Human Lysosomal and Jack Bean α-Mannosidases Are Retaining Glycosidases

Abstract

The stereochemical course of the hydrolyses catalysed by two α-mannosidases has been determined directly by1H NMR. Synthetic substrates were incubated with the enzymes and the anomeric configuration of the initially formed product was ascertained in each case by observation of the chemical shift of the anomeric proton at the hemiacetal centre. Both mannosidases were found to catalyse hydrolysis with retention of stereochemistry at the anomeric position. Human lysosomal α-mannosidase (a class II mannosidase) is a member of the glycosidase family 38 and thus has sequence similarity with several α-mannosidases responsible for glycoprotein biosynthesis. Jack bean α-mannosidase was shown to be mechanistically similar to the lysosomal enzyme and will provide a useful model system in mechanistic studies and inhibitor design.