Loll Bernhard, Kern Jan, Saenger Wolfram, Zouni Athina, Biesiadka Jacek
Institut für Chemie und Biochemie/Kristallographie, Freie Universität Berlin, Takustrasse 6, D-14195 Berlin, Germany.
Nature. 2005 Dec 15;438(7070):1040-4. doi: 10.1038/nature04224.
Oxygenic photosynthesis in plants, algae and cyanobacteria is initiated at photosystem II, a homodimeric multisubunit protein-cofactor complex embedded in the thylakoid membrane. Photosystem II captures sunlight and powers the unique photo-induced oxidation of water to atmospheric oxygen. Crystallographic investigations of cyanobacterial photosystem II have provided several medium-resolution structures (3.8 to 3.2 A) that explain the general arrangement of the protein matrix and cofactors, but do not give a full picture of the complex. Here we describe the most complete cyanobacterial photosystem II structure obtained so far, showing locations of and interactions between 20 protein subunits and 77 cofactors per monomer. Assignment of 11 beta-carotenes yields insights into electron and energy transfer and photo-protection mechanisms in the reaction centre and antenna subunits. The high number of 14 integrally bound lipids reflects the structural and functional importance of these molecules for flexibility within and assembly of photosystem II. A lipophilic pathway is proposed for the diffusion of secondary plastoquinone that transfers redox equivalents from photosystem II to the photosynthetic chain. The structure provides information about the Mn4Ca cluster, where oxidation of water takes place. Our study uncovers near-atomic details necessary to understand the processes that convert light to chemical energy.
植物、藻类和蓝细菌中的氧光合作用起始于光系统II，它是一种嵌入类囊体膜的同型二聚体多亚基蛋白质-辅因子复合体。光系统II捕获阳光，并驱动将水独特地光诱导氧化为大气中的氧气。对蓝细菌光系统II的晶体学研究提供了几种中等分辨率的结构（3.8至3.2埃），这些结构解释了蛋白质基质和辅因子的总体排列，但并未完整呈现该复合体的全貌。在此，我们描述了迄今为止获得的最完整的蓝细菌光系统II结构，展示了每个单体中20个蛋白质亚基和77个辅因子的位置及相互作用。11个β-胡萝卜素的归属为反应中心和天线亚基中的电子和能量转移以及光保护机制提供了见解。14个紧密结合的脂质数量众多，反映了这些分子对于光系统II内部灵活性和组装的结构与功能重要性。提出了一条亲脂性途径用于次生质体醌的扩散，次生质体醌将氧化还原当量从光系统II转移到光合链。该结构提供了有关水氧化发生的锰钙簇的信息。我们的研究揭示了理解光转化为化学能过程所需的近原子细节。
