Molecular mechanism of β-arrestin-2 interaction with phosphatidylinositol 4,5-bisphosphate

Phosphorylated residues of G protein-coupled receptors bind to the N-domain of arrestin, resulting in {beta}XX release. This induces further allosteric conformational changes, such as polar core disruption, alteration of interdomain loops, and domain rotation, which transform arrestins into the active state. It is widely accepted that arrestin activation occurs by conformational changes propagated from the N-to the C-domain. However, recent studies have revealed that binding of phosphatidylinositol 4,5-bisphosphate (PIP2) to the C-domain transforms arrestins into an active state. In this study, we aimed to elucidate the mechanisms underlying PIP2-induced arrestin activation. We compared the conformational changes of {beta}-arrestin-2 upon binding of PIP2 or phosphorylated C-tail peptide of vasopressin receptor type 2 using hydrogen/deuterium exchange mass spectrometry (HDX-MS). Introducing point mutations on the potential routes of the allosteric conformational changes and analyzing these mutant constructs with HDX-MS revealed that PIP2-binding at the C-domain affects the back loop, which destabilizes the gate loop and {beta}XX to transform {beta}-arrestin-2 into the pre-active state.