Interaction of Th(IV), Pu(IV) and Fe(III) with ferritin protein: how similar?

Ferritin is the main protein of Fe storage in eukaryote and prokaryote cells. It is a large multifunctional, multi-subunit protein consisting of heavy H and light L subunits. In the field of nuclear toxicology, it has been suggested that some actinide elements, such as thorium and plutonium at oxidation state +IV, have a comparable `biochemistry' to iron at oxidation state +III owing to their very high tendency for hydrolysis and somewhat comparable ionic radii. Therefore, the possible mechanisms of interaction of such actinide elements with the Fe storage protein is a fundamental question of bio-actinidic chemistry. We recently described the complexation of Pu(IV) and Th(IV) with horse spleen ferritin (composed mainly of L subunits). In this article, we bring another viewpoint to this question by further combining modeling with our previous EXAFS data for Pu(IV) and Th(IV). As a result, the interaction between the L subunits and both actinides appears to be non-specific but driven only by the density of the presence of Asp and Glu residues on the protein shell. The formation of an oxyhydroxide Th or Pu core has not been observed under the experimental conditions here, nor the interaction of Th or Pu with the ferric oxyhydroxide core.

Analysis of the VIT1 Promoter Activity in Developing Arabidopsis thaliana Plants

Iron (Fe) deficiency in plants is one of the widespread problems limiting agricultural production. Generating crops more tolerant to Fe deficiency by genetic engineering or breeding is of great interest but challenging due to the knowledge gaps in general plant Fe homeostasis. Although several genes involved in Fe homeostasis have been identified, characterization of their roles is mainly limited to specific organs at specific developmental stages of the plant, where their mutants show the most striking phenotype. Vacuolar Iron Transporter 1 (VIT1) is a well-known gene that has been characterized for its function in the mature seed of Arabidopsis thaliana. VIT1 is an Fe transporter that determines the correct distribution of Fe storage in this organ. The study aimed to explore new physiological functions for VIT1. As a first step, Arabidopsis thaliana plants that contain PromoterVIT1: GUS constructs were used to study the temporal and spatial expression of the gene throughout the plant’s lifecycle. GUS histochemical staining revealed the VIT1 promoter is active in the mature leaves and mature reproductive organs. VIT1 promoter activity in the stamen increased developmentally and was limited to tapetum and guard cells in the pollen sac. In the female organ, VIT1 promoter activity increased as the pistil developed into a silique. Although all the silique exhibited staining, staining density was higher in the peduncle, replum, and stigma regions. Inside the developing silique, funicles were heavily stained. Furthermore, in silico analyses of VT1 transcriptome and protein levels confirmed flower and the silique are hot spots for VT1 activity. Thus, the results may suggest a possible involvement of VT1 protein in several stages of the reproductive system, specifically in the flowering and in the fruit development.

Iron fertilization of the Southern Ocean: Synergy between sea ice, icebergs and ice shelves

<p><span>Glacial iron (Fe) sources associated with continental ice (ice shelves and icebergs) and sea ice have recently been suggested as important to Southern Ocean (SO) biogeochemistry, where Fe limits primary production. Icebergs and ice shelves act as fully external sources of Fe while sea ice, which has a great Fe storage capacity, efficiently conveys Fe from the coasts to offshore locations. Large Fe concentrations in sea ice are typically explained by a sedimentary origin, however recent observations suggest an additional contribution from continental ice to the sea ice Fe inventory. Here, to further explore this hypothesis, we analyze factorial simulations performed with an ocean sea-ice biogeochemical model (NEMO-LIM3-PISCES version 3.6) in which interactive Fe sources from continental and marine glacial sources are activated, separately and in concert. Our simulations indicate that (i) about 15% of the iron content of sea ice comes from icebergs and ice shelves, (ii) sea ice motion conveys this extra Fe to regions where it limits productivity</span><span>, which results in (iii) a modest increase in primary and export production, reaching ~1% of the SO total, or </span><span>~10% of the contribution of the SO cryosphere.</span></p>

