Preparation of glycopeptides

Generation of glycopeptides from glycoproteins is frequently useful when analyzing a protein's oligosaccharide side chains. Freed from the bulk of the polypeptide backbone by proteolysis, glycopeptides can be characterized by a variety of techniques. Extensive proteolysis with pronase or proteinase K results in oligosaccharides with one or a few amino acid residues attached. This technique, detailed in this unit, is often employed as a first step in characterizing oligosaccharides on very large glycoproteins such as proteoglycans and mucins. Limited proteolysis with a specific endoproteinase (e.g., trypsin, alpha-chymotrypsin, and V8 protease) is also described, and leaves a larger peptide attached to the oligosaccharide. The resulting glycopeptides are generally suitable substrates for Peptide:N-glycosidase F, an enzyme useful in defining oligosaccharide-peptide linkages. Additionally, they can be separated by reversed-phase chromatography, resulting in a glycopeptide map that is analogous to a peptide map, and used for detection of glycosylation sites.