A Novel Plant Ferritin Subunit from Soybean That Is Related to a Mechanism in Iron Release

Masuda, Taro; Goto, Fumiyuki; Yoshihara, Toshihiro

doi:10.1074/jbc.m011399200

Cited by 123 publications

(118 citation statements)

References 48 publications

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“…Preparation of WT SSF, rH-1, rH-2, and rH-1H-2-SSF was purified as recently described (8,13). rH-1 was prepared according to reported methods (8,18).…”

Section: Methodsmentioning

confidence: 99%

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Role of H-1 and H-2 Subunits of Soybean Seed Ferritin in Oxidative Deposition of Iron in Protein

Deng

Liao

Yang

et al. 2010

Journal of Biological Chemistry

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Naturally occurring phytoferritin is a heteropolymer consisting of two different H-type subunits, H-1 and H-2. Prior to this study, however, the function of the two subunits in oxidative deposition of iron in ferritin was unknown. The data show that, upon aerobic addition of 48 -200 Fe 2؉ /shell to apoferritin, iron oxidation occurs only at the diiron ferroxidase center of recombinant H1 (rH-1). In addition to the diiron ferroxidase mechanism, such oxidation is catalyzed by the extension peptide (a specific domain found in phytoferritin) of rH-2, because the H-1 subunit is able to remove Fe 3؉ from the center to the inner cavity better than the H-2 subunit. These findings support the idea that the H-1 and H-2 subunits play different roles in iron mineralization in protein. Interestingly, at medium iron loading (200 irons/shell), wild-type (WT) soybean seed ferritin (SSF) exhibits a stronger activity in catalyzing iron oxidation (1.10 ؎ 0.13 M iron/subunit/s) than rH-1 (0.59 ؎ 0.07 M iron/subunit/s) and rH-2 (0.48 ؎ 0.04 M iron/subunit/s), demonstrating that a synergistic interaction exists between the H-1 and H-2 subunits in SSF during iron mineralization. Such synergistic interaction becomes considerably stronger at high iron loading (400 irons/shell) as indicated by the observation that the iron oxidation activity of WT SSF is ϳ10 times larger than those of rH-1 and rH-2. This helps elucidate the widespread occurrence of heteropolymeric ferritins in plants.Iron and oxygen chemistry, in a variety of non-heme diiron proteins, has drawn considerable attention because of their various roles in reversible O 2 binding for respiration in hemerythrin, oxidation and desaturation of organic substrates in methane monooxygenase, R2 subunit of ribonucleotide reductase, stearoyl-acyl carrier protein ⌬-9 desaturase, as well as the detoxification and concentration of iron in Dps and ferritin (1-6). Diiron centers have similar structural motifs containing a combination of carboxylate and histidine ligands that either bind or bridge the two metal ions of the dinuclear active site. Although the dinuclear centers of the protein are very similar in structure, each of the proteins fulfills a different biological function that appears to be mediated by the nature of the first and second coordination sphere of the diiron center.Ferritins are a special class of diiron proteins that play a role in both iron housekeeping and iron detoxification. They are widely distributed in animals, plants, and bacteria (but not in yeast) and are typically composed of 24 similar or identical subunits assembled into a shell-like structure. In vertebrates, ferritins consist of two types of subunits, H and L, respectively. The two types have about 55% identity in amino acid sequence.

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“…Preparation of WT SSF, rH-1, rH-2, and rH-1H-2-SSF was purified as recently described (8,13). rH-1 was prepared according to reported methods (8,18).…”

Section: Methodsmentioning

confidence: 99%

“…rH-1 was prepared according to reported methods (8,18). The expression plasmid for rH-2 was constructed by inserting the H-2 cDNA into the NcoI/BamHI site of pET21d using a PCR-based method.…”

Section: Methodsmentioning

confidence: 99%

Role of H-1 and H-2 Subunits of Soybean Seed Ferritin in Oxidative Deposition of Iron in Protein

Deng

Liao

Yang

et al. 2010

Journal of Biological Chemistry

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“…In mammals, the ferritin complex is localized in the cytosol (Harrison and Arosio, 1996) and is composed of the H and L subunits in a tissuedependent stoichiometry (Galatro and Puntarulo, 2007). The plant ferritin complex is formed and stored in the plastid stroma (Waldo et al, 1995), although mitochondrial localization has recently been described (Zancani et al, 2004), and it is made of only one type of subunit, although evidence for a second subunit has been found (Masuda et al, 2001).…”

