Discovery and Structural Characterization of Fucosylated Oligomannosidic N-Glycans in Mushrooms

L-Fucose is a common constituent of Asn-linked glycans in vertebrates, invertebrates, and plants, but in fungal glycoproteins, fucose has not been found so far. However, by mass spectrometry we detected N-glycans and O-glycans containing one to six deoxyhexose residues in fruit bodies of several basidiomycetes. The N-glycans of chanterelles (Cantharellus cibarius) contained a deoxyhexose chromatographically identical to fucose and sensitive to alpha-L-fucosidase. Analysis of individual glycan species by tandem MS, glycosidase digestion, and finally H-1 NMR revealed the presence of L-fucose in alpha 1,6-linkage to an alpha 1,6-mannose of oligomannosidic N-glycans. The substitution by alpha 1,6-mannose of alpha 1,2-mannosyl residues of the canonical precursor structure was yet another hitherto unknown modification. No indication for the occurrence of yet other modifications, e. g. bisecting N-acetylglucosamine, was seen. Besides fucosylated N-glycans, short O-linked mannan chains substituted with fucose were present on chanterelle proteins. Although undiscovered so far, L-fucose appears to represent a prominent feature of protein-linked glycans in the fungal kingdom.