INFLUENCE OF L-FUCOSE ATTACHED ALPHA-1-]6 TO THE ASPARAGINE-LINKED N-ACETYLGLUCOSAMINE ON THE HYDROLYSIS OF THE N-GLYCOSIDIC LINKAGE BY HUMAN GLYCOSYLASPARAGINASE

The sequence of hydrolytic reactions in the catabolism of the N-glycos idic oligosaccharide-to-protein region containing 6-linked fucose on t he asparagine-linked N-acetylglucosamine may vary from species to spec ies, When eta-L-aspartyl)-2-deoxy-beta-D-glucopyranosylamine (Fuc-GlcN Ac-Asn) was incubated with recombinant human glycosylasparaginase, no hydrolysis of the N-glycosidic bond was detected, After removal of the alpha 1-->6-linked fucose from the compound by alpha-fucosidase, the residual GlcNAc-Asn was rapidly hydrolyzed by glycosylasparaginase. En zymologically this demonstrates for the first time that the catabolism of Fuc-GlcNAc-Asn in humans occurs via consecutive action of alpha-fu cosidase and glycosylasparaginase. The hydrolysis rate of GlcNAc-Asn b y glycosylasparaginase remained unaffected in the presence of Fuc-GlcN Ac-Asn or several different monosaccharides including fucose. This ind icates that any fucose attached (alpha 1-->6 to the asparagine-linked N-acetylglucosamine residue prevents the access of the L-asparagine re sidue of Fuc-GlcNAc-Asn into the deep, funnel-shaped active site of hu man glycosylasparaginase. These findings explain the accumulation of f ucosylated and normal catabolism of nonfucosylated glycoasparagines in fucosidosis.