Structures of two novel, serologically nonrelated core oligosaccharides of Yokenella regensburgei lipopolysaccharides differing only by a single hexose substitution

Immunochemical analysis of the Yokenella regensburgei lipopolysaccharides (LPS) indicated the presence of the core oligosaccharide-related immunotypes among the investigated strains. The structure of the core oligosaccharide segment of the Y. regensburgei LPS has been investigated using chemical methods, mass spectrometry, and H-1, C-13 NMR spectroscopy. It was concluded that the core oligosaccharides of the strains PCM 2476 and PCM 2477 are composed of an undecasaccharide. The combined data revealed two immunotypes of the core oligosaccharide recognized by antibodies against the whole bacterial cells. The structural differences between the core oligosaccharides are limited to the outermost terminal hexopyranose residue. In the core oligosaccharide of the strain PCM 2476, it was identified as alpha-D-Glcp and in that of the strain PCM 2477 as alpha-D-Galp. This subtle difference between the glycoforms of the LPS core appeared to be essential for formation of the epitopes recognized by the specific antibodies directed against the Y. regensburgei whole bacterial cells. The oligosaccharides are not substituted by phosphate groups. Instead, the carboxyl groups of Kdo and galacturonic acid residues present in the core provide the negative charges. The undecasaccharides represent a novel core type of bacterial LPS, which is characteristic for Y. regensburgei.