Functional Characterization of a Highly Efficient Endoglucanase from Bacillus licheniformis BJ2022 and Its Application in the Preparation of Low-Molecular-Weight Konjac Glucomannan

Endoglucanases may not only act on β-1,4-linkages in β-glucan but also target d-glucose in glucomannan, which can expand their utility in the preparation of prebiotics. In this study, a highly efficient endoglucanase (BlGH5) from Bacillus licheniformis BJ2022 was expressed and characterized. BlGH5 exhibited the highest activity at pH 7.0 and 60 °C. It maintained over 80% activity at pH 4.0–7.0 and 30–60 °C. BlGH5 specifically cleaved β-1,4-glycosidic bonds linked to d-glucose. Site-directed mutagenesis results suggested that Arg⁹¹, Asn¹⁶⁷, Glu¹⁶⁸, Trp²⁰⁶, His²²⁸, Tyr²³⁰, Ser²⁶³, and Trp²⁹⁰ are key residues for its binding and catalytic activity. Moreover, BlGH5 displayed high activity against konjac glucomannan (KGM), indicating that BlGH5 could be used to prepare low-molecular-weight konjac glucomannan (KGM-L). Based on the physicochemical properties of KGM and KGM-L, KGM-L was characterized by reduced molecular weight and viscosity. Fecal fermentation experiments demonstrated that KGM and KGM-L could promote the production of short-chain fatty acids (SCFAs). Still, KGM-L was more conducive to the growth of the gut probiotics. In conclusion, we identified an endoglucanase for the degradation of KGM. Results indicated that KGM-L would have superior prebiotic effects. Thus, our study provides a basis for the future development and application of KGM-L as a prebiotic.