title: Protein-disulfide isomerase-mediated reduction of two disulfide bonds of HIV envelope glycoprotein 120 occurs post-CXCR4 binding and is required for fusion.
abstract: The human immunodeficiency virus (HIV) envelope (Env) glycoprotein (gp) 120 is a highly disulfide-bonded molecule that attaches HIV to the lymphocyte surface receptors CD4 and CXCR4. Conformation changes within gp120 result from binding and trigger HIV/cell fusion. Inhibition of lymphocyte surface-associated protein-disulfide isomerase (PDI) blocks HIV/cell fusion, suggesting that redox changes within Env are required. Using a sensitive assay based on a thiol reagent, we show that (i) the thiol content of gp120, either secreted by mammalian cells or bound to a lymphocyte surface enabling CD4 but not CXCR4 binding, was 0.5-1 pmol SH/pmol gp120 (SH/gp120), whereas that of gp120 after its interaction with a surface enabling both CD4 and CXCR4 binding was raised to 4 SH/gp120; (ii) PDI inhibitors prevented this change; and (iii) gp120 displaying 2 SH/gp120 exhibited CD4 but not CXCR4 binding capacity. In addition, PDI inhibition did not impair gp120 binding to receptors. We conclude that on average two of the nine disulfides of gp120 are reduced during interaction with the lymphocyte surface after CXCR4 binding prior to fusion and that cell surface PDI catalyzes this process. Disulfide bond restructuring within Env may constitute the molecular basis of the post-receptor binding conformational changes that induce fusion competence.
authors.affiliation: CNRS, Faculté de Médecine Nord, Boulevard Pierre Dramard, Marseille, 13015 France.
authors.forename: Rym
authors.initials: R
authors.lastname: Barbouche
authors.forename: Raymond
authors.initials: R
authors.lastname: Miquelis
authors.forename: Ian M
authors.initials: IM
authors.lastname: Jones
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Fenouillet
mesh_terms: D001665:Binding Sites; D015704:CD4 Antigens / Q000737:chemistry / Q000502:physiology; D002460:Cell Line; D004220:Disulfides / Q000378:metabolism*; D015699:HIV Envelope Protein gp120 / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008561:Membrane Fusion; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011487:Protein Conformation; D019704:Protein Disulfide-Isomerases / Q000378:metabolism*; D012680:Sensitivity and Specificity; D013438:Sulfhydryl Compounds / Q000032:analysis / Q000494:pharmacology
chemical_list: D015704:CD4 Antigens; D004220:Disulfides; D015699:HIV Envelope Protein gp120; D013438:Sulfhydryl Compounds; D019704:Protein Disulfide-Isomerases