Determining the solution conformational entropy of O-linked oligosaccharides at quasi-physiological conditions: size-exclusion chromatography and molecular dynamics

The physiological functions of oligosaccharides are influenced by a number of structural parameters such as anomeric configuration, glycosidic linkage, and degree of polymerization. These parameters affect the conformation of the oligosaccharides which, in turn, is responsible for characteristics such as aptameric and enzymatic binding, chiral recognition, and the structural targeting of bacterial and parasitic recognition events. Here, we measure the solution conformational entropy (ΔS) of two series of oligosaccharides, linear malto- and cellooligosaccharides, using size-exclusion chromatography (SEC). For each series, we have determined ΔS as a function of degree of polymerization (DP). The choice of oligosaccharides studied also allowed us to compare the influence of anomeric configuration on ΔS, and to do so as a function of DP. Studies were conducted in water at physiological temperature and pH in order to resemble conditions within the human body. Experimental results were augmented with results from molecular dynamics computer modeling simulations in aqueous solvent. A comparison between experimental and computational data showed how the techniques can complement each other. An example of the latter is the considerable enthalpic contribution to the chromatographic separation of α- and γ-cyclodextrin, which may have gone unnoticed if not for the large discrepancy between the results obtained by the separate techniques.