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.