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Accueil > Départements > Biochimie, Biophysique et Biologie Structurale > Diana KIRILOVSKY : Mécanismes régulateurs chez les organismes photosynthétiques

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Articles syndiqués

  • State transitions in the cyanobacterium Synechococcus elongatus 7942 involve reversible quenching of the photosystem II core.

    15 juin, par Choubeh RR, Wientjes E, Struik PC, Kirilovsky D, van Amerongen H
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    State transitions in the cyanobacterium Synechococcus elongatus 7942 involve reversible quenching of the photosystem II core.

    Biochim Biophys Acta. 2018 Jun 11;:

    Authors: Choubeh RR, Wientjes E, Struik PC, Kirilovsky D, van Amerongen H

    Abstract
    Cyanobacteria use chlorophyll and phycobiliproteins to harvest light. The resulting excitation energy is delivered to reaction centers (RCs), where photochemistry starts. The relative amounts of excitation energy arriving at the RCs of photosystem I (PSI) and II (PSII) depend on the spectral composition of the light. To balance the excitations in both photosystems, cyanobacteria perform state transitions to equilibrate the excitation energy. They go to state I if PSI is preferentially excited, for example after illumination with blue light (light I), and to state II after illumination with green-orange light (light II) or after dark adaptation. In this study, we performed 77-K time-resolved fluorescence spectroscopy on wild-type Synechococcus elongatus 7942 cells to measure how state transitions affect excitation energy transfer to PSI and PSII in different light conditions and to test the various models that have been proposed in literature. The time-resolved spectra show that the PSII core is quenched in state II and that this is not due to a change in excitation energy transfer from PSII to PSI (spill-over), either direct or indirect via phycobilisomes.

    PMID: 29902424 [PubMed - as supplied by publisher]

  • Glycolate induces redox tuning of photosystem II in vivo : study of a photorespiration mutant.

    31 mai, par Messant M, Timm S, Fantuzzi A, Weckwerth W, Bauwe H, Rutherford B, Krieger-Liszkay A
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    Glycolate induces redox tuning of photosystem II in vivo: study of a photorespiration mutant.

    Plant Physiol. 2018 May 23;:

    Authors: Messant M, Timm S, Fantuzzi A, Weckwerth W, Bauwe H, Rutherford B, Krieger-Liszkay A

    Abstract
    Bicarbonate removal from the non-heme iron at the acceptor side of photosystem II (PSII) was recently shown to shift the midpoint potential of the primary quinone acceptor QA to a more positive potential and lowers the yield of singlet oxygen (1O2) production. The presence of QA- results in weaker binding of bicarbonate, suggesting a redox-based regulatory and protective mechanism where loss of bicarbonate or exchange of bicarbonate by other small carboxylic acids may protect PSII against 1O2 in vivo under photorespiratory conditions. Here we compared the properties of QA in the Arabidopsis (Arabidopsis thaliana) photorespiration mutant hpr1-1, deficient in NADH-dependent, peroxisomal hydroxypyruvate reductase 1 (HPR1), which accumulates glycolate in leaves, to the wild type. Photosynthetic electron transport was affected in the mutant, and chlorophyll fluorescence showed slower electron transport between QA and QB in the mutant. Glycolate induced an increase in the temperature maximum of thermoluminescence emission indicating a shift of the midpoint potential of QA to a more positive value. The yield of 1O2 production was lowered in thylakoid membranes isolated from hpr1-1 compared to the wild type, consistent with a higher potential of QA/QA-. In addition, electron donation to photosystem I was affected in hpr1-1 at higher light intensities consistent with diminished electron transfer out of photosystem II. This study indicates that replacement of bicarbonate at the non-heme iron by a small carboxylate anion occurs in plants in vivo. These findings suggested that replacement of the bicarbonate on the non-heme iron by glycolate may represent a regulatory mechanism that protects PSII against photo-oxidative stress under low CO2 conditions.

    PMID: 29794021 [PubMed - as supplied by publisher]

  • Switching an Individual Phycobilisome Off and On.

    25 avril, par Gwizdala M, Botha JL, Wilson A, Kirilovsky D, van Grondelle R, Krüger TPJ
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    Switching an Individual Phycobilisome Off and On.

