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Model of the Oxygen Evolving Complex Which Is Highly Predisposed to O-O Bond Formation
Yulia Pushkar1, Katherine M Davis2, Mark C Palenik3
1Department of Physics and Astronomy , Purdue University , West Lafayette , Indiana 47907 , United States.
The Journal of Physical Chemistry Letters
|June 5, 2018
Summary
Understanding oxygen evolution in photosynthesis is key. This study reveals a novel S3 state model for the manganese-calcium cluster in photosystem II, clarifying the O-O bond formation timing during water oxidation.
Area of Science:
- Biochemistry
- Photosynthesis research
- Bioinorganic chemistry
Background:
- Light-driven water oxidation by photosystem II (PSII) is crucial for life.
- The Mn4Ca cluster in PSII cycles through redox states S0-S4 to produce oxygen.
- The precise timing of O-O bond formation in the Kok cycle is currently unknown.
Purpose of the Study:
- To elucidate the atomistic details of the S3 and S4 redox states in the Kok cycle.
- To determine the mechanism and timing of O-O bond formation during water oxidation.
- To explain the kinetic behavior of oxygen evolution and potential evolutionary adaptations.
Main Methods:
- Integration of recent crystallographic data.
- Application of spectroscopic techniques.
- Density Functional Theory (DFT) calculations.
Main Results:
- An atomistic model for the S3 state is proposed, featuring a low barrier for O-O bond formation before the final oxidation step.
- The S4 state offers no significant advantages for spin alignment or O-O bond formation energy.
- A high-energy peroxide isoform of the S3 state is suggested to be preferentially oxidized by Tyrz(ox).
Conclusions:
- The proposed S3 state mechanism explains the observed kinetics of oxygen evolution.
- This mechanism may represent an evolutionary adaptation to prevent the release of harmful peroxides.
- The findings provide a refined understanding of the final steps in photosynthetic water oxidation.
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