SPECIFICITY STUDIES ON THE HEPARIN LYASES FROM FLAVOBACTERIUM-HEPARINUM

An understanding of the substrate specificity study of the heparin lyases (heparinase and heparitinases) is crucial for elucidation of the sequence of heparin and heparan sulfate. Four chemically modified heparins have been used to study the substrate specificity of the three heparin lyases. These modified heparins include the N- and O-desulfated and then specifically N-sulfated or N-acetylated derivatives of heparin and a modified heparin containing L-galactopyranosyluronic acid residues. These chemically modified heparins were degraded to various extents by the three heparin lyases. Differences in degree of sulfation have profound impact on the ease of cleavage of glycosidic linkages. Heparin lyase I (EC 4.2.2.7) is selective in cleaving highly sulfated polysaccharide chains containing linkages to 2-O-sulfated alpha-L-idopyranosyluronic acid residues. Heparin lyase III (EC 4.2.2.8) cleaves linkages that have reduced density of sulfation and that contain beta-D-glucopyranosyluronic acid residues. The ability of heparin lyase III to act on linkages to unsulfated alpha-L-idopyranosyluronic acid residues is observed for the first time. Heparin lyase II (no assigned EC number) demonstrates an unparalleled, wide specificity for substrates comprised of linkages containing both alpha-L-idopyranosyluronic and beta-D-glucopyranosyluronic acid residues. Heparin lyase II can also act on substrates containing linkages to unnatural alpha-L-galactopyranosyluronic acid residues. The high level of specificity of heparin lyase I makes it particularly suitable for use in the sequencing of heparin and heparan sulfate, while caution must be excercised in using heparin lyases II and III to sequence heparin and heparan sulfate because of their relatively broad specificity.