Interaction of heparin with rat mast cell protease 1

Heparin is a sulfated glycosaminoglycan, synthesized by connective tissue-type mast cells. Rat mast cell protease 1 (RMCP-1), a chymotrypsin-like serine protease expressed specifically by connective tissue-type mast cells, is recovered in a macromolecular complex with heparin proteoglycan. The heparin.RMCP-1 complexes are stored in the secretory granules of the cells and are released following mast cell activation. We showed previously that dissociation of RMCP-1 from heparin resulted in loss of protease activity, as measured by its ability to inactivate thrombin. In the present report the binding of heparin to RMCP-1 was characterized. Affinity chromatography on heparin-Sepharose showed that RMCP-1 displayed high affinity for heparin, with approximately 1.2 M NaCl being required for elution of RMCP-1 from the affinity matrix. The structural requirements for the binding of heparin to RMCP-1 were investigated. Heparan sulfate, chondroitin sulfate, and dermatan sulfate, three glycosaminoglycans structurally related to heparin, were > or = 80-fold less effective in binding to RMCP-1 than heparin. The 2-O-sulfate, 6-O-sulfate, and N-sulfate groups in heparin were all shown to contribute in the binding. The minimal heparin sequence required for binding to RMCP-1 was found in a 14-saccharide fraction. 14-Saccharide species, obtained after separation by anion exchange chromatography, showed continuously increased binding with increasing anionic charge densities. The 16-18-saccharides were the smallest heparin oligosaccharides capable of accelerating the inactivation of thrombin by RMCP-1.