| Budget Amount *help |
¥24,570,000 (Direct Cost: ¥18,900,000、Indirect Cost: ¥5,670,000)
Fiscal Year 2018: ¥4,680,000 (Direct Cost: ¥3,600,000、Indirect Cost: ¥1,080,000)
Fiscal Year 2017: ¥5,850,000 (Direct Cost: ¥4,500,000、Indirect Cost: ¥1,350,000)
Fiscal Year 2016: ¥14,040,000 (Direct Cost: ¥10,800,000、Indirect Cost: ¥3,240,000)
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| Outline of Final Research Achievements |
Photosystem II (PSII) catalyzes photo-oxidation of water into dioxygen through an S-state cycle of the oxygen evolving complex (OEC). The structure of PSII has been analyzed at resolutions higher than 2.0A by using X-ray as well as XFEL. The mechanism of O=O bond formation, however, remains obscure owing to the lack of intermediate-state structures determined at atomic resolution. We prepared PSII in the S3 state by providing two-flash illumination into micro-sized crystals at room temperature and determined the structure at 2.35A resolution by using an XFEL. An isomorphous difference Fourier map between the two-flash-illuminated and dark-adapted states revealed apparent structural changes. Among them, the insertion of a new oxygen atom O6 close to the putative substrate oxo-bridge O5 was observed. We proposed the mechanism of O=O bond formation between O5 and O6. The findings provide a structural basis for the mechanism of oxygen evolution.
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