Nature and location of amide-bound (R)-3-acyloxyacyl groups in lipid A of lipopolysaccharides from various gram-negative bacteria

Structure of the O-Antigen and the Lipid A from the Lipopolysaccharide of Fusobacterium nucleatum ATCC 51191

Fusobacterium nucleatum is a common member of the oral microbiota. However, this symbiont has been found to play an active role in disease development. As a Gram-negative bacterium, F. nucleatum has a protective outer membrane layer whose external leaflet is mainly composed of lipopolysaccharides (LPSs). LPSs play a crucial role in the interaction between bacteria and the host immune system. Here, we characterised the structure of the O-antigen and lipid A from F. nucleatum ssp. animalis ATCC 51191 by using a combination of GC-MS, MALDI and NMR techniques. The results revealed a novel repeat of the O-antigen structure of the LPS, [→4)-β-d-GlcpNAcA-(1→4)-β-d-GlcpNAc3NAlaA-(1→3)-α-d-FucpNAc4NR-(1→], (R=acetylated 60 %), and a bis-phosphorylated hexa-acylated lipid A moiety. Taken together these data showed that F. nucleatum ATCC 51191 has a distinct LPS which might differentially influence recognition by immune cells.

Bacterial medium-chain 3-hydroxy fatty acid metabolites trigger immunity in Arabidopsis plants

Plants and animals respond to the microbial communities around them, whether in antagonistic or mutualistic ways. Some of these interactions are mediated by lipopolysaccharide—a large, complex, and irregular molecule on the surface of most Gram-negative bacteria. Studying the small mustard plant Arabidopsis , Kutschera et al. identified a 3-hydroxydecanoyl chain as the structural element sensed by the plant's lectin receptor kinase. Indeed, synthetic 3-hydroxydecanoic acid alone was sufficient to produce a response. A small microbial metabolite may thus suffice to trigger immune responses.

Science , this issue p. 178

Activity in the Limulus amebocyte lysate assay and induction of tumor necrosis factor-α by diverse Helicobacter pylori lipopolysaccharide preparations

Different chemically characterized H. pylori LPS preparations, such as smooth (S)- and rough (R)-form LPS, a completely dephosphorylated R-LPS, and three lipid A chemotypes, from the S- and R- form LPS (S- and R-lipid A) as well as a dephosphorylated derivative of S-lipid A, respectively, were evaluated for expression of potency in a quantitative chromogenic Limulus amebocyte (CLAL) lysate assay and for release of tumor necrosis factor-α (TNF-α) from activated human mononuclear cells. As far as the CLAL activity is concerned, no statistically significant differences could be observed between S- and R-LPS. Dephosphorylation of both R-LPS and S-lipid A caused a significant decrease of CLAL activity. In general terms, all the lipid A chemotypes were significantly less effective than the native LPS molecule and, in particular, R-lipid A expressed the lowest Limulus activity of all preparations. With regard to TNF-α release, R-LPS was the most potent inducer of this cytokine, even though its dephosphorylation reduced activity. In conclusion, the results show that phosphate groups influence both CLAL activity and, to a lesser extent, TNF-α release, and that the core oligosaccharide synergically cooperates with lipid A for the production of this cytokine, being, however, not essential for the expression of CLAL activity. Furthermore, preliminary structural data show that H. pylori D-glucosamine disaccharide backbone, besides being underphosphorylated at position 4', is also characterized by a reduced number of acyloxyacyl residues in comparison with enterobacterial lipid A. These findings, besides providing useful information on the structure-bioactivity relationships within H. pylori LPS, further support the evidence that this non-invasive, slow bacterium possesses the ability to modulate the local cellular immune response via LPS and related inflammatory cytokines.

Structural analysis of the lipid A derived from the lipopolysaccharide of Brucella abortus

Lipopolysaccharide (LPS) of Brucella abortus strain 45/20 was purified using a novel method. Monophosphoryl lipid A (MPLA) was prepared from this LPS, methylated, and purified by high performance liquid chromatography. Chemical, mass spectral, and nuclear magnetic resonance analyses showed that MPLA consists of heptaacyl lipid As with molecular weights of 2095, 2123, 2151 and 2179. They contained the β-1,6-linked 2,3-diamino-2,3,-dideoxy-glucose disaccharide backbone and a phosphate group at the 4' position. Bisphosphoryl lipid A was also prepared and completely O-deacylated. It contained an additional phosphate group, and either 2 hydroxyhexadecanoic, 1 hydroxytetradecanoic, 1 hydroxydodecanoic acids or 2 hydroxyhexadecanoic and 2 hydroxydodecanoic acids, all in amide linkage. The predominant ester-linked fatty acyl group in acyloxyacyl linkage was hexadecanoate.

The purified LPS, bisphosphoryl lipid A, and MPLA from B. abortus showed about 14%, 3% and 1%, respectively, of the B cell mitogen activity of ReLPS from Escherichia coli at 1.0 μg/ml.

The chemical composition of endotoxin isolated from intestinal strain of Desulfovibrio desulfuricans

Desulfovibrio desulfuricans anaerobes are constituents of human alimentary tract microflora. There are suggestions that they take part in the pathogenesis of periodontitis and some gastrointestinal inflammatory disorders, such as ulcerative colitis or Crohn's disease. Endotoxin is one of Gram-negative bacteria cellular components that influence these microorganisms pathogenicity. Endotoxin is a lipid-polisaccharide heteropolymer consisting of three elements: lipid A, core oligosaccharide, and O-specific polysaccharide, also called antigen-O. The biological activity of lipopolysaccharide (LPS) is determined by its structure. In this study, we show that rhamnose, fucose, mannose, glucose, galactose, heptose, and 2-keto-3-deoxyoctulosonic acid (Kdo) are constituents of D. desulfuricans endotoxin oligosaccharide core and O-antigen. Lipid A of these bacteria LPS is composed of glucosamine disaccharide substituted by 3-acyloxyacyl residues: ester-bound 3-(dodecanoyloxy)tetradecanoic, 3-(hexadecanoyloxy)tetradecanoic acid, and amide-bound 3-(tetradecanoyloxy)tetradecanoic acid.

