2022 Fiscal Year Final Research Report

Elucidation of the water-splitting reaction mechanism by high-resolution, time-resolved structural analysis

Planned Research

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Project Area	Creation of novel light energy conversion system through elucidation of the molecular mechanism of photosynthesis and its artificial design in terms of time and space
Project/Area Number	17H06434
Research Category	Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
Allocation Type	Single-year Grants
Review Section	Complex systems
Research Institution	Okayama University
Principal Investigator	SHEN Jian-Ren 岡山大学, 異分野基礎科学研究所, 教授 (60261161)
Co-Investigator(Kenkyū-buntansha)	神谷信夫大阪公立大学, 人工光合成研究センター, 名誉教授 (60152865) 山口兆大阪大学, 産業科学研究所, 招へい教授 (80029537)
Project Period (FY)	2017-06-30 – 2022-03-31
Keywords	光合成 / 水分解反応 / 酸素発生反応 / 光エネルギー / 光化学系II / 光化学系I / 光捕集アンテナ / 理論計算
Outline of Final Research Achievements	The present study is performed in the purpose of elucidating the mechanisms of photosynthetic water-oxidation and light-energy absorption, transfer within photosystem (PS)-light harvesting protein (LHC) supercomplexes from various photosynthetic organisms. We analyzed the structures of multiple reaction intermediates of water-oxidation by a pump-probe approach using X-ray free electron laser, and found that an oxygen atom O6 is inserted into the vicinity of O5 within the Mn4CaO5 cluster, the catalyst for water-oxidation, at S3-state generated by 2 flash illumination. This enables formation of an oxygen molecule between O5 and O6. We also analyzed the structures of various PS-LHCs from various organisms, and revealed various light energy transfer pathways in these organisms as well as the changes of PS-LHC supercomplexes occurred during evolution, which provide important insights into the evolution of photosynthetic systems.
Free Research Field	生物物理学
Academic Significance and Societal Importance of the Research Achievements	光合成の酸素発生反応は、可視光を利用して水を常温・常圧で分解し、電子と水素イオンを取り出すもので、地球上天然状態で大規模に行われている唯一の反応で、この反応により光エネルギーは生物が利用可能な化学エネルギーに変換される。この反応の触媒や機構の解明は、学術的に重要な意味を持っているだけでなく、人工合成におけるクリーンエネルギーの獲得にも重要な指針を提供する。また、光合成における光エネルギーの吸収・伝達機構の解明は、異なる光環境に適応するための生物の生存戦略を明らかにするたけでなく、やはり人工光合成において、光エネルギーの高効率利用に重要なヒントを提供することが期待される。