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Structural changes in the S3 state of the oxygen evolving complex in photosystem II.

ABSTRACT: The S3 state of the Mn4 CaO5 -cluster in photosystem II was investigated by DFT calculations and compared with EXAFS data. Considering previously proposed mechanism; a water molecule is inserted into an open coordination site of Mn upon S2 to S3 transition that becomes a substrate water, we examined if the water insertion is essential for the S3 formation, or if one cannot eliminate other possible routes that do not require a water insertion at the S3 stage. The novel S3 state structure consisting of only short 2.7-2.8 Å Mn-Mn distances was discussed.

SUBMITTER: Hatakeyama M

PROVIDER: S-EPMC6013076 | biostudies-literature | 2016 May

REPOSITORIES: biostudies-literature

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Structural changes in the S3 state of the oxygen evolving complex in photosystem II.

Hatakeyama Makoto M Ogata Koji K Fujii Katsushi K Yachandra Vittal K VK Yano Junko J Nakamura Shinichiro S

Chemical physics letters 20160319

The S3 state of the Mn4 CaO5 -cluster in photosystem II was investigated by DFT calculations and compared with EXAFS data. Considering previously proposed mechanism; a water molecule is inserted into an open coordination site of Mn upon S2 to S3 transition that becomes a substrate water, we examined if the water insertion is essential for the S3 formation, or if one cannot eliminate other possible routes that do not require a wate ...[more]

PMID: 29937550

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Project description:The oxygen-evolving complex of Photosystem II in plants and cyanobacteria catalyzes the oxidation of two water molecules to one molecule of dioxygen. A tetranuclear Mn complex is believed to cycle through five intermediate states (S0-S4) to couple the four-electron oxidation of water with the one-electron photochemistry occurring at the Photosystem II reaction center. We have used X-ray absorption spectroscopy to study the local structure of the Mn complex and have proposed a model for it, based on studies of the Mn K-edges and the extended X-ray absorption fine structure of the S1 and S2 states. The proposed model consists of two di-?-oxo-bridged binuclear Mn units with Mn-Mn distances of ~2.7 Å that are linked to each other by a mono-?-oxo bridge with a Mn-Mn separation of ~3.3 Å. The Mn-Mn distances are invariant in the native S1 and S2 states. This report describes the application of X-ray absorption spectroscopy to S3 samples created under physiological conditions with saturating flash illumination. Significant changes are observed in the Mn-Mn distances in the S3 state compared to the S1 and the S2 states. The two 2.7 Å Mn-Mn distances that characterize the di-?-oxo centers in the S1 and S2 states are lengthened to ~2.8 and 3.0 Å in the S3 state, respectively. The 3.3 Å Mn-Mn and Mn-Ca distances also increase by 0.04-0.2 Å. These changes in Mn-Mn distances are interpreted as consequences of the onset of substrate/water oxidation in the S3 state. Mn-centered oxidation is evident during the S0?S1 and S1?S2 transitions. We propose that the changes in Mn-Mn distances during the S2?S3 transition are the result of ligand or water oxidation, leading to the formation of an oxyl radical intermediate formed at a bridging or terminal position. The reaction of the oxyl radical with OH(-), H2O, or an oxo group during the subsequent S state conversion is proposed to lead to the formation of the O-O bond. Models that can account for changes in the Mn-Mn distances in the S3 state and the implications for the mechanism of water oxidation are discussed.

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Structural changes in the S3 state of the oxygen evolving complex in photosystem II.

Publications

Structural changes in the S<sub>3</sub> state of the oxygen evolving complex in photosystem II.

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