Glycoform analysis of N-glycans linked to glycoproteins expressed in rice culture cells: Predominant occurrence of complex type N-glycans

Although it has been found that plant endo-β-N-acetylglucosaminidase shows strong activity towards denatured glycoproteins and glycopeptides with high-mannose type N-glycans and free high-mannose type N-glycans bearing the chitobiosyl unit, the endogenous substrates for plant endoglycosidase have not yet been identified. Recently we purified and characterized an endo-β-N-acetylglucosaminidase from rice culture cells and identified the gene encoded (Maeda, M., and Kimura, Y., Trends Glycosci. Glycotech., 17, 205-214 (2005)). Furthermore, we found structural features of free N-glycans in the cells, indicating that high-mannose type species (Man _9-5GlcNAc₁) occur at concentration of several micromolar (μM). Hence, in this study we analyzed glycoform of N-glycans linked to glycoproteins expressed in rice culture cells to see whether endogenous glycoproteinous substrate occurs in reasonable amounts. Structural analysis revealed that more than 95% of total N-glycans linked to glycoproteins in the rice cells had the plant complex type structure, including Lewis a epitope-harboring type, although high-mannose type structures account for less than 5% of total N-glycans.