A Novel Non-heme Iron-binding Ferritin Related to the DNA-binding Proteins of the Dps Family in Listeria innocua

107

110

Evolution of an oxygenic atmosphere required primordial life to accommodate the toxicity associated with reactive oxygen species. We have characterized an archaeal antioxidant from the hyperthermophilic acidophile Sulfolobus solfataricus. The amino acid sequence of this Ϸ22-kDa protein shares little sequence similarity with proteins with known function. However, the protein shares high sequence similarity with hypothetical proteins in other archaeal and bacterial genomes. Nine of these hypothetical proteins form a monophyletic cluster within the broad superfamily of ferritin-like diiron-carboxylate proteins. Higher order structural predictions and image reconstructions indicate that the S. solfataricus protein is structurally related to a class of DNA-binding protein from starved cells (Dps). The recombinant protein self assembles into a hollow dodecameric protein cage having tetrahedral symmetry (SsDps). The outer shell diameter is Ϸ10 nm, and the interior diameter is Ϸ5 nm. Dps proteins have been shown to protect nucleic acids by physically shielding DNA against oxidative damage and by consuming constituents involved in Fenton chemistry. In vitro, the assembled archaeal protein efficiently uses H2O2 to oxidize Fe(II) to Fe(III) and stores the oxide as a mineral core on the interior surface of the protein cage. The ssdps gene is upregulated in S. solfataricus cultures grown in iron-depleted media and upon H2O2 stress, but is not induced by other stresses. SsDps-mediated reduction of hydrogen peroxide and possible DNA-binding capabilities of this archaeal Dps protein are mechanisms by which S. solfataricus mitigates oxidative damage.ferritin ͉ iron ͉ oxidative stress ͉ biomineralization ͉ hyperthermophile

Section: Resultsmentioning

confidence: 99%

An archaeal antioxidant: Characterization of a Dps-like protein from Sulfolobus solfataricus

Wiedenheft

Mosolf

Willits

et al. 2005

107

110

“…A short distance of 2.2 Å between two peaks (N11 and N13) can be explained only by their proximity to the twofold axis and the exclusive occupancy of this site by a single iron atom. Because the iron ligands Glu-72 and Glu-75 are not conserved among Dps-like ferritins and a further polynuclear nucleation center (NII) was identified, the mechanism of Ilari et al (13) for iron accumulation in Listeria ferritin (12,13) is not directly applicable to the halophilic DpsA.…”

Section: Structural Comparison Of Dpsa With 24-mer Ferritins and Dps-mentioning

confidence: 99%

“…Consequently, the iron-storage capacity of these proteins is smaller, and ferritin dodecamers from Helicobacter pylori and Listeria innocua were reported to oxidize and sequester up to 500 iron atoms inside their cavity (9,12,13). Hereby, the main entry of iron and other ionic species into these members of the Dps subfamily is postulated to occur along pores that penetrate the protein shell at the threefold axes of symmetry (9,13), and that were also identified as entrance sites in the 24-mer ferritins (2).…”

Section: And References Therein)mentioning

confidence: 99%

Iron-oxo clusters biomineralizing on protein surfaces: Structural analysis of Halobacterium salinarum DpsA in its low- and high-iron states

Zeth

Offermann

Essen

et al. 2004

107

122

The crystal structure of the Dps-like (Dps, DNA-protecting protein during starvation) ferritin protein DpsA from the halophile Halobacterium salinarum was determined with low endogenous iron content at 1.6-Å resolution. The mechanism of iron uptake and storage was analyzed in this noncanonical ferritin by three highresolution structures at successively increasing iron contents. In the high-iron state of the DpsA protein, up to 110 iron atoms were localized in the dodecameric protein complex. For ultimate iron storage, the archaeal ferritin shell comprises iron-binding sites for iron translocation, oxidation, and nucleation. Initial iron-protein interactions occur through acidic residues exposed along the outer surface in proximity to the iron entry pore. This narrow pore permits translocation of ions toward the ferroxidase centers via two discrete steps. Iron oxidation proceeds by transient formation of tri-iron ferroxidase centers. Iron storage by biomineralization inside the ferritin shell occurs at two iron nucleation centers. Here, a single iron atom provides a structural seed for iron-oxide cluster formation. The clusters with up to five iron atoms adopt a geometry that is different from natural biominerals like magnetite but resembles iron clusters so far known only from bioinorganic model compounds.ferritin ͉ iron-binding ͉ inorganic cluster formation ͉ x-ray crystal structure

“…These results suggest that Lsr2 does not efficiently remove hydroxyl radicals. Most proteins of the Dps family have been shown to specifically bind iron (12,13,14). Iron sequestration interferes with the Fenton reaction, reduces ROI generation, and thereby reduces potential DNA damage.…”

Section: Protectingmentioning

confidence: 99%

The multifunctional histone-like protein Lsr2 protects mycobacteria against reactive oxygen intermediates

Colangeli

Haq

Arcus

et al. 2009

117

112

Mycobacterium tuberculosis has evolved a number of strategies to survive within the hostile environment of host phagocytes. Reactive nitrogen and oxygen intermediates (RNI and ROI) are among the most effective antimycobacterial molecules generated by the host during infection. Lsr2 is a M. tuberculosis protein with histonelike features, including the ability to regulate a variety of transcriptional responses in mycobacteria. Here we demonstrate that Lsr2 protects mycobacteria against ROI in vitro and during macrophage infection. Furthermore, using macrophages derived from NOS ؊/؊ and Phox ؊/؊ mice, we demonstrate that Lsr2 is important in protecting against ROI but not RNI. The protection provided by Lsr2 protein is not the result of its ability to either bind iron or scavenge hydroxyl radicals. Instead, electron microscopy and DNAbinding studies suggest that Lsr2 shields DNA from reactive intermediates by binding bacterial DNA and physically protecting it. Thus, Lsr2 appears to be a unique protein with both histone-like properties and protective features that may be central to M. tuberculosis pathogenesis. In addition, evidence indicates that lsr2 is an essential gene in M. tuberculosis. Because of its essentiality, Lsr2 may represent an excellent candidate as a drug target.Mycobacterium tuberculosis ͉ ROI ͉ DPS ͉ DNA