The Structure of the Lipid A of Gram-Negative Cold-Adapted Bacteria Isolated from Antarctic Environments

Gram-negative Antarctic bacteria adopt survival strategies to live and proliferate in an extremely cold environment. Unusual chemical modifications of the lipopolysaccharide (LPS) and the main component of their outer membrane are among the tricks adopted to allow the maintenance of an optimum membrane fluidity even at particularly low temperatures. In particular, the LPS’ glycolipid moiety, the lipid A, typically undergoes several structural modifications comprising desaturation of the acyl chains, reduction in their length and increase in their branching. The investigation of the structure of the lipid A from cold-adapted bacteria is, therefore, crucial to understand the mechanisms underlying the cold adaptation phenomenon. Here we describe the structural elucidation of the highly heterogenous lipid A from three psychrophiles isolated from Terra Nova Bay, Antarctica. All the lipid A structures have been determined by merging data that was attained from the compositional analysis with information from a matrix-assisted laser desorption ionization (MALDI) time of flight (TOF) mass spectrometry (MS) and MS² investigation. As lipid A is also involved in a structure-dependent elicitation of innate immune response in mammals, the structural characterization of lipid A from such extremophile bacteria is also of great interest from the perspective of drug synthesis and development inspired by natural sources.

Identification and structural characterization of lipid A from Escherichia coli, Pseudomonas putida and Pseudomonas taiwanensis using liquid chromatography coupled to high-resolution tandem mass spectrometry

RATIONALE

Lipid A is a part of the lipopolysaccharide layer, which is a main component of the outer membrane from Gram-negative bacteria. It can be sensed by mammalians to identify the presence of Gram-negative bacteria in their tissues and plays a key role in the pathogenesis of bacterial infections. Lipid A is also used as an adjuvant in human vaccines, emphasizing the importance of its structural analysis.

METHODS

In order to distinguish and characterize various lipid A species, a liquid chromatography coupled to tandem mass spectrometry (LC/MS/MS) method was developed. Isolation of lipid A from different bacteria was carried out using a modified Bligh and Dyer extraction following a mild acid hydrolysis. Chromatography was performed using a bifunctional reversed-phase-based stationary phase. High-resolution MS using negative electrospray ionization was applied and MS/MS experiments utilizing high-energy collisional dissociation generated diagnostic product ions, which allowed the assignment of the side chains to distinct positions of the lipid A backbone.

RESULTS

The method was applied to lipid A isolations of Escherichia coli (E. coli), Pseudomonas putida (P. putida) and Pseudomonas taiwanensis (P. taiwanensis). Various lipid A species were identified by their accurate masses and their structures were characterized using MS/MS experiments. Previously described lipid A structures from E. coli were identified and their structures confirmed by MS/MS. For the biotechnologically relevant strains P. putida and P. taiwanensis, we confirmed species by MS/MS, which have previously only been analyzed using MS. In addition, several lipid A species were discovered that have not been previously described in the literature.

CONCLUSIONS

The combination of LC and MS/MS enabled the selective and sensitive identification and structural characterization of various lipid A species from Gram-negative bacteria. These species varied in their substituted side chains, speaking of fatty acids and phosphate groups. Characteristic product ions facilitated the assignment of side chains to distinct positions of the lipid A backbone.

Metabolic engineering of Escherichia coli to produce a monophosphoryl lipid A adjuvant

Monophosphoryl lipid A (MPLA) species, including MPL (a trade name of GlaxoSmithKline) and GLA (a trade name of Immune Design, a subsidiary of Merck), are widely used as an adjuvant in vaccines, allergy drugs, and immunotherapy to boost the immune response. Even though MPLA is a derivative of lipopolysaccharide (LPS), a component of the outer membrane of Gram-negative bacteria, bacterial strains producing MPLA have not been found in nature nor engineered. In fact, MPLA generation involves expensive and laborious procedures based on synthetic routes or chemical transformation of precursors isolated from Gram-negative bacteria. Here, we report the engineering of an Escherichia coli strain for in situ production and accumulation of MPLA. Furthermore, we establish a succinct method for purifying MPLA from the engineered E. coli strain. We show that the purified MPLA (named EcML) stimulates the mouse immune system to generate antigen-specific IgG antibodies similarly to commercially available MPLA, but with a dramatically reduced manufacturing time and cost. Our system, employing the first engineered E. coli strain that directly produces the adjuvant EcML, could transform the current standard of industrial MPLA production.

The Structure of the Lipid A from the Halophilic Bacterium Spiribacter salinus M19-40T

The study of the adaptation mechanisms that allow microorganisms to live and proliferate in an extreme habitat is a growing research field. Directly exposed to the external environment, lipopolysaccharides (LPS) from Gram-negative bacteria are of great appeal as they can present particular structural features that may aid the understanding of the adaptation processes. Moreover, through being involved in modulating the mammalian immune system response in a structure-dependent fashion, the elucidation of the LPS structure can also be seen as a fundamental step from a biomedical point of view. In this paper, the lipid A structure of the LPS from Spiribacter salinus M19-40^T, a halophilic gamma-proteobacteria, was characterized through chemical analyses and matrix-assisted laser desorption ionization (MALDI) mass spectrometry. This revealed a mixture of mono- and bisphosphorylated penta- to tri-acylated species with the uncommon 2 + 3 symmetry and bearing an unusual 3-oxotetradecaonic acid.

Hypoacylated LPS from Foodborne Pathogen Campylobacter jejuni Induces Moderate TLR4-Mediated Inflammatory Response in Murine Macrophages

Toll-like receptor 4 (TLR4) initiates immune response against Gram-negative bacteria upon specific recognition of lipid A moiety of lipopolysaccharide (LPS), the major component of their cell wall. Some natural differences between LPS variants in their ability to interact with TLR4 may lead to either insufficient activation that may not prevent bacterial growth, or excessive activation which may lead to septic shock. In this study we evaluated the biological activity of LPS isolated from pathogenic strain of Campylobacter jejuni, the most widespread bacterial cause of foodborne diarrhea in humans. With the help of hydrophobic chromatography and MALDI-TOF mass spectrometry we showed that LPS from a C. jejuni strain O2A consists of both hexaacyl and tetraacyl forms. Since such hypoacylation can result in a reduced immune response in humans, we assessed the activity of LPS from C. jejuni in mouse macrophages by measuring its capacity to activate TLR4-mediated proinflammatory cytokine and chemokine production, as well as NFκB-dependent reporter gene transcription. Our data support the hypothesis that LPS acylation correlates with its bioactivity.

