Two distinct CCR5 domains can mediate coreceptor usage by human immunodeficiency virus type 1

Abstract

The chemokine receptor CCR5 is the major fusion coreceptor for macrophage-tropic strains of human immunodeficiency virus type 1 (HIV-1). To define the structures of CCR5 that can support envelope (Env)mediated membrane fusion, we analyzed the activity of homologs, chimeras, and mutants of human CCR5 in a sensitive gene reporter cell-cell fusion assay. Simian, but not murine, homologs of CCR5 were fully active as HIV-1 fusion coreceptors. Chimeras between CCR5 and divergent chemokine receptors demonstrated the existence of two distinct regions of CCR5 that could be utilized for Env-mediated fusion, the amino-terminal domain and the extracellular loops. Dual-tropic Env proteins were particularly sensitive to alterations in the CCR5 amino-terminal domain, suggesting that this domain may play a pivotal role in the evolution of coreceptor usage in vivo. We identified individual residues in both functional regions, Asp-11, Lys-197, and Asp-276, that contribute to coreceptor function. Deletion of a highly conserved cytoplasmic motif rendered CCR5 incapable of signaling but did not abrogate its ability to function as a coreceptor, implying the independence of fusion and G-protein-mediated chemokine receptor signaling. Finally, we developed a novel monoclonal antibody to CCR5 to assist in future studies of CCR5 expression.

Human chemokine receptors CCR5, CCR3 and CCR2B share common polarity motif in the first extracellular loop with other human G‐protein coupled receptors

“…However, these results should in no way be taken to reflect that the common motif identified in the EL-1 region is the only determinant for M-tropic HIV-1 coreceptor activity. This is further substantiated by results from other studies [3,4,6,8,9,11], demonstrating the involvement of multiple sites on the receptor in this process.…”

“…Other lines of evidence, discussed above, have supported an important role of the N t -domain and, probably, the participation of EL-2 and EL-3 of CCR5 in the coreceptor activity. Putative involvement of multiple CR sites in coreceptor functioning [3,4,6,8,9,11] makes it difficult to distinguish between the role of different ECDs, although the motif found in EL-1 might be considered as important for M-tropic HIV-1 entry. Also, we should note that in the literature, EL-1 was not attributed to regions involved in ligand binding and signaling.…”

An extended CCR5 ECL2 peptide forms a helix that binds HIV‐1 gp120 through non‐specific hydrophobic interactions

“…Thus, from comparison of the spectra of ECL2S in the presence of a 1 : 1 molar ratio of mut gp120 core / CD4M33 or mut gp120 core (+V3)/CD4M33, we conclude that the V3 loop does not contribute to gp120 binding to the ECL2S peptide, and in fact actually decreases binding affinity, especially below physiological pH. This is seemingly in contrast to biochemical data suggesting that ECL2 in the intact receptor is involved in V3 binding [7,[11][12][13].…”

Monoclonal antibody screening of a phage-displayed random peptide library reveals mimotopes of chemokine receptor CCR5: implications for the tertiary structure of the receptor and for an N-terminal binding site for HIV-1 gp120

“…Despite the large variation in contact residues according to cell type and HIV-1 strain, most of the contact residues for 3A9 and 5C7 identified in this study contributed to gp120 binding; thus residues 1-19 and 4-25 were identified as crucial for coreceptor function [34,35]. Among these residues, coreceptor function was attributed to 6S [36], 10Y [35,37,38], 11D [35,37,39], with other residues defined for various isolates (reviewed in [33,40]). There are no data available for residues 94W, 95D, 96F and 97G of the first extracellular loop.…”