Cyanobacterial photosystem II at 2.9-A resolution and the role of quinones, lipids, channels and chloride. Nat Struct Mol Biol

Institut für Chemie und Biochemie/Kristallographie, Freie Universität Berlin, Takustrasse 6, D-14195 Berlin, Germany.
Nature Structural & Molecular Biology (Impact Factor: 13.31). 03/2009; 16(3):334-42. DOI: 10.1038/nsmb.1559
Source: PubMed


Photosystem II (PSII) is a large homodimeric protein-cofactor complex located in the photosynthetic thylakoid membrane that acts as light-driven water:plastoquinone oxidoreductase. The crystal structure of PSII from Thermosynechococcus elongatus at 2.9-A resolution allowed the unambiguous assignment of all 20 protein subunits and complete modeling of all 35 chlorophyll a molecules and 12 carotenoid molecules, 25 integral lipids and 1 chloride ion per monomer. The presence of a third plastoquinone Q(C) and a second plastoquinone-transfer channel, which were not observed before, suggests mechanisms for plastoquinol-plastoquinone exchange, and we calculated other possible water or dioxygen and proton channels. Putative oxygen positions obtained from a Xenon derivative indicate a role for lipids in oxygen diffusion to the cytoplasmic side of PSII. The chloride position suggests a role in proton-transfer reactions because it is bound through a putative water molecule to the Mn(4)Ca cluster at a distance of 6.5 A and is close to two possible proton channels.

