Angiotensin receptor conformations stabilized by biased ligands differentially modulate β-arrestin interactions

“Biased” ligands of the angiotensin II type 1 receptor (AT1R) preferentially activate Gq pathways, which promote vasoconstriction, or β-arrestin-mediated pathways, which have salutary cardiac effects. We previously demonstrated that pharmacologically indistinguishable β-arrestin-biased ligands stabilize different AT1R conformational ensembles. Here we show these ligand-specific conformational changes determine whether β-arrestin interacts with the AT1R seven-transmembrane (7TM) core or only the phosphorylated C-terminus. We developed a method to form complexes between non-phosphorylated AT1R and β-arrestin1 mediated only through the 7TM core. β-Arrestin-biased ligands vary substantially in their ability to stabilize these complexes, with less effective ligands promoting intracellular conformations characterized by an intermediate rather than a fully outward-tilted position of transmembrane helix 6. Since certain β-arrestin functions are promoted by interactions with the GPCR 7TM core and others by interactions with phosphorylated regions, GPCR drugs could exploit this mechanism to achieve finer levels of bias and further diversify their therapeutic effects.