Certain strains of Bradyrhizobium japonicum and B. elkanii produce a polysaccharide within the root nodules of their legume host, soybean. These nodule polysaccharides (NPSs) were isolated and characterized. The NPS produced by B. elkanii strains proved to be identical in glycosyl composition and linkages to the extracellular polysaccharide (EPS) of this species indicating that the NPS and EPS for B. elkanii have identical structures (W.F. Dudman, Carbohydr. Res., 66 (1978) 9-23), →4)[O-Me-b-D-GlcAp-(1→3)]-a-L-Rhap-(1→3)-b-L-Rhap-(1→4)-b-L-Rhap-(1→. However, the structure of the NPS from B. japonicum proved to be quite different from that of its EPS. Methylation analysis of this NPS showed that it consists of 3-linked Gal, 3-linked Rha, 2,4-linked Rha, 4-linked Rha, and terminal 2-O-methyl GIcA in a 1:1:1:1:1 ratio. Stereochemical configurations of the glycosyl residues were determined by the preparation and analysis of trimethylsilyl (Me3Si) (-)-2-butyl glycosides. NMR spectroscopy (both 1H and 13C) showed that the Gal residue is a-linked, while all the other glycosyl residues are b-linked. Oligosaccharides produced by periodate oxidation-Smith degradation were purified, as were oligosaccharides produced by partial acid hydrolysis. Characterization of the Smith degradation products by methylation analysis, NMR spectroscopy, electrospray-mass spectrometry, and characterization of the partial acid hydrolysate oligosaccharides showed that the repeating oligosaccharide unit of the NFS has the structure, →3)-a-D-Galp-(1→3)-b-L-Rhap-(1→4)-[2-O-Me-b-GlcAp-(1→2)]b-L-Rhap-(1→4)-b-L-Rhap-(1→.
polysaccharide, Bradyrhizobium japonicum, Bradyrhizobium elkanii, Nodules, soybean
NCBI PubMed ID: 7780995Journal NLM ID: 0043535Publisher: Elsevier
Institutions: Complex Carbohydrate Center, University of Georgia, Athens, GA 30602-4712, USA, Department of Agronomy, The Ohio State University, Wooster, OH, USA
Methods: NMR-2D, ESI-MS, acid hydrolysis, HPAEC, Smith degradation
Found