Spectroscopic and computational insights into second-sphere amino-acid tuning of substrate analogue/active-site interactions in iron(III) superoxide dismutase.
Spectroscopic and computational insights into second-sphere amino-acid tuning of substrate analogue/active-site interactions in iron(III) superoxide dismutase.
复制标题
对铁（III）超氧化物歧化酶中底物类似物/活性位点相互作用的第二球氨基酸调节的光谱和计算见解。
DOI：
10.1021/ic702414m
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发表时间：
2008
影响因子：
4.6
通讯作者：
Brunold,ThomasC
中科院分区：
文献类型：
--
作者：
Grove,LaurieE;Xie,Juan;Yikilmaz,Emine;Karapetyan,Anush;Miller,Anne-Frances;Brunold,ThomasC
在这项研究中，第二球残基调制的铁依赖性超氧化物歧化酶（FeSOD）的底物类似物复合物的结构和电子性质的机制进行了探索。利用光谱和计算方法研究了Fe 3 +SOD（N3− Fe 3 +SOD）及其Q69 E突变体，以及Fe 3+取代的MnSOD（N3 − Fe 3+（Mn）SOD）及其Y34 F突变体的叠氮（N3−）加合物。电子吸收、圆二色性和磁性圆二色性光谱数据表明，主要的N3−→ Fe 3+配体-金属电荷转移（LMCT）跃迁的能量按N3− Fe 3+（Mn）SOD > N3− Fe 3 +SOD > Q69 E N3− Fe 3 +SOD的顺序降低。有趣的是，LMCT跃迁能几乎与不存在叠氮化物的情况下相应的Fe 3+结合SOD物种的Fe 3 +/2+还原电位线性相关，其范围为1001 V（见前一篇论文）。为了探索这种相关性的起源，结合量子力学/分子力学（QM/MM）的几何优化进行完整的酶模型。INDO/S-CI计算的电子跃迁能与实验结果吻合较好，表明QM/MM优化的活性位模型是合理的.对这些实验验证的活性中心模型的密度泛函理论计算表明，四种N3−加合物之间光谱和电子性质的差异主要来自于涉及保守的第二球谷氨酰胺（在Q69 E FeSOD中突变为Glu）和溶剂配体的氢键网络的差异。我们的研究结果与第二协调领域调制底物类似物结合的机制，以及FeSOD的催化性能的影响进行了讨论。
In this study, the mechanism by which second-sphere residues modulate the structural and electronic properties of substrate-analogue complexes of the Fe-dependent superoxide dismutase (FeSOD) has been explored. Both spectroscopic and computational methods were used to investigate the azide (N3−) adducts of Fe3+SOD (N3−Fe3+SOD) and its Q69E mutant, as well as Fe3+-substituted MnSOD (N3−Fe3+(Mn)SOD) and its Y34F mutant. Electronic absorption, circular dichroism, and magnetic circular dichroism spectroscopic data reveal that the energy of the dominant N3−→ Fe3+ligand-to-metal charge transfer (LMCT) transition decreases in the order N3−Fe3+(Mn)SOD > N3−Fe3+SOD > Q69E N3−Fe3+SOD. Intriguingly, the LMCT transition energies correlate almost linearly with the Fe3+/2+reduction potentials of the corresponding Fe3+-bound SOD species in the absence of azide, which span a range of ∼1 V (see the preceding paper). To explore the origin of this correlation, combined quantum mechanics/molecular mechanics (QM/MM) geometry optimizations were performed on complete enzyme models. The INDO/S−CI computed electronic transition energies satisfactorily reproduce the experimental trend in LMCT transition energies, indicating that the QM/MM optimized active-site models are reasonable. Density functional theory calculations on these experimentally validated active-site models reveal that the differences in spectral and electronic properties among the four N3−adducts arise primarily from differences in the hydrogen-bond network involving the conserved second-sphere Gln (mutated to Glu in Q69E FeSOD) and the solvent ligand. The implications of our findings with respect to the mechanism by which the second-coordination sphere modulates substrate−analogue binding as well as the catalytic properties of FeSOD are discussed.