Studies on lipid A isolated from Phyllobacterium trifolii PETP02T lipopolysaccharide

The structure of lipid A from lipopolysaccharide of Phyllobacterium trifolii PETP02T, a nitrogen-fixing symbiotic bacterium, was studied. It was found that the lipid A backbone was composed of two 2,3-diamino-2,3-dideoxy-D-glucose (GlcpN3N) residues connected by a β-(1 → 6) glycosidic linkage, substituted by galacturonic acid (GalpA) at position C-1 and partly decorated by a phosphate residue at C-4' of the non-reducing GlcpN3N. Both diaminosugars were symmetrically substituted by 3-hydroxy fatty acids (14:0(3-OH) and 16:0(3-OH)). Ester-linked secondary acyl residues [i.e. 19:0cyc and 28:0(27-OH) or 28:0(27-4:0(3-OMe))] were located in the distal part of lipid A. A high similarity between the lipid A of P. trifolii and Mesorhizobium was observed and discussed from the perspective of the genetic context of both genomes.

Structural and biological characteristics of different forms of V. filiformis lipid A: use of MS to highlight structural discrepancies

Vitreoscilla filiformis is a Gram-negative bacterium isolated from spa waters and described for its beneficial effects on the skin. We characterized the detailed structure of its lipopolysaccharide (LPS) lipid A moiety, an active component of the bacterium that contributes to the observed skin activation properties. Two different batches differing in postculture cell recovery were tested. Chemical analyses and mass spectra, obtained before and after mild-alkali treatments, revealed that these lipids A share the common bisphosphorylated β-(1→6)-linked d-glucosamine disaccharide with hydroxydecanoic acid in an amide linkage. Short-chain FAs, hydroxydecanoic and dodecanoic acid, were found in a 2:1 ratio. The two lipid A structures differed by the relative amount of the hexa-acyl molecular species and phosphoethanolamine substitution of the phosphate groups. The two V. filiformis LPS batches induced variable interleukin-6 and TNF-α secretion by stimulated myelomonocytic THP-1 cells, without any difference in reactive oxygen species production or activation of caspase 3/7. Other different well-known highly purified LPS samples were characterized structurally and used as standards. The structural data obtained in this work explain the low inflammatory response observed for V. filiformis LPS and the previously demonstrated beneficial effects on the skin.

Marine compounds with therapeutic potential in gram-negative sepsis

This paper concerns the potential use of compounds, including lipid A, chitosan, and carrageenan, from marine sources as agents for treating endotoxemic complications from Gram-negative infections, such as sepsis and endotoxic shock. Lipid A, which can be isolated from various species of marine bacteria, is a potential antagonist of bacterial endotoxins (lipopolysaccharide (LPSs)). Chitosan is a widespread marine polysaccharide that is derived from chitin, the major component of crustacean shells. The potential of chitosan as an LPS-binding and endotoxin-neutralizing agent is also examined in this paper, including a discussion on the generation of hydrophobic chitosan derivatives to increase the binding affinity of chitosan to LPS. In addition, the ability of carrageenan, which is the polysaccharide of red alga, to decrease the toxicity of LPS is discussed. We also review data obtained using animal models that demonstrate the potency of carrageenan and chitosan as antiendotoxin agents.

Construction of monophosphoryl lipid A producing Escherichia coli mutants and comparison of immuno-stimulatory activities of their lipopolysaccharides

The lipid A moiety of Escherichia coli lipopolysaccharide is a hexaacylated disaccharide of glucosamine phosphorylated at the 1- and 4'-positions. It can be recognized by the TLR4/MD-2 complex of mammalian immune cells, leading to release of proinflammatory cytokines. The toxicity of lipid A depends on its structure. In this study, two E. coli mutants, HW001 and HW002, were constructed by deleting or integrating key genes related to lipid A biosynthesis in the chromosome of E. coli W3110. HW001 was constructed by deleting lacI and replacing lacZ with the Francisella novicida lpxE gene in the chromosome and only synthesizes monophosphoryl lipid A. HW002 was constructed by deleting lpxM in HW001 and synthesizes only the pentaacylated monophosphoryl lipid A. The structures of lipid A made in HW001 and HW002 were confirmed by thin layer chromatography and electrospray ionization mass spectrometry. HW001 and HW002 grew as well as the wild-type W3110. LPS purified from HW001 or HW002 was used to stimulate murine macrophage RAW264.7 cells, and less TNF-α were released. This study provides a feasible way to produce interesting lipid A species in E. coli.

Structural features of lipid A of Rickettsia typhi

Lipid A isolated from the Rickettsia typhi lipopolysaccharide (LPS) was investigated for its composition and structure using chemical analyses, gas chromatography-mass spectrometry (GC-MS), and electrospray ionization (ESI) combined with the tandem mass spectrometry (MS/MS). Our studies revealed a noticeable compositional and structural heterogeneity of lipid A with respect to the content of phosphate groups and the degree of acylation. It appeared that at least two molecular species were present in lipid A. The major species represented the hexaacyl lipid A consisting of the β-(1--> 6)-linked D-glucosamine (GlcN) disaccharide backbone carrying two phosphate groups. One of them was linked to the glycosidic hydroxyl group of the reducing GlcN I and the other was ester linked to the O-4´ position of the non-reducing GlcN II. The primary fatty acids consisted of two 3-hydroxytetradecanoic [C14:0(3-OH)] and two 3-hydroxyhexadecanoic [C16:0(3-OH)] acids. The former were ester- and the latter amide-linked to both GlcN. Two secondary fatty acids were represented by the octadecanoic (C18:0) and hexadecanoic (C16:0) acids that were ester-linked at the N-2´ and O-3´ positions, respectively. In the minor lipid A species, ester-linked C18:0 was substituted by C16:0 at the C16:0(3-OH) of GlcN II. The R. typhi lipid A resembles structurally the classical forms of enterobacterial lipids A with high endotoxicity.

Comprehensive structure characterization of lipid A extracted from Yersinia pestis for determination of its phosphorylation configuration

We report on comprehensive structure characterization of lipid A extracted from Yersinia pestis (Yp) for determination of its phosphorylation configuration that was achieved by combining the methods of molecular biology with high-resolution tandem mass spectrometry. The phosphorylation pattern of diphosphorylated lipid A extracted from Yp has recently been found to be a heterogeneous mixture of C-1 and C-4' bisphosphate, C-1 pyrophosphate, and C-4' pyrophosphate (Proc. Natl. Acad. Sci. 2008, 105, 12742). To reduce the inherent phosphate heterogeneity of diphosphorylated lipid A extracted from Yp, we incorporated specific C-1 and C-4' position phosphatases into wild type KIM6+ Yp grown at 37 degrees C. Comprehensive high-resolution tandem mass spectrometric analyses of lipid A extracted from Yp modified with either the C-1 or C-4' phosphatase allowed for unambiguous structure assignment of monophosphorylated and diphosphorylated lipid A and distinction of isomeric bisphosphate and pyrophosphate forms. The prevalent aminoarabinose modification was determined to be exclusively attached to the lipid A disaccharide via a phospho-diester linkage at either or both the C-1 and C-4' positions.

