Recent Progress in the Crystallographic Studies of Photosystem II

Guskov, Albert; Габдулхаков, А.Г.; Broser, Matthias; Glöckner, Carina; Hellmich, Julia; Kern, Jan; Frank, Joachim; Müh, Frank; Saenger, Wolfram; Zouni, Athina

doi:10.1002/cphc.200900901

Cited by 102 publications

(90 citation statements)

References 111 publications

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“…On the average, if N electrons are transferred through each PSII per second, then each PSI transfers N∕1.8 electrons per second. In cyanobacteria, each PSII complex is associated with roughly 35 molecules of Chl (16), while each PSI is associated with 96 Chl molecules (17). Therefore, the total number of Chl molecules in the cell associated with PSI is about five times larger than the total number of Chl molecules associated with PSII.…”

Section: Resultsmentioning

confidence: 99%

Solar hydrogen-producing bionanodevice outperforms natural photosynthesis

Lubner

Applegate

Knörzer

et al. 2011

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

155

123

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Although a number of solar biohydrogen systems employing photosystem I (PSI) have been developed, few attain the electron transfer throughput of oxygenic photosynthesis. We have optimized a biological/organic nanoconstruct that directly tethers F B , the terminal þ þ 2 ferredoxin red is carried out in two separate photochemical half-reactions. Photosystem II (PSII) catalyzes the anodic half-cell reaction H 2 O þ plastoquinone-9 þ 2 hν → 1∕2 O 2 þ plastoquinol-9, while photosystem I (PSI) catalyzes the cathodic half-cell reaction cytochrome c 6ðredÞ þ ferredoxin ox þ 1 hν → cytochrome c 6ðoxÞ þ ferredoxin red . Visible photons provide the energy necessary to drive these otherwise thermodynamically unfavorable half-cell reactions to completion (1). Cyanobacteria evolve O 2 at a rate of approximately 400 μmol mg Chl −1 h −1 (2, 3) in a process limited by diffusiongoverned electron transfer steps (Fig. 1A), in particular the slow interaction of plastoquinol-9 with the cytochrome b 6 f complex (4). Once electrons leave PSI, diffusionally governed electron transfer steps constrain the rate of interaction of ferredoxin with other enzymes, including ferredoxin:NADP þ oxidoreductase. Were it possible to directly connect redox proteins through their redox centers, electrons could be vectored preferentially thereby eliminating any dependence on diffusional electron transfer (5, 6, 7). Here we report that by engineering a nanoconstruct in which both the electron donor (cytochrome c 6 ) and acceptor (here: ½FeFe-H 2 ase) are tethered to PSI in vitro, rate-limiting, diffusion-based electron transfer reactions are eliminated (Fig. 1B), resulting in electron transfer rates that exceed those of natural photosynthesis.The approach connects PSI to an ½FeFe-H 2 ase (8) using a molecular wire, which separates the [4Fe-4S] clusters of each enzyme by a defined distance (5). By introducing an exchangeable sulfhydryl ligand to the most solvent-exposed iron atom of PSI, the molecular wire can be attached by a ligand exchange mechanism. This is achieved by site-specific conversion of a ligating Cys residue (C13) of F B , the terminal [4Fe-4S] cluster, to a Gly (9-11) and by chemically rescuing the cluster with a small sulfhydrylcontaining molecule (11). Because ½FeFe-H 2 ases also contain [4Fe-4S] clusters, which constitute an electron transfer pathway between the surface of the enzyme and its catalytic site (12, 13), a similar strategy is used to introduce an exchangeable ligand at the distal [4Fe-4S] cluster (C97G). A tether that contains two sulfhydryl groups serves as a chemical rescue agent for both the F B cluster of PSI and the distal [4Fe-4S] cluster of ½FeFe-H 2 ase, thereby providing a pathway for electrons to quantum mechanically tunnel between the two proteins.

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Section: Resultsmentioning

confidence: 99%

Solar hydrogen-producing bionanodevice outperforms natural photosynthesis

Lubner

Applegate

Knörzer

et al. 2011

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

155

123

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“…Functional and spectroscopic studies showed that HCO − 3 facilitates the reduction of the secondary plastoquinone electron acceptor (Q B ) of PSII by participating in the protonation of Q 2− B . Binding of HCO − 3 (or CO 2− 3 ) to the nonheme Fe between the quinones Q A and Q B was recently confirmed by X-ray crystallography (3,13,14). Despite this functional role at the acceptor side, the very tight binding of HCO − 3 to this site makes it impossible for the activity of PSII to be affected by changing the C i level of the medium; instead inhibitors such as formate need to be added to induce the acceptor-side effect (15).…”

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confidence: 88%

“…11 and 12). Although a tight binding of C i near the Mn 4 CaO 5 cluster is excluded on the basis of X-ray crystallography (3,14), FTIR spectroscopy (16), and mass spectrometry (17,18), the possibility that a weakly bound HCO − 3 affects the activity of PSII at the donor side remains a viable option (reviewed in refs. 10 and 19).…”

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confidence: 99%

Mobile hydrogen carbonate acts as proton acceptor in photosynthetic water oxidation

