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Biochem Biophys Res Commun. 1999 May 27;259(1):224-9.

Overexpression of wild-type and catalytically inactive forms of GRK2 and GRK6 fails to alter the agonist-induced phosphorylation of the C5a receptor (CD88): evidence that GRK6 is autophosphorylated in COS-7 cells.

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DBMS/Laboratoire de Biochimie et de Biophysique des Systèmes Intégrés (UMR 314 CEA/CNRS), CEA/Grenoble, 17 rue des Martyrs, Grenoble Cedex 9, 38054, France.


The G protein-coupled receptor kinase family comprises six members (GRK1 to GRK6) that phosphorylate and desensitize a number of agonist-occupied G protein-coupled receptors. Overexpression of the dominant negative mutant GRK2-K220R is often accompanied by an inhibition of the agonist-mediated phosphorylation of G protein-coupled receptors. In the case of the C5a receptor (C5aR), the overexpression of wild-type GRK2 or GRK6 as well as of catalytically inactive forms of these kinases (GRK2-K220R and GRK6-K215R) failed to increase or to inhibit the agonist-mediated phosphorylation of C5aR, respectively. Replacement of Lys215 by an arginine residue in GRK6 yielded a protein with a relative molecular mass of 63 kDa, whereas wild-type GRK6 had a relative molecular mass of 66 kDa on polyacrylamide gel. The mutations S484D and T485D in the catalytically inactive mutant GRK6-K215R resulted in a protein (GRK6-RDD) with the same electrophoretic mobility as wild-type GRK6. Furthermore, in the absence of phosphatase inhibitors, GRK6 was rapidly converted into the 63 kDa species, whereas GRK6-RDD was not. Overepression of GRK6-RDD failed to alter the agonist-mediated phosphorylation of C5aR. Taken together, the results suggest that C5aR is not a substrate for either GRK2 or GRK6 and that GRK6 is very likely autophosphorylated on Ser484 and Thr485 in vivo.

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