IDENTIFICATION AND CHARACTERIZATION OF A CANDIDA-ALBICANS BINDING PROTEOGLYCAN SECRETED FROM RAT SUBMANDIBULAR SALIVARY-GLANDS

A previously identified Candida albicans-binding glycoprotein secreted from rat submandibular glands (RSMG) has been further purified from a n aqueous RSMG extract by ion-exchange chromatography and gel filtrati on. Biochemical analysis of the glycoprotein revealed high levels of u ronic acid and sulfate, suggesting that it was a proteoglycan. Its ami no acid and carbohydrate compositions were similar to those observed f or other proteoglycans and differed significantly from those of RSMG m ucin, the major secretory glycoprotein of RSMG. In addition, the appar ent molecular weight of the glycoprotein was reduced following treatme nt with either chondroitinase ABC or heparitinase, demonstrating the p resence of chondroitin sulfate and heparan sulfate. On the basis of it s structure and anatomical source, the glycoprotein is referred to as submandibular gland secreted proteoglycan 1 (SGSP1). SGSP1 also binds monoclonal antibody 1F9, which recognizes the human blood group A carb ohydrate epitope found on RSMG mucin. Hence, SGSP1 appears to be a hyb rid molecule with carbohydrate structures found in both proteoglycans and RSMG mucin. Enzymatic digestion of SGSP1, followed by its interact ion with a radiolabelled C. albicans strain in a filter-binding assay, demonstrated that binding to this strain appears to be mediated prima rily via the heparan sulfate side chains of SGSP1 and not via the bloo d group A oligosaccharide.