title: Contribution of monosaccharide residues in heparin binding to antithrombin III.
abstract: The importance of 3-O- and 6-O-sulfated glucosamine residues within the heparin octasaccharide iduronic acid(1)----N-acetylglucosamine 6-O-sulfate(2)----glucuronic acid(3)----N-sulfated glucosamine 3,6-di-O-sulfate(4)----iduronic acid 2-O-sulfate(5)----N-sulfated glucosamine 6-O-sulfate(6)----iduronic acid 2-O-sulfate(7)----anhydromannitol 6-O-sulfate(8) was determined by comparing with synthetic tetra- and penta-saccharides its ability to bind human antithrombin. The octasaccharide had an affinity for antithrombin of 1 X 10(-8) M (10.2 kcal/mol) measured by intrinsic fluorescence enhancement at 6 degrees C. The synthetic pentasaccharide, consisting of residues 2-6, had an affinity of 3 X 10(-8) M (9.6 kcal/mol). The same pentasaccharide, except lacking the 3-O-sulfate on residue 4, had an affinity of 5 X 10(-4) M (4.5 kcal/mol) measured by equilibrium dialysis. The tetrasaccharide, consisting of residues 2-5, bound antithrombin with an affinity of 5 X 10(-6) M (6.8 kcal/mol). The tetrasaccharide, consisting of residues 3-6, had an affinity of 5 X 10(-5) M (5.5 kcal/mol). Since the loss of either the 6-O-sulfated residue 2 or the 3-O-sulfate of residue 4 results in a 4-5 kcal/mol or a 40-50% loss in binding energy of the pentasaccharide, these two residues must be the major contributors to the binding and must be linked to the biologic activity of the octasaccharide.
mesh_terms: D000818:Animals; D000990:Antithrombin III / Q000302:isolation & purification / Q000378:metabolism*; D002151:Calorimetry; D002240:Carbohydrate Sequence; D002417:Cattle; D006493:Heparin / Q000302:isolation & purification / Q000378:metabolism*; D007202:Indicators and Reagents; D007413:Intestinal Mucosa / Q000378:metabolism; D009844:Oligosaccharides / Q000032:analysis / Q000138:chemical synthesis*; D013050:Spectrometry, Fluorescence; D013552:Swine
chemical_list: D007202:Indicators and Reagents; D009844:Oligosaccharides; D000990:Antithrombin III; D006493:Heparin