Characterization of the rabbit homolog of human MUC1 glycoprotein isolatedfrom bladder by affinity chromatography on immobilized jacalin

The urinary bladder is lined by transitional epithelium, the glycocalyx on the luminal surface has interesting properties and is implicated in protect ive functions. Glycoconjugates are major components of the glycocalyx, but their biochemical nature is not well understood, Previous studies on rabbit bladder indicated the presence of significant levels of sialoglycoproteins compared to glycosaminoglycans in the epithelium. In this study, rabbit ex plant cultures were radiolabeled by precursor sugars or amino acids and a m ajor lectin-reactive glycoprotein of rabbit bladder mucosa was isolated by affinity chromatography on jacalin-agarose, The radiolabeled glycoprotein w as purified to homogeneity by a second cycle on the lectin column, followed by gel filtration and density gradient centrifugation. The average molecul ar mass of the glycoprotein was estimated to be 245 kDa and 210 kDa by gel filtration and SDS-PAGE, respectively. Its buoyant density was 1.40 g/ml, s uggesting a carbohydrate content of similar to 50%, The percent distributio n of glucosamine-derived tritium label in sialic acid, galactosamine, and g lucosamine was 30, 52, and 18, respectively. The glycoprotein consisted ent irely of small sialylated and neutral oligosaccharides O-glycosidically lin ked to serine and threonine residues. The same glycoprotein could be immuno precipitated with an antibody against the carboxy terminal 17 amino acid pe ptide of human MUC1 mucin glycoprotein, This suggests that this mucin glyco protein is the rabbit homolog of MUC1 glycoprotein, which has been previous ly established to be a component of human bladder urothelium acid has been purified from human urine and biochemically characterized.