Guskov Albert, Kern Jan, Gabdulkhakov Azat, Broser Matthias, Zouni Athina, Saenger Wolfram
Institut für Chemie und Biochemie/Kristallographie, Freie Universität Berlin, Takustrasse 6, D-14195 Berlin, Germany.
Nat Struct Mol Biol. 2009 Mar;16(3):334-42. doi: 10.1038/nsmb.1559. Epub 2009 Feb 15.
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.
光系统II（PSII）是一种位于光合类囊体膜中的大型同型二聚体蛋白质 - 辅因子复合物，作为光驱动的水：质体醌氧化还原酶发挥作用。嗜热栖热菌PSII的晶体结构在2.9埃分辨率下，使得所有20个蛋白质亚基得以明确归属，并对每个单体中的所有35个叶绿素a分子、12个类胡萝卜素分子、25个整合脂质和1个氯离子进行了完整建模。之前未观察到的第三个质体醌Q(C)和第二个质体醌转移通道的存在，提示了质体醌 - 质体醌交换的机制，并且我们计算了其他可能的水、或双氧和质子通道。从氙衍生物获得的假定氧位置表明脂质在氧向PSII细胞质侧扩散中起作用。氯离子位置表明其在质子转移反应中起作用，因为它通过一个假定的水分子与距离为6.5埃的Mn(4)Ca簇结合，并且靠近两个可能的质子通道。
