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首页> 外文期刊>Biochemistry >Functionality of the Three-Site Ferroxidase Center of Escherichia coli Bacterial Ferritin (EcFtnA)
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Functionality of the Three-Site Ferroxidase Center of Escherichia coli Bacterial Ferritin (EcFtnA)

机译：大肠杆菌细菌铁蛋白（EcFtnA）的三点铁氧化酶中心的功能

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摘要

At least three ferritins are found in the bacterium Escherichia coli: the heme-containing bacterioferritin (EcBFR) and two nonheme bacterial ferritins (EcFtnA and EcFtnB). In addition to the conserved A and B sites of the diiron ferroxidase center, EcFtnA has a third iron-binding site (the C site) of unknown function that is nearby the diiron site. In the present work, the complex chemistry of iron oxidation and deposition in EcFtnA was further defined through a combination of oximetry, pH stat, stopped-flow and conventional kinetics, UV?vis, fluorescence, and EPR spectroscopic measurements on both the wild-type protein and site-directed variants of the A, B, and C sites. The data reveal that although H_2O_2 is a product of dioxygen reduction in EcFtnA and oxidation occurs with a stoichiometry of Fe~(2+)/O_2 ～ 3:1 most of the H_2O_2 produced is consumed in subsequent reactions with a 2:1 Fe~(2+)/H_2O_2 stoichiometry, thus suppressing hydroxyl-radical formation. Although the A and B sites are essential for rapid iron oxidation, the C site slows oxidation and suppresses iron turnover at the ferroxidase center. A tyrosyl radical, assigned to Tyr24 near the ferroxidase center, is formed during iron oxidation, and its possible significance to the function of the protein is discussed. Taken as a whole, the data indicate that there are multiple iron-oxidation pathways in EcFtnA with O_2 and H_2O_2 as oxidants. Furthermore, our data do not support a universal mechanism for iron oxidation in all ferritins whereby the C site acts as transit site, as has been recently proposed.
机译：在细菌大肠杆菌中至少发现了三种铁蛋白：含血红素的细菌铁蛋白（EcBFR）和两种非血红素细菌铁蛋白（EcFtnA和EcFtnB）。除二铁亚铁氧化酶中心的保守的A和B位点外，EcFtnA在二铁位点附近还有一个功能未知的铁结合位点（C位）。在目前的工作中，通过结合血氧测定法，pH stat，停止流和常规动力学，UV可见光，荧光和EPR光谱测量，对EcFtnA中铁的氧化和沉积的复杂化学进行了进一步的定义。蛋白，A，B和C位点的定点变异体。数据显示，尽管H_2O_2是EcFtnA中双氧还原的产物，并且氧化反应发生在化学计量为Fe〜（2 +）/ O_2〜3：1的情况下，但大部分的H_2O_2在随后的反应中以2：1的Fe〜被消耗。 （2 +）/ H_2O_2化学计量，从而抑制了羟基自由基的形成。尽管A和B位对于快速的铁氧化至关重要，但C位可减缓氧化并抑制铁氧化酶中心的铁转换。在铁氧化过程中形成了一个在铁氧化酶中心附近分配给Tyr24的酪氨酸基团，并讨论了其对蛋白质功能的可能意义。总体而言，数据表明，以O_2和H_2O_2为氧化剂的EcFtnA中存在多个铁氧化途径。此外，我们的数据不支持所有铁蛋白中铁氧化的普遍机制，因此C位点充当转运位点，正如最近提出的那样。

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