[Chemical characterisation of structural components of Rahnella aquatilis lipopolysaccharides]

The studies of lipopolysaccharides (LPS) of eight Rahnella aquatilis strains, isolated from different sources have shown that they contain both S- and R-types of molecules. This fact is evidenced by the presence of high-molecular fraction of O-specific polysaccharides (O-PS) and low-molecular fraction of core oligosaccharides. The predominant monosaccharides of core oligosaccharides were glucose, galactose. The presence of only one high-molecular fraction O-PS was a characteristic feature of all investigated strains. The predominant monosaccharides of O-PS were galactose, glucose, mannose, rhamnose and fucose. 3-hydroxytetradecanoic (48.9-93.1%), dodecanoic (2.9-12.1%), tetradecanoic (4.1-25.3%) and hexadecanoic (2.8-15.3%) acids have been obtained in lipids A of LPS depending on the strain. The presence in lipid A of R. aquatilis of only 3-hydroxytetradecanoic acid which is characteristic of Enterobacteriaceae proves the correct ascribing of the isolated strains to this family.

Structure of compositionally simple lipopolysaccharide from marine synechococcus

Lipopolysaccharide (LPS) is the first defense against changing environmental factors for many bacteria. Here, we report the first structure of the LPS from cyanobacteria based on two strains of marine Synechococcus, WH8102 and CC9311. While enteric LPS contains some of the most complex carbohydrate residues in nature, the full-length versions of these cyanobacterial LPSs have neither heptose nor 3-deoxy-D-manno-octulosonic acid (Kdo) but instead 4-linked glucose as their main saccharide component, with low levels of glucosamine and galacturonic acid also present. Matrix-assisted laser desorption ionization mass spectrometry of the intact minimal core LPS reveals triacylated and tetraacylated structures having a heterogeneous mix of both hydroxylated and nonhydroxylated fatty acids connected to the diglucosamine backbone and a predominantly glucose outer core-like region for both strains. WH8102 incorporated rhamnose in this region as well, contributing to differences in sugar composition and possibly nutritional differences between the strains. In contrast to enteric lipid A, which can be liberated from LPS by mild acid hydrolysis, lipid A from these organisms could be produced by only two novel procedures: triethylamine-assisted periodate oxidation and acetolysis. The lipid A contains odd-chain hydroxylated fatty acids, lacks phosphate, and contains a single galacturonic acid. The LPS lacks any limulus amoebocyte lysate gelation activity. The highly simplified nature of LPSs from these organisms leads us to believe that they may represent either a primordial structure or an adaptation to the relatively higher salt and potentially growth-limiting phosphate levels in marine environments.

[Chemical characteristic of structure components of Pragia fontium lipopolysaccharides]

Structure components (lipid A. oligosaccharide core, and O-specific polysaccharide) of the lipopolysaccharide from 8 strains of Pragia fontium were obtained as a result of mild acidic hydrolysis. The macromolecular organization of lipopolysaccharides of studied strains was heterogeneous and presented both by S-forms, and R- or SR-forms. It was established that as to fatty acid composition lipids A of tested strains were represented by one chemotype with predominant 3-hydroxytetradecanoic fatty acid. An analysis ofmonosaccharide composition of core oligosaccharides has detected 5 chemotypes, and glucose, galactose, rhamnose, ribose, arabinose, xylose and mannose were identified in them. It was shown that O-specific polysaccharides consisted of glucose, galactose, rhamnose, and mannose that demonstrated their belonging to 4 chemotypes.

A rapid, small-scale procedure for the structural characterization of lipid A applied to Citrobacter and Bordetella strains: discovery of a new structural element

Endotoxins [lipopolysaccharides (LPSs)] are part of the outer cell membrane of Gram-negative bacteria. Their biological activities are associated mainly with the lipid component (lipid A) and even more specifically with discrete aspects of their fine structure. The need for a rapid and small-scale analysis of lipid A motivated us to develop a procedure that combines direct isolation of lipids A from bacterial cells with sequential release of their ester-linked fatty acids by a mild alkali treatment followed by MALDI-MS analysis. This method avoids the multiple-step LPS extraction procedure and lipid A isolation. The whole process can be performed in a working day and applied to lyophilized bacterial samples as small as 1 mg. We illustrate the method by applying it to the analysis of lipids A of three species of Citrobacter that were found to be identical. On the other hand, when applied to two batches of Bordetella bronchiseptica strain 4650, it highlighted the presence, in one of them, of hitherto unreported hexosamine residues substituting the lipid A phosphate groups, possibly a new camouflage opportunity to escape a host defense system.

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.

Structure and biosynthesis of free lipid A molecules that replace lipopolysaccharide in Francisella tularensis subsp. novicida

Francisella tularensis subsp. novicida U112 phospholipids, extracted without hydrolysis, consist mainly of phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, and two lipid A species, designated A1 and A2. These lipid A species, present in a ratio of 7:1, comprise 15% of the total phospholipids, as judged by 32Pi labeling. Although lipopolysaccharide is detectable in F. tularensis subsp. novicida U112, less than 5% of the total lipid A is covalently linked to it. A1 and A2 were analyzed by electrospray ionization and matrix-assisted laser desorption ionization mass spectrometry, gas chromatography/mass spectrometry, and NMR spectroscopy. Both compounds are disaccharides of glucosamine, acylated with primary 3-hydroxystearoyl chains at positions 2, 3, and 2' and a secondary palmitoyl residue at position 2'. Minor isobaric species and some lipid A molecules containing a 3-hydroxypalmitoyl chain in place of 3-hydroxystearate are also present. The 4'- and 3'-positions of A1 and A2 are not derivatized, and 3-deoxy-d-manno-octulosonic acid (Kdo) is not detectable. The 1-phosphate groups of both A1 and A2 are modified with an alpha-linked galactosamine residue, as shown by NMR spectroscopy and gas chromatography/mass spectrometry. An alpha-linked glucose moiety is attached to the 6'-position of A2. The lipid A released by mild acid hydrolysis of F. tularensis subsp. novicida lipopolysaccharide consists solely of component A1. F. tularensis subsp. novicida mutants lacking the arnT gene do not contain a galactosamine residue on their lipid A. Formation of free lipid A in F. tularensis subsp. novicida might be initiated by an unusual Kdo hydrolase present in the membranes of this organism.

