Molecular size of dermatan sulfate oligosaccharides required to bind and activate heparin cofactor II.

Heparin cofactor II (HCII) inhibits thrombin rapidly in human plasma in the presence of heparin or dermatan sulfate. To determine the minimum structure of dermatan sulfate required to activate HCII, the glycosaminoglycan was partially degraded by sequential treatment with periodate, [3H]borohydride, and sulfuric acid. Labeled oligosaccharide fragments were separated by gel filtration chromatography. Purified fragments were then applied to a column of HCII bound to concanavalin A-Sepharose, and bound oligosaccharides were eluted with a gradient of sodium chloride. Di-, tetra-, and hexasaccharide fragments did not bind to HCII, while 15% of the octasaccharides and up to 45% of larger fragments bound. Octasaccharides that bound to the HCII column had a greater negative charge than the run-through material based on anion-exchange chromatography, suggesting that they contained a greater number of sulfate groups per molecule. Fragments of dermatan sulfate containing a minimum of 12-14 sugar residues accelerated inhibition of thrombin by HCII. Fragments of this length that bound to the column of immobilized HCII had molar specific activities greater than those of the fragments that did not bind. These studies suggest that HCII is activated by dermatan sulfate fragments greater than or equal to 12 residues in length that contain a specific octasaccharide sequence required for binding to the inhibitor.