Identification of the critical residues of bradykinin receptor B1 for interaction with the kinins guided by site-directed mutagenesis and molecular modeling.

We report the critical residues for the interaction of the kinins with human bradykinin receptor 1 (Bl) using site-directed mutagenesis in conjunction with molecular modeling of the binding modes of the kinins in the homology model of the Bl receptor. Mutation of Lys 118 in transmembrane (TM) helix 3, Ala 270 in TM6, and Leu 294 in TM7 causes a significant decrease in the affinity for the peptide agonists des-Arg 10 kallidin (KD) and des-Arg 9 BK but not the peptide antagonist des-Arg 10 Leu 9 KD. In contrast, mutations in TM2, TM3, TM6, and TM7 cause a significant decrease in the affinity for both the peptide agonists and the antagonist. These data indicate that the Bl bradykinin binding pocket for agonists and antagonists is similar, but the manners in which they interact with the receptor do not completely overlap. Therefore, there is a potential to influence the receptor's ligand selectivity.