Characterization of a novel bifunctional endo-β-1,4-glucanase/mannanase from Aspergillus oryzae

The present study involved a global search of the Aspergillus oryzae genome database. As a result, the gene (gene ID: AO090011000715) encoding a putative endo-β-1,4-glucanase of the glycoside hydrolase family 5 possessing a carbohydrate-binding module was identified. Overexpression of this gene in A. oryzae, followed by the purification of the gene product, revealed that the protein exhibits endoglucanase activity with carboxymethyl cellulose as a substrate. Notably, further enzymatic characterization showed that this enzyme could also hydrolyze glucomannan and galactomannan with relatively lower activity than that of endoglucanase, indicating that the enzyme is likely a bifunctional endoglucanase/mannanase. Detailed analyses of the substrate specificity revealed that the enzyme could hydrolyze cello-oligosaccharides larger than cellotetraose, whereas manno-oligosaccharides could not be hydrolyzed unless they were larger than mannopentaose. Therefore, this enzyme has different modes of action toward cello- and manno-oligosaccharides. To the best of our knowledge, this is the first study to purify and characterize a bifunctional endo-β-1,4-glucanase/mannanase from the Aspergillus genus. The ability of the enzyme to degrade both mannan and cellulose could be used for more efficient degradation of lignocellulosic biomass, indicating that the enzyme shows promise for applications in biomass utilization and the food industry. KEY POINTS: • A novel bifunctional endoglucanase/mannanase, EgmA, is identified from Aspergillus oryzae. • EgmA is the second bifunctional endo-β-1,4-glucanase/mannanase of fungal origin. • EgmA has different mechanisms of action toward cello- and manno-oligosaccharides.