Chemical composition of Desulfovibrio desulfuricans lipid A

Lipopolysaccharides also called endotoxins are an integral component of the outer membrane of Gram-negative bacteria. When released from the bacterial surface, they interact with a host immune system, triggering excessive inflammatory response. Lipid A is the biologically most active part of endotoxin, and its activity is modulated by the quantity, quality and arrangement of its fatty acids. Desulfovibrio desulfuricans is sulfate-reducing, Gram-negative bacterium that is supposed to be opportunistic pathogens of humans and animals. In the present study, chemical composition of lipid A from various strains of D. desulfuricans was analyzed by gas chromatography/mass spectrometry. It was found that the fatty acid component of the lipid A contains dodecanoic, tetradecanoic, 3-hydroxytetradecanoic and hexadecanoic acids, and its carbohydrate core is composed of glucosamine. The analysis of 3-acyloxyacyl residue of the lipid A revealed the presence of amide-bound 3-(dodecanoyloxy)tetradecanoic and 3-(hexadecanoyloxy)tetradecanoic acids and ester-bound 3-(tetradecanoyloxy)tetradecanoic acid. It was concluded that both fatty acid and 3-acyloxyacyl residue profiles of the lipid A from the studied bacteria were similar to those of E. coli and S.enterica.

Sphingolipid-mediated restoration of Mitf expression and repigmentation in vivo in a mouse model of hair graying

Recent advances in the identification and characterisation of stem cell populations has led to substantial interest in understanding the precise triggers that would operate to induce activation of quiescent stem cells. Melanocyte stem cells (MSCs) reside in the bulge region of the hair follicles and are characterised by reduced expression of the microphthalmia-associated transcription factor (Mitf) and its target genes implicated in differentiation. Vitiligo is characterised by progressive destruction of differentiated melanocytes. However, therapies using UV irradiation therapy can induce a degree of repigmentation, suggesting that MSCs may be activated. As Mitf is implicated in control of proliferation, we have explored the possibility that inducing Mitf expression via lipid-mediated activation of the p38 stress-signalling pathway may represent a re-pigmentation strategy. Here we have isolated from placental extract a C18:0 sphingolipid able to induce Mitf and tyrosinase expression via activation of the p38 stress-signalling pathway. Strikingly, in age-onset gray-haired C57BL/6J mice that exhibit decaying Mitf expression, topical application of placental sphingolipid leads to increased Mitf in follicular melanocytes and fresh dense black hair growth. The results raise the possibility that lipid-mediated activation of the p38 pathway may represent a novel approach to an effective vitiligo therapy.

Detailed characterization of the lipid A fraction from the nonpathogen Acinetobacter radioresistens strain S13

The genus Acinetobacter is composed of ubiquitous, generally nonpathogen environmental bacteria. Interest concerning these microorganisms has increased during the last 30 years, because some strains, belonging to the so-called A. baumannii-A. calcoaceticus complex, have been implicated in some severe pathological states in debilitated and hospitalized patients. The involvement of lipopolysaccharides (LPSs) as virulence factors in infections by Acinetobacter has been proven, and ongoing studies are aimed toward the complete serological characterization of the O-polysaccharides from LPSs isolated in clinical samples. Conversely, no characterization of the lipid A fraction from Acinetobacter strains has been performed. Here, the detailed structure of the lipid A fraction from A. radioresistens S13 is reported for the first time. A. radioresistens strains have never been isolated in cases of infectious disease. Nevertheless, it is known that the lipid A structure, with minor variations, is highly conserved across the genus; thus, structural details acquired from studies of this nonpathogen strain represent a useful basis for further studies of pathogen species.

Fatty acid and hydroxy acid adaptation in three gram-negative hydrocarbon-degrading bacteria in relation to carbon source

The lipids of three gram-negative bacteria, Acinetobacter calcoaceticus, Marinobacter aquaeolei, and Pseudomonas oleovorans grown on mineral media supplemented with ammonium acetate or hydrocarbons, were isolated, purified, and their structures determined. Three pools of lipids were isolated according to a sequential procedure: unbound lipids extracted with organic solvents, comprising metabolic lipids and the main part of membrane lipids, OH--labile lipids (mainly ester-bound in the lipopolysaccharides, LPS) and H+-labile lipids (mainly amide-bound in the LPS). Unsaturated FA composition gave evidence for an aerobic desaturation pathway for the synthesis of these acids in A. calcoaceticus and M. aquaeolei, a nonclassic route in gram-negative bacteria. Surprisingly, both aerobic and anaerobic pathways are operating in the studied strain of P. oleovorans. The increase of the proportion of saturated FA observed for the strain of P. oleovorans grown on light hydrocarbons would increase the temperature transition of the lipids for maintaining the inner membrane fluidity. An opposite phenomenon occurs in A. calcoaceticus and M. aquaeolei grown on solid or highly viscous C19 hydrocarbons. The increases of FA < C18 when the bacteria were grown on n-nonadecane, or of iso-FA in cultures on isononadecane would decrease the transition temperature of the lipids, to maintain the fluidity of the inner membranes. Moreover, P. oleovorans grown on hydrocarbons greatly decreases the proportion of P-hydroxy acids of LPS, thus likely maintaining the physical properties of the outer membrane. By contrast, no dramatic change in hydroxy acid composition occurred in the other two bacteria.

