[PDF][PDF] Mucin genes: structure, expression and regulation

M Verma, EA Davidson - Glycoconjugate Journal, 1994 - academia.edu
M Verma, EA Davidson
Glycoconjugate Journal, 1994academia.edu
Mucus is defined as a viscous secretion of one or more glycoproteins (mucins) secreted by
epithelial cells of normal and cancerous tissues. Mucins isolated from the gastrointestinal,
respiratory, or urinary tracts exhibit different properties (for example, amino acid
composition) fl]. Mucin has been isolated and characterized from the submaxillary gland of
bovine and porcine species, skin of frog, mammary gland of mouse and human, intestine of
rat and human, trachea of dog, human, rat and saliva of human and from other sources [2 …
Mucus is defined as a viscous secretion of one or more glycoproteins (mucins) secreted by epithelial cells of normal and cancerous tissues. Mucins isolated from the gastrointestinal, respiratory, or urinary tracts exhibit different properties (for example, amino acid composition) fl]. Mucin has been isolated and characterized from the submaxillary gland of bovine and porcine species, skin of frog, mammary gland of mouse and human, intestine of rat and human, trachea of dog, human, rat and saliva of human and from other sources [2, 33. Mucins are defined by their characteristic O-glycosylated domains. Typically, the domains contain a (semi) repetitive protein backbone with a particularly high content of Thr and Ser residues interspersed by Pro residues. This reflects the importance of local secondary structure for O-glycosylation by the polypeptide GalNAc transferase. The clustered O-linked oligosaccharides result in a stiff, extended conformation of the glycoprotein. Due to the presence of charge (sulfation of carbohydrate moieties and sialic acid residues), mucin can be considered as a highly charged thread-like polymer. As a consequence, during exocytosis the mucin matrix undergoes an ion-triggered transition from a condensed to an expanded hydrated phase, caused by the mutual repulsion of the anionic charges. This massive swelling is the biophysical basis for many general properties typical of mucin, particularly their high viscosity. These molecules have a strong tendency to bind to various proteins and peptides and their purification is difficult. On the basis of their sensitivity to proteases, mucins contain two different types of domains: highly glycosylated regions (rich in Set and Thr) and naked hydrophobic regions that are exclusively devoid of carbohydrates. Due to the high carbohydrate content of mucins, the elucidation of the
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