Presence of sulfate in N-glycosidically linked carbohydrate units of calf thyroid plasma membrane glycoproteins.

Abstract

Calf thyroid slices were found to incorporate [35S] sulfate into two major plasma membrane glycoproteins, which have been previously designated as GP-1 and GP-3 (Okada, Y., and Spiro, R. G. (1980) J. Biol. Chem. 255, 8865-8872). The 35S-glycoproteins were identified on the basis of their characteristic solubility and electrophoretic migration as well as their affinity for Bandeiraea simplicifolia I lectin. After pronase digestion of these glycoproteins, the 35S-label remained associated with the glycopeptides primarily on asparagine-linked carbohydrate units which were released by hydrazinolysis. Examination of the reduced radio-labeled products obtained by nitrous acid cleavage of the hydrazine-liberated oligosaccharides indicated that sulfate esters of N-acetylglucosamine occurred at three locations on the carbohydrate units; two 35S-monosaccharides (2,5-anhydromannitol 4- and 6-sulfate) and one 35S-disaccharide (beta-Gal(1----4)-2,5-anhydromannitol(6-SO4] were formed. The disaccharide is believed to be derived from an internal sulfated N-acetyllactosamine sequence while the monosaccharides most likely originate from 4- and 6-sulfated N-acetylglucosamine residues situated, respectively, at the non-reducing and reducing termini of the oligosaccharide units. Quantitation by NaB[3H]4 reduction of the sulfated saccharides obtained by nitrous acid treatment of hydrazine-released oligosaccharides from unlabeled GP-3 indicated that about 20% of the asparagine-linked carbohydrate units contain sulfate substituents.