| C-C chemokine receptor 5 (CCR5) acts as the principal coreceptor during HIV-1 transmission and early stages of infection. The importance of CCR5 is highlighted by evidence that persons carrying a 32-base pair deletion mutation (CCR5-Delta32) within the CCR5 gene exhibit a slower progression to AIDS, or are highly resistant to acquiring HIV-1. Distinct populations of CCR5 have been identified, and can be recognized by monoclonal antibodies (MAbs) detecting epitope-specific conformations. Although it is apparent that CCR5 populations exist, much remains to be identified regarding how receptor-specific processes influence conformational heterogeneity. Using MAbs to recognize CCR5 conformational variants utilized by HIV-1, we investigated these antibody-defined CCR5 conformations relative to their localization and features of receptor function such as ligand engagement, trafficking and G protein association. In various cell lines, we reveal that CCR5 conformations differ in their distribution patterns and expression at the cell surface and internally. We find that CD4+ T cells, target cells for HIV-1 entry and infection, also vary in their surface expression of CCR5 conformations, and that HIV-1 infection reduces the number of such conformation-expressing cells. Relative to trafficking, we show that CCR5 populations have distinct sensitivities to endocytosis inhibition. Furthermore, we reveal conformation-specific changes upon engagement with both CCR5 chemokine analogs and a clinically used HIV-1 inhibitor, and upon disruption of the G protein alpha subunit association. Overall, we establish distinct characteristics for CCR5 conformations that likely explain their preferential use by HIV-1. |
