Exo- and endoglycosidases revisited

Many glycosidases, which work as useful reagents for the studies of structures and functions of free and conjugated oligosaccharides, have been found and thoroughly purified. These enzymes are classified into exo- and endoglycosidases by their glycon specificities. Their usefulness and limits as reagents are explained in detail in this review. Endoglycosidases, which were originally found in the culture fluid of bacteria and in the extracts of plants, are now widely found in the mammals including humans. The physiological roles of these enzymes are discussed in relation to the oligosaccharides accumulated in the urine of patients with exoglycosidase deficiencies. Furthermore, PNGase is found to play important roles in the ER-associated degradation pathway of glycoproteins. Recent studies of the glycosidases in Bifidobacteria have revealed that GNB/LNB pathway, which uniquely exist in this bacteria, works for the expression of Bifidus factor activity of human milk oligosaccharides, an important topic in the baby nutrition. This interesting field will be introduced in detail in one section of this article.