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Accueil > Départements > Biochimie, Biophysique et Biologie Structurale > Alain BOUSSAC : Photosystème II

pubmed : boussac, alain

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NCBI : db=pubmed ; Term=Boussac, Alain[Full Author Name] AND CEA[All Fields]

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  • Photochemistry beyond the red limit in chlorophyll f-containing photosystems.

    16 juin, par Nürnberg DJ, Morton J, Santabarbara S, Telfer A, Joliot P, Antonaru LA, Ruban AV, Cardona T, Krausz E, Boussac A, Fantuzzi A, Rutherford AW
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    Photochemistry beyond the red limit in chlorophyll f-containing photosystems.

    Science. 2018 Jun 15;360(6394):1210-1213

    Authors: Nürnberg DJ, Morton J, Santabarbara S, Telfer A, Joliot P, Antonaru LA, Ruban AV, Cardona T, Krausz E, Boussac A, Fantuzzi A, Rutherford AW

    Abstract
    Photosystems I and II convert solar energy into the chemical energy that powers life. Chlorophyll a photochemistry, using red light (680 to 700 nm), is near universal and is considered to define the energy "red limit" of oxygenic photosynthesis. We present biophysical studies on the photosystems from a cyanobacterium grown in far-red light (750 nm). The few long-wavelength chlorophylls present are well resolved from each other and from the majority pigment, chlorophyll a. Charge separation in photosystem I and II uses chlorophyll f at 745 nm and chlorophyll f (or d) at 727 nm, respectively. Each photosystem has a few even longer-wavelength chlorophylls f that collect light and pass excitation energy uphill to the photochemically active pigments. These photosystems function beyond the red limit using far-red pigments in only a few key positions.

    PMID: 29903971 [PubMed - in process]

  • Consequences of structural modifications in cytochrome b559 on the electron acceptor side of Photosystem II.

    22 mai, par Nakamura M, Boussac A, Sugiura M
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    Consequences of structural modifications in cytochrome b559 on the electron acceptor side of Photosystem II.

    Photosynth Res. 2018 May 19;:

    Authors: Nakamura M, Boussac A, Sugiura M

    Abstract
    Cytb559 in Photosystem II is a heterodimeric b-type cytochrome. The subunits, PsbE and PsbF, consist each in a membrane α-helix. Mutants were previously designed and studied in Thermosynechococcus elongatus (Sugiura et al., Biochim Biophys Acta 1847:276-285, 2015) either in which an axial histidine ligand of the haem-iron was substituted for a methionine, the PsbE/H23M mutant in which the haem was lacking, or in which the haem environment was modified, the PsbE/Y19F and PsbE/T26P mutants. All these mutants remained active showing that the haem has no structural role provided that PsbE and PsbF subunits are present. Here, we have carried on the characterization of these mutants. The following results were obtained: (i) the Y19F mutation hardly affect the Em of Cytb559, whereas the T26P mutation converts the haem into a form with a Em much below 0 mV (so low that it is likely not reducible by QB-) even in an active enzyme; (ii) in the PsbE/H23M mutant, and to a less extent in PsbE/T26P mutant, the electron transfer efficiency from QA- to QB is decreased; (iii) the lower Em of the QA/QA- couple in the PsbE/H23M mutant correlates with a higher production of singlet oxygen; (iv) the superoxide and/or hydroperoxide formation was not increased in the PsbE/H23M mutant lacking the haem, whereas it was significantly larger in the PsbE/T26P. These data are discussed in view of the literature to discriminate between structural and redox roles for the haem of Cytb559 in the production of reactive oxygen species.

    PMID: 29779191 [PubMed - as supplied by publisher]

  • Properties and structure of a low-potential, penta-heme cytochrome c 552 from a thermophilic purple sulfur photosynthetic bacterium Thermochromatium tepidum.

    25 avril, par Chen JH, Yu LJ, Boussac A, Wang-Otomo ZY, Kuang T, Shen JR
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    Properties and structure of a low-potential, penta-heme cytochrome c 552 from a thermophilic purple sulfur photosynthetic bacterium Thermochromatium tepidum.

    Photosynth Res. 2018 Apr 24;:

    Authors: Chen JH, Yu LJ, Boussac A, Wang-Otomo ZY, Kuang T, Shen JR

    Abstract
    The thermophilic purple sulfur bacterium Thermochromatium tepidum possesses four main water-soluble redox proteins involved in the electron transfer behavior. Crystal structures have been reported for three of them: a high potential iron-sulfur protein, cytochrome c', and one of two low-potential cytochrome c 552 (which is a flavocytochrome c) have been determined. In this study, we purified another low-potential cytochrome c 552 (LPC), determined its N-terminal amino acid sequence and the whole gene sequence, characterized it with absorption and electron paramagnetic spectroscopy, and solved its high-resolution crystal structure. This novel cytochrome was found to contain five c-type hemes. The overall fold of LPC consists of two distinct domains, one is the five heme-containing domain and the other one is an Ig-like domain. This provides a representative example for the structures of multiheme cytochromes containing an odd number of hemes, although the structures of multiheme cytochromes with an even number of hemes are frequently seen in the PDB database. Comparison of the sequence and structure of LPC with other proteins in the databases revealed several characteristic features which may be important for its functioning. Based on the results obtained, we discuss the possible intracellular function of this LPC in Tch. tepidum.

    PMID: 29691716 [PubMed - as supplied by publisher]

  • The low spin - high spin equilibrium in the S2-state of the water oxidizing enzyme.

    3 mars, par Boussac A, Ugur I, Marion A, Sugiura M, Kaila VRI, William Rutherford A

    The low spin - high spin equilibrium in the S2-state of the water oxidizing enzyme.

    Biochim Biophys Acta. 2018 Feb 27;:

    Authors: Boussac A, Ugur I, Marion A, Sugiura M, Kaila VRI, William Rutherford A

    Abstract
    In Photosystem II (PSII), the Mn4CaO5-cluster of the active site advances through five sequential oxidation states (S0 to S4) before water is oxidized and O2 is generated. Here, we have studied the transition between the low spin (LS) and high spin (HS) configurations of S2 using EPR spectroscopy, quantum chemical calculations using Density Functional Theory (DFT), and time-resolved UV-visible absorption spectroscopy. The EPR experiments show that the equilibrium between S2LS and S2HS is pH dependent, with a pKa ≈ 8.3 (n ≈ 4) for the native Mn4CaO5 and pKa ≈ 7.5 (n ≈ 1) for Mn4SrO5. The DFT results suggest that exchanging Ca with Sr modifies the electronic structure of several titratable groups within the active site, including groups that are not direct ligands to Ca/Sr, e.g., W1/W2, Asp61, His332 and His337. This is consistent with the complex modification of the pKa upon the Ca/Sr exchange. EPR also showed that NH3 addition reversed the effect of high pH, NH3-S2LS being present at all pH values studied. Absorption spectroscopy indicates that NH3 is no longer bound in the S3TyrZ state, consistent with EPR data showing minor or no NH3-induced modification of S3 and S0. In both Ca-PSII and Sr-PSII, S2HS was capable of advancing to S3 at low temperature (198 K). This is an experimental demonstration that the S2LS is formed first and advances to S3via the S2HS state without detectable intermediates. We discuss the nature of the changes occurring in the S2LS to S2HS transition which allow the S2HS to S3 transition to occur below 200 K. This work also provides a protocol for generating S3 in concentrated samples without the need for saturating flashes.

    PMID: 29499187 [PubMed - as supplied by publisher]