A new bacterial polysaccharide (YAS34). I. Characterization of the conformations and conformational transition

This paper concerns the study of the conformational transition of a new exo polysaccharide (YAS34) using experimental techniques such as optical rotati on, conductimetric and microcalorimetric measurements as a function of temp erature. The behaviors of this polysaccharide in the acid or sodium salt fo rm are compared; a deacetylated sample is also prepared to demonstrate the role of substituents. For the native structure (never heated), a conformati onal transition is observed but the deacetylated polysaccharide exhibits no ordered conformation. Multidetection size exclusion chromatography (SEC) a nalyses and conductimetric experiments allowed to determine the nature of e ach conformation and the molecular dimensions. From these results, it is su ggested that the native conformation is a double helix which by heating ove r T-m (temperature corresponding to half conformational transition) dissoci ates into disordered single chains. In the acid and sodium salt forms, by c ooling below T-m, an ordered conformation is restored. This conformation se ems to be an intramolecular double helix 'hairpin-like turn' (called renatu red conformation). Nevertheless an irreversible denaturation is obtained pr ogressively in the sodium salt form when the time of heating over T-m incre ases. The conformation of the deacetylated polysaccharide corresponds to th at of a single flexible chain (disordered conformation). The conformational transition for the native conformation was studied also in relation to the polyelectrolytic character of the polysaccharide: stability as a function of salt nature and salt and polymer concentrations was investigated for the polymer initially in the sodium and acid forms. (C) 2000 Elsevier Science B.V. All rights reserved.