Energetics of Proton-Coupled Electron Transfer in High-Valent Mn2(μ-O)2Systems:  Models for Water Oxidation by the Oxygen-Evolving Complex of Photosystem II

The biological water oxidation takes place in Photosystem II (PSII), a multi-subunit protein located in thylakoid membranes of higher plant chloroplasts and cyanobacteria. The catalytic site of PSII is a Mn4Ca cluster and is known as the oxygen evolving complex (OEC) of PSII. Two tyrosine residues D1-Tyr161 (YZ) and D2-Tyr160 (YD) are symmetrically placed in the two core subunits D1 and D2 and participate in proton coupled electron transfer reactions. YZ of PSII is near the OEC and mediates electron coupled proton transfer from Mn4Ca to the photooxidizable chlorophyll species P680+. YD does not directly interact with OEC, but is crucial for modulating the various S oxidation states of the OEC. In PSII from higher plants the environment of YD• radical has been extensively characterized only in spinach (Spinacia oleracea) Mn- depleted non functional PSII membranes. Here, we present a 2D-HYSCORE investigation in functional PSII of spinach to determine the electronic structure of YD• radical. The hyperfine couplings of the protons that interact with the YD• radical are determined and the relevant assignment is provided. A discussion on the similarities and differences between the present results and the results from studies performed in non functional PSII membranes from higher plants and PSII preparations from other organisms is given.

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New Linear High-Valent Tetranuclear Manganese-Oxo Cluster Relevant to the Oxygen-Evolving Complex of Photosystem II with Oxo, Hydroxo, and Aqua Coordinated to a Single Mn(IV)

Inorganic Chemistry ◽

10.1021/ic051462m ◽

2005 ◽

Vol 44 (25) ◽

pp. 9567-9573 ◽

Cited By ~ 40

Author(s):

Chen ◽

Marie-Noëlle Collomb ◽

Carole Duboc ◽

Geneviève Blondin ◽

Eric Rivière ◽

...

Keyword(s):

Photosystem Ii ◽

Oxygen Evolving Complex ◽

High Valent ◽

Oxygen Evolving

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Simulation of the isotropic EXAFS spectra for the S2 and S3 structures of the oxygen evolving complex in photosystem II

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1422058112 ◽

2015 ◽

Vol 112 (13) ◽

pp. 3979-3984 ◽

Cited By ~ 26

Author(s):

Xichen Li ◽

Per E. M. Siegbahn ◽

Ulf Ryde

Keyword(s):

Photosystem Ii ◽

Water Oxidation ◽

Density Functional ◽

Structural Changes ◽

Complete Agreement ◽

Oxygen Evolving Complex ◽

Chemical Modeling ◽

Oxygen Evolving ◽

High Degree ◽

Exafs Spectra

Most of the main features of water oxidation in photosystem II are now well understood, including the mechanism for O–O bond formation. For the intermediate S2 and S3 structures there is also nearly complete agreement between quantum chemical modeling and experiments. Given the present high degree of consensus for these structures, it is of high interest to go back to previous suggestions concerning what happens in the S2–S3 transition. Analyses of extended X-ray adsorption fine structure (EXAFS) experiments have indicated relatively large structural changes in this transition, with changes of distances sometimes larger than 0.3 Å and a change of topology. In contrast, our previous density functional theory (DFT)(B3LYP) calculations on a cluster model showed very small changes, less than 0.1 Å. It is here found that the DFT structures are also consistent with the EXAFS spectra for the S2 and S3 states within normal errors of DFT. The analysis suggests that there are severe problems in interpreting EXAFS spectra for these complicated systems.

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