Swapping metals in Fe- and Mn-dependent dioxygenases: Evidence for oxygen activation without a change in metal redox state
Swapping metals in Fe- and Mn-dependent dioxygenases: Evidence for oxygen activation without a change in metal redox state
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DOI：
10.1073/pnas.0711179105
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发表时间：
2008-05-27
影响因子：
11.1
通讯作者：
Que, Lawrence, Jr.
中科院分区：
文献类型：
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作者：
Emerson, Joseph P.;Kovaleva, Elena G.;Que, Lawrence, Jr.
生物O-2激活通常发生在与酶活性位点的还原金属结合后[例如M(II)]。随后M（II）到o- 2的电子转移产生6个反应性M(III)-超氧物种。对于外二醇芳环切割双加氧酶，我们提出了一种不同的模型，其中电子通过它们都结合的M（II）中心从底物转移到O-2，从而避免了金属氧化还原状态的整体变化。该模型使用同源原茶酸2,3-双加氧酶进行了测试，这些酶来自fuscum短杆菌（Fe-HPCD）和globiformarthrobacter (Mn-MndD)，它们具有高序列同一性和非常相似的结构。尽管有这些相似之处，Fe- hpcd结合Fe(II)，而Mn- mndd结合Mn（II）。描述了将非生理性金属（Mn-HPCD和Fe-MndD）掺入每种酶的方法。在1.7埃下，Mn- hpcd的x射线晶体结构与Fe- hpcd没有明显区别，而EPR研究表明，Mn- mndd和Mn- hpcd的Mn（II）位以及Fe- hpcd和Fe- mndd的NO配合物的Fe（II）位非常相似。这些酶的均匀金属位点结构表明，外二醇双加氧酶不能区别地补偿游离铁和锰氧化还原电位的0.7 v间隙。尽管如此，这四种酶的K-m和V-max值几乎相同。这些酶组成了一对不寻常的金属加氧酶，在金属交换后仍保持完全活性，这暗示了金属在不改变金属氧化还原状态的情况下促进氧活化的不同方式。
Biological O-2 activation often occurs after binding to a reduced metal [e.g., M(II)] in an enzyme active site. Subsequent M(II)-to-O-2 electron transfer results in 6 reactive M(III)-superoxo species. For the extradiol aromatic ring-cleaving dioxygenases, we have proposed a different model where an electron is transferred from substrate to O-2 via the M(II) center to which they are both bound, thereby obviating the need for an integral change in metal redox state. This model is tested by using homoprotocatechuate 2,3-dioxygenases from Brevibacterium fuscum (Fe-HPCD) and Arthrobacter globiformis (Mn-MndD) that share high sequence identity and very similar structures. Despite these similarities, Fe-HPCD binds Fe(II) whereas Mn-MndD incorporates Mn(II). Methods are described to incorporate the non physiological metal into each enzyme (Mn-HPCD and Fe-MndD). The x-ray crystal structure of Mn-HPCD at 1.7 angstrom is found to be indistinguishable from that of Fe-HPCD, while EPR studies show that the Mn(II) sites of Mn-MndD and Mn-HPCD, and the Fe(II) sites of the NO complexes of Fe-HPCD and Fe-MndD, are very similar. The uniform metal site structures of these enzymes suggest that extradiol dioxygenases cannot differentially compensate for the 0.7-V gap in the redox potentials of free iron and manganese. Nonetheless, all four enzymes exhibit nearly the same K-m and V-max values. These enzymes constitute an unusual pair of metallo-oxygenases that remain fully active after a metal swap, implicating a different way by which metals are used to promote oxygen activation without an integral change in metal redox state.