Pyranose ring flexibility. Mapping of physical data for iduronate in continuous conformational space

Abstract

A method for relating pyranose ring conformation to experimental measurements is presented. A three-dimensional conformational space (Q, θ, P₂) based on a torsion angle formalism is projected in two dimensions (θ, P₂) and contours of calculable physical properties are plotted and compared to experimentally determined values. With this approach, conformations in a continuous conformational space that fit the physical data can be identified rapidly and the conformational space available to pyranose rings can be visualized easily. Iduronate, which is part of biologically important glycosaminoglycans such as dermatan sulfate, shows similar stability in several ring conformations. Thus, we find it is desired to extend the conformational analysis from canonical chair and skew-boat conformations to a continuous conformational space, when interpreting biophysical data related to the iduronate ring conformation. When the method is applied to the physical data available for dermatan sulfate, the results indicate that two families of α-l-iduronate conformations each can explain both 2D-NMR and X-ray diffraction data for dermatan sulfate. Further, the mapping technique was used to investigate the interconversion between different conformations of the iduronate residue. The method described here offers a systematic search of conformations beyond the canonical chair, boat, and skew boat conformations and provides a graphical description of the deviations from these ideal conformers. The approach thus can be extended to ring conformational analysis of other pyranoses.