Bacterial Cu/Zn-superoxide dismutase (SodC) is an enzyme catalyzing the disproportionation of superoxide radicals, to which the binding of copper and zinc ions and the formation of an intramolecular disulfide bond are essential. We previously showed that Escherichia coli SodC (SodC) was prone to spontaneous degradation in vivo in an immature form prior to the introduction of the disulfide bond. The post-translational maintenance involving the metal binding and the disulfide formation would thus control the stability as well as the enzymatic function of SodC; however, a mechanism of the SodC maturation remains obscure. Here, we show that the disulfide-reduced SodC can secure a copper ion as well as a zinc ion through the thiolate groups. Furthermore, the disulfide-reduced SodC was found to bind cuprous and cupric ions more tightly than SodC with the disulfide bond. The thiolate groups ligating the copper ion were then autooxidized to form the intramolecular disulfide bond, leading to the production of enzymatically active SodC. Based upon the experiments in vitro, therefore, we propose a mechanism for the activation of SodC, in which the conserved Cys residues play a dual role: the acquisition of a copper ion for the enzymatic activity and the formation of the disulfide bond for the structural stabilization.

中文翻译：

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半胱氨酸残基在原核生物铜/锌超氧化物歧化酶成熟中的双重作用。

细菌 Cu/Zn-超氧化物歧化酶 (SodC) 是一种催化超氧自由基歧化的酶，其中铜和锌离子的结合和分子内二硫键的形成是必不可少的。我们之前表明，在引入二硫键之前，大肠杆菌 SodC (SodC) 易于在体内以未成熟的形式自发降解。因此，涉及金属结合和二硫化物形成的翻译后维持将控制 SodC 的稳定性和酶促功能；然而，SodC 成熟的机制仍然不清楚。在这里，我们表明二硫化物还原的 SodC 可以通过硫醇基团确保铜离子和锌离子。此外，发现二硫键还原的 SodC 比具有二硫键的 SodC 更紧密地结合亚铜和铜离子。然后将连接铜离子的硫醇基自动氧化形成分子内二硫键，从而产生具有酶活性的 SodC。因此，基于体外实验，我们提出了一种激活 SodC 的机制，其中保守的 Cys 残基发挥双重作用：获得铜离子用于酶活性和形成二硫键用于结构稳定。