Crystallographic study of water-spilitting reaction in photosystem II

2019 Fiscal Year Final Research Report

• Project/Area Number: 16KT0058
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Multi-year Fund
• Section: 特設分野
• Research Field: Transition State Control
• Research Institution: Okayama University
• Principal Investigator: Umena Yasufumi 岡山大学, 異分野基礎科学研究所, 特別契約職員(准教授) (10468267)
• Project Period (FY): 2016-07-19 – 2020-03-31
• Keywords: 光合成 / 結晶構造解析 / マンガン金属錯体 / 放射光X線 / 異常分散効果 / 反応中間体 / 時間分割構造解析

Outline of Final Research Achievements

Oxygen-evolving Photosystem II (PSII) protein in photosynthetic organisms has a Mn4CaO5 cluster as the reaction center of catalyzing a water-splitting reaction. In this study, the oxidation state in each of four Mn atoms in the cluster was investigated as well as the crystal structure of PSII in the four intermediate states of the reaction. To understand the detailed process of the water-splitting reaction in PSII, we developed a novel crystallographic analysis method using the wavelength of the absorption inflection point of a target metal atom. We prepared a lot of tinny PSII crystal, excited by pulse-laser, and then cryo-fixed. Both redox properties of each Mn atom in the cluster and crystal structure of PSII were simultaneously analyzed. As a result, we observed the redox changes in each Mn atom in the process of water-splitting reaction. Simultaneously with this redox analysis, we also captured the movements of water and proteins in PSII in the process of PSII.

Free Research Field

構造生物化学

Academic Significance and Societal Importance of the Research Achievements

本研究は、光合成の光と水によるエネルギー変換の仕組みを理解するため、光化学系II蛋白質(photosystem II; PSII)の触媒中心の４つMn金属原子と蛋白質構造の構造化学的な研究を行った。まず、Mnの電子状態と蛋白質の動きを同時に分析する結晶学的手法を開発した。この手法により、PSIIが水を分解する反応過程におけるMnとPSIIの原子レベルの変化を捉えることができた。もし光合成反応を化学的に理解できれば、太陽電池のような電力ではなく、水からエネルギー源を作り出す人工光合成の手がかりが期待される。