Specificity for a CCR5 inhibitor is conferred by a single amino acid residue: role of Ile198 [Molecular Bases of Disease]

March 12th, 2015 by Lau, G., Labrecque, J., Metz, M., Vaz, R., Fricker, S. P.

The chemokine receptors CCR5 and CCR2b share 89% amino acid homology. CCR5 is a co-receptor for HIV and CCR5 antagonists have been investigated as inhibitors of HIV infection. We describe the use of two CCR5 antagonists, Schering-C (SCH-C) which is specific for CCR5 and TAK-779 a dual inhibitor of CCR5 and CCR2b, to probe the CCR5 inhibitor binding site using CCR5/CCR2b chimeric receptors. Compound inhibition in the different chimeras was assessed by inhibition of chemokine-induced calcium flux. SCH-C inhibited RANTES (CCL5)-mediated calcium flux on CCR5 with an IC50 of 22.8 nM but was inactive against MCP-1 (CCL2)-mediated calcium flux on CCR2b. However SCH-C inhibited CCL2-induced calcium flux against a CCR5/CCR2b chimera consisting of transmembrane domains (TM) four to six of CCR5 with an IC50 of 55 nM. A sequence comparison of CCR5 and CCR2b identified a divergent amino acid sequence located at the junction of TM-V and second extracellular loop (ECL2). Transfer of the CCR5 sequence KNFQTLKIV into CCR2b conferred SCH-C inhibition (IC50 of 122 nM) into the predominantly CCR2b chimera. Furthermore, a single substitution R206I conferred partial but significant inhibition (IC50 of 1023 nM) by SCH-C. These results show that a limited amino acid sequence is responsible for SCH-C specificity to CCR5, and we propose a model showing the interaction with CCR5 Ile198.