Non-enterobacterial endotoxins stimulate human coronary artery but not venous endothelial cell activation via Toll-like receptor 2

OBJECTIVE

To determine whether non-enterobacterial endotoxins, which are likely to constitute the majority of the circulating endotoxin pool, may stimulate coronary artery endothelial cell activation.

METHODS AND RESULTS

Interleukin-8 secretion, monocyte adhesion, and E-selectin expression were measured in human umbilical vein endothelial cells (HUVECs) and coronary artery endothelial cells (HCAECs) challenged in vitro with highly purified endotoxins of common host colonisers Escherichia coli, Porphyromonas gingivalis, Pseudomonas aeruginosa, and Bacteroides fragilis. HCAECs but not HUVECs expressed Toll-like receptor (TLR)-2 and were responsive to non-enterobacterial endotoxins. Transfection of TLR-deficient HEK-293 cells with TLR2 or TLR4/MD2 revealed that while E. coli endotoxin utilised solely TLR4 to signal, the endotoxins, deglycosylated endotoxins (lipid-A), and whole heat-killed bacteria of the other species stimulated TLR2-but not TLR4-dependent cell-signalling. Blockade of TLR2 with neutralizing antibody prevented HCAEC activation by non-enterobacterial endotoxins. Comparison of each endotoxin with E. coli endotoxin in limulus amoebocyte lysate assay revealed that the non-enterobacterial endotoxins are greatly underestimated by this assay, which has been used in all previous studies to estimate plasma endotoxin concentrations.

CONCLUSION

Circulating non-enterobacterial endotoxins may be an underestimated contributor to endothelial activation and atherosclerosis in individuals at risk of increased plasma endotoxin burden.

[An unusual lipid A from a marine bacterium Chryseobacterium scophtalmum CIP 104199T]

The hydrolysis of defatted cells of the marine bacterium Chryseobacterium scophtalmum CIP 104199T with 10% acetic acid (3 h, 100 degrees C) led to an unusual lipid A (LA) (yield 0.6%), obtained for the first time. Using chemical analysis, FAB MS, and NMR spectroscopy, it was shown to be D-glucosamine 1-phosphate acylated with (R)-3-hydroxy-15-methylhexadecanoic and (R)-3-hydroxy-13-methyltetradecanoic acids at the C2 and C3 atoms, respectively. It is similar to the monosaccharide biosynthetic precursor of lipopolysaccharide (LPS), so-called lipid X (LX). Unlike LX, LA can be isolated by the treatment of bacteria with organic solvents only after the preliminary acidic hydrolysis of the cells, which suggests that LA might be strongly, probably chemically, linked to other components of the outer membrane. However, LPS cannot be such a component, because extraction with phenol-water or phenol-chloroform-petroleum ether mixtures in high yields (5.34% and 0.5%, respectively) leads to preparations that do not contain 3-deoxy-D-manno-oct-2-ulopyranosonic acid, 3-hydroxyalkanoic acids, or LA.

Complete Lipopolysaccharide of Plesiomonas shigelloides O74:H5 (Strain CNCTC 144/92). 2. Lipid A, Its Structural Variability, the Linkage to the Core Oligosaccharide, and the Biological Activity of the Lipopolysaccharide,

Plesiomonas shigelloides is a Gram-negative bacterium associated with waterborne infections, which is common in tropical and subtropical habitats. Contrary to the unified antigenic classification of P. shigelloides, data concerning the structure and activity of their lipopolysaccharides (LPS and endotoxin) are limited. This study completes the structural investigation of phenol- and water-soluble fractions of P. shigelloides O74 (strain CNCTC 144/92) LPS with the emphasis on lipid A heterogeneity, describing the entire molecule and some of its biological in vitro activities. Structures of the lipid A and the affinity-purified decasaccharide obtained by de-N,O-acylation of P. shigelloides O74 LPS were elucidated by chemical analysis combined with electrospray ionization multiple-stage mass spectrometry (ESI-MS(n)), MALDI-TOF MS, and NMR spectroscopy. Lipid A of P. shigelloides O74 is heterogeneous, and three major forms have been identified. They all were asymmetric, phosphorylated, and hexaacylated, showing different acylation patterns. The beta-GlcpN4P-(1-->6)-alpha-GlcpN1P disaccharide was substituted with the primary fatty acids: (R)-3-hydroxytetradecanoic acid [14:0(3-OH)] at N-2 and N-2' and (R)-3-hydroxydodecanoic acid [12:0(3-OH)] at O-3 and O-3'. The heterogeneity among the three forms (I-III) of P. shigelloides O74 lipid A was attributed to the substitution of the acyl residues at N-2' and O-3' with the secondary acyls: (I) cis-9-hexadecenoic acid (9c-16:1) at N-2' and 12:0 at O-3', (II) 14:0 at N-2' and 12:0 at O-3', and (III) 12:0 at N-2' and 12:0 at O-3'. The pro-inflammatory cytokine-inducing activities of P. shigelloides O74 LPS were similar to those of Escherichia coli O55 LPS.

Expression of a Porphyromonas gingivalis lipid A palmitylacyltransferase in Escherichia coli yields a chimeric lipid A with altered ability to stimulate interleukin-8 secretion

In Escherichia coli the gene htrB codes for an acyltransferase that catalyses the incorporation of laurate into lipopolysaccharide (LPS) as a lipid A substituent. We describe the cloning, expression and characterization of a Porphyromonas gingivalis htrB homologue. When the htrB homologue was expressed in wild-type E. coli or a mutant strain deficient in htrB, a chimeric LPS with altered lipid A structure was produced. Compared with wild-type E. coli lipid A, the new lipid A species contained a palmitate (C16) in the position normally occupied by laurate (C12) suggesting that the cloned gene performs the same function as E. coli htrB but preferentially transfers the longer-chain palmitic acid that is known to be present in P. gingivalis LPS. LPS was purified from wild-type E. coli, the E. coli htrB mutant strain and the htrB mutant strain expressing the P. gingivalis acyltransferase. LPS from the palmitate bearing chimeric LPS as well as the htrB mutant exhibited a reduced ability to activate human embryonic kidney 293 (HEK293) cells transfected with TLR4/MD2. LPS from the htrB mutant also had a greatly reduced ability to stimulate interleukin-8 (IL-8) secretion in both endothelial cells and monocytes. In contrast, the activity of LPS from the htrB mutant bacteria expressing the P. gingivalis gene displayed wild-type activity to stimulate IL-8 production from endothelial cells but a reduced ability to stimulate IL-8 secretion from monocytes. The intermediate activation observed in monocytes for the chimeric LPS was similar to the pattern seen in HEK293 cells expressing TLR4/MD2 and CD14. Thus, the presence of a longer-chain fatty acid on E. coli lipid A altered the activity of the LPS in monocytes but not endothelial cell assays and the difference in recognition does not appear to be related to differences in Toll-like receptor utilization.

