Visual G Protein-Coupled Receptor Kinases

Discovered in the 1970s, cloned in the 1990s, and extensively studied both biochemically and genetically over the past four decades, G protein-coupled receptor kinase 1 (GRK1), and a close homolog GRK7, are indispensable for timely phototransduction recovery and dark adaptation of retinal rod and cone photoreceptors. By phosphorylating activated visual pigments, these GRKs enable the binding of visual arrestins to photoexcited pigments to stop phototransduction at the receptor level. Mutations in the GRK1 gene cause a form of stationary night blindness in humans called Oguchi disease, with peculiar physiological and anatomical symptoms. Whereas the importance of these visual GRKs is well established, many questions remain unanswered with regard to expression, posttranslational modifications, substrate specificity, enzymatic actions, intracellular targeting, and regulation by other proteins. This chapter summarizes the current state of knowledge, discusses the relationship between GRK1 and GRK7 in the context of Oguchi disease, and pinpoints fruitful future directions for advancement of the vision research field.