title: The V3 loop of human immunodeficiency virus type-1 envelope protein is a high-affinity ligand for immunophilins present in human blood.
abstract: Human immunodeficiency virus type-1 (HIV-1) infection requires binding of the envelope protein gp120 to host CD4 receptors and the action of the chemokine receptors CXCR4 or CCR5, which define cell tropism. The proline-containing V3 loop of gp120 determines the selection of the chemokine receptor and participates in conformational changes on binding of gp120 to CD4. In this study, we show that macrophage-tropic and T-cell-tropic V3 loop peptides bind specifically to the active site of the immunophilins FK506-binding protein (FKBP12), and cyclophilins A and B. Macrophage-tropic and T-cell-tropic V3 loop peptides inhibited the peptidyl-prolyl cis-trans isomerase (PPIase) activities of the immunophilins. Kd values in the range 0.036-4.1 microM were determined with V3 loop peptides labeled with an environmentally sensitive fluorophore. The observed binding properties of the V3 loop peptides reveal structural motifs of linear water-soluble peptidic substrates for tight interaction with immunophilins. FKBP12, and cyclophilins A and B were found to be present in normal human blood in the ranges 0.8-1.7, 1.4-2.3 and 2.4-3.1 nM, respectively, as demonstrated by PPIase activity measurements and western blot analysis. Cyclophilins A and B levels in serum of HIV-1-infected individuals were increased 3.6-fold and 1.6-fold. Due to the interaction of immunophilins with V3 loop peptides and with the envelope protein gp120, a role of immunophilins in HIV pathogenesis as conformases or docking mediators seems possible, since immunophilin receptors on cell membranes and immunophilin-related virulence factors of pathogens have been identified.
authors.affiliation: Biochemisches Institut, Universität Zürich, Switzerland.
authors.forename: M M
authors.initials: MM
authors.lastname: Endrich
authors.forename: H
authors.initials: H
authors.lastname: Gehring
mesh_terms: D000591:Amino Acid Isomerases / Q000097:blood* / Q000737:chemistry; D000595:Amino Acid Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000097:blood* / Q000737:chemistry; D021983:Cyclophilins; D004268:DNA-Binding Proteins / Q000097:blood* / Q000737:chemistry; D015699:HIV Envelope Protein gp120 / Q000737:chemistry* / Q000378:metabolism*; D015497:HIV-1 / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000097:blood* / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D008024:Ligands; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D019696:Peptidylprolyl Isomerase / Q000097:blood* / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016559:Tacrolimus / Q000378:metabolism; D022021:Tacrolimus Binding Proteins
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D015699:HIV Envelope Protein gp120; D006360:Heat-Shock Proteins; D008024:Ligands; D010446:Peptide Fragments; D011994:Recombinant Proteins; C081786:cyclophilin B; D000591:Amino Acid Isomerases; D021983:Cyclophilins; D022021:Tacrolimus Binding Proteins; D019696:Peptidylprolyl Isomerase; D016559:Tacrolimus