title: Light-dependent activation of G proteins by two isoforms of chicken melanopsins.
abstract: In the chicken pineal gland, light stimuli trigger signaling pathways mediated by two different subtypes, Gt and G11. These G proteins may be activated by any of the three major pineal opsins, pinopsin, OPN4-1 and OPN4-2, but biochemical evidence for the coupling has been missing except for functional coupling between pinopsin and Gt. Here we investigated the relative expression levels and the functional difference among the three pineal opsins. In the chicken pineal gland, the pinopsin mRNA level was significantly more abundant than the others, of which the OPN4-2 mRNA level was higher than that of OPN4-1. In G protein activation assays, Gt was strongly activated by pinopsin in a light-dependent manner, being consistent with previous studies, and weakly activated by OPN4-2. Unexpectedly, illuminated OPN4-2 more efficiently activated G protein(s) that was endogenously expressed in HEK293T cells in culture. On the other hand, Gq, the closest analogue of G11, was activated only by OPN4-1 although the activity was relatively weak under these conditions. These results suggest that OPN4-1 and OPN4-2 couple with Gq and Gt, respectively. Two melanopsins, OPN4-1 and OPN4-2, appear to have acquired mutually different functions through the evolution.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, Japan. sdkojima@mail.ecc.u-tokyo.ac.jp sfukada@mail.ecc.u-tokyo.ac.jp.
authors.forename: Masaki
authors.initials: M
authors.lastname: Torii
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, Japan. sdkojima@mail.ecc.u-tokyo.ac.jp sfukada@mail.ecc.u-tokyo.ac.jp.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kojima
authors.affiliation: Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, Japan.
authors.forename: Akiyuki
authors.initials: A
authors.lastname: Nishimura
authors.affiliation: Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Itoh
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, Japan. sdkojima@mail.ecc.u-tokyo.ac.jp sfukada@mail.ecc.u-tokyo.ac.jp.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Fukada
mesh_terms: D000818:Animals; D002645:Chickens; D004789:Enzyme Activation / Q000528:radiation effects; D019204:GTP-Binding Proteins / Q000378:metabolism*; D008027:Light; D010870:Pineal Gland / Q000737:chemistry / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017299:Rod Opsins / Q000235:genetics / Q000378:metabolism*; D000099210:Melanopsin
chemical_list: D019204:GTP-Binding Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; D017299:Rod Opsins; D000099210:Melanopsin