title: The opsins.
abstract: The photosensitive molecule rhodopsin and its relatives consist of a protein moiety - an opsin - and a non-protein moiety - the chromophore retinal. Opsins, which are G-protein-coupled receptors (GPCRs), are found in animals, and more than a thousand have been identified so far. Detailed molecular phylogenetic analyses show that the opsin family is divided into seven subfamilies, which correspond well to functional classifications within the family: the vertebrate visual (transducin-coupled) and non-visual opsin subfamily, the encephalopsin/tmt-opsin subfamily, the Gq-coupled opsin/melanopsin subfamily, the Go-coupled opsin subfamily, the neuropsin subfamily, the peropsin subfamily and the retinal photoisomerase subfamily. The subfamilies diversified before the deuterostomes (including vertebrates) split from the protostomes (most invertebrates), suggesting that a common animal ancestor had multiple opsin genes. Opsins have a seven-transmembrane structure similar to that of other GPCRs, but are distinguished by a lysine residue that is a retinal-binding site in the seventh helix. Accumulated evidence suggests that most opsins act as pigments that activate G proteins in a light-dependent manner in both visual and non-visual systems, whereas a few serve as retinal photoisomerases, generating the chromophore used by other opsins, and some opsins have unknown functions.
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University and Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency, Kyoto 606-8502, Japan. terakita@photo2.biophys.kyoto-u.ac.jp
authors.forename: Akihisa
authors.initials: A
authors.lastname: Terakita
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D017124:Conserved Sequence; D019143:Evolution, Molecular; D006801:Humans; D008958:Models, Molecular; D005810:Multigene Family / Q000235:genetics / Q000502:physiology*; D010802:Phylogeny; D011487:Protein Conformation; D017299:Rod Opsins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*
chemical_list: D017299:Rod Opsins