Characterization of the Fe Metalloproteome of a Ubiquitous Marine Heterotroph, Pseudoalteromonas (BB2-AT2): Multiple Bacterioferritin Copies Enable Significant Fe Storage

<p>Fe is a critical nutrient to the marine biological pump, which is the process that exports photosynthetically fixed carbon in<br>the upper ocean to the deep ocean. Fe limitation controls photosynthetic activity in large regions of the oceans, and the subsequent degradation of exported photosynthetic material is facilitated particularly by marine heterotrophic bacteria. Despite their importance in the carbon cycle and the scarcity of Fe in seawater, the Fe requirements, storage and cytosolic utilization of these marine heterotrophs has been less studied. Here, we characterized the Fe metallome of Pseudoalteromonas (BB2-AT2). We found that with two copies of bacterioferritin (Bfr), Pseudoalteromonas possesses substantial capacity for luxury uptake of Fe. Fe:C in the whole cell metallome was estimated (assuming C:P stoichiometry ~51:1) to be between ~83 μmol:mol Fe:C, ~11 fold higher than prior marine bacteria surveys, that could support growth for at least 2.6 divisions in the absence of further Fe acquisition. Under these replete conditions, other major cytosolic Fe associated proteins were observed including superoxide dismutase (SodA; with other metal SOD isoforms absent under Fe replete conditions) and catalase (KatG) involved in reactive oxygen stress mitigation and aconitase (AcnB), succinate dehydrogenase (FrdB) and cytochromes (QcrA and Cyt1) involved in respiration. With the aid of singular value decomposition (SVD), we were able to computationally attribute peaks within the metallome to specific metalloproteins contributors. An Fe complex TonB transporter associated with the closely related Alteromonas bacterium was found to be abundant within the Pacific Ocean mesopelagic environment. Despite the extreme scarcity of Fe in seawater, the marine heterotroph, Pseudoalteromonas, has expansive Fe storage capacity and utilization strategies, implying that, within detritus and sinking particle environments, there is significant opportunity for Fe acquisition. Together these results imply an evolved dedication of marine Pseudoalteromonas to maintaining an Fe metalloproteome, likely due to its dependence on Fe-based respiratory metabolism.<br></p>

Characterization of the Fe Metalloproteome of a Ubiquitous Marine Heterotroph, Pseudoalteromonas (BB2-AT2): Multiple Bacterioferritin Copies Enable Significant Fe Storage

<p>Fe is a critical nutrient to the marine biological pump, which is the process that exports photosynthetically fixed carbon in<br>the upper ocean to the deep ocean. Fe limitation controls photosynthetic activity in large regions of the oceans, and the subsequent degradation of exported photosynthetic material is facilitated particularly by marine heterotrophic bacteria. Despite their importance in the carbon cycle and the scarcity of Fe in seawater, the Fe requirements, storage and cytosolic utilization of these marine heterotrophs has been less studied. Here, we characterized the Fe metallome of Pseudoalteromonas (BB2-AT2). We found that with two copies of bacterioferritin (Bfr), Pseudoalteromonas possesses substantial capacity for luxury uptake of Fe. Fe:C in the whole cell metallome was estimated (assuming C:P stoichiometry ~51:1) to be between ~83 μmol:mol Fe:C, ~11 fold higher than prior marine bacteria surveys, that could support growth for at least 2.6 divisions in the absence of further Fe acquisition. Under these replete conditions, other major cytosolic Fe associated proteins were observed including superoxide dismutase (SodA; with other metal SOD isoforms absent under Fe replete conditions) and catalase (KatG) involved in reactive oxygen stress mitigation and aconitase (AcnB), succinate dehydrogenase (FrdB) and cytochromes (QcrA and Cyt1) involved in respiration. With the aid of singular value decomposition (SVD), we were able to computationally attribute peaks within the metallome to specific metalloproteins contributors. An Fe complex TonB transporter associated with the closely related Alteromonas bacterium was found to be abundant within the Pacific Ocean mesopelagic environment. Despite the extreme scarcity of Fe in seawater, the marine heterotroph, Pseudoalteromonas, has expansive Fe storage capacity and utilization strategies, implying that, within detritus and sinking particle environments, there is significant opportunity for Fe acquisition. Together these results imply an evolved dedication of marine Pseudoalteromonas to maintaining an Fe metalloproteome, likely due to its dependence on Fe-based respiratory metabolism.<br></p>

Handing off iron to the next generation: how does it get into seeds and what for?

