Abstract
The human and simian immunodeficiency virus envelope glycoproteins, which mediate virus-induced cell fusion, contain two putative amphipathic helical segments with large helical hydrophobic moments near their carboxyl-terminal ends. In an attempt to elucidate the biological role of these amphipathic helical segments, we have synthesized peptides corresponding to residues 768-788 and 826-854 of HIV-1/WMJ-22 gp160. Circular dichroism studies of the peptides showed that the alpha helicity of the peptides increased with the addition of dimyristoyl phosphatidylcholine (DMPC) indicating that the peptides form lipid-associating amphipathic helixes. The peptides solubilized turbid suspensions of DMPC vesicles, and electron microscopy of peptide-DMPC mixtures revealed the formation of discoidal complexes, suggesting that the peptides bind to and perturb lipid bilayers. The peptides were found to lyse lipid vesicles and caused carboxyfluorescein leakage from dye-entrapped egg phosphatidylcholine liposomes. The peptides also lysed human erythrocytes and were found to be toxic to cell cultures. At subtoxic concentrations, the peptides effectively inhibited the fusion of CD4+ cells infected with recombinant vaccinia virus expressing human immunodeficiency virus (HIV)-1 envelope proteins. Based on these results, and reported studies on the mutational analysis of HIV envelope proteins, we suggest that the amphipathic helical segments near the carboxyl terminus of HIV envelope proteins may play a role in lysis of HIV-infected cells and also may modulate the extent of cell fusion observed during HIV infection of CD4+ cells.
Highlights
Membrane Interactions of Synthetic PeptidesCorresponding to Amphipathic Helical Segmentsof the Human Immunodeficiency Virus Type- 1 Envelope Glycoprotein*
Reported studoiensthe mutational analysis of human immunodeficiency virus (HIV) envelope proteins, we suggest that the amphipathic helical segments near thecarboxyl terminus of protein is transported to the plasma membrane where it is available for virus assembly and budding
I; residues 826-854 ), whereas the other (Segment 11) corresponds to residue7s68-788, near the carboxyl terminuosf t h e molecule(Fig. 1).Similar segments with large hydrophobic momentsarealsoobservednearthecarboxyltermini of various strains of HIV-2 and simian immunodeficiencyvirus (SIV), and representative examples are shown in Fig1. .Interestingly, envelope glycoproteins of bovine (BIV) and feline (FIV) immunodeficiency viruses and otheranimallentiviruses(notshown)didnotdisplay such amphipathic helical segments near their carboxyl termini
Summary
Research Hospital, 332 North Lauderdale Blvd., Memphis, TN 38101. that lack the amphipathic helical segments [15, 16]. Plots of helical hydrophobic moment versus amino acid groups at each stage of the synthesis were removed bytreatment with residues ofgp160 from different lentiviruses The concentrations of peptide solutions were determined by amino acid analysis and Pierce protein assay reagent. VVenvl, a recombinant vaccinia virus which expresses the HIV-1 envelope protein [25], was used to study the effects of peptides on HIV-induced cell fusion. Chatterjee (University of Alabama at Birmingham) and effects of peptides on HSV-induced cell fusion was assayed according to previously described procedures [27]. Surface Expression of Envelope Proteins-Monolayers of CD4+ HeLa cells grown on 12-mm glass coverslips in 24-well cluster plates were infected at a multiplicity of 0.1 and treated with peptide solutions as described above. At 10 h post-infection, intact unfixed monolayers were examined by indirect immunofluorescence assay using HIV immunoglobulinand fluorescein isothiocyanate-conjugatedgoat antihuman Ig (Southern Biotechnology, Inc., Birmingham, AL) as described previously [28]
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