Investigation of the Calcium-Binding Site of the Oxygen Evolving Complex of Photosystem II Using <sup>87</sup>Sr ESEEM Spectroscopy

Kim, Sun Hee; Gregor, Wolfgang; Peloquin, John M.; Brynda, Marcin; Britt, R. David

doi:10.1021/ja030614e

Cited by 30 publications

(23 citation statements)

References 63 publications

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“…Biochemical and biophysical experiments have long established that manganese is essential for photosynthetic water oxidation and EPR experiments have set the number of manganese atoms in the OEC at four [8,9,23]. In addition to the four manganese atoms, a calcium atom has been shown to be part of the OEC through EPR [10], EXAFS [24] and X-ray diffraction [1] experiments. Beyond the core structure of four manganese atoms and one calcium atom, a number of other components have been suggested for the OEC.…”

Section: Structurementioning

confidence: 99%

“…Decades of biophysical study have provided a solid groundwork for this project. Crystal structures of photosystem II [1,2] (PSII) have revealed the location of many important components such as chlorophylls and the oxygen-evolving center (OEC) while spectroscopy such as EXAFS [3][4][5][6][7], EPR [8][9][10][11][12], and IR [13,14] have allowed the study of reactive intermediates, the composition of the OEC and the protein ligation of the metal centers. Unfortunately, while we now have a much better structural and mechanistic basis for PSII, we still are some way from the goal of a molecular mechanistic understanding of water oxidation.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Structurementioning

confidence: 99%

Section: Introductionmentioning

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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“…Much research effort has been focused on obtaining ESEEM and ENDOR spectra of the various states of PSII [67][68][69][70][71][72][73][74][75]. While the Mn(II) oxidation state is likely not accessed during any of the so-called S states of the water oxidation reaction2 [76,77], Mn(II) ions are necessary for the in vivo photoassembly of the Mn cluster [78].…”

Section: Past Studiesmentioning

confidence: 99%

Multifrequency pulsed EPR studies of biologically relevant manganese(II) complexes

et al. 2007

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Electron paramagnetic resonance studies at multiple frequencies (MF EPR) can provide detailed electronic structure descriptions of unpaired electrons in organic radicals, inorganic complexes, and metalloenzymes. Analysis of these properties aids in the assignment of the chemical environment surrounding the paramagnet and provides mechanistic insight into the chemical reactions in which these systems take part. Herein, we present results from pulsed EPR studies performed at three different frequencies (9, 31, and 130 GHz) on [Mn(II)(H 2 O) 6 ] 2+ , Mn(II) adducts with the nucleotides ATP and GMP, and the Mn(II)-bound form of the hammerhead ribozyme (MnHH). Through line shape analysis and interpretation of the zero-field splitting values derived from successful simulations of the corresponding continuous-wave and field-swept echodetected spectra, these data are used to exemplify the ability of the MF EPR approach in distinguishing the nature of the first ligand sphere. A survey of recent results from pulsed EPR, as well as pulsed electron-nuclear double resonance and electron spin echo envelope modulation spectroscopic studies applied to Mn(II)-dependent systems, is also presented. Mn-Containing Biological SystemsManganese operates as a cofactor in numerous proteins, serving both catalytic and structural roles [1][2][3][4]. Many Mn-dependent enzymes take advantage o f the rich redox chemistry available to the metal, accessing the +2, +3, +4, and perhaps even the +5 oxidation states during their turnover. For example, Mn-superoxide dismutase (MnSOD), which detoxifies the cell of the superoxide radical , cycles between the Mn(II) and Mn(III) oxidation states via the ping-pong type mechanism shown below [5][6][7][8][9].(1a) (1b) Other examples of such mononuclear redox-active enzymes include the manganese peroxidase responsible for lignin degradation by white-rot fungus [10][11][12]; a unique Mndependent form of lipoxygenase [13][14][15][16]; oxalate decarboxylase [17,18]; as well as an extradiol catechol dioxygenase [19][20][21]. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptIn order to help minimize kinetic and thermodynamic penalties associated with electron transfer events and the execution of chemical reactions, two or more metal centers can be coupled together to provide active sites capable of conducting multiple electrons while still operating within a physiologically accessible range of reduction potentials [22]. Only three such examples of redox-active polynuclear Mn enzymes are known: Mn-catalase that disproportionates hydrogen peroxide [23][24][25][26]; a Mn form of ribonucleotide reductase (Mn-RNR) [27,28]; and, arguably the most recognized Mn-dependent enzyme, the photosynthetic core of green plants, algae, and certain cyanobacteria termed photosystem II (PSII) [29,30]. Through a series of photoinitiated electron transfer events, oxidizing equivalents are stored on the tetranuclear Mn core of PSII -the oxygen-evolving complex (OEC) -which then extracts four electr...

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“…Calcium is believed to bind close to the Mn cluster, and extended x-ray absorption fine structure measurements report Ca-Mn distances of 3.3-4.2 Å (13,14). Recent 87 Sr 12 ESEEM experiments confirm that strontium is 3-5 Å from Mn (15). Four x-ray diffraction studies of PSII crystals from thermophilic cyanobacteria have been presented at 3.8 (16), 3.7 (17), 3.5 (18), and 3.2 Å (19), respectively.…”

Section: Introductionmentioning

confidence: 99%

Calcium Ligation in Photosystem II under Inhibiting Conditions

Barry

Hicks

Riso

et al. 2005

Biophysical Journal

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In oxygenic photosynthesis, PSII carries out the oxidation of water and reduction of plastoquinone. The product of water oxidation is molecular oxygen. The water splitting complex is located on the lumenal side of the PSII reaction center and contains manganese, calcium, and chloride. Four sequential photooxidation reactions are required to generate oxygen from water; the five sequentially oxidized forms of the water splitting complex are known as the Sn states, where n refers to the number of oxidizing equivalents stored. Calcium plays a role in water oxidation; removal of calcium is associated with an inhibition of the S state cycle. Although calcium can be replaced by other cations in vitro, only strontium maintains activity, and the steady-state rate of oxygen evolution is decreased in strontium-reconstituted PSII. In this article, we study the role of calcium in PSII that is limited in water content. We report that strontium substitution or 18OH2 exchange causes conformational changes in the calcium ligation shell. The conformational change is detected because of a perturbation to calcium ligation during the S1 to S2 and S2 to S3 transition under water-limited conditions.

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Investigation of the Calcium-Binding Site of the Oxygen Evolving Complex of Photosystem II Using ⁸⁷Sr ESEEM Spectroscopy

Cited by 30 publications

References 63 publications

Functional models for the oxygen-evolving complex of photosystem II

Functional models for the oxygen-evolving complex of photosystem II

Multifrequency pulsed EPR studies of biologically relevant manganese(II) complexes

Calcium Ligation in Photosystem II under Inhibiting Conditions

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Investigation of the Calcium-Binding Site of the Oxygen Evolving Complex of Photosystem II Using 87Sr ESEEM Spectroscopy

Cited by 30 publications

References 63 publications

Functional models for the oxygen-evolving complex of photosystem II

Functional models for the oxygen-evolving complex of photosystem II

Multifrequency pulsed EPR studies of biologically relevant manganese(II) complexes

Calcium Ligation in Photosystem II under Inhibiting Conditions

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Investigation of the Calcium-Binding Site of the Oxygen Evolving Complex of Photosystem II Using ⁸⁷Sr ESEEM Spectroscopy