title: Visual pigment: G-protein-coupled receptor for light signals.
abstract: The visual pigment present in photoreceptor cells is a prototypical G-protein-coupled receptor (GPCR) that receives a light signal from the outer environment using a light-absorbing chromophore, 11-cis-retinal. Through cis-trans isomerization of the chromophore, light energy is transduced into chemical free energy, which is in turn utilized for conformational changes in the protein to activate the retinal G-protein. In combination with site-directed mutagenesis, various spectroscopic and biochemical studies identified functional residues responsible for chromophore binding, color regulation, intramolecular signal transduction and G-protein coupling. Extensive studies reveal that these residues are localized into specific domains of visual pigments, suggesting a highly manipulated molecular architecture in visual pigments. In addition to the recent findings on dysfunctional mutations in patients with retinitis pigmentosa or congenital night blindness, the mechanism of intramolecular signal transduction in visual pigments and their evolutionary relationship are discussed.
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Japan. shichida@photo2.biophys.kyoto-u.ac.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Shichida
authors.forename: H
authors.initials: H
authors.lastname: Imai
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003118:Color Perception / Q000502:physiology*; D019143:Evolution, Molecular; D019204:GTP-Binding Proteins / Q000502:physiology; D006801:Humans; D008027:Light; D008969:Molecular Sequence Data; D010786:Photoreceptor Cells / Q000502:physiology; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000502:physiology; D012168:Retinal Pigments / Q000737:chemistry / Q000502:physiology; D015398:Signal Transduction
chemical_list: D011956:Receptors, Cell Surface; D012168:Retinal Pigments; D019204:GTP-Binding Proteins