Kojima Keisuke, Sunagawa Naoki, Yoshimi Yoshihisa, Tryfona Theodora, Samejima Masahiro, Dupree Paul, Igarashi Kiyohiko
1 Department of Biomaterial Sciences, The University of Tokyo.
2 Department of Biochemistry, University of Cambridge.
J Appl Glycosci (1999). 2022 May 25;69(2):35-43. doi: 10.5458/jag.jag.JAG-2021_0017. eCollection 2022.
Endo-type xylanases are key enzymes in microbial xylanolytic systems, and xylanases belonging to glycoside hydrolase (GH) families 10 or 11 are the major enzymes degrading xylan in nature. These enzymes have typically been characterized using xylan prepared by alkaline extraction, which removes acetyl sidechains from the substrate, and thus the effect of acetyl groups on xylan degradation remains unclear. Here, we compare the ability of GH10 and 11 xylanases, Xyn10A and Xyn11B, from the white-rot basidiomycete to degrade acetylated and deacetylated xylan from various plants. Product quantification revealed that Xyn10A effectively degraded both acetylated xylan extracted from and the deacetylated xylan obtained by alkaline treatment, generating xylooligosaccharides. In contrast, Xyn11B showed limited activity towards acetyl xylan, but showed significantly increased activity after deacetylation of the xylan. Polysaccharide analysis using carbohydrate gel electrophoresis showed that Xyn11B generated a broad range of products from native acetylated xylans extracted from birch wood and rice straw, including large residual xylooligosaccharides, while non-acetylated xylan from Japanese cedar was readily degraded into xylooligosaccharides. These results suggest that the degradability of native xylan by GH11 xylanases is highly dependent on the extent of acetyl group substitution. Analysis of 31 fungal genomes in the Carbohydrate-Active enZymes database indicated that the presence of GH11 xylanases is correlated to that of carbohydrate esterase (CE) family 1 acetyl xylan esterases (AXEs), while this is not the case for GH10 xylanases. These findings may imply co-evolution of GH11 xylanases and CE1 AXEs.
内切型木聚糖酶是微生物木聚糖分解系统中的关键酶，属于糖苷水解酶（GH）家族10或11的木聚糖酶是自然界中降解木聚糖的主要酶。这些酶通常使用通过碱性提取制备的木聚糖进行表征，碱性提取可从底物中去除乙酰侧链，因此乙酰基团对木聚糖降解的影响仍不清楚。在这里，我们比较了来自白腐担子菌的GH10和GH11木聚糖酶Xyn10A和Xyn11B降解各种植物中乙酰化和脱乙酰化木聚糖的能力。产物定量分析表明，Xyn10A能有效降解从[具体植物]中提取的乙酰化木聚糖和通过碱性处理获得的脱乙酰化木聚糖，生成木寡糖。相比之下，Xyn11B对乙酰化木聚糖的活性有限，但在木聚糖脱乙酰化后活性显著增加。使用碳水化合物凝胶电泳进行的多糖分析表明，Xyn11B从桦木和稻草中提取的天然乙酰化木聚糖产生了广泛的产物，包括大量残留的木寡糖，而日本雪松的非乙酰化木聚糖很容易降解为木寡糖。这些结果表明，GH11木聚糖酶对天然木聚糖的降解能力高度依赖于乙酰基团的取代程度。对碳水化合物活性酶数据库中31个真菌基因组的分析表明，GH11木聚糖酶的存在与碳水化合物酯酶（CE）家族1的乙酰木聚糖酯酶（AXE）相关，而GH10木聚糖酶则不然。这些发现可能意味着GH11木聚糖酶和CE1 AXE共同进化。
