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Biophys. J. BioFAST: First Published March 30, 2007. doi:10.1529/biophysj.106.096495
© 2007 by the Biophysical Society.

A more recent version of this article appeared on June 15, 2007.
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MEMBRANES

ATOMIC FORCE MICROSCOPE STUDIES OF THE FUSION OF FLOATING LIPID BILAYERS

Midhat H Abdulreda 1 and Vincent T. Moy 2*

1 University of Miami Miller School of Medicine
2 Univ. of Miami Miller School of Medicine

* To whom correspondence should be addressed. E-mail: vmoy{at}newssun.med.miami.edu.

Submitted on August 31, 2006
Revised on October 10, 2006
Accepted on 13 February 2007


  Abstract
This study investigated the fusion of apposing floating bilayers of egg L-{alpha}-phosphatidylcholine (egg PC) or 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DMPC). Atomic force microscope (AFM) measurements of fusion forces under different compression rates were acquired to reveal the energy landscape of the fusion process under varied lipid composition and temperature. Between compression rates of ~1000 and ~100000 pN/s, applied forces in the range ~100 to ~500 pN resulted in fusion of floating bilayers. Our AFM force measurements indicated that one main energy barrier dominated the fusion process. The acquired dynamic force spectra were fit with a simple model based on the transition state theory with the assumption that the fusion activation potential is linear. A significant shift in the energy landscape was observed when bilayer fluidity and composition were modified, respectively, by temperature and different cholesterol concentrations (15% ≤ chol. ≤ 25%). Such modifications resulted in a more than two fold increase in the width of the fusion energy barrier for egg PC and DMPC floating bilayers. The addition of 25% cholesterol to egg PC bilayers increased the activation energy by ~1.0 kBT compared with that of bilayers with egg PC alone. These results reveal that widening of the energy barrier and consequently reduction in its slope facilitated membrane fusion.

Key Words: AFM, DMPC, Egg PC, cholesterol, dynamic fusion force, membrane fusion




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M. H. Abdulreda, A. Bhalla, E. R. Chapman, and V. T. Moy
Atomic Force Microscope Spectroscopy Reveals a Hemifusion Intermediate during Soluble N-Ethylmaleimide-Sensitive Factor-Attachment Protein Receptors-Mediated Membrane Fusion
Biophys. J., January 15, 2008; 94(2): 648 - 655.
[Abstract] [Full Text] [PDF]


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Copyright © 2007 by the Biophysical Society.