The third transmembrane domains of the human B1 and B2 bradykinin receptor subtypes are involved in discriminating between subtype-selective ligands
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The B1 and B2 bradykinin (BK) receptor subtypes belong to the GPCR faro ily, and they discriminate between peptides that differ only by the absence and presence of a C-terminal Arg, To identify receptor residues conferring tigand spe.cificity, chimeric constructs in which TM-III were exchanged between the receptors were expressed and assayed by radioligand binding and fluorescence Ca2+ imaging in t1EK293 and A10 cells, respectively. Substitution of B1 TMIII into the B2 receptor (B2(B1III) decreased the affinity for the B2-selective agonist BK and antagonist NPC17731, while substitution of B2 TM-III into the Bt receptor decreased the affinity for the Bl-selective agonist des-Argm-Lys BK. High affinity binding to B2(B1III) was fully restored when one residue, Lys-11, in TMdlI was replaced with the corresponding residue, Serltl, in the wild-type B2 receptor. Binding was also restored by replacement with Ala, tlis, and Met, but not by' Arg. These results show that TM-III contributes significantly to the ability of these receptors to diseriminate between subtype selective ligands. We believe that the low affinity of B2-selective peptides for the B1 receptor is due in part to the positive charge of Lys-1. facing the ligand binding pocket which repels the positive charge of the C terminal Arg in these peptides.
Ämnesklassifikation (UKÄ) – OBLIGATORISK
|Status||Published - 1997 dec 1|
|Peer review utförd||Ja|