In recent years, carbohydrate-processing enzymes have become the enzymes of choice in many applications thanks to their stereoselectivity and efficiency. This chapter presents recent development in glycosidase-catalyzed synthesis of unnatural semisynthetic carbohydrate structures via two complementary approaches: the use of wild-type enzymes with engineered substrates and mutant glycosidases. Genetic engineering has recently produced glucuronyl synthases, an inverting xylosynthase and the first mutant endo-β-Nacetylglucosaminidase. A careful selection of enzyme producing strains and aptly modified substrates has resulted in rare glycostructures, such as N-acetyl-β-galactosaminuronates, β1,4-linked mannosides and β1,4-linked galactosides. The efficient selection of mutant enzymes is facilitated by high-throughput screening assays involving the co-expression of coupled enzymes or chemical complementation. Selective glycosidase inhibitors and highly specific glycosidases are finding attractive applications in biomedicine, biology and proteomics.
Keywords: Glycosidase, glycosynthase, thioglycoligase, glycosyl azide, transglycosylation
