A Diatom Ferritin Optimized for Iron Oxidation but Not Iron Storage.
A Diatom Ferritin Optimized for Iron Oxidation but Not Iron Storage.
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DOI：
10.1074/jbc.m115.669713
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发表时间：
2015-11-20
期刊：
影响因子：
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通讯作者：
Murphy MEP
中科院分区：
文献类型：
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作者：
Pfaffen S;Bradley JM;Abdulqadir R;Firme MR;Moore GR;Le Brun NE;Murphy MEP
背景：铁蛋白储存铁使硅藻在铁输入后水华。结果：铁氧化酶中心变体显示更快的铁矿化和铁的氧化后重组速率。结论：Glu-130和Glu-44通过亚铁氧化酶中心调节铁的通量。重要性：铁蛋白的铁氧化而不是矿化的优化表明，除了长期的铁储存铁缓冲功能。海洋羽状硅藻多系拟菱形藻（Pseudo-nitzschia multiseries，PmFTN）中的铁蛋白在铁有限的海洋环境中维持生长中起着关键作用。PmFTN的二铁催化亚铁氧化酶中心（位点A和B）在原核铁蛋白中通常观察到的排列中具有附近的第三个铁位点（位点C）。在这里，我们证明，Glu-44，一个网站C的配体，和Glu-130，一个残基，桥铁结合在网站B和C，限制后氧化重组的铁配位和速度，其中Fe 3+退出铁氧化酶中心的矿物核心内的存储。特别是后者，严重限制了铁矿化的总体速率。因此，硅藻铁蛋白是优化的初始Fe 2+氧化，但不是矿化，指出这种蛋白质的作用，在缓冲铁的可用性和促进铁节约，而不仅仅是长期的铁存储。
Background: Iron storage by ferritin enables diatom bloom upon iron input. Results: Ferroxidase center variants show faster iron mineralization and rate of post-oxidation reorganization of iron. Conclusion: Glu-130 and Glu-44 regulate the flux of iron through the ferroxidase center. Significance: Optimization of ferritin for iron oxidation but not mineralization suggests an iron buffering function in addition to long-term iron storage. Ferritin from the marine pennate diatom Pseudo-nitzschia multiseries (PmFTN) plays a key role in sustaining growth in iron-limited ocean environments. The di-iron catalytic ferroxidase center of PmFTN (sites A and B) has a nearby third iron site (site C) in an arrangement typically observed in prokaryotic ferritins. Here we demonstrate that Glu-44, a site C ligand, and Glu-130, a residue that bridges iron bound at sites B and C, limit the rate of post-oxidation reorganization of iron coordination and the rate at which Fe3+ exits the ferroxidase center for storage within the mineral core. The latter, in particular, severely limits the overall rate of iron mineralization. Thus, the diatom ferritin is optimized for initial Fe2+ oxidation but not for mineralization, pointing to a role for this protein in buffering iron availability and facilitating iron-sparing rather than only long-term iron storage.