β-arrestin plays an important role in GPCR deactivation, binding to phosphorylated GPCRs to diminish the receptor’s ability to activate further G proteins, reducing its activity.
If a ligand has not dissociated from a GPCR, a receptor kinase can phosphorylate the intracellular domain of the receptor. This encourages β-arrestin to bind to the receptor to suppress the receptor’s signalling ability. This is due to there being no mechanism, other than removal of the receptor from the membrane, to induce the removal of the ligand. To stop signalling, the ligand must dissociate naturally. It is therefore beneficial to have other mechanisms to stop signalling.