光系统II是光合水氧化站，它包括，总分子量为350 kDa的20个亚基。光系统II的结构已报道的分辨率为3.8 ~2.9 Å。这些分辨率提供了很多蛋白亚基和共组合因子的排列信息，但这些不足以揭示水分离反应中心的详细结构。日本大阪市立大学的Yasufumi Umena 等报道了分辨率1.9 Å的光系统的晶体结构。“从我们的电子密度图，我们定位了Mn4CaO5蔟的所有金属原子以及配体。我们发现，5个氧原子作为氧络桥连接5个金属原子，4个水分子束缚到Mn4CaO5蔟上，因此，它们部分作为分子氧形成的底物。我们在每个光系统II单体中分别鉴别了1300个以上的水分子。它们的一部分形成广泛的氢结合网络，服务为质子、水或氧分子通道，” Yasufumi Umena说。“光系统II的高分辨率结构的确定将允许我们进一步详细地分析与理解其功能。”（生物谷Bioon.com）
生物谷推荐原文出处：
Nature doi:10.1038/nature09913
Crystal structure of oxygen-evolving photosystem II at a resolution of 1.9 Å
Yasufumi Umena,1, 3, 4 Keisuke Kawakami,2, 3, 4 Jian-Ren Shen2 & Nobuo Kamiya1, 3
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 Mn4CaO5 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 Mn4CaO5 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.
