G protein-coupled receptor kinases (GRK) are serine/threonine kinases that phosphorylate a variety of G-protein-coupled receptors (GPCRs), specifically activated forms, including adrenergic receptors, muscarinic acetylcholine receptors, dopamine receptors and opioid receptors. GRK receptor phosphorylation initiates B-arrestin-mediated receptor desensitization, internalization, and signaling events leading to their down-regulation.
