A critical site in the core of the CCR5 chemokine receptor required for binding and infectivity of human immunodeficiency virus type 1

Like the CCR5 chemokine receptors of humans and rhesus macaques, the very h omologous (similar to 98-99% identical) CCR5 of African green monkeys (AGMs ) avidly binds beta-chemokines and functions as a coreceptor for simian imm unodeficiency viruses. However, AGM CCR5 is a weak coreceptor for tested ma crophage-tropic (R5) isolates of human immunodeficiency virus type 1 (HIV-1 ), Correspondingly, gp120 envelope glycoproteins derived from R5 isolates o f HIV-1 bind poorly to AGM CCR5, We focused on a unique extracellular amino acid substitution at the juncture of transmembrane helix 4 (TM4) and extra cellular loop 2 (ECL2) (Arg for Gly at amino acid 163 (G163R)) as the likel y source of the weak R5 gp120 binding and HIV-1 coreceptor properties of AG M CCR5, Accordingly, a G163R mutant of human CCR5 was severely attenuated i n its ability to bind R5 gp120s and to mediate infection by R5 HIV-X isolat es. Conversely, the R163G mutant of AGRI CCR5 was substantially strengthene d as a coreceptor for HIV-1 and had improved R5 gp120 binding affinity rela tive to the wild-type AGM CCR5, These substitutions at amino acid position 163 had no effect on chemokine binding pr signal transduction, suggesting t he absence of structural alterations. The 2D7 monoclonal antibody has been reported to bind to ECL2 and to block HIV-1. binding and infection. Whereas 2D7 antibody binding to CCR5 was unaffected by the G163R mutation, it was prevented by a conservative ECL2 substitution (K171R), shared between rhesu s and AGM CCR5s, Thus, it appears that the 2D7 antibody binds to an epitope that includes Lys-171 and may block HIV-1 infection mediated by CCR5 by oc cluding an HIV-l-binding site in the vicinity of Gly-163, In summary, our r esults identify a site for gp120 interaction that is critical for R5 isolat es of HIV-1 in the central core of human CCR5, and we propose that this sit e collaborates with a previously identified region in the CCR5 amino termin us to enable gp120 binding and HIV-1 infections.