Intrinsic conformation of lipid A is responsible for agonistic and antagonistic activity

Lipopolysaccharides (LPS, endotoxin) represent a major virulence factor of Gram-negative bacteria, which can cause septic shock in mammals, including man. The lipid anchor of LPS to the bacterial outer membrane, lipid A, exhibits a peculiar chemical structure, harbours the 'endotoxic principle' of LPS and is also responsible for the expression of pathophysiological effects. Chemically modified lipid A can be endotoxically inactive, but may express strong antagonistic activity against endotoxically active LPS. By applying orientation measurements with attenuated total reflectance (ATR) infrared spectroscopy on hydrated lipid A samples, we show here that these different biological activities are directly correlated to the intrinsic conformation of lipid A. Bisphosphoryl-hexaacyl lipid A molecules with an asymmetric (4/2) distribution of the acyl chains linked to the diglucosamine backbone have a large tilt angle (> 45 degrees ) of the diglucosamine backbone with respect to the membrane surface, a conical molecular shape (larger cross-section of the hydrophobic than the hydrophilic moiety), and are endotoxically highly active. Monophosphoryl hexaacyl lipid A has a smaller tilt angle, and the conical shape is less expressed in favour of a more cylindrical shape. This correlates with decreasing endotoxic activity. Penta- and tetraacyl lipid A or hexaacyl lipid A with a symmetric acyl chain distribution (3/3) have a small tilt angle (< 25 degrees ) and a cylindrical shape and are endotoxically inactive, but may be antagonistic.

The potential of various lipopolysaccharides to release IL-8 and G-CSF

Lipopolysaccharide (LPS) derived from Pseudomonas aeruginosa is less cytotoxic than that from Escherichia coli. But P. aeruginosa induces a prominent sustained lung inflammation as in cystic fibrosis and diffuse panbronchiolotis. The present study examined the potential for several LPSs obtained from E. coli and P. aeruginosa to release neutrophil chemotactic activity (NCA) from lung cells. LPSs differently stimulated A549 cells, BEAS-2B cells, and lung fibroblasts to release NCA [P. aeruginosa > E. coli 0127:B8 (Difco) > E. coli 055:B5 (Sigma) > E. coli 026:B6 (Sigma)]. E. coli 0127:B8 (Sigma) and 0111:B4 (Sigma) did not stimulate these cells. NCA was chemotactic by checkerboard analysis. Molecular-sieve column chromatography revealed three chemotactic peaks. The release of NCA was inhibited by cycloheximide and lipoxygenase inhibitors. Experiments with blocking antibodies suggested that much of the NCA was secondary to the release of interleukin (IL)-8 and granulocyte colony-stimulating factor (G-CSF). Thus we examined the concentrations of IL-8 and G-CSF and found that the potency of the various LPSs to stimulate NCA closely paralleled the potency in releasing IL-8 and G-CSF. But a difference among LPSs to stimulate A549 cells was observed. Finally, the release of IL-6 showed similar results. These data suggest that P. aeruginosa LPS may stimulate lung cells to release more NCA than E. coli LPSs, leading to sustained lung inflammation.

Structural characterization of the lipid A component of Helicobacter pylori rough- and smooth-form lipopolysaccharides

The chemical structure of free lipid A isolated from rough- and smooth-form lipopolysaccharides (R-LPS and S-LPS, respectively) of the human gastroduodenal pathogen Helicobacter pylori was elucidated by compositional and degradative analysis, nuclear magnetic resonance spectroscopy, and mass spectrometry. The predominant molecular species in both lipid A components are identical and tetraacylated, but a second molecular species which is hexaacylated is also present in lipid A from S-LPS. Despite differences in substitution by acyl chains, the hydrophilic backbone of the molecules consisted of beta(1,6)-linked D-glucosamine (GlcN) disaccharide 1-phosphate. Because of microheterogeneity, nonstoichiometric amounts of ethanolamine-phosphate were also linked to the glycosidic hydroxyl group. In S-LPS, but not in R-LPS, the hydroxyl group at position 4' was partially substituted by another phosphate group. Considerable variation in the distribution of fatty acids on the lipid A backbone was revealed by laser desorption mass spectrometry. In tetraacyl lipid A, the amino group of the reducing GlcN carried (R)-3-hydroxyoctadecanoic acid (position 2), that of the nonreducing GlcN carried (R)-3-(octadecanoyloxy)octadecanoic acid (position 2'), and ester-bound (R)-3-hydroxyhexadecanoic acid was attached at position 3. Hexaacyl lipid A had a similar substitution by fatty acids, but in addition, ester-bound (R)-3-(dodecanoyloxy)hexadecanoic acid or (R)-3(tetradecanoyloxy)hexadecanoic acid was attached at position 3'. The predominant absence of ester-bound 4'-phosphate and the presence of tetraacyl lipid A with fatty acids of 16 to 18 carbons in length differentiate H. pylori lipid A from that of other bacterial species and help explain the low endotoxic and biological activities of H. pylori LPS.

