Glucose-6-Phosphate Dehydrogenase Protects Escherichia coli from Tellurite-Mediated Oxidative Stress

Abstract

The tellurium oxyanion tellurite induces oxidative stress in most microorganisms. In Escherichia coli, tellurite exposure results in high levels of oxidized proteins and membrane lipid peroxides, inactivation of oxidation-sensitive enzymes and reduced glutathione content. In this work, we show that tellurite-exposed E. coli exhibits transcriptional activation of the zwf gene, encoding glucose 6-phosphate dehydrogenase (G6PDH), which in turn results in augmented synthesis of reduced nicotinamide adenine dinucleotide phosphate (NADPH). Increased zwf transcription under tellurite stress results mainly from reactive oxygen species (ROS) generation and not from a depletion of cellular glutathione. In addition, the observed increase of G6PDH activity was paralleled by accumulation of glucose-6-phosphate (G6P), suggesting a metabolic flux shift toward the pentose phosphate shunt. Upon zwf overexpression, bacterial cells also show increased levels of antioxidant molecules (NADPH, GSH), better-protected oxidation-sensitive enzymes and decreased amounts of oxidized proteins and membrane lipids. These results suggest that by increasing NADPH content, G6PDH plays an important role in E. coli survival under tellurite stress.

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“…To determine the kinetic parameters for the isomerization of F6P to G6P catalyzed by Q5LIW1, a coupled assay was used, in which the G6P produced by Q5LIW1 was oxidized to 6-phosphoglucono-␦-lactone by glucose-6-phosphate dehydrogenase and the cofactor NADP ϩ . The formation of NADPH was measured at 340 nm, which allowed for reaction progress to be monitored (17). Individual reactions were performed in a quartz cuvette, in triplicate.…”

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“…molecules glutathione and nicotinamide adenine dinucleotide phosphate. 46 Glutamate decarboxylase has been shown to play an important role in antioxidation in E coli O157:H7 and Saccharomyces cerevisiae. 47,48 In addition, glyoxylate and dicarboxylate metabolism was shown to be involved in the antioxidation process.…”

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