Optimum substrate size and specific anomer requirements for the reducing-end glycoside hydrolase Di-N-acetylchitobiase

Abstract

Di-N-acetylchitobiase is a family 18 glycoside hydrolase that splits the reducing-end GlcNAc from chitooligosaccharides. The enzyme hydrolyzed only the α-anomer of five tested substrates, chitin di- through hexasaccharide. In all cases the glycosyl fragment retained its β-configuration while the split monosaccharide was α-D-GlcNAc. Chitobiose was hydrolyzed less than half as fast as the other larger substrates. All four of them, tri- to hexasaccharide, reacted at the same rate. The biochemical behavior of di-N-acetylchitobiase indicates it has three subsites, -2, -1, +1, in which the reducing-end trimer of any sized chitooligosaccharide is bound. The +1 site is specific for an α-anomer.