Improved reaction pattern of an endoglycanase from Paenibacillus cookii for chitosan oligosaccharide production

The reaction pattern of an endoglycanase from Paenibacillus cookii SS-24 (Pgl8A) was improved to facilitate chitosan oligosaccharide production. Based on the sequence alignment with chitosanase of a known structure, we performed site-directed mutagenesis of possible substrate-binding residues in Pgl8A. The mutants were expressed in Escherichia coli cells, and their cellulase and chitosanase activities were then characterised. Our results indicated that three amino acid residues (W139, W208 and E285) were important for the substrate specificity of Pgl8A. D156 and Y390 were also essential for the cellulase and chitosanase activities of Pgl8A. The products of chitosan degradation by W139A, W208A and E285Q mutants were different from those by the wild type. A chitosan pentamer accumulated following chitosan degradation by W139A, W208A and E285Q mutants. Thus, the mutants obtained in this study are potentially useful for the production of biofunctional chitosan oligosaccharides.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Pgl8A was improved by site-directed mutagenesis of substrate-binding residues. ► Eight amino acid residues in Pgl8A were classified as substrate-binding residues. ► Chitosan hydrolysis by three mutants resulted in accumulation of a pentamer. ► W139A, W208A and E285Q mutants did not hydrolyse the chitosan pentamer.