The Catalytic Activity of Protein Disulfide Isomerase Is Involved in Human Immunodeficiency Virus Envelope–Mediated Membrane Fusion after CD4 Cell Binding

Abstract

Protein disulfide isomerase (PDI) is a multifunctional protein with thiol-disulfide redox-isomerase activities. It catalyzes thiol-disulfide interchange reactions on the cell surface that may cause structural modifications of exofacial proteins. PDI inhibitors alter human immunodeficiency virus (HIV) spread, and it has been suggested that PDI may be necessary to trigger HIV entry. This study examined this hypothesis by using cell-to-cell fusion assays, in which the HIV envelope (Env) expressed on the cell surface interacts with CD4(+) lymphocytes. PDI is clustered at the lymphocyte surface in the vicinity of CD4-enriched regions, but both antigens essentially do not colocalize. Anti-PDI antibodies and 2 inhibitors of its catalytic function altered Env-mediated membrane fusion at a post-CD4 cell binding step. The fact that the PDI catalytic activity present on lymphocytes is required for fusion supports the hypothesis that catalysts assist post-CD4 cell binding conformational changes within Env.

Time-resolved Imaging of HIV-1 Env-mediated Lipid and Content Mixing between a Single Virion and Cell Membrane

“…Error bars, SEM. There is considerable evidence in the literature that molecules other than CD4 and chemokine receptors, such as ceramide (Finnegan et al, 2004), glycosphingolipids (Puri et al, 1999;Fantini et al, 2000), and protein disulfide isomerases (Fenouillet et al, 2001;Gallina et al, 2002;Barbouche et al, 2003;Markovic et al, 2004), affect efficiency of fusion and/or infection. Such molecules or other factors may strongly influence the transfer of aqueous contents from virus to the cell interior.…”

Significant Redox Insensitivity of the Functions of the SARS-CoV Spike Glycoprotein

“…On the other hand, natural and specific thiol/disulfide rearrangements occur within several viral envelopes to trigger conformational changes that insert the fusion peptide into the cell surface leading to virus entry (20,21,23,(25)(26)(27). For HIV, gentle chemical reduction of Env efficiently prevents viral infectivity by inhibiting the capacity of the surface subunit (SU) to bind its ligands on the target cell surface (15,19). In contrast, after receptor binding, fusion mediated by the transmembrane subunit occurs solely following reduction of SU by a cell-surface protein-disulfide isomerase (PDI) activity (19,(25)(26)(27).…”

“…For these reasons, reducing or free sulfhydryl reagents and nonpermeant inhibitors of PDI (e.g. the thiol reagent DTNB and bacitracin, an oxidoreductive inhibitor) block entry (15,19).A proper disulfide network within MLV-and human T-leukemia virus-Env is also a determinant of virus entry. Incubation in the presence of dithiothreitol (DTT) of cell-bound virus inhibits Env fusogenicity.…”

“…A variety of evidence has shown that the capacity of the viral envelope glycoproteins to mediate virus/cell membrane fusion depends on a precise thiol/disulfide balance within the viral surface complex (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29). On one hand, manipulation of the native disulfide network of mature envelopes at the virus surface using reducing or alkylating reagents has important consequences for their subsequent capacity to carry out the virus/cell interaction process (15, 16, 19, 20, 23, 24, 26, and 28).…”

“…For HIV, gentle chemical reduction of Env efficiently prevents viral infectivity by inhibiting the capacity of the surface subunit (SU) to bind its ligands on the target cell surface (15,19). In contrast, after receptor binding, fusion mediated by the transmembrane subunit occurs solely following reduction of SU by a cell-surface protein-disulfide isomerase (PDI) activity (19,(25)(26)(27). For these reasons, reducing or free sulfhydryl reagents and nonpermeant inhibitors of PDI (e.g.…”