Substrate specificity of the heparin lyases from Flavobacterium heparinum.
A detailed knowledge about the substrate specificities of the heparin lyases is necessary when using these enzymes as tools for elucidating the sequence of heparin and heparan sulfate. The substrate specificity of heparin lyases I, II, and III have been profiled with structurally defined, heparin-derived oligosaccharides. The primary substrate specificities of heparin lyases I and III require the presence of 2-O-sulfated alpha-L-idopyranosyluronic acid and beta-D-glucopyranosyluronic acid residues, respectively, at the linkages being cleaved. Heparin lyase II demonstrates an intriguingly broad primary specificity for oligosaccharides, acting at linkages containing alpha-L-idopyranosyluronic and beta-D-glucopyranosyluronic acid as well as at linkages containing alpha-L-galactopyranosyluronic acid residues. In addition to their primary specificities, each lyase also demonstrates secondary specificities under forcing conditions. Differences in the sulfation pattern within uronic acid residues and sulfation of adjacent residues has profound impact on the ease of lyase cleavage of a glycosidic linkage. Specifically, heparin lyases I and III exhibit secondary specificity for oligosaccharides containing an unsulfated alpha-L-idopyranosyluronic acid residue. The lack of sulfation on residues adjacent to the linkage undergoing cleavage increases the action of heparin lyase III on a glycosidic linkage. In contrast, reduced sulfation on adjacent residues make glycosidic linkage resistant to heparin lyase I. The primary and secondary specificity can be rationalized on the basis of most favorable solution conformation of the uronic acid residues.