Distinct C-tail dynamics between β-arrestin isoforms in forming GPCR tail- and core-engaged complexes

The two non-visual β-arrestins (βarrs) are essential scaffolding proteins involved in desensitization, internalization and signaling of G protein-coupled receptors (GPCRs), and they show functional divergence despite high structural similarity. By employing NMR, cryo-EM and computational methods, we herein report previously unanticipated differences between the two isoforms in the basal and both the receptor tail- and core-engaged states. The autoinhibitory C-tails of the two βarrs show distinct dynamics in the basal state, and only that of βarr2 robustly transitions into an α-helix that docks at the central crest in the tail-engaged state. This difference is encoded in the amino acid sequences of the disordered regions flanking the chameleon motif. Moreover, core interaction releases βarr2 C-tail, and the core-engaged complex structures determined in lipid nanodiscs reveal a less tilted binding angle of βarr2 due to a shallower insertion of its C-edge loops into the membrane. Our findings provide a conceptual molecular framework for understanding the functional divergence between the βarr isoforms in regulating GPCR signaling.