We investigated the ability of a baculovirus–insect cell system to produce sialylated glycoproteins. Despite the presence of enzymes for synthesizing complex type N-glycans, the most frequent structure of insect N-glycan is the paucimannosidic type, Man3GlcNAc2(±Fuc). The reason for the overwhelming assembly of paucimannosidic N-glycans is not yet well understood. We hypothesized that this predominance might be due to insect-specific, Golgi-associated β-N-acetylglucosaminidase (GlcNAcase)-mediated removal of N-acetylglucosamine (GlcNAc) residues from the precursor N-glycan, thereby preventing its galactosylation and terminal sialylation. As we expected, the suppression of intrinsic GlcNAcase activity with a specific inhibitor, 2-acetamido-1,2-dideoxynojirimycin, allowed the accumulation of sialylated glycoproteins in the supernatants of insect cell cultures after baculoviral infection. Our observation indicates that GlcNAcase-dependent depletion of N-acetylglucosamine residues from intermediate N-glycans is critical for the assembly of paucimannosidic N-glycans in insect cells, and that, more importantly, insect cells (under specific conditions) retain the ability to construct sialylated N-glycans like those in mammalian cells. (Comparative Immunology Section, Department of Immunology TEL +81-29-838-7864)
Reference:
Watanabe et al. (2002) J. Biol. Chem. 277:5090-5093.
