Structural basis for selectivity and diversity in angiotensin II receptors

The angiotensin II receptors AT₁R and AT₂R serve as key components of the renin-angiotensin-aldosterone system. AT₁R has a central role in the regulation of blood pressure, but the function of AT₂R is unclear and it has a variety of reported effects. To identify the mechanisms that underlie the differences in function and ligand selectivity between these receptors, here we report crystal structures of human AT₂R bound to an AT₂R-selective ligand and to an AT₁R/AT₂R dual ligand, capturing the receptor in an active-like conformation. Unexpectedly, helix VIII was found in a non-canonical position, stabilizing the active-like state, but at the same time preventing the recruitment of G proteins or β-arrestins, in agreement with the lack of signalling responses in standard cellular assays. Structure-activity relationship, docking and mutagenesis studies revealed the crucial interactions for ligand binding and selectivity. Our results thus provide insights into the structural basis of the distinct functions of the angiotensin receptors, and may guide the design of new selective ligands.