The membrane-spanning domain (MSD) of human immunodeficiency virus type I (HIV-1) envelope glycoprotein (Env) is critical for its biological activity. Initial studies have defined an almost invariant "core" structure in the MSD and demonstrated that it is crucial for anchoring Env in the membrane and virus entry. We show here that amino acid substitutions in the MSD "core" do not influence specific virus-cell attachment, nor CD4 receptor and CXCR4 coreceptor recognition by Env. However, substitutions within the MSD "core" delayed the kinetics and reduced the efficiency of cell-cell fusion mediated by Env. Although we observed no evidence that membrane fusion mediated by the MSD core mutants was arrested at a hemifusion stage, impaired Env fusogenicity was correlated with minor conformational changes in the V2, C1, and C5 regions in gp120 and the immunodominant loop in gp41. These changes could delay initiation of the conformational changes required in the fusion process.
Bibliographical noteFunding Information:
We thank Drs. Lara Pereira and Malinda Schaefer for critical reading of the manuscript. The pooled HIV-1 patient sera were kindly provided by Jeffery Lennox through the Clinical Core, and flow cytometry was performed in the Immunology Core of the Emory Center for AIDS Research ( P30 AI050409 ). The antibodies, immunoglobulin, and fusion inhibitors used in this study were obtained from the AIDS Research and Reference Reagent Program, Division of AIDS, National Institute of Allergy and Infectious Diseases, National Institutes of Health: D50 and T32 from Dr. Patricia Earl; NC-1 from Dr. Shibo Jiang; b12 from Dr. Dennis Burton and Carlos Barbas; F425 A1g8 and F425 B4a1 from Dr. Marshall Posner and Dr. Lisa Cavacini; 17b, E51, and A32 from Dr. James E. Robinson; 902 from Dr. Bruce Chesebro; 697-30D and 670-30D from Dr. Susan Zolla-Pazner; ID6 from Dr Kenneth Ugen and Dr. David Weiner; Chessie 6 and Chessie 13-39.1 from Dr. George K. Lewis, and 4E10 from Dr. Hermann Katinger. This work was supported by grant R01 AI33319 (E.H.) from the National Institute of Allergy and Infectious Diseases at the National Institutes of Health .
- Conformational changes
- Membrane fusion
- Membrane-spanning domain