Second-sphere contributions to substrate-analogue binding in iron(III) superoxide dismutase.
Second-sphere contributions to substrate-analogue binding in iron(III) superoxide dismutase.
复制标题
第二领域对铁（III）超氧化物歧化酶中底物类似物结合的贡献。
DOI：
10.1021/ja016254h
复制
发表时间：
2002
影响因子：
15
通讯作者：
Brunold,ThomasC
中科院分区：
文献类型：
--
作者：
Xie,Juan;Yikilmaz,Emine;Miller,Anne-Frances;Brunold,ThomasC
使用光谱和计算方法相结合的方法来探索黄色和粉红色低温叠氮化铁(III)超氧化物歧化酶(N3FeSODFeSOD2)加合物的性质，这种加合物已经被人们发现了20多年。变温变场磁性圆二色谱(MCD)数据表明，这两个物种都具有相似的铁中心，只有一个叠氮化物配体结合，这与之前提出的以粉红色形式调用两个叠氮化物配体的提议相矛盾。对Q69E−突变体叠氮络合物的补充数据表明，金属中心环境中相对较小的扰动足以产生显著的光谱变化；Q69E N3 FeSOD物种在所有温度下都是红色的。野生型和Q69E突变体N3−FeSOD络合物的共振拉曼(RR)光谱与所有三个物种中类似的Fe−N3单元一致；然而，与此单元相关的RR特征的能量和相对强度的变化揭示了(N3-)−Fe3+键的细微差异。为了在定量水平上理解这些差异，我们用密度泛函理论和半经验的INDO/S-CI方法对N3−铁超氧化物歧化模型进行了计算。这些计算支持我们的模型，即在所有三个−−加合物中都存在一个叠氮配体，并表明它们不同的外观反映了Fe-−-N-FeSODN键角的差异。Fe−N−N键角增加10°足以解释黄色和粉色野生型N3−FeSOD种之间的光谱差异。我们发现这个键角受到第二配位球的强烈影响，因此第二配位球也可能在引导输入底物与FeSOD活性中心反应的方向上发挥重要作用。
A combination of spectroscopic and computational methods has been employed to explore the nature of the yellow and pink low-temperature azide adducts of iron(III) superoxide dismutase (N3−FeSOD), which have been known for more than two decades. Variable-temperature variable-field magnetic circular dichroism (MCD) data suggest that both species possess similar ferric centers with a single azide ligand bound, contradicting previous proposals invoking two azide ligands in the pink form. Complementary data obtained on the azide complex of the Q69E FeSOD mutant reveal that relatively minor perturbations in the metal-center environment are sufficient to produce significant spectral changes; the Q69E N3−FeSOD species is red in color at all temperatures. Resonance Raman (RR) spectra of the wild-type and Q69E mutant N3−FeSOD complexes are consistent with similar Fe−N3units in all three species; however, variations in energies and relative intensities of the RR features associated with this unit reveal subtle differences in (N3-)−Fe3+bonding. To understand these differences on a quantitative level, density functional theory and semiempirical INDO/S-CI calculations have been performed on N3−FeSOD models. These computations support our model that a single azide ligand is present in all three N3−FeSOD adducts and suggest that their different appearances reflect differences in the Fe−N−N bond angle. A 10° increase in the Fe−N−N bond angle is sufficient to account for the spectral differences between the yellow and pink wild-type N3−FeSOD species. We show that this bond angle is strongly affected by the second coordination sphere, which therefore might also play an important role in orienting incoming substrate for reaction with the FeSOD active site.