ATP-Dependent C–F Bond Cleavage Allows the Complete Degradation of 4-Fluoroaromatics without Oxygen
ATP-Dependent C–F Bond Cleavage Allows the Complete Degradation of 4-Fluoroaromatics without Oxygen
复制标题
ATP 依赖性 CâF 键断裂可在无氧条件下完全降解 4-氟芳族化合物
作者：
Tiedt O;Mergelsberg M;Boll K;Müller M;Adrian L;Jehmlich N;von Bergen M;Boll M
丰富且持久的含氟芳香族化合物的完全生物降解需要芳基 C-F 键的酶裂解，这可能是可生物降解有机分子中最稳定的单键。虽然在需氧微生物中，含氟芳香族化合物的脱氟是由加氧酶引发的，但在缺氧的情况下从未观察到芳基 C-F 键断裂。在这里，描述了在反硝化的 Thaueraaromatica 中 4-氟苯甲酸酯或 4-氟甲苯完全降解为 CO2 和 HF 的过程中，不依赖于氧的酶促芳基氟键断裂：4-氟苯甲酰辅酶 A (4-F-BzCoA) 到苯甲酰辅酶 A (BzCoA) 和 HF 的 ATP 依赖性脱氟，由 I 类催化BzCoA 还原酶 (BCR)。通过在转录水平上下调混杂的苯甲酸酯-CoA 连接酶并同时上调 4-F-BzCoA-脱氟/脱芳构化 BCR 来适应含氟芳香族化合物的生长。我们提出了一种前所未有的还原芳基 C-F 键断裂机制，通过类似 Birch 还原的机制，导致正式的亲核芳香取代。在所提出的阴离子 4-氟二烯酰基-CoA 过渡态中，氟化物消除为 BzCoA 优于质子化为氟化环状二烯酰基-CoA。它们被认为是一类不断增长的与环境相关的持久性污染物。特别是对于含氟芳香族化合物，芳基 C-F 键的极端稳定性阻碍了生物降解。在需氧微生物中，降解通过加氧酶依赖性 C-F 键裂解反应进行，而缺氧位点参与含氟芳香族化合物降解的酶尚不清楚。在此，我们报告了一种在反硝化细菌中通过活化为 CoA 酯，然后由 ATP 依赖性酶催化的不依赖于氧的芳基 C-F 键裂解，将氟芳香族化合物完全生物降解为 CO2 和 HF 的策略。该反应与对氟化生长底物的转录适应相结合，对于 4-氟苯甲酸酯/4-F-甲苯以及可能的其他含氟芳香族化合物的缺氧生物降解至关重要。
Complete biodegradation of the abundant and persistent fluoroaromatics requires enzymatic cleavage of an arylic C–F bond, probably the most stable single bond of a biodegradable organic molecule. While in aerobic microorganisms defluorination of fluoroaromatics is initiated by oxygenases, arylic C–F bond cleavage has never been observed in the absence of oxygen. Here, an oxygen-independent enzymatic aryl fluoride bond cleavage is described during the complete degradation of 4-fluorobenzoate or 4-fluorotoluene to CO2and HF in the denitrifying Thauera aromatica: the ATP-dependent defluorination of 4-fluorobenzoyl-coenzyme A (4-F-BzCoA) to benzoyl-coenzyme A (BzCoA) and HF, catalyzed by class I BzCoA reductase (BCR). Adaptation to growth with the fluoroaromatics was accomplished by the downregulation of a promiscuous benzoate-CoA ligase and the concomitant upregulation of 4-F-BzCoA-defluorinating/dearomatizing BCR on the transcriptional level. We propose an unprecedented mechanism for reductive arylic C–F bond cleavage via a Birch reduction-like mechanism resulting in a formal nucleophilic aromatic substitution. In the proposed anionic 4-fluorodienoyl-CoA transition state, fluoride elimination to BzCoA is favored over protonation to a fluorinated cyclic dienoyl-CoA.IMPORTANCEOrganofluorides are produced as pesticides, pharmaceuticals, and other chemicals and comprise approximately one quarter of all organic compounds in the pharmaceutical and agricultural sectors; they are considered a growing class of environmentally relevant persistent pollutants. Especially in the case of fluoroaromatics, biodegradation is hampered by the extreme stability of the arylic C–F bond. In aerobic microorganisms, degradation proceeds via oxygenase-dependent C–F bond cleavage reactions, whereas the enzymes involved in the degradation of fluoroaromatics at anoxic sites are unknown. Here we report a strategy for the complete biodegradation of a fluoroaromatic to CO2and HF in a denitrifying bacterium via activation to a CoA ester, followed by oxygen-independent arylic C–F bond cleavage catalyzed by an ATP-dependent enzyme. This reaction, in conjunction with a transcriptional adaptation to fluorinated growth substrates, is essential for the anoxic biodegradation of 4-fluorobenzoate/4-F-toluene and probably other fluoroaromatics.
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DOI：
10.1039/c1cp20505f
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