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首页> 外文期刊>Chemistry: A European journal >Bridge Over Troubled Water:Resolving the Competing Photosystem II Crystal Structures
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Bridge Over Troubled Water:Resolving the Competing Photosystem II Crystal Structures

机译：困扰水上的桥梁：解决竞争的Photosystem II晶体结构

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摘要

Density functional theory (DFT) calculations,at the Becke-Perdew/TZP level of theory,were used to investigate a set of CaMn4-contain-ing clusters that model the active site of the water-oxidizing complex (WOC) of photosystem II (PSII).Metal-atom positions for three representative isomeric clusters of the formula [CaMn4C9N2O16H10]+4H2O are in good agreement with the disparate Mn4 geometries of the three most recent X-ray crystal structures.Remarkably,in-terconversion between these three isomeric clusters is found to be facile,resulting from subtle changes in the coor-dination environment around the CaMn4 centre.This result provides a clear rationalisation of the marked differences in reported crystal structures.Recent concerns have been raised regarding the opportunity for X-ray-damage-induced distortion of the metal-containing active centre during crystallographic analysis.Our calcula-tions suggest that an even greater problem may be presented by the apparent fluxionality of the CaMn4 skeleton within the active centre.Structural rearrangement may well precede crystallographic analysis,for example by the preferential "freezing-out" of one of several near-isoenergetic structures during the workup for crystallisation.This prospect,which our calculations cannot exclude,highlights the difficulties that will continue to be faced by experimentalists seeking unambiguous structural information on the WOC's active site.
机译：在Becke-Perdew / TZP理论水平上的密度泛函理论（DFT）计算用于研究一组包含CaMn4的簇，这些簇模拟了光系统II的水氧化复合物（WOC）的活性位点（ PSII）。分子式为[CaMn4C9N2O16H10] + 4H2O的三个代表性异构簇的金属原子位置与最新的三个X射线晶体结构的Mn4几何形状非常吻合。值得注意的是，这三个异构簇之间的相互转换由于CaMn4中心周围的配位环境发生了细微的变化，因此被发现很容易。这一结果为报道的晶体结构的明显差异提供了合理的理由。最近人们对X射线损坏的可能性提出了关注。在晶体学分析中引起含金属活性中心的扭曲。我们的计算表明，CaMn4的表观通量可能会带来更大的问题结构重排可能早于晶体学分析，例如在结晶处理期间通过优先“冻结”几种近等能结构之一来冻结。我们的计算不能排除这一前景，突出了困难。在WOC的活动现场寻求明确结构信息的实验人员将继续面临这种挑战。

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