GPCR targeting of E3 ubiquitin ligase MDM2 by inactive β-arrestin

E3 ubiquitin ligase Mdm2 facilitates P- arrestin ubiquitination, leading to the internalization of G protein-coupled receptors (GPCRs). In this process, P- arrestins bind to Mdm2 and recruit it to the receptor; however, the molecular architecture of the P-arrestin-Mdm2 complex has not been elucidated yet. Here, we identified the P-arrestin-binding region (ABR) on Mdm2 and solved the crystal structure of P- arrestin1 in complex with Mdm2ABR peptide. The acidic residues of Mdm2ABR bind to the positively charged concave side of the P- arrestin1 N-domain. The C -tail of P- arrestin1 is still bound to the N-domain, indicating that Mdm2 binds to the inactive state of P- arrestin1, whereas the phosphorylated C-terminal tail of GPCRs binds to activate P- arrestins. The overlapped binding site of Mdm2 and GPCR C -tails on P- arrestin1 suggests that the binding of GPCR C -tails might trigger the release of Mdm2. Moreover, hydrogen/deuterium exchange experiments further show that Mdm2ABR binding to P- arrestin1 induces the interdomain interface to be more dynamic and uncouples the IP6- induced oligomer of P- arrestin1. These results show how the E3 ligase, Mdm2, interacts with P- arrestins to promote the internalization of GPCRs.