Functional comparison of Deinococcus radiodurans Dps proteins suggests distinct in vivo roles

Abstract

Deinococcus radiodurans exhibits extreme resistance to DNA damage and is one of only few bacteria that encode two Dps (DNA protection during starvation) proteins. Dps-1 was shown previously to bind DNA with high affinity and to localize to the D. radiodurans nucleoid. A unique feature of Dps-2 is its predicted signal peptide. In the present paper, we report that Dps-2 assembly into a dodecamer requires the C-terminal extension and, whereas Dps-2 binds DNA with low affinity, it protects against degradation by reactive oxygen species. Consistent with a role for Dps-2 in oxidative stress responses, the Dps-2 promoter is up-regulated by oxidative stress, whereas the Dps-1 promoter is not. Although DAPI (4',6-diamidino-2-phenylindole) staining of Escherichia coli nucleoids shows that Dps-1 can compact genomic DNA, such nucleoid condensation is absent from cells expressing Dps-2. A fusion of EGFP (enhanced green fluorescent protein) to the Dps-2 signal peptide results in green fluorescence at the perimeter of D. radiodurans cells. The differential response of the Dps-1 and Dps-2 promoters to oxidative stress, the distinct cellular localization of the proteins and the differential ability of Dps-1 and Dps-2 to attenuate hydroxyl radical production suggest distinct functional roles; whereas Dps-1 may function in DNA metabolism, Dps-2 may protect against exogenously derived reactive oxygen species.

Dps from Deinococcus radiodurans: oligomeric forms of Dps1 with distinct cellular functions and Dps2 involved in metal storage

“…Our data indicate that Dr Dps1 remains constitutively expressed after the addition of hydrogen peroxide, iron or manganese (Fig. ), in agreement with the study mentioned before .…”

“…Therefore, under control cell growth conditions both Dr Dps would be able to oxidize the iron using hydrogen peroxide almost at the same oxidation rates, since the concentration of hydrogen peroxide is low, whereas in an eventual oxidative stress burst the intracellular hydrogen peroxide concentration increases and in this condition Dr Dps1 becomes much more efficient for iron oxidation than Dr Dps2. The effect of ROS on Dr Dps promoter activity has been described previously : the dps1 promoter was shown to respond to the hydrogen peroxide addition, whilst dps2 promoter activity increased under the same conditions in both the exponential and stationary phases. This is in agreement with our data, in which the addition of hydrogen peroxide does not induce a change in the Dr Dps1 expression levels, but a change in its oligomeric form is observed, dimer to trimer (Fig.…”

“…The first 30 amino acid residues from Dr Dps2 are predicted to be a signal peptide . This protein was found to be localized in the cell periphery region ; based on this and on the intracellular iron localization in D. radiodurans , it was suggested that this protein is associated mainly with iron storage .…”

“…In this N-terminal region DrDps1 has a metal binding site, which has been proposed to be important for DNA binding [51]; this protein is weakly associated with the nucleoid [52]. The first 30 amino acid residues from DrDps2 are predicted to be a signal peptide [38,53,54]. This protein was found to be localized in the cell periphery region [54]; based on this and on the intracellular iron localization in D. radiodurans [7], it was suggested that this protein is associated mainly with iron storage [54].…”

“…Although some studies have been performed on both DrDps proteins [40,50,51,54,55], several questions remain to be answered regarding their interaction with DNA and their metal storage ability. Our work shows that DrDps2 and both dimeric and dodecameric forms of DrDps1 are able to protect the DNA against ROS at different Fe/12-mer Dps ratios.…”