SNARE Complex Zipping as a Driving Force in the Dilation of Proteinaceous Fusion Pores

SNARE Complex Zipping as a Driving Force in the Dilation of Proteinaceous Fusion Pores The assembly of SNARE proteins into a tight complex has been hypothesized to drive membrane fusion. A model of the initial fusion pore as a proteinaceous channel formed by SNARE proteins places their membrane anchors in separate membranes. This leaves the possibility of a final assembly step that brings the membrane anchors together and drives fusion pore expansion. The present study develops a model for expansion in which the final SNARE complex zipping step drives a transition from a proteinaceous fusion pore to a lipidic fusion pore. An estimate of the energy released upon merger of the helical segments of the SNARE motifs with the helical segments of the membrane anchors indicates that completing the assembly of a few SNARE complexes can overcome the elastic energy that opposes lipid bilayer deformation into a narrow fusion pore. The angle between the helical axes of the membrane anchor and SNARE motif serves as a useful reaction coordinate for this transition. Energy was calculated as a function of this angle, incorporating contributions from membrane bending, SNARE complex assembly, membrane anchor flexing and hydrophobic interactions. The rate of this transition was evaluated as a process of diffusion over the barrier imposed by these combined energies, and the rates estimated were consistent with experimental measurements. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

SNARE Complex Zipping as a Driving Force in the Dilation of Proteinaceous Fusion Pores

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Publisher
Springer-Verlag
Copyright
Copyright © 2010 by Springer Science+Business Media, LLC
Subject
Life Sciences; Human Physiology ; Biochemistry, general
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s00232-010-9258-1
Publisher site
See Article on Publisher Site

Abstract

The assembly of SNARE proteins into a tight complex has been hypothesized to drive membrane fusion. A model of the initial fusion pore as a proteinaceous channel formed by SNARE proteins places their membrane anchors in separate membranes. This leaves the possibility of a final assembly step that brings the membrane anchors together and drives fusion pore expansion. The present study develops a model for expansion in which the final SNARE complex zipping step drives a transition from a proteinaceous fusion pore to a lipidic fusion pore. An estimate of the energy released upon merger of the helical segments of the SNARE motifs with the helical segments of the membrane anchors indicates that completing the assembly of a few SNARE complexes can overcome the elastic energy that opposes lipid bilayer deformation into a narrow fusion pore. The angle between the helical axes of the membrane anchor and SNARE motif serves as a useful reaction coordinate for this transition. Energy was calculated as a function of this angle, incorporating contributions from membrane bending, SNARE complex assembly, membrane anchor flexing and hydrophobic interactions. The rate of this transition was evaluated as a process of diffusion over the barrier imposed by these combined energies, and the rates estimated were consistent with experimental measurements.

Journal

The Journal of Membrane BiologySpringer Journals

Published: May 30, 2010

References

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