Fluorescence resonance energy transfer analysis of lipopolysaccharide in detergent micelles

Bacterial endotoxins or lipopolysaccharides (LPS), cell wall components of gram-negative bacteria, are involved in septic shock. LPS consists of a lipid A tail attached to core and O-antigen polysaccharides, but little is known about the supramolecular structure of LPS in blood. We have developed an approach to locate donor and acceptor probes in sulfobetaine palmitate detergent micelles using steady-state and time-resolved fluorescence resonance energy transfer. C18-fluorescein and several LPS species of varying molecular weight labeled with fluorescein isothiocyanate (FITC-LPS) were the donor probes. Acceptor probes were 1,1-dilinoleyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate (Fast C18-Dil, Ro approximately 68 A), and octadecyl B rhodamine chloride (C18-Rhd, Ro approximately 58 A). With either acceptor, the transfer was of similar high efficiency when FITC-LPS Salmonella minnesota Re 595 (2,500 mol wt, lacking both core and O-antigen) or C18-fluorescein were the fluorescent donor probes. Thus, the donor FITC-LPS with short polysaccharide chain S. minnesota Re 595 and the control donor C18-fluorescein appear to be close to the micelle surface. The transfer efficiency decreased as the molecular weight of the LPS increased. Separation distances between the longest FITC-LPS, S. minnesota (20,000 mol wt, with a long O-antigen), and the micelle were estimated to be 1.5 Ro or more (approximately 100 A), consistent with an extended conformation for the longer O-antigen polysaccharide chain in the detergent.

Molecular structures that influence the immunomodulatory properties of the lipid A and inner core region oligosaccharides of bacterial lipopolysaccharides

The relationship between chain length as well as the position of fatty acyl groups to the ability of lipid A to abolish the expression of suppressor T-cell (Ts) activity was examined. Fatty acyl chain lengths of C12 to C14, as in the lipid A of Escherichia coli and Salmonella minnesota, appear to be optimal for this bioactivity, since lipid A preparations with fatty acyl groups of relatively short chain length (C10 to C12 for Pseudomonas aeruginosa and Chromobacterium violaceum) or predominantly long chain length (C18 for Helicobacter pylori) are without effect. The presence of an acyloxyacyl group of appropriate chain length at the 3' position of the glucosamine disaccharide backbone of lipid A also plays a decisive role. By contrast, the lipid A proximal inner core region oligosaccharides of some bacterial lipopolysaccharides increase the expression of Ts activity; this is due mainly to the capacity of such oligosaccharides, which are relatively conserved in structure among gram-negative bacteria, to enlarge or expand upon the population of CD8+ Ts generated during the course of a normal antibody response to unrelated microbial antigens. The minimal structure required for the expression of the added immunosuppression observed appears to be a hexasaccharide containing one 2-keto-3-deoxyoctonate residue, two glucose residues, and three heptose residues to which are attached two pyrophosphorylethanolamine groups. The relevance of these findings to virulence and to the pathogenesis of gram-negative infections is discussed.

Characterization of the lipopolysaccharide of Moraxella catarrhalis. Structural analysis of the lipid A from M. catarrhalis serotype A lipopolysaccharide

The lipopolysaccharide of Moraxella catarrhalis serotype A (ATCC 25238) was found to consist of a short-chain oligosaccharide attached to a lipid A moiety. Composition and NMR analyses showed the oligosaccharide component in O-deacylated LPS to be composed of D-glucose, D-galactose, 2-acetamido-2-deoxy-D-glucose and 3-deoxy-D-manno-octulosonic acid in the molar ratio of 5:2:1:2. In addition, the lipid A region contained phosphate, D-glucosamine, 3-hydroxydodecanoic acid, dodecanoic acid and decanoic acid. The lipid A was examined in detail by high-field NMR spectroscopy and mass spectrometry. It was found to consist of a beta-1,6-D-glucosamine disaccharide backbone esterified at C4' by a phosphomonoester and glycosidically at C1 by diphosphoethanolamine or phosphomonoester. The amide group of the reducing and nonreducing glucosamine residues were acylated by 3-dodecanoyloxydodecanoic acid and 3-decanoyl-oxydodecanoic acid, respectively. The hydroxyl group at C3 and C3' were acylated by 3-decanoyl-oxydodecanoic acid and 3-hydroxydodecanoic acid respectively, while the hydroxyl groups at C4 and C6' were unsubstituted.

The chemical structure of bacterial endotoxin in relation to bioactivity

Lipopolysaccharides (LPS) constitute the O-antigens and endotoxins of Gram-negative bacteria. Whereas both the polysaccharide and lipid portion of LPS contribute to the pathogenic potential of this class of bacteria, it is the lipid component (lipid A) which determines the endotoxic properties of LPS. The primary structure of lipid A of various bacterial origin has been elucidated and Escherichia coli lipid A has been chemically synthesized. The biological analysis of synthetic lipid A partial structures proved that the expression of endotoxic activity depends on a unique structural arrangement and conformation. Such analyses have furthermore provided insight into the determinants required for lipid A binding to and activation of human target cells. Present research efforts aim at the molecular characterization of the specificity, modulation and biomedical consequences of the interaction of lipid A with host cells.

Defective biosynthesis of the lipid A component of temperature-sensitive firA (omsA) mutant of Escherichia coli

The biosynthesis of lipid A component was shown to be defective in a temperature-sensitive firA mutant of Escherichia coli. Cells were biosynthetically labelled with [14C]acetate and incorporation of radioactivity into the glycerophospholipid compared to lipid A fractions was measured. The lipid A/glycerophospholipid biosynthesis ratio of the firA mutant at 37 degrees C was approximately 50%, and at the nonpermissive temperature of 42 degrees C was less than 20% of that observed in the corresponding wild-type strain. Analysis of radiolabelled lipid A 4'-monophosphate derivatives and glycerophospholipids by thin-layer chromatography revealed that the firA mutant at 42 degrees C elaborated an altered lipid A, and its phosphatidylglycerol content was low. The chemical composition of the extracted lipopolysaccharides differed significantly between the firA and the wild-type strain only in the proportion of hexadecanoic acid, which was minimal in the wild type grown at 37 degrees C and 42 degrees C and in firA lipopolysaccharide grown at 37 degrees C. In the firA mutant lipopolysaccharide produced at 42 degrees C, hexadecanoic acid was present in approximately every third molecule, attached to the hydroxyl group of the amide-linked (R)-3-hydroxytetradecanoic acid at the reducing glucosamine of lipid A. Inspection of dephosphorylated free lipid A preparations by laser-desorption mass spectrometry confirmed that significant amounts of heptaacyl lipid A was elaborated by the firA strain grown at 42 degrees C.

