CDB15:0000962 KNG1 — BDKRB1

ABSTRACT: Bradykinin and kallidin are endogenous kinin peptide hormones that belong to the kallikrein-kinin system and are essential to the regulation of blood pressure, inflammation, coagulation and pain control. Des-Arg10-kallidin, the carboxy-terminal des-Arg metabolite of kallidin, and bradykinin selectively activate two G protein-coupled receptors, type 1 and type 2 bradykinin receptors (B1R and B2R), respectively. The hyperactivation of bradykinin receptors, termed 'bradykinin storm', is associated with pulmonary edema in COVID-19 patients, suggesting that bradykinin receptors are important targets for COVID-19 intervention. Here we report two G protein-coupled complex structures of human B1R and B2R bound to des-Arg10-kallidin and bradykinin, respectively. Combined with functional analysis, our structures reveal the mechanism of ligand selectivity and specific activation of the bradykinin receptor. These findings also provide a framework for guiding drug design targeting bradykinin receptors for the treatment of inflammation, cardiovascular disorders and COVID-19.

ABSTRACT: A cDNA clone encoding a human B1 bradykinin receptor was isolated from a human embryonic lung fibroblast cDNA library by expression cloning. The photoprotein aequorin was utilized as an indicator of the ability of the B1 receptor agonist [des-Arg10]kallidin to mediate Ca2+ mobilization in Xenopus laevis oocytes injected with RNA. A clone was isolated with a 1307-nucleotide insert which contains an open reading frame encoding a 353-amino acid protein with the characteristics of a G-protein-coupled receptor. The amino acid sequence of the B1 bradykinin receptor is 36% identical to the amino acid sequence of the B2 bradykinin receptor. The cloned B1 bradykinin receptor expressed in mammalian cells exhibits high affinity binding for 3H-labeled [des-Arg10]kallidin and low affinity for bradykinin. The B1 receptor antagonist [des-Arg10,Leu9]kallidin effectively displaces 3H-labeled [des-Arg10]kallidin from the cloned receptor, whereas the B2 receptor antagonist Hoe-140 (D-Arg0-[Hyp3,Thi5,D-Tic7,Oic8]bradykinin, where Thi is L-[3-(2-thienyl)alanyl], Tic is D-(1,2,3,4-tetrahydroisoquinolin-3-yl-carbonyl), and Oic is L-[(3aS, 7aS)-octahydroindol-2-yl-carbonyl]) does not. Therefore, the expressed receptor has the pharmacological characteristics of the B1 receptor subtype. The availability of both the cloned human B1 and B2 bradykinin receptors should allow the elucidation of the relative contributions of these two receptor subtypes in acute and chronic inflammatory processes.

ABSTRACT: To delineate ligand binding and functional characteristics of the human B1 kinin receptor, a stable clone of Chinese hamster ovary cells expressing a single class of binding sites for [3H]des-Arg10-lysylbradykinin with a Kd of 0.3 nM and a Bmax of 38 fmol/mg protein ( approximately 40,000 receptors/cell) was isolated. Studies with peptide analogs showed that a lysine residue at position 1 (based on the lysylbradykinin sequence) of ligands was essential for high affinity binding to the human B1 receptor. In marked contrast to cloned Chinese hamster ovary cells expressing the human kinin B2 receptor, which internalized approximately 80% of the ligand within 5 min upon exposure to 2 nM [3H]bradykinin, exposure of cells expressing the B1 receptor to 1 nM [3H]des-Arg10-lysylbradykinin resulted in minimal ligand internalization. Stimulation of the B1 receptor led to inositol phosphate generation and transient increases in intracellular calcium, confirming coupling to phospholipase C, while immunoprecipitation of photoaffinity-labeled G-proteins from membranes indicated specific coupling of the receptor to Galphaq/11 and Galphai1,2. The B1, unlike the B2, receptor does not desensitize (as demonstrated by continuous phosphoinositide hydrolysis), enhancing the potential role of this receptor during inflammatory events.