Structural and electronic properties of the [FeFe] hydrogenase H-cluster in different redox and protonation states. A DFT investigation
Structural and electronic properties of the [FeFe] hydrogenase H-cluster in different redox and protonation states. A DFT investigation
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DOI：
10.1021/ic8006298
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发表时间：
2008-07-07
影响因子：
4.6
通讯作者：
De Gioia, Luca
中科院分区：
文献类型：
--
作者：
Bruschi, Maurizio;Greco, Claudio;De Gioia, Luca
用密度泛函理论研究了[FeFe]氢酶的Fe6S6H-簇在相应的氧化还原和质子化状态下的分子和电子结构。计算采用破坏对称法，并考虑了不同的环境条件。在真空中，H团簇的大负电荷导致了与实验观察到的蛋白质结构不同的结构。对于溶剂化的络合物，观察到了与实验数据更好的一致性，这表明蛋白质环境可以缓冲H-簇的大负电荷。Fe6S6和Fe2S2DFT模型的比较表明，Fe4S4部分的存在对[2Fe](H)团簇的几何形状没有明显的影响。特别是，单独的Fe4S4簇不能解释酶中观察到的Mu-CO形式的稳定性(相对于所有末端的CO物种)。至于氢团簇的质子化，结果表明，Mu-H物种总是比末端氢化物异构体更稳定，从而得出结论：为了颠倒Mu-H和末端氢化物的稳定顺序，我们的计算中没有考虑H-团簇与环境的特定相互作用。此外，金属中心的质子化和酶中H-2的释放被预测为动力学控制的过程。最后，H团簇环境中的细微变化可以改变关键前线轨道的相对稳定性，触发形成H团簇的Fe4S4和Fe2S2部分之间的电子转移。
The molecular and electronic structure of the Fe6S6 H-cluster of [FeFe] hydrogenase in relevant redox and protonation states have been investigated by DFT. The calculations have been carried out according to the broken symmetry approach and considering different environmental conditions. The large negative charge of the H-cluster leads, in a vacuum, to structures different from those observed experimentally in the protein. A better agreement with experimental data is observed for solvated complexes, suggesting that the protein environment could buffer the large negative charge of the H-cluster. The comparison of Fe6S6 and Fe2S2 DFT models shows that the presence of the Fe4S4 moiety does not affect appreciably the geometry of the [2Fe](H) cluster. In particular, the Fe4S4 cluster alone cannot be invoked to explain the stabilization of the mu-CO forms observed in the enzyme (relative to all-terminal CO species). As for protonation of the hydrogen cluster, it turned out that mu-H species are always more stable than terminal hydride isomers, leading to the conclusion that specific interactions of the H-cluster with the environment, not considered in our calculations, would be necessary to reverse the stability order of mu-H and terminal hydrides. Otherwise, protonation of the metal center and H-2 evolution in the enzyme are predicted to be kinetically controlled processes. Finally, subtle modifications in the H-cluster environment can change the relative stability of key frontier orbitals, triggering electron transfer between the Fe4S4 and the Fe2S2 moieties forming the H-cluster.