title: Light-dependent phosphorylation of the carboxy tail of mouse melanopsin.
abstract: Melanopsin-based phototransduction is involved in non-image forming light responses including circadian entrainment, pupil constriction, suppression of pineal melatonin synthesis, and direct photic regulation of sleep in vertebrates. Given that the functions of melanopsin involve the measurement and summation of total environmental luminance, there would appear to be no need for the rapid deactivation typical of other G-protein coupled receptors. In this study, however, we demonstrate that heterologously expressed mouse melanopsin is phosphorylated in a light-dependent manner, and that this phosphorylation is involved in regulating the rate of G-protein activation and the lifetime of melanopsin's active state. Furthermore, we provide evidence for light-dependent phosphorylation of melanopsin in the mouse retina using an in situ proximity ligation assay. Finally, we demonstrate that melanopsin preferentially interacts with the GRK2/3 family of G-protein coupled receptor kinases through co-immunoprecipitation assays. Based on the complement of G-protein receptor kinases present in the melanopsin-expressing retinal ganglion cells, GRK2 emerges as the best candidate for melanopsin's cognate GRK.
authors.affiliation: Department of Biological Sciences, University of Maryland, Baltimore County, Baltimore, MD 21250, USA.
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Blasic
authors.forename: R
authors.initials: R
authors.lastname: Lane Brown
authors.forename: Phyllis R
authors.initials: PR
authors.lastname: Robinson
mesh_terms: D000818:Animals; D020013:Calcium Signaling; D054769:G-Protein-Coupled Receptor Kinase 2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D054770:G-Protein-Coupled Receptor Kinase 3 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D066298:In Vitro Techniques; D008027:Light; D051379:Mice; D008810:Mice, Inbred C57BL; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D034622:RNA Interference; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects; D012160:Retina / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects; D012165:Retinal Ganglion Cells / Q000378:metabolism; D017299:Rod Opsins / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects*; D014785:Vision, Ocular; D000099210:Melanopsin
chemical_list: D054769:G-Protein-Coupled Receptor Kinase 2; D054770:G-Protein-Coupled Receptor Kinase 3; D011994:Recombinant Proteins; D017299:Rod Opsins; D000099210:Melanopsin; C496568:GRK2 protein, mouse; C517850:GRK3 protein, mouse