The calcium and chloride requirements of the O2 evolving complex

Yocum, Charles F.

doi:10.1016/j.ccr.2007.08.010

Cited by 236 publications

(280 citation statements)

References 95 publications

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“…Computational studies of the mechanism of the OEC have suggested a Mn IV -oxyl site as the key reactive species in O-O bond formation (Fig. 1C) (11)(12)(13)(14)(15). Experimental support of such a species requires systems, like the synthetic complexes considered here, that can be studied without the interference of other paramagnetic species that are present in the OEC.…”

Section: Resultsmentioning

confidence: 90%

High-spin Mn–oxo complexes and their relevance to the oxygen-evolving complex within photosystem II

Gupta

Taguchi

Lassalle‐Kaiser

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

133

162

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The structural and electronic properties of a series of manganese complexes with terminal oxido ligands are described. The complexes span three different oxidation states at the manganese center (III-V), have similar molecular structures, and contain intramolecular hydrogen-bonding networks surrounding the Mn-oxo unit. Structural studies using X-ray absorption methods indicated that each complex is mononuclear and that oxidation occurs at the manganese centers, which is also supported by electron paramagnetic resonance (EPR) studies. This gives a high-spin Mn V -oxo complex and not a Mn IV -oxy radical as the most oxidized species. In addition, the EPR findings demonstrated that the Fermi contact term could experimentally substantiate the oxidation states at the manganese centers and the covalency in the metal-ligand bonding. Oxygen-17-labeled samples were used to determine spin density within the Mn-oxo unit, with the greatest delocalization occurring within the Mn V -oxo species (0.45 spins on the oxido ligand). The experimental results coupled with density functional theory studies show a large amount of covalency within the Mn-oxo bonds. Finally, these results are examined within the context of possible mechanisms associated with photosynthetic water oxidation; specifically, the possible identity of the proposed high valent Mn-oxo species that is postulated to form during turnover is discussed.metal-oxo complexes | water oxidation | inorganic chemistry | photosynthesis | oxygen-evolving complex P hotosynthetic water oxidation is an essential chemical reaction that is responsible for producing Earth's aerobic environment. Dioxygen production occurs at the active site of the enzyme photosystem II, referred to as the oxygen-evolving complex (OEC), which contains a unique Mn 4 CaO cluster (1, 2). Several features of the OEC are known, including an approximate arrangement of the metal ions within the cluster (Fig. 1A) (3, 4), its structural flexibility during turnover (5, 6), and its ability to store oxidizing equivalents via five photo-induced redox states (S i , i = 0-4 and known as the Kok cycle) (7). Substrate water molecules bind to the cluster and, upon oxidation, are coupled to produce dioxygen and 4 eq of protons. There is agreement that formation of the O-O bond occurs in the highest oxidized state of the Mn 4 CaO 5 cluster (S 4 ), after which the cluster reverts to the most reduced state, S 0 (1-6, 8-10). The transient S 4 state has eluded detection, making it difficult to experimentally probe the structural and physical requirements necessary to promote dioxygen production. Magnetic resonance and density functional theory (DFT) studies of the S 2 and S 3 states have been used to infer that the beginning and ending oxidation states of the Kok cycle are Mn 3 III Mn IV (S 0 ) and Mn 3 IV Mn V or Mn 3 IV Mn IV O • (S 4 ) (11-14). The location of the Mn V center within the cluster is not certain, yet one possibility is the dangling Mn A4 site, which is coordinated to anionic donors and is surrounded by a ne...

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Section: Resultsmentioning

confidence: 90%

High-spin Mn–oxo complexes and their relevance to the oxygen-evolving complex within photosystem II

Gupta

Taguchi

Lassalle‐Kaiser

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

133

162

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“…Extensive studies have been performed on the roles of Ca 2+ in the oxygen-evolving reaction, and perturbations of the S-state transition have been well documented upon replacement of Ca 2+ by Sr 2+ (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29). Substitution by Sr 2+ slows down S-state transition beyond S 2 and S 3 -states, leading to the formation of an S 2 -state with somewhat different properties in terms of its redox potential, stability, and the EPR multiline signal (17)(18)(19)(20)(22)(23)(24)(25)(26).…”

Section: Discussionmentioning

confidence: 99%

“…Substitution by Sr 2+ slows down S-state transition beyond S 2 and S 3 -states, leading to the formation of an S 2 -state with somewhat different properties in terms of its redox potential, stability, and the EPR multiline signal (17)(18)(19)(20)(22)(23)(24)(25)(26). However, because of the absence of detailed structural information, the exact role of Ca 2+ and the causes underlying the effects of substitution by Sr 2+ are not clear.…”

Section: Discussionmentioning

confidence: 99%

“…Removal of Ca from higher plant PSII blocked the S-state transition beyond S 2 -state, resulting in a complete loss of the oxygenevolving activity (14)(15)(16)(17)(18). Among various other cations, only Sr 2+ was shown to be able to partially replace the role of Ca 2+ , resulting in an OEC with approximately half of the activity compared with that having Ca 2+ -associated activity (15,(17)(18)(19)(20). Similar results were obtained with cyanobacteria, where Ca 2+ cannot be removed and replaced in isolated PSII so that it has to be replaced by Sr 2+ in culture medium (21,22).…”

