The linkage of phosphate groups and of 2-keto-3-deoxyoctonate to the lipid A component in a Salmonella minnesota lipopolysaccharide

Synthetic chemistry with friendships that unveiled the long-lasting mystery of lipid A

Endotoxin research in recent years at the molecular level has required chemically synthesized lipid A without contamination by other bioactive components. Total synthesis of Escherichia coli-type lipid A was achieved in the 1980s by the challenging spirits of the scientists at Osaka University, Japan. They clarified the role of lipid A in the immunological activities of endotoxin in collaboration with Japanese and German researchers, based on the friendships that existed between them. This article introduces the great contributions made by three generations of professors, Tetsuo Shiba, Shoichi Kusumoto, and Koichi Fukase, at the Laboratory of Natural Product Chemistry at Osaka University, to the study over four decades of endotoxin.

Lipopolysaccharides from Yersinia pestis. Studies on lipid A of lipopolysaccharides I and II

The chemical structure of the lipid A of lipopolysaccharide I and II from Yersinia pestis, strain EV 40, was studied. It consists of a (1 ---- 6), beta-linked D-glucosamine disaccharide which carries two phosphate groups; one phosphate is linked glycosidically with a glucosamine unit, the other one is linked to the non-reducing glucosamine. Various degradation methods combined with 31P nuclear magnetic resonance spectroscopy showed that the ester-bound phosphate group is linked to a 4-aminoarabinosyl residue and the glycosidically linked phosphate group is linked to a D-arabinofuranosyl residue in lipopolysaccharide II and to the phosphorylethanolamine in lipopolysaccharide I. The hydroxyl groups of the disaccharide are acylated by dodecanoic, hexadecenoic, 3-hydroxytetradecanoic and 3-dodecanoyloxytetradecanoic acids. The amino groups of the disaccharide carry 3-hydroxytetradecanoic and 3-dodecanoyloxytetradecanoic acids. In addition smaller amounts of 3-tetradecanoyloxyltetradecanoic and 3-hexadecanoyloxytetradecanoic acids are present in ester linkage.

Chemical synthesis and immunological activities of glycolipids structurally related to lipid A

Complete chemical syntheses of a number of monosaccharides derived from 2-deoxy-2-[(3R)-3-hydroxytetradecanamido]-D-glucopyranose and structurally related to the hydrophobic moiety (lipid A) of several bacterial endotoxins are described. Selected humoral (complement activation) and cellular (mitogenicity and induction of interleukin 1 production) in vitro activities of a lipid A preparation obtained from the Bordetella pertussis endotoxin were compared with those of ten of these monosaccharides and with those of previously synthesized, analogous disaccharides. Results show that each of these in vitro activities of the lipid A preparation can be efficiently induced by at least one of the monosaccharide derivatives.

Endotoxic properties of chemically synthesized lipid A part structures. Comparison of synthetic lipid A precursor and synthetic analogues with biosynthetic lipid A precursor and free lipid A

Synthetic lipid A part structures corresponding structurally to a biosynthetic lipid A disaccharide precursor have been analyzed for endotoxic activity in several systems in vivo and in vitro. It was found that a synthetic beta-1,6-linked D-glucosamine disaccharide, which carries four molar equivalents of (R)-3-hydroxytetradecanoyl residues in positions 2, 3, 2' and 3' and phosphoryl groups in positions 1 and 4' (preparation 406), exhibited lethal toxicity, B lymphocyte mitogenicity, the capacity to engender prostaglandin formation in macrophages and to induce endotoxic tolerance, as well as serological lipid A antigenicity. On a weight basis, preparation 406 was of comparable activity to lipid A precursor and bacterial free lipid A. Preparation 406, like lipid A precursor, lacked, however, the ability to induce the local Shwartzman phenomenon and both preparations were of moderate pyrogenicity. Two further synthetic analogues which contained only one phosphoryl group (preparation 404 at C-4', preparation 405 at C-1) showed comparable or diminished activity depending on the test system employed, except in the capacity to inactivate complement where they exhibited, in contrast to preparation 406, significant activity. The results show that the endotoxic principle of lipopolysaccharides, as postulated previously is embedded in the lipid A component. Our results also suggest initial conclusions on the structural requirements for the expression of endotoxin activities.