To ensure the success of the new generation in annual species, the mother plant transfers a large proportion of the nutrients it has accumulated during its vegetative life to the next generation through its seeds. Iron (Fe) is required in large amounts to provide the energy and redox power to sustain seedling growth. However, free Fe is highly toxic as it leads to the generation of reactive oxygen species. Fe must, therefore, be tightly bound to chelating molecules to allow seed survival for long periods of time without oxidative damage. Nevertheless, when conditions are favorable, the seed's Fe stores have to be readily remobilized to achieve the transition toward active photosynthesis before the seedling becomes able to take up Fe from the environment. This is likely critical for the vigor of the young plant. Seeds constitute an important dietary source of Fe, which is essential for human health. Understanding the mechanisms of Fe storage in seeds is a key to improve their Fe content and availability in order to fight Fe deficiency. Seed longevity, germination efficiency and seedling vigor are also important traits that may be affected by the chemical form under which Fe is stored. In this review, we summarize the current knowledge on seed Fe loading during development, long-term storage and remobilization upon germination. We highlight how this knowledge may help seed Fe biofortification and discuss how Fe storage may affect the seed quality and germination efficiency.

Characterization of the Fe metalloproteome of a ubiquitous marine heterotroph, Pseudoalteromonas (BB2-AT2): multiple bacterioferritin copies enable significant Fe storage

Despite the extreme scarcity of Fe in seawater, the marine heterotroph Pseudoalteromonas has expansive Fe storage capacity and utilization strategies.

Localisation cytologique du cuivre et de quelques autres métaux dans la glande digestive de la seiche, Sepia officinalis L (Mollusque Céphalopode)

The cuttlefish, Sepia officinalis L., liver was investigated by histochemical and microanalytical methods. The greater part of the accumulated Cu is concentrated in spherulae which are elaborated by the basal cells. Cu is associated with both Ag and Zn. Fe is also found but the digestive cells are the most important site of Fe storage. Our data show that the spherulae are made of metallothionein-like proteins. The occurrence of these metal-binding proteins has ecological effects. The metals are easily assimilable and can be transferred to higher levels of the food chain.

Growth, ascorbic acid and iron contents of tissues of young guinea-pigs whose dams received high or low levels of dietary ascorbic acid or Fe during pregnancy and suckling

1. Guinea-pig dams were fed on purified diets containing high (5 g/kg diet plus 1 g/l drinking water) or moderate (0.5 g/kg diet) levels of ascorbic acid, in combination with high (1 g/kg diet) or moderate (0.043 g/kg diet) levels of iron, during pregnancy and suckling. Their offsprings' diets contained 0.1 g ascorbic acid/kg and 0.04 g Fe/kg.2. High ascorbic acid intake clearly enhanced both tissue ascorbate and Fe storage in the dams, and high Fe intake increased both the dams' and the pups' tissue Fe stores.3. In the animals receiving high Fe intake, a co-existing high ascorbate intake by the dams reduced the growth rate of the offspring, but only during the early stages of development, not during the later stages of post-weaning growth. All the pups' tissue ascorbate levels fell after weaning, but those born of the dams receiving the high ascorbic acid diets did not fall to levels lower than those of the other pups.4. Thus, although certain disadvantages to the offspring resulting from very-high ascorbic acid intake by pregnant guinea-pig dams were detected, these did not include permanently increased ascorbate requirements, and hence a progression to scurvy as the pups grew and matured.