Regulation of G protein-coupled receptor kinase 5 (GRK5) by actin.
G protein-coupled receptor kinases (GRKs) initiate pathways leading to the desensitization of agonist-occupied G-protein-coupled receptors (GPCRs). Here we report that the cytoskeletal protein actin binds and inhibits GRK5. Actin inhibits the kinase activity directly, reducing GRK5-mediated phosphorylation of both membrane-bound GPCRs and soluble substrates. GRK5 binds actin monomers with a Kd of 0.6 microM and actin filaments with a Kd of 0. 2 microM. Mutation of 6 amino acids near the amino terminus of GRK5 eliminates actin-mediated inhibition of GRK5. Calmodulin has previously been shown to bind to the amino terminus of GRK5 (Pronin, A. N., and Benovic, J. L. (1997) J. Biol. Chem. 272, 3806-3812) and here we show calmodulin displaces GRK5 from actin. Calmodulin inhibits GRK5-mediated phosphorylation of GPCRs, but not soluble substrates such as casein. Thus in the presence of actin, calmodulin determines the substrate specificity of GRK5 by preferentially allowing phosphorylation of soluble substrates over membrane-bound substrates.
Howard Hughes Medical Institute and Departments of Medicine and Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA.
J L
JL
Freeman
E M
EM
De La Cruz
T D
TD
Pollard
R J
RJ
Lefkowitz
J A
JA
Pitcher
D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D002147:Calmodulin / Q000378:metabolism; D002364:Caseins / Q000378:metabolism; D005453:Fluorescence; D054774:G-Protein-Coupled Receptor Kinase 5; D019204:GTP-Binding Proteins / Q000502:physiology*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation; D011485:Protein Binding / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D012243:Rhodopsin / Q000378:metabolism; D013379:Substrate Specificity / Q000187:drug effects
D000199:Actins; D002147:Calmodulin; D002364:Caseins; D012243:Rhodopsin; D020794:Receptor Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D054774:G-Protein-Coupled Receptor Kinase 5; D019204:GTP-Binding Proteins