RGS domain‐mediated dimerization regulates GRK5 plasma membrane localization and function

Abstract

G protein‐coupled receptor (GPCR) kinases (GRKs) phosphorylate activated GPCRs at the plasma membrane (PM) to both terminate further activation of G proteins and promote G protein‐independent signaling. Our goal is to elucidate the mechanisms of PM targeting of GRKs. Despite high sequence similarity, GRK5 and GRK6 constitutively localize at the PM whereas expressed GRK4 is predominantly cytoplasmic. GRK5/GRK4 chimeras and point mutations in GRK5 identified a short sequence within the Regulator of G protein Signaling (RGS) domain in GRK5 that is critical for GRK5 PM localization. Interestingly, this region of the RGS domain of GRK5 coincided with a region of GRK6 shown to form a dimeric interface in the published GRK6 crystal structure. Using co‐immunoprecipitation and Bimolecular Fluorescence Complementation assays, results were consistent with GRK5, but not the RGS domain mutant, GRK5‐M165E/F166E, existing as homodimers in cells. In addition, we showed that GRK5‐ M165E/F166E is deficient in inhibiting PAR‐1‐induced calcium release and in promoting neurite extension. The results in this study suggest a novel model in which GRK5 dimerization is important for its plasma membrane localization and function. Supported by NIH R01 GM56444.