Crystal structures of oxidized dinuclear manganese centres in Mn-substituted class I ribonucleotide reductase from Escherichia coli:: carboxylate shifts with implications for O2 activation and radical generation
Crystal structures of oxidized dinuclear manganese centres in Mn-substituted class I ribonucleotide reductase from Escherichia coli:: carboxylate shifts with implications for O2 activation and radical generation
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DOI：
10.1007/s007750000205
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发表时间：
2001-03-01
影响因子：
3
通讯作者：
Nordlund, P
中科院分区：
文献类型：
--
作者：
Högbom, M;Andersson, ME;Nordlund, P
羧酸二铁蛋白构成多种非血红素铁酶，执行多种氧化还原反应。这些反应通常涉及高价铁氧物种，并被认为是由羧酸盐位移控制的。由于其寿命短，这些中间结构迄今为止未能通过 X 射线晶体学进行结构表征。为了绘制不同氧化还原状态和不同配体环境下蛋白质可用的羧酸盐构象，我们研究了大肠杆菌核糖核苷酸还原酶 R2 蛋白的金属取代形式。在目前的工作中，我们已经解决了以两种不同方式氧化的Mn取代R2的晶体结构。使用一氧化氮或过氧化氢和羟胺的组合进行氧化。这两种结构实际上相同，表明氧化态相同，很可能是混合价 Mn-II-Mn-III 中心。其中一个羧酸配体 (D84) 采用了一种迄今为止未见的新构象，它可以参与 R2 中自由基生成的机制。 E238 采用桥接螯合构象，该构象对于适当的 O-2 激活很重要，但之前在野生型酶中未观察到。在 H2O2 氧化过程中也观察到了可能的过氧化氢酶活性，表明其与二锰过氧化氢酶的机制相似。
The di-iron carboxylate proteins constitute a diverse class of non-heme iron enzymes performing a multitude of redox reactions. These reactions usually involve high-valent Fe-oxo species and are thought to be controlled by carboxylate shifts. Owing to their short lifetime, the intermediate structures have so far escaped structural characterization by X-ray crystallography. In an attempt to map the carboxylate conformations available to the protein during different redox states and different ligand environments, we have studied metal-substituted forms of the R2 protein of ribonucleotide reductase from Escherichia coli. In the present work we have solved the crystal structures of Mn-substituted R2 oxidized in two different ways. Oxidation was performed using either nitric oxide or a combination of hydrogen peroxide and hydroxylamine. The two structures are virtually identical, indicating that the oxidation states are the same, most likely a mixed-valent Mn-II-Mn-III centre. One of the carboxylate ligands (D84) adopts a new, so far unseen, conformation, which could participate in the mechanism for radical generation in R2. E238 adopts a bridging-chelating conformation proposed to be important for proper O-2 activation but not previously observed in the wild-type enzyme. Probable catalase activity was also observed during the oxidation with H2O2 indicating mechanistic similarities to the di-Mn catalases.