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).[5] Phosphorylated, light-activated photopsin binds to the cone arrestin protein arrestin-4 to terminate the light-activated signaling cascade.[5] 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.[6][7] 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.[4]
Arrestin-1 bound to rhodopsin in retinal rods prevents rhodopsin activation of the transducin protein to turn off photo-transduction completely.[8] 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.
↑"Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
↑Weiss ER, Raman D, Shirakawa S, Ducceschi MH, Bertram PT, Wong F, Kraft TW, Osawa S (1998). "The cloning of GRK7, a candidate cone opsin kinase, from cone- and rod-dominant mammalian retinas". Mol Vis. 4: 27. PMID9852166.
12Chen CK, Zhang K, Church-Kopish J, Huang W, Zhang H, Chen YJ, Frederick JM, Baehr W (December 2001). "Characterization of human GRK7 as a potential cone opsin kinase". Molecular Vision. 7: 305–13. PMID11754336.
