The Novel Bacterial N-Demethylase PdmAB Is Responsible for the Initial Step of N,N-Dimethyl-Substituted Phenylurea Herbicide Degradation
The Novel Bacterial N-Demethylase PdmAB Is Responsible for the Initial Step of N,N-Dimethyl-Substituted Phenylurea Herbicide Degradation
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新型细菌 N-去甲基酶 PdmAB 负责 N,N-二甲基取代的苯脲除草剂降解的第一步
DOI：
10.1128/aem.02478-13
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发表时间：
2013-12-01
影响因子：
4.4
通讯作者：
Li, Shunpeng
中科院分区：
文献类型：
--
作者：
Gu, Tao;Zhou, Chaoyang;Li, Shunpeng
摘要苯脲类除草剂的环境归趋问题在近几十年来引起了人们的广泛关注。N，N-二甲基取代苯基脲类除草剂的微生物代谢一般可通过单N-脱甲基作用启动。在这项研究中，揭示了这一过程的分子基础。Sphingobium sp.菌株YBL 2中的pdmAB基因被证明负责常用的N，N-二甲基取代苯基脲除草剂的初始单-N-脱甲基化。PdmAB是细菌Rieske非血红素铁加氧酶（RO）系统的加氧酶组分。编码α亚基PdmA和β亚基PdmB的基因pdmAB被组织在转座元件中，该转座元件两侧是类似ISRh1的插入元件的两个直接重复序列。此外，这种转座因子是高度保守的苯脲除草剂降解鞘氨醇单胞菌来自世界不同地区。然而，没有证据表明电子载体（铁氧还蛋白或还原酶）基因位于pdmAB附近。没有它的同源电子传递组件，在大肠杆菌，恶臭假单胞菌，和其他鞘单胞菌中的PdmAB的表达导致功能酶。此外，从鞘氨醇单胞菌菌株RW 1的推定的[3Fe-4S]型铁氧还蛋白的共表达大大提高了PdmAB在E.杆菌这些数据表明PdmAB对电子传递组分的特异性较低，其最佳铁氧还蛋白可能是[3Fe-4S]型。PdmA表现出与先前表征的RO的α亚基的低同源性（小于37%的同一性），并且不与参与O-或N-脱甲基化反应的RO基团聚簇，表明PdmAB是一种独特的细菌RO N-脱甲基酶。
ABSTRACT The environmental fate of phenylurea herbicides has received considerable attention in recent decades. The microbial metabolism of N,N-dimethyl-substituted phenylurea herbicides can generally be initiated by mono-N-demethylation. In this study, the molecular basis for this process was revealed. The pdmAB genes in Sphingobium sp. strain YBL2 were shown to be responsible for the initial mono-N-demethylation of commonly used N,N-dimethyl-substituted phenylurea herbicides. PdmAB is the oxygenase component of a bacterial Rieske non-heme iron oxygenase (RO) system. The genes pdmAB, encoding the α subunit PdmA and the β subunit PdmB, are organized in a transposable element flanked by two direct repeats of an insertion element resembling ISRh1. Furthermore, this transposable element is highly conserved among phenylurea herbicide-degrading sphingomonads originating from different areas of the world. However, there was no evidence of a gene for an electron carrier (a ferredoxin or a reductase) located in the immediate vicinity of pdmAB. Without its cognate electron transport components, expression of PdmAB in Escherichia coli, Pseudomonas putida, and other sphingomonads resulted in a functional enzyme. Moreover, coexpression of a putative [3Fe-4S]-type ferredoxin from Sphingomonas sp. strain RW1 greatly enhanced the catalytic activity of PdmAB in E. coli. These data suggested that PdmAB has a low specificity for electron transport components and that its optimal ferredoxin may be the [3Fe-4S] type. PdmA exhibited low homology to the α subunits of previously characterized ROs (less than 37% identity) and did not cluster with the RO group involved in O- or N-demethylation reactions, indicating that PdmAB is a distinct bacterial RO N-demethylase.