The influence of the hexopyranose ring geometry on the conformation of glycosidic linkages investigated using molecular dynamics simulations.

The conformation of the carbohydrate molecules is a subject of many theoretical and experimental studies. The different timescales associated with the particular degrees of freedom hinder the progress in both those fields. The present paper reports the results of computational studies aimed at elucidating and characterizing the potential correlations between the two main structural determinants of the carbohydrate structure, i.e. the ring conformation and the orientation of the glycosidic bonds (expressed in terms of the ϕ and ψ glycosidic dihedral angles). The free energy landscapes computed for 16 different oligomers composed of unsubstituted, 1,4-linked hexopyranose residues allowed for a detailed insight into how the ring geometry affects the glycosidic linkage conformation. The factor of main importance appeared to be the local changes of the chain length induced by the ring conformational rearrangements. This effect is important mainly for the carbohydrate chains exploiting the glycosidic bonds of uniform orientation with respect to the ring (i.e. either exclusively axially or exclusively equatorially oriented). The shape of the ring may affect the (ϕ,ψ) free energy maps but only if the population of the alternative ring conformers is relatively high and (at the same time) the presence of such conformers is associated with the significant shifts of the favorable ϕ and ψ values.