Mechanism of photosynthetic water oxidation: combining biophysical studies of photosystem II with inorganic model chemistry

Vrettos, John S.; Limburg, Julian; Brudvig, Gary W.

doi:10.1016/s0005-2728(00)00214-0

Cited by 261 publications

(277 citation statements)

References 143 publications

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“…The QM/MM hybrid models of the OEC in PSII suggest that the two substrate water molecules can bind to Ca 2C and Mn(4) on the 'active face' of the OEC (Sproviero et al 2006a), consistent with the previously proposed mechanistic hypothesis (Pecoraro et al 1998;Vrettos et al 2001;McEvoy et al 2005b; figure 2). Two redox states of comparable energies are predicted: model (a) where the dangling manganese Mn (4) is pentacoordinated and the oxidation states are Mn 4 ( IV,IV,III,III ) (i.e.…”

Section: Structural Models Of the O 2 -Evolving Centresupporting

confidence: 84%

“…Considering that the S 1 /S 2 transition involves oxidation of a manganese centre, the observed acceleration of the exchange of W slow is also intriguing since it implies that the oxidation of a manganese centre must indirectly affect the exchange rate of a calcium-bound water molecule. While these observations are reproducible and unambiguous, it is not clear whether they can be rationalized by previously proposed mechanistic models (Pecoraro et al 1998;Vrettos et al 2001;Messinger 2004). The calculations reported in this paper address both of these observations through the analysis of structural models of the OEC in the S 1 and S 2 states (Sproviero et al 2006a(Sproviero et al ,b, 2007.…”

Section: Introductionmentioning

confidence: 82%

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QM/MM computational studies of substrate water binding to the oxygen-evolving centre of photosystem II

Sproviero

Shinopoulos

Gascón

et al. 2007

Phil. Trans. R. Soc. B

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This paper reports computational studies of substrate water binding to the oxygen-evolving centre (OEC) of photosystem II (PSII ), completely ligated by amino acid residues, water, hydroxide and chloride. The calculations are based on quantum mechanics/molecular mechanics hybrid models of the OEC of PSII, recently developed in conjunction with the X-ray crystal structure of PSII from the cyanobacterium Thermosynechococcus elongatus. The model OEC involves a cuboidal Mn 3 CaO 4 Mn metal cluster with three closely associated manganese ions linked to a single m 4 -oxo-ligated Mn ion, often called the 'dangling manganese'. Two water molecules bound to calcium and the dangling manganese are postulated to be substrate molecules, responsible for dioxygen formation. It is found that the energy barriers for the Mn(4)-bound water agree nicely with those of model complexes. However, the barriers for Ca-bound waters are substantially larger. Water binding is not simply correlated to the formal oxidation states of the metal centres but rather to their corresponding electrostatic potential atomic charges as modulated by charge-transfer interactions. The calculations of structural rearrangements during water exchange provide support for the experimental finding that the exchange rates with bulk 18 O-labelled water should be smaller for water molecules coordinated to calcium than for water molecules attached to the dangling manganese. The models also predict that the S 1 /S 2 transition should produce opposite effects on the two waterexchange rates.

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Section: Structural Models Of the O 2 -Evolving Centresupporting

confidence: 84%

Section: Introductionmentioning

confidence: 82%

QM/MM computational studies of substrate water binding to the oxygen-evolving centre of photosystem II

Sproviero

Shinopoulos

Gascón

et al. 2007

Phil. Trans. R. Soc. B

Self Cite

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“…This family of mechanisms can be viewed as an adaptation of the 2+2 mechanism mentioned above that has been refashioned to reflect the most recent OEC structural model [45][46][47][48][49]. The result is a mechanism where a high-valent manganese-oxo is formed on the lone dangler manganese.…”

Section: 23mentioning

confidence: 99%

Functional models for the oxygen-evolving complex of photosystem II

Cady

Crabtree

Brudvig

2008

Coordination Chemistry Reviews

387

255

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In the last ten years, a number of advances have been made in the study of the oxygen-evolving complex (OEC) of photosystem II (PSII). Along with this new understanding of the natural system has come rapid advance in chemical models of this system. The advance of PSII model chemistry is seen most strikingly in the area of functional models where the few known systems available when this topic was last reviewed has grown into two families of model systems. In concert with this work, numerous mechanistic proposals for photosynthetic water oxidation have been proposed. Here, we review the recent efforts in functional model chemistry of the oxygen-evolving complex of photosystem II.

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“…The probable function of Ca 2+ as a H 2 O binding site in the OEC is the centerpiece of contemporary models for the mechanism of water oxidation (Pecoraro et al 1998;Vrettos et al 2001b;McEvoy and Brudvig 2004). The major proposition in these mechanisms is that Ca 2+ , functioning as a Lewis acid, deprotonates H 2 O to form Ca 2+ -OH; the hydroxyl group, an excellent nucleophile, attacks a Mn 5+ = O group in S 4 to form the O-O bond that precedes reduction of the Mn cluster and release of O 2 .…”

Section: S 3 To S 0 Transitionmentioning

confidence: 99%

The PSII calcium site revisited

2007

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Oxidation of H 2 O by photosystem II is a unique redox reaction in that it requires Ca 2+ as well as Cl -as obligatory activators/cofactors of the reaction, which is catalyzed by Mn atoms. The properties of the binding site for Ca 2+ in this reaction resemble those of other Ca 2+ binding proteins, and recent X-ray structural data confirm that the metal is in fact ligated at least in part by amino acid side chain oxo anions. Removal of Ca 2+ blocks water oxidation chemistry at an early stage in the cycle of redox reactions that result in O-O bond formation, and the intimate involvement of Ca 2+ in this reaction that is implied by this result is confirmed by an ever-improving set of crystal structures of the cyanobacterial enzyme. Here, we revisit the photosystem II Ca 2+ site, in part to discuss the additional information that has appeared since our earlier review of this subject (van Gorkom HJ, Yocum CF In: Wydrzynski TJ, Satoh K (eds) Photosystem II: the light-driven water:plastoquinone oxidoreductase), and also to reexamine earlier data, which lead us to conclude that all S-state transitions require Ca 2+ .

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Mechanism of photosynthetic water oxidation: combining biophysical studies of photosystem II with inorganic model chemistry

Cited by 261 publications

References 143 publications

QM/MM computational studies of substrate water binding to the oxygen-evolving centre of photosystem II

QM/MM computational studies of substrate water binding to the oxygen-evolving centre of photosystem II

Functional models for the oxygen-evolving complex of photosystem II

The PSII calcium site revisited

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