Sulfur K-Edge XAS and DFT calculations on nitrile hydratase: Geometric and electronic structure of the non-heme iron active site
Sulfur K-Edge XAS and DFT calculations on nitrile hydratase: Geometric and electronic structure of the non-heme iron active site
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DOI：
10.1021/ja0549695
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发表时间：
2006-01-18
影响因子：
15
通讯作者：
Solomon, EI
中科院分区：
文献类型：
--
作者：
Dey, A;Chow, M;Solomon, EI
用硫K边XAS和密度泛函理论方法研究了非血红素铁酶腈水合酶(NHase)活性中心的几何结构和电子结构。用硫酸盐(RS-)、亚硫酸盐(RSO-)和亚硫酸盐(RSO2-)连接的模型络合物提供基准光谱参数，结果表明S K边XAS对含S配体的氧化态很敏感，并且随着S-O键的拉长(类似于0.1埃)，RSO-物种的光谱随着质子化而发生变化。这些特征被用来鉴定与NHase活性中心中低自旋Fe-III配位的三个半胱氨酸残基为CysS(-)、CysSOH和CySSO2-两者都处于非结合的非活性形式和光解活性形式。这些结果与几何优化的DFT计算相关联。X射线吸收光谱的前缘区对Fe的Z(Ef)很敏感，表明[FeNO](6)NHase物种中的Fe具有与其光解的Fe-III相类似的Z(Ef)。密度泛函理论计算表明，这是由于强pi反键进入NO的pi*反键轨道，从而将大量电荷从形式上的t(2)(6)低自旋金属转移到配位的NO。
The geometric and electronic structure of the active site of the non-heme iron enzyme nitrile hydratase (NHase) is studied using sulfur K-edge XAS and DFT calculations. Using thiolate (RS-)-, sulfenate (RSO-)-, and sulfinate (RSO2-)-ligated model complexes to provide benchmark spectral parameters, the results show that the S K-edge XAS is sensitive to the oxidation state of S-containing ligands and that the spectrum of the RSO- species changes upon protonation as the S-O bond is elongated (by similar to 0.1 angstrom). These signature features are used to identify the three cysteine residues coordinated to the low-spin Fe-III in the active site of NHase as CysS(-), CysSOH, and CYSSO2- both in the NO-bound inactive form and in the photolyzed active form. These results are correlated to geometry-optimized DFT calculations. The preedge region of the X-ray absorption spectrum is sensitive to the Z(eff) of the Fe and reveals that the Fe in [FeNO](6) NHase species has a Z(eff) very similar to that of its photolyzed Fe-III counterpart. DFT calculations reveal that this results from the strong pi back-bonding into the pi* antibonding orbital of NO, which shifts significant charge from the formally t(2)(6) low-spin metal to the coordinated NO.