A Novel Subfamily of Endo-β-1,4-Glucanases in Glycoside Hydrolase Family 10.

As classified by the Carbohydrate-Active Enzymes (CAZy) database, enzymes in glycoside hydrolase (GH) family 10 (GH10) are all monospecific or bifunctional xylanases (except a tomatinase), and no endo-β-1,4-glucanase has been reported in the family. Here, we identified carboxymethyl cellulase (CMCase) as a GH10 endo-β-1,4-glucanase. CMCase originated from an Arctic marine bacterium, SM1504 It shows low identity (<35%) with other GH10 xylanases. The gene encoding CMCase was overexpressed in Biochemical characterization showed that recombinant CMCase is a cold-adapted and salt-tolerant enzyme. CMCase hydrolyzes cello- and xylo-configured substrates via an endoaction mode. However, in comparison to its significant cellulase activity, the xylanase activity of CMCase is negligible. Correspondingly, CMCase has remarkable binding capacity for cello-oligosaccharides but no obvious binding capacity for xylo-oligosaccharides. CMCase and its homologs are grouped into a branch separate from other GH10 xylanases in a phylogenetic tree, and two homologs also displayed the same substrate specificity as CMCase. These results suggest that CMCase and its homologs form a novel subfamily of GH10 enzymes that have robust endo-β-1,4-glucanase activity. In addition, given the cold-adapted and salt-tolerant characters of CMCase, it may be a candidate biocatalyst under certain industrial conditions, such as low temperature or high salinity. Cellulase and xylanase have been widely used in the textile, pulp and paper, animal feed, and food-processing industries. Exploring novel cellulases and xylanases for biocatalysts continues to be a hot issue. Enzymes derived from the polar seas might have novel hydrolysis patterns, substrate specificities, or extremophilic properties that have great potential for both fundamental research and industrial applications. Here, we identified a novel cold-adapted and salt-tolerant endo-β-1,4-glucanase, CMCase, from an Arctic marine bacterium. It may be useful in certain industrial processes, such as under low temperature or high salinity. Moreover, CMCase is a bifunctional representative of glycoside hydrolase (GH) family 10 that preferentially hydrolyzes β-1,4-glucans. With its homologs, it represents a new subfamily in this family. Thus, this study sheds new light on the substrate specificity of GH10.