Structural and biological characterization of highly purified hepta-acyl lipid A present in the lipopolysaccharide of the Salmonella enterica sv. Minnesota Re deep rough mutant strain R595

One major component of the Salmonella enterica sv. Minnesota Re deep rough mutant (strain R595) lipopolysaccharide is hepta-acyl lipid A (LA(hepta)). In a recent publication [Tanamoto K-I, Azumi S. Salmonella-type heptaacylated lipid A is inactive and acts as an antagonist of lipopolysaccharide action on human line cells. J Immunol 2000; 164: 3149-3156] the corresponding synthetic hepta-acyl lipid A (compound 516) was reported to be agonistically inactive but to rather suppress pro-inflammatory activation by the endotoxic hexa-acyl lipid A (LA(hexa), compound 506) and S-form LPS from Escherichia coli in the human macrophage-like cell lines THP-1 and U937. These results, however, were in contrast to previous findings with human mononuclear cells (hMNC) isolated from peripheral blood, in which compound 516 was found to be an agonist, expressing low, but significant, cytokine-inducing activity as compared to LA(hexa). We have investigated the structure of natural LA(hepta) from the S. enterica sv. Minnesota Re deep rough mutant strain (R595) by TLC immunoblot, MALDI-TOF mass spectrometry and NMR spectroscopy. Using these techniques, the structural identity between LA(hepta) and the synthetic compound 516 was confirmed. In corroboration of previous findings with studies employing compound 516, purified LA(hepta) was found to induce the production of TNF-alpha, IL-1beta and IL-6 in hMNC, thus displaying moderate agonistic activity. Furthermore, we showed that LA(hepta) agonistically activated nuclear translocation of NF-kappaB in THP-1 cells, thus clearly ruling out the possibility that LA(hepta) is an antagonist and that its biological activity is influenced by the type of human myeloid cells used for testing endotoxicity (hMNC versus THP-1 cells).

Purification and characterization of deacylated and/or palmitoylated lipid A species unique to Salmonella enterica serovar Typhimurium

The Salmonella enterica serovar Typhimurium virulence gene products PhoP/PhoQ sense host microenvironments to regulate the expression of a lipid A 3-O-deacylase, PagL, and a lipid A palmitoyltransferase, PagP. Therefore, deacylation and/or palmitoylation of lipid A could occur in Salmonellae adapted to host environments. The PhoP/PhoQ-regulated modification of lipid A alters host recognition and signaling, and may play an important role in host defense against Salmonellae infection. Here we report the purification and characterization of modified lipid A species. Deacylated lipid A, deacylated and palmitoylated lipid A, and palmitoylated lipid A species were generated in Escherichia coli cells heterologously expressing salmonellae PagL and/or PagP, and then purified by sequential thin-layer chromatography. The purified lipid A species showed m/z values that correspond to single lipid A species on mass spectrometry analysis. The modified lipid A species showed reduced ability to induce cellular signaling through Toll-like receptor 4, suggesting a specific function of the lipid A modifications in the pathogenesis of salmonellae infection.

[Characterization of the lipopolysaccharide from Rahnella aquatilis 1-95]

The lipopolysaccharide from the freshwater bacterium Rahnella aquatilis 1-95 has been isolated and investigated for the first time. The structural components of the lipopolysaccharide molecule: lipid A, core oligosaccharide, and O-specific polysaccharide were isolated by mild acidic hydrolysis. In lipid A, 3-hydroxytetradecanoic and tetradecanoic acids were found to be the predominant fatty acids. In the core oligosaccharide, galactose, arabinose, fucose, and an unidentified component were shown to be the major monosaccharides. The O-specific polysaccharide consists of a regularly repeating trisaccharide unit with the acyl and phosphate following structure: [structure: see text] groups have been shown to be responsible for the toxic and pyrogenic properties of the lipopolysaccharide of R. aquatilis.

[The structure of uncommon lipid A from the marine bacterium Marinomonas communis ATCC 27118T]

Lipid A was obtained in a high yield (27%) by the hydrolysis of lipopolysaccharide from the marine gamma proteobacterium Marinomonas communis ATCC 27118T with 1% AcOH. Using chemical analysis and ID and 2D NMR spectroscopic and fast atom bombardment mass spectrometric methods, it was shown to be beta-(1',6)-linked D-glucosaminobiose 1-phosphate acylated with (R)-3-dodecanoyl- or (R)-3-decanoyloxydecanoic acid, (R)-3-[(R)-3-hydroxydecanoyloxy)]decanoic acid, and (R)-3-hydroxydecanoic acid at the C2, C2' and C3 positions, respectively. Uncommon structural peculiarities (a low acylation and phosphorylation degree) of the M. communis lipid A in comparison with those of terrestrial bacteria may be of pharmacological interest. The potential physiological meaning of this lipid A and compounds of similar structure are discussed.

Microextraction of bacterial lipid A: easy and rapid method for mass spectrometric characterization

Endotoxins (lipopolysaccharides) are the main components of Gram-negative bacterial outer membranes. A quick and simple way to isolate their lipid region (lipid A) directly from whole bacterial cells was devised. This method using hot ammonium-isobutyrate solvent was applied to small quantities of cells and proved to be indispensable when a rapid characterization of lipid A structure by mass spectrometry was required. Biological activities of endotoxins are directly related to the lipid A structures, which vary greatly with cell growth conditions. This method is suitable for rough- and smooth-type bacteria and very efficient for screening variations in lipid A structures. Data are acquired in a few hours and avoid the use of phenol in extraction.

Complete structural characterization of the lipid A fraction of a clinical strain of B. cepacia genomovar I lipopolysaccharide

Burkholderia cepacia, a Gram-negative bacterium ubiquitous in the environment, is a plant pathogen causing soft rot of onions. This microorganism has recently emerged as a life-threatening multiresistant pathogen in cystic fibrosis patients. An important virulence factor of B. cepacia is the lipopolysaccharide (LPS) fraction. Clinical isolates and environmental strains possess LPS of high inflammatory nature, which induces a high level production of cytokines. For the first time, the complete structure of the lipid A components isolated from the lipopolysaccharide fraction of a clinical strain of B. cepacia is described. The structural studies carried out by selective chemical degradations, MS, and NMR spectroscopy revealed multiple species differing in the acylation and in the phosphorylation patterns. The highest mass species was identified as a penta-acylated tetrasaccharide backbone containing two phosphoryl-arabinosamine residues in addition to the archetypal glucosamine disaccharide [Arap4N-l-beta-1-P-4-beta-D-GlcpN-(1-6)-alpha-D-GlcpN-1-P-1-beta-L-Arap4N]. Lipid A fatty acids substitution was also deduced, with two 3-hydroxytetradecanoic acids 14:0 (3-OH) in ester linkage, and two 3-hydroxyhexadecanoic acids 16:0 (3-OH) in amide linkage, one of which was substituted by a secondary 14:0 residue at its C-3. Other lipid A species present in the mixture and exhibiting lower molecular weight lacked one or both beta-L-Arap4N residues.

