Core region of Citrobacter lipopolysaccharide from strain PCM 1487. Structure elucidation by two-dimensional 1H-NMR spectroscopy at 500 MHz and methylation analysis/mass spectrometry

The sugar 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) as a characteristic component of bacterial endotoxin — a review of its biosynthesis, function, and placement in the lipopolysaccharide core

The sugar 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) is a characteristic component of bacterial lipopolysaccharide (LPS, endotoxin). It connects the carbohydrate part of LPS with C6 of glucosamine or 2,3-diaminoglucose of lipid A by acid-labile α-ketosidic linkage. The number of Kdo units present in LPS, the way they are connected, and the occurrence of other substituents (P, PEtn, PPEtn, Gal, or β-l-Ara4N) account for structural diversity of the inner core region of endotoxin. In a majority of cases, Kdo is crucial to the viability and growth of bacterial cells. In this paper, the biosynthesis of Kdo and the mechanism of its incorporation into the LPS structure, as well as the location of this unique component in the endotoxin core structures, have been described.

Structural and serological studies on a new 4-deoxy-d-arabino-hexose-containing O-specific polysaccharide from the lipopolysaccharide of Citrobacter braakii PCM 1531 (serogroup O6)

The O-specific polysaccharide of Citrobacter braakii PCM 1531 (serogroup O6) was isolated by mild acid hydrolysis of the lipopolysaccharide (LPS) and found to contain d-fucose, l-rhamnose, 4-deoxy-d-arabino-hexose and O-acetyl groups in molar ratios 2 : 1 : 1 : 1. On the basis of methylation analysis and 1H and 13C NMR spectroscopy data, the structure of the branched tetrasaccharide repeating unit of the O-specific polysaccharide was established. Using various serological assays, it was demonstrated that the LPS of strain PCM 1531 is not related serologically to other known 4-deoxy-d-arabino-hexose-containing LPS from Citrobacter PCM 1487 (serogroup O5) or C. youngae PCM 1488 (serogroup O36). Two other strains of Citrobacter, PCM 1504 and PCM 1505, which, together with strain PCM 1531, have been classified in serogroup O6, were shown to be serologically distinct from strain PCM 1531 and should be reclassified into another serogroup.

Serological characterization of anti-endotoxin serum directed against the conjugate of oligosaccharide core of Escherichia coli type R4 with tetanus toxoid

The covalent conjugate of oligosaccharide core of Escherichia coli type R4 with tetanus toxoid was prepared using reaction of reductive amination. The neoglycoconjugate was a good immunogen in rabbits yielding a high level of anti-lipopolysaccharide (LPS) antibodies of the IgG class. It was found that antiserum was able to react with the smooth LPS molecules of identical (R4) or related (R1) core type. The reactions were shown in the enzyme-linked immunosorbent assay and the immunoblotting test. Flow cytometry showed that anti-core antibodies reacted with LPS present on intact, live, smooth bacteria labelling more than 90% of cells. The anti-OS R4-TT serum used for in vitro studies showed high endotoxin neutralization activity. The serum inhibited endotoxin-induced tumor necrosis factor alpha and nitric oxide synthesis by the J-774A.1 cell line and attenuated pulmonary retention of YAC-1 cells.

Structure of the O-specific polysaccharide isolated from the lipopolysaccharide of Citrobacter gillenii serotype O12a, 12b strain PCM 1544

A neutral O-specific polysaccharide was isolated from the lipopolysaccharide of Citrobacter gillenii strain PCM 1544, representing serotype O12a,12b. The polysaccharide was studied by sugar and methylation analyses and Smith degradation along with 1H and 13C NMR spectroscopy, including a ROESY experiment. The following structure of the tetrasaccharide repeating unit was established, in which substitution with terminal GlcNAc is approximately 60%. [structure: see text]

Structure of the lipopolysaccharide core region of Hafnia alvei strains 1185 and 1204

Sugar and methylation analyses using gas chromatography/mass spectrometry and NMR spectroscopy proved that the core oligosaccharides of Hafnia alvei strains 1185 and 1204 have the following formula: carbohydrate sequence [see text] where Kdo = 3-deoxy-oct-2-ulosonic acid and P-PEtN = diphosphorylethanolamine. The structure shown above is a slight modification of the typical core region of H. alvei lipopolysaccharides. The difference refers to one sugar only: terminal galactose is present in the core of strains of 1185 and 1204, while terminal glucose in the typical core.

