Title :
N-glycan patterns of human
transferrin produced in Trichoplusia ni insect cells: effects of mammalian
galactosyltransferase
Abstract :
- The N-glycans of human serum transferrin produced in Trichopulsia ni cells were analyzed to examine N-linked oligosaccharide processing in insect cells
- Metabolic radiolabeling of the intra- and extracellular protein fractions revealed the presence of multiple transferrin glycoforms with molecular weights lower than that observed for native human transferrin
- Consequently, the N-glycan structures of transferrin in the culture medium were determined using three-dimensional high performance liquid chromatography
- The attached oligosaccharides included high mannose, paucimannosidic, and hybrid structures with over 50% of these structures containing one fucose, alpha(1,6)-, or two fucoses , alpha(1,6)- and alpha(1,3)-, linked to the Asn-linked N-acetylglucosamine. Asn-linked N-acetylglucosamine
- Neither sialic acid nor galactose was detected on any of the N-glycans
- However, when transferrin was coexpressed with beta(1,4)- galactosyltransferase three additional galactose-containing hybrid oligosaccharides were obtained
- The galactose attachments were exclusive to the alpha(1, 3)-mannose branch and the structures varied by the presence of zero, one, or two attached fucose residues.
- Furthermore, the presence of the galactosyltransferase appeared to reduce the number of paucimannosidic structures, which suggests that galactose attachment inhibits the ability of hexosaminidase activity to remove the terminal N-acetylglucosamine.
- The ability to promote galactosylation and reduce paucimannosidic N-glycans suggests that the oligosaccharide processing pathway in insect cells may be manipulated to mimic more closely that of mammalian cells