Structure of the O-Antigen of the Main Lipopolysaccharide Isolated from Sinorhizobium fredii SMH12

• Published in: Biomacromolecules Vol. 9; no. 2; pp. 678 - 685
• Main Authors: Fernández de Córdoba, Francisco J, Rodríguez-Carvajal, Miguel A, Tejero-Mateo, Pilar, Corzo, Javier, Gil-Serrano, Antonio M
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01-02-2008
• Subjects: Applied sciences; Bacteriology; Biological and medical sciences; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Lipopolysaccharides - chemistry; Lipopolysaccharides - isolation & purification; Microbiology; Molecular Structure; Morphology, structure, chemical composition; Natural polymers; O Antigens - chemistry; O Antigens - isolation & purification; Physicochemistry of polymers; Polysaccharides, Bacterial - chemistry; Polysaccharides, Bacterial - isolation & purification; Sinorhizobium fredii; Starch and polysaccharides; O antigen; Microbial origin; Molecular structure; Lipopolysaccharide; Bacteria; Chemical isolation; Rhizobiaceae; Experimental study; Solvent extraction; Rhizobium fredii
• ISSN: 1525-7797; 1526-4602
• DOI: 10.1021/bm701011d

The lipopolysaccharide of Sinorhizobium fredii SMH12, a wide-range host bacterium isolated from nodulated soybean plants growing in Vietnam, has been studied. Isolation of lipopolysaccharide by the phenol−water method leads to a mixture of two polysaccharides; polyacrylamide gel electrophoresis indicates that both are possibly lipopolysaccharides. The structures of the O-antigen of the main lipopolysaccharide and its deacetylated form are determined by sugar and methylation analysis, partial hydrolysis, lithium degradation, ESI-MS/MS, and NMR studies. Here we show that the fast-growing S. fredii SMH12 produces a lipopolysaccharide whose O-antigen has a repeating unit consisting of the trisaccharide →4)-α-d-GalpA-(1→3)-2-O-Ac-α-l-Rhap-(1→3)-2-O-Ac-α-d-Manp-(1→. The position O-6 of the mannose residue in the repeating unit is unsubstituted, acetylated, or methylated in an approximate ratio 1:1:2. The tandem mass spectrometry studies rule out both an alternating and a random distribution of methyl groups and suggest the existence of zones in the polysaccharide rich in methyl groups interspersed with zones without methyl groups.