Lipid A in Helicobacter pylori

Free lipid A of Helicobacter pylori was characterized with regard to chemical composition, reactivity with anti-lipid A antibodies, and activity in a Limulus lysate assay. The predominant fatty acids of H. pylori lipid A were 3-OH-18:0, 18:0, 3-OH-16:0, 16:0, and 14:0. Hexosamine was present in amounts similar to those in Campylobacter jejuni or Salmonella typhimurium lipid A. The lipopolysaccharide of H. pylori contained 2-keto-3-deoxyoctonic acid, a common constituent of enterobacterial and C. jejuni lipopolysaccharides. In the enzyme-linked immunosorbent assay, the doses of lipid A required to inhibit anti-lipid A by 50% (EI50 values) by absorption of the immune (rabbit) serum were 7.9, 1.2, and 1.4 micrograms of O-deacylated lipid A's from H. pylori, C. jejuni, and S. typhimurium per ml, respectively. The lower reactivity of H. pylori lipid A compared with those of the other two lipid A preparations (as shown by the higher EI50 value) was underscored by the use of a murine monoclonal anti-lipid A antibody in the inhibition assay. An EI50 value was not obtained at the concentrations tested for H. pylori lipid A; the corresponding figures for C. jejuni and S. typhimurium lipid A's were 13 and 14 micrograms/ml, respectively. No inhibition was obtained with H. pylori lipopolysaccharide, which showed a low-molecular-weight profile on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The activity of H. pylori lipid A in the Limulus assay was approximately 71 and 650 times lower than those of C. jejuni and S. typhimurium lipid A's, respectively. These findings suggest that lipid A is an integral part of the outer cell wall of H. pylori. The lower reactivity of H. pylori lipid A with anti-lipid A antibodies and in the Limulus assay compared with that of C. jejuni or S. typhimurium lipid A may be explained by a different composition of the fatty acids, especially the 3-hydroxy fatty acids, and a possible deviating phosphorylation pattern.

Preferential synthesis of heptaacyl lipopolysaccharide by the ssc permeability mutant of Salmonella typhimurium

In Salmonella typhimurium, a chromosomal gene termed ssc has been shown to cause an antibiotic-supersensitive phenotype. We studied the effect of the ssc gene on the chemical composition of the lipopolysaccharide component, using a thermosensitive ssc1 mutant (SH7622) that grows poorly at 42 degrees C. Analysis of the lipopolysaccharide by various techniques including fast-atom-bombardment mass spectrometry of lipid A, and determination of the type of linkage of fatty acids, revealed a profound temperature-dependent effect associated with the ssc1 mutation. At the non-permissive temperature, SH7622 contained hexadecanoic acid in the majority of lipid A molecules, resulting in the exclusive presence of heptaacyl lipopolysaccharide. This effect was largely reversed by the introduction of the cloned wild-type ssc gene to SH7622 and much reduced by growth of SH7622 at 37 degrees C.

Structural characterization of the lipid A component of pathogenic Neisseria meningitidis

The lipid A component of meningococcal lipopolysaccharide was structurally characterized by using chemical modification methods, methylation analysis, 31P nuclear magnetic resonance, and laser desorption mass spectroscopy. It was shown that Neisseria meningitidis lipid A consists of a 1,4'-bisphosphorylated beta(1'----6)-linked D-glucosamine disaccharide (lipid A backbone), both phosphate groups being largely replaced by O-phosphorylethanolamine. This disaccharide harbors two nonsubstituted hydroxyl groups at positions 4 and 6', the latter representing the attachment site of the oligosaccharide portion in lipopolysaccharide. In addition, it is substituted by up to six fatty acid residues. In the major lipid A component, representing a hexaacyl species, the hydroxyl groups at positions 3 and 3' carry (R)-3-hydroxydodecanoic acid [12:0(3-OH)], whereas the amino groups at positions 2 and 2' are substituted by (R)-3-(dodecanoyloxy)tetradecanoic acid [3-O(12:0)-14:0]. A minor portion was present as a tetraacyl lipid A component lacking either dodecanoic acid (12:0) or 12:0 and 12:0(3-OH). N. meningitidis lipid A, therefore, significantly differs from Escherichia coli lipid A by the nature and locations of fatty acids and the substitution of O-phosphorylethanolamine for the nonglycosyl (4'-P) and glycosyl phosphate.

Investigation of the structure of lipid A from Actinobacillus actinomycetemcomitans strain Y4 and human clinical isolate PO 1021-7

