Elucidating the Role of O(2) Uncoupling in the Oxidative Biodegradation of Organic Contaminants by Rieske Non-heme Iron Dioxygenases.
Elucidating the Role of O(2) Uncoupling in the Oxidative Biodegradation of Organic Contaminants by Rieske Non-heme Iron Dioxygenases.
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DOI：
10.1021/acsenvironau.2c00023
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发表时间：
2022-09-21
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影响因子：
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通讯作者：
Hofstetter, Thomas B
中科院分区：
文献类型：
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作者：
Bopp, Charlotte E;Bernet, Nora M;Kohler, Hans-Peter E;Hofstetter, Thomas B
芳香族土壤和水污染物的氧化与分子O2催化的Rieske双加氧酶是常见的生物降解在自然和工程环境中的初始步骤。已知许多这些非血红素亚铁酶参与污染物代谢，但对导致成功生物降解的酶-底物相互作用的理解仍然难以捉摸。在这里，我们研究了两种硝基芳烃双加氧酶的O2活化和底物羟基化机制，以评估决定氧化产物形成效率的酶和底物特异性因素。2-硝基甲苯双加氧酶（2NTDO）和硝基苯双加氧酶（NBDO）与甲基-、氟-、氯-和羟基取代的硝基芳族底物的酶测定中的实验揭示，通常20-100%的酶活性涉及通过所谓的O2解偶联产生活性氧物质的O2活化的非生产性路径。18 O和13 C动力学同位素效应的O2活化和硝基芳族底物羟基化，分别表明，O2解偶联后发生生成的Fe III-（氢）过氧物种的催化循环。虽然2NTDO更有效地羟基化邻位取代的硝基芳族底物，但NBDO有利于间位取代，这可能是由于两种酶的不同活性位点残基。然而，我们的数据意味着，O2解偶联和羟基化活性不能从简单的结构-反应性关系进行评估。通过量化O2解偶联的Rieske双加氧酶，我们的工作提供了污染物生物降解，活性氧的产生，和可能的适应策略的微生物暴露于新的污染物之间的机械联系。
Oxygenations of aromatic soil and water contaminants with molecular O2 catalyzed by Rieske dioxygenases are frequent initial steps of biodegradation in natural and engineered environments. Many of these non-heme ferrous iron enzymes are known to be involved in contaminant metabolism, but the understanding of enzyme–substrate interactions that lead to successful biodegradation is still elusive. Here, we studied the mechanisms of O2 activation and substrate hydroxylation of two nitroarene dioxygenases to evaluate enzyme- and substrate-specific factors that determine the efficiency of oxygenated product formation. Experiments in enzyme assays of 2-nitrotoluene dioxygenase (2NTDO) and nitrobenzene dioxygenase (NBDO) with methyl-, fluoro-, chloro-, and hydroxy-substituted nitroaromatic substrates reveal that typically 20–100% of the enzyme’s activity involves unproductive paths of O2 activation with generation of reactive oxygen species through so-called O2 uncoupling. The 18O and 13C kinetic isotope effects of O2 activation and nitroaromatic substrate hydroxylation, respectively, suggest that O2 uncoupling occurs after generation of FeIII-(hydro)peroxo species in the catalytic cycle. While 2NTDO hydroxylates ortho-substituted nitroaromatic substrates more efficiently, NBDO favors meta-substituted, presumably due to distinct active site residues of the two enzymes. Our data implies, however, that the O2 uncoupling and hydroxylation activity cannot be assessed from simple structure–reactivity relationships. By quantifying O2 uncoupling by Rieske dioxygenases, our work provides a mechanistic link between contaminant biodegradation, the generation of reactive oxygen species, and possible adaptation strategies of microorganisms to the exposure of new contaminants.