Article

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

ABSTRACT

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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    • "These are the home of several large complexes, with photosystem II (PSII) being one of the key elements for the photosynthetic process. PSII is composed of 17 integral and 3 peripheral membrane proteins, several β-carotene, chlorophyll a and pheophytin molecules (Loll et al. 2005; Guskov et al. 2009; Umena et al. 2011; Suga et al. 2015) and its assembly has been the object of many studies (Nixon et al. 2010; Boehm et al. 2011; Stengel et al. 2012). Unlike photosystem I (PSI), which is rather stable and assembled extremely fast (Duhring et al. 2007), PSII assembly is more complex, requiring the association of several different functional " modules " in a specific order (Boehm et al. 2012; Komenda et al. 2012b). "
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    ABSTRACT: Thylakoid biogenesis is an intricate process requiring accurate and timely assembly of proteins, pigments and other cofactors into functional, photosynthetically-competent membranes. Photosystem II (PSII) assembly is especially studied as its core protein, D1, is very susceptible to photodamage and has a high turnover rate, particularly in high light. PSII assembly is a modular process, with assembly steps proceeding in a specific order. Using aqueous two-phase partitioning to separate plasma membranes (PM) and thylakoid membranes (TM) we studied the subcellular localization of PSII biogenesis early assembly steps in a Synechocystis sp. PCC6803 cyanobacterium strain lacking CP47 antenna. This strain accumulates the early D1-D2 assembly complex which was localized in TM along with associated PSII assembly factors. We also followed insertion and processing of the D1 precursor (pD1) by radioactive pulse-chase labelling. D1 is inserted into the membrane with a C-terminal extension which requires cleavage by a specific protease, the C-terminal processing protease (CtpA), to allow subsequent assembly of the oxygen evolving complex. pD1 insertion as well as its conversion to mature D1 under various light conditions was seen only in the TM. Epitope-tagged CtpA was also localized in the same membrane giving further support for the thylakoid location of pD1 processing. However, Vipp1 and PratA, two proteins suggested to be part of the so-called "thylakoid centers", were found to associate with PM. Together, these results suggest that early PSII assembly steps occur in TM or specific areas derived from them, with interaction with PM needed for efficient PSII and thylakoid biogenesis.
    Full-text · Article · Nov 2015 · Plant and Cell Physiology
    • "[6] "
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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.
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    • "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.
    No preview · Article · Sep 2015 · Biochimica et Biophysica Acta
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