Arrestin can Bind to a Single G-Protein Coupled Receptor

Termination of G protein-coupled receptor (GPCR) signaling typically involves phosphorylation of the receptor, followed by binding of a protein called arrestin. Here we tested the minimal stoichiometry required for this interaction, by determining if a single rhodopsin molecule can bind arrestin. To do this, we prepared nanoscale phospholipids particles, so-called nanodiscs, which contain only monomeric rhodopsin and measured their ability to bind visual arrestin. Our data clearly show that visual arrestin can bind to monomeric phosphorylated rhodopsin to stabilize its active form, called metarhodopsin II. Interestingly, we find beta-arrestin can also bind to monomeric rhodopsin in nanodiscs and stabilize metarhodopsin II. Together, these results suggest that in general, the minimal unit for arrestin binding is a monomeric GPCR.