Threonine carbohydrate chains linked

Figure 4. Structures of the carbohydrate chains linked to protein in Saccharo-myces cerevisiae X2180 mannoprotein. Four types of mannose units are linked to serine (Ser) and threonine (Thr whereas a more complex polysaccharide chain is attached to asparagine (Asn). All anomeric linkages are a, except for the trisaccharide unit l3Man-> fiGNAc- ffGNAc- by which the polysaccharide is linked to asparagine.

Fig. 9. Proposed composite structure showing the relationship of the A, B, H, Le , and Le antigenic determinants of the water-soluble human blood group substances from ovarian cysts. The structure of the side chain in brackets has not been established, but the existence of such a chain is indicated by the mechanism of alkaline borohydride degradation and the oligosaccharides isolated. The carbohydrate chain shown is one of many linked to the serines and threonines of the polypeptide backbone. Chains are not homogeneous and may be of various lengths depending upon genetic composition, incomplete biosynthesis, and unknown factors. From Pereira and Kabat, modified from Lloyd and Kabat cf. Kabat. ...

The 0-glycosically linked carbohydrate chains of fetuin have been cleaved from the protein by alkaline borohydride treatment. Structural analysis revealed the existence of tri- and tetra-saccharides linked 0-glycosidically to L-serine or L-threonine and having structures identical to those previously identified for bovine K-casein and human chorionic gonadotrophin [(27) and (28)]. The A-glycosidically linked chains of fetuin have been assigned structures (36) %r (37). ... 

The third domain, rich in serine and threonine residues, contains eight hydroxy amino acids among 34 residues. This domain may bear clustered 0-linked carbohydrate chains as are found in the corresponding domain in LDL receptor (232). This segment shows the most variation between human and bovine sequence (35). 

While the structure of the carbohydrate chains and of the peptides linked to the muramic acid residues is fundamentally the same in gram positive as in gram negative bacteria, the mode of linkage of the peptide chains in the individual species and strains appears to be specific. In Staphylococcus aureus the cross linkages form a fine network made up of five glycine units. In a certain strain of Micrococcus roseus the cross links are composed of a peptide made up of three molecules of L-alanine and one molecule of L-threonine, while in another strain three molecules of L-alanine are involved. The peptide chains are linked directly... 

Three homogeneous glycoproteins have been isolated from reduced and S -carboxymethylated canine tracheal pouch mucous. Alkaline borohydride reduction indicates that the majority of carbohydrate chains are linked to the protein core by O-glycosidic bonds involving 2-acetamido-2-deoxy-D-galactose residues and either L-serine or L-threonine. 

The carbohydrate moieties of erythrocytes from patients with Tn-syndrome have been shown to contain less o-galactose and sialic acid. - The work suggested that alkali-labile carbohydrate chains of these erythrocytes consist solely of 2-acetamido-2-deoxy-D-galactosyl residues linked either to serine or to threonine. 

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