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Available from: Azat Gabdulkhakov, Apr 03, 2014
    • "Therefore, it is probable that the protective function of HliC and HliD bound to D1m in the RCII complex is taken over by HliA, HliB and HliC now bound to CP47m. With knowledge of the detailed structure of the cyanobacterial PSII complex (including the precise location of Chl and β-car molecules [45] [46] [47]) and using our model of pigment location in the Hlip pair [23] we drew a hypothetical model of the CP47m-HliA/B complex (Fig. 1). The model assumes interaction of the Chls and/or -car of the Hlip pair with exposed Chls of CP47, for instance Chl 620. "
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    ABSTRACT: Cyanobacteria contain a family of genes encoding one-helix high-light-inducible proteins (Hlips) that are homologous to light harvesting chlorophyll a/b-binding proteins of plants and algae. Based on various experimental approaches, a spectrum of functions that includes regulation of chlorophyll biosynthesis, transient chlorophyll binding, quenching of singlet oxygen and non-photochemical quenching of absorbed energy is ascribed to these proteins. However, these functions had not been supported by conclusive experimental evidence until recently when it became clear that Hlips are able to quench absorbed light energy and assist during terminal step(s) of the chlorophyll biosynthesis and early stages of Photosystem II assembly. In this review we summarize and discuss the present knowledge about Hlips and provide a model of how individual members of the Hlip family operate during the biogenesis of chlorophyll-proteins, namely Photosystem II. Copyright © 2015. Published by Elsevier B.V.
    Biochimica et Biophysica Acta 09/2015; DOI:10.1016/j.bbabio.2015.08.011 · 4.66 Impact Factor
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    • "In cyanobacteria the most abundant Cars are β-carotene and various xanthophylls, such as synechoxanthin, canthaxanthin, caloxanthin, echinenone, myxoxanthophyll, nostoxanthin and zeaxanthin [10] [11]. X-ray crystallographic studies have revealed that in the cyanobacterium Thermosynechococcus elongatus 22 and 12 β-carotene molecules are located in photosystem I (PSI) [12] and photosystem II (PSII) [13] Biochimica et Biophysica Acta 1847 (2015) 1153–1165 Abbreviations: APC, allophycocyanin; Car, carotenoid; DAS, decay associated spectrum/spectra; EET, excitation energy transfer; FLIM, Fluorescence Lifetime Imaging Microscopy; LAHG, light activated heterotrophic growth; L R 33 , 33 kDa rod linker protein; PAG, photoautotrophic growth; PC, phycocyanin; PBS, phycobilisome; PSI and PSII, photosystems I and II; RC, reaction center; RC47, PSII monomeric core complex lacking CP43; τ av , average lifetime; PPFD, Photosynthetic Photon Flux Density; TEs, terminal emitters of the phycobilisomes. ⁎ Corresponding author at: Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, P.O. "
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    ABSTRACT: In photosynthetic organisms, carotenoids (carotenes or xanthophylls) are important for light harvesting, photoprotection and structural stability of a variety of pigment-protein complexes. Here, we investigated the consequences of altered carotenoid composition for the functional organization of photosynthetic complexes in wild-type and various mutant strains of the cyanobacterium Synechocystis sp. PCC 6803. Although it is generally accepted that xanthophylls do not play a role in cyanobacterial photosynthesis in low-light conditions, we have found that the absence of xanthophylls leads to reduced oligomerization of photosystems I and II. This is remarkable because these complexes do not bind xanthophylls. Oligomerization is even more disturbed in crtH mutant cells, which show limited carotenoid synthesis; in these cells also the phycobilisomes are distorted despite the fact that these extramembranous light-harvesting complexes do not contain carotenoids. The number of phycocyanin rods connected to the phycobilisome core is strongly reduced leading to high amounts of unattached phycocyanin units. In the absence of carotenoids the overall organization of the thylakoid membranes is disturbed: Photosystem II is not formed, photosystem I hardly oligomerizes and the assembly of phycobilisomes remains incomplete. These data underline the importance of carotenoids in the structural and functional organization of the cyanobacterial photosynthetic machinery. Copyright © 2015. Published by Elsevier B.V.
    Biochimica et Biophysica Acta 06/2015; 1847(10):1153-1165. DOI:10.1016/j.bbabio.2015.05.020 · 4.66 Impact Factor
    • ". b [32]. c [34]. "
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    ABSTRACT: To identify energy traps in CP43, a subcomplex of the photosystem II antenna system, site energies and excitonic couplings of the QY transitions of chlorophyll (Chl) a pigments bound to CP43 are computed using electrostatic models of pigment-protein and pigment-pigment interactions. The computations are based on recent crystal structures of the photosystem II core complex with resolutions of 1.9 and 2.1Å and compared to earlier results obtained at 2.9Å resolution. Linear optical spectra (i.e., absorption, linear dichroism, circular dichroism, and fluorescence) are simulated using the computed excitonic couplings, a refinement fit for the site energies, and a dynamical theory of optical lineshapes. A comparison of the obtained root mean square deviation of about 100cm(-1) between directly calculated and refined site energies with the maximum range of about 350cm(-1) of directly calculated site energies shows that the combined quantum chemical/electrostatic approach provides a semi-quantitative agreement with experiment. Possible reasons for the deviations are discussed, including limits of the electrostatic models and the lineshape theory as well as structural alterations of CP43 upon detachment from the core complex. Based on the simulations, an assignment of the two low-energy exciton states A and B of CP43, that where observed earlier in hole burning studies, is suggested. State A is assigned to a localized exciton state on Chl 37 in the lumenal layer of pigments. State B is assigned to an exciton state that is delocalized over several pigments in the cytoplasmic layer. The delocalization explains the smaller inhomogeneous width of state B compared to state A observed in hole burning spectra, which is proposed to be due to exchange narrowing. The assignment of states A and B largely confirms our earlier suggestion that was based on a fit of linear optical spectra and electrostatic calculations using the 2.9Å resolution structure. Interestingly, for the latter structure, the site energy of Chl 37 is obtained closer to the refined value than for 1.9 and 2.1Å resolution. This is explained by a variation of the site energy due to the influence of lipids that might be different in the core complex and isolated CP43. To remove remaining uncertainties in the assignment of states A and B, target sites for mutagenesis experiments are proposed based on the electrostatic computations. In particular, it is suggested to mutate Trp C63 close to Chl 37 to probe the identity of state A and to mutate Arg C41 close to Chl 47 to probe state B. Copyright © 2015 Elsevier B.V. All rights reserved.
    Journal of photochemistry and photobiology. B, Biology 05/2015; DOI:10.1016/j.jphotobiol.2015.05.023 · 2.96 Impact Factor
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