Photochemical nature of parietopsin

Kazumi Sakai, Yasushi Imamoto, Chih Ying Su, Hisao Tsukamoto, Takahiro Yamashita, Akihisa Terakita, King Wai Yau, Yoshinori Shichida

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Parietopsin is a nonvisual green light-sensitive opsin closely related to vertebrate visual opsins and was originally identified in lizard parietal eye photoreceptor cells. To obtain insight into the functional diversity of opsins, we investigated by UV-visible absorption spectroscopy the molecular properties of parietopsin and its mutants exogenously expressed in cultured cells and compared the properties to those of vertebrate and invertebrate visual opsins. Our mutational analysis revealed that the counterion in parietopsin is the glutamic acid (Glu) in the second extracellular loop, corresponding to Glu181 in bovine rhodopsin. This arrangement is characteristic of invertebrate rather than vertebrate visual opsins. The photosensitivity and the molar extinction coefficient of parietopsin were also lower than those of vertebrate visual opsins, features likewise characteristic of invertebrate visual opsins. On the other hand, irradiation of parietopsin yielded meta-I, meta-II, and meta-III intermediates after batho and lumi intermediates, similar to vertebrate visual opsins. The pH-dependent equilibrium profile between meta-I and meta-II intermediates was, however, similar to that between acid and alkaline metarhodopsins in invertebrate visual opsins. Thus, parietopsin behaves as an "evolutionary intermediate" between invertebrate and vertebrate visual opsins.

Original languageEnglish (US)
Pages (from-to)1933-1941
Number of pages9
Issue number9
StatePublished - Mar 6 2012

ASJC Scopus subject areas

  • Biochemistry


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