SOLUTION CONFORMATION AND DYNAMICS OF AN EXTRACELLULAR POLYSACCHARIDEISOLATED FROM BRADYRHYZOBIUM AS DEDUCED FROM H-1-NMR OFF-RESONANCE ROESY AND C-13-NMR RELAXATION MEASUREMENTS

The conformational and dynamical features of an extracellular branched deacetylated polysaccharide isolated from Bradyrhizobium (Chamaecytis us proliferus) have been investigated by homo and heteronuclear NMR me thods. H-1-NMR cross relaxation rates have been obtained for this poly saccharide through regular NOESY and ROESY spectra as well as by moder n off resonance ROESY techniques. Local proton-proton correlation time s as well as interproton distances have been obtained. C-13-NMR relaxa tion parameters (T-1, T-2, NOE) have also been measured at two differe nt magnetic fields and interpreted using different approximations base d on the Lipari and Szabo model free approach. The analysis of the dat a indicates the existence of important flexibility for the different l inkages of the polysaccharide. Motions in the range of several ns cont ribute to the relaxation of the macromolecule, although faster interna l motions in the 600-800 ps timescales are also present. These time sc ales indicate that segmental motions as well as internal motions aroun d the glycosidic linkages are the major sources of relaxation for this molecule at 299 K. (C) 1997 Elsevier Science Ltd. All rights reserved .