Superoxide poisons mononuclear iron enzymes by causing mismetallation
Superoxide poisons mononuclear iron enzymes by causing mismetallation
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DOI：
10.1111/mmi.12263
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发表时间：
2013-07-01
影响因子：
3.6
通讯作者：
Imlay, James A.
中科院分区：
文献类型：
--
作者：
Gu, Mianzhi;Imlay, James A.
超氧化物 (O2-) 是细胞内氧化应激的主要因素。许多生物体的遗传学研究已证实过量的 O2- 会扰乱新陈代谢，但迄今为止，只有一小部分 [4Fe-4S] 脱水酶被确定为直接靶标。这项研究表明，在大肠杆菌中，O2- 还会毒害更广泛的非氧化还原酶，这些酶采用亚铁原子作为催化辅助因子。这些酶在体外和体内均被 O2- 灭活。尽管这些酶是已知的过氧化氢目标，但 O2- 的结果却有很大不同。当纯化的酶在体外被O2-损伤时，通过添加铁可以完全恢复活性，这表明O2-处理产生了脱辅基蛋白而不损伤蛋白多肽。细胞内的超氧化物应激导致这些酶与锌逐渐错位，从而几乎没有活性。当氧气应激终止时，细胞通过从蛋白质中提取锌逐渐恢复活性。即使没有氧气压力，电池中锌的过载也会导致金属错位。这些结果支持了一个模型，其中 O2- 反复从这些酶中切除铁，使锌与铁竞争其脱辅基蛋白形式的重金属化。这一作用大大扩展了 O2- 应激的生理印记。
Superoxide (O2-) is a primary agent of intracellular oxidative stress. Genetic studies in many organisms have confirmed that excess O2- disrupts metabolism, but to date only a small family of [4Fe-4S] dehydratases have been identified as direct targets. This investigation reveals that in Escherichia coliO2- also poisons a broader cohort of non-redox enzymes that employ ferrous iron atoms as catalytic cofactors. These enzymes were inactivated by O2- both in vitro and in vivo. Although the enzymes are known targets of hydrogen peroxide, the outcome with O2- differs substantially. When purified enzymes were damaged by O2- in vitro, activity could be completely restored by iron addition, indicating that the O2- treatment generated an apoprotein without damaging the protein polypeptide. Superoxide stress inside cells caused the progressive mismetallation of these enzymes with zinc, which confers little activity. When O2- stress was terminated, cells gradually restored activity by extracting zinc from the proteins. The overloading of cells with zinc caused mismetallation even without O2- stress. These results support a model in which O2- repeatedly excises iron from these enzymes, allowing zinc to compete with iron for remetallation of their apoprotein forms. This action substantially expands the physiological imprint of O2- stress.