Mucin-type sequences

Figure 1.9 Mucin-type Sequences of Glycoproteins. These structures share the common feature of N-acetylgalactosamine a-linked to the hydroxyl groups of seryl or threonyl residues otherwise they are extremely variable. Structures (a) to (d) occur in rat colonic mucus (Slomiany, Murty and Slomiany, 1980) (e) and (f) are of widespread occurrence and (g) is known from human gastric mucin and forms the inner part of several larger saccharides from human and porcine sources. Structure (a) is also very commonly found.

Few studies have been made of changes in mucin-type sequences following transformation, though the careful analysis of melanoma cells by Satoh et al. (1974) and Bhavanandan etal. (1977) suggest that there is a large increase in short mucin-type saccharides with sialyl terminals at the surface of the neoplastic cells. Information on fucose-containing mucin sequences is less... 

Hansen, J. E., Lund, O., Tolstrup, N., Gooley, A. A., Williams, K. L. Brunak, S. (1998). NetOglyc prediction of mucin type O-glycosylation sites based on sequence context and surface accessibility. Glycoconj J15,115-30. 

Core 1, the most common mucin-type O-linked core structure, is formed by the action of fSl-3 galactosyltransferase (fS3GalT), which adds galactose to form Galfi 1-3GalNAc (Fig. 2a). fS3GalT is expressed in most mammalian cells. The substrate specificity of this enzyme, like others involved in O-hnked core synthesis, is influenced by the amino acid sequences of substrate proteins and their glycosylation patterns. 

For some polysaccharides, such as keratan sulphate, the linkage sequences seem to have the same sfructixres as the oligosaccharides of conventional glycoproteins and the pathways of their synthesis are presumably the same. Hence mucin-type or complex-type chains can act as link sequences and so dolichol can be involved in some forms of link production. Some other polysaccharides, such as heparin, are attached to sequences that have no known counterpart in typical glycoprotein assembly. 

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