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Separation and purification of glycans out of glycoproteins

The majority of all membrane and secreted proteins, as well as numerous cytoplasmic proteins, have one or several specific branched oligosaccharide chains (glycans) attached to their backbone. Those proteins are referred to as glycoproteins and the process of oligosaccharide attachment to a protein is called glycosylation. Glycans have numerous important structural, functional and regulatory roles including protein degradation, folding and secretion, cell signalling, immune function and transcription. Glycoproteins are found in almost all living organisms that have been studied, including eukaryotes, eubacteria and archae. The high levels of diversity encountered in the best- studied vertebrate species indicate similar diversity in other groups of organisms. There can also be significant variation in glycosylation among members of the same species. Glycosylation is thought to be the most complex post- translational modification because of the large number of enzymatic steps involved. Differences in monosaccharide composition, anomeric state, linkage of the subunits, branching and linkage to the peptide part of a glycoprotein are all contributing to the diversity of the glycan portion of the glycoprotein. In view of this heterogeneity the analysis of glycans is a very hard and demanding task. Therefore sample preparation is a crucial step when studying glycans. In this chapter we discuss some of most widely used methods for separation and purification of glycans out of glycoproteins.

Glycans, Glycosylation, Glycoproteins, Deglycosylation, Labeling, Purification

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