Photosynthesis Research Center, Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan; email:
Annu Rev Plant Biol. 2015;66:23-48. doi: 10.1146/annurev-arplant-050312-120129. Epub 2015 Feb 26.
Oxygenic photosynthesis forms the basis of aerobic life on earth by converting light energy into biologically useful chemical energy and by splitting water to generate molecular oxygen. The water-splitting and oxygen-evolving reaction is catalyzed by photosystem II (PSII), a huge, multisubunit membrane-protein complex located in the thylakoid membranes of organisms ranging from cyanobacteria to higher plants. The structure of PSII has been analyzed at 1.9-Å resolution by X-ray crystallography, revealing a clear picture of the Mn4CaO5 cluster, the catalytic center for water oxidation. This article provides an overview of the overall structure of PSII followed by detailed descriptions of the specific structure of the Mn4CaO5 cluster and its surrounding protein environment. Based on the geometric organization of the Mn4CaO5 cluster revealed by the crystallographic analysis, in combination with the results of a vast number of experimental studies involving spectroscopic and other techniques as well as various theoretical studies, the article also discusses possible mechanisms for water splitting that are currently under consideration.
光合作用通过将光能转化为生物可用的化学能，并通过分解水来产生分子氧，从而为地球上有氧生命奠定了基础。水的分解和氧的释放反应是由光合作用系统 II（PSII）催化的，PSII 是一种位于从蓝藻到高等植物等生物体类囊体膜中的巨大的、多亚基膜蛋白复合物。通过 X 射线晶体学分析，PSII 的结构已经在 1.9 Å 的分辨率下进行了分析，揭示了 Mn4CaO5 簇的清晰图像，该簇是水氧化的催化中心。本文概述了 PSII 的整体结构，然后详细描述了 Mn4CaO5 簇的特定结构及其周围的蛋白质环境。基于晶体学分析揭示的 Mn4CaO5 簇的几何组织，结合大量涉及光谱学和其他技术以及各种理论研究的实验结果，本文还讨论了目前正在考虑的水分解的可能机制。
