The functional screening of a Pseudacanthotermes militaris termite gut metagenomic library revealed an array of xylan-degrading enzymes, including P. militaris 25 (Pm25), a multimodular glycoside hydrolase family 10 (GH10). Sequence analysis showed details of the unusual domain organization of this enzyme. It consists of one catalytic domain, which is intercalated by two carbohydrate binding modules (CBMs) from family 4. The genes upstream of the genes encoding Pm25 are susC-susD-unk, suggesting Pm25 is a Xyn10C-like enzyme belonging to a polysaccharide utilization locus. The majority of Xyn10C-like enzymes shared the same interrupted domain architecture and were vastly distributed in different xylan utilization loci found in gut Bacteroidetes, indicating the importance of this enzyme in glycan acquisition for gut microbiota. To understand its unusual multimodularity and the possible role of the CBMs, a detailed characterization of the full-length Pm25 and truncated variants was performed. Results revealed that the GH10 catalytic module is specific toward the hydrolysis of xylan. Ligand binding results indicate that the GH10 module and the CBMs act independently, whereas the tandem CBM4s act synergistically with each other and improve enzymatic activity when assayed on insoluble polysaccharides. In addition, we show that the UNK protein upstream of Pm25 is able to bind arabinoxylan. Altogether, these findings contribute to a better understanding of the potential role of Xyn10C-like proteins in xylan utilization systems of gut bacteria.

中文翻译：

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在白蚁肠道元基因组中发现的GH10木聚糖酶的多模块性。

功能化筛选的Pseudacanthotermes militaris白蚁肠道宏基因组库显示了一系列木聚糖降解酶，包括P. militaris 25（Pm 25），一种多模块糖苷水解酶家族10（GH10）。序列分析显示了该酶异常域结构的细节。它由一个催化结构域组成，该催化结构域插入了来自家族4的两个碳水化合物结合模块（CBM）。编码Pm 25的基因上游的基因是susC - susD - unk，表明Pm。25是属于多糖利用基因座的Xyn10C样酶。大多数Xyn10C样酶具有相同的中断结构域结构，并广泛分布于肠道拟杆菌中的不同木聚糖利用位点，表明该酶在肠道微生物的聚糖收购中具有重要意义。要了解其异常的多模量以及CBM的可能作用，请详细描述全长Pm25和截短的变体被执行。结果表明，GH10催化模块对木聚糖水解具有特异性。配体结合结果表明，GH10模块和CBMs各自独立发挥作用，而串联CBM4s在不溶性多糖上进行检测时可相互协同发挥作用并提高酶活性。另外，我们显示Pm 25上游的UNK蛋白能够结合阿拉伯木聚糖。总之，这些发现有助于更好地了解Xyn10C样蛋白在肠道细菌木聚糖利用系统中的潜在作用。