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Nat Struct Mol Biol. 2009 Mar;16(3):334-42. doi: 10.1038/nsmb.1559. Epub 2009 Feb 15.

Cyanobacterial photosystem II at 2.9-A resolution and the role of quinones, lipids, channels and chloride.

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  • 1Institut für Chemie und Biochemie/Kristallographie, Freie Universität Berlin, Takustrasse 6, D-14195 Berlin, Germany.

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.

PMID:
19219048
[PubMed - indexed for MEDLINE]
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