Biased Agonists of the Type 1 Angiotensin II Receptor Promote Distinct Subcellular β-Arrestin Conformations.

Abstract

G protein-coupled receptors (GPCRs) are central to cellular signaling and therapeutic targeting. Ligands that activate the same GPCR can selectively activate some signaling pathways over others, a phenomenon termed biased agonism. Additionally, the same ligand and receptor complex can elicit distinct signaling profiles in different subcellular locations (location bias). Here, we examine how various biased agonists influence the recruitment of β-arrestins 1 and 2 induced by the angiotensin II type 1 receptor at the receptor, plasma membrane, and early endosomes. We also assessed β-arrestin conformational states at the receptor and plasma membrane. Using split luciferase and BRET assays, we demonstrate that angiotensin II, its G protein-biased analogs (TRV055, TRV056), and its β-arrestin-biased analogs (TRV023, TRV026, TRV027, TRV034) functionally stratify into two clusters. G protein-biased agonists and AngII predominantly favor a receptor-β-arrestin core complex conformation driven by engagement of the β-arrestin finger loop with the receptor core. In contrast, β-arrestin-biased agonists promote a tail complex configuration of receptor-associated β-arrestins. However, the conformations of β-arrestins monitored at the plasma membrane were found to be unaffected by ligand bias. Furthermore, balanced and G protein-biased ligands induced higher levels of ERK activation in subcellular locations (nucleus, cytosol, and early endosomes) over the β-arrestin-biased ligands, but equal ERK activity at the plasma membrane. Our findings highlight the interplay between ligand and location biases in dictating GPCR signaling, revealing new insights into the molecular mechanisms driving selective signal propagation.