Primary structure of the carbohydrate chain of soybean agglutinin. A reinvestigation by high resolution 1H NMR spectroscopy.

In an earlier report (Lis, H., and Sharon, N. (1978) J. Biol. Chem. 253, 3468-3476) it was concluded that the plant glycoprotein soybean agglutinin contains two types of N-glycosidically linked carbohydrate units, both consisting of mannose and N-acetylgucosamine, in a molar ratio of 9:2. Both were described to have the same core structure, Man alpha (1 leads to 6)[Man alpha (1 leads to 3)]Man beta (1 leads to 4)GlcNAc beta (1 leads to 4)GlcNAc, but different patterns of branching. Here we present data showing that the asparagine-linked carbohydrate moiety of soybean agglutinin is homogeneous and possesses the following structure: (formula, see text) This conclusion is based on high resolution 1H NMR spectroscopy at 500 MHz of the isolated glycopeptide, and at 360 MHz of the oligosaccharide Man9GlcNAc obtained after digestion of the crude soybean agglutinin glycopeptide by endo-beta-N-acetylglucosaminidase H. The revised structure is identical in all respects with that of the high mannose N-glycosidic units of porcine thyroglobulin, of bovine lactotransferrin, and of the glycoprotein from Chinese hamster ovary cell membranes.