Chemical structure of the lipid A component of the lipopolysaccharide from a Proteus mirabilis Re-mutant

The chemical structure of the lipid A component from the lipopolysaccharide of a Proteus mirabilis Re-mutant (strain R45) was analysed. It consists of a beta(1-6)-linked D-glucosamine disaccharide which carries two phosphate groups, one being ester-linked to position 4' of the nonreducing glucosaminyl residue and the other being bound to the glycosidic hydroxyl group of the reducing glucosaminyl residue. The ester-bound phosphate group is quantitatively substituted by a 4-amino-4-deoxy-L-arabinopyranosyl residue, the glycosidic phosphoryl group appears to be unsubstituted. Two available hydroxyl groups of the disaccharadide (probably at positions 3 and 3') are acylated by approximately 1 mol each of (R)-3-tetradecanoyloxytetradecanoic and (R)-3-hydroxytetradecanoic acid/mol. The amino group of the nonreducing glucosaminyl residue carries (R)-3-tetradecanoyloxytetradecanoic and that of the reducing residue (R)-3-hydroxytetradecanoic acid. In addition smaller amounts of (R)-3-hexadecanoyloxytetradecanoic acid are present in amide linkage. The attachment site of the oligosaccharide portion to lipid A was also investigated. It was found that the hydroxyl group at position 6' of the nonreducing glucosaminyl residue carries 3-deoxy-D-manno-octulosonic acid. This indicates that the saccharide portion in this Proteus lipopolysaccharide is linked to lipid A via the primary hydroxyl group in position 6'.

Chemical structure and biological activities of lipid A's from various bacterial families

The endotoxic principle of lipopolysaccharides (LPS) is localized in their lipid A component. Biological effects of LPS on, for instance, body temperature, blood pressure, and blood picture, are also induced by free lipid A. In contrast to the great variability of the 0-specific chains, the chemical structure of lipid A is much more constant. It is common for Salmonella and similar for other genera of the Enterobacteriaceae. Recently, a number of lipid A's have been recognized that exhibited distinct structural features compared with Enterobacteriaceae. These lipid A's were found to be also distinct with regard to some of their biological properties.

Structural studies on the D-arabinose-containing lipid A from Rhodospirillum tenue 2761

Structural studies carried out on the isolated free lipid A of Rhodospirillum tenue 2761 revealed a new type of structure for this lipid. The lipid A backbone of 1',6-linked glucosamine disaccharide (central disaccharide) is substituted by three different sugar residues: the non-reducing end of the disaccharide by 4-amino-4-deoxy-L-arabinose 1-phosphate and its reducing end glycosidically by D-arabinofuranose 1-phosphate; further, the reducing glucosamine of the disaccharide is branched to a third glucosamine residue by a 1'',4-glycosidic linkage. The amino and the hydroxyl groups of the central disaccharide are acylated by 3-hydroxydecanoic acid (amide-linked) and palmitic and myristic acids (ester-linked). Neither amino nor hydroxyl groups of the three external sugar residues are acylated. The results suggest the following chemical structure for the lipid A of R. tenue 2761: (formula: see text).

A 31P-nuclear-magnetic-resonance study of the phosphate groups in lipopolysaccharide and lipid A from Salmonella

Untreated and partially deacylated lipopolysaccharides from various P- and P+ strains of Salmonella were studied with 31P nuclear magnetic resonance spectroscopy and by conventional analytical methods. The spectral signals were assigned to various phosphate groups in the lipid A moiety and in the oligosaccharide part. A signal at +2.3 ppm could be assigned to a phosphodiester linkage formed between 4-amino-4-deoxyl-L-arabinose linked via the glycosidic hydroxyl group to the 4'-phosphate group of the glucosamine disaccharide in the lipid A moiety. A strong pyrophosphate signal at +11 ppm in P- strains was identified as a pyrophosphoryl ethanolamine group at the glycosidic end of this glucosamine disaccharide unit. No evidence was found for phosphodiester or pyrophosphodiester bonds crosslinking lipopolysaccharide 'subunits'. A revised version of the lipid A structure of Salmonella is presented. By a combination of 31P nuclear magnetic resonance spectroscopy data and conventional analytical methods the extent to which the lipopolysaccharides are substituted by various phosphate groups on the lipid A and the oligosaccharide moiety could be estimated. It was thus shown that substantial heterogeneity, leading to several molecular species of lipopolysaccharides is caused by addition or omission of certain groups. Since changes in substitution were found to be dependent on the growth conditions, it is thought possible that the overall negative surface charge of Salmonella can be modified by addition or omission of neutralising amino groups from ethanolamine and/or 4-amino-4-deoxy-L-arabinose, and can thus be adapted to the environment.

