PYRANOSE RING FLEXIBILITY - MAPPING OF PHYSICAL DATA FOR IDURONATE INCONTINUOUS CONFORMATIONAL SPACE

A method for relating pyranose ring conformation to experimental measu rements is presented. A three-dimensional conformational space (Q, the ta, P-2) based on a torsion angle formalism is projected in two dimens ions (theta, P-2) and contours of calculable physical properties are p lotted and compared to experimentally determined values. With this app roach, 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 cano nical chair and skew-boat conformations to a continuous conformational space, when interpreting biophysical data related to the iduronate ri ng conformation. When the method is applied to the physical data avail able for dermatan sulfate, the results indicate that two families of a lpha-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 conforma tions of the iduronate residue. The method described here offers a sys tematic search of conformations beyond the canonical chair, boat, and skew boat conformations and provides a graphical description of the de viations from these ideal conformers. The approach thus can be extende d to ring conformational analysis of other pyranoses.