Solution conformation and dynamics of an extracellular polysaccharide isolated from Bradyrhyzobium as deduced from 1H-NMR off resonance ROESY and 13C-NMR relaxation measurements

The conformational and dynamical features of an extracellular branched deacetylated polysaccharide isolated from Bradyrhizobium (Chamaecytisus proliferus) have been investigated by homo and heteronuclear NMR methods. 1H-NMR cross relaxation rates have been obtained for this polysaccharide through regular NOESY and ROESY spectra as well as by modern off resonance ROESY techniques. Local proton-proton correlation times as well as interproton distances have been obtained. 13C-NMR relaxation parameters (T1, T2, NOE) have also been measured at two different magnetic fields and interpreted using different approximations based on the Lipari and Szabo model free approach. The analysis of the data indicates the existence of important flexibility for the different linkages of the polysaccharide. Motions in the range of several ns contribute to the relaxation of the macromolecule, although faster internal motions in the 600–800 ps timescales are also present. These time scales indicate that segmental motions as well as internal motions around the glycosidic linkages are the major sources of relaxation for this molecule at 299 K.