Multimodularity of a GH10 Xylanase Found in the Termite Gut Metagenome

• Published in: Applied and environmental microbiology 2021-01, Vol.87 (3), p.1
• Main Authors: Wu, Haiyang, Ioannou, Eleni, Henrissat, Bernard, Montanier, Cédric Y, Bozonnet, Sophie, O'Donohue, Michael J, Dumon, Claire
• Format: Article
• Language: English
• Subjects: Animals; Bacterial Proteins - genetics; Bacteroidetes - enzymology; Bacteroidetes - genetics; Bacteroidetes - isolation & purification; Binding; Carbohydrates; Domains; Endo-1,4-beta Xylanases - chemistry; Endo-1,4-beta Xylanases - genetics; Endo-1,4-beta Xylanases - metabolism; Enzymatic activity; Enzymes; Enzymology and Protein Engineering; Gastrointestinal Microbiome; Genes; Glycan; Glycosidases; Glycoside hydrolase; Hydrolase; Intestinal microflora; Isoptera - microbiology; Life Sciences; Loci; Metagenome; Metagenomics; Microbiota; Modules; Polysaccharides; Proteins; Saccharides; Sequence analysis; Termites; Utilization; Xylan; Xylanase; Xylans - metabolism
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/AEM.01714-20

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.