The iron redox and hydrolysis chemistry of the ferritins |
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Authors: | Fadi Bou-Abdallah |
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Affiliation: | Department of Chemistry, State University of New York at Potsdam, Potsdam, NY 13676, USA |
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Abstract: | BackgroundFerritins are ubiquitous and well-characterized iron storage and detoxification proteins. In bacteria and plants, ferritins are homopolymers composed of H-type subunits, while in vertebrates, they typically consist of 24 similar subunits of two types, H and L. The H-subunit is responsible for the rapid oxidation of Fe(II) to Fe(III) at a dinuclear center, whereas the L-subunit appears to help iron clearance from the ferroxidase center of the H-subunit and support iron nucleation and mineralization.Scope of reviewDespite their overall similar structures, ferritins from different origins markedly differ in their iron binding, oxidation, detoxification, and mineralization properties. This chapter provides a brief overview of the structure and function of ferritin, reviews our current knowledge of the process of iron uptake and mineral core formation, and highlights the similarities and differences of the iron oxidation and hydrolysis chemistry in a number of ferritins including those from archaea, bacteria, amphibians, and animals.General SignificanceProkaryotic ferritins and ferritin-like proteins (Dps) appear to preferentially use H2O2 over O2 as the iron oxidant during ferritin core formation. While the product of iron oxidation at the ferroxidase centers of these and other ferritins is labile and is retained inside the protein cavity, the iron complex in the di-iron cofactor proteins is stable and remains at the catalytic site. Differences in the identity and affinity of the ferroxidase center ligands to iron have been suggested to influence the distinct reaction pathways in ferritins and the di-iron cofactor enzymes.Major conclusionsThe ferritin 3-fold channels are shown to be flexible structures that allow the entry and exit of different ions and molecules through the protein shell. The H- and L-subunits are shown to have complementary roles in iron oxidation and mineralization, and hydrogen peroxide appears to be a by-product of oxygen reduction at the FC of most ferritins. The di-iron(III) complex at the FC of some ferritins acts as a stable cofactor during iron oxidation rather than a catalytic center where Fe(II) is oxidized at the FC followed by its translocation to the protein cavity. |
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Keywords: | Dps, DNA binding proteins from starved cell HuHF and HuLF, human H-chain and L-chain ferritins MtF, human mitochondrial ferritin HoSF, horse spleen ferritin BfMF, bullfrog M-chain ferritin EcBFR and EcFtnA, heme- and nonheme-containing Escherichia coli ferritins AvBF and DdBF, Azotobacter vinelandii and Desulfovibrio desulfuricans bacterioferritins PfFtn and AfFtn, Pyrococcus furiosus and Archaeoglobus fulgidus archaeal ferritins ITC, isothermal titration calorimetry EXAFS, extended X-ray absorption fine structure EPR, electron paramagnetic resonance spectroscopy FC, ferroxidase center |
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