Structural studies of the Vibrio salmonicida lipopolysaccharide

The oligosaccharide part of the Vibrio salmonicida (strain NCMB 2262) lipopolysaccharide was isolated by mild acid hydrolysis followed by gel-permeation chromatography. The structure was established mainly by methylation analysis, mass spectrometry, and NMR spectroscopy. It is concluded that the oligosaccharide has the following structure, in which l-α-d-Hep p is l-glycero-α-d-manno-heptopyranose, d-α-d-Hepp is d-glycero-α-d-manno-heptopyranose, α-d-Fuc p4N is 4-amino-4,6-dideoxy-α-d-galactopyranose, α-NonA is 5-acetamidino-7-acetamido-3,5,7,9-tetradeoxy-l-glycero-α-d-galacto-nonulosonic acid, BA is (R)-3-hydroxybutanoyl, and PEA is phosphoethanolamine. The substitution pattern of the branching heptosyl residue was deduced from 1H NMR chemical shifts and conformations of the branching region, obtained by molecular modelling. The absolute configuration for NonA was determined by NMR spectroscopy from NOE correlations to the neighbouring sugar and 13C NMR chemical shift data. It could also be shown that assignments of nonulosonic acids with the d-glycero-l-galacto configuration, reported by previous investigators, are erroneous and should be changed to l-glycero-d-galacto. The oligosaccharide is assumed to be linked to the 5-position of a Kdo residue, phosphorylated in the 4-position as observed for other lipopolysaccharides from Vibrionaceae.