Affiliation:
1. Department of Microbiology, University of Illinois, Urbana, Illinois 61801
2. Department of Soil, Water, and Environmental Science, University of Arizona, Tucson, Arizona 85721
Abstract
ABSTRACT
Because copper catalyzes the conversion of H
2
O
2
to hydroxyl radicals in vitro, it has been proposed that oxidative DNA damage may be an important component of copper toxicity. Elimination of the copper export genes,
copA
,
cueO
, and
cusCFBA
, rendered
Escherichia coli
sensitive to growth inhibition by copper and provided forcing circumstances in which this hypothesis could be tested. When the cells were grown in medium supplemented with copper, the intracellular copper content increased 20-fold. However, the copper-loaded mutants were actually less sensitive to killing by H
2
O
2
than cells grown without copper supplementation. The kinetics of cell death showed that excessive intracellular copper eliminated iron-mediated oxidative killing without contributing a copper-mediated component. Measurements of mutagenesis and quantitative PCR analysis confirmed that copper decreased the rate at which H
2
O
2
damaged DNA. Electron paramagnetic resonance (EPR) spin trapping showed that the copper-dependent H
2
O
2
resistance was not caused by inhibition of the Fenton reaction, for copper-supplemented cells exhibited substantial hydroxyl radical formation. However, copper EPR spectroscopy suggested that the majority of H
2
O
2
-oxidizable copper is located in the periplasm; therefore, most of the copper-mediated hydroxyl radical formation occurs in this compartment and away from the DNA. Indeed, while
E. coli
responds to H
2
O
2
stress by inducing iron sequestration proteins, H
2
O
2
-stressed cells do not induce proteins that control copper levels. These observations do not explain how copper suppresses iron-mediated damage. However, it is clear that copper does not catalyze significant oxidative DNA damage in vivo; therefore, copper toxicity must occur by a different mechanism.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
291 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献