Structures of the N-Linked Oligosaccharides of the Membrane Glycoproteins from Three Lepidopteran Cell Lines (Sf-21, IZD-Mb-0503, Bm-N)

The primary structures of the Asn-Iinked carbohydrate chains isolated from membrane glycoproteins of the three insect cell lines Mamestra brassicae (Mb-0503), Bombyx mori (Bm-N), and Spodoptera frugiperda (Sf-21) have been determined. Tryptic glycopeptides derived from the membrane fraction were digested with peptide-N-glycanase A. The resulting oligosaccharides were reductively aminated with 2-aminopyridine and identified by two-dimensional HPLC mapping in combination with exoglycosidase digestions. Oligomannose-type structures ranging from Man2GlcNAc2 to Man9GlcNAc2 occurred in all three cell lines. The pattern of Man5- to Man9GlcNAc2-isomers suggests an α-mannosidase trimming pathway very similar to that in mammalian cells. In each cell line, the small (Man2, Man3) oligosaccharides were partly fucosylated at the asparagine-linked GlcNAc residue, but distinct fucosylation patterns were observed: while only a low degree of α1,3-fucosylation was detected in Sf-21 and Bm-N cells, the glycoproteins isolated from Mb-0503 cells contained 30% of α1,3-fucosylated glycans, predominantly in the difucosylated form, i.e., with two fucoses linked to the same N-acetylglucosamine residue. Additionally, the following α1,6-fucosylated (Bm-N cells) or difucosylated (Sf-21, Mb-0503 cells) GlcNAc-terminated structures were found: [formula]