13C-nuclear magnetic resonance-spectral studies of the interactions of metal ions with carbohydrates: use of relaxation probes

Solution conformation of various uridine diphosphoglucose salts as probed by NMR spectroscopy

The solution conformations of uridine diphosphoglucose (UDP-Glc) under a variety of conditions (solvent, ionic strength, various mono- and divalent cations) have been studied by NMR spectroscopy (1H, 13C, 31P, and 25Mg). In the case of divalent cations (Ca2+, Mg2+, Mn2+) the phosphate oxygens are the preferred coordination sites and analysis of the 25Mg linewidths of solutions with various [Mg2+]/[UDP-Glc] ratios, indicates that the 1:1 Mg2+ UDP-Glc complex is the major species. From 13C relaxation data and hydrodynamic theory, it has been demonstrated that under all conditions UDP-Glc adopts a fairly extended overall shape and that magnesium ions lead to a significant increase in the average length of the UDP-Glc molecule as compared to monovalent cations. Thus, one of the roles of the metal ion in enzymic reactions involving nucleotide sugars may be to preorganize the nucleotide sugar.

NMR study of a Lewis(X) pentasaccharide derivative: solution structure and interaction with cations

The structure and conformation of the synthetic pentasaccharide Gal(beta 1-4){Fuc(alpha 1-3)}GlcNAc(beta 1-3)Gal(beta 1-4)Glc-beta OMe of the Lewis(X) family has been determined by NMR spectroscopy in dimethyl sulfoxide and methanol. In these solvents, the binding constants with calcium have been evaluated as 9.5 and 29.6 M-1, respectively. Study of the interaction sites has been achieved through the use of paramagnetic divalent cations and distance triangulation methods. Two regions have been found, the first one in the vicinity of the fucose unit, the second one closer to the lactose part.