Characterization of lipid A and polysaccharide moieties of the lipopolysaccharides from Vibrio cholerae

Lipid A and polysaccharide moieties obtained by mild acid hydrolysis of the lipopolysaccharides from Vibrio cholerae 569 B (Inaba) and Vibrio el-tor (Inaba) were characterized. Heterogeneity of lipid A fractions was indicated by t.l.c. and by gel filtration of the de-O-acylated products from mild alkaline methanolysis of the lipids. Presumably lipid A contains a glucosamine backbone, and the fatty acids are probably bound to the hydroxyl and amino groups of glucosamine residues. Approximately equal amounts of fatty acids C16:0, C18:1 and 3-hydroxylauric acid were involved in ester linkages, but 3-hydroxymyristic acid was the only amide-linked fatty acid. Sephadex chromatography of the polysaccharide moiety showed the presence of a high-molecular-weight heptose-free fraction and a low-molecular-weight heptose-containing fraction. Haemagglutination-inhibition assays of these fractions showed the heptose-free fraction to be an O-specific side-chain polysaccharide, whereas the heptose-containing fraction was the core polysaccharide region of the lipopolysaccharides. Identical results were obtained for both organisms.

Biochemical studies on the cell wall lipopolysaccharides (O-antigens) of Vibrio cholerae 569 B (Inaba) and El-tor (Inaba)

Lipopolysaccharides were isolated from the cell walls of Vibrio cholerae 569 B (Inaba) and El-tor (Inaba). Chemical analysis revealed the presence of glucose, fructose, mannose, heptose, rhamnose, ethanolamine, fatty acids and glucosamine. The lipopolysaccharides do not contain 2-keto-3-deoxyoctonate, the typical linking sugar of polysaccharide and lipid moieties of enterobacterial lipopolysaccharides. Galactose, a typical core polysaccharide component of many gram-negative bacteria was also absent from lipopolysaccharides of these organisms. By hydrolysis in 1% acetic acid, the lipopolysaccharides have been separated into a polysaccharide part (degraded polysaccharide) and a lipid part (lipid A). Components of degraded polysaccharide and lipid A moiety were identified and determined. The lipid A fractions contained fatty acids, phosphorus and glucosamine. All the neutral sugars detected in lipopolysaccharides were shown to be the constituents of its polysaccharide moiety. The fatty acid analysis of lipopolysaccharide and lipid A showed the presence of both hydroxy and non hydroxy acids. They were different from those of lipids extracted from cell walls before the extraction of lipopolysaccharides. 3-Hydroxylauric and 3-hydroxymyristic acids predominated in lipopolysaccharide and lipid A of Vibrio cholerae and El-tor (Inaba).

Isolation and analysis of the lipid A backbone. Lipid A structure of lipopolysaccharides from various bacterial groups

A degradation procedure of lipopolysaccharides was worked out which allows the isolation of the reduced backbone of lipid A in a total yield of between 20 and 30%. This procedure was applied to lipopolysaccharides of S forms (Salmonella minnesota, Shigella flexneri 5b, Escherichia coli 086, E. coli 0111, Xanthomonas sinensis, Rhodopseudomonas gelatinosa) and R mutants (Salmonella minnesota, Shigella flexneri, 5b, E. coli BB9 and E. coli EH 100). Chemical analysis, reaction with beta-N-acetyl-glucosaminidase and application of methylation analysis revealed that the lipid A backbone of all strains contains beta 1', 6-linked glucosamine disaccharides carrying two phosphate groups, one in glycosidic and one in ester linkage, a structure, identified previously in the Salmonella minnesota Re mutant.

