An estimation of the size of the water cluster present at the cleavage site of the water splitting enzyme

Burda, Květoslava; Bader, Klaus P.; Schmid, Georg

doi:10.1016/s0014-5793(01)02175-5

Cited by 22 publications

(14 citation statements)

References 18 publications

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“…This approach also avoids errors/ assumptions in the estimation of volume. Therefore, the reported data indicating the existence of non-exchangeable water clusters within PSII (40,41), which is not supported by our data, needs to be reassessed in a more careful manner.…”

Section: Resultscontrasting

confidence: 70%

Substrate Water Exchange in Photosystem II Depends on the Peripheral Proteins

Hillier¹,

Hendry²,

Burnap³

et al. 2001

Journal of Biological Chemistry

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The 18 O exchange rates for the substrate water bound in the S 3 state were determined in different photosystem II sample types using time-resolved mass spectrometry. The samples included thylakoid membranes, saltwashed Triton X-100-prepared membrane fragments, and purified core complexes from spinach and cyanobacteria. For each sample type, two kinetically distinct isotopic exchange rates could be resolved, indicating that the biphasic exchange behavior for the substrate water is inherent to the O 2 -evolving catalytic site in the S 3 state. However, the fast phase of exchange became somewhat slower (by a factor of ϳ2) in NaClwashed membrane fragments and core complexes from spinach in which the 16-and 23-kDa extrinsic proteins have been removed, compared with the corresponding rate for the intact samples. For CaCl 2 -washed membrane fragments in which the 33-kDa manganese stabilizing protein (MSP) has also been removed, the fast phase of exchange slowed down even further (by a factor of ϳ3). Interestingly, the slow phase of exchange was little affected in the samples from spinach. For core complexes prepared from Synechocystis PCC 6803 and Synechococcus elongatus, the fast and slow exchange rates were variously affected. Nevertheless, within the experimental error, nearly the same exchange rates were measured for thylakoid samples made from wild type and an MSP-lacking mutant of Synechocystis PCC 6803. This result could indicate that the MSP has a slightly different function in eukaryotic organisms compared with prokaryotic organisms. In all samples, however, the differences in the exchange rates are relatively small. Such small differences are unlikely to arise from major changes in the metal-ligand structure at the catalytic site. Rather, the observed differences may reflect subtle long range effects in which the exchange reaction coordinates become slightly altered. We discuss the results in terms of solvent penetration into photosystem II and the regional dielectric around the catalytic site.The oxidation of water during photosynthesis is catalyzed by the membrane-bound pigment protein complex photosystem II (PSII).1 In the net reaction, four electrons, four protons, and one molecule of O 2 are liberated from the splitting of two water molecules. A key insight into the reaction mechanism was the observation that the O 2 produced in brief, saturating light flashes follows a periodicity of four (1). The period four phenomenon is now universally interpreted in terms of the S-state model, in which the catalytic site cycles through five intermediary S n states (n ϭ 0 -4) (2). Beginning in S 0 and traversing to S 4 , each S n state is driven forward by a single quantum event at the PSII reaction center. Upon reaching the S 4 state (which may be equivalent to S 3 Y Z ⅐ ) O 2 is released, S 0 is regenerated, and the cycle begins anew. The catalytic site for water oxidation involves an inorganic metal cluster consisting of four manganese ions, one Ca 2ϩ ion, possibly one Cl Ϫ ion, and the redox-active Tyr-161 resid...

