The type 2 bradykinin receptor (B2R) is a G protein-coupled receptor (GPCR) in the cardiovascular system, and the dysfunction of B2R leads to inflammation, hereditary angioedema, and pain. Bradykinin and kallidin are both endogenous peptide agonists of B2R, acting as vasodilators to protect the cardiovascular system. Here we determine two cryo-electron microscopy (cryo-EM) structures of human B2R-Gq in complex with bradykinin and kallidin at 3.0 Å and 2.9 Å resolution, respectively. The ligand-binding pocket accommodates S-shaped peptides, with aspartic acids and glutamates as an anion trap. The phenylalanines at the tail of the peptides induce significant conformational changes in the toggle switch W2836.48, the conserved PIF, DRY, and NPxxY motifs, for the B2R activation. This further induces the extensive interactions of the intracellular loops ICL2/3 and helix 8 with Gq proteins. Our structures elucidate the molecular mechanisms for the ligand binding, receptor activation, and Gq proteins coupling of B2R.
The peptide hormone angiotensin II regulates blood pressure mainly through the type 1 angiotensin II receptor AT1R and its downstream signaling proteins Gq and β‐arrestin. AT1R blockers, clinically used as antihypertensive drugs, inhibit both signaling pathways, whereas AT1R β‐arrestin‐biased agonists have shown great potential for the treatment of acute heart failure. Here, we present a cryo‐electron microscopy (cryo‐EM) structure of the human AT1R in complex with a balanced agonist, Sar1‐AngII, and Gq protein at 2.9 Å resolution. This structure, together with extensive functional assays and computational modeling, reveals the molecular mechanisms for AT1R signaling modulation and suggests that a major hydrogen bond network (MHN) inside the receptor serves as a key regulator of AT1R signal transduction from the ligand‐binding pocket to both Gq and β‐arrestin pathways. Specifically, we found that the MHN mutations N1113.35A and N2947.45A induce biased signaling to Gq and β‐arrestin, respectively. These insights should facilitate AT1R structure‐based drug discovery for the treatment of cardiovascular diseases.
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