PHOSPHOLIPID-STIMULATED AUTOPHOSPHORYLATION ACTIVATES THE G-PROTEIN-COUPLED RECEPTOR KINASE GRK5

G protein-coupled receptor kinases (GRKs) play an important role in me diating agonist-specific desensitization of numerous G protein-coupled receptors. GRK5, a recently identified member of the GRK family, unde rgoes a rapid phospholipid-stimulated autophosphorylation to a stoichi ometry of similar to 2 mol of phosphate/mol of GRK5. The ability of ph ospholipids to stimulate autophosphorylation is largely blocked by a g lutathione S-transferase fusion protein containing the last 102 amino acids of GRK5 (amino acids 489-590), suggesting that this is a primary region involved in GRK5/phospholipid interaction. Phosphoamino acid d etermination and mutagenesis studies demonstrate that autophosphorylat ion of GRK5 occurs primarily at residues Ser-484 and Thr-485. Expressi on and characterization of a mutant GRK5 that does not autophosphoryla te (S484A and T485A) reveals that the mutant has a similar to 15-20-fo ld reduced ability to phosphorylate the beta(2)-adrenerse receptor and rhodopsin compared to wild type GRK5. These results suggest that phos pholipid-stimulated autophosphorylation may represent a novel mechanis m for membrane association and regulation of GRK5 activity,