Figure 27.

Common glycosaminoglycan depolymerization strategies shown through the example of heparan sulfate/heparin. (A, left) Enzymatic depolymerization of GAG chains may be performed using glycosidases, resulting in hydrolytic cleavage that preserves the hexuronic acid stereochemistry. To obtain oligosaccharide fragments covering the full sequence, enzymes with endolytic activity are necessary. Heparanases are endo-β-glucuronidases cleaving at the reducing end of GlcA residues in moderately sulfated HS/heparin chains. (A, right) Prokaryotic lyases, such as heparinase I–III, act via a β-eliminative mechanism, leading to Δ^4,5-unsaturated uronic acid residues at the new nonreducing end. Consequently, stereochemical information is lost in the process. (B, left) Benzyl esterification with alkaline β-elimination may be applied for the depolymerization of GAGs, mimicking lyase activity. (B, right) Deaminative cleavage preserves hexuronic acid stereochemical information at the cleavage site but alters the structure of the glucosamine through the formation of 2,5-anhydromannose. The reaction is blocked in the presence of N-acetyl groups on glucosamines, making prior deacetylation necessary.