Superoxide accelerates DNA damage by elevating free-iron levels
Superoxide accelerates DNA damage by elevating free-iron levels
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DOI：
10.1073/pnas.93.24.13635
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发表时间：
1996-11-26
影响因子：
11.1
通讯作者：
Imlay, JA
中科院分区：
文献类型：
--
作者：
Keyer, K;Imlay, JA
超氧化物促进羟基自由基的形成，并导致所有类型细胞中的DNA损伤。长期以来的假设，即它主要是通过提供电子给DNA上的外来铁，被最近在大肠杆菌中的研究所驳斥。其他建议表明，超氧化物可能会加速氧化DNA损伤的浸出铁从存储蛋白质或酶[4Fe-4S]集群。释放出的铁可能会存款在DNA的表面，在那里它可以催化形成DNA氧化剂使用其他电子供体。后一种模型被这里描述的实验所证实。全细胞电子顺磁共振表明，超氧化物应激细胞中的松散铁水平大大超过未应激细胞。细菌铁储存蛋白不是游离铁的主要来源，因为超氧化物也增加了缺乏这些铁储存蛋白的突变体中的铁水平。然而，当细胞在空气中生长时，含有不稳定的[4Fe-4S]簇的酶的过量产生显著增加了细胞的游离铁含量。外源性H_2O_2引起的自发突变率和DNA损伤率也随之增加。令人惊讶的是，超氧化物引起的生长缺陷和DNA损伤都是由于其破坏铁硫簇的能力。
Superoxide promotes hydroxyl-radical formation and consequent DNA damage in cells of all types. The long-standing hypothesis that it primarily does so by delivering electrons to adventitious iron on DNA was refuted by recent studies in Escherichia coli. Alternative proposals have suggested that superoxide may accelerate oxidative DNA damage by leaching iron from storage proteins or enzymic [4Fe-4S] clusters. The released iron might then deposit on the surface of the DNA, where it could catalyze the formation of DNA oxidants using other electron donors. The latter model is affirmed by the experiments described here. Whole-cell electron paramagnetic resonance demonstrated that the level of loose iron in superoxide-stressed cells greatly exceeds that of unstressed cells. Bacterial iron storage proteins were not the major source for free iron, since superoxide also increased iron levels in mutants lacking these iron storage proteins. However, overproduction of an enzyme containing a labile [4Fe-4S] cluster dramatically increased the free iron content of cells when they were growing in air. The rates of spontaneous mutagenesis and DNA damage from exogenous H2O2 increased commensurately. It is striking that both growth defects and DNA damage caused by superoxide ensue from its ability to damage a subset of iron-sulfur clusters.