A novel esterase LanE from Edaphocola flava HME-24 and the enantioselective degradation mechanism of herbicide lactofen
A novel esterase LanE from Edaphocola flava HME-24 and the enantioselective degradation mechanism of herbicide lactofen
复制标题
Edaphocola flava HME-24新型酯酶LanE及除草剂lactofen的对映选择性降解机制
DOI：
10.1016/j.ecoenv.2020.111141
复制
发表时间：
2020-12-01
影响因子：
6.8
通讯作者：
Huang, Xing
中科院分区：
文献类型：
--
作者：
Hu, Ting;Xiang, Yun;Huang, Xing
乳酰氟草醚是一种手性除草剂，广泛应用于农业上防治阔叶杂草。作为农药，它直接释放到环境中，容易对土壤和水生生态系统造成污染。乳氟菌醚在环境中的对映体选择性降解已有报道，但其分子生物学机制尚不清楚。在本研究中，菌株黄地粪杆菌HME-24在72 h内对50 mg L（-1）乳氟醚的降解率可达96.7%。乳酸菌醚最初被水解为去乙基乳酸菌醚，随后被菌株HME-24水解为三氟羧草醚。从黄地霉HME-24中获得了一个新的基因lanE，该基因参与乳芬转化。lanE基因编码471个氨基酸，含有保守的GXSXG酯酶基序，与海栖热袍菌MSB 8的酯酶EstD（Q9 WYH 1）同源性最高（29.14%）。该酯酶也能转化对硝基苯基酯（C4-C8），且活性随碳链长度的增加而降低。LanE对乳酰草醚、禾草灵和精喹禾灵的降解表现出对映体选择性，（S）-对映体的降解效率高于（R）-对映体。通过分子对接模拟了LanE的三维结构，发现当乳酰菌酯的（S）-对映体占据活性中心时，配体分子与配位原子之间的距离比（R）-对映体占据活性中心时的距离短，有利于过渡态配合物的形成。本研究结果在分子水平上加深了我们对乳氟菌醚（S）-对映体的优先催化作用的理解，并可以解释已报道的乳氟菌醚在环境中的对映体选择性降解。
Lactofen is a chiral herbicide and widely used against broadleaf weeds in agriculture. As a pesticide, it is directly released to the environment, and easily caused contamination in soil and aquatic ecosystem. The enantioselective degradation of lactofen in the environment has been reported, but the molecular biological mechanism of this phenomenon is still unclear. In this study, strain Edaphocola flava HME-24 could degrade 96.7% of 50 mg L(-1 )lactofen within 72 h. Lactofen was initially hydrolyzed to desethyl lactofen and subsequently acifluorfen by strain HME-24. A novel gene lanE, involved in lactofen transformation, was obtained from Edaphocola flava HME-24. Gene lanE encoded a protein of 471 amino acids that contained the conserved GXSXG esterase motif and clustered into esterase subfamily V. LanE shared the highest identity with esterase EstD (Q9WYH1) from Thermotoga maritima MSB8 (29.14%). This esterase was also able to transform p-nitrophenyl esters (C4-C8), and the activity decreased when the carbon chain length increased. LanE showed enantioselectivity during the degradation of lactofen, diclofop-methyl, and quizalofop-ethyl, with a higher degradation efficiency of (S)-enantiomers than (R)-enantiomers. The three-dimensional structure of LanE was simulated, and molecular docking revealed that when the (S)-enantiomers of lactofen occupied the active sites, the distance between the ligand molecule and the coordination atom was shorter than that when the (R)-enantiomers occupied the active sites, which facilitated the formation of the transition state complex. The results in this study enhanced our understanding of the preferential catabolism of the (S)-enantiomers of lactofen on the molecular level and could illustrate the reported enantioselective degradation of lactofen in the environment.