Endo-enzymes

Abstract

Endoglycosidases release oligosaccharides from a sugar chain by cleaving defined sites within the sugar chain of glycoconjugates. There are two types of endoglycosidases acting on the sugar chains of glycoproteins. One is an endoglycosidase that hydrolytically cleaves the core region of N-linked sugar chains of glycoproteins, and the representative member of this type is endo-β-N-acetylglucosaminidase. The second type of endoglycosidases hydrolyzes the linkage between the O-linked sugar chain and the protein of glycoproteins, and endo-α-N-acetylgalactosaminidase is a representative member of this class. These endoglycosidases from microbial sources are indispensable tools for analyzing the structure and function of sugar chains in glycoproteins and glycopeptides. Endo-β-mannosidase is a plant-specific endoglycosidase that acts on the N-linked sugar chain of glycoproteins. It is suggested that there are three enzymes acting on the common core region between the peptide and the glycosaminoglycan in various proteoglycans. They are endo-β-xylosidase, endo-β-galactosidase, and endo-β-glucuronidase. The catabolic mechanism of glycosaminoglycans is complex and the role of these endoglycosidases is important. In regard to glycosphingolipid-degrading enzymes, real glycosphingolipid-degrading enzymes had remained undiscovered until endoglycoceramidase was isolated and characterized. This novel enzyme hydrolyzes the β-glucosidic linkage between oligosaccharides and ceramides of various acidic and neutral glycosphingolipids. Most endoglycosidases show transglycosylation activity and this activity is useful for synthesizing various glycosylated compounds, including bioactive glycoconjugates. Some bioactive compounds have been synthesized with the transglycosylation activity of microbial endo-β-N-acetylglucosaminidase.