Epoxide hydrolases catalyze the conversion of epoxides to vicinal diols in a range of cellular processes such as signaling, detoxification, and virulence. These enzymes typically utilize a pair of tyrosine residues to orient the substrate epoxide ring in the active site and stabilize the hydrolysis intermediate. A new subclass of epoxide hydrolases that utilize a histidine in place of one of the tyrosines was established with the discovery of the CFTR Inhibitory Factor (Cif) from Pseudomonas aeruginosa. Although the presence of such Cif-like epoxide hydrolases was predicted in other opportunistic pathogens based on sequence analyses, only Cif and its homologue aCif from Acinetobacter nosocomialis have been characterized. Here we report the biochemical and structural characteristics of Cfl1 and Cfl2, two Cif-like epoxide hydrolases from Burkholderia cenocepacia. Cfl1 is able to hydrolyze xenobiotic as well as biological epoxides that might be encountered in the environment or during infection. In contrast, Cfl2 shows very low activity against a diverse set of epoxides. The crystal structures of the two proteins reveal quaternary structures that build on the well-known dimeric assembly of the α/β hydrolase domain, but broaden our understanding of the structural diversity encoded in novel oligomer interfaces. Analysis of the interfaces reveals both similarities and key differences in sequence conservation between the two assemblies, and between the canonical dimer and the novel oligomer interfaces of each assembly. Finally, we discuss the effects of these higher-order assemblies on the intra-monomer flexibility of Cfl1 and Cfl2 and their possible roles in regulating enzymatic activity.

中文翻译：

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洋葱伯克霍尔德菌中两种类似Cif的环氧水解酶的生化和结构表征

环氧水解酶在一系列细胞过程中（例如信号传导，解毒和毒力）催化环氧化物向邻二醇的转化。这些酶通常利用一对酪氨酸残基来使底物环氧环在活性位点定向并稳定水解中间体。随着铜绿假单胞菌的CFTR抑制因子（Cif）的发现，建立了一种利用组氨酸代替酪氨酸的新型环氧化物水解酶亚类。尽管基于序列分析预测在其他机会性病原体中会存在这种Cif样环氧化物水解酶，但只有Cif及其来自医院不动杆菌的同系物aCif已被表征。在这里，我们从两个到岸价格状的环氧化物水解酶报告CFL1和CFL2，生化和结构特点新洋葱伯克霍尔德菌。Cfl1能够水解环境或感染期间可能遇到的异种生物以及生物环氧化物。相反，Cf12对各种环氧化物显示出非常低的活性。两种蛋白质的晶体结构揭示了基于已知的α/β水解酶结构域的二聚体组装的四级结构，但拓宽了我们对新型低聚物界面中编码的结构多样性的理解。对界面的分析揭示了两个组件之间，以及每个组件的规范二聚体和新型低聚物界面之间在序列保守性上的相似性和关键差异。最后，我们讨论了这些高级组装体对Cfl1和Cfl2单体内柔性的影响以及它们在调节酶活性中的可能作用。