The lipopolysaccharides of Actinobacillus actinomycetemcomitans strain Y4 and a human clinical isolate PO 1021-7 were examined by SDS/PAGE, deoxycholate/PAGE and mass spectrometry. PAGE analysis revealed an electrophoretic pattern similar to the SR-type lipopolysaccharide (LPS) of Salmonella. Deoxycholate/PAGE indicated the LPS of A. actinomycetemcomitans to consist of short sugar chains. Chemical analysis revealed the presence of thiobarbituric-acid-positive material (3-deoxy-D-manno-octulosonic acid equivalents) and four neutral sugars: glucose, galactose, D-glycero-D-manno-heptose and L-glycero-D-manno-heptose. Phosphate, glucosamine, glycine, and the fatty acids, 3-hydroxymyristic acid, myristic acid and palmitic acid, comprised the remainder of the molecule. The structure of the free lipid A revealed it to consist of a 1,6-glucosamine disaccharide esterified at C4' by a phosphomonoester. The hydroxyl group at C3 and the amide group of the non-reducing glucosamine were both acylated by 3-myristoylmyristic acid; analogous sites on the reducing glucosamine were acylated by 3-hydroxymyristic acid. Hydroxyl groups at C4 and C6' in the free lipid A were unsubstituted, with C6 being the proposed attachment site of the polysaccharide moiety. Chemical analysis revealed the presence of glycine in the intact LPS; its exact location in the A. actinomycetemcomitans LPS is still to be determined. Both intact LPS and free lipid A were highly lethal to galactosamine-sensitized mice, comparable to that of Salmonella.

Structural characterization of the lipid A component of Pseudomonas aeruginosa wild-type and rough mutant lipopolysaccharides

The structure of the lipid A component of lipopolysaccharides isolated from two wild-type strains (Fisher 2 and 7) and one rough mutant (PAC 605) of Pseudomonas aeruginosa was investigated using chemical analysis, methylation analysis, combined gas-liquid chromatography/mass spectrometry, laser-desorption mass spectrometry and NMR spectroscopy. The lipid A backbone was found to consist of a pyranosidic beta 1,6-linked D-glucosamine disaccharide [beta-D-GlcpN-(1----6)-D-GlcpN], phosphorylated in positions 4' and 1. Position 6' of the beta-D-GlcpN-(1----6)-D-GlcpN disaccharide was identified as the attachment site of the core oligosaccharide and the hydroxyl group at C-4 was not substituted. Lipid A of the three P. aeruginosa strains expressed heterogeneity with regard to the degree of acylation: a hexaacyl as well as a pentaacyl component were structurally characterized. The hexaacyl lipid A contains two amide-bound 3-O-acylated (R)-3-hydroxydodecanoic acid groups [12:0(3-OH)] at positions 2 and 2' of the GlcN dissacharide and two ester-bound (R)-3-hydroxydecanoic acid groups [10:0(3-OH)] at positions 3 and 3'. The pentaacyl species, which represents the major lipid A component, lacks one 10:0(3-OH) residue, the hydroxyl group in position 3 of the reducing GlcN residue being free. In both hexa- and pentaacyl lipid A the 3-hydroxyl group of the two amide-linked 12:0(3-OH) residues are acylated by either dodecanoic (12:0) or (S)-2-hydroxydodecanoic acid [12:0(2-OH)], the lipid A species with two 12:0(2-OH) residues, however, being absent. The presence of only five acyl residues in the major lipid A fraction may account for the low endotoxic activity observed with P. aeruginosa lipopolysaccharide.

Enzymatically deacylated Neisseria lipopolysaccharide (LPS) inhibits murine splenocyte mitogenesis induced by LPS

Acyloxyacyl hydrolase is a leukocyte enzyme that selectively removes the secondary acyl chains from the lipid A moiety of gram-negative bacterial lipopolysaccharides (LPS). As predicted by the reported contribution of secondary acyl chains to the bioactivities of lipid A analogs, enzymatic deacylation of Salmonella typhimurium Rc LPS substantially reduces its potency in the dermal Shwartzman reaction and in several in vitro assays that measure responses of human endothelial cells and neutrophils, whereas the potency of this LPS for inducing murine splenocyte mitogenesis is affected much less. In the experiments described here, we studied the impact of acyloxyacyl hydrolysis on the bioactivities of several LPS that differ from Salmonella LPS in carbohydrate and lipid A structures. Deacylated LPS from Escherichia coli, Haemophilus influenzae, Neisseria meningitidis, and S. typhimurium were similarly reduced in potency in the Limulus lysate test (30- to 60-fold reduction in potency relative to the corresponding mock-treated LPS), and the ability of all of these deacylated LPS to stimulate neutrophil adherence to human endothelial cells was reduced by a factor of 100 or more. For LPS from E. coli, H. influenzae, and Pseudomonas aeruginosa, the impact of deacylation on spleen cell mitogenesis was also similar to that observed for S. typhimurium LPS: deacylation reduced potency by less than 15-fold. Unexpectedly, the potency of Neisseria LPS in the murine splenocyte mitogenicity test was reduced over 100-fold by deacylation, and deacylated Neisseria LPS could block the mitogenic activity of Neisseria and Salmonella LPS. These studies indicate that the contribution of secondary acyl chains to the bioactivities of a given LPS cannot be predicted with confidence from the reported structure-activity relationships of lipid A or from the behavior of other deacylated LPS.

Acyl-acyl carrier protein specificity of UDP-GlcNAc acyltransferases from gram-negative bacteria: relationship to lipid A structure

Lipid A, the component of lipopolysaccharide that provides the membrane anchor of the core and O-antigen sugars, is known to contain characteristic R-3-hydroxy fatty acids bound to the 2,2' (N-linked) and 3,3' (O-linked) positions of the glucosamine disaccharide in different gram-negative bacteria. The studies reported here show that it is the acyl-acyl carrier protein specificities of the enzymes UDP-GlcNAc-O-acyltransferase and UDP-3-O-[(R)-3-hydroxyacyl]-GlcN-N-acyltransferase that determine the nature of these fatty acids.

