Structural elucidation of the O-specific polysaccharide of the phenol-phase soluble lipopolysaccharide of Vibrio anguillarum

Structural reinvestigation of the core oligosaccharide of a mutant form of Aeromonas salmonicida lipopolysaccharide containing an O-4 phosphorylated and O-5 substituted Kdo reducing end group using electrospray QqTOF-MS/MS

The molecular structure of the mutant form of the lipopolysaccharide of Aeromonas salmonicida was determined to contain an O-4 phosphorylated and O-5 substituted Kdo reducing group, and is proposed as the following: [molecular structure: see text] It was established that during the cleavage of this LPS with 1% acetic acid, to release the core oligosaccharide from the Lipid A portion, we obtained a degraded core oligosaccharide which eliminated its phosphate group with extreme facility. The precise molecular structure of this dephosphorylated core was deduced by electrospray mass spectrometry and is proposed as the following:[molecular structure: see text] Low energy collision ESI-QqTOF-MS/MS analysis of the dephosphorylated core oligosaccharide confirmed the presence of the O-5 glycosylated 4,8- and 4,7-anhydro derivatives of the enolizable alpha-keto-acids. The CID tandem mass spectrometric analysis of the heterogeneous mixture of the permethylated core oligosaccharide established the unreported methylation reaction on the diastereomeric 4,8- and 4,7-anhydro alpha-keto-acids and the complete permethylation and addition reaction of the O-5 glycosylated open chain reducing end terminal D-arabino-3-en-2-ulonic acid. The stereo-specific fragmentation routes obtained during the tandem mass spectrometric analysis permitted the precise sequencing of this dephosphorylated rough core oligosaccharide of the mutant LPS of A. salmonicida.

Characterization of the O-4 phosphorylated and O-5 substituted Kdo reducing end group and sequencing of the core oligosaccharide of Aeromonas salmonicida ssp salmonicida lipopolysaccharide using tandem mass spectrometry

The molecular structure of the wild strain of the lipopolysaccharide core of Aeromonas salmonicida, ssp salmonicida has been sequenced using tandem mass spectrometry. The core oligosaccharide was determined to contain an O-4 phosphorylated and O-5 substituted Kdo reducing group, and its structure is proposed as the follows: [structure: see text] After the core oligosaccharide of LPS was released from the lipid A portion by conventional treatment with 1% acetic acid, we demonstrated the existence of a homogeneous mixture composed mainly of the native core oligosaccharide containing the Kdo with its O-4 phosphate group intact, and a degraded core oligosaccharide mixture, which eliminated the O-4 phosphate group with extreme facility. The precise molecular structure and glycone sequence of the homogeneous mixture of phosphorylated and dephosphorylated core oligosaccharides was determined by electrospray ionization (ESI) mass spectrometry and tandem mass spectrometric analysis. CID-MS/MS of the homogeneous mixture of permethylated core oligosaccharides afforded a series of diagnostic product ions which confirmed the established sequence of the glycones to be determined. Matrix-assisted laser desorption/ionization (MALDI) tandem mass spectrometry reconfirmed the molecular structure of the dephosphorylated homogeneous permethylated mixture of the core oligosaccharides containing the diastereomeric 4,8- and 4,7-anhydro-alpha-keto acids.

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-alpha-D-Hep p is L-glycero-alpha-D-manno-heptopyranose, D-alpha-D-Hepp is D-glycero-alpha-D-manno-heptopyranose, alpha-D-Fuc p4N is 4-amino-4,6-dideoxy-alpha-D-galactopyranose, alpha-NonA is 5-acetamidino-7-acetamido-3,5,7, 9-tetradeoxy-L-glycero-alpha-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. [formula: see text]

Structural studies of the lipopolysaccharide O-antigen and capsular polysaccharide of Vibrio anguillarum serotype O:2

Vibriosis caused by Vibrio anguillarum affects salmonid and marine fish species worldwide and is considered to be one of the most serious threats to the success of commercial fish farming. In the course of this study, it was found that V. anguillarum serotype O:2 strains produce an acidic capsular polysaccharide having the identical structure to that of the O-chain polysaccharide. One-dimensional and two-dimensional nuclear magnetic resonance techniques, together with partial hydrolysis and various specific modifications, were used to determine the structure of these polysaccharides. It is proposed that both O-chain and capsular polysaccharide of V. anguillarum serotype O:2 are composed of linear tetrasaccharide repeating units having the following structure, in which Glc2NAc3NAN represents 2-acetamido-3-amino-2,3-dideoxy-D-glucuronamide, Man2NAc3AmA is 3-acetamidino-2-acetamido-2,3-dideoxy-D-mannuronic acid. Am represents an acetamidino group, Gal(NAc)2A is 2,3-diacetamido-2,3-dideoxy-L-galacturonic acid, Bac(NAc)2 is 2,4-diacetamido-2,4,6-trideoxy-D-glucose (N,N'-diacetylbacillosamine) and Fo is formyl.

Structure of the O-polysaccharide chain of the lipopolysaccharide of Vibrio anguillarum V-123

The O-polysaccharide chain (PS-1), released by mild acidic treatment of the LPS of V. anguillarum V-123 (serogroup JO-2), a pathogenic bacterium of marine and estuarine fish, consists of 2-amino-2-deoxy-D-galacturonic acid, 2-amino-2,6-dideoxy-D-glucose (D-quinovosamine), and 4-amino-4,6-dideoxy-D-glucose (D-viosamine) N-acylated with 2,4-dihydroxy-3,3,4-trimethylpyroglutamic acid. Strong-acid hydrolysis of PS-1 afforded alpha-GalNA-(1----4)-alpha-GalNA-(1----3)-QuiN (A1) and alpha-GalNA-(1----3)-QuiN (A2), and hydrolysis with hydrogen fluoride gave N-acetylated A1 and 4-amino-4,6-dideoxy-D-glucose N-acylated by 2,4-dihydroxy-3,3,4-trimethylpyroglutamic acid. Mild treatment of PS-1 with alkali removed the N-formyl substituents and Smith degradation of the product gave alpha-QuiNAc-(1----3)-beta-VioNAcyl-(1----3)-alpha-GalNAc A-(1----3)-2,3,4- trihydroxybutanoic acid (S1) and S2 in which the carboxyl group of the GalNAcA residue was amidated. Thus, the repeating unit of the O-polysaccharide is----3)-alpha-GalNAcA(amino)-(1----4)-alpha-GalNFoA-(1----3 )- alpha-QuiNAc-(1----3)-beta-VioNAcyl-(1----in which the N-Acyl group is 2,4-dihydroxy-3,3,4-trimethylpyroglutamic acid and Fo is formyl.

Synthesis of glycoconjugates derived from various lipopolysaccharides of the Vibrionaceae family

Conjugation of simple ketoses (such as 3-deoxy-D-manno-2-octulosonic acid and N-acetylneuraminic acid) and of various O-specific polysaccharides (from Aeromonas hydrophila and Aeromonas salmonicida) to the bifunctional spacer 1,6-hexanediamine, was achieved by reductive amination. The saccharide--1-(6-amino)-hexane alkyamines obtained were converted into the corresponding isothiocyanate derivatives and coupled to the free epsilon-amino group of lysine residues of the protein carrier bovine serum albumin. In similar manner, the aldehyde group introduced by selective periodate oxidation into the partially O-deacylated lipopolysaccharide of Vibrio anguillarum was conjugated to 1,6-hexanediamine, converted into the corresponding isothiocyanate and covalently attached to bovine serum albumin.