Structural analysis of the carbohydrate backbone of Vibrioparahaemolyticus O2 lipopolysaccharides

Abstract

A structural investigation has been carried out on the carbohydrate backbone of Vibrio parahaemolyticus O2 lipopolysaccharides (LPS) isolated by dephosphorylation, O-deacylation and N-deacylation. The carbohydrate backbone is a short-chain saccharide consisting of nine monosaccharide units i.e., 1 mol each of d-galactose (Gal), d-glucose (Glc), d-glucuronic acid (GlcA), l- glycero- d- manno-heptose ( l, d-Hep), d- glycero- d- manno-heptose ( d, d-Hep), 3-deoxy- d- manno-oct-2-ulosonic acid (Kdo), 5,7-diacetamido-3,5,7,9-tetradeoxy- d- glycero- d- galacto-non-2-ulosonic acid (NonlA), and 2 mol of 2-amino-2-deoxy- d-glucose ( d-glucosamine, GlcN). Based on the data obtained by NMR spectroscopy, fast-atom bombardment mass spectrometry (FABMS) and methylation analysis, a structure was elucidated for the carbohydrate backbone of O2 LPS. In the native O2 LPS, the 2-amino-2-deoxy- d-glucitol (GlcN-ol) at the reducing end of the nonasaccharide is present as GlcN. The lipid A backbone is a β- d-GlcN-(1→6)- d-GlcN disaccharide as is the case for many Gram-negative bacterial LPS. The lipid A proximal Kdo is substituted by the distal part of the carbohydrate chain at position-5. In the native O2 LPS, d-galacturonic acid, which is liberated from LPS by mild acid treatment or by dephosphorylation in hydrofluoric acid, is present although its binding position is unknown at present.