European Synchrotron Radiation Facility , 71 Avenue des Martyrs, 38000 Grenoble, France.
Max Planck Institute for Chemical Energy Conversion , Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany.
J Am Chem Soc. 2017 Oct 18;139(41):14340-14343. doi: 10.1021/jacs.7b06351. Epub 2017 Sep 27.
The site of biological water oxidation is highly conserved across photosynthetic organisms, but differences of unidentified structural and electronic origin exist between taxonomically discrete clades, revealed by distinct spectroscopic signatures of the oxygen-evolving MnCaO cluster and variations in active-site accessibility. Comparison of atomistic models of a native cyanobacterial form (Thermosynechococcus vulcanus) and a chimeric spinach-like form of photosystem II allows us to identify the precise atomic-level differences between organisms in the vicinity of the manganese cluster. Substitution of cyanobacterial D1-Asn87 by higher-plant D1-Ala87 is the principal discriminating feature: it drastically rearranges a network of proximal hydrogen bonds, modifying the local architecture of a water channel and the interaction of second coordination shell residues with the manganese cluster. The two variants explain species-dependent differences in spectroscopic properties and in the interaction of substrate analogues with the oxygen-evolving complex, enabling assignment of a substrate delivery channel to the active site.
生物水氧化的位点在光合生物中高度保守，但在分类学上不同的分支之间存在着结构和电子起源不明的差异，这可以通过氧释放 MnCaO 簇的不同光谱特征和活性位点可及性的变化来揭示。对天然蓝藻形式（Thermosynechococcus vulcanus）和类菠菜形式的光系统 II 的嵌合形式的原子模型的比较，使我们能够确定锰簇附近生物之间的精确原子水平差异。将蓝藻 D1-Asn87 替换为高等植物 D1-Ala87 是主要的鉴别特征：它彻底重新排列了一个氢键网络，改变了水通道的局部结构以及第二配位壳残基与锰簇的相互作用。这两种变体解释了光谱特性和底物类似物与氧释放复合物相互作用的种间差异，从而使底物输送通道能够被分配到活性位点。
