PMID: 9530955

 

    Legend: Sugar

Title : Purification and characterization of the MUC1 mucin-type glycoprotein , epitectin , from human urine: structures of the major oligosaccharide alditols

Abstract :
  1. The MUC1 glycoprotein , epitectin , a component of the human bladder epithelium, was purified from human urine
  2. Sedimentation equilibrium analysis and gel filtration using polysaccharide or protein standards revealed a polydisperse preparation with molecular weights ranging from about 0.9 to 1.3 x 10(6)
  3. This suggests that in the native state epitectin exists as aggregates of three or four monomer units of 350-400 kDa
  4. Epitectin was found to have significant affinity to hexyl-, octyl- or phenyl agarose indicating that hydrophobic interactions and possibly carbohydrate-carbohydrate interactions may be responsible for the self-association
  5. Chemical and enzymic deglycosylation of [125I]-labeled urine epitectin and metabolically labeled H.Ep.2 epitectin resulted in extremely polydisperse products
  6. The buoyant densities of epitectin purified from urine and H.Ep.2 cells were found to be 1. 39-1 .40 g ml(-1 ), suggesting that the total carbohydrate content of these preparations is not significantly different
  7. The O-linked saccharides of epitectin were fractionated by HPLC and analyzed by permethylation and FAB-MS
  8. The neutral saccharides from both sources contain three common structures, namely Gal1 --> 3GalNAc, GlcNAc1 --> 6 (Gal1 --> 3) GalNAc and Gal1 --> 4GlcNAc --> 6 (Gal1 --> 3)GalNAc.
  9. The sialic acid of urine epitectin consisted entirely of N-acetylneuraminic acid
  10. The two sources of epitectin , in vitro labeled on sialic acid, were found to have the same sialyl oligosaccharides but in different proportions
  11. Metabolic labeling and N-glycanase susceptibility experiments firmly established the presence of N-linked saccharides in epitectin as minor components
  12. The remarkable similarities in the total carbohydrate content , the carbohydrate composition and structures of saccharides between epitectin from urine, a non-malignant source, and H.Ep.2 cells is surprising in view of the prevailing view that MUC1 glycoproteins of cancer cells are underglycosylated compared to those produced by non-malignant cells