Characterization of High Molecular Weight Mucins of Rabbit Bladder

Epithelial mucin glycoproteins of bladder act as an effective barrier against invasion by pathogenic microorganisms and injury by toxic substances in urine. Although these glycoconjugates play important roles in the pathophysiology of bladder disorders such as intestinal cystisis, cancer, and urinary tract infections, they have not been characterized in detail either in humans or in animals. Rabbits could be useful for developing models for studying bladder disorders. In this study, we purified and partially characterized two major high molecular weight rabbit bladder mucin glycoproteins, designated RBM1 and RBM2, found in urine. Consistent with their mucin characteristics, amino acid compositions showed have high levels of serine, glutamic acid, proline, glycine and alanine, which together comprise 34% and 42% of the total amino acids in RBM1 and RBM2, respectively. Carbohydrate compositional analysis indicated that RBM1 and RBM2 consist of N-acetylgalactosamine (GalNAc), N-acetylglucosamine (GlcNAc), galactose (Gal), N-acetylneuraminic acid (NeuAc) and fucose (Fuc) in the molar ratio of 1.0: 0.82: 0.12: 0.30: 0.02 and 1.0: 1.03: 0.46: 0.16: 0.05, respectively; mannose (Man) was not detected in either mucin. Both mucin fractions were strongly reactive to wheat germ agglutinin, but not to Ca2 antibody specific to a human tumor mucin antigen (asialylated carbohydrate linked to protein core), suggesting that most of the galactosyl residues of oligosaccharides are sialylated. Together, the data suggest that rabbit mucin glycoproteins characterized here are distinctively different from MUC1 mucin glycoprotein found in human urine.