Chemical genetic engineering of G protein-coupled receptor kinase 2

G protein-coupled receptor kinases (GRKs) play a pivotal role in receptor regulation. Efforts to study the acute effects of GRKs in intact cells have been limited by a lack of specific inhibitors. In the present study we have developed an engineered version of GRK2 that is specifically and reversibly inhibited by the substituted nucleotide analog 1-naphthyl-PP1 (1Na-PP1), and we explored GRK2 function in regulated internalization of the mu-opioid receptor (muOR). A previously described method that conferred analog sensitivity on various kinases, by introducing a space-creating mutation in the conserved active site, failed when applied to GRK2 because the corresponding mutation (L271G) rendered the mutant kinase (GRK2-as1) catalytically inactive. A sequence homology-based approach was used to design second-site suppressor mutations. A C221V second-site mutation produced a mutant kinase (GRK2-as5) with full functional activity and analog sensitivity as compared with wild-type GRK2 in vitro and in intact cells. The role of GRK2-as5 activity in the membrane trafficking of the muOR was also characterized. Morphine-induced internalization was completely blocked when GRK2-as5 activity was inhibited before morphine application. However, inhibition of GRK2-as5 during recycling and reinternalization of the muOR did not attenuate these processes. These results suggest there is a difference in the GRK requirement for initial ligand-induced internalization of a G protein-coupled receptor compared with subsequent rounds of reinternalization.