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Abstract:
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Modulation of bacterial chromosomal supercoiling is a function of DNA
gyrase-catalyzed strand breakage and rejoining. This reaction is exploited by both
antibiotic and proteic gyrase inhibitors, which trap the gyrase molecule at the DNA cleavage
stage. Owing to this interaction, double-stranded DNA breaks are introduced and replication
machinery is arrested at blocked replication forks. This immediately results in
bacteriostasis and ultimately induces cell death. Here we demonstrate, through a series of
phenotypic and gene expression analyses, that superoxide and hydroxyl radical oxidative
species are generated following gyrase poisoning and play an important role in cell killing
by gyrase inhibitors. We show that superoxide-mediated oxidation of iron�sulfur clusters
promotes a breakdown of iron regulatory dynamics; in turn, iron misregulation drives the
generation of highly destructive hydroxyl radicals via the Fenton reaction. Importantly, our
data reveal that blockage of hydroxyl radical formation increases the survival of
gyrase-poisoned cells. Together, this series of biochemical reactions appears to compose a
maladaptive response, that serves to amplify the primary effect of gyrase inhibition by
oxidatively damaging DNA, proteins and lipids. |
