Oxidation States and Structure of the Manganese Cluster in the S0 State of the Oxygen Evolving Complex
Johannes MessingerJohn H. RobbleeCarmen FernándezRoehl M. CincoH.G. VisserUwe BergmannPieter GlatzelStephen P. CramerKristy A. CampbellJohn M. PeloquinR. David BrittKenneth SauerVittal K. YachandraM. P. Klein
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Oxidizing agent
Plastoquinone
Oxidation state
Oxygen-evolving complex
Oxygen evolution
Plastoquinone
DCMU
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Photosystem II (PSII) represents the most vulnerable component of the photosynthetic machinery and its response in plants subjected to abiotic stress has been widely studied over many years. PSII is a thylakoid membrane-located multiprotein pigment complex that catalyses the light-induced electron transfer from water to plastoquinone with the concomitant production of oxygen. PSII is rich in intrinsic (PsbA and PsbD, namely D1 and D2, CP47 or PsbB and CP43 or PsbC) but also extrinsic proteins. The first ones are more largely conserved from cyanobacteria to higher plants while the extrinsic proteins are different among species. It has been found that extrinsic proteins involved in oxygen evolution change dramatically the PSII efficiency and PSII repair systems. However, little information is available on the effects of abiotic stress on their function and structure.
Plastoquinone
Photoinhibition
Oxygen evolution
Oxygen-evolving complex
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The photosynthetic oxygen-evolving photosystem II (PSII) is the only known biochemical system that is able to oxidize water molecules and thereby generates almost all oxygen in the Earth's atmosphere. The elucidation of the structural and mechanistic aspects of PSII keeps scientists all over the world engaged since several decades. In this Minireview, we outline the progress in understanding PSII based on the most recent crystal structure at 2.9 A resolution. A likely position of the chloride ion, which is known to be required for the fast turnover of water oxidation, could be determined in native PSII and is compared with work on bromide and iodide substituted PSII. Moreover, eleven new integral lipids could be assigned, emphasizing the importance of lipids for the perfect function of PSII. A third plastoquinone molecule (Q(C)) and a second quinone transfer channel are revealed, making it possible to consider different mechanisms for the exchange of plastoquinone/plastoquinol molecules. In addition, possible transport channels for water, dioxygen and protons are identified.
Plastoquinone
Oxygen-evolving complex
Oxygen evolution
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Plastoquinone
Cytochrome b6f complex
Oxygen evolution
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Plastoquinone
Oxygen evolution
Oxygen-evolving complex
Molecular oxygen
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Abstract Photosynthetic oxygen evolution is performed at the Mn cluster in photosystem II (PSII). The advent of this reaction on ancient Earth changed its environment by generating an oxygenic atmosphere. However, how oxygen evolution originated during the PSII evolution remains unknown. Here, we characterize the site-directed mutants at the carboxylate ligands to the Mn cluster in cyanobacterial PSII. A His residue replaced for D1-D170 is found to be post-translationally converted to the original Asp to recover oxygen evolution. Gln/Asn residues in the mutants at D1-E189/D1-D342 are also converted to Glu/Asp, suggesting that amino-acid conversion is a common phenomenon at the ligand sites of the Mn cluster. We hypothesize that post-translational generation of carboxylate ligands in ancestral PSII could have led to the formation of a primitive form of the Mn cluster capable of partial water oxidation, which could have played a crucial role in the evolutionary process of photosynthetic oxygen evolution.
Oxygen evolution
Carboxylate
Oxygen-evolving complex
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Abstract Photosystem II herbicides act by blocking electron transport at the secondary electron acceptor ‘Q B ’, thought to be a non‐covalently bound plastoquinone. Recent evidence suggests that these compounds work by displacing the plastoquinone from its site in the thylakoid. Since the herbicides cannot act as electron carriers, electron transport is then blocked. In this report a model is presented for the site of action of Photosystem II herbicides that encompasses biochemical, biophysical, and structure‐activity considerations. The essence of the model is that Photosystem II herbicides are non‐reducible analogues of plastoquinone or its semiquinone anion. As examples of the ways in which known herbicidal classes fit the model, the possible interactions of diuron, atrazine, the putative urea‐triazine hybrid MBAT (the a‐methylbenzyl analogue of atrazine), and dinoseb with the active site are discussed. This model provides a stereochemical basis for herbicidal activity and offers a qualitative approach for the design of novel Photosystem II herbicides.
Plastoquinone
P700
Cytochrome b6f complex
Triazine
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Oxygen evolution
Oxygen-evolving complex
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Plastoquinone
P700
Electron acceptor
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Plastoquinone
Oxygen-evolving complex
Bicarbonate
Electron acceptor
Oxygen evolution
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