title: Constitutive activation of phototransduction by K296E opsin is not a cause of photoreceptor degeneration.
abstract: The missense mutation Lys-296-->Glu (K296E) in the rhodopsin gene produces an opsin with no chromophore binding site and therefore is not activated by light. Nevertheless, the mutant opsin constitutively activates transducin in vitro and causes photoreceptor degeneration in vivo, possibly by continuously activating the phototransduction cascade, analogous to constant exposure to environmental light. We studied the K296E mutation in eight lines of transgenic mice. Each line developed photoreceptor degeneration with the rate of degeneration increasing monotonically as the ratio of mutant:wild-type opsin mRNA increased. At no time in the course of degeneration was there endogenous light adaptation in the retina as measured by the electroretinogram. The mutant opsin was found to be invariably phosphorylated and stably bound to arrestin. Light-independent activation of transducin was demonstrated only after the removal of arrestin and dephosphorylation of K296E opsin. Thus, K296E opsin in vivo does not activate the phototransduction cascade because it is shut off by photoreceptor inactivation mechanisms. Our data show that the K296E mutation does not cause photoreceptor degeneration by continuous activation of phototransduction.
authors.affiliation: Berman-Gund Laboratory for the Study of Retinal Degenerations, Harvard Medical School, Massachusetts Eye and Ear Infirmary, Boston 02114, USA.
authors.forename: T
authors.initials: T
authors.lastname: Li
authors.forename: W K
authors.initials: WK
authors.lastname: Franson
authors.forename: J W
authors.initials: JW
authors.lastname: Gordon
authors.forename: E L
authors.initials: EL
authors.lastname: Berson
authors.forename: T P
authors.initials: TP
authors.lastname: Dryja
mesh_terms: D000818:Animals; D000941:Antigens / Q000378:metabolism; D019393:Arrestin; D001483:Base Sequence; D003624:Darkness; D004596:Electroretinography; D004789:Enzyme Activation; D005136:Eye Proteins / Q000378:metabolism; D007150:Immunohistochemistry; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D009154:Mutation; D010766:Phosphorylation; D010786:Photoreceptor Cells / Q000473:pathology*; D011485:Protein Binding; D012174:Retinitis Pigmentosa / Q000209:etiology / Q000235:genetics / Q000503:physiopathology*; D012374:Rod Cell Outer Segment / Q000378:metabolism*; D017299:Rod Opsins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D015293:Transducin / Q000378:metabolism
chemical_list: D000941:Antigens; D019393:Arrestin; D005136:Eye Proteins; D017299:Rod Opsins; D015293:Transducin