CD and MCD Spectroscopic Studies of the Two Dps Miniferritin Proteins from Bacillus anthracis: Role of O2 and H2O2 Substrates in Reactivity of the Diiron Catalytic Centers
CD and MCD Spectroscopic Studies of the Two Dps Miniferritin Proteins from Bacillus anthracis: Role of O2 and H2O2 Substrates in Reactivity of the Diiron Catalytic Centers
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DOI：
10.1021/bi101346c
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发表时间：
2010-12-14
期刊：
影响因子：
2.9
通讯作者：
Solomon, Edward I.
中科院分区：
文献类型：
--
作者：
Schwartz, Jennifer K.;Liu, Xiaofeng S.;Solomon, Edward I.
饥饿期间的DNA保护（Dps）蛋白是在细菌和古细菌中发现的微铁蛋白，其提供对不受控制的Fe（II）/O自由基化学的保护;因此催化位点是针对病原体（例如炭疽）的抗生素的靶标。铁蛋白蛋白笼合成铁氧矿物从Fe（II）和O-2/H2 O2，它积累在大的中央腔; Dps，H2 O2是更常见的Fe（II）氧化剂与真核maxiferritins，往往喜欢分子氧。为了更好地理解大铁蛋白与小铁蛋白催化位点的差异，我们使用了NIR圆二色性（CD）、磁性圆二色性（MCD）和变温变场MCD的组合。（VTVH MCD）研究Fe（II）与两种炭疽杆菌微铁蛋白催化位点的结合：一种是两个Fe（II）只与O-2反应（Dps 1），另一种是O-2或H2 O2都能与两个Fe（II）反应（Dps 2）。两者都导致铁氧化物矿物的形成。数据显示，在不存在氧化剂的情况下，单个5-或6-配位Fe（II）; Fe（II）与Dps 2的结合比Dps 1稳定30倍;并且在不存在氧化剂的情况下，结合第二个Fe（II）的K-D下限比结合单个Fe（II）弱2-3个数量级。数据拟合的平衡模型，其中氧化剂的结合促进形成的催化位点，在形成鲜明对比的真核M-铁蛋白的双核Fe（II）中心的O-2结合前预形成。这两个不同的结合序列说明了铁蛋白家族的催化位点可能的机制范围。
DNA protection during starvation (Dps) proteins are miniferritins found in bacteria and archaea that provide protection from uncontrolled Fe(II)/O radical chemistry; thus the catalytic sites are targets for antibiotics against pathogens, such as anthrax. Ferritin protein cages synthesize ferric oxymineral from Fe(II) and O-2/H2O2, which accumulates in the large central cavity; for Dps, H2O2 is the more common Fe(II) oxidant contrasting with eukaryotic maxiferritins that often prefer dioxygen. To better understand the differences in the catalytic sites of maxi- versus miniferritins, we used a combination of NIR circular dichroism (CD), magnetic circular dichroism (MCD), and variable-temperature, variable-field MCD (VTVH MCD) to study Fe(II) binding to the catalytic sites of the two Bacillus anthracis miniferritins: one in which two Fe(II) react with O-2 exclusively (Dps1) and a second in which both O-2 or H2O2 can react with two Fe(II) (Dps2). Both result in the formation of iron oxybiomineral. The data show a single 5- or 6-coordinate Fe(II) in the absence of oxidant; Fe(II) binding to Dps2 is 30x more stable than Dps1; and the lower limit of K-D for binding a second Fe(II), in the absence of oxidant, is 2-3 orders of magnitude weaker than for the binding of the single Fe(II). The data fit an equilibrium model where binding of oxidant facilitates formation of the catalytic site, in sharp contrast to eukaryotic M-ferritins where the binuclear Fe(II) centers are preformed before binding of O-2. The two different binding sequences illustrate the mechanistic range possible for catalytic sites of the family of ferritins.