THE AMINO-TERMINUS OF HUMAN CCR5 IS REQUIRED FOR ITS FUNCTION AS A RECEPTOR FOR DIVERSE HUMAN AND SIMIAN IMMUNODEFICIENCY VIRUS ENVELOPE GLYCOPROTEINS

The chemokine receptor CCR5 plays a key role in the CD4-dependent entr y of human and simian immunodeficiency viruses into target cells. We h ave mapped the interaction sites on CCR5 for a number of novel anti-CC R5 monoclonal antibodies and have used these to study the role of the CCR5 N-terminal ectodomain in viral entry and to demonstrate different ial CCR5 epitope expression on different cell types. Deletions of the CCR5 amino terminal domain or substitution with equivalent regions fro m other chemokine receptors did not affect cell surface expression or reactivity with loop-specific antibodies, suggesting that the loop reg ions remained conformationally intact. Exchanges of the amino terminal segment of CCR5 with the equivalent domains of CCR1, CCR2, and CXCR4 did not significantly affect infection with virus pseudotyped with env elope glycoproteins (Envs) from HIV-2 and SIV, but substitution with t he CXCR4 sequence abrogated entry mediated by Env from HIV-1. In contr ast, deletion of the amino terminus abrogated CCR5 receptor activity f or all viral Envs examined. These data indicate that the amino terminu s of CCR5 has an essential rule in entry mediated by diverse viral Env s but that the sequence requirements are more relaxed for the HIV-2 ar d SIV Envs compared to the HIV-I Env examined. This suggests that diff erent viral Envs make distinct and specific interactions with the amin o terminus of CCR5. Viral Env utilization of CCR5 expressed on 293-T c ells does not always correlate with the cellular tropism pi the virus, and one possible explanation is that Env-accessible interaction sites on CCR5 differ on different cell types. We therefore analyzed binding of several anti-CCR5 monoclonal antibodies to cell lines and primary cells that express this chemokine receptor and found that whereas all antibodies bound to CCR5-transfected 293T cells, several did not bind to PBMC. The results suggest that CCR5 undergoes cell type specific st ructural modifications which may affect interaction with different HIV and SIV envelope glycoproteins. (C) 1998 Academic Press.