| G protein-coupled receptor kinase 7 | |
| Hgncid: | 17031 |
| Symbol: | GRK7 |
| Altsymbols: | GPRK7 |
| Entrezgene: | 131890 |
| Omim: | 606987 |
| Refseq: | NM_139209 |
| Uniprot: | Q8WTQ7 |
| Ecnumber: | 2.7.11.14 |
| Chromosome: | 3 |
| Arm: | q |
| Band: | 24 |
G-protein-coupled receptor kinase 7 (GRK7, cone opsin kinase, iodopsin kinase) is a serine/threonine-specific protein kinase involved in phototransduction.[1] [2] [3] This enzyme catalyses the phosphorylation of cone (color) photopsins in retinal cones during high acuity color vision primarily in the fovea.
GRK7 is a member of the family of G protein-coupled receptor kinases, and is officially named G protein-coupled receptor kinase 7. GRK7 is found primarily in mammalian retinal cone cells, where it phosphorylates light-activated photopsins, members of the family of G protein-coupled receptors that recognize light of various wavelengths (red, green, blue). Phosphorylated, light-activated photopsin binds to the cone arrestin protein arrestin-4 to terminate the light-activated signaling cascade. The related GRK1, also known as rhodopsin kinase, serves a similar function in retinal rod cells subserving dim light black-and-white peripheral vision outside the fovea.[4] [5] The post-translational modification of GRK7 by geranylgeranylation and α-carboxyl methylation is important for regulating the ability of the enzyme to recognize color opsins in cone outer segment disk membranes.[2]
Arrestin-1 bound to rhodopsin in retinal rods prevents rhodopsin activation of the transducin protein to turn off photo-transduction completely.[6] While cone visual transduction is much less well characterized, it is expected that arrestin-4 bound to GRK7-phosphorylated color photopsin prevents opsin activation of the transducin protein to turn off photo-transduction completely.