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

E3 ubiquitin ligase Mdm2 facilitates β-arrestin ubiquitination, leading to the internalization of G protein-coupled receptors (GPCRs). In this process, β-arrestins bind to Mdm2 and recruit it to the receptor; however, the molecular architecture of the β-arrestin-Mdm2 complex has not been elucidated yet. Here, we identified the β-arrestin-binding region (ABR) on Mdm2 and solved the crystal structure of β-arrestin1 in complex with Mdm2 ABR peptide. The acidic residues of Mdm2 ABR bind to the positively charged concave side of the β-arrestin1 N-domain. The C-tail of β-arrestin1 is still bound to the N-domain, indicating that Mdm2 binds to the inactive state of β-arrestin1, whereas the phosphorylated C-terminal tail of GPCRs binds to activate β-arrestins. The overlapped binding site of Mdm2 and GPCR C-tails on β-arrestin1 suggests that the binding of GPCR C-tails might trigger the release of Mdm2. Moreover, hydrogen/deuterium exchange experiments further show that Mdm2 ABR binding to β-arrestin1 induces the interdomain interface to be more dynamic and uncouples the IP 6 -induced oligomer of β-arrestin1. These results show how the E3 ligase, Mdm2, interacts with β-arrestins to promote the internalization of GPCRs.