Abstract:25Dps proteins (DNA-binding proteins from starved cells) have been found to detoxify H 2 O 2 . At 26 their catalytic centers, the ferroxidase center (FOC), Dps proteins utilize Fe 2+ to reduce H 2 O 2 27 and therefore play an essential role in the protection against oxidative stress and maintaining 28 iron homeostasis. Whereas most bacteria accommodate one or two Dps, there are five 29 different Dps proteins in Nostoc punctiforme, a phototrophic and filamentous cyanobacterium. 30 This uncommonly high number… Show more
“…The ligation of the ferroxidase center in this protein differs markedly from canonical Dps proteins and closely resembles that of bacterial Bfrs discussed above (191). Finally NpDps4 possesses unusually His-rich ligation of iron at the ferroxidase center and utilizes only O2 and not H2O2 as an oxidant for iron (198). Accordingly a role for this protein has been proposed as an O2 scavenger within heterocysts where nitrogenase activity requires that a microoxic (< 10 μM O2) environment be maintained (199).…”
Section: Fe Storage In Cyanobacteriamentioning
confidence: 76%
“…Accordingly a role for this protein has been proposed as an O2 scavenger within heterocysts where nitrogenase activity requires that a microoxic (< 10 μM O2) environment be maintained (199). Based on sequence comparisons to other Dps proteins, it has been suggested that this type of reaction center, which is common amongst, but restricted to, the cyanobacteria (198) be classified as the His-type ferroxidase center.…”
Iron is an essential micro-nutrient and, in the case of bacteria, its availability is commonly a growth-limiting factor. However, correct functioning of cells requires that the labile pool of chelatable ‘free’ iron is tightly regulated. Correct metalation of proteins requiring iron as a cofactor demands that such a readily accessible source of iron exists, but over-accumulation results in an oxidative burden that, if unchecked, would lead to cell death. The toxicity of iron stems from its potential to catalyze formation of reactive oxygen species (ROS) that, in addition to causing damage to biological molecules, can also lead to the formation of reactive nitrogen species (RNS). In order to avoid iron-mediated oxidative stress, bacteria utilize iron-dependent global regulators to sense the iron status of the cell and regulate the expression of proteins involved in the acquisition, storage and efflux of iron accordingly. Here, we survey the current understanding of the structure and mechanism of the important members of each of these classes of protein. Diversity in the details of iron homeostasis mechanisms reflect the differing nutritional stresses resulting from the wide variety of ecological niches that bacteria inhabit. However, in this review we seek to highlight the similarities of iron homeostasis between different bacteria, whilst acknowledging important variations. In this way we hope to illustrate how bacteria have evolved common approaches to overcome the dual problems of the insolubility and potential toxicity of iron.
“…The ligation of the ferroxidase center in this protein differs markedly from canonical Dps proteins and closely resembles that of bacterial Bfrs discussed above (191). Finally NpDps4 possesses unusually His-rich ligation of iron at the ferroxidase center and utilizes only O2 and not H2O2 as an oxidant for iron (198). Accordingly a role for this protein has been proposed as an O2 scavenger within heterocysts where nitrogenase activity requires that a microoxic (< 10 μM O2) environment be maintained (199).…”
Section: Fe Storage In Cyanobacteriamentioning
confidence: 76%
“…Accordingly a role for this protein has been proposed as an O2 scavenger within heterocysts where nitrogenase activity requires that a microoxic (< 10 μM O2) environment be maintained (199). Based on sequence comparisons to other Dps proteins, it has been suggested that this type of reaction center, which is common amongst, but restricted to, the cyanobacteria (198) be classified as the His-type ferroxidase center.…”
Iron is an essential micro-nutrient and, in the case of bacteria, its availability is commonly a growth-limiting factor. However, correct functioning of cells requires that the labile pool of chelatable ‘free’ iron is tightly regulated. Correct metalation of proteins requiring iron as a cofactor demands that such a readily accessible source of iron exists, but over-accumulation results in an oxidative burden that, if unchecked, would lead to cell death. The toxicity of iron stems from its potential to catalyze formation of reactive oxygen species (ROS) that, in addition to causing damage to biological molecules, can also lead to the formation of reactive nitrogen species (RNS). In order to avoid iron-mediated oxidative stress, bacteria utilize iron-dependent global regulators to sense the iron status of the cell and regulate the expression of proteins involved in the acquisition, storage and efflux of iron accordingly. Here, we survey the current understanding of the structure and mechanism of the important members of each of these classes of protein. Diversity in the details of iron homeostasis mechanisms reflect the differing nutritional stresses resulting from the wide variety of ecological niches that bacteria inhabit. However, in this review we seek to highlight the similarities of iron homeostasis between different bacteria, whilst acknowledging important variations. In this way we hope to illustrate how bacteria have evolved common approaches to overcome the dual problems of the insolubility and potential toxicity of iron.
Dps (DNA-binding protein from starved cells) is well known for the structural protection of bacterial DNA by the formation of highly ordered intracellular assemblies under stress conditions. Moreover, this ferritin-like protein can perform fast oxidation of ferrous ions and subsequently accumulate clusters of ferric ions in its nanocages, thus providing the bacterium with physical and chemical protection. Here, cryo-electron microscopy was used to study the accumulation of iron ions in the nanocage of a Dps protein from Escherichia coli. We demonstrate that Fe2+ concentration in the solution and incubation time have an insignificant effect on the volume and the morphology of iron minerals formed in Dps nanocages. However, an increase in the Fe2+ level leads to an increase in the proportion of larger clusters and the clusters themselves are composed of discrete ~1–1.5 nm subunits.
Dps proteins (DNA-binding proteins from starved cells) are multifunctional stress defense proteins from the Ferritin family expressed in Prokarya during starvation and/or acute oxidative stress. Besides shielding bacterial DNA through binding and condensation, Dps proteins protect the cell from reactive oxygen species by oxidizing and storing ferrous ions within their cavity, using either hydrogen peroxide or molecular oxygen as the co-substrate, thus reducing the toxic effects of Fenton reactions. Interestingly, the interaction between Dps and transition metals (other than iron) is a known but relatively uncharacterized phenomenon. The impact of non-iron metals on the structure and function of Dps proteins is a current topic of research. This work focuses on the interaction between the Dps from Marinobacter nauticus (a marine facultative anaerobe bacterium capable of degrading petroleum hydrocarbons) and the cupric ion (Cu2+), one of the transition metals of greater biological relevance. Results obtained using electron paramagnetic resonance (EPR), Mössbauer and UV/Visible spectroscopies revealed that Cu2+ ions bind to specific binding sites in Dps, exerting a rate-enhancing effect on the ferroxidation reaction in the presence of molecular oxygen and directly oxidizing ferrous ions when no other co-substrate is present, in a yet uncharacterized redox reaction. This prompts additional research on the catalytic properties of Dps proteins.
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