A novel form of rhodopsin kinase from chicken retina and pineal gland.

The G protein-coupled receptor kinases (GRKs) are important enzymes in the desensitization of activated G protein-coupled receptors (GPCR). Seven members of the GRK family have been identified to date. Among these enzymes, GRK1 is involved in phototransduction and is the most specialized kinase of the family. GRK1 phosphorylates photoactivated rhodopsin (Rho*), initiating steps in its deactivation. In this study, we found that chicken retina and pineal gland express a novel form of GRK that has sequence features characteristic of GRK1. However, unlike bovine GRK1 which is farnesylated, chicken GRK1 contains a consensus sequence for geranylgeranylation. Peptides corresponding to the C-terminal sequence of chicken GRK1 are geranylgeranylated by a cytosolic extract of chicken liver. Based on results of molecular cloning and immunolocalization, it appears that both rod and cone photoreceptors express this novel GRK1. These data indicate a larger sequence diversity of photoreceptor GRKs than anticipated previously.