In vivo glycosylation of mucin tandem repeats

The biochemical and biophysical properties of mucins are largely determined by extensive O-glycosylation of serine- and threonine-rich tandem repeat ( TR) domains. In a number of human diseases aberrant O-glycosylation is asso ciated with variations in the properties of the cell surface-associated and secreted mucins, To evaluate in vivo the O-glycosylation of mucin TR domai ns, we generated recombinant chimeric mucins with TR sequences from MUC2, M UC4 MUC5AC, or MUC5B, which were substituted for the native TRs of epitope- tagged MUC1 protein (MUC1F), These hybrid mucins were extensively O-glycosy lated and showed the expected association with the cell surface and release into culture media. The presence of different TR domains within the chimer ic mucins appears to have limited influence on their posttranslational proc essing. Alterations in glycosylation were detailed by fast atom bombardment mass spectrometry and reactivity with antibodies against particular blood- group and tumor-associated carbohydrate antigens, Future applications of th ese chimeras will include investigations of mucin posttranslational modific ation in the context of disease.