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Oxygen-evolving photosystem II structures during S1-S2-S3 transitions
Hongjie Li1, Yoshiki Nakajima1, Eriko Nango2,3
1Research Institute for Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan.
Researchers used ultrafast X-ray crystallography to observe structural changes in Photosystem II (PSII) during water oxidation. They identified a water molecule
Area of Science:
- Biochemistry
- Photosynthesis
- Structural Biology
Background:
- Photosystem II (PSII) drives water oxidation via a four-step S-state cycle at the Mn4CaO5 cluster.
- Previous studies examined S-state transitions on microsecond timescales.
Purpose of the Study:
- To reveal the structural dynamics of PSII from nanoseconds to milliseconds after illumination.
- To understand the mechanism of O-O bond formation during water oxidation.
Main Methods:
- Pump-probe serial femtosecond crystallography.
- Illumination with one flash (1F) and two flashes (2F).
Main Results:
- Observed nanosecond timescale structural changes in YZ, surrounding residues, and water molecules.
- Identified a water molecule binding to the Ca2+ ion near D1-E189 on a sub-microsecond timescale after 2F illumination.
- This water molecule's disappearance correlated with O6 formation, suggesting it is the source of O6.
Conclusions:
- Provided crucial insights into PSII structural dynamics during S-state transitions.
- Elucidated the role of specific water molecules and channels in electron transfer, proton release, and substrate water delivery.
- Offered a structural basis for O-O bond formation in photosynthesis.
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