Vanillyl alcohol oxidase (VAO) and eugenol oxidase (EUGO) are flavin-dependent enzymes that catalyse the oxidation of para-substituted phenols. This makes them potentially interesting biocatalysts for the conversion of lignin-derived aromatic monomers to value-added compounds. To facilitate their biocatalytic exploitation, it is important to develop methods by which variants of the enzymes can be rapidly screened for increased activity towards substrates of interest. Here, we present the development of a screening assay for the substrate specificity of para-phenol oxidases based on the detection of hydrogen peroxide using the ferric-xylenol orange complex method. The assay was used to screen the activity of VAO and EUGO towards a set of twenty-four potential substrates. This led to the identification of 4-cyclopentylphenol as a new substrate of VAO and EUGO and 4-cyclohexylphenol as a new substrate of VAO. Screening of a small library of VAO and EUGO active-site variants for alterations in their substrate specificity led to the identification of a VAO variant (T457Q) with increased activity towards vanillyl alcohol (4-hydroxy-3-methoxybenzyl alcohol) and a EUGO variant (V436I) with increased activity towards chavicol (4-allylphenol) and 4-cyclopentylphenol. This assay provides a quick and efficient method to screen the substrate specificity of para-phenol oxidases, facilitating the enzyme engineering of known para-phenol oxidases and the evaluation of the substrate specificity of novel para-phenol oxidases.
香草醇氧化酶(VAO)和
丁香酚氧化酶(EUGO)是依赖黄素的酶,可催化对位取代
酚的氧化。这使它们成为将
木质素衍生的芳香族单体转化为高附加值化合物的潜在
生物催化剂。为了促进它们的
生物催化利用,重要的是要开发出可以快速筛选酶变体的方法,以提高它们对相关底物的活性。在此,我们介绍了对位
苯酚氧化酶底物特异性筛选测定法的开发情况,该测定法基于使用
铁-
二甲酚橙复合物法检测
过氧化氢。该检测方法用于筛选 VAO 和 EUGO 对二十四种潜在底物的活性。结果发现
4-环戊基苯酚是 VAO 和 EUGO 的新底物,4-
环己基苯酚是 VAO 的新底物。通过筛选 VAO 和 EUGO 活性位点变体的小型文库以确定其底物特异性的变化,结果发现 VAO 变体(T457Q)对
香草醇(
4-羟基-3-
甲氧基苯甲醇)的活性增强,而 EUGO 变体(V436I)对辣椒
酚(4-烯丙基
苯酚)和
4-环戊基苯酚的活性增强。这种检测方法为筛选对位
苯酚氧化酶的底物特异性提供了一种快速有效的方法,有助于对已知的对位
苯酚氧化酶进行酶工程改造和评估新型对位
苯酚氧化酶的底物特异性。