GRK1
Description
The GRK1 (G protein-coupled receptor kinase 1) is a protein-coding gene located on chromosome 13.
Rhodopsin kinase (EC 2.7.11.14, rod opsin kinase, G-protein-coupled receptor kinase 1, GPCR kinase 1, GRK1, opsin kinase, opsin kinase (phosphorylating), rhodopsin kinase (phosphorylating), RK, STK14) is a serine/threonine-specific protein kinase involved in phototransduction. This enzyme catalyzes the following chemical reaction: ATP + rhodopsin ⇌ ADP + phospho-rhodopsin Mutations in rhodopsin kinase are associated with a form of night blindness called Oguchi disease. Rhodopsin kinase is a member of the family of G protein-coupled receptor kinases, and is officially named G protein-coupled receptor kinase 1, or GRK1. Rhodopsin kinase is found primarily in mammalian retinal rod cells, where it phosphorylates light-activated rhodopsin, a member of the family of G protein-coupled receptors that recognizes light. Phosphorylated, light-activated rhodopsin binds to the protein arrestin to terminate the light-activated signaling cascade. The related GRK7, also known as cone opsin kinase, serves a similar function in retinal cone cells subserving high-acuity color vision in the fovea. The post-translational modification of GRK1 by farnesylation and α-carboxyl methylation is important for regulating the ability of the enzyme to recognize rhodopsin in rod outer segment disk membranes. Arrestin-1 bound to rhodopsin prevents rhodopsin activation of the transducin protein to turn off photo-transduction completely. Rhodopsin kinase is inhibited by the calcium-binding protein recoverin in a graded manner that maintains rhodopsin sensitivity to light despite large changes in ambient light conditions. That is, in retinas exposed to only dim light, calcium levels are high in retinal rod cells and recoverin is bound to and inhibits rhodopsin kinase, leaving rhodopsin exquisitely sensitive to photons to mediate low-light, low-acuity vision; in bright light, rod cell calcium levels are low so recoverin cannot bind or inhibit rhodopsin kinase, resulting in greater rhodopsin kinase/arrestin inhibition of rhodopsin signaling at baseline to preserve visual sensitivity.
GRK1 is a retina-specific kinase that plays a crucial role in terminating the light-activated signaling cascade in the eye. It achieves this by phosphorylating rhodopsin (RHO), a G protein-coupled receptor that initiates phototransduction. This phosphorylation process is essential for scotopic vision, allowing rapid adaptation to changes in illumination. Additionally, GRK1 may contribute to the maintenance of the outer nuclear layer in the retina.
GRK1 is also known as GPRK1, RHOK, RK.
