Elucidation of the mechanism of water-splitting in photosystem II

2017 Fiscal Year Final Research Report

• Project/Area Number: 24000018
• Research Category: Grant-in-Aid for Specially Promoted Research
• Allocation Type: Single-year Grants
• Review Section: Biological Sciences
• 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): NOGUCHI Takumi 名古屋大学, 大学院理学研究科, 教授 (60241246) ; YAMAGUCHI Kizashi 大阪大学, 産業科学研究所, 特任教授 (80029537) ; SHOJI Mitsuo 筑波大学, 計算科学研究センター, 助教 (00593550)
• Co-Investigator(Renkei-kenkyūsha): SUGA Michihiro 岡山大学, 異分野基礎科学研究所, 准教授 (60634920) ; AKITA Fusamichi 岡山大学, 異分野基礎科学研究所, 准教授 (50751418) ; MINO Hiroyuki 名古屋大学, 大学院理学研究科, 准教授 (70300902) ; KATO Yuki 名古屋大学, 大学院理学研究科, 准教授 (10376634)
• Research Collaborator: ISOBE Hiroshi 岡山大学, 異分野基礎科学研究所, 准教授 (00379281)
• Project Period (FY): 2012 – 2017
• Keywords: 光合成 / 水分解 / 膜タンパク質 / X線自由電子レーザー / 反応機構 / 結晶構造解析 / 理論計算 / 赤外分光法

Outline of Final Research Achievements

In order to elucidate the reaction mechanism of water-splitting performed by photosystem II (PSII) in photosynthesis, we used femtosecond X-ray free electron laser (XFEL) to analyze the radiation damage-free, high-resolution crystal structure of PSII, which revealed the Mn_4CaO_5-cluster structure in its native state. We further used XFEL to analyze the structure of one of the intermediate state, S_3-state, which identified the site of O=O bond formation. Based on these structures, theoretical calculations were performed, which identified possible reaction pathways for the water-splitting. Furthermore, spectroscopic analysis, especially Fourier-transformed infrared spectroscopic analysis, was performed, which elucidated the structural changes of amino acid residues surrounding the Mn_4CaO_5-cluster and identified hydrogen-bond pathways that may participate in the proton exit from the water-splitting reaction site.

Free Research Field

生物物理学