed a method for determining the shape that minimizes bending energy. This was first applied to a fusion pore modeled as a single surface and then extended to a more realistic model treating a bilayer as two monolayers. For the two-monolayer model, fusion pores were found to have metastable states with energy minima at particular values of the pore diameter and bilayer separation. Fusion pore energies were relatively insensitive to membrane thickness but highly sensitive to spontaneous curvature and membrane asymmetry. With symmetrical bilayers and monolayer spontaneous curvatures of −0.1 nm−1 (a typical value) separated by 6 nm (closest distance determined by repulsive hydration forces), fusion pore formation required 43–65 kT. The pore radius of ~2.25 nm fell within the range estimated from conductance measurements. With bilayer separation >6 nm, fusion pore formation required less energy, suggesting that protein scaffolds can promote fusion by bending membranes toward one another. With nonzero spontaneous monolayer curvature, the shape that minimized the energy change during fusion pore formation differed from the shape that minimized its energy after it formed. Thus, a nascent fusion pore will relax spontaneously to a new shape, consistent with the experimentally observed expansion of nascent fusion pores during viral fusion.

Keywords

Membrane fusion Exocytosis Membrane mechanics Membrane elasticity 

Supplementary material

232_2009_9209_MOESM1_ESM.doc (154 kb)
Supplementary material 1 (DOC 154 kb)

Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  1. 1.Department of PhysiologyUniversity of Wisconsin MadisonMadisonUSA