Primary Structures of N-Linked Oligosaccharides of Momordin-a, a Ribosome-inactivating Protein from Momordica charantia Seeds

The structures of the N-linked oligosaccharides of momordin-a, which is a ribosome-inactivating protein from the seeds of Momordica charantia, were analyzed. First, the N-linked oligosaccharides of this glycoprotein were liberated by hydrazinolysis. After N-acetylation, the reducing ends of the oligosaccharides were coupled with 2-aminopyridine and the pyridylamino (PA-) derivatives were purified by gel filtration and high performance liquid chromatography (HPLC) on an ODS-silica column. Three kinds of oligosaccharide fractions were separated by HPLC. The structure of each oligosaccharide isolated was analyzed by a combination of sugar component analysis, exoglycosidase digestion, another kind of HPLC using an amide-silica column, and 500-MHz ¹H NMR spectroscopy. The structures of two main oligosaccharides were established to be: Xyl1β2Manβ4GlcNAcβ4GlcNAc Fucα3 and Xylβ2Manβ4GlcNAcβ4GlcNAc These two oligosaccharides were the first examples having xylose (or fucose) but no α-mannosyl linkage among the N-linked oligosaccharides of glycoproteins from both animal and plant origins.