The structure of an acidic extracellular polysaccharide isolated from Bradyrhizobium (Chamaecytisus proliferus) has been elucidated by hydrolysis, methylation analysis, and 1D and 2D 1H- and 13C NMR spectroscopy of the complete polysaccharide. The NMR spectrum showed that microheterogeneity was present due to the minor existence of a variety of O-acetyl groups. Thus, a deacetylated sample was prepared by alkaline treatment which was then fully analysed. The deacetylated polysaccharide has the following sequence: →3)-[α-D-Galp-(1→6)-α-D-Glcp-(1→3)-β-D-Glcp-(1→3)-α-D-GalpA-(1→3)-α-D-Manp-(1→ The sample is partially O-methylated at position 4 of the α-D-Galp-(1→6) unit. In addition, the same moiety of the native sample is also partially and heterogeneously O-acetylated. The conformational features of the deacetylated sample have been evaluated by molecular mechanics and dynamics calculations and NOE spectroscopy. The results indicate that the polysaccharide may adopt a variety of three dimensional shapes, and that there is a fair agreement between the NMR-derived distances and those provided by the calculations.
conformation, structure, polysaccharide, acidic, NMR spectroscopy, molecular modeling, extracellular polysaccharide, extracellular, solution, acidic extracellular polysaccharide, Bradyrhizobium, extracellular polysaccharides
NCBI PubMed ID: 9468626Journal NLM ID: 0043535Publisher: Elsevier
Correspondence: iqojj01@pinarl.csic.es
Institutions: Instituto Quimica Organica, CSIC, Juan de la Cierva 3, 28006 Madrid, Spain, Servicio Interdepartamental de Investigacion, Universidad Autonoma de Madrid, Cantoblanco 28049 Madrid, Spain, Departamento de Bioquimica e Biologla Molecular, Universidad de la Laguna, 38071 Tenerife, Spain, Centro de Investigaciones Biologicas, CSIC, Velazquez, 28006 Madrid, Spain, Instituto Estructura de la Materia, CSIC, Serrano 117, 28006 Madrid, Spain
Methods: 13C NMR, 1H NMR, methylation, NMR-2D, alkaline degradation, NMR-1D
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