Section: Introductionmentioning

confidence: 99%

Ferritin is required for rapid remodeling of the photosynthetic apparatus and minimizes photo‐oxidative stress in response to iron availability in Chlamydomonas reinhardtii

et al. 2008

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SummaryFerritin is a key player in the iron homeostasis due to its ability to store large quantities of iron. Chlamydomonas reinhardtii contains two nuclear genes for ferritin (ferr1 and ferr2) that are induced when Chlamydomonas cells are shifted to iron-deficient conditions. In response to the reduced iron availability, degradation of photosystem I (PSI) and remodeling of its light-harvesting complex occur. This active PSI degradation slows down under photo-autotrophic conditions where photosynthesis is indispensable. We observed a strong induction of ferritin correlated with the degree of PSI degradation during iron deficiency. The PSI level can be restored to normal within 24 h after iron repletion at the expense of the accumulated ferritin, indicating that the ferritin-stored iron allows fast adjustment of the photosynthetic apparatus with respect to iron availability. RNAi strains that are significantly reduced in the amount of ferritin show a striking delay in the degradation of PSI under iron deficiency. Furthermore, these strains are more susceptible to photo-oxidative stress under high-light conditions. We conclude that (i) ferritin is used to buffer the iron released by degradation of the photosynthetic complexes, (ii) the physiological status of the cell determines the strategy used to overcome the impact of iron deficiency, (iii) the availability of ferritin is important for rapid degradation of PSI under iron deficiency, and (iv) ferritin plays a protective role under photo-oxidative stress conditions.

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“…It is absent in animal ferritins. For soybean ferritin, further processing of the 26.5-kDa subunit occurs through excising a short C-terminal amino acid sequence (16 amino acid residues) that corresponds to the E helix of the mammalian ferritin subunit (9). Compared with their own precursors, H-1 is devoid of both the N-terminal TP domain and the C-terminal E helix, whereas H-2 lacks the N-terminal TP domain only (13).…”

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confidence: 99%

“…where iron is incorporated into the ferritin shell to form the mineral core, whereas animal ferritins are largely found in the cytoplasm of cell (1,8). Ferritins from dried soybean and pea seed consist of two subunits of 26.5 and 28.0 kDa, which are designated H-1 and H-2, respectively, share ϳ80% amino acid sequence identity (9,10), and contain ferroxidase centers. The two subunits are synthesized from a 32-kDa precursor with a unique two-domain N-terminal sequence containing a transit peptide (TP) 2 and an extension peptide (EP).…”

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Protein Association and Dissociation Regulated by Ferric Ion

et al. 2009

Journal of Biological Chemistry

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Iron stored in phytoferritin plays an important role in the germination and early growth of seedlings. The protein is located in the amyloplast where it stores large amounts of iron as a hydrated ferric oxide mineral core within its shell-like structure. The present work was undertaken to study alternate mechanisms of core formation in pea seed ferritin (PSF). The data reveal a new mechanism for mineral core formation in PSF involving the binding and oxidation of iron at the extension peptide (EP) located on the outer surface of the protein shell. This binding induces aggregation of the protein into large assemblies of ϳ400 monomers. The bound iron is gradually translocated to the mineral core during which time the protein dissociates back into its monomeric state. Either the oxidative addition of Fe 2؉ to the apoprotein to form Fe 3؉ or the direct addition of Fe 3؉ to apoPSF causes protein aggregation once the binding capacity of the 24 ferroxidase centers (48 Fe 3؉ /shell) is exceeded. When the EP is enzymatically deleted from PSF, aggregation is not observed, and the rate of iron oxidation is significantly reduced, demonstrating that the EP is a critical structural component for iron binding, oxidation, and protein aggregation. These data point to a functional role for the extension peptide as an iron binding and ferroxidase center that contributes to mineralization of the iron core. As the iron core grows larger, the new pathway becomes less important, and Fe 2؉ oxidation and deposition occurs directly on the surface of the iron core.The chemistry of iron and oxygen in a number of non-heme di-iron proteins has been a subject of intense interest because of their varied roles in oxygen activation and catalysis, substrate hydrolysis, oxygen transport, redox reactions, H 2 O 2 , and iron detoxification and iron storage. Di-iron centers have similar structural motifs consisting of a combination of carboxylate and histidine ligands that either bind or bridge the two metal ions of the di-nuclear active site; di-iron proteins containing these centers include methane monooxygenase, ribonucleotide reductase, rubrerythrin, stearoyl desaturase, purple acid phosphatase, hemerythrin, the Dps proteins, and ferritins (1-6). Despite their similar di-nuclear centers, each of these proteins fulfills a distinct biological role that seems to be mediated by the nature of the first and second coordination sphere of the di-iron center.Ferritins are a class of intracellular iron storage and detoxification proteins that facilitate the oxidation of iron by molecular oxygen or hydrogen peroxide to form a hydrous ferric oxide mineral core within their interiors (1-3). Rapid Fe 2ϩ oxidation occurs at the di-iron ferroxidase center located on the H-subunit of the mammalian protein. Unlike the H-chain, the more acidic L-subunit lacks the ferroxidase center but contains a putative nucleation site responsible for slower iron oxidation and mineralization (7). The shapes of both the H-and L-subunit are nearly cylindrical and composed of a four...

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A Novel Plant Ferritin Subunit from Soybean That Is Related to a Mechanism in Iron Release

Cited by 123 publications

References 48 publications

Role of H-1 and H-2 Subunits of Soybean Seed Ferritin in Oxidative Deposition of Iron in Protein

Role of H-1 and H-2 Subunits of Soybean Seed Ferritin in Oxidative Deposition of Iron in Protein

Ferritin is required for rapid remodeling of the photosynthetic apparatus and minimizes photo‐oxidative stress in response to iron availability in Chlamydomonas reinhardtii

Protein Association and Dissociation Regulated by Ferric Ion

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