Phosphorylation of GRK1 and GRK7 by cAMP-dependent protein kinase attenuates their enzymatic activities

J Biol Chem. 2005 Aug 5;280(31):28241-50. doi: 10.1074/jbc.M505117200. Epub 2005 Jun 9.


Phosphorylation of G protein-coupled receptors is a critical step in the rapid termination of G protein signaling. In rod cells of the vertebrate retina, phosphorylation of rhodopsin is mediated by GRK1. In cone cells, either GRK1, GRK7, or both, depending on the species, are speculated to initiate signal termination by phosphorylating the cone opsins. To compare the biochemical properties of GRK1 and GRK7, we measured the K(m) and V(max) of these kinases for ATP and rhodopsin, a model substrate. The results demonstrated that these kinases share similar kinetic properties. We also determined that cAMP-dependent protein kinase (PKA) phosphorylates GRK1 at Ser(21) and GRK7 at Ser(23) and Ser(36) in vitro. These sites are also phosphorylated when FLAG-tagged GRK1 and GRK7 are expressed in HEK-293 cells treated with forskolin to stimulate the endogenous production of cAMP and activation of PKA. Rod outer segments isolated from bovine retina phosphorylated the FLAG-tagged GRKs in the presence of dibutyryl-cAMP, suggesting that GRK1 and GRK7 are physiologically relevant substrates. Although both GRKs also contain putative phosphorylation sites for PKC and Ca(2+)/calmodulin-dependent protein kinase II, neither kinase phosphorylated GRK1 or GRK7. Phosphorylation of GRK1 and GRK7 by PKA reduces the ability of GRK1 and GRK7 to phosphorylate rhodopsin in vitro. Since exposure to light causes a decrease in cAMP levels in rod cells, we propose that phosphorylation of GRK1 and GRK7 by PKA occurs in the dark, when cAMP levels in photoreceptor cells are elevated, and represents a novel mechanism for regulating the activities of these kinases.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cattle
  • Cell Line
  • Consensus Sequence
  • Cyclic AMP / metabolism
  • Cyclic AMP-Dependent Protein Kinases / metabolism
  • Darkness
  • Eye Proteins / chemistry
  • Eye Proteins / genetics
  • Eye Proteins / metabolism*
  • G-Protein-Coupled Receptor Kinase 1
  • G-Protein-Coupled Receptor Kinases
  • Humans
  • Kidney
  • Kinetics
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Phosphorylation
  • Phosphoserine / metabolism
  • Protein Kinases / chemistry
  • Protein Kinases / genetics
  • Protein Kinases / metabolism*
  • Protein-Serine-Threonine Kinases / chemistry
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism*
  • Recombinant Proteins / metabolism
  • Rhodopsin / metabolism*
  • Rod Cell Outer Segment / metabolism
  • Urea / isolation & purification


  • Eye Proteins
  • Recombinant Proteins
  • Phosphoserine
  • Urea
  • Rhodopsin
  • Cyclic AMP
  • Protein Kinases
  • Protein-Serine-Threonine Kinases
  • Cyclic AMP-Dependent Protein Kinases
  • G-Protein-Coupled Receptor Kinase 1
  • GRK1 protein, human
  • GRK7 protein, human
  • G-Protein-Coupled Receptor Kinases