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confidence: 99%

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Structure of Sr-substituted photosystem II at 2.1 Å resolution and its implications in the mechanism of water oxidation

Koua

Umena

Kawakami

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

147

180

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Oxygen-evolving complex of photosystem II (PSII) is a tetramanganese calcium penta-oxygenic cluster (Mn 4 CaO 5 ) catalyzing light-induced water oxidation through several intermediate states (S-states) by a mechanism that is not fully understood. To elucidate the roles of Ca 2+ in this cluster and the possible location of water substrates in this process, we crystallized Sr 2+ -substituted PSII from Thermosynechococcus vulcanus, analyzed its crystal structure at a resolution of 2.1 Å, and compared it with the 1.9 Å structure of native PSII. Our analysis showed that the position of Sr was moved toward the outside of the cubane structure of the Mn 4 CaO 5 -cluster relative to that of Ca 2+ , resulting in a general elongation of the bond distances between Sr and its surrounding atoms compared with the corresponding distances in the Ca-containing cluster. In particular, we identified an apparent elongation in the bond distance between Sr and one of the two terminal water ligands of Ca 2+ , W3, whereas that of the Sr-W4 distance was not much changed. This result may contribute to the decrease of oxygen evolution upon Sr 2+ -substitution, and suggests a weak binding and rather mobile nature of this particular water molecule (W3), which in turn implies the possible involvement of this water molecule as a substrate in the O-O bond formation. In addition, the PsbY subunit, which was absent in the 1.9 Å structure of native PSII, was found in the Sr-PSII structure.membrane protein | water-splitting | structural changes | cyanobacteria | artificial photosynthesis P hotosynthetic light-induced water-splitting produces electrons, protons, and molecular oxygen from water; the latter product maintains the oxygenic atmosphere indispensable for sustaining oxygenic life on the earth. This process takes place in photosystem II (PSII), a multisubunit membrane protein complex containing 20 subunits with an overall molecular mass of 350 kDa (1, 2). In PSII, light is absorbed by the reaction center chlorophyll a molecules (P680), which initiates a series of electron transfer reactions leading to the formation of the charge separated state P 680 + /Q A − (the first quinone acceptor of PSII). The oxidized reaction center chlorophyll is rapidly reduced by a redox active tyrosine (Y Z ), which is the Tyr161 residue of the D1 protein. Subsequently, the oxidized Y Z abstracts an electron from an oxygen-evolving complex (OEC), which is located close to Y Z . Upon abstraction of four electrons from OEC, two water molecules are split into protons and molecular oxygen. Thus, the structure of OEC cycles through five distinct states termed S i (where i = 0-4), with the S 0 -state being the most reduced one, and the S 4 -state a transit one. Among these S-states, the S 1 -state is dark stable, and the molecular oxygen is produced in the transition of S 3 -(S 4 )-S 0 (3).To understand the mechanism of photo-induced water-splitting, extensive studies have been carried out to reveal the structure of OEC (4-10). From these studies, it has been clear th...

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“…For example, in plants, the three extrinsic lumenal subunits (PsbO, PsbP, and PsbQ) are necessary to maintain high steady-state rates of oxygen evolution activity (17). One proposed role of the extrinsic polypeptides, PsbP and PsbQ, is in the retention of the OEC calcium and chloride ions (18). PsbO also plays a role in retention of calcium and chloride and accelerates the steady-state rate of oxygen evolution (reviewed in Ref.…”

Section: And References Therein)mentioning

confidence: 99%

An Intrinsically Disordered Photosystem II Subunit, PsbO, Provides a Structural Template and a Sensor of the Hydrogen-bonding Network in Photosynthetic Water Oxidation

Offenbacher

Polander

Barry

2013

Journal of Biological Chemistry

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Background:PsbO is an intrinsically disordered subunit of photosystem II. Results: Temperature-sensitive PsbO dynamics are identified by reaction-induced Fourier transform infrared spectroscopy and the removal and reconstitution of PsbO. Conclusion: PsbO serves as an organizational template and undergoes flash-induced hydrogen-bonding changes, coupled with the catalytic cycle of water oxidation. Significance: PsbO samples a rough conformational landscape when bound to its target, the photosystem II reaction center.

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The calcium and chloride requirements of the O2 evolving complex

Cited by 236 publications

References 95 publications

High-spin Mn–oxo complexes and their relevance to the oxygen-evolving complex within photosystem II

High-spin Mn–oxo complexes and their relevance to the oxygen-evolving complex within photosystem II

Structure of Sr-substituted photosystem II at 2.1 Å resolution and its implications in the mechanism of water oxidation

An Intrinsically Disordered Photosystem II Subunit, PsbO, Provides a Structural Template and a Sensor of the Hydrogen-bonding Network in Photosynthetic Water Oxidation

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