A density functional theory investigation of Fe-N-O bonding in heme proteins and model systems.
A density functional theory investigation of Fe-N-O bonding in heme proteins and model systems.
复制标题
血红素蛋白和模型系统中 Fe-N-O 键合的密度泛函理论研究。
DOI：
10.1021/ja030340v
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
Oldfield,Eric
中科院分区：
文献类型：
--
作者：
Zhang,Yong;Gossman,William;Oldfield,Eric
本文报道了用密度泛函理论计算无铁血红素模型化合物的穆斯堡尔四极分裂和异构体位移的结果，以及模型Fe(II)(NO)(咪唑)络合物的穆斯堡尔四极分裂、异构体位移和电子顺磁共振超精细耦合常数随Fe−NO键长和Fe−N−O键角变化的计算结果。对非血红素模型化合物的穆斯堡尔四极分裂和同分异构体位移的计算结果表明，理论和实验符合得很好，最大误差出现在具有最大结晶学R1值的结构上。然后，利用属性面计算的结果，使用能量滤光片，计算了亚硝基血红蛋白的Fe−NO键长和Fe−N−O键角概率面(Z面)。结果表明，Fe-−-NO键长(R)和Fe-−-N-−-O键角(β)分别为1.79和136°−-137°。这种键长比在大多数模型化合物中观察到的要长一些，但可能至少部分是由于与远端His残基形成氢键所致。对咪唑残基上的Fe(II)(NO)(咪唑)络合物氢键进行了几何构型优化，得到−=1.76，β=137°−138°，并观察到了键的伸长。计算的键角接近于大多数模型体系中发现的典型∼140°值。高弯曲的Fe−N−O键角或很长的Fe−NO键长似乎不太可能在蛋白质中出现，因为它们的能量很高。我们还研究了六个坐标系中的分子轨道和自旋密度，发现轨道和自旋密度与前面描述的五个坐标系中的轨道和自旋密度大体相似。综上所述，这些结果表明，除了电子顺磁共振超精细耦合常数外，现在还可以较准确地计算亚硝基血红素体系的穆斯堡尔四极分裂和异构体位移，所得到的结果可用于确定金属蛋白中的Fe−N−O几何构型。因此，Z表面方法适用于抗磁(CO)和顺磁(NO)血红素蛋白，在这两种情况下，在蛋白质中发现的金属−配体结合几何非常接近于模型体系中的几何构型。
We report the results of a series of density functional theory (DFT) calculations of the Mössbauer quadrupole splittings and isomer shifts in NO heme model compounds, together with the results of calculations of the Mössbauer quadrupole splittings, isomer shifts, and electron paramagnetic resonance hyperfine coupling constants in a model Fe(II)(NO)(imidazole) complex as a function of Fe−NO bond length and Fe−N−O bond angle. The results of the Mössbauer quadrupole splitting and isomer shift calculations on the NO heme model compounds show good accord between theory and experiment, with the largest errors being observed for structures having the largest crystallographicR1values. The results of the property surface calculations were then used to calculate Fe−NO bond length and Fe−N−O bond angle probability surfaces (Z-surfaces) for a nitrosyl hemoglobin, using, in addition, an energy filter. The results obtained yielded a most probable Fe−NO bond length (r) of 1.79 Å and an Fe−N−O bond angle (β) of 136°−137°. This bond length is somewhat longer than those observed in most model compounds but may be due, at least in part, to hydrogen bond formation with the distal His residue. Bond elongation was also observed in a geometry optimized Fe(II)(NO)(imidazole) complex hydrogen bonded to an imidazole residue, in which we findr= 1.76−1.78 Å and β = 137°−138°. The computed bond angles are close to the canonical ∼140° value found in most model systems. Highly bent Fe−N−O bond angles or very long Fe−NO bond lengths seem unlikely to occur in proteins, due to their high energies. We also investigated the molecular orbitals and spin densities in each of the six coordinate systems investigated and found the orbitals and spin densities to be generally similar those described previously for five coordinate systems. Taken together, these results show that Mössbauer quadrupole splittings and isomer shifts, in addition to electron paramagnetic resonance hyperfine coupling constants, can now be calculated for nitrosyl heme systems with relatively good accuracy and that the results so obtained can be used to determine Fe−N−O geometries in metalloproteins. The Z-surface approach is thus applicable to both diamagnetic (CO) and paramagnetic (NO) heme proteins with in both cases the metal−ligand binding geometries found in the proteins being very close to those seen in model systems.