Geometric and electronic structures of manganese-substituted iron superoxide dismutase.
Geometric and electronic structures of manganese-substituted iron superoxide dismutase.
复制标题
锰取代的铁超氧化物歧化酶的几何和电子结构。
DOI：
10.1021/ic302867y
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发表时间：
2013
影响因子：
4.6
通讯作者：
Brunold,ThomasC
中科院分区：
文献类型：
--
作者：
Jackson,TimothyA;Gutman,CraigT;Maliekal,James;Miller,Anne-Frances;Brunold,ThomasC
锰取代的铁超氧化物歧化酶（Mn（Fe）SOD）的氧化和还原形式的活性位点结构的检查，第一次，使用光谱和计算方法相结合。电子吸收，圆二色性（CD），磁性CD（MCD），并获得氧化锰（Fe）SOD的变温变场MCD数据的基础上，我们提出，这个物种的活性位点几乎是相同的野生型锰SOD（MnSOD），都含有一个金属离子，驻留在一个三角双锥配体环境。这一建议是证实了量子力学/分子力学（QM/MM）计算Mn（Fe）SOD在其氧化和还原状态，并进行比较，野生型（WT）MnSOD完整的蛋白质模型。WT MnSOD和Mn（Fe）SOD的QM/MM优化活性位点之间的主要差异是金属取代蛋白中的（His）N-Mn-N（His）赤道角较小和（Gln 146（69））NH··O（sol）氢键距离较长。重要的是，这些适度的几何差异是一致的，我们的光谱数据获得的氧化蛋白质和高场电子顺磁共振光谱先前报道的还原锰（铁）SOD和MnSOD。由于Mn（Fe）SOD表现出比MnSOD高几乎700 mV的还原中点电位（Em），这已被证明足以解释金属取代的物质所表现出的SOD活性的缺乏（万斯，C. K.的;米勒，A. F. Biochemistry 2001，40，13079-13087），对于我们实验验证的Mn（Fe）SOD和MnSOD的QM/MM优化模型计算Em。这些计算正确地再现了实验趋势，并揭示了金属取代的蛋白质的Em急剧升高源于Mn（Fe）SOD中第二球Gln残基与配位溶剂之间的较大分离，这导致氧化态下相应的氢键相互作用减弱，并消除了还原态下的空间拥挤。
The active-site structures of the oxidized and reduced forms of manganese-substituted iron superoxide dismutase (Mn(Fe)SOD) are examined, for the first time, using a combination of spectroscopic and computational methods. On the basis of electronic absorption, circular dichroism (CD), magnetic CD (MCD), and variable-temperature variable-field MCD data obtained for oxidized Mn(Fe)SOD, we propose that the active site of this species is virtually identical to that of wild-type manganese SOD (MnSOD), with both containing a metal ion that resides in a trigonal bipyramidal ligand environment. This proposal is corroborated by quantum mechanical/molecular mechanical (QM/MM) computations performed on complete protein models of Mn(Fe)SOD in both its oxidized and reduced states and, for comparison, wild-type (WT) MnSOD. The major differences between the QM/MM optimized active sites of WT MnSOD and Mn(Fe)SOD are a smaller (His)N–Mn–N(His) equatorial angle and a longer (Gln146(69))NH···O(sol) H-bond distance in the metal-substituted protein. Importantly, these modest geometric differences are consistent with our spectroscopic data obtained for the oxidized proteins and high-field electron paramagnetic resonance spectra reported previously for reduced Mn(Fe)SOD and MnSOD. As Mn(Fe)SOD exhibits a reduction midpoint potential (Em) almost 700 mV higher than that of MnSOD, which has been shown to be sufficient for explaining the lack of SOD activity displayed by the metal-subtituted species (Vance, C. K.; Miller, A. F.Biochemistry2001,40, 13079–13087),Em’s were computed for our experimentally validated QM/MM optimized models of Mn(Fe)SOD and MnSOD. These computations properly reproduce the experimental trend and reveal that the drastically elevatedEmof the metal substituted protein stems from a larger separation between the second-sphere Gln residue and the coordinated solvent in Mn(Fe)SOD relative to MnSOD, which causes a weakening of the corresponding H-bond interaction in the oxidized state and alleviates steric crowding in the reduced state.