TY - JOUR T1 - Role for the RH Domain of GRK5 and 6 in β2-Adrenergic Receptor and Rhodopsin Phosphorylation JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.109.058115 SP - mol.109.058115 AU - Faiza Baameur AU - Daniel H. Morgan AU - Hui Yao AU - Tuan M. Tran AU - Richard A. Hammitt AU - Subir Sabui AU - John S. McMurray AU - Olivier Lichtarge AU - Richard B. Clark Y1 - 2009/01/01 UR - http://molpharm.aspetjournals.org/content/early/2009/12/28/mol.109.058115.abstract N2 - Phosphorylation of G Protein-Coupled Receptors (GPCRs) by GPCR Kinases (GRKs) is a major mechanism of desensitization of these receptors. GPCR activation of GRKs involves an allosteric site on GRKs distinct from the catalytic site. While recent studies have suggested an important role of the N- and C-termini and domains surrounding the kinase active site in allosteric activation, the nature of that site and the relative roles of the RH domain in particular remain unknown. Based on Evolutionary Trace (ET) analysis of both the RH and kinase domains of the GRK family, we identified an important cluster encompassing helices 3, 9 and 10 in the RH domain in addition to sites in the kinase domain. To define its function, a panel of GRK5 and 6 mutants was generated and screened by intact-cell assay of constitutive GRK phosphorylation of the β2-adrenergic receptor (β2AR), in vitro GRK phosphorylation of light-activated rhodopsin, and basal catalytic activity measured by tubulin phosphorylation and autophosphorylation. A number of double mutations within helices 3, 9, and 10 reduced phosphorylation of the β2AR and rhodopsin by 50-90% relative to WT GRK, as well as autophosphorylation and tubulin phosphorylation. Based on these results, helix 9 peptide mimetics were designed, and several were found to inhibit rhodopsin phosphorylation by GRK5 with an IC50 of ~ 30 μM. In summary our studies have uncovered previously unrecognized functionally important sites in the RH domain of GRK5 and 6, and identified a peptide inhibitor with potential for specific blockade of GRK-mediated phosphorylation of receptors.The American Society for Pharmacology and Experimental Therapeutics ER -