    J Phys Chem Lett. 2018 Apr 24;:

    Authors: Gwizdala M, Botha JL, Wilson A, Kirilovsky D, van Grondelle R, Krüger TPJ

    Abstract
    Photosynthetic organisms have found various smart ways to cope with unexpected changes in light conditions. In many cyanobacteria, the lethal effects of a sudden increase in light intensity are mitigated mainly by the interaction between phycobilisomes (PBs) and the Orange Carotenoid Protein (OCP). The latter senses high light intensities by means of photoactivation and triggers thermal energy dissipation from the PBs. Due to the brightness of their emission, PBs can be characterized at the level of individual complexes. Here, energy dissipation from individual PBs was reversibly switched on and off using only light and OCP. We reveal the presence of quasistable intermediate states during the binding and unbinding of OCP to PB, with a spectroscopic signature indicative of transient decoupling of some of the PB rods during docking of OCP. Real-time control of emission from individual PBs has the potential to contribute to the development of new superresolution imaging techniques.

    PMID: 29688018 [PubMed - as supplied by publisher]

  • X-ray structure of an asymmetrical trimeric ferredoxin-photosystem I complex.

    4 avril, par Kubota-Kawai H, Mutoh R, Shinmura K, Sétif P, Nowaczyk MM, Rögner M, Ikegami T, Tanaka H, Kurisu G
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    X-ray structure of an asymmetrical trimeric ferredoxin-photosystem I complex.

    Nat Plants. 2018 Apr 02;:

    Authors: Kubota-Kawai H, Mutoh R, Shinmura K, Sétif P, Nowaczyk MM, Rögner M, Ikegami T, Tanaka H, Kurisu G

    Abstract
    Photosystem I (PSI), a large protein complex located in the thylakoid membrane, mediates the final step in light-driven electron transfer to the stromal electron carrier protein ferredoxin (Fd). Here, we report the first structural description of the PSI-Fd complex from Thermosynechococcus elongatus. The trimeric PSI complex binds three Fds in a non-equivalent manner. While each is recognized by a PSI protomer in a similar orientation, the distances between Fds and the PSI redox centres differ. Fd binding thus entails loss of the exact three-fold symmetry of the PSI's soluble subunits, inducing structural perturbations which are transferred to the lumen through PsaF. Affinity chromatography and nuclear magnetic resonance analyses of PSI-Fd complexes support the existence of two different Fd-binding states, with one Fd being more tightly bound than the others. We propose a dynamic structural basis for productive complex formation, which supports fast electron transfer between PSI and Fd.

    PMID: 29610537 [PubMed - as supplied by publisher]

  • A tribute to Ulrich Heber (1930-2016) for his contribution to photosynthesis research : understanding the interplay between photosynthetic primary reactions, metabolism and the environment.

    26 janvier, par Dietz KJ, Krause GH, Siebke K, Krieger-Liszkay A
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    A tribute to Ulrich Heber (1930-2016) for his contribution to photosynthesis research: understanding the interplay between photosynthetic primary reactions, metabolism and the environment.

    Photosynth Res. 2018 Jan 24;:

    Authors: Dietz KJ, Krause GH, Siebke K, Krieger-Liszkay A

    Abstract
    The dynamic and efficient coordination of primary photosynthetic reactions with leaf energization and metabolism under a wide range of environmental conditions is a fundamental property of plants involving processes at all functional levels. The present historical perspective covers 60 years of research aiming to understand the underlying mechanisms, linking major breakthroughs to current progress. It centers on the contributions of Ulrich Heber who had pioneered novel concepts, fundamental methods, and mechanistic understanding of photosynthesis. An important first step was the development of non-aqueous preparation of chloroplasts allowing the investigation of chloroplast metabolites ex vivo (meaning that the obtained results reflect the in vivo situation). Later on, intact chloroplasts, retaining their functional envelope membranes, were isolated in aqueous media to investigate compartmentation and exchange of metabolites between chloroplasts and external medium. These studies elucidated metabolic interaction between chloroplasts and cytoplasm during photosynthesis. Experiments with isolated intact chloroplasts clarified that oxygenation of ribulose-1.5-bisphosphate generates glycolate in photorespiration. The development of non-invasive optical methods enabled researchers identifying mechanisms that balance electron flow in the photosynthetic electron transport system avoiding its over-reduction. Recording chlorophyll a (Chl a) fluorescence allowed one to monitor, among other parameters, thermal energy dissipation by means of 'nonphotochemical quenching' of the excited state of Chl a. Furthermore, studies both in vivo and in vitro led to basic understanding of the biochemical mechanisms of freezing damage and frost tolerance of plant leaves, to SO2 tolerance of tree leaves and dehydrating lichens and mosses.

    PMID: 29368118 [PubMed - as supplied by publisher]