title: High-affinity binding of southern African HIV type 1 subtype C envelope protein, gp120, to the CCR5 coreceptor.
abstract: HIV-1 subtype C is the fastest spreading subtype worldwide and predominantly uses the CCR5 coreceptor, showing minimal transition to the X4 phenotype. This raises the possibility that envelope proteins of HIV-1 subtype C have structural features that favor interaction with CCR5. Preference for CCR5 could arise from enhanced affinity of HIV-1 subtype C for CCR5. To test this, we have characterized the interaction of gp120 envelope proteins from HIV-1 subtype C clones with CD4 and CCR5. Recombinant gp120 proteins from isolates of HIV-1 subtypes B and C were expressed, purified, and assessed in a CD4 binding assay and a CCR5 chemokine competition binding assay. All gp120 proteins bound to CD4-expressing cells, except one, 97ZA347ts, which had Arg substituted for the Cys239 in the conserved C2 loop. Reconstitution of Cys239, using site-directed mutagenesis, restored CD4 binding, while introducing Arg or Ser into position 239 of the functional Du151 gp120 protein abrogated CD4 binding. This shows that the Cys228-Cys239 disulfide bond of gp120 is required for high-affinity binding to CD4. Recombinant gp120 proteins from two HIV-1 subtype B clones bound CCR5 in the presence of CD4, while gp120 from the X4-tropic, HxB2, clone did not bind CCR5. gp120 from two functional HIV-1 subtype C clones, Du151 and MOLE1, bound CCR5 with high affinity in the presence of CD4 and Du151 showed significant CCR5 binding in the absence of CD4. A gp120 from a nonfunctional subtype C clone had lower affinity for CCR5. These results indicate that HIV-1 subtype C proteins have high affinity for CCR5 with variable dependence on CD4.
authors.affiliation: MRC/UCT Research Group for Receptor Biology, University of Cape Town, Cape Town, South Africa.
authors.forename: Bernhard J
authors.initials: BJ
authors.lastname: Fromme
authors.forename: Marla
authors.initials: M
authors.lastname: Coetsee
authors.forename: Pauline
authors.initials: P
authors.lastname: Van Der Watt
authors.forename: Mei-Chi
authors.initials: MC
authors.lastname: Chan
authors.forename: Karin M
authors.initials: KM
authors.lastname: Sperling
authors.forename: Arieh A
authors.initials: AA
authors.lastname: Katz
authors.forename: Colleen A
authors.initials: CA
authors.lastname: Flanagan
mesh_terms: D000163:Acquired Immunodeficiency Syndrome / Q000821:virology*; D000353:Africa, Southern; D019943:Amino Acid Substitution / Q000235:genetics; D015704:CD4 Antigens / Q000378:metabolism; D015699:HIV Envelope Protein gp120 / Q000378:metabolism*; D015497:HIV-1 / Q000302:isolation & purification* / Q000502:physiology*; D006801:Humans; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D011485:Protein Binding; D019713:Receptors, CCR5 / Q000378:metabolism*
chemical_list: D015704:CD4 Antigens; D015699:HIV Envelope Protein gp120; D019713:Receptors, CCR5; C514793:gp120 protein, Human immunodeficiency virus 1