Résumé
β-arrestins are key privileged molecular partners of G-Protein Coupled Receptors (GPCRs), triggering not only their desensitization but also intracellular signaling. Existing structures point to a high conformational plasticity of β-arrestin:GPCRs interaction, with two completely different orientations between receptor and β-arrestin. The same set of structures also indicates that the C-edge loop of β-arrestin could contribute to its anchoring to the membrane, through an interaction with specific lipids, namely PI(4,5)P2. Combining molecular dynamics simulations and fluorescence spectroscopy, we show that β-arrestin 1 interacts with membranes even in the absence of a receptor, an interaction that is enhanced by PI(4,5)P2 presumably holding the β-arrestin 1 C-edge loop into the lipid bilayer. This key interaction helps β-arrestin 1 to adopt a “receptor ready” orientation. As a consequence, PI(4,5)P2 also favors the coupling of β-arrestin 1 to the ghrelin receptor (GHSR). In addition, we show that β-arrestin can adopt the two known extreme orientations when complexed with GHSR. Of importance, PI(4,5)P2 shifts the equilibrium between the two different arrangements, favoring one of them. Simulations performed on the GHSR:β-arrestin complex suggest that release of the C-edge loop is required for these transitions to occur and point to a different distribution of PI(4,5)P2 around the complex depending on the orientation of receptor-bound arrestin. Taken together, our results highlight how PI(4,5)P2 plays a true third player role in the β-arrestin:GPCRs interaction, not only by preparing β-arrestin for its further interaction with receptors but also by modulating its orientation once the protein:protein complex is formed.