Capsular polysaccharide structure of a clinical isolate of Vibrio vulnificus strain BO62316 determined by heteronuclear NMR spectroscopy and high-performance anion-exchange chromatography.

Virulence of Vibrio vulnificus has been strongly associated with encapsulation. Capsular polysaccharide was purified from a virulent strain of Vibrio vulnificus BO62316, a clinical isolate, by dialysis, centrifugation, enzymatic digestion, and phenol-chloroform extraction. This polysaccharide shows partial reactivity with antibodies to the capsular polysaccharide of a related pathogenic strain of V. vulnificus (MO6-24) whose structure was recently reported. Nuclear magnetic resonance spectroscopic analysis of the purified polysaccharide from strain BO62316 showed that the polymer is composed of a repeating structure with four sugar residues per subunit: a residue of 2-acetamido-2,6-dideoxy-hexo pyranose in the alpha-gluco configuration (QuiNAc), a residue of 2-acetamido-2,6-dideoxy hexopyranose in the alpha-galacto configuration (FucNAc), a residue of 2-acetamido-2,6-dideoxy hexopyranose in the alpha-manno configuration (RhaNAc), and a residue of 2-acetamido-2,6-dideoxy hexouronate in the alpha-galacto configuration (GalNAcA). The complete carbohydrate structure of the capsular polysaccharide was determined by heteronuclear nuclear magnetic resonance spectroscopy and by high-performance anion-exchange chromatography. The 1H and 13C spectra were completely assigned, and vicinal coupling relationships were used to establish the stereochemistry of each sugar residue, its anomeric configuration, and the position of the glycosidic linkages. The complete structure is Formular; [see text]. This is the first reported occurrence of RhaNAc in a capsular polysaccharide.