Evidence for the covalent linkage of carbohydrate polymers to a glycoprotein from Streptococcus sanguis

The platelet aggregation-associated protein (PAAP) from Streptococcus sanguis contains 39% carbohydrate in rhamnose-rich polysaccharides. Synthesized by cultured protoplasts, these polysaccharides were shown to be covalently linked to this cell wall protein using specific inhibitors of glycosylation, glycosidase treatment, amino acid and carbohydrate analyses of prepared minimal glycopeptides and isolated protein, and NMR spectroscopy. To our knowledge, this is the first direct proof of an N-asparaginyl linkage of carbohydrate to a eubacterial protein.