Limited Addition of the 6-Arm 1,2-Linked N-Acetylglucosamine (GlcNAc) Residue Facilitates the Formation of the Largest N-Glycan in Plants

Abstract

The most abundant N-glycan in plants is the paucimannosidic N-glycan with core 1,2-xylose and 1,3-fucose residues (Man 3 XylFuc(GlcNAc) ). Here, we report a mechanism in Arabidopsis thaliana that efficiently produces the largest N-glycan in plants. Genetic and biochemical evidence indicates that the addition of the 6-arm 1,2-GlcNAc residue by N-acetylglucosaminyltransferase II (GnTII) is less effective than additions of the core 1,2-xylose and 1,3-fucose residues by XylT, FucTA, and FucTB in Arabidopsis. Furthermore, analysis of gnt2 mutant and 35S:GnTII transgenic plants shows that the addition of the 6-arm non-reducing GlcNAc residue to the common N-glycan acceptor GlcNAcMan 2 3 (GlcNAc) inhibits additions of the core 1,2-xylose and 1,3-fucose residues. Our findings indicate that plants limit the rate of the addition of the 6-arm GlcNAc residue to the common N-glycan acceptor as a mechanism to facilitate formation of the prevalent N-glycans with Man 3 XylFuc(GlcNAc) 2 and (GlcNAc) 2 2 Man XylFuc(GlcNAc) 2 structures.