Structural analysis of the lipid A component of Campylobacter jejuni CCUG 10936 (serotype O:2) lipopolysaccharide. Description of a lipid A containing a hybrid backbone of 2-amino-2-deoxy-D-glucose and 2,3-diamino-2,3-dideoxy-D-glucose

The chemical structure of Campylobacter jejuni CCUG 10936 lipid A was elucidated. The hydrophilic backbone of the lipid A was shown to consist of three (1----6)-linked bisphosphorylated hexosamine disaccharides. Neglecting the phosphorylation pattern, a D-glucosamine (2-amino-2-deoxy-D-glucose) disaccharide [beta-D-glucosaminyl-(1----6)-D-glucosamine], a hybrid disaccharide of 2,3-diamino-2,3-dideoxy-D-glucose and D-glucosamine [2,3-diamino-2,3-dideoxy-beta-D-glucopyranosyl-(1----6)-D-glucosamine], and a 2,3-diamino-2,3-dideoxy-D-glucose disaccharide were present in a molar ratio of 1:6:1.2. Although the backbones are bisphosphorylated, heterogeneity exists in the substitution of the polar head groups. Phosphorylethanolamine is alpha-glycosidically bound to the reducing sugar residue of the backbone, though C-1 is also non-stoichiometrically substituted by diphosphorylethanolamine. Position 4' of the non-reducing sugar residue carries an ester-bound phosphate group or is non-stoichiometrically substituted by diphosphorylethanolamine. By methylation analysis it was shown that position 6' is the attachment site for the polysaccharide moiety in lipopolysaccharide. These backbone species carry up to six molecules of ester- and amide-bound fatty acids. Four molecules of (R)-3-hydroxytetradecanoic acid are linked directly to the lipid A backbone (at positions 2, 3, 2', and 3'). Laser desorption mass spectrometry showed that both (R)-3-hydroxytetradecanoic acids linked to the non-reducing sugar unit carry, at their 3-hydroxyl group, either two molecules of hexadecanoic acid or one molecule of tetradecanoic and one of hexadecanoic acid. It also suggested that the (R)-3-(tetradecanoyloxy)-tetradecanoic acid was attached at position 2', whereas (R)-3-(hexadecanoyloxy)-tetradecanoic acid was attached at position 3', or at positions 2' and 3'. Therefore, the occurrence of three backbone disaccharides differing in amino sugar composition and presence of a hybrid disaccharide differentiate the lipid A of this C. jejuni strain from enterobacterial and other lipids A described previously.

Factors in virulence expression and their role in periodontal disease pathogenesis

The classic progression of the development of periodontitis with its associated formation of an inflammatory lesion is characterized by a highly reproducible microbiological progression of a Gram-positive microbiota to a highly pathogenic Gram-negative one. While this Gram-negative microbiota is estimated to consist of at least 300 different microbial species, it appears to consist of a very limited number of microbial species that are involved in the destruction of periodontal diseases. Among these "putative periodontopathic species" are members of the genera Porphyromonas, Bacteroides, Fusobacterium, Wolinella, Actinobacillus, Capnocytophaga, and Eikenella. While members of the genera Actinomyces and Streptococcus may not be directly involved in the microbial progression, these species do appear to be essential to the construction of the network of microbial species that comprise both the subgingival plaque matrix. The temporal fluctuation (emergence/disappearance) of members of this microbiota from the developing lesion appears to depend upon the physical interaction of the periodontal pocket inhabitants, as well as the utilization of the metabolic end-products of the respective species intimately involved in the disease progression. A concerted action of the end-products of prokaryotic metabolism and the destruction of host tissues through the action of a large number of excreted proteolytic enzymes from several of these periodontopathogens contribute directly to the periodontal disease process.(ABSTRACT TRUNCATED AT 250 WORDS)

Structural studies of lipid A from Pseudomonas aeruginosa PAO1: occurrence of 4-amino-4-deoxyarabinose

Lipid A derived from Pseudomonas aeruginosa PAO1 contains a biphosphorylated 1-6-linked glucosamine disaccharide backbone. The reducing glucosamine has an unsubstituted glycosidically linked phosphate at C-1. The nonreducing glucosamine has an ester-bound phosphate at C-4' which is nonstoichiometrically substituted with 4-amino-4-deoxyarabinose. Induction of 4-amino-4-deoxyarabinose was dependent on cultural conditions. No pyrophosphate groups were detected. Acyloxyacyl diesters are formed by esterification of the amide-bound 3-hydroxydodecanoic acid with dodecanoic acid and 2-hydroxydodecanoic acids in an approximate molar ratio of 2:1. Dodecanoic and 3-hydroxydecanoic acids are esterified to positions C-3 and C-3' in the sugar backbone. All hydroxyl groups of the glucosamine disaccharide except C-4 and C-6' are substituted. Lipopolysaccharide chemical analyses measured glucose, rhamnose, heptose, galactosamine, alanine, phosphate, and glucosamine. The proposed lipid A structure differs from previous models. There are significant differences in acyloxyacyl diesters, and the proposed model includes an aminopentose substituent.

Brucella abortus 16S rRNA and lipid A reveal a phylogenetic relationship with members of the alpha-2 subdivision of the class Proteobacteria