Novel modification of lipid A of Francisella tularensis

We have investigated the lipid A of Francisella tularensis subsp. holarctica strain 1547-57, a type B strain, by using matrix-assisted laser desorption ionization-time-of-flight mass spectrometry, nanoelectrospray quadrupole ion-trap mass spectrometry, and chemical methods. In accordance with the previously published structures of the lipid A from F. tularensis live vaccine strain (LVS) (ATCC 29684) (E. Vinogradov et al., Eur. J. Biochem. 269:6112-6118, 2002), all of the major lipid A forms from strain 1547-57 were tetraacylated. As in the LVS strain, the major fatty acids detected in the F. tularensis 1547-57 lipid A sample included 3-hydroxyoctadecanoic acid, 3-hydroxyhexadecanoic acid, hexadecanoic acid, and tetradecanoic acid. However, several of the lipid A components present in strain 1547-57 were of higher molecular weight than the previously published structures. A major component with an M(r) of 1,666 was found to contain three C(18:0)(3-OH) fatty acids, one C(16:0) fatty acid, one phosphate group, and one 161-Da moiety. This 161-Da moiety could be removed from the lipid A by treatment with aqueous hydrofluoric acid and was identified as galactosamine following peracetylation and analysis by gas chromatography-mass spectrometry. Detailed investigations of the M(r)-1,666 species by ion-trap mass spectrometry with multiple stages of fragmentation suggested that the galactosamine-1-phosphate was linked to the reducing terminus of the lipid A. Similar to the modification of lipid A with arabinosamine, lipopolysaccharide species from F. tularensis containing a phosphate-linked galactosamine could potentially influence its intracellular survival by conferring resistance to antimicrobial peptides.

Lipid A components from Pseudomonas aeruginosa PAO1 (serotype O5) and mutant strains investigated by electrospray ionization ion-trap mass spectrometry

The lipid A components of the Pseudomonas aeruginosa strains PAO1 (wild-type) and derived mutants PAO1 algC::tet and PAO1 PDO100 were isolated after mild acetic acid hydrolysis of LPS. Their structural heterogeneities were characterized using electrospray ionization (ESI) ion-trap mass spectrometry (MS) with direct infusion in the negative ion mode without prior derivatization. The ESI-mass spectra revealed monophosphorylated molecules corresponding to known tetra-, penta- and hexaacylated structures of P. aeruginosa lipid A. The MS/MS fragmentation patterns allowed the location of fatty acyl chains on the disaccharide backbone of lipid A. In addition, a hexaacylated lipid A containing a hexadecanoyl chain was detected for the first time in strain P. aeruginosa PAO1. With multiple stages of fragmentation (MS(n)), the position of this hexadecanoyl chain O-linked to the decanoyl chain at the C-3(') position of the glucosamine backbone was determined. This sensitive method is suitable to reveal lipid A heterogeneity, i.e. the nature, number and distribution of acyl chains, without prior lipopolysaccharide purification. The lipid A from mutant strains were also characterized and significant differences were shown in the abundance of monophosphorylated lipid A components between the wild-type and the mutant strains.

Structural analysis of lipid A from Escherichia coli O157:H7:K- using thin-layer chromatography and ion-trap mass spectrometry

Rapid separation and structural identification of lipid A from Escherichia coli were performed using thin-layer chromatography (TLC) and mass spectrometry (MS). After the resolved spot of the lipid A had been scraped from TLC plate, the sample was re-extracted from the removed powder with chloroform-methanol (2 : 1, v/v) and analyzed by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and electrospray ionization (ESI) ion-trap MS. For detailed structural characterization, multiple-stage mass analysis (MS(4)) of the major species in ESI-MS/MS provided important information about the series of fragment ions. The dominant fragment ions in each MS stage were produced from the loss of fatty acyl groups mainly driven by charge-remote processes, and this information about the fragment ions can be used to deduce the composition or the position of the fatty acid substituent in the lipid A. In contrast, MALDI-TOFMS indicated that fragmentation resulted from charge-driven processes. Molecular mass profiling and fragmentation analysis provides essential information for clarifying the detailed structure of the lipid A from E. coli O157:H7:K(-).

A methylated phosphate group and four amide-linked acyl chains in leptospira interrogans lipid A. The membrane anchor of an unusual lipopolysaccharide that activates TLR2

Leptospira interrogans differs from other spirochetes in that it contains homologs of all the Escherichia coli lpx genes required for the biosynthesis of the lipid A anchor of lipopolysaccharide (LPS). LPS from L. interrogans cells is unusual in that it activates TLR2 rather than TLR4. The structure of L. interrogans lipid A has now been determined by a combination of matrix-assisted laser desorption ionization time-of-flight mass spectrometry, NMR spectroscopy, and biochemical studies. Lipid A was released from LPS of L. interrogans serovar Pomona by 100 degrees C hydrolysis at pH 4.5 in the presence of SDS. Following purification by anion exchange and thin layer chromatography, the major component was shown to have a molecular weight of 1727. Mild hydrolysis with dilute NaOH reduced this to 1338, consistent with the presence of four N-linked and two O-linked acyl chains. The lipid A molecules of both the virulent and nonvirulent forms of L. interrogans serovar Icterohaemorrhagiae (strain Verdun) were identical to those of L. interrogans Pomona by the above criteria. Given the selectivity of L. interrogans LpxA for 3-hydroxylaurate, we propose that L. interrogans lipid A is acylated with R-3-hydroxylaurate at positions 3 and 3' and with R-3-hydroxypalmitate at positions 2 and 2'. The hydroxyacyl chain composition was validated by gas chromatography and mass spectrometry of fatty acid methyl esters. Intact hexa-acylated lipid A of L. interrogans Pomona was also analyzed by NMR, confirming the presence a beta-1',6-linked disaccharide of 2,3-diamino-2,3-dideoxy-d-glucopyranose units. Two secondary unsaturated acyl chains are attached to the distal residue. The 1-position of the disaccharide is derivatized with an axial phosphate moiety, but the 4'-OH is unsubstituted. (1)H and (31)P NMR analyses revealed that the 1-phosphate group is methylated. Purified L. interrogans lipid A is inactive against human THP-1 cells but does stimulate tumor necrosis factor production by mouse RAW264.7 cells.

