Abstract
Bacteria deficient in the DNA-binding protein from starved cells (Dps) are viable under controlled conditions but show dramatically increased mortality rates when exposed to any of a wide range of stresses, including starvation, oxidative stress, metal toxicity, or thermal stress. It remains unclear whether the protective action of Dps against specific stresses derives from its DNA-binding activity, which may exclude destructive agents from the chromosomal region, or its ferroxidase activity, which neutralizes and sequesters potentially damaging chemical species. To resolve this question, we have identified the critical residues of Escherichia coli Dps that bind to DNA and modulate iron oxidation. We uncoupled the biochemical activities of Dps, creating Dps variants and mutant E. coli strains that are defective in either DNA-binding or ferroxidase activity. Quantification of the contribution of each activity to the protection of DNA integrity and cellular viability revealed that both activities of Dps are required in order to counteract many differing stresses. These findings demonstrate that Dps plays a multipurpose role in stress protection via its dual activities, explaining how Dps can be of vital importance to bacterial viability over a wide range of stresses. IMPORTANCE: The DNA-binding protein from starved cells (Dps) protects bacterial cells against many different types of stressors. We find that DNA binding and iron oxidation by Dps are performed completely independently of each other. Both biochemical activities are required to protect E. coli against stressors, as well as to protect DNA from oxidative damage in vitro. These results suggest that many stressors may cause both oxidative stress and direct DNA damage.