The use of non-covalent as well as covalent inhibitors can be a useful tool to approach the mechanism of activity of glycosidases. An efficient method to determine the essential amino-acid groups directly or indirectly involved in the catalytic process is the use of active site directed irreversible inhibitors. Epoxide derivatives from conduritol B and conduritol C are the most important inhibitors in this group. The use of active site reversible inhibitors: cationic and basic glycosyl derivatives, glycals, glyconolactones, thioglycosides, is effective to study the different charges at the active site or the transition state during catalysis and also to detect conformational adaptability of an enzyme. Furthermore, inhibitors can be valuable tools to investigate various aspects of the physiological role of glycosidases.

1-Deoxynojirimycin↗

PubMedDate not supplied

Novel mannosidase inhibitor blocking conversion of high mannose to complex oligosaccharides.

Many secretory and membrane proteins are glycoproteins carrying asparagine-linked (N-linked) oligosaccharides. There are two types of N-linked glycans, referred to as high-mannose and complex type, respectively. Biosynthesis of N-linked glycans of the complex type proceeds via a high-mannose intermediate. After the initial transfer of a high-mannose oligosaccharide with the composition (Glc)3(Man)9(GlcNAc)2 from a lipid carrier to the nascent polypeptide chain, trimming reactions take place. Trimming glucosidases remove the glucose residues quantitatively and mannosidases IA/B and II can remove all but three mannose residues. After trimming, terminal sugars such as N-acetylglucosamine, galactose, sialic acid and fucose may be added and result in the conversion to a glycan of the complex type. Because suitable inhibitors were lacking, it was difficult to assess the importance of the trimming reactions for proper intracellular traffic, modification reactions other than the addition of terminal sugars, or as regulatory steps in glycoprotein processing. Here we describe the action of 1-deoxymannojirimycin (1,5-dideoxy-1,5-imino-D-mannitol, dMM; Fig. 1) on the biosynthesis of IgM and IgD. dMM is the mannose analogue of 1-deoxynojirimycin (dNM; Fig. 1), itself a glucosidase inhibitor. We present evidence that dMM is a mannosidase inhibitor. In vivo dMM inhibits the equivalent of the mannosidase IA/B activities and blocks conversion of high-mannose to complex oligosaccharides. It is the first such inhibitor to be reported. Interference with the biosynthetic pathway of N-linked glycans could prove to be a powerful way to manipulate carbohydrate structure in vivo.

1-Deoxynojirimycin↗