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Cyanobacterial photosystem II at 2. A resolution role of quinones lipids channels and chloride.

Institut für Chemie und Biochemie/Kristallographie, Freie Universität Berlin, Takustrasse 6, D-14195 Berlin, Germany.
Nature Structural & Molecular Biology (Impact Factor: 11.63). 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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    • "They instead contain PsbP, PsbQ, and PsbR, which appear to serve as their functional replacements (Bricker et al. 2012). Although it is not observed in the available PSII crystal structures from either Thermosynechococcus elongatus BP- 1 or Thermosynechococcus vulcanus (Suga et al. 2015; Umena et al. 2011; Zouni et al. 2001; Kamiya and Shen 2003; Ferreira et al. 2004; Loll et al. 2005; Guskov et al. 2009), experimental evidence indicates that active cyanobacterial PSII contains a fourth extrinsic protein, PsbQ (Roose et al. 2007a, b, Kashino et al. 2002; Thornton et al. 2004). Recently, we used chemical cross-linking and mass spectrometry to demonstrate that PsbQ binds to the lumenal side of PSII, and interacts closely with both PsbO and CP47 (Liu et al. 2014). "
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    • "which are structural lipids of both photosystems and whose levels were found to decrease during HS (Jordan et al., 2001; Guskov et al., 2009; Hemme et al., 2014). As the abundances of enzymes involved in chlorophyll biosynthesis decreased during HS, also the insufficient incorporation of pigments might have interfered with proper photosystem assembly (M€ uhlhaus et al., 2011; Hemme et al., 2014). "
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    • "3 and 5). This tryptophan is homologous to W253 strictly conserved in all D2 sequences and helps to keep Q A fixed in position by stacking of the indole ring with the plastoquinone head group, but occurring in an offset-stacked manner (Loll et al. 2005; Guskov et al. 2009; Hasegawa and Noguchi 2014; Lambreva et al. 2014). In all standard D1 and also Group 2 sequences, glycine is found at this position. "
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