pH Modulates the Quinone Position in the Photosynthetic Reaction Center from Rhodobacter sphaeroides in the Neutral and Charge Separated States

Koepke, Juergen; Krammer, Eva-Maria; Klingen, Astrid R.; Sebban, Pierre; Ullmann, G. Matthias; Fritzsch, Günter

doi:10.1016/j.jmb.2007.04.082

Cited by 136 publications

(195 citation statements)

References 61 publications

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“…In the used PSII membrane particle preparation, the carboxylate shift occurred prior to the Q A Ϫ 3 Q B reaction and was reverted concomitantly with the ET. The DFT data and previous XAS and crystallography studies (20,26) on BRCs, in which the BC is replaced by the carboxyl group of glutamate, favor a similar coordination change also in this system. Thus, we propose that a coordination change of the Fe(II)-bound carboxyl is a general feature of the type II photosynthetic reaction centers.…”

Section: Discussionsupporting

confidence: 63%

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Carboxylate Shifts Steer Interquinone Electron Transfer in Photosynthesis

Chernev

Zaharieva

Dau

et al. 2011

Journal of Biological Chemistry

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Understanding the mechanisms of electron transfer (ET) in photosynthetic reaction centers (RCs) may inspire novel catalysts for sunlight-driven fuel production. The electron exit pathway of type II RCs comprises two quinone molecules working in series and in between a non-heme iron atom with a carboxyl ligand (bicarbonate in photosystem II (PSII), glutamate in bacterial RCs). For decades, the functional role of the iron has remained enigmatic. We tracked the iron site using microsecond-resolution x-ray absorption spectroscopy after laser-flash excitation of PSII. After formation of the reduced primary quinone, Q A ؊ , the x-ray spectral changes revealed a transition (t1 ⁄ 2 ≈ 150 s) from a bidentate to a monodentate coordination of the bicarbonate at the Fe(II) (carboxylate shift), which reverted concomitantly with the slower ET to the secondary quinone Q B . A redox change of the iron during the ET was excluded. Density-functional theory calculations corroborated the carboxylate shift both in PSII and bacterial RCs and disclosed underlying changes in electronic configuration. We propose that the iron-carboxyl complex facilitates the first interquinone ET by optimizing charge distribution and hydrogen bonding within the Q A FeQ B triad for high yield Q B reduction. Formation of a specific priming intermediate by nuclear rearrangements, setting the stage for subsequent ET, may be a common motif in reactions of biological redox cofactors.

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Section: Discussionsupporting

confidence: 63%

“…Fe K-edge Spectral Simulations-Calculations of XANES spectra were performed with FEFF8.2 using the full multiplescattering and self-consistent field options (34) with Fe-site models for PSII and BRC based on crystallographic data (8,20) (see supplemental information, section 5).…”

Section: Proteinmentioning

confidence: 99%

Carboxylate Shifts Steer Interquinone Electron Transfer in Photosynthesis

Chernev

Zaharieva

Dau

et al. 2011

Journal of Biological Chemistry

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“…The mixture of complementary protein surfaces (contributing rigidity to the cofactors) and the flexibility imparted by the lipid bilayer enable both exact positioning of the three previously described components and also afford the dynamic movements required to enable efficient forward electron transfer and inefficient back electron transfer. The additional requirement for proton translocation in PSII, whether it be through a series of residues (39) or via channels to the outer solvent (40), requires additional structural changes that must occur without disturbing the continued flow of electrons. The result of the optimization of aforementioned parameters make the possibility of changing or improving a photosystems activity in vivo or in vitro very difficult (41,42).…”

