G protein signaling capabilities at the bradykinin 2 receptor.

The bradykinin 2 receptor (B2R) is one of two members of the kinin receptor family and is a G protein-coupled receptor (GPCR) that regulates important physiological processes including pain, inflammation, and cardiovascular homeostasis. Functionally, B2R is activated by the kinin peptides, bradykinin and kallidin. Carboxypeptidase cleavage of bradykinin and kallidin results in the formation of des-Arg9-bradykinin (DABK) and des-Arg10-kallidin (DAKD) respectively, which are classically described as agonists of the bradykinin 1 receptor (B1R), the other member of the kinin family. Affinity binding studies have reported that DABK and DAKD can also bind to B2R. Upon activation, B2R signals through the recruitment of heterotrimeric G proteins, and earlier work has highlighted the promiscuous G protein coupling to B2R in response to bradykinin. However, a comprehensive G protein activation profile of the B2R receptor when activated by the other endogenous agonists has not yet been established. In this study, we used Bioluminescence Resonance Energy Transfer (BRET)-based in vitro assays to monitor the coupling of 14 different Gα proteins upon B2R activation. Our results show that there is a shift in G protein activation profiles and kinetics among the different peptides. By analyzing responses across a range of agonist concentrations, we further identified biased signaling among these peptides, with differential activation of specific Gα subtypes. These results improve understanding of intracellular mechanisms through which the kinin system regulates different aspects of its physiological role and provide valuable information for the design of drugs targeting the kinin receptors.