A 23-KDA MEMBRANE GLYCOPROTEIN BEARING NEUNAC-ALPHA-2-3GAL-BETA-1-3GALNAC O-LINKED CARBOHYDRATE CHAINS ACTS AS A RECEPTOR FOR STREPTOCOCCUS-SANGUIS OMZ-9 ON HUMAN BUCCAL EPITHELIAL-CELLS

Streptococcus sanguis colonizes several human oral surfaces, including both hard and soft tissues, Large salivary mucin-like glycoproteins b earing Sialic acid residues are known to bind various S.sanguis strain s, However, the molecular basis for the adhesion of S.sanguis to human buccal epithelial cells (HBEC) has not been established, The present study shows that S.sanguis OMZ 9 binds to exfoliated HBEC in a sialic acid-sensitive manner, The desialylation of such cells invariably abol ishes adhesion of S.sanguis OMZ 9 to the cell surface, A soluble glyco peptide bearing short sialylated O-linked carbohydrate chains behaves as a potent inhibitor of the attachment of S.sanguis OMZ 9 to exfoliat ed HBEC, The resialylation of desialylated HBEC with CMP-sialic acid a nd Gal beta 1,3GalNAc alpha 2,3-sialyltransferase specific for O-glyca ns restores the receptor function for S.sanguis OMZ 9, whereas a simil ar cell resialylation with the Gal beta 1,4GlcNAc alpha 2,6-sialyl-tra nsferase specific for N-glycans is without effect. Finally, the same r esialylation reaction carried out with CMP-9-fluoresceinyl-sialic acid as a substrate yields exfoliated HBEC bearing fluorescence on a singl e 23 kDa protein, when using the alpha 2,3-sialyltransferase as the ca talyst, The latter finding demonstrates that this 23 kDa cell surface glycoprotein bears NeuNAc alpha 2-3Gal beta 1-3GalNAc O-linked sugar c hains, a carbohydrate sequence which is recognized by S.sanguis OMZ 9 on exfoliated HBEC, In similar experiments carried out with a buccal c arcinoma cell line termed SqCC/Y1, S.sanguis OMZ 9 did not attach in g reat numbers to such cultured cells, and these cells were shown to not express membrane glycoprotein bearing alpha 2,3-sialylated O-linked c arbohydrate chains,