Conversion of the carbohydrate structures of glycoproteins in roots of Raphanus sativus using several glycosidase inhibitors.

An attempt was made to convert the N-glycan structures in Raphanus sativus seeds during germination with a view to develop a method for regulating the N-glycan structures using glycosidase inhibitors. The N-glycan structures of glycoproteins in the roots of seedlings germinated for three days were analyzed by hydrazinolysis followed by N-acetylation, pyridylamination and HPLC. Pyridylaminated sugar chains obtained in the absence of the inhibitors had plant type structures consisting of Man(3)FucXylGlcNAc(2)(M3FX), Man(5-9)GlcNAc(2)(high-Man) and GlcNAc(1-2)Man(3)FucXylGlcNAc(2)(GnM3FX and Gn2M3FX). When germinated in the presence of a glucosidase inhibitor (castanospermine or deoxynojirimycin), the amount of glucosyl high-Man-type structure increased and plant growth was inhibited. When germinated in the presence of a mannosidase inhibitor (swainsonine or deoxymannojirimycin), the amount of the high-Man-type structure increased and that of M3FX was low, and the growth was normal. In the presence of 2-acetamido 1, 2 di-deoxynojirimycin, those of GnM3FX and Gn2M3FX increased and the growth was normal. These results show that the N-glycan processing in both the endoplasmic reticulum (ER) and Golgi apparatus can be controlled artificially using glycosidase inhibitors, and that the glucosidase inhibitors could be useful for the study of the function of N-glycans in plants.