1887

Abstract

possesses two aconitases, a stationary-phase enzyme (AcnA), which is induced by iron and oxidative stress, and a major but less stable enzyme (AcnB), synthesized during exponential growth. In addition to the catalytic activities of the holo-proteins, the apo-proteins function as post-transcriptional regulators by site-specific binding to mRNAs. Thus, it has been suggested that inactivation of the enzymes could mediate a rapidly reacting post-transcriptional component of the bacterial oxidative stress response. Here it is shown that mutants are hypersensitive to the redox-stress reagents HO and methyl viologen. Proteomic analyses further revealed that the level of superoxide dismutase (SodA) is enhanced in and mutants, and by exposure to methyl viologen. The amounts of other proteins, including thioredoxin reductase, 2-oxoglutarate dehydrogenase, succinyl-CoA synthetase and chaperone proteins, were also affected in the mutants. The altered patterns of expression were confirmed in studies with reporter strains. Quantitative Northern blotting indicated that AcnA enhances the stability of the transcript, whereas AcnB lowers its stability. Direct evidence that the apo-proteins have positive (AcnA) and negative (AcnB) effects on SodA synthesis was obtained from transcription–translation experiments. It is suggested that the aconitase proteins of serve as a protective buffer against the basal level of oxidative stress that accompanies aerobic growth by acting as a sink for reactive oxygen species and by modulating translation of the transcript.

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2002-04-01
2019-10-22
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