Mechanism of ferrous iron binding and oxidation by ferritin from a pennate diatom.
Mechanism of ferrous iron binding and oxidation by ferritin from a pennate diatom.
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DOI：
10.1074/jbc.m113.454496
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发表时间：
2013-05-24
期刊：
影响因子：
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通讯作者：
Murphy ME
中科院分区：
文献类型：
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作者：
Pfaffen S;Abdulqadir R;Le Brun NE;Murphy ME
背景：铁蛋白通过铁氧化来储存铁，形成矿物核心，使硅藻在铁输入时大量繁殖。结果：亚铁以厌氧方式与铁氧合酶A结合。铁氧化动力学有两个观察阶段。结论：亚铁和氧气与二铁氧化铁酶的结合是逐步进行的。意义：铁蛋白储存铁需要铁和氧气的协调结合。一种新的铁蛋白最近在伪菱形藻多系列(PmFTN)中被发现，PmFTN是一种海洋羽状硅藻，在全球初级生产和深海固碳中发挥着重要作用。将重组PmFTN的晶体浸泡在铁和锌溶液中，结构解析到1.65-2.2-Å。三个不同的铁结合位置被确定为从好氧生长的浸泡亚铁晶体的异常分散数据中确定的。位点A和B包含保守的铁氧合酶活性位点，而位点C形成一条通向发生铁存储的中央空腔的路径。相反，从厌氧生长和铁浸泡的晶体中得到的晶体结构显示，在活性位上只有一个亚铁占据A位。在氧气的存在下，锌与所有三个位都结合在一起。停流吸收光谱分析表明，在apo-PmFTN(每个亚单位两个亚铁)中加入48个亚铁后，在氧化铁酶中心有一个相当于Fe(II)氧化的极快相，而由于铁核的形成，这一相达到饱和。这些结果表明，在准备催化的过程中，亚铁和氧气有序地逐步结合到亚铁氧基酶的位置上，并在氧化后从该位置部分动员了铁。
Background: Ferritin stores iron by ferroxidation to form a mineral core, enabling diatom blooms upon iron input. Results: Ferrous iron binds solely to ferroxidase site A anaerobically. Ferroxidation kinetics has two observed phases. Conclusion: Ferrous iron and dioxygen binding to the di-iron ferroxidase site is stepwise. Significance: Iron storage by ferritins requires a coordinated binding of iron and dioxygen. A novel ferritin was recently found in Pseudo-nitzschia multiseries (PmFTN), a marine pennate diatom that plays a major role in global primary production and carbon sequestration into the deep ocean. Crystals of recombinant PmFTN were soaked in iron and zinc solutions, and the structures were solved to 1.65–2.2-Å resolution. Three distinct iron binding sites were identified as determined from anomalous dispersion data from aerobically grown ferrous soaked crystals. Sites A and B comprise the conserved ferroxidase active site, and site C forms a pathway leading toward the central cavity where iron storage occurs. In contrast, crystal structures derived from anaerobically grown and ferrous soaked crystals revealed only one ferrous iron in the active site occupying site A. In the presence of dioxygen, zinc is observed bound to all three sites. Iron oxidation experiments using stopped-flow absorbance spectroscopy revealed an extremely rapid phase corresponding to Fe(II) oxidation at the ferroxidase site, which is saturated after adding 48 ferrous iron to apo-PmFTN (two ferrous iron per subunit), and a much slower phase due to iron core formation. These results suggest an ordered stepwise binding of ferrous iron and dioxygen to the ferroxidase site in preparation for catalysis and a partial mobilization of iron from the site following oxidation.