Non-typical lipopolysaccharide core regions of some Hafnia alvei strains: structural and serological studies

The lipopolysaccharides of Hafnia alvei strains 23, 1222 and 39 were found to have non-typical core region. On the basis of sugar and methylation analyses, 1H-nuclear magnetic resonance spectra and matrix-assisted laser-desorption ionization-time of flight mass spectrometry, it was concluded that the core oligosaccharide of strains 23 and 1222 has the same structure as Escherichia coli R4 core region, and the core oligosaccharide of strain 39 has the structure of Salmonella Ra core. Using the serological methods (passive hemagglutination, enzyme-linked immunosorbent assay and immunoblotting) and the anti-conjugate sera directed against E. coli R4 and Salmonella Ra core oligosaccharides we have confirmed the structural results presented above.

The occurrence of glycine in bacterial lipopolysaccharides

The aminoacyl analysis of endotoxic lipopolysaccharides (LPS) isolated from several bacteria revealed essential amounts of glycine, among the inherent LPS components. Significant amounts of the glycine was detected in lipopolysaccharides isolated from over 30 strains of Escherichia, Salmonella, Hafnia, Citrobacter and Shigella species. Glycine as a single amino acid was found only in a core part of LPS. Molar ratio of glycine in core oligosaccharide fraction ranged from 0.2 to 0.6 per 3 heptoses. The oligosaccharide enriched in glycine was isolated using the HPLC. The amino acid appeared to be terminally located in a core oligosaccharide. The labelling of the lipopolysaccharide cores was achieved when the bacteria were cultivated in the presence of radioactive [14C]glycine. The labelled core oligosaccharide released the radioactivity during treatment with mild alkali or acid (0.1 M NaOH or HCl, 100 degrees C, 4 h). The radioactivity in SDS-polyacrylamide gel electrophoresis migrated exclusively with LPS. The results indicate that amino acid is an integral constituent of core oligosaccharide in lipopolysaccharide.

Lipopolysaccharide core region of Hafnia alvei: structure elucidation using chemical methods, gas chromatography-mass spectrometry, and NMR spectroscopy

Sugar and methylation analysis with the use of gas chromatography-mass spectrometry and 1H NMR spectroscopy proved that the core oligosaccharides isolated from lipopolysaccharides of eight Hafnia alvei strains have the identical hexasaccharide skeleton. However, 1H, 31P heterocorrelated spectra showed that the phosphorylation pattern is not the same. The branched heptose for the ATCC 13337, 1187, 2, 1191, 1196, 1220, and 481L strains is phosphorylated as in the following formula, where P = -O-P(O)(O-)2 and P-PEtN = [-O-P(O)(O-)]2-O(CH2)2NH3+ [formula: see text] A different phosphorylation pattern was found for the 1211 strain, where the branched heptose residue is 6-substituted by a monophosphorylethanolamine group, ...-->3(-->7)(PEtN-->6)-alpha-LD-Hepp-(1-->3)..., where PEtN = -O-P(O)(O-)-O(CH2)2NH3+.

A broadly cross-protective monoclonal antibody binding to Escherichia coli and Salmonella lipopolysaccharides

During the last decade, episodes of sepsis have increased and Escherichia coli has remained the most frequent clinical isolate. Lipopolysaccharides (LPS; endotoxin) are the major toxic and antigenic components of gram-negative bacteria and qualify as targets for therapeutic interventions. Molecules that neutralize the toxic effects of LPS are actively investigated. In this paper, we describe a murine monoclonal antibody (MAb; WN1 222-5), broadly cross-reactive and cross-protective for smooth (S)-form and rough (R)-form LPS. As shown in enzyme-linked immunosorbent assay and the passive hemolysis assay, WN1 222-5 binds to the five known E. coli core chemotypes, to Salmonella core, and to S-form LPS having these core structures. In immunoblots, it is shown to react with both the nonsubstituted core LPS and with LPS carrying O-side chains, indicating the exposure of the epitope in both S-form and R-form LPS. This MAb of the immunoglobulin G2a class is not lipid A reactive but binds to E. coli J5, an RcP+ mutant which carries an inner core structure common to many members of the family Enterobacteriaceae. Phosphate groups present in the inner core contribute to the epitope but are not essential for the binding of WN1 222-5 to complete core LPS. Cross-reactivity for clinical bacterial isolates is broad. WN1 222-5 binds to all E. coli clinical isolates tested so far (79 blood isolates, 80 urinary isolates, and 21 fecal isolates) and to some Citrobacter, Enterobacter, and Klebsiella isolates. This pattern of reactivity indicates that its binding epitope is widespread among members of the Enterobacteriaceae. WN1 222-5 exhibits biologically relevant activities. In vitro, it inhibits the Limulus amoebocyte lysate assay activity of S-form and R-form LPS in a dose-dependent manner and it neutralizes the LPS-induced release of clinically relevant monokines (interleukin 6 and tumor necrosis factor). In vivo, WN1 222-5 blocks endotoxin-induced pyrogenicity in rabbits and lethality in galactosamine-sensitized mice. The discovery of WN1 222-5 settles the long-lasting controversy over the existence of anti-core LPS MAbs with both cross-reactive and cross-protective activity, opening new possibilities for the immunotherapy of sepsis caused by gram-negative bacteria.

