New insights into the action of bacterial chondroitinase AC I and hyaluronidase on hyaluronic acid

Hyaluronic acid (HA), a glycosaminoglycan, is a linear polysaccharide with negative charge, composed of a repeating disaccharide unit [→4)-β-D-glucopyranosyluronic acid (1 → 3)-β-D- N-acetyl-D-glucoaminopyranose (1 → ]_n ([→4) GlcA (1 → 3) GlcNAc 1 → ]_n). It is widely used in different applications based on its physicochemical properties associated with its molecular weight. Enzymatic digestion by polysaccharides lyases is one of the most important ways to decrease the molecular weight of HA. Thus, it is important to understand the action patterns of lyases acting on HA. In this study, the action patterns of two common lyases, Flavobacterial chondroitinase AC I and Streptomyces hyaluronidase, were investigated by analyzing HA oligosaccharide digestion products. HA oligosaccharides having an odd-number of saccharide residues were observed in the products of both lyases, but their distributions were quite different. Chondroitinase AC acted more efficiently at the β 1–4 glycosidic bond linking GlcNAc and GlcA. Oligosaccharides, having an even number of saccharide residues, and with an unsaturated uronic acid (4-deoxy-α-L-threo-hex-4-enepyranosyluronic acid, △UA) residue at their non-reducing end represent the major product. A minor amount of oligosaccharides having an odd number of saccharide residues resulted from the irregular terminal residues of HA substrate chains. Hyaluronidase showed a more complicated product mixture. Its minimum recognition and digestion domain is HA heptasaccharide and it could cleave both β 1–4 and β 1–3 glycosidic linkages. The HA oligosaccharides, generated with a 2-acetamido-2,3-di-deoxy-β-D-erythro-hex-2-enopyranose (△HexNAc) at the non-reducing end, are believed to be unstable and undergo breakdown immediately after their generation, and the oligosaccharides with △UA residue at the non-reducing end are formed. Thus, oligosaccharides having both an even and odd-number saccharide residues with a △UA residue at their non-reducing ends, represent the major products of hyaluronidase acting on HA.