Glycobiology Glycoforms

TABLE 17.1 Terminal oligosaccharide sequences recognized by some sialic acid binding lectins 

Sialic acid containing Glycan sequence Vertebrate Insect slug Plant Viral  

Notes 1. Sialic acid has an uncon romising role in v tebrates as it is often at the capping position of cell surface glycan and is therefore exposed for interactions with exo nous cells and proteins. Sialic acid is a critical component of glycan epitopes responsible for initiating inflammatory leukocyte adhesion, B-ceU signaling and activation and viral binding. 

Terminal and minimum sialic acid (NN)-containing ohgosaccharide sequences are shown in LinearCode. The continuing chains are either O-GalNAc-linked, or N-GlcNAC-/0-GalNAC-/cCTamide-linked. 

All glycoforms show the same amino acid sequence but differ in the location, number or sequence of attached glycan, and importantly their bioactivities. For example, bovine pancreatic ribonuclease (RNase) occurs naturally as a mixture of the unglycosylated protein (RNase A) and five glycoforms (RNase B, Man 5-9), in which 5-9 mannose residues are attached to the di-A-acetylchitobiose core. These glycoforms differ in their enzyme activities, i.e. decreasing activities in the order of RNase A RNase ManO = RNase Manl RNase Man5 = RNase B (Rudd et al, 1994). 

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Opdenakker, G., Rudd, P., Pouting, C., Dwek, R. (1993) Concepts and principles of glycobiology. FASEB J. 7, 1330-1337. This review considers the genesis of glycoforms, functional roles for glycosylation, and structure-function relationships for several glycoproteins. 

Aplin JD, Hey NA, Graham RA. Human endometrial MUCl carries keratan sulfate characteristic glycoforms in the luminal epithelium at receptivity. Glycobiology 1998 8 269-276. 

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