The structure of the O-specific polysaccharide from Hafnia alvei strain 38 lipopolysaccharide

The O-specific polysaccharide of the lipopolysaccharide from H. alvei strain 38 has been established by NMR spectroscopy (13C and 1H) and methylation analysis to have the repeating unit-->4)-beta-D-ManpNAc-(1-->4)-alpha-D-GlcpNAc(1-->.

Immunochemical characterization of Citrobacter strain PCM 1487 O-specific polysaccharide- and core oligosaccharide-protein conjugates

O-specific-polysaccharide and core oligosaccharide were isolated from Citrobacter strain PCM 1487 lipopolysaccharide and purified. The polysaccharide was selectively devoid of 4-deoxy-D-arabinohexose residues. Covalent conjugates of the modified O-specific polysaccharide and of the core oligosaccharide with tetanus toxoid were prepared. Immunochemical characterization of these conjugates proved that they are strong immunogens. Using monospecific rabbit antisera raised against the conjugates, the antigenic relationships between lipopolysaccharides of various strains of Citrobacter, Shigella sonnei, and Shigella flexneri were studied by quantitative microprecipitin and quantitative microprecipitin inhibition and immunoblotting tests.

Core region of Citrobacter O23 lipopolysaccharide. Structure elucidation by chemical methods, gas chromatography/mass spectrometry and NMR spectroscopy at 500 MHz

A novel enterobacterial core region in Citrobacter O23 lipopolysaccharide is described. Its structure was determined by methylation analysis/mass spectrometry, chemical degradation and one- and two-dimensional 1H-NMR spectroscopy: [formula; see text] where PPEtN stands for diphosphorylethanolamine, and dOclA for 3-deoxy-D-manno-octulosonic acid.

G.l.c.-m.s. of partially methylated and acetylated derivatives of L-glycero-D-manno- and D-glycero-D-manno-heptopyranoses and -heptitols

Methylated or acetylated heptopyranose derivatives were prepared variously from L-glycero-D-manno- and D-glycero-D-manno-heptopyranose, O-L- glycero-alpha-D-manno-heptopyranosyl-(1----3)-L-glycero-D-manno- heptopyranose, O-L-glycero-alpha-D-manno-heptopyranosyl-(1----7)-L-glycero- D-manno-heptopyranose, and O-L-glycero-alpha-D-manno- heptopyranosyl-(1----7)-O-L-glycero-alpha-D-manno- heptopyranosyl-(1----3)-L-glycero-D-manno- heptopyranose, which are structural elements of the heptose region of enterobacterial lipopolysaccharides. Each derivative was investigated by g.l.c. and g.l.c.-m.s., and the retention times and fragmentation patterns were used to identify partial structures of the heptose region of the core oligosaccharide of bacterial LPS.

O-specific polysaccharides of Hafnia alvei lipopolysaccharides isolated from two serologically related strains: ATCC 13337 and 1187. A serological and structural study using chemical methods, gas chromatography/mass spectrometry and NMR spectroscopy at 500 MHz

The O-specific polysaccharides of Hafnia alvei ATCC 13337 standard strain and 1187 strain have been isolated and characterized. By means of 1H-NMR spectroscopy, methylation analysis and periodate oxidation, the repeating unit of the polysaccharides could be allocated the respective structures. (formula; see text) where Acyl = D-3-hydroxybutyryl, and 3-O-acetylation was to about 66%. The structural similarity of the polysaccharides was confirmed in the serological study; their epitopes were determined and the importance of various structural elements for the serological specificity was discussed.

The core region of Proteus mirabilis R110/1959 lipopolysaccharide

The complete core structure present in the lipopolysaccharide of the R mutant R110/1959 from Proteus mirabilis (Proteus type II core) was investigated using methylation analysis and a number of degradation methods such as Smith degradation and beta-elimination. These studies combined with earlier work on a Rc-type mutant of P. mirabilis O28 (R4/O28) which shares the same inner core region, allowed formulation of the complete core structure of the Proteus type II core as shown in Scheme 1. (formula; see text) A characteristic feature of the Proteus core of type II is the presence of two units of D-galacturonic acid (DGalA); one in terminal, the other one in a chain-linked position. In addition, the presence of the two isomers of glycero-D-manno-heptose (LDHep and DDHep) and the lack of galactose are conspicuous. DDHep occupies a terminal position in the external core region, whereas the three units of LDHep in addition to dOclA form, as in other enterobacterial core types, the internal core region. The taxonomic significance of the presence of DGalA in the Proteus type II core, but also in all R cores of other Proteeae investigated so far, will be discussed.