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Section: Resultscontrasting

confidence: 70%

Substrate Water Exchange in Photosystem II Depends on the Peripheral Proteins

Hillier¹,

Hendry²,

Burnap³

et al. 2001

Journal of Biological Chemistry

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“…At present, direct structural information is lacking and even the number of water molecules bound to the WOC is not known. Indirect lines of evidence for the existence of a cluster of 6-12 water molecules was gathered from EPR and mass spectrometry data (Hansson et al 1986;Bader et al 1993;Burda et al 2001). Measurements of the exchange kinetics in the different S i -states revealed that two substrate water molecules are bound in a different manner (Hillier and Wydrzynski 2000).…”

Section: Trapping Of Lightmentioning

confidence: 99%

Photosystem II: The machinery of photosynthetic water splitting

2008

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This review summarizes our current state of knowledge on the structural organization and functional pattern of photosynthetic water splitting in the multimeric Photosystem II (PS II) complex, which acts as a light-driven water: plastoquinone-oxidoreductase. The overall process comprises three types of reaction sequences: (1) photon absorption and excited singlet state trapping by charge separation leading to the ion radical pair [Formula: see text] formation, (2) oxidative water splitting into four protons and molecular dioxygen at the water oxidizing complex (WOC) with P680+* as driving force and tyrosine Y(Z) as intermediary redox carrier, and (3) reduction of plastoquinone to plastoquinol at the special Q(B) binding site with Q(A)-* acting as reductant. Based on recent progress in structure analysis and using new theoretical approaches the mechanism of reaction sequence (1) is discussed with special emphasis on the excited energy transfer pathways and the sequence of charge transfer steps: [Formula: see text] where (1)(RC-PC)* denotes the excited singlet state (1)P680* of the reaction centre pigment complex. The structure of the catalytic Mn(4)O(X)Ca cluster of the WOC and the four step reaction sequence leading to oxidative water splitting are described and problems arising for the electronic configuration, in particular for the nature of redox state S(3), are discussed. The unravelling of the mode of O-O bond formation is of key relevance for understanding the mechanism of the process. This problem is not yet solved. A multistate model is proposed for S(3) and the functional role of proton shifts and hydrogen bond network(s) is emphasized. Analogously, the structure of the Q(B) site for PQ reduction to PQH(2) and the energetic and kinetics of the two step redox reaction sequence are described. Furthermore, the relevance of the protein dynamics and the role of water molecules for its flexibility are briefly outlined. We end this review by presenting future perspectives on the water oxidation process.

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“…Interestingly there is an open space in the electron density between Mn4 and D1-Ile60, D1-Asn181, D2-Phe314. Since EPR and mass spectrometric data (Hansson et al 1986;Burda et al 2001) indicated that a water cluster of at least six or 12 H 2 O molecules could be located in the vicinity of the Mn 4 -Ca cluster, it seems feasible to assume that some of these water molecules may be located in this open space (Fig. 6).…”

Section: Coordination Of Manganesementioning

confidence: 99%

Structure of the Mn4–Ca cluster as derived from X-ray diffraction

et al. 2007

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The catalytic centre for light-induced water oxidation in photosystem II (PSII) is a multinuclear metal cluster containing four manganese and one calcium cations. Knowing the structure of this biological catalyst is of utmost importance for unravelling the mechanism of water oxidation in photosynthesis. In this review we describe the current state of the X-ray structure determination at 3.0 A resolution of the water oxidation complex (WOC) of PSII. The arrangement of metal cations in the cluster, their coordination and protein surroundings are discussed with regard to spectroscopic and mutagenesis studies. Limitations of the presently available structural data are pointed out and possible perspectives for the future are outlined, including the combination of X-ray diffraction and X-ray spectroscopy on single crystals.

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An estimation of the size of the water cluster present at the cleavage site of the water splitting enzyme

Abstract: 2 O for an infinite cluster. The presence of this deviation means that there is a typical size of water clusters having access to cleavage by the water splitting enzyme. We estimated that this cluster contains about 12 þ 2 water molecules. ß

Cited by 22 publications

References 18 publications

Substrate Water Exchange in Photosystem II Depends on the Peripheral Proteins

Substrate Water Exchange in Photosystem II Depends on the Peripheral Proteins

Photosystem II: The machinery of photosynthetic water splitting

Structure of the Mn4–Ca cluster as derived from X-ray diffraction

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