Computational studies of the H-cluster of Fe-only hydrogenases:: Geometric, electronic, and magnetic properties and their dependence on the [Fe4S4] cubane
Computational studies of the H-cluster of Fe-only hydrogenases:: Geometric, electronic, and magnetic properties and their dependence on the [Fe4S4] cubane
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DOI：
10.1021/ic050946f
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发表时间：
2005-12-12
影响因子：
4.6
通讯作者：
Brunold, TC
中科院分区：
文献类型：
--
作者：
Fiedler, AT;Brunold, TC
铁氢化酶（FeHases）的活性位点具有不寻常的多核铁硫簇，称为H簇，其由通过桥接半胱氨酸配体（S-Cys）连接到二铁亚基（[2Fe]（H）组分）的[Fe4S4]立方烷组成。虽然以前的计算研究FeHases采用H-簇模型，只包括[2Fe] H组件，我们利用密度泛函理论（DFT），结合破缺对称（BS）的方法，探索整个H-簇的几何，电子和磁性。这些计算使我们能够评估，为第一次，在其活性（H-ox）和CO抑制（H-ox-CO）状态下的H-簇的[2Fe]（H）组分的影响，这两个都是顺磁性的（S = 1/2）。我们的研究结果表明，立方烷的存在调节了S-Cys配体的位置和给体强度，进而调节了[2Fe]（H）亚簇的内部几何结构和电子结构.重要的是，BS方法提供了H-团簇内交换相互作用的准确描述，允许洞察在H-ox转化为H-ox-CO时实验观察到的磁性变化的电子起源。具体地说，虽然H-ox状态下的未成对自旋密度位于远端Fe中心，但在H-ox-CO状态下，它在[2Fe]（H）组分上离域，使得近端Fe中心获得显著的自旋密度（其中远端和近端是指Fe中心相对于立方烷的位置）。为了验证我们的H团簇模型的实验数据的基础上，两个DFT为基础的方法和半经验INDO/S方法已被用来计算电子顺磁共振参数的H团簇状态。虽然大多数计算产生相当准确的g值和配体超精细耦合常数（即，A值）的H-ox和H-ox-CO状态，他们未能再现实验发现的各向同性Fe-57 A张量。最后，将成功用于H-ox和H-ox-CO态的计算方法扩展到亚稳态H-ox "光态，通过在低温下照射H-ox-CO态产生，使我们能够区分这种物质的拟议结构模型。
The active sites of Fe-only hydrogenases (FeHases) feature an unusual polynuclear iron-sulfur cluster, known as the H-cluster, that consists of a [Fe4S4] cubane linked to a di-iron subunit (the [2Fe](H) component) via a bridging cysteine ligand (S-Cys). While previous computational studies of FeHases employed H-cluster models that only included the [2Fe]H component, we have utilized density functional theory (DFT), in conjunction with the broken-symmetry (BS) approach, to explore the geometric, electronic, and magnetic properties of the entire H-cluster. These calculations have allowed us to evaluate, for the first time, the influence of the [Fe4S4] cubane on the [2Fe](H) component of the H-cluster in its active (H-ox) and CO-inhibited (H-ox-CO) states, both of which are paramagnetic (S = 1/2). Our results reveal that the presence of the cubane tunes both the position and the donor strength of the S-Cys ligand, which, in turn, modulates the internal geometric and electronic structures of the [2Fe](H) subduster. Importantly, the BS methodology provides an accurate description of the exchange interactions within the H-cluster, permitting insight into the electronic origin of the changes in magnetic properties observed experimentally upon conversion of H-ox to H-ox-CO. Specifically, while the unpaired spin density in the H-ox state is localized on the distal Fe center, in the H-ox-CO state, it is delocalized over the [2Fe](H) component, such that the proximal Fe center acquires significant spin density (where distal and proximal refer to the positions of the Fe centers relative to the cubane). To validate our H-cluster models on the basis of experimental data, two DFT-based approaches and the semiempirical INDO/S method have been employed to compute electron paramagnetic resonance parameters for the H-cluster states. While most computations yield reasonably accurate g values and ligand hyperfine coupling constants (i.e., A values) for the H-ox and H-ox-CO states, they fail to reproduce the isotropic Fe-57 A tensors found experimentally. Finally, extension of the computational methodology employed successfully for the H-ox and H-ox-CO states to the metastable H-ox "photo state, generated by irradiation of the H-ox-CO state at cryogenic temperatures, has allowed us to discriminate between proposed structural models for this species.