Chemical structure and immunobiological activity of lipid A from Prevotella intermedia ATCC 25611 lipopolysaccharide

The novel chemical structure and immunobiological activities of Prevotella intermedia ATCC 25611 lipid A were investigated. A lipopolysaccharide (LPS) preparation of P. intermedia was extracted using a phenol-chloroform-petroleum ether method, after which its purified lipid A was prepared by weak acid hydrolysis followed by chromatographic separations. The lipid A structure was determined by mass spectrometry and nuclear magnetic resonance to be a diglucosamine backbone with a phosphate at the 4-position of the non-reducing side sugar, as well as five fatty acids containing branched long chains. It was similar to that of Bacteroides fragilis and Porphyromonas gingivalis, except for the phosphorylation site. P. intermedia lipid A induced weaker cytokine production and NF-kappaB activation in murine cells via Toll-like receptor (TLR) 4 as compared to Escherichia coli synthetic lipid A (compound 506). Our results indicate that P. intermedia lipid A activates cells through a TLR4-dependent pathway similar to E. coli-type lipid A, even though these have structural differences.

Mice intradermally-inoculated with the intact lipopolysaccharide, but not the lipid A or O-chain, from Francisella tularensis LVS rapidly acquire varying degrees of enhanced resistance against systemic or aerogenic challenge with virulent strains of the pathogen

The present study examines the relationship between the structure and important biological effects of the lipopolysaccharide (LPS) of the intracellular bacterial pathogen, Francisella tularensis LVS. It shows that treating mice with sub-immunogenic amounts of intact F. tularensis LPS rapidly induces an enhanced resistance to intradermal or aerogenic challenge with strains of the pathogen of varying virulence. However, neither the free Lipid A nor core-O-chain produced by mild acid hydrolysis of LPS appeared able to elicit this host defense mechanism.

Quadrupole ion-trap mass spectrometry to locate fatty acids on lipid A from Gram-negative bacteria

The structure of lipid A released by mild acid hydrolysis from lipopolysaccharide from two strains of Shigella flexneri with different degrees of acylation was characterized using electrospray ionization (ESI) and ion-trap mass spectrometry. The lipid A was analyzed underivatized with ESI in negative-ion mode. With multiple stages of fragmentation (MS(n)), both the degree of acylation and the positions of the fatty acids on the disaccharide backbone could be determined. It was possible to determine the degree of acylation by the MS(n) technique, where in each MS stage the parent ion was an ion where one fatty acid had been eliminated. One way to determine the location of the fatty acids was by identifying cross-ring fragments of the reducing sugar from parent ions containing different numbers of fatty acids. Another was by identifying a possible charge-driven release of fatty acids situated close to a phosphate group. The fatty acids were otherwise eliminated by a charge-remote fragmentation mechanism. The combined data show the usefulness of ion-trap mass spectrometers for this type of analysis.

Lipid A structure of Pseudoalteromonas haloplanktis TAC 125: use of electrospray ionization tandem mass spectrometry for the determination of fatty acid distribution

The use of electrospray Ionization (ESI) tandem mass spectrometry (MS/MS) for the structural determination of the lipid A components of the psychrophilic bacterium Pseudoalteromonas haloplanktis TAC 125 is reported. The lipid A contains the classical bisphosphorylated beta-(1' --> 6)-linked D-glucosamine disaccharide with 3-hydroxydodecanoyl residues (12 : 0 (3-OH)) linked both as esters and amides to 2', 3' (distal glucosamine) and 2, 3 positions (proximal glucosamine) of the sugar backbone. The hydroxyl of 12 : 0 (3-OH) fatty acid linked at the 3' position is esterified by a dodecanoyl residue (12 : 0). In addition to the pentaacyl component, a minor tetraacyl lipid A, lacking the acyl residue at position 3, was also found in the lipid A fraction. The advantage of this MS technique for the investigation of the intra-ring fragmentation, which is useful for the determination of fatty acyl residue distribution on each glucosamine unit, is emphasized.

Structural determination of lipid A of the lipopolysaccharide from Pseudomonas reactans. A pathogen of cultivated mushrooms

The chemical structure of lipid A from the lipopolysaccharide of the mushroom-associated bacterium Pseudomonas reactans, a pathogen of cultivated mushroom, was elucidated by compositional analysis and spectroscopic methods (MALDI-TOF and two-dimensional NMR). The sugar backbone was composed of the beta-(1'-->6)-linked d-glucosamine disaccharide 1-phosphate. The lipid A fraction showed remarkable heterogeneity with respect to the fatty acid and phosphate composition. The major species are hexacylated and pentacylated lipid A, bearing the (R)-3-hydroxydodecanoic acid [C12:0 (3OH)] in amide linkage and a (R)-3-hydroxydecanoic [C10:0 (3OH)] in ester linkage while the secondary fatty acids are present as C12:0 and/or C12:0 (2-OH). A nonstoichiometric phosphate substitution at position C-4' of the distal 2-deoxy-2-amino-glucose was detected. Interestingly, the pentacyl lipid A is lacking a primary fatty acid, namely the C10:0 (3-OH) at position C-3'. The potential biological meaning of this peculiar lipid A is also discussed.

Structural and biological characterisation of a novel tetra-acyl lipid A from Escherichia coli F515 lipopolysaccharide acting as endotoxin antagonist in human monocytes

We here report on the structural analysis of a novel tetra-acyl lipid A (LA (tetra) ) isolated from Escherichia coli deep rough (Re)-mutant strain F515. In addition to the biologically active hexa-acyl E. coli-type lipid A (compound 506), this incompletely acylated lipid A was found to be also present in the native LPS. Its structure was studied without further derivatisation by chemical analysis, matrix-assisted laser desorption/ionization mass spectrometry, and one- and two-dimensional (1)H- and (13)C-NMR spectroscopy. It was found to be structurally distinct from the tetra-acyl lipid A biosynthetic precursor Ia (compound 406) in lacking the primary (R)-3-hydroxytetradecanoic acid 14:0(3-OH) in position 3' ester-linked to the 'non-reducing' glucosamine (GlcN II). The hydroxyl group at the (R)-3-hydroxytetradecanoic acid attached to position 2' of GlcN II was found to be substituted by dodecanoic acid (12:0), thus forming a dodecanoyloxytetradecanoyl residue 14:0[3-O(12:0)]. The acylation pattern at the 'reducing' GlcN I was identical to that of compound 406 in having two primary (R)-3-hydroxy tetradecanoic acid residues [14:0(3-OH)] attached to positions 3 (ester-linked) and 2 (amide-linked), respectively. In human mononuclear cells (hMNC) the new LA (tetra) antagonized LPS-induced release of interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor (TNF) in a dose-dependent manner with identical antagonistic potency as compared with compound 406. Also like compound 406, it was found to be an agonist in murine macrophage-like J774.1 cells.

