Processing pathway deduced from the structures of N-glycans in Carica papaya

A processing The processing pathway of N-glycans in Carica papaya was deduc ed from the structures of N-glycans. The N-glycans were liberated by hydraz inolysis followed by N-acetylation, Their reducing-end sugar residues were tagged with 2-aminopyridine and the pyridylamino (PA-) sugar chains thus ob tained were purified by HPLC, Eleven PA-sugar chains were found, and their structures were analyzed by two-dimensional sugar mapping combined with par tial acid hydrolysis and exoglycosidase digestion. The structures of the N- glycans were of the highmannose types with xylose and fucose; however, amon g them two new N-glycans, Man alpha 1-6(Man alpha 1-3)Man alpha 1-6(Xyl bet a 1-2)Man beta 1-4GlcNAc beta 1-4(Fuc alpha 1-3)GlcNAc and Man alpha 1-3Man alpha 1-6(Xyl beta 1-2)Man beta 1-4GlcNAc beta 1-4(Fuc alpha 1-3)GlcNAc, w ere found. Judging from these structures together with Man alpha 1-6(Man al pha 1-3)Man alpha 1-6(Man alpha 1-3)(Xyl beta 1-2)Man beta 1-4GlcNAc beta 1 -4(Fuc beta 1-3)GlcNAc reported previously [Shimazaki, A., Makino, Y., Omic hi, K., Odani, S., and Hase, S. (1999) J. Biochem. 125, 560-565], a process ing pathway for N-glycans in C. papaya is inferred in which the activity of Golgi alpha-mannosidase II is incomplete.