Synthetic model of the asymmetric [Mn3CaO4] cubane core of the oxygen-evolving complex of photosystem II
Synthetic model of the asymmetric [Mn3CaO4] cubane core of the oxygen-evolving complex of photosystem II
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DOI：
10.1073/pnas.1115290109
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发表时间：
2012-02-14
影响因子：
11.1
通讯作者：
Christou, George
中科院分区：
文献类型：
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作者：
Mukherjee, Shreya;Stull, Jamie A.;Christou, George
自20世纪70年代初以来，光系统II的出氧络合物（OEC）的实验室合成一直是合成化学家的目标。但是，由于缺乏关于经合组织的结构性资料，妨碍了这些努力。在过去十年中，关于光系统II的晶体学报告以不断提高的分辨率出现，最终提供了关于OEC的宝贵结构信息，并表明它包含一个[Mn3CaO4]扭曲的立方体，其上附着第四个外部Mn原子，整个单元主要通过天冬氨酸和谷氨酸羧酸基团附着在多肽上。这种带有附加金属的异质金属Mn/Ca cubane在文献中是未知的。本文报道了一种外部金属原子结合的不对称含立方烷化合物[Mn-IV 3Ca2O4(O2CBut)(8) ((BuCO2H)-C-t)(4)(1)]的实验室合成。所有外围配体都是羧酸盐或羧酸基。变温磁化率数据已确定1具有S 9/2基态。EPR谱证实了这一点，Davies电子核双共振数据显示了与其他Mn-IV物质类似的超精细耦合，包括OEC S-2态。与OEC的x射线吸收数据的比较表明，1具有结构参数，使其成为不对称立方OEC单元的紧密结构模型。这种几何和电子结构的对应关系为这一重要生物单位的性质和功能的多学科研究开辟了新的前沿。
The laboratory synthesis of the oxygen-evolving complex (OEC) of photosystem II has been the objective of synthetic chemists since the early 1970s. However, the absence of structural information on the OEC has hampered these efforts. Crystallographic reports on photosystem II that have been appearing at ever-improving resolution over the past ten years have finally provided invaluable structural information on the OEC and show that it comprises a [Mn3CaO4] distorted cubane, to which is attached a fourth, external Mn atom, and the whole unit attached to polypeptides primarily by aspartate and glutamate carboxylate groups. Such a heterometallic Mn/Ca cubane with an additional metal attached to it has been unknown in the literature. This paper reports the laboratory synthesis of such an asymmetric cubane-containing compound with a bound external metal atom, [Mn-IV 3Ca2O4(O2CBut)(8) ((BuCO2H)-C-t)(4)(1)]. All peripheral ligands are carboxylate or carboxylic acid groups. Variable-temperature magnetic susceptibility data have established 1 to possess an S 9/2 ground state. EPR spectroscopy confirms this, and the Davies electron nuclear double resonance data reveal similar hyperfine couplings to those of other Mn-IV species, including the OEC S-2 state. Comparison of the X-ray absorption data with those for the OEC reveal 1 to possess structural parameters that make it a close structural model of the asymmetric-cubane OEC unit. This geometric and electronic structural correspondence opens up a new front in the multidisciplinary study of the properties and function of this important biological unit.