Evidence That Azide Occupies the Chloride Binding Site near the Manganese Cluster in Photosystem II

Yu, Hui; Aznar, Constantino P.; Xu, Xia; Britt, R. David

doi:10.1021/bi0505767

Cited by 23 publications

(17 citation statements)

References 50 publications

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“…However, they did not provide any information about the number and location of Cl Ϫ ions within the OEC. The inhibition of particular S-state transitions upon depletion of Cl Ϫ has been taken as evidence of the close proximity of Cl Ϫ to the Mn 4 Ca cluster, a proximity that also was suggested by studies of electron spin echo envelope modulation (19,20) and Fourier transform infrared spectroscopic studies (21). Recent EXAFS studies, however, suggested that Cl Ϫ ions do not bind to the Mn 4 Ca cluster in its S 1 state, and that no Cl Ϫ is present within a distance of 5 Å from the metal center (13).…”

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confidence: 87%

Location of chloride and its possible functions in oxygen-evolving photosystem II revealed by X-ray crystallography

Kawakami

Umena

Kamiya

et al. 2009

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

214

141

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The chloride ion, Cl ؊ , is an essential cofactor for oxygen evolution of photosystem II (PSII) and is closely associated with the Mn 4Ca cluster. Its detailed location and function have not been identified, however. We substituted Cl ؊ with a bromide ion (Br ؊ ) or an iodide ion (I ؊ ) in PSII and analyzed the crystal structures of PSII with Br ؊ and I ؊ substitutions. Substitution of Cl ؊ with Br ؊ did not inhibit oxygen evolution, whereas substitution of Cl ؊ with I ؊ completely inhibited oxygen evolution, indicating the efficient replacement of Cl ؊ by I ؊ . PSII with Br ؊ and I ؊ substitutions were crystallized, and their structures were analyzed. The results showed that there are 2 anion-binding sites in each PSII monomer; they are located on 2 sides of the Mn 4Ca cluster at equal distances from the metal cluster. Anion-binding site 1 is close to the main chain of D1-Glu-333, and site 2 is close to the main chain of CP43-Glu-354; these 2 residues are coordinated directly with the Mn 4Ca cluster. In addition, site 1 is located in the entrance of a proton exit channel. These results indicate that these 2 Cl ؊ anions are required to maintain the coordination structure of the Mn4Ca cluster as well as the proposed proton channel, thereby keeping the oxygen-evolving complex fully active. membrane proteins ͉ oxygen evolution ͉ photosynthesis ͉ manganese enzyme P hotosynthetic water oxidation produces the oxygen required for life on the earth and is catalyzed by Photosystem II (PSII), a multiprotein complex with a total molecular mass of 350 kDa (1). The catalytic center for water splitting, i.e., the oxygen-evolving complex (OEC), is located in the membrane surface of the luminal side of thylakoid membranes and is composed of 4 Mn atoms and 1 Ca atom in the protein matrix of PSII. Oxygen is produced from 2 molecules of water by sequential, light-induced electron-abstracting events at the Mn 4 Ca cluster that cycle through the Si states with i ϭ 0-4 (2). One or more Cl Ϫ ions are required for the water oxidation cycle to proceed, a requirement not often found in other biological systems (3, 4). Depletion of Cl Ϫ has been shown to inhibit the S 2 3 S 3 and S 3 3 S 0 transitions (5). The roles of Cl Ϫ proposed for OEC include ligation to Mn or Ca atoms (6-8), regulation of the redox potential of the Mn 4 Ca cluster (9), maintaining a hydrogen bond network (10), and activation of the substrate water (11). In addition, an association of Cl Ϫ with amino acid residues in the Mn coordination shell has been proposed (12, 13).The structure of PSII, including the Mn 4 Ca cluster, has been analyzed by x-ray crystallography (14-17). These studies, together with polarized extended x-ray absorption fine structure (EXAFS) measurements (18), have provided much information about the structure of the Mn 4 Ca cluster. However, they did not provide any information about the number and location of Cl Ϫ ions within the OEC. The inhibition of particular S-state transitions upon depletion of Cl Ϫ has been taken as evidence of the close p...

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mentioning

confidence: 87%

Location of chloride and its possible functions in oxygen-evolving photosystem II revealed by X-ray crystallography

Kawakami

Umena

Kamiya

et al. 2009

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

214

141

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“…While there is compelling biochemical evidence for a functional role of Cl K (van Gorkom & Yocum 2005), it is controversial whether it is (in some S states) a direct ligand of the Mn 4 O x Ca cluster. Binding of the Cl K analogue azide within 5 Å of the Mn 4 O x Ca cluster was demonstrated by electron spin-echo envelope modulation (ESEEM) spectroscopy (Yu et al 2005). Similarly, extended EXAFS measurements show an extra peak that may be assigned to Cl K (Pushkar et al 2007).…”

Section: Introductionmentioning

confidence: 93%

Focusing the view on nature's water-splitting catalyst

Zein

Кулик

Yano

et al. 2007

Phil. Trans. R. Soc. B

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Nature invented a catalyst about 3 Gyr ago, which splits water with high efficiency into molecular oxygen and hydrogen equivalents (protons and electrons). This reaction is energetically driven by sunlight and the active centre contains relatively cheap and abundant metals: manganese and calcium. This biological system therefore forms the paradigm for all man-made attempts for direct solar fuel production, and several studies are underway to determine the electronic and geometric structures of this catalyst. In this report we briefly summarize the problems and the current status of these efforts and propose a density functional theory-based strategy for obtaining a reliable high-resolution structure of this unique catalyst that includes both the inorganic core and the first ligand sphere.

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“…[232][233][234] The results of a recent combined EPR-FTIR study are consistent with N 3 À binding in the immediate vicinity of the Mn cluster and show that Cl À binding is competitive with N 3 À binding at this site. [235] McEvoy and Brudvig [35] suggested that activation by Cl À binding to Mn(4) could occur by coordination expansion or Cl À bridging between Ca and Mn(4). In either case, a coordinated anion could play an indirect role through its electronic influence on pK a values and intermolecular proton transfer.…”

Section: Angewandte Chemiementioning

confidence: 99%

The Possible Role of Proton‐Coupled Electron Transfer (PCET) in Water Oxidation by Photosystem II

2007

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All higher life forms use oxygen and respiration as their primary energy source. The oxygen comes from water by solar-energy conversion in photosynthetic membranes. In green plants, light absorption in photosystem II (PSII) drives electron-transfer activation of the oxygen-evolving complex (OEC). The mechanism of water oxidation by the OEC has long been a subject of great interest to biologists and chemists. With the availability of new molecular-level protein structures from X-ray crystallography and EXAFS, as well as the accumulated results from numerous experiments and theoretical studies, it is possible to suggest how water may be oxidized at the OEC. An integrated sequence of light-driven reactions that exploit coupled electron-proton transfer (EPT) could be the key to water oxidation. When these reactions are combined with long-range proton transfer (by sequential local proton transfers), it may be possible to view the OEC as an intricate structure that is "wired for protons".

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Evidence That Azide Occupies the Chloride Binding Site near the Manganese Cluster in Photosystem II

Cited by 23 publications

References 50 publications

Location of chloride and its possible functions in oxygen-evolving photosystem II revealed by X-ray crystallography

Location of chloride and its possible functions in oxygen-evolving photosystem II revealed by X-ray crystallography

Focusing the view on nature's water-splitting catalyst

The Possible Role of Proton‐Coupled Electron Transfer (PCET) in Water Oxidation by Photosystem II

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