Structural organization of the oxidizing side of photosystem II. Exogenous reductants reduce and destroy the Mn-complex in photosystems II membranes depleted of the 17 and 23 kDa polypeptides

Ghanotakis, Demetrios F.; Topper, James N.; Youcum, Charles F.

doi:10.1016/0005-2728(84)90051-3

Cited by 157 publications

(119 citation statements)

References 21 publications

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“…As already described, in spinach PSII preparations that retain all of the extrinsic polypeptides, Ca 2+ extraction appears to open an access channel to the Mn cluster that can be closed, or partially blocked, by readdition of Ca 2+ (Vander Meulen et al 2002. Extraction of the PsbP and PsbQ subunits exposes the Mn cluster to reduction and loss of Mn(II) catalyzed by hydroquinone and NH 2 OH (Ghanotakis et al 1984c), and it was later shown Yocum 1991, 1992) that Ca 2+ added to PSII in the absence of the PsbP and PsbQ subunits could stabilize the Mn cluster in reduced states. The S -1 state formed by hydroquinone reduction was extensively characterized by XAFS and XANES spectroscopy and shown to consist of a 2 Mn(II)/2 Mn(IV) oxidation state (Riggs et al 1992) that was reversed to the S 1 oxidation state by illumination (Riggs-Gelasco et al 1996).…”

Section: Introductionmentioning

confidence: 71%

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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Section: Introductionmentioning

confidence: 71%

The PSII calcium site revisited

2007

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“…A number of studies have suggested that the extrinsic subdomain of PSII may provide some kind of accessibility barrier. The removal of the 16-and 23-kDa polypeptides (51,52) and the MSP (53,54) results in an increased reactivity of the Mn 4 Ca 1 Cl X cluster toward exogenous reductants. Also, the recent crystallographic structure of PSII clearly identifies a large luminal PSII domain comprised of the extrinsic polypeptides (9).…”

Section: Resultsmentioning

confidence: 99%

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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“…In contrast, only about 50% loss of Vo2 (measured in continuous light at either quantum yield or saturating light intensity, or in a train of actinic flashes and also in absence of Ca2+ addition) is observed on 17,24 kD protein depletion from wheat PSII membranes (37 Tables I-III), and similarly, Ca2' addition to EDTA preincubated 17,24 kD-less spinach PSII membranes of Ono and Inoue (35) gave only about 41 to 48% increase of Vo2 measured in continuous or flash illumination.…”

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confidence: 98%

“…According to Ghanotakis et al (15,16), these polypeptides promote high affinity Ca2' binding in spinach PSII membranes; however, other workers (6, 7) indicate both high and low affinity Ca2+ effects on 02 evolution in spinach 17,24 kD-less PSII membranes. Moreover, indirect evidence suggests that the Ca bound with high affinity in 17,24 kD depleted PSII membranes can be dissociated reversibly by either flash illumination in the presence of EDTA (12) or by continuous illumination of PSII membranes in the presence of 1 to 2 M NaCl (6, 7). According to Dekker et al (12), Ghanotakis et al (15), and Jansson et al (21), such dissociation results in a reversible decoupling of Z from the S-state complex.…”

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confidence: 99%

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Studies on 17,24 kD Depleted Photosystem II Membranes

Cammarata

Cheniae²

1987

Plant Physiol.

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Analyses were made of the effects of extraction of the 17,24 kilodalton extrinsic proteins from spinach versus wheat photosystem II (PSII) membranes on Ca abundance and 02 evolution capacity determined in the absence and presence of either ClO or Ca22. Extraction of these proteins from spinach PSII routinely diminished steady state 02 evolution by about 70% when assayed in the presence ofsufficient Cl1. Additionally, 02 evolution of 17,24 kilodalton-less spinach PSI1 membranes showed about 2-fold more enhancement by Ca22 than by Cl-during assay. When the same extraction and assay procedures were applied to wheat PSII membranes, we observed, in contrast to 17,24 kilodalton-less spinach PSII, only about 50% inhibition of 02 evolution and about 2-fold greater enhancement by Cl-than by Ca21. Irrespective of differences in the magnitude of enhancement of 02 evolution by Ca2' versuC a-in spinach versus wheat, the K., values for Cl-(about 1.7 millimolar) and Ca2l (about 1.5 millimolar) were similar for both type preparations. The abundance of Ca specifically associated with fully functional PSII (about 2 and about 3 Ca/200 chlorophyll for spinach and wheat, respectively) was diminished to about 1 per 200 chlorophyll upon 17.24 kilodalton protein depletion. Further treatment of wheat 17,24 kilodalton-less PSII in darkness with 2 molar NaClI/ millimolar ethyleneglycol-bis(O-aminoethyl ether)-N,N'-tetraacetic acid/20 micromolar A231872 made 02 evolution highly dependent on Ca2 addition, much like the 17,24 kilodaltonless spinach PSII. Analyses of this Ca2' effect on 02 evolution revealed both high (K. about 65 micromolar) and low (K. about 1.5 millimolar) affinity Ca2 sites in wheat 17,24 kilodalton-less PSII. The results suggest that during 17,24 kilodalton extraction by NaCl, spinach PSII is more susceptible than wheat PSII to loss of high affinity Ca and irreversible inhibition of 02 evolution.The realization of 02 evolving everted thylakoid vesicles (1, 21) and Triton X-100 prepared PSII membranes (3, 24), also having everted membrane orientation (14,24), has led to intensive research focused on defining the polypeptides essential for efficient functioning of the PSII/water oxidizing complex. Parallel research has been directed towards identifying which poly- 90% (4-7, 15, 16, 21, 25, 27) when determined in the presence of saturating concentrations of Cl-. Subsequently, it was shown (6,7,15,16) that addition of 10 to 20 mM Ca2+ to 17,24 kDless, Cl-sufficient spinach PSII membranes increased rates of 02 evolution as much as 4-to 6-fold to rates sometimes nearly equivalent to those observed with unextracted membranes. However, no Ca2' additions were necessary to observe substantial period-4 oscillations of the S-states with only about 25% disconnection of the S-state complexes from PSII traps (12).Conceivably, at least some of the rather large variability in extent of loss of 02 evolution following depletion of the 17,24 kD proteins could reflect inadvertent dissociation of high affinity Ca2`during extraction....

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Structural organization of the oxidizing side of photosystem II. Exogenous reductants reduce and destroy the Mn-complex in photosystems II membranes depleted of the 17 and 23 kDa polypeptides

Cited by 157 publications

References 21 publications

The PSII calcium site revisited

The PSII calcium site revisited

Substrate Water Exchange in Photosystem II Depends on the Peripheral Proteins

Studies on 17,24 kD Depleted Photosystem II Membranes

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