Glycoproteins secreted from suspension-cultured tobacco BY2 cells have distinct glycan structures from intracellular glycoproteins.

Glycan structures of glycoproteins secreted in the spent medium of tobacco BY2 suspension-cultured cells were analyzed. The N-glycans were liberated by hydrazinolysis and the resulting oligosaccharides were labeled with 2-aminopyridine. The pyridylaminated (PA) glycans were purified by reversed-phase and size-fractionation HPLC. The structures of the PA sugar chains were identified by a combination of the two-dimensional PA sugar chain mapping, MS analysis, and exoglycosidase digestion. The ratio (40:60) of the amount of glycans with high-mannose-type structure to that with plant-complex-type structure of extracellular glycoproteins is significantly different from that (ratio 10:90) previously found in intracellular glycoproteins [Palacpac et al., Biosci. Biotechnol. Biochem. 63 (1999) 35-39]. Extracellular glycoproteins have six distinct N-glycans (marked by ) from intracellular glycoproteins, and the high-mannose-type structures account for nearly 40% (Man5GlcNAc2, 28.8%; Man6GlcNAc2, 6.4%; and Man7GlcNAc2*, 3.8%), while the plant-complex-type structures account for nearly 60% (GlcNAc2Man3Xyl1GlcNAc2*, 32.1%; GlcNAc1Man3Xyl1GlcNAc2 (containing two isomers), 6.2%; GlcNAc2Man3GlcNAc2, 4.9%; Man3Xyl1Fuc1GlcNAc2, 8.3%; and Man3Xyl1GlcNAc2, 3.7%).