Šuchová Katarína, Puchart Vladimír, Spodsberg Nikolaj, Mørkeberg Krogh Kristian B R, Biely Peter
Institute of Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, 84538 Bratislava, Slovakia.
Novozymes A/S, Krogshøjvej 36, 2880 Bagsværd, Denmark.
Molecules. 2021 Jul 27;26(15):4528. doi: 10.3390/molecules26154528.
Catalytic properties of GH30 xylanases belonging to subfamilies 7 and 8 were compared on glucuronoxylan, modified glucuronoxylans, arabinoxylan, rhodymenan, and xylotetraose. Most of the tested bacterial GH30-8 enzymes are specific glucuronoxylanases (EC 3.2.1.136) requiring for action the presence of free carboxyl group of MeGlcA side residues. These enzymes were not active on arabinoxylan, rhodymenan and xylotetraose, and conversion of MeGlcA to its methyl ester or its reduction to MeGlc led to a remarkable drop in their specific activity. However, some GH30-8 members are nonspecific xylanases effectively hydrolyzing all tested substrates. In terms of catalytic activities, the GH30-7 subfamily is much more diverse. In addition to specific glucuronoxylanases, the GH30-7 subfamily contains nonspecific endoxylanases and predominantly exo-acting enzymes. The activity of GH30-7 specific glucuronoxylanases also depend on the presence of the MeGlcA carboxyl, but not so strictly as in bacterial enzymes. The modification of the carboxyl group of glucuronoxylan had only weak effect on the action of predominantly exo-acting enzymes, as well as nonspecific xylanases. Rhodymenan and xylotetraose were the best substrates for exo-acting enzymes, while arabinoxylan represented hardly degradable substrate for almost all tested GH30-7 enzymes. The results expand current knowledge on the catalytic properties of this relatively novel group of xylanases.
对属于第7和第8亚家族的GH30木聚糖酶在葡糖醛酸木聚糖、修饰的葡糖醛酸木聚糖、阿拉伯木聚糖、红藻多糖和木四糖上的催化特性进行了比较。大多数测试的细菌GH30 - 8酶是特异性葡糖醛酸木聚糖酶（EC 3.2.1.136），其作用需要MeGlcA侧链残基的游离羧基存在。这些酶对阿拉伯木聚糖、红藻多糖和木四糖无活性，将MeGlcA转化为其甲酯或还原为MeGlc会导致其比活性显著下降。然而，一些GH30 - 8成员是能有效水解所有测试底物的非特异性木聚糖酶。就催化活性而言，GH30 - 7亚家族更加多样化。除了特异性葡糖醛酸木聚糖酶外，GH30 - 7亚家族还包含非特异性内切木聚糖酶和主要为外切作用的酶。GH30 - 7特异性葡糖醛酸木聚糖酶的活性也取决于MeGlcA羧基的存在，但不像细菌酶那样严格。葡糖醛酸木聚糖羧基的修饰对主要为外切作用的酶以及非特异性木聚糖酶的作用只有微弱影响。红藻多糖和木四糖是外切作用酶的最佳底物，而阿拉伯木聚糖对几乎所有测试的GH30 - 7酶来说几乎是不可降解的底物。这些结果扩展了目前关于这一相对新颖的木聚糖酶组催化特性的知识。