Section: Discussion Critical Parameters Affecting the Photosynthetic mentioning

confidence: 99%

Engineering of an alternative electron transfer path in photosystem II

Larom

Salama

Schuster

et al. 2010

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

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The initial steps of oxygenic photosynthetic electron transfer occur within photosystem II, an intricate pigment/protein transmembrane complex. Light-driven electron transfer occurs within a multistep pathway that is efficiently insulated from competing electron transfer pathways. The heart of the electron transfer system, composed of six linearly coupled redox active cofactors that enable electron transfer from water to the secondary quinone acceptor Q B , is mainly embedded within two proteins called D1 and D2. We have identified a site in silico, poised in the vicinity of the Q A intermediate quinone acceptor, which could serve as a potential binding site for redox active proteins. Here we show that modification of Lysine 238 of the D1 protein to glutamic acid (Glu) in the cyanobacterium Synechocystis sp. PCC 6803, results in a strain that grows photautotrophically. The Glu thylakoid membranes are able to perform light-dependent reduction of exogenous cytochrome c with water as the electron donor. Cytochrome c photoreduction by the Glu mutant was also shown to significantly protect the D1 protein from photodamage when isolated thylakoid membranes were illuminated. We have therefore engineered a novel electron transfer pathway from water to a soluble protein electron carrier without harming the normal function of photosystem II. cyanobacteria | energy conversion | proinhibition | photosynthesis | protein engineering P hotosynthesis is the major source of useful chemical energy in the biosphere. All photosynthetic processes require efficient electron transfer (ET) pathways that are utilized for proton gradient formation (to be used for the production of ATP) and/or accumulation of reducing equivalents (1, 2). Light energy, absorbed by light-harvesting antenna complexes, is transferred to photochemical reaction centers (RC), initiating charge separation in specific chlorophyll molecules bound to the RC proteins. Following charge separation, electrons are transferred sequentially to a series of acceptor molecules, each with a redox potential determined by its immediate environment (3, 4). The source of electron replenishment differs according to the reaction center type. For instance in purple non-sulfur bacteria, electrons are cycled back to the oxidized reaction center by a soluble cytochrome c (cyt c) type protein (5, 6). Oxygenic photosynthetic organisms (cyanobacteria, red and green algae and plants) contain two photosystems: photosystem I (PSI) and photosystem II (PSII) that work linearly (1, 7), and the source of electrons is water. One common facet of all ET pathways is the requirement for insulation of the redox active cofactors from potentially reducing/oxidizing molecules within the RC or in the surrounding media. Insulation provides the system with maximal ET rates and efficiencies and also prevents damage to the RC.PSII has a redox potential of up to 1.2 V (8, 9), required to abstract electrons from water (Fig. 1A). The photoexcited P 680 reaction center chlorophyll a primary donor transfers electron...

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“…Sphaeroides (PDB id 2J8C). 24 To reduce computational effort and yet to keep the essential feature of the isomerization mechanism, we adopted truncated models shown in were optimized followed by frequency calculations by using the B3LYP functional 54, 55 with 6-311G(d) basis set. 56 These frequency calculations were used to show that the optimized structures are minima on their respective potential energy surfaces.…”

Section: Computational Detailsmentioning

confidence: 99%

Energy dissipative photoprotective mechanism of carotenoid spheroidene from the photoreaction center of purple bacteria Rhodobacter sphaeroides

Arulmozhiraja

Nakatani

Nakayama

et al. 2015

Phys. Chem. Chem. Phys.

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Carotenoid spheroidene (SPO) works for photoprotection in the photosynthetic reaction centers (RC) and effectively dissipates its triplet excitation energy. Sensitized cis-totrans isomerization was proposed as the possible mechanism for a singlet-triplet energy crossing for the 15,15′-cis-SPO; however, it has been questioned recently. To understand the dissipative proto-protective mechanism of this important SPO and to overcome the existing controversies on this issue, we carried out a theoretical investigation using density functional theory on the possible triplet energy relaxation mechanism through the cis-to-trans isomerization. Together with the earlier experimental observations, the possible mechanism was discussed for the triplet energy relaxation of the 15,15′-cis-SPO. The result shows that complete cis-to-trans isomerization is not necessary. Twisting C15-C15′ bond leads singlettriplet energy crossing at (14,15,15′,14′) = 77 o at the energy 32.5 kJ/mol (7.7 kcal/mol) higher than that of the T 1 15,15′-cis minimum. Further exploration of the minimum-energy intersystem crossing (MEISC) point shows that triplet relaxation could happen at a less distorted structure ( =58.4 o ) with the energy height of 6.3 kcal/mol. Another important reaction coordinate to reach the MEISC point is the bond-length alternation. The model truncation effect, the solvent effect, and the spin-orbit coupling were also investigated. The singlet-triplet crossing was also investigated for the 13,14-cis stereoisomer and locked-13,14-cis-SPO. We also discussed the origin of the natural selection of cis over trans isomer in the RC.

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pH Modulates the Quinone Position in the Photosynthetic Reaction Center from Rhodobacter sphaeroides in the Neutral and Charge Separated States

Cited by 136 publications

References 61 publications

Carboxylate Shifts Steer Interquinone Electron Transfer in Photosynthesis

Carboxylate Shifts Steer Interquinone Electron Transfer in Photosynthesis

Engineering of an alternative electron transfer path in photosystem II

Energy dissipative photoprotective mechanism of carotenoid spheroidene from the photoreaction center of purple bacteria Rhodobacter sphaeroides

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