Structures of the N-linked oligosaccharides of the membrane glycoproteins from three lepidopteran cell lines (Sf-21, IZD-Mb-0503, Bm-N).

Abstract 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 Man 2 GlcNAc 2 to Man 9 GlcNAc 2 occurred in all three cell lines. The pattern of Man 5 - to Man 9 GlcNAc 2 -isomers suggests an α-mannosidase trimming pathway very similar to that in mammalian cells. In each cell line, the small (Man 2 , Man 3 ) 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]