Hayes Robert P, Webb Brian N, Subramanian Arun Kumar, Nissen Mark, Popchock Andrew, Xun Luying, Kang ChulHee
Department of Chemistry, Washington State University, Pullman, WA 99164, USA.
School of Molecular Biosciences, Washington State University, Pullman, WA 99164, USA.
Int J Mol Sci. 2012;13(8):9769-9784. doi: 10.3390/ijms13089769. Epub 2012 Aug 6.
2,4,5-TCP 4-monooxygenase (TftD) and 2,4,6-TCP 4-monooxygenase (TcpA) have been discovered in the biodegradation of 2,4,5-trichlorophenol (2,4,5-TCP) and 2,4,6-trichlorophenol (2,4,6-TCP). TcpA and TftD belong to the reduced flavin adenine dinucleotide (FADH(2))-dependent monooxygenases and both use 2,4,6-TCP as a substrate; however, the two enzymes produce different end products. TftD catalyzes a typical monooxygenase reaction, while TcpA catalyzes a typical monooxygenase reaction followed by a hydrolytic dechlorination. We have previously reported the 3D structure of TftD and confirmed the catalytic residue, His289. Here we have determined the crystal structure of TcpA and investigated the apparent differences in specificity and catalysis between these two closely related monooxygenases through structural comparison. Our computational docking results suggest that Ala293 in TcpA (Ile292 in TftD) is possibly responsible for the differences in substrate specificity between the two monooxygenases. We have also identified that Arg101 in TcpA could provide inductive effects/charge stabilization during hydrolytic dechlorination. The collective information provides a fundamental understanding of the catalytic reaction mechanism and the parameters for substrate specificity. The information may provide guidance for designing bioremediation strategies for polychlorophenols, a major group of environmental pollutants.
在2,4,5-三氯苯酚（2,4,5-TCP）和2,4,6-三氯苯酚（2,4,6-TCP）的生物降解过程中发现了2,4,5-TCP 4-单加氧酶（TftD）和2,4,6-TCP 4-单加氧酶（TcpA）。TcpA和TftD属于依赖于还原型黄素腺嘌呤二核苷酸（FADH₂）的单加氧酶，二者均以2,4,6-TCP为底物；然而，这两种酶产生不同的终产物。TftD催化典型的单加氧酶反应，而TcpA催化典型的单加氧酶反应后接着进行水解脱氯反应。我们之前报道了TftD的三维结构并确定了催化残基His289。在此，我们测定了TcpA的晶体结构，并通过结构比较研究了这两种密切相关的单加氧酶在特异性和催化作用方面的明显差异。我们的计算对接结果表明，TcpA中的Ala293（TftD中的Ile292）可能是这两种单加氧酶底物特异性差异的原因。我们还确定，TcpA中的Arg101在水解脱氯过程中可提供诱导效应/电荷稳定作用。这些综合信息为催化反应机制和底物特异性参数提供了基本认识。该信息可为设计针对多氯苯酚（一类主要的环境污染物）的生物修复策略提供指导。
