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A mammalian N-acetylglucosamine (GlcNAc) transferase I (GnT I)-independent fucosylation pathway is revealed by the use of matrix-assisted laser desorption/ionization (MALDI) and negative-ion nano-electrospray ionization (ESI) mass spectrometry of N-linked glycans from natively folded recombinant glycoproteins, expressed in both human embryonic kidney (HEK) 293S and Chinese hamster ovary (CHO) Lec3.2.8.1 cells deficient in GnT I activity. The biosynthesis of core fucosylated Man5GlcNAc2 glycans was enhanced in CHO Lec3.2.8.1 cells by the alpha-glucosidase inhibitor, N-butyldeoxynojirimycin (NB-DNJ), leading to the increase in core fucosylated Man5GlcNAc2 glycans and the biosynthesis of a novel core fucosylated monoglucosylated oligomannose glycan, Glc1Man7GlcNAc2Fuc. Furthermore, no fucosylated Man9GlcNAc2 glycans were detected following inhibition of alpha-mannosidase I with kifunensine. Thus, core fucosylation is prevented by the presence of terminal alpha1-2 mannoses on the 6-antennae but not the 3-antennae of the trimannosyl core. Fucosylated Man5GlcNAc2 glycans were also detected on recombinant glycoprotein from HEK 293T cells following inhibition of Golgi alpha-mannosidase II with swainsonine. The paucity of fucosylated oligomannose glycans in wild-type mammalian cells is suggested to be due to kinetic properties of the pathway rather than the absence of the appropriate catalytic activity. The presence of the GnT I-independent fucosylation pathway is an important consideration when engineering mammalian glycosylation.

Original publication




Journal article



Publication Date





748 - 756


1-Deoxynojirimycin, Alkaloids, Animals, CHO Cells, Cell Line, Cricetinae, DNA, Complementary, Enzyme Inhibitors, Fucose, Glycoproteins, Glycosylation, Humans, N-Acetylglucosaminyltransferases, Recombinant Proteins, Spectrometry, Mass, Electrospray Ionization, Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization, Swainsonine, alpha-Mannosidase