Paired Bacillus anthracis Dps (Mini-ferritin) Have Different Reactivities with Peroxide

Abstract

reactions. Sequence similarities between Ba Dps1 and Bacillus subtilis DpsA (Dps1), which is regulated by general stress factor (SigmaB) and Fur, and between Ba Dps2 and B. subtilis MrgA, which is regulated by H 2 O 2 (PerR), suggest the function of Ba Dps1 is iron sequestration and the function of Ba Dps2 is H 2 O 2 destruction, important in host/pathogen interactions. Destruction of H 2 O 2 by Ba Dps2 proceeds via an unknown mechanism with an intermediate similar spectrally (A 650 nm ) and kinetically to the maxi-ferritin diferric peroxo complex.Dps (DNA protection during starvation) proteins are a family of bacterial proteins in the ferritin superfamily, first identified in Escherichia coli as dodecameric DNA-binding proteins in cells stressed by starvation (1). The proteins are stable nanocages with large (5-nm diameter) central cavities (2, 3) and have been observed in vivo as part of biocrystalline complexes with DNA (e.g. see Ref. 4). Protection of DNA from damage by free radicals, the common property of Dps proteins, is accomplished by converting oxidants and iron released during stress to benign, hydrated, ferric oxide minerals inside the Dps protein cage (2, 3). Because only some Dps protein dodecamers bind DNA but all protect DNA from hydroxyl radical damage in vitro, the mechanisms of Dps protein protection of DNA from oxidant damage and other stresses such as nucleases, radiation, and heat are subjects of active study (e.g. Refs. 2-9). When DNA-Dps interactions occur, N-or C-terminal protein extensions that protrude from the protein nanocages are thought to be involved (10, 11). The ability of Helicobacter pylori, Borrelia burgdorferi, and other pathogens to survive oxidative burst killing within macrophages and neutrophils has been attributed to Dps protein dodecamer protection of DNA based on the increased oxidant sensitivity of dps deletion mutants (e.g. Refs. 12-18). Bacteria with two dps genes are rare although present in many Bacilli (see Fig. 1). No comparative studies of the reaction properties of pairs of Dps proteins have been made to our knowledge.The ferritin superfamily, of which Dps protein dodecamers are members, are protein nanocages that form protein-encased minerals of hydrated ferric oxide through a series of steps. First, oxidation of two ferrous ions occurs at catalytic sites in the protein cage that are related to catalytic sites in di-iron oxygenases, such as stearoyl-acyl carrier protein ⌬9-fatty acyl desaturase, ribonucleotide reductase, and methane monooxygenase, except that in the ferritins the iron is a substrate (3). In maxiferritins, the first step in iron mineralization is the oxidation of coupled diferrous ions with O 2 via a diferric peroxo complex (19 -23), with partly characterized decay products such as diferric hydroperoxide complex (24) to form diferric oxy mineral precursors. Then, by mechanisms unknown, the mineral precursors move through the protein cage to the cavity and are concentrated by clustered carboxylates on the inner surface of the protein cavity an...

Characterization of the Bacteroides fragilis bfr Gene Product Identifies a Bacterial DPS-Like Protein and Suggests Evolutionary Links in the Ferritin Superfamily

“…In addition, the bfr and ftnA genes are regulated differently, and deletion of the ftnA gene did not directly affect expression of BfDPSL under conditions of aerobic stress or stationary phase. Differential expression of ferritin superfamily members has also been observed in other organisms, including Bacillus subtilis (5,16,26), Bacillus anthracis (3,39,45), Salmonella enterica serovar Typhimurium (66), and Pseudomonas putida (17). Thus, as the B. fragilis dps gene is extremely responsive to peroxide or oxygen (49,61), B. fragilis may hold the activity of BfDPSL in reserve for iron storage and/or DNA protection during the transition to stationary phase or for prolonged O 2 exposure.…”

The N-terminal Extensions of Deinococcus radiodurans Dps-1 Mediate DNA Major Groove Interactions as well as Assembly of the Dodecamer

“…Once assembly has occurred, stability of the dodecamer is accomplished through extensive interactions between neighboring four-helix bundles. An N-terminal deletion mutant of L. lactis DpsA (lacking residues [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], in which the N-terminal metal coordination was also disrupted by site directed mutagenesis, was unable to interact with DNA (16). But this DpsA variant eluted from a gel filtration column at a similar elution volume as native DpsA, suggesting that unlike Dps-1, disruption of the metal center at the N terminus has no effect on the dodecameric assembly of DpsA (16).…”

“…Secondly, the ferroxidase site in Dps is usually generated at the interface between two subunits and, with one reported exception, is not within the four-helix bundle as in the case of ferritin (14,15). It is also notable that not all Dps homologs follow the same catalytic mechanism, as exemplified by the absence of a conserved ferroxidase center in Lactococcus lactis DpsB and the failure of Bacillus anthracis Dps1 to utilize H 2 O 2 in the ferroxidation reaction (16,17).In contrast to the highly conserved ferroxidase center, Dps homologs have a variable N-terminal extension. This N-terminal tail, which contains multiple positively charged residues, extends from the four-helix bundle core into the solvent (11,18,19).…”

“…Secondly, the ferroxidase site in Dps is usually generated at the interface between two subunits and, with one reported exception, is not within the four-helix bundle as in the case of ferritin (14,15). It is also notable that not all Dps homologs follow the same catalytic mechanism, as exemplified by the absence of a conserved ferroxidase center in Lactococcus lactis DpsB and the failure of Bacillus anthracis Dps1 to utilize H 2 O 2 in the ferroxidation reaction (16,17).…”

A Histidine Aspartate Ionic Lock Gates the Iron Passage in Miniferritins from Mycobacterium smegmatis

“…The presence of more than one Dps homolog is also observed in some bacteria. Bacillus anthracis has BaDps1, which is involved in iron sequestration, and BaDps2 conferring protection against H 2 O 2 damage (18,19). In Deinococcus radiodurans, Dps1 binds DNA but is unable to protect the organism from H 2 O 2 -mediated degradation, whereas Dps2 binds DNA and also protects the bacterium against reactive oxygen speciesmediated damage (20,21).…”