2022 Fiscal Year Final Research Report

Structural analyses of reaction states of ion-pumping rhodopsin

Research Project

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Project/Area Number	19K06582
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Multi-year Fund
Section	一般
Review Section	Basic Section 43040:Biophysics-related
Research Institution	Nagoya University
Principal Investigator	Kouyama Tsutomu 名古屋大学, 理学研究科, 名誉教授 (30170210)
Co-Investigator(Kenkyū-buntansha)	井原邦夫名古屋大学, 遺伝子実験施設, 准教授 (90223297)
Project Period (FY)	2019-04-01 – 2023-03-31
Keywords	レチナール蛋白質 / 光駆動プロトンポンプ / 光駆動塩素イオンポンプ
Outline of Final Research Achievements	In bacteriorhodopsin (bR), the proton pumping cycle is initiated by the photo-isomerization of the retinal chromophore with the 13-trans configuration into the 13-cis configuration, and thermal re-isomerization into the initial trans configuration occurs in the final step of the reaction cycle. We have shown that the O intermediate formed during the photo cycle has two substates (O1 and O2) with different spectral characteristics, and thermally activated isomerization of retinal into the all-trans configurotion occurs at the O1→O2 transition. We also observed that the blue all-trans isomer at acidic pH has similar spectroscopic properties to the O2 intermediate, and discussed the possibility that that the mechanism of the retinal re-isomerization taking place in the late stage of the proton pumping cycle is analogous to that of thermal isomerization during dark adaptation in bR, which involves red shifted intermediates (isomers of blue membrane).
Free Research Field	生物物理学
Academic Significance and Societal Importance of the Research Achievements	バクテリオロドプシン（BR)の発見以来、たくさんの微生物型ロドプシンが古細菌、真正細菌、真核生物に見出されており、それらのいくつかはニューロン活動を光制御するのに利用されている。新しく発見された微生物ロドプシンの機能・構造が精力的に調べられているが、多くの場合、微生物ロドプシンの反応スキームはBRの従来の反応スキーム（＝レチナール再異性化の記述が曖昧）を参考にして組み上げられている。本研究ではO中間体には2種類のサブ状態（O1とO2）が存在し、O1→O2 転移でレチナールの再異性化が起こることが示された。我々が提唱した反応スキームは、より強力な光遺伝学的ツールを設計するのに役立つであろう。