Fucosylated Hybrid-Type N-Glycans on the Secreted Human Epidermal Growth Factor Receptor from Swainsonine-Treated A431 Cells

N-Glycans linked to the human secreted form of epidermal growth factor receptor were isolated from A431 cells after swainsonine treatment. Analysis of the oligosaccharides by 1H NMR spectroscopy and mass spectrometry shows the presence of oligomannose- and (α2-3)-sialylated hybrid-type glycans. The major hybrid-type oligosaccharide chains are fucosylated at the Asn-bound GlcNAc residue. Smaller amounts of the hybrid-type structures are also fucosylated at peripheral GlcNAc residues, constituting the sialyl-Lex antigen. No complex-type glycans are found, suggesting the absence of α-mannosidase III. An assay for α-mannosidase III on the A431 cells in the absence and presence of 6 μM swainsonine shows that Man5GlcNAc2 is not converted into Man3GlcNAc2, thereby confirming that these cells do not contain α-mannosidase III activity.