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The surface of the gastrointestinal tract is coated by mucus, which plays a critical role in the protection of the gastrointestinal epithelium.1,2 Mucins are high molecular weight glycoproteins containing a large number of carbohydrate side chains attached via Oglycosidic linkage to hydroxy amino acids of the protein backbone. The heavy glycosylation and large molecular size of mucin glycoproteins confers viscosity and adhesiveness upon mucus, thus providing protection and lubrication for the gastrointestinal tract.1,2 This heavy glycosylation has made determination of mucin peptide structure difficult because the deglycosylation of mucins requires harsh chemical treatment that also results in the degradation of the protein backbone. This problem has been circumvented by using cDNA and genomic DNA sequencing however, and at least 15 different mucin genes have been identified to date, MUC1 through MUC17, numbered according to the order of their discovery.3,4 These mucins may be broadly classified into two main types, membrane-bound and secretory, which are expressed in a tissue and cell-specific manner.
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