Structural insights into angiotensin receptor signaling modulation by balanced and biased agonists.

The peptide hormone angiotensin II regulates blood pressure mainly through the type 1 angiotensin II receptor AT R and its downstream signaling proteins G and β-arrestin. AT R blockers, clinically used as antihypertensive drugs, inhibit both signaling pathways, whereas AT R 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 AT R in complex with a balanced agonist, Sar -AngII, and G protein at 2.9 Å resolution. This structure, together with extensive functional assays and computational modeling, reveals the molecular mechanisms for AT R signaling modulation and suggests that a major hydrogen bond network (MHN) inside the receptor serves as a key regulator of AT R signal transduction from the ligand-binding pocket to both G and β-arrestin pathways. Specifically, we found that the MHN mutations N111 A and N294 A induce biased signaling to G and β-arrestin, respectively. These insights should facilitate AT R structure-based drug discovery for the treatment of cardiovascular diseases.