Sulfamate Proton Solvent Exchange in Heparin Oligosaccharides – Evidence for a Persistent Hydrogen Bond in the Antithrombin-binding Pentasaccharide Arixtra
Sulfamate groups (NHSO3-) are important structural elements in the glycosaminoglycans (GAGs) heparin and heparan sulfate (HS). In this work proton NMR resonance line shape analysis is used to explore the solvent exchange properties of the sulfamate NH groups within heparin-related mono-, di-, tetra- and pentasaccharides as a function of pH and temperature. The results of these experiments identified a persistent hydrogen bond within the Arixtra (Fondaparinux sodium) pentasaccharide between the internal glucosamine sulfamate NH and the adjacent 3-O-sulfo group. This discovery provides new insights into the solution structure of the Artixtra pentasaccharide and suggests that 3-O-sulfation of the heparin N-sulfoglucosamine residues pre-organize the secondary structure in a way that facilitates binding to antithrombin-III. NMR studies of the N-sulfoglucosamine NH groups can provide important information about heparin structure complementary to that available from NMR spectral analysis of the carbon-bound protons.