An Aspergillus nidulans endo-β-1,3-glucanase exhibited specific catalytic features and was used to prepare 3-O-β-cellobiosyl-D-glucose and 3-O-β-gentiobiosyl-D-glucose with high antioxidant activity from barley β-glucan and laminarin, respectively

An endo-beta-1,3(4)-glucanase AnENG16A from Aspergillus nidulans shows distinctive catalytic features for hydrolysis of beta-glucans. AnENG16A hydrolyzed Eisenia bicyclis laminarin to mainly generate 3-O-beta gentiobiosyl-D-glucose and hydrolyzed barley beta-glucan to mainly produce 3-O-beta cellobiosyl-D-glucose. Using molecular exclusion chromatography, we isolated and purified 3-O-beta cellobiosyl-D-glucose and 3-O-beta-gentiobiosyl-D-glucose, respectively, from AnENG16A-hydrolysate of barley beta-glucan and E. bicyclis laminarin. Further study reveals that 3-O-beta-cellobiosyl-D-glucose had 8.99 fold higher antioxidant activity than barley p glucan and 3-O-beta-gentiobiosyl-D-glucose exhibited 43.0% higher antioxidant activity than E. bicyclis laminarin. Notably, 3-O-beta-cellobiosyl-D-glucose and 3-O-beta-gentiobiosyl-D-glucose exhibited 148.9% and 116.0% higher antioxidant activity than laminaritriose, respectively, indicating that beta-1,4-linkage or -1,6-linkage at non-reducing end of beta-glucotrioses had enhancing effect on antioxidant activity compared to beta-1,3-linkage. Furthermore, 3-O-beta-cellobiosyl-D-glucose showed 237.9% higher antioxidant activity than cellotriose, and laminarin showed 5.06-fold higher antioxidant activity than barley beta-glucan, indicating that beta-1,4-linkage at reducing end of beta-glucans or oligosaccharides resulted in decrease of antioxidant activity compared to beta-1,3-linkage.

Automated summary

An endo-beta-1,3(4)-glucanase AnENG16A from Aspergillus nidulans exhibits distinctive catalytic features, producing 3-O-beta cellobiosyl-D-glucose and 3-O-beta gentiobiosyl-D-glucose with high antioxidant activity. The linkage type at the non-reducing end of beta-glucotrioses may enhance antioxidant activity compared to beta-1,3-linkage.