The role of histidine 265 in antagonist binding to the neurokinin-1 receptor.

Previous studies suggested that the antagonist binding site in the neurokinin-1 receptor is composed of phylogenetically conserved residues, while phylogenetically divergent residues affect the conformation of the binding site. To test this hypothesis, we investigated the role of conserved residues in antagonist binding. Histidine 197 in the human receptor was found to interact with CP-96,345 but not RP67580. In addition, a nearby residue, histidine 265 of the human receptor, is required for the binding of RP67580 but not CP-96,345 or substance P. The interaction between residue 265 and RP67580 is consistent with a hydrogen bonding interaction. Analysis of several analogs of CP-96,345 revealed that histidine 265 of the human receptor is in proximity to the substituted benzyl moiety of CP-96,345, and can interact with other analogs of CP-96,345. In contrast to the human neurokinin-1 receptor, both histidine 197 and histidine 265 in the rat neurokinin-1 receptor appear to interact with both CP-96,345 and RP67580. These results support a conformational difference between the antagonist binding sites of the rat and human neurokinin-1 receptors and provide a model for examining specific interactions between antagonists and the receptor.