CHARACTERIZATION OF THE EXTENT OF INTERNAL MOTIONS IN OLIGOSACCHARIDES

A detailed investigation has been undertaken on the extent and nature of torsional fluctuations about the glycosidic linkage of the model di saccharide Manalpha1-3Manalpha1-OMe. In particular, we sought to deter mine whether the three nuclear Overhauser effects and the two long-ran ge heteronuclear 3J(CH) spin coupling constants measurable across the glycosidic linkage were consistent with a single conformation or multi ple conformations about that linkage. Within experimental error, we ha ve found that these five parameters can be interpreted in terms of a s ingle, rigid geometry. Alternatively, the data are also consistent wit h a model in which the glycosidic torsional angles exhibit significant but restricted fluctuations about the global minimum energy conformat ion. Evidence from restrained molecular dynamics simulations both in v acuo and with explicit inclusion of solvent water and from C-13 relaxa tion measurements upon an oligomannose glycan in covalent association with protein suggests that the latter model is the most accurate repre sentation of the conformational behavior of oligosaccharides in soluti on.