The opsins |
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Authors: | Email author" target="_blank">Akihisa?TerakitaEmail author |
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Institution: | (1) 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 |
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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. |
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