Asn-linked saccharides

Complex-type sugar chains exhibit a wide spectrum of structures, since both 

FIGURE 1. Three major types of Asn-linked saccharide structures found in glycoproteins. The core pentasaccharide is shown boxed in panel a. 

FIGURE 2. Branch variations in the complex-type Asn-linked oligosaccharides which give rise to multiantennary structures. 

FIGURE 3. List of peripheral saccharide structures that terminate the complex-type Asn-linked oligosaccharides of glycoproteins. 

A general structure for the saccharides linked to Ser/Thr could be depicted as follows  

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The basis for the existence of extreme diversity of both Asn- and Ser/ Thr-saccharides. In the case of the Asn-linked saccharides since all of the structures are derived from the common precursor, Glc3Man9GlcNAc2-Asn, there must be fine-tuning at the processing level. The peptide sequence and overall protein structure/conformation are believed to play major roles in this. 

The identity of the monosaccharide and amino acid involved in linkage is not the only characteristic by which the classes of sialoglycoproteins could be distinguished. The composition and structure of the saccharides linked to Asn or Ser/Thr are also markedly different. Compositionally the most distinctive feature is that the former always contain Man and seldom contain GalNAc, the latter always contain GalNAc and never Man. Therefore, it is possible to obtain tenta-... 

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