PICOSECOND DYNAMICS OF SIMPLE MONOSACCHARIDES AS PROBED BY NMR AND MOLECULAR-DYNAMICS SIMULATIONS

Carbon-13 T1 and NOE measurements have been performed on D-glucose, D-galactose, D-mannose, and L-idose, and molecular dynamics calculations have been performed on alpha-D-glucose and alpha-L-idose. Order parameters were obtained both from the relaxation data, at various field strengths and temperatures, and from the dynamics simulations. Results from both calculations and experimental data indicate that, on the picosecond time scale, all carbon sites in the sugar ring have some degree of motional freedom, most likely in the form of ring librations, but that both the ring and hydroxymethyl carbons maintain a single global conformation. The rate of interconversion among hydroxymethyl rotamers for all sugars and the various ring conformations for idose would have to occur on a time scale of 10(-9) to 10(-3) s to account for the experimental data. The results presented here have implications for the flexibility of idose-related residues in heparin and heparan sulfate, and for the relationship between restricted rotation of hydroxymethyl groups and intramolecular hydrogen bonds.