Photochemical Nature of Parietopsin

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• 作者：Kazumi Sakai ; Yasushi Imamoto ; Chih-Ying Su ; Hisao Tsukamoto ; Takahiro Yamashita ; Akihisa Terakita ; King-Wai Yau ; Yoshinori Shichida
• 刊名：Biochemistry
• 出版年：2012
• 出版时间：March 6, 2012
• 年：2012
• 卷：51
• 期：9
• 页码：1933-1941
• 全文大小：439K
• 年卷期：v.51,no.9(March 6, 2012)
• ISSN：1520-4995

文摘

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鈥搗isible 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 鈥渆volutionary intermediate鈥?between invertebrate and vertebrate visual opsins.