Substrate specificity of N-acetylhexosaminidase from Aspergillus oryzae to artificial glycosyl acceptors having various substituents at the reducing ends

The substrate specificity of N-acetylhexosaminidase (E.C. 3.2.1.51) from Aspergillus oryzae was examined using p-nitrophenyl 6-O-sulfo-N-acetyl-β-d-glucosaminide (6-O-sulfo-GlcNAc-O-pNP) as the glycosyl donor and a series of β-d-glucopyranosides and N-acetyl-β-d-glucosaminides with variable aglycons at the anomeric positions as the acceptors. When β-d-glucopyranosides with methyl (CH3), allyl (CH2CHCH2), and phenyl (C6H5) groups at the reducing end were used as the acceptors, this enzyme transferred the 6-O-sulfo-GlcNAc moiety in the donor to the location of O-4 in these glycosyl acceptors with a high regioselectivity, producing the corresponding 6-O-sulfo-N-acetylglucosaminyl β-d-glucopyranosides. However, β-d-glucopyranose lacking aglycon was a poor substrate for transglycosylation. This A. oryzae enzyme could also accept various N-acetyl-β-d-glucosaminides carrying hydroxyl (OH), methyl (CH3), propyl (CH2CH2CH3), allyl (CH2CHCH2) and p-nitrophenyl (pNP; C6H4-NO2) groups at their aglycons, yielding 6-O-sulfo-N-acetylglucosaminyl-β(1→4)-disaccharide products.