New approach towards deglycosylation of sialoglycoproteins and mucins.

A modified procedure for chemical deglycosylation of glycoproteins containing sialylated and/or O-linked oligosaccharides, using anhydrous trifluoromethane sulfonic acid (TFMSA) is described. Although sialic acid residues are acid labile, it has been known that anhydrous TFMSA does not effectively remove carbohydrate side chains from glycoproteins if they are sialylated. In this procedure, sialic acid residues were removed by mild acid hydrolysis and the desialylated glycoprotein was treated with anhydrous TFMSA reagent under conditions which remove all the carbohydrate residues except the core D-GalNAc linked to serine/threonine. The core D-GalNAc residues were removed by reacting the glycoprotein with periodate followed by a second treatment with anhydrous TFMSA; this procedure gave a completely deglycosylated protein. The protein thus obtained was soluble in aqueous buffers and useful for biochemical and biophysical studies. The method was successfully employed to isolate polypeptides from alpha 1-acid glycoprotein (N-linked), fetuin, canine tracheal mucin and gastric mucin.