Article

Functional architecture of higher plant photosystem II supercomplexes. EMBO J

Faculté des Sciences Luminy, Laboratoire de Génétique et Biophysique des Plantes, Université Aix Marseille, Marseille, France.
The EMBO Journal (Impact Factor: 10.43). 09/2009; 28(19):3052-63. DOI: 10.1038/emboj.2009.232
Source: PubMed

ABSTRACT

Photosystem II (PSII) is a large multiprotein complex, which catalyses water splitting and plastoquinone reduction necessary to transform sunlight into chemical energy. Detailed functional and structural studies of the complex from higher plants have been hampered by the impossibility to purify it to homogeneity. In this work, homogeneous preparations ranging from a newly identified particle composed by a monomeric core and antenna proteins to the largest C(2)S(2)M(2) supercomplex were isolated. Characterization by biochemical methods and single particle electron microscopy allowed to relate for the first time the supramolecular organization to the protein content. A projection map of C(2)S(2)M(2) at 12 A resolution was obtained, which allowed determining the location and the orientation of the antenna proteins. Comparison of the supercomplexes obtained from WT and Lhcb-deficient plants reveals the importance of the individual subunits for the supramolecular organization. The functional implications of these findings are discussed and allow redefining previous suggestions on PSII energy transfer, assembly, photoinhibition, state transition and non-photochemical quenching.

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    • "Immunoblot analyses of fractions taken from these gradients revealed that sample processing resulted in the separation of PSII cores from LHCII and the OEC. This was observed before when Suc density gradient centrifugation was employed to analyze PSII supercomplex compositions (Caffarri et al., 2009;Tokutsu et al., 2012) and, in our hands, for unknown reasons occurred predominantly with cells lacking cell walls. TEF30 clearly comigrated with monomeric PSII core complexes (Drop et al., 2014) and not with LHCII, the OEC, PSI, the cytochrome b 6 /f complex, or the ATP synthase (Fig. 4A). "
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    ABSTRACT: The remarkable capability of photosystem (PS) II to oxidize water comes along with its vulnerability to oxidative damage. Accordingly, organisms harboring PSII have developed strategies to protect PSII from oxidative damage and to repair damaged PSII. Here we report on the characterization of the TEF30 protein in Chlamydomonas reinhardtii that is conserved in the green lineage and induced by high light. Fractionation studies revealed that TEF30 is associated with the stromal side of thylakoid membranes. By using blue native / Deriphat-PAGE, sucrose density gradients, and isolated PSII particles, we found TEF30 to quantitatively interact with monomeric PSII complexes. Electron microscopy images revealed significantly reduced thylakoid membrane stacking in TEF30-underexpressing cells when compared with control cells. Biophysical and immunological data point to an impaired PSII repair cycle in TEF30-underexpressing cells and a reduced ability to form PSII supercomplexes after high light exposure. Taken together, our data suggest potential roles for TEF30 in facilitating the incorporation of a new D1 protein and/or the reintegration of CP43 into repaired PSII monomers, protecting repaired PSII monomers from undergoing repeated repair cycles, or facilitating the migration of repaired PSII monomers back to stacked regions for supercomplex reassembly.
    Preview · Article · Dec 2015 · Plant physiology
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    • "Several interrelated effects should be considered, including the role of phosphorylation in the regulated assembly of the complexes and in their stability in vivo, as well as the effect of phosphorylation on the lability of the complexes in vitro upon detergent extraction. Indeed, after BN-PAGE, a large proportion of LHCII is in the form of free trimers, which are most likely loosely bound in supercomplexes in vivo (Caffarri et al., 2009; Järvi et al., 2011; Pagliano et al., 2014; Grieco et al., 2015). Furthermore, PSII supercomplexes in the grana core may not be accessible to phosphorylation for steric reasons, because the tight appression of the membranes could hinder the access of the corresponding protein kinases (Zer et al., 2003; Kirchhoff, 2014). "
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    ABSTRACT: Light harvesting complex II (LHCII) is a crucial component of the photosynthetic machinery, with central roles in light capture and acclimation to changing light. The association of a LHCII trimer with Photosystem I in the PSI-LHCII supercomplex is strictly dependent on LHCII phosphorylation mediated by the kinase STN7, and is directly related to the light acclimation process called state transitions. In Arabidopsis thaliana the LHCII trimers contain isoforms that belong to three classes: Lhcb1, Lhcb2, and Lhcb3. Only Lhcb1 and Lhcb2 can be phosphorylated in the N-terminal region. Here we present an improved Phos-tag{trade mark, serif}-based method to determine the absolute extent of phosphorylation of Lhcb1 and Lhcb2. Both classes show very similar phosphorylation kinetics during state transition. Nevertheless, only Lhcb2 is extensively phosphorylated (>98%) in PSI-LHCII, whereas phosphorylated Lhcb1 is largely excluded from this supercomplex. Both isoforms are phosphorylated to different extents in other photosystem supercomplexes and in different domains of the thylakoid membranes. The data imply that despite their high sequence similarity, differential phosphorylation of Lhcb1 and Lhcb2 plays contrasting roles in light acclimation of photosynthesis.
    Full-text · Article · Oct 2015 · Plant physiology
    • "Triton solubilization allows the isolation of purer grana membranes than those that can be obtained with digitonin. This is demonstrated by the absence of PSI in BBY prepared with triton [11] [37], and the presence of significant amounts of PSI in grana cores membranes prepared with digitonin [20] "
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    ABSTRACT: State transitions are an important photosynthetic short-term response that maintains the excitation balance between photosystems I (PSI) and II (PSII). In plants, when PSII is preferentially excited, LHCII, the main heterotrimeric light harvesting complex of PSII, is phosphorylated by the STN7 kinase, detaches from PSII and moves to PSI to equilibrate the relative absorption of the two photosystems (State II). When PSI is preferentially excited LHCII is dephosphorylated by the PPH1 (TAP38) phosphatase, and returns to PSII (State I). Phosphorylation of LHCII that remain bound to PSII has also been observed. Although the kinetics of LHCII phosphorylation are well known from a qualitative standpoint, the absolute phosphorylation levels of LHCII (and its isoforms) bound to PSI and PSII have been little studied. In this work we thoroughly investigated the phosphorylation level of the Lhcb1 and Lhcb2 isoforms that compose LHCII in PSI-LHCII and PSII-LHCII supercomplexes purified from WT and state transition mutants of Arabidopsis thaliana. We found that, at most, 40% of the monomers that make up PSI-bound LHCII trimers are phosphorylated. Phosphorylation was much lower in PSII-bound LHCII trimers reaching only 15-20%. Dephosphorylation assays using a recombinant PPH1 phosphatase allowed us to investigate the role of the two isoforms during state transitions. Our results strongly suggest that a single phosphorylated Lhcb2 is sufficient for the formation of the PSI-LHCII supercomplex. These results are a step towards a refined model of the state transition phenomenon and a better understanding of the short-term response to changes in light conditions in plants.
    No preview · Article · Sep 2015 · Biochimica et Biophysica Acta
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