title: Disulfide reduction in CD4 domain 1 or 2 is essential for interaction with HIV glycoprotein 120 (gp120), which impairs thioredoxin-driven CD4 dimerization.
abstract: Human CD4 is a membrane-bound glycoprotein expressed on the surface of certain leukocytes, where it plays a key role in the activation of immunostimulatory T cells and acts as the primary receptor for human immunodeficiency virus (HIV) glycoprotein (gp120). Although growing evidence suggests that redox exchange reactions involving CD4 disulfides, potentially catalyzed by cell surface-secreted oxidoreductases such as thioredoxin (Trx) and protein disulfide isomerase, play an essential role in regulating the activity of CD4, their mechanism(s) and biological utility remain incompletely understood. To gain more insights in this regard, we generated a panel of recombinant 2-domain CD4 proteins (2dCD4), including wild-type and Cys/Ala variants, and used these to show that while protein disulfide isomerase has little capacity for 2dCD4 reduction, Trx reduces 2dCD4 highly efficiently, catalyzing the formation of conformationally distinct monomeric 2dCD4 isomers, and a stable, disulfide-linked 2dCD4 dimer. Moreover, we show that HIV gp120 is incapable of binding a fully oxidized, monomeric 2dCD4 in which both domain 1 and 2 disulfides are intact, but binds robustly to reduced counterparts that are the ostensible products of Trx-mediated isomerization. Finally, we demonstrate that Trx-driven dimerization of CD4, a process believed to be critical for the establishment of functional MHCII-TCR-CD4 antigen presentation complexes, is impaired when CD4 is bound to gp120. These observations reinforce the importance of cell surface redox activity for HIV entry and posit the intriguing possibility that one of the many pathogenic effects of HIV may be related to gp120-mediated inhibition of oxidoreductive CD4 isomerization.
authors.affiliation: HIV Pathogenesis Research Laboratory, Department of Molecular Medicine and Haematology, University of Witwatersrand Medical School, 7 York Road Parktown, 2193 Johannesburg, South Africa.
authors.forename: Nichole
authors.initials: N
authors.lastname: Cerutti
authors.affiliation: HIV Pathogenesis Research Laboratory, Department of Molecular Medicine and Haematology, University of Witwatersrand Medical School, 7 York Road Parktown, 2193 Johannesburg, South Africa.
authors.forename: Mark
authors.initials: M
authors.lastname: Killick
authors.affiliation: HIV Pathogenesis Research Laboratory, Department of Molecular Medicine and Haematology, University of Witwatersrand Medical School, 7 York Road Parktown, 2193 Johannesburg, South Africa.
authors.forename: Vinesh
authors.initials: V
authors.lastname: Jugnarain
authors.affiliation: HIV Pathogenesis Research Laboratory, Department of Molecular Medicine and Haematology, University of Witwatersrand Medical School, 7 York Road Parktown, 2193 Johannesburg, South Africa.
authors.forename: Maria
authors.initials: M
authors.lastname: Papathanasopoulos
authors.affiliation: HIV Pathogenesis Research Laboratory, Department of Molecular Medicine and Haematology, University of Witwatersrand Medical School, 7 York Road Parktown, 2193 Johannesburg, South Africa. Electronic address: alexio.capovilla@wits.ac.za.
authors.forename: Alexio
authors.initials: A
authors.lastname: Capovilla
mesh_terms: D017951:Antigen Presentation; D015704:CD4 Antigens / Q000737:chemistry*; D002462:Cell Membrane / Q000737:chemistry; D019281:Dimerization; D004220:Disulfides / Q000737:chemistry; D004797:Enzyme-Linked Immunosorbent Assay; D057809:HEK293 Cells; D015699:HIV Envelope Protein gp120 / Q000737:chemistry*; D015497:HIV-1 / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D013816:Thermodynamics; D013879:Thioredoxins / Q000737:chemistry*
chemical_list: D015704:CD4 Antigens; D004220:Disulfides; D015699:HIV Envelope Protein gp120; D011994:Recombinant Proteins; D013879:Thioredoxins; D010088:Oxidoreductases; D010100:Oxygen
keywords: CD4; Disulfide; HIV; Redox; Thiol; Thioredoxin; gp120