A binding pocket for a small molecule inhibitor of HIV-1 entry within the transmembrane helices of CCR5

HIV-1 entry into CD4+ cells requires the sequential interactions of the vir al envelope glycoproteins with CD4 and a coreceptor such as the chemokine r eceptors CCR5 and CXCR4. A plausible approach to blocking this process is t o use small molecule antagonists of coreceptor function. One such inhibitor has been described for CCR5: the TAK-779 molecule. To facilitate the furth er development of entry inhibitors as antiviral drugs, we have explored how TAK-779 acts to prevent HIV-1 infection. and we have mapped its site of in teraction with CCR5. We find that TAK-779 inhibits HIV-1 replication at the membrane fusion stage by blocking the interaction of the viral surface gly coprotein gp120 with CCR5. We could identify no amino acid substitutions wi thin the extracellular domain of CCR5 that affected the antiviral action of TAK-779. However, alanine scanning mutagenesis of the transmembrane domain s revealed that the binding site for TAK-779 on CCR5 is located near the ex tracellular surface of the receptor, within a cavity formed between transme mbrane helices 1, 2, 3, and 7.