On the basis of ribosomal 16S sequence comparison, Brucella abortus has been found to be a member of the alpha-2 subdivision of the class Proteobacteria (formerly named purple photosynthetic bacteria and their nonphototrophic relatives). Within the alpha-2 subgroup, brucellae are specifically related to rickettsiae, agrobacteria, and rhizobiae, organisms that also have the faculty or the obligation of living in close association to eucaryotic cells. The composition of Brucella lipid A suggests a close phylogenetical relationship with members of the alpha-2 group. The chemical analysis of the lipid A fraction revealed that Brucella species contain both glucosamine and diaminoglucose, thus suggesting the presence of a so-called mixed lipid A type. The serological analysis with polyclonal and monoclonal antibodies is in agreement with the existence of mixed lipid A type in B. abortus. The amide-linked fatty acid present as acyl-oxyacyl residues were 3-O-C(16:0)12:0, 3-O-C(16:0)13:0, 3-O-C(16:0)14:0, and 3-O-C(18:0)14:0. The only amide-linked unsubstituted fatty acid detected was 3-OH-C16:0. The ester-linked fatty acids are 3-OH-C16:0, 3-OH-C18:0, C16:0, C17:0, and C18:0. Significant amounts of the large-chain 27-OH-C28:0 were detected together with traces of 25-OH-C26:0 and 29-OH-C30:0. Comparison of the Brucella lipid composition with that of the other Proteobacteria also suggests a close phylogenetical relationship with members of the alpha-2 subdivision. The genealogical grouping of Brucella species with pericellular and intracellular plant and animal pathogens as well as with intracellular plant symbionts suggests a possible evolution of Brucella species from plant-arthropod-associated bacteria.

Polysaccharide antigens of Pseudomonas aeruginosa

The major polysaccharide antigens of P. aeruginosa are the cell-wall lipopolysaccharides many of which have an acidic polysaccharide chain (O-antigen) rich in unusual amino sugars. The D-rhamnose-rich polysaccharide antigen common to many serologically distinct strains is also associated with the lipopolysaccharide. The high-molecular-weight polysaccharides with O-specificity are present in extracellular slime produced by strains isolated from the environmental and from the immunocompromised hosts. The extracellular antigenic polysaccharide of another type (bacterial alginate) is expressed by mucoid strains isolated from patients with cystic fibrosis. Serotype-specific immune responses after infection are directed at the lipopolysaccharides and these heat-stable antigens serve as the basis for differentiation of P. aeruginosa strains. Both the cell-wall antigens including conjugates of the O-polysaccharides with different proteins and the extracellular antigens have been used to prepare specific antibodies tested for protection against infections due to P. aeruginosa.

Chromogenic endotoxin assay in plasma. Selection of plasma pretreatment and production of standard curves

The aim of this study was to define the optimal conditions for the plasma pretreatment and to improve the production of standard curves for plasma endotoxin determination by a chromogenic substrate assay. Endotoxin standard from E. coli O 111:B 4 (0-50 ng/l) was added to pyrogen-free water or to plasma samples from 12 healthy subjects and 24 alcoholics, before pretreatment by heating (75 degrees C, 5 minutes) or with perchloric acid (0.32 mol/l). When endotoxin standard curves were determined using a microprocessor-controlled reader, the slopes of the curves obtained with plasma differed from those with pyrogen-free water. The slope of the standard curve prepared with plasma samples from different patients exhibited marked interindividual variations. Compared with the heating method, the perchloric acid method gave more variable results and a lower recovery of added endotoxin, especially in plasma from alcoholics. The results permit the following conclusion: 1. For plasma endotoxin determination, a standard curve should be prepared for each individual plasma sample. 2. The endotoxin standard should be added before pretreatment of the plasma. 3. Pretreatment of the plasma by heating at 75 degrees C for 5 minutes provides more reliable results than pretreatment with perchloric acid.

Structural characterization of the lipid A component of Bacteroides fragilis strain NCTC 9343 lipopolysaccharide

The chemical structure of Bacteroides fragilis NCTC 9343 lipid A was characterized by using conventional chemical procedures, methylation analysis, and laser desorption mass spectrometry. It was found that B. fragilis lipid A consists of a beta-D-glucosaminyl-(1-6)-D-glucosaminyl-1-O-phosphate backbone whose hydroxyl groups in positions 4, 4' and 6' are free, the latter serving as the attachment site for the polysaccharide component in lipopolysaccharide. This backbone molecule carries up to of five molecules of ester- and amide-bound long chain non-hydroxylated and (R)-3-hydroxy fatty acids. With regard to the distribution on the fatty acids on the lipid A backbone, a considerable heterogeneity was revealed by laser desorption mass spectrometry. Despite this heterogeneity, a major species of B. fragilis lipid A could be defined in which the hydroxyl group at position 3' of the distal GlcN carries (R)-3-hydroxyhexadecanoic acid and the hydroxyl group at position 3 of the reducing GlcN is acylated by (R)-3-hydroxypentadecanoic acid. The amino group of the distal GlcN residue carries (R)-3-(13-methyltetradecanoyloxy)-15-methylhexadecanoic acid and that of the reducing GlcN group (R)-3-hydroxyhexadecanoic acid. The absence of ester-bound phosphate and ester-linked 3-acyloxyacyl groups, the presence of not more than five acyl residues and the predominance of fatty acids possessing 15-17 carbon atoms are unique features of B. fragilis lipid A which differentiate it from enterobacterial and other lipids A and which are likely to be related to its low endotoxic activity.

Cleavage of the O antigen 4, 5, 12 of Salmonella typhimurium by hydrofluoric acid

The effect of hydrofluoric acid (aqueous 48% HF) upon different lipopolysaccharides (LPS) was studied, employing conditions (48 h at +4 degrees C) that are commonly used to dephosphorylate LPS. From the LPS of Salmonella typhimurium having the O antigen 4,5,12 almost all of the O-antigenic sugars (Abe, Gal, Glc, Man, Rha) were liberated in dialysable form, whereas the saccharide chains of Salmonella LPS with O antigen 6,7 (Man, Glc, GlcNAc) were resistant to HF. The lability towards HF was shown to be due to the presence of the deoxysugar L-rhamnose in the saccharide backbone of the O antigen 4,5,12, since only Rha was found as the terminal sugar in the corresponding dialysable material. Hydrofluoric acid can thus be used to specifically cleave Rha-containing polysaccharides.