Abstract
Storage of iron in a nontoxic and bioavailable form is essential for many forms of life. Three subfamilies of the ferritin-like superfamily, namely, ferritin, bacterioferritin, and Dps (DNA-binding proteins from starved cells), are able to store iron. Although the function of these iron-storage proteins is constitutive to many organisms to sustain life, the genome of some organisms appears not to encode any of these proteins. In an attempt to identify new iron-storage systems, we have found and characterized a new member of the ferritin-like superfamily of proteins, which unlike the multimeric storage system of ferritin, bacterioferritin, and Dps is monomeric in the absence of iron. Monomers catalyze oxidation of Fe(II) and they store the Fe(III) product as they assemble to form structures comparable to those of 24-meric ferritin. We propose that this mechanism is an alternative method of iron storage by the ferritin-like superfamily of proteins in organisms that lack the regular preassociated 24-meric/12-meric ferritins.Electronic supplementary materialThe online version of this article (doi:10.1007/s00775-012-0913-0) contains supplementary material, which is available to authorized users.
Highlights
Iron is involved in many biocatalytic reactions and electron transport processes in the cell [1]
In an attempt to identify new iron-storage systems, we have found and characterized a new member of the ferritin-like superfamily of proteins, which unlike the multimeric storage system of ferritin, bacterioferritin, and Dps is monomeric in the absence of iron
Monomers catalyze oxidation of Fe(II) and they store the Fe(III) product as they assemble to form structures comparable to those of 24-meric ferritin. We propose that this mechanism is an alternative method of iron storage by the ferritin-like superfamily of proteins in organisms that lack the regular preassociated 24-meric/12-meric ferritins
Summary
Iron is involved in many biocatalytic reactions and electron transport processes in the cell [1]. Storage of iron in a nontoxic form as iron(III) oxide mineral nanoparticles has been reported for ferritin, bacterioferritin, and Dps (DNAbinding proteins from starved cells), which are members of the ferritin-like superfamily of proteins. Because the structural genes for ferritin and Dps in Pyrococcus furiosus have no orthologs in the closely related species Pyrococcus abyssi and Pyrococcus horikoshii, we have searched for the presence of alternative iron-storage proteins in these organisms. Their genomes carry several genes encoding proteins that are members of the ferritin-like superfamily and which have ferritin-like and rubrerythrin-like domains. Addition of Fe(II) leads to oxidation by the protein and to oligomerization of monomers, which in turn affords the storage of the Fe(III) product in a mineral form comparable to the core in ferritin
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