Chemical structure and biological activity of endotoxins (lipopolysaccharides) and lipid A

Lipopolysaccharides (endotoxins) of gram-negative bacteria consist of two components with distinct physico-chemical character: a heteropolysaccharide and a covalently linked lipid, termed lipid A. Chemically, lipid A is made up of acylated glucosamine disaccharides, which are interlinked by pyrophosphate bridges. Lipid A represents the toxic center of lipopolysaccharides. In rabbits, lipid A also induces pyrogen tolerance as well as pyrogen cross-tolerance. Fever tolerance can be passively transferred with serum from rabbits immunized with lipid A. The protective power of lipid A antiserum, however, is only expressed in amimals which have been pretreated with lipid A or lipopolysaccharide, indicating that other than humoral factors, perhaps cellular, also participate in endotoxin tolerance. Lipid A antiserum also prevents the local Shwartzman reaction in rabbits. The possible potency of lipid A antiserum to prevent other endotoxin effects such as lethal shock is presently investigated.

Studies of lipid A fractions from the lipopolysaccharides of Pseudomonas aeruginosa and Pseudomonas alcaligenes

Lipid A fractions from Pseudomonas aeruginosa and Pseudomonas alcaligenes have similar compositions and structural features. By means of hydrazinolysis of the parent lipopolysaccharides and partial hydrolysis of the deacylation products, it was established that both lipids are derived from the beta-(1-->6)-linked disaccharide of glucosamine. Phosphorylated derivatives of the disaccharide from Ps. aeruginosa were also characterized. The lipids differ mainly in the absence of hexadecanoic acid and 2-hydroxydodecanoic acid from the lipid from Ps. alcaligenes. Evidence that in Ps. aeruginosa these acids are ester-linked to residues of 3-hydroxyalkanoic acids (including 3-hydroxydecanoic acid) was obtained. Heterogeneity of lipid A fractions was indicated by t.l.c., and by gel filtration of de-O-acylation products from mild alkaline methanolysis of the lipids.

Isolation of a mutant of Salmonella typhimurium dependent on D-arabinose-5-phosphate for growth and synthesis of 3-deoxy-D-mannoctulosonate (ketodeoxyoctonate)

A new type of auxotrophic mutant of Salmonella typhimurium has been isolated that is defective in the synthesis of the 3-deoxy-D-mannooctulosonate (ketodeoxyoctonate) region of the lipopolysaccharide and requires D-arabinose-5-phosphate for growth. Genetic and biochemical evidence indicated that the mutant defect was due to an altered ketodeoxyoctonate-8-phosphate synthetase with an apparent K(m) for D-arabinose-5-phosphate 35-fold higher than that of the parental enzyme. As a result of this enzymatic lesion, the mutant strain was dependent on exogenous D-arabinose-5-phosphate both for growth and for synthesis of a complete lipopolysaccharide.

Isolation and characterization of 2-keto-3-deoxyoctonate-lipid A from a heptose-deficient mutant of Escherichia coli

A heptose-deficient mutant of Escherichia coli has been isolated and from it a glycolipid, consisting of lipid A and 2-keto-3-deoxyoctonate (KDO), has been extracted with diisobutylketone-acetic acid-water. Based on beta-hydroxymyristic acid, the extractable glycolipid accounts for a major portion of the total lipid A in this mutant. A glycolipid, purified from the lipid extract by a combination of silicic acid and Sephadex LH-60 chromatography, contains glucosamine, phosphate, KDO, acetyl groups, and fatty acids in the following molar ratios: 1:2:2:1.7:5. These components account for over 80% of the lipid by weight. The fatty acid pattern of the glycolipid is typical of lipid A, the major component being beta-hydroxymyristic acid. The lipid also contains an amino sugar which appears to be 4-amino-4-deoxyarabinose. With the use of an ion-exchange paper chromatographic technique, gram-negative bacteria can be rapidly screened for the presence of this glycolipid. The mutant is believed to have a leaky defect in either biosynthesis of heptose or its incorporation into lipopolysaccharide. The lipopolysaccharide from the mutant contains only about a third as much heptose, glucose, and galactose as the parent CR34, a K-12 derivative. Chemical analysis and phage typing suggest that CR34 contains an incomplete core polysaccharide devoid of glucosamine.