In contrast, the N-terminus of CCR5 is a critical element in coreceptor activity with 89.6. These results suggest that multiple domains of CCR5 are involved in the interaction with env. Chimeras were tested for coreceptor activity in fusion assays using effector cells expressing the indicated env glycoproteins and T7 polymerase. Target cells were programmed to express human CD4. LucWero.se activity in detergent lysates was determined 8 hours after mixing.
Results are the mean values of duplicate analysis in at least three independent experiments.
Surprisingly, similar experiments using CXCR4 gave different results. I and 2 were required for coreceptor activity with the IJIB strain and that 89.6 could fuse with receptors containing only loop 2 of CXCR4. Alanine scanning mutagenesis of extracellular domains of CCR5 revealed that no single charged amino acid residue was essential for interaction with env. These findings further implicate the involvement of multiple domains of CCR5 in the interaction with env and clearly illustrate that detailed molecular anatomy of the engagement of chemokine receptors with env from different HIV-1 strains varies. Unexpectedly, env from dual tropic strains of HJV- 1 were found to use different regions of CCR5 and CXCR4, indicating a high degree of diversity in this interaction.