A Retaining Endo-β-Mannosidase from a Dicot Plant, Cabbage

Degradation pathway of plant complex-type N-glycans: identification and characterization of a key α1,3-fucosidase from glycoside hydrolase family 29

Plant complex-type N-glycans are characterized by the presence of α1,3-linked fucose towards the proximal N-acetylglucosamine residue and β1,2-linked xylose towards the β-mannose residue. These glycans are ultimately degraded by the activity of several glycoside hydrolases. However, the degradation pathway of plant complex-type N-glycans has not been entirely elucidated because the gene encoding α1,3-fucosidase, a glycoside hydrolase acting on plant complex-type N-glycans, has not yet been identified, and its substrate specificity remains to be determined. In the present study, we found that AtFUC1 (an Arabidopsis GH29 α-fucosidase) is an α1,3-fucosidase acting on plant complex-type N-glycans. This fucosidase has been known to act on α1,4-fucoside linkage in the Lewis A epitope of plant complex-type N-glycans. We found that this glycoside hydrolase specifically acted on GlcNAcβ1-4(Fucα1-3)GlcNAc, a degradation product of plant complex-type N-glycans, by sequential actions of vacuolar α-mannosidase, β1,2-xylosidase, and endo-β-mannosidase. The AtFUC1-deficient mutant showed no distinct phenotypic plant growth features; however, it accumulated GlcNAcβ1-4(Fucα1-3)GlcNAc, a substrate of AtFUC1. These results showed that AtFUC1 is an α1,3-fucosidase acting on plant complex-type N-glycans and elucidated the degradation pathway of plant complex-type N-glycans.

Plant glycosidases acting on protein-linked oligosaccharides

Glycosidases have been used as invaluable tools in glycobiology research for decades, and their role in glycoprotein maturation has been amply studied. The molecular biological coverage of this large group of enzymes has only recently reached an appreciable level. In this review, we present an overview of plant glycosidases, whose DNA/protein sequence has been identified and for which recombinant enzymes have been characterized. The physiological role in the maturation of glycoproteins is discussed as well as the biotechnological prospects arising from knowing the enzymes responsible for the removal of terminal N-acetylglucosamine residues. The current knowledge on plant fucosidases and of the first bits of information on glycosidases acting on arabinogalactan proteins is presented.