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J. Cell Biol.,
Volume 140, Number 2, January 26, 1998 315-323


* Laboratory of Experimental and Computational Biology, National Institutes of Health, Frederick, MD; and We have monitored fusion between cell pairs
consisting of a single human immunodeficiency virus-1
(HIV-1) envelope glycoprotein-expressing cell and a
CD4+ target cell, which had been labeled with both a
fluorescent lipid in the membrane and a fluorescent solute in the cytosol. We developed a new three-color assay to keep track of the cell into which fluorescent lipids and/or solutes are redistributed. Lipid and solute
redistribution occur as a result of opening a lipid-permissive fusion pore and a solute-permissive fusion pore
(FPS), respectively. A synthetic peptide (DP178) corresponding to residues 643-678 of the HIV-1LAI gp120-gp41 sequence (Wild, C.T., D.C. Shugars, T.K. Greenwell, C.B. McDanal, and T.J. Matthews. 1994. Proc.
Natl. Acad. Sci. USA. 91:12676-12680) completely inhibited FPS at 50 ng/ml, whereas at that concentration
there was 20-30% fusion activity measured by the lipid
redistribution. The differences detected in lipid mixing
versus contents mixing are maintained up to 6 h of coculture of gp120-41-expressing cells with target cells,
indicating that DP178 can "clamp" the fusion complex
in the lipid mixing intermediate for very long time periods. A peptide from the NH2-terminal of gp41, DP107,
inhibited HIV-1LAI gp120-gp41-mediated cell fusion at
higher concentrations, but with no differences between
lipid and aqueous dye redistribution at the different inhibitor concentrations. The inhibition of solute redistribution by DP178 was complete when the peptide was
added to the fusion reaction mixture during the first 15 min of coculture. We have analyzed the inhibition data
in terms of a fusion pore dilation model that incorporates the recently determined high resolution structure
of the gp41 core.
Laboratory of Cell
Biology, Division of Basic Sciences, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 21702-1201
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