Crystal Structure of β-Arrestin 2 in Complex with CXCR7 Phosphopeptide

beta-Arrestins (beta arrs) critically regulate G-protein-coupled receptor (GPCR) signaling and trafficking. beta arrs have two isoforms, beta arr1 and beta arr2. Receptor phosphorylation is a key determinant for the binding of beta arrs, and understanding the intricate details of receptor-beta arr interaction is the next frontier in GPCR structural biology. The high-resolution structure of active beta arr1 in complex with a phosphopeptide derived from GPCR has been revealed, but that of beta arr2 remains elusive. Here, we present a 2.3-A crystal structure of beta arr2 in complex with a phosphopeptide (C7pp) derived from the carboxyl terminus of CXCR7. The structural analysis of C7pp-bound beta arr2 reveals key differences from the previously determined active conformation of beta arr1. One of the key differences is that C7pp-bound beta arr2 shows a relatively small inter-domain rotation. Antibody-fragment-based conformational sensor and hydrogen/deuterium exchange experiments further corroborated the structural features of beta arr2 and suggested that beta arr2 adopts a range of inter-domain rotations.