Heterogeneity of early intermediates in cell-liposome fusion mediated by influenza hemagglutinin
Mikhail A. Zhukovsky 1*, Eugenia Leikina 2, Ingrid Markovic 3, Austin L. Bailey 4 and Leonid V. Chernomordik 2
1 Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, Harvard Medical School
2 Section on Membrane Biology, Laboratory of Cellular and Molecular Biophysics, NICHD, NIH
3 Division of Therapeutic Proteins, Center for Drug Evaluation and Research, FDA
4 Medical Science Liaison, Oncology, Scientific Communications, Cephalon, Inc.
* To whom correspondence should be addressed. E-mail: mikhail_zhukovsky{at}dfci.harvard.edu.
Submitted on May 10, 2006
Revised on May 30, 2006
Accepted on 27 July 2006
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Abstract |
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To explore early intermediates in membrane fusion mediated by influenza virus hemagglutinin (HA) and their dependence on the composition of the target membrane, we studied lipid mixing between HA-expressing cells and liposomes containing phosphatidylcholine (PC) with different hydrocarbon chains. For all tested compositions, our results indicate the existence of at least two types of intermediates, which differ in their lifetime. The composition of the target membrane affects the stability of fusion intermediates at a stage prior to lipid mixing. For less fusogenic distearoyl PC-containing liposomes at 4°C, some of the intermediates inactivate and no intermediates advanced to lipid mixing. Fusion intermediates that formed for the more fusogenic dioleoyl PC-containing liposomes did not inactivate and even yielded partial lipid mixing at 4°C. Thus, a more fusogenic target membrane effectively blocks non-productive release of the conformational energy of HA. Even for the same liposome composition, HA forms two types of fusion intermediates, dissimilar in their stability and propensity to fuse. This diversity of the fusion intermediates emphasizes the importance of local membrane composition and local protein concentration in fusion of heterogeneous biological membranes.
Key Words:
hemagglutinin-expressing cell, inactivation, influenza virus, membrane fusion, surface density, target membrane composition
