Distribution and Carbohydrate Structures of High Molecular Weight Glycoproteins, MUC1 and MUCX, in Bovine Milk*

High molecular weight glycoproteins, MUC1 and MUCX, originating from bovine milk, were compared with regard to their distribution in milk fat and skim milk fractions and for presence of carbohydrate structures. Polymorphic MUC1, which migrated into 6% resolving SDS-PAGE gels, was found in both milk fat globule membrane and skim milk phases of bovine milk. In contrast, MUCX, appearing as a non-polymorphic single band in 3% polyacrylamide stacking gels, was present only in the skim milk fraction. Peptide-N-glycosidase F digestion studies indicated that MUC1 and MUCX possessed N-glycans with MUC1 containing more N-glycans than MUCX. Exoglycosidase digestion studies revealed the existence of abundant terminal sialic acid residues in both MUC1 and MUCX. Lectin-binding studies showed that MUCX likely possessed more complex carbohydrate structures than MUC1. The complex carbohydrate structures carried by both MUC1 and MUCX suggest that they may have potential to bind a wide spectrum of pathogenic microorganisms. If that proves to be the case in vivo, such structures could have a role in preventing or reducing some infectious diseases.