O-Linked glycosylation occurs on basic parotid salivary proline-rich proteins

Interactions between salivary glycoproteins and many oral bacteria have been shown to depend on O-linked glycans on salivary glycoproteins. Basic proline-rich proteins form the largest group of proteins within human parotid saliva. In the present study human parotid salivary glycoproteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis or two-dimensional electrophoresis, electroblotted onto nitrocellulose and probed with two biotin-labelled lectins from Maclura pomifera (MPA) and Arachis hypogaea (PNA) which are specific for O-linked (galactose beta 1,3 N-Acetylgalactosamine) glycans. Lectin binding was detected with avidin-biotin complex and enhanced chemiluminescence. Two-dimensional electrophoresis in combination with lectin binding indicated that only basic parotid salivary glycoproteins bind the lectin MPA. Following removal of terminal sialic acid residues by sialidase digestion the same glycoproteins were detected by the lectin PNA. Glycosidase digestion with endo-alpha-N-acetylgalactosaminidase (O-glycanase) in conjunction with sialidase eliminated MPA binding. Taken together these results indicate that many basic parotid salivary glycoproteins contain O-glycans, all of which are sialylated.