Radiation damage free structure of photosystem II revealed by X-ray free electron laser.

2015 Fiscal Year Final Research Report

• Project/Area Number: 26840023
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Structural biochemistry
• Research Institution: Okayama University
• Principal Investigator: Suga Michi 岡山大学, 自然科学研究科, 助教 (60634920)
• Project Period (FY): 2014-04-01 – 2016-03-31
• Keywords: 光化学系II / 膜タンパク質 / 光合成 / 結晶構造解析 / X線自由電子レーザー / 無損傷

Outline of Final Research Achievements

The initial reaction of photosynthesis takes place in photosystem II (PSII), a 700 kDa membrane protein complex that catalyzes water-splitting reaction through an S-state cycle of the oxygen evolving complex (OEC). The structure of PSII has been solved by XRD at 1.9 A resolution, which revealed that the OEC is a Mn4CaO5 cluster. However, the manganese atoms in the OEC are easily reduced by X-ray irradiation.
Recently, it was demonstrated that radiation damage free structure can be obtainable using X-ray free electron lasers (XFEL). We determined a radiation damage free structure of PSII in the S1 state at a resolution of 1.95 A using XFEL pulses. Compared with the structure from XRD, the OEC in the XFEL structure has Mn-Mn distances that are shorter by 0.1-0.2A. Based on the XFEL structure, the valences of each manganese atom were assigned as Mn1(+3), Mn2(+4), Mn3(+4) and Mn4(+3) in the S1 state. These findings provide a structural basis for the mechanism of oxygen evolution.

Free Research Field

構造生物化学