Referenced in: none

Automatically associated channels: Kir2.3

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

Authors: Albert Guskov, Jan Kern, Azat Gabdulkhakov, Matthias Broser, Athina Zouni, Wolfram Saenger

Journal, date & volume: Nat. Struct. Mol. Biol., 2009 Mar , 16, 334-42

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/19219048

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.