Department of Chemistry, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi, Osaka 558-8585, Japan.
Nature. 2011 May 5;473(7345):55-60. doi: 10.1038/nature09913. Epub 2011 Apr 17.
Photosystem II is the site of photosynthetic water oxidation and contains 20 subunits with a total molecular mass of 350 kDa. The structure of photosystem II has been reported at resolutions from 3.8 to 2.9 Å. These resolutions have provided much information on the arrangement of protein subunits and cofactors but are insufficient to reveal the detailed structure of the catalytic centre of water splitting. Here we report the crystal structure of photosystem II at a resolution of 1.9 Å. From our electron density map, we located all of the metal atoms of the Mn(4)CaO(5) cluster, together with all of their ligands. We found that five oxygen atoms served as oxo bridges linking the five metal atoms, and that four water molecules were bound to the Mn(4)CaO(5) cluster; some of them may therefore serve as substrates for dioxygen formation. We identified more than 1,300 water molecules in each photosystem II monomer. Some of them formed extensive hydrogen-bonding networks that may serve as channels for protons, water or oxygen molecules. The determination of the high-resolution structure of photosystem II will allow us to analyse and understand its functions in great detail.
光系统 II 是光合作用水氧化的场所，包含 20 个亚基，总分子量为 350 kDa。光系统 II 的结构已在 3.8 至 2.9 Å 的分辨率下报告。这些分辨率提供了大量关于蛋白质亚基和辅助因子排列的信息，但不足以揭示水分解催化中心的详细结构。在这里，我们报道了分辨率为 1.9 Å 的光系统 II 的晶体结构。从我们的电子密度图中，我们定位了 Mn(4)CaO(5)簇的所有金属原子及其所有配体。我们发现五个氧原子作为 oxo 桥连接五个金属原子，四个水分子与 Mn(4)CaO(5)簇结合；其中一些可能是氧气形成的底物。我们在每个光系统 II 单体中鉴定了超过 1300 个水分子。其中一些形成了广泛的氢键网络，可能作为质子、水或氧分子的通道。高分辨率结构的确定将使我们能够详细分析和理解其功能。
