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在白蚁肠道宏基因组中发现的 GH10 木聚糖酶的多功能性。

Multimodularity of a GH10 Xylanase Found in the Termite Gut Metagenome.

机构信息

TBI, Université de Toulouse, CNRS, INRAE, INSA, Toulouse, France.

Institute of Biological Environmental and Rural Sciences, Aberystwyth University, Aberystwyth, United Kingdom.

出版信息

Appl Environ Microbiol. 2021 Jan 15;87(3). doi: 10.1128/AEM.01714-20.

Abstract

The functional screening of a termite gut metagenomic library revealed an array of xylan-degrading enzymes, including 25 (25), 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 25 are --, suggesting 25 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 , 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 25 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 25 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. Xylan is the major hemicellulosic polysaccharide in cereals and contributes to the recalcitrance of the plant cell wall toward degradation. Members of the , one of the main phyla in rumen and human gut microbiota, have been shown to encode polysaccharide utilization loci dedicated to the degradation of xylan. Here, we present the biochemical characterization of a xylanase encoded by a strain isolated from the termite gut metagenome. This xylanase is a multimodular enzyme, the sequence of which is interrupted by the insertion of two CBMs from family 4. Our results show that this enzyme resembles homologues that were shown to be important for xylan degradation in rumen or human diet and show that the CBM insertion in the middle of the sequence seems to be a common feature in xylan utilization systems. This study shed light on our understanding of xylan degradation and plant cell wall deconstruction, which can be applied to several applications in food, feed, and bioeconomy.

摘要

从白蚁肠道宏基因组文库中筛选功能性酶发现了一系列木聚糖降解酶,包括 25(25),一种多模块糖苷水解酶家族 10(GH10)。序列分析显示了该酶不寻常的结构域组织的细节。它由一个催化结构域组成,该结构域被来自家族 4 的两个碳水化合物结合模块(CBM)插入。编码 25 的基因上游基因表明,25 是一种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,并且在肠道中发现的不同木聚糖利用基因座中广泛分布,这表明该酶在肠道微生物群获取糖方面的重要性。为了了解其不寻常的多模块性以及 CBMs 的可能作用,对全长 25 和截短变体进行了详细表征。结果表明,GH10 催化模块特异性水解木聚糖。配体结合结果表明,GH10 模块和 CBMs 独立作用,而串联 CBM4 协同作用,当在不溶性多糖上测定时,可提高酶活性。此外,我们表明,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理解 Xyn10C 样蛋白在肠道细菌木聚糖利用系统中的潜在作用。木聚糖是谷物中主要的半纤维素多糖,导致植物细胞壁对降解具有抗性。瘤胃和人类肠道微生物群的主要门之一的成员已被证明编码专门用于降解木聚糖的多糖利用基因座。在这里,我们介绍了从白蚁肠道宏基因组中分离的一株菌编码的木聚糖酶的生化特性。这种木聚糖酶是一种多模块酶,其序列被来自家族 4 的两个 CBM 插入所中断。我们的结果表明,这种酶类似于被证明对瘤胃或人类饮食中的木聚糖降解很重要的同源物,并且表明序列中间的 CBM 插入似乎是木聚糖利用系统的共同特征。这项研究阐明了我们对木聚糖降解和植物细胞壁解构的理解,这可以应用于食品、饲料和生物经济中的几个应用。

https://cdn.ncbi.nlm.nih.gov/pmc/blobs/44ac/7848910/b16f5451e2f3/AEM.01714-20-f0001.jpg

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