Question

Mucin (MUC) is a glycoprotein secreted in the mucus of the respiratory and digestive tracts. The sugars when attached to mucins give them considerable water-holding capacity and also make them resistant to proteolysis by digestive enzymes. MUC1 substype if a protein that has a core protein mass of 120-225 kDa, which increases to 250-500 kDa with glycosylation.

Explain why MUC1 has high apparent molecular weight on SDS-gels?

Answer 1

MUC1 has a high apparent molecular weight on SDS-gels because of glycosylation of the protein. Glycosylation is a covalent modification process, which after protein denaturation before SDS gel running, does not break. So, the cumulative weight of the sugar moieties will increase the overall weight of the single protein molecule and you will get a band at higher molecular weight region on the SDS gel than the normal non-glycosylated protein band.