Conformational Sensors and Domain Swapping Reveal Structural and Functional Differences between β-Arrestin Isoforms

Desensitization, signaling, and trafficking of G-protein-coupled receptors (GPCRs) are critically regulated by multifunctional adaptor proteins, beta-arrestins (beta arrs). The two isoforms of beta arrs (beta arr1 and 2) share a high degree of sequence and structural similarity; still, however, they often mediate distinct functional outcomes in the context of GPCR signaling and regulation. A mechanistic basis for such a functional divergence of beta arr isoforms is still lacking. By using a set of complementary approaches, including antibody-fragment-based conformational sensors, we discover structural differences between beta arr1 and 2 upon their interaction with activated and phosphorylated receptors. Interestingly, domain-swapped chimeras of beta arrs display robust complementation in functional assays, thereby linking the structural differences between receptor-bound beta arr1 and 2 with their divergent functional outcomes. Our findings reveal important insights into the ability of beta arr isoforms to drive distinct functional outcomes and underscore the importance of integrating this aspect in the current framework of biased agonism.