Koroidov

Shevela

Shutova

et al. 2014

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

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Cyanobacteria, algae, and plants oxidize water to the O 2 we breathe, and consume CO 2 during the synthesis of biomass. Although these vital processes are functionally and structurally well separated in photosynthetic organisms, there is a long-debated role for CO 2 /HCO − 3 in water oxidation. Using membrane-inlet mass spectrometry we demonstrate that HCO − 3 acts as a mobile proton acceptor that helps to transport the protons produced inside of photosystem II by water oxidation out into the chloroplast's lumen, resulting in a light-driven production of O 2 and CO 2 . Depletion of HCO − 3 from the media leads, in the absence of added buffers, to a reversible down-regulation of O 2 production by about 20%. These findings add a previously unidentified component to the regulatory network of oxygenic photosynthesis and conclude the more than 50-y-long quest for the function of CO 2 / HCO − 3 in photosynthetic water oxidation.O xygenic photosynthesis in cyanobacteria, algae, and higher plants leads to the reduction of atmospheric CO 2 to energy-rich carbohydrates. The electrons needed for this process are extracted in a cyclic, light-driven process from water that is split into dioxygen (O 2 ) and protons. This reaction is catalyzed by a penta-μ-oxo bridged tetra-manganese calcium cluster (Mn 4 CaO 5 ) within the oxygen-evolving complex (OEC) of photosystem II (PSII) (1-4). The possible roles of inorganic carbon, C i ðC i = CO 2 ; H 2 CO 3 ; HCO − 3 ; CO 2− 3 Þ, in this process have been a controversial issue ever since Otto Warburg and Günter Krippahl (5) reported in 1958 that oxygen evolution by PSII strictly depends on CO 2 and therefore has to be based on the photolysis of H 2 CO 3 ("Kohlensäure") and not of water. These first experiments were indirect and, as became apparent later, were wrongly interpreted (6-8). Several research groups followed up on these initial results and identified two possible sites of C i interaction within PSII (reviewed in refs. 9-12). Functional and spectroscopic studies showed that HCO − 3 facilitates the reduction of the secondary plastoquinone electron acceptor (Q B ) of PSII by participating in the protonation of Q 2− B . Binding of HCO − 3 (or CO 2− 3 ) to the nonheme Fe between the quinones Q A and Q B was recently confirmed by X-ray crystallography (3,13,14). Despite this functional role at the acceptor side, the very tight binding of HCO − 3 to this site makes it impossible for the activity of PSII to be affected by changing the C i level of the medium; instead inhibitors such as formate need to be added to induce the acceptor-side effect (15). Consequently, the watersplitting electron-donor side of PSII has also been studied intensively (for recent reviews, see refs. 11 and 12). Although a tight binding of C i near the Mn 4 CaO 5 cluster is excluded on the basis of X-ray crystallography (3, 14), FTIR spectroscopy (16), and mass spectrometry (17, 18), the possibility that a weakly bound HCO − 3 affects the activity of PSII at the donor side remains a viable option (reviewed i...

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“…Some examples are CaMn 4 cluster of oxygen evolving complex (OEC) in Photosystem II (PSII) [17 -20], Fe 3þ involved in the diferric tyrosyl radical in subunit b2 of the ribonucleotide reductase (RNR) [21], and the known m-oxo-bridged ruthenium bipyridine complex (blue dimer) [5] capable of H 2 O oxidation. Furthermore, some ions involved in a PCET system are not involved directly in a redox process; Ca 2þ in CaMn 4 cluster of the OEC in PSII [18] [19], where the OEC is the active site for the H 2 O oxidation, might be an example; the Ca 2þ is not oxidized or reduced in the PCET processes, occurring on the OEC, however, being in a near proximity of the redox site. Theoretical studies dealing with the role of cations involved in the PCET systems have appeared recently [22] [23].…”

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confidence: 97%

Ions Can Move a Proton‐Coupled Electron‐Transfer Reaction into Tunneling Regime

Brala

Pilepić

Sajenko

et al. 2011

Helvetica Chimica Acta

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The effects of charged species on proton-coupled electron-transfer (PCET) reaction should be of significance for understanding/application of important chemical and biological PCET systems. Such species can be found in proximity of activated complex in a PCET reaction, although they are not involved in the charge transfer process. Reported here is the first study of the above-mentioned effects. Here, the effects of Na , 5.5 (0.9) (at 0.001m Ca 2þ ), and 7.9 (2.8) (at 0.001m Mg 2þ ) kJ mol À1 ; e) nonlinear proton inventory in reaction. In the H 2 O/dioxane 1 : 1, the observed KIE is 7.8 and 4.4 in the absence and in the presence of 0.1m K þ , respectively, and A H /A D ¼ 0.14 (0.03). The changes when cations are present in the reaction are explained in terms of termolecular encounter complex consisting of redox partners, and the cation where the cation can be found in a near proximity of the reaction-activated complex thus influencing the proton/electron double tunneling event in the PCET process. A molecule of H 2 O is involved in the transition state. The resulting configuration is more rigid and more appropriate for efficient tunneling with Na þ or K þ (extensive tunneling observed), i.e., there is more precise organized H transfer coordinate than in the case of Ca 2þ and Mg 2þ (moderate tunneling observed) in the reaction.Introduction. -Proton-coupled electron-transfer (PCET) reactions are of crucial importance in a wide range of biological, biochemical, and chemical systems [1 -16], including those related to artificial photosynthesis and solar fuels [4 -8], and nanostructures and interfaces [14] [15]. It is recognized now that many processes in biology would not be possible without the coupling of proton and electron motion [3] [5]. Within a unified theoretical framework, both sequential electron transfer, followed by proton transfer (ET/PT) or vice versa (PT/ET), and the concerted transfer of these particles with conspicuous quantum-mechanical character could be viewed as PCET reactions [16]. However, the concerted transfer of a proton and an electron should be of central importance in the issue; here, the single chemical reaction step and

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Recent Progress in the Crystallographic Studies of Photosystem II

Cited by 102 publications

References 111 publications

Solar hydrogen-producing bionanodevice outperforms natural photosynthesis

Solar hydrogen-producing bionanodevice outperforms natural photosynthesis

Mobile hydrogen carbonate acts as proton acceptor in photosynthetic water oxidation

Ions Can Move a Proton‐Coupled Electron‐Transfer Reaction into Tunneling Regime

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