New insights into the role of Fur proteins: FurB (All2473) from Anabaena protects DNA and increases cell survival under oxidative stress
Résumé
The ferric uptake regulator (Fur) is a prokaryotic transcriptional regulator that controls a large number of genes mainly related to iron metabolism. Frequently, several Fur homologues with different physiological roles are found in the same organism. The genome of the filamentous cyanobacterium Anabaena (Nostoc) sp. PCC 7120 codes for three different fur genes. FurA is an essential protein involved in iron homeostasis that also modulates dinitrogen fixation. FurA interacts with heme, impairing its DNA-binding ability. To explore functional differences between Fur homologues in Anabaena, factors affecting their regulation, as well as some biochemical characteristics have been investigated. While incubation of FurB with heme severely hinders it ability to interact with DNA, binding of heme to FurC could not be detected. Oxidative stress enhances the transcription of the three fur genes, especially of furB and furC. In addition, overexpression of FurA and FurB in E. coli increases survival when the cells are challenged with hydrogen peroxide or methyl viologen, a superoxide anion-generating reagent. When present in saturating concentrations, FurB exhibits unspecific DNA-binding activity and protects DNA from cleavage produced by hydroxyl radicals or DNaseI. Based on these results, it can be suggested that whereas at low concentration FurB would act as a member of the Fur family, at saturating concentrations FurB protects DNA, showing a Dps (DNA protection during starvation)-like behaviour.
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