The Neisseria gonorrhoeae lpxLII gene encodes for a late-functioning lauroyl acyl transferase, and a null mutation within the gene has a significant effect on the induction of acute inflammatory responses

LPS is a fundamental constituent of the outer membrane of all Gram-negative bacteria, and the lipid A domain plays a central role in the induction of inflammatory responses. We identified genes of the Neisseria gonorrhoeae lipid A biosynthetic pathway by searching the complete gonococcal genome sequence with sequences of known enzymes from other species. The lpxLII gene was disrupted by an insertion-deletion in an attenuated aroA mutant of the gonococcal strain MS11. Lipopolysaccharide (LPS) and lipid A analysis demonstrated that the lpxLII mutant had synthesized an altered LPS molecule lacking a single lauric fatty acid residue in the GlcN II of the lipid A backbone. LPS of the lpxLII mutant had a markedly reduced ability to induce the proinflammatory cytokines tumour necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-6 and IL-8 from human macrophages and IL-8 from polymorphonuclear cells. This study demonstrates that the lpxLII gene in gonococci encodes for a late-functioning lauroyl acyl transferase that adds a lauric acid at position 2' in the lipid A backbone. The presence of lauric acid at such a position appears to be crucial for the induction of full inflammatory responses by N. gonorrhoeae LPS.

Helicobacter pylori lipopolysaccharide from type I, but not type II strains, stimulates apoptosis of cultured gastric mucosal cells

The cag pathogenicity island (cag PAI) genes are a major determinant of virulence of Helicobacter pylori (Hp). Lipopolysaccharide (LPS) purified from the cag PAI-positive (type I) strains induced apoptosis of primary cultures of guinea pig gastric mucosal cells. Lipid A catalyzed this apoptosis. These cells expressed the Toll-like receptor 4 (TLR4) mRNA and its protein, and type I Hp LPS phosphorylated transforming growth factor beta-activated kinase 1 (TAK1) and TAK1-binding protein 1 (TAB1) in association with up-regulation of the TLR4 expressions, suggesting that type I Hp LPS evoked distinct TLR4 signaling. In contrast, Hp LPS from type II strains with complete or partial deletion of the cag PAI genes did not phosphorylate TAK1 and TAB1 and failed to induce apoptosis. Accelerated apoptosis of gastric epithelial cells is one of the important events relevant to chronic, atrophic gastritis caused by Hp infection. The difference in proapoptotic action of LPS between the type I and II strains may support an important role of the cag PAI genes in the pathogenesis of gastric lesions caused by Hp infection.

Biological properties of lipid A isolated from Flavobacterium meningosepticum

The biological properties of the lipid A from Flavobacterium meningosepticum, which we recently isolated and whose complete chemical structure has been determined (H. Kato, T. Iida, Y. Haishima, A. Tanaka, and K. Tanamoto. J. Bacteriol. 180:3891--3899, 1998), were studied. The lipid A exhibited generally moderate activity compared to Salmonella enterica subsp. enterica serovar abortus equi lipopolysaccharide (LPS) used as a control in the assay systems tested; lethal toxicity in galactosamine-sensitized mice, mitogenicity in mouse spleen cells, induction of tumor necrosis factor alpha (TNF-alpha) release from mouse peritoneal macrophages and J774-1 mouse macrophage-like and human THP-1 line cells, nitric oxide induction activity from J774-1 cells, and Limulus gelation activity. The moderate activity of the F. meningosepticum lipid A may be explained by its unique fatty acid composition and the lack of a phosphate group in position 4'. It is noteworthy that the lipid A apparently induced TNF-alpha release from peritoneal macrophages in LPS-unresponsive C3H/HeJ mice and that the activation was suppressed by the LPS-specific antagonist, succinylated lipid A precursor. Significant splenocyte mitogenicity in C3H/HeJ mice was also observed with the lipid A. Taken together with the previous results concerning Porphyromonas gingivalis lipid A, which has a high level of structural similarity to the lipid A of F. meningosepticum, and the induction of TNF-alpha release in macrophages from C3H/HeJ mice, the lipid A of F. meningosepticum, which has novel fatty acids, may possibly play an role for the activation of C3H/HeJ macrophages.

Characterization of the lipopolysaccharide and structure of the O-specific polysaccharide of the bacterium Pseudomonas syringae pv. atrofaciens IMV 948

Lipopolysaccharide (LPS) was isolated from the phytopathogenic bacterium Pseudomonas syringae pv. atrofaciens IMV 948 by mild extraction of the microbial cells with saline, and the properties, composition, and structure of the LPS were studied. The LPS showed low toxicity in D- galactosamine-sensitized mice and low biological activity in plants. Structural components of LPS--lipid A, core oligosaccharide, and O-specific polysaccharide (OPS)--were obtained by mild acid degradation and characterized. The lipid A contained fatty acids 3-HO-C10:0, C12:0, 2-HO-C12:0, 3-HO-C12:0, C16:0, C16:1, C18:0, and C18:1, as well as components of the hydrophilic moiety: GlcN, ethanolamine, phosphate, and phosphoethanolamine. The LPS core contained components typical of pseudomonads: glucose, rhamnose (Rha), L-glycero-D-manno-heptose, GlcN, GalN, 2-keto-3-deoxy-D-manno-octonic acid, alanine, and phosphate. The OPS consisted of L-Rha and D-GlcNAc in the ratio 4 : 1 and was structurally heterogeneous. The main pentasaccharide repeating unit of the OPS has the following structure: [structure see text]. Immunochemical studies showed that P. syringae pv. atrofaciens IMV 948 is serologically separate from other P. syringae strains, including those that have structurally similar OPS.

Induction of innate immune responses by Escherichia coli and purified lipopolysaccharide correlate with organ- and cell-specific expression of Toll-like receptors within the human urinary tract

Mucosal epithelial linings function as physical barriers against microbes. In addition, they participate in the first line of host defence by production of a variety of proinflammatory mediators when exposed to microbes and microbial agents. Here, we use a human urinary tract infection model to demonstrate that organ- and cell-specific innate responses induced by lipopolysaccharides (LPS) present on Gram-negative bacteria correlates with the expression of Toll-like receptor 4 (TLR4). The presence of TLR4 on human bladder epithelial cells enables them to rapidly respond to bacterial infections in vitro and in vivo. In contrast, TLR4 is not expressed on human proximal tubule cells isolated from the renal cortex, which may explain the cortical localization of bacteria in pyelonephritis. TLR4-negative renal epithelial cells, A498, are non-responsive to purified LPS, however, they respond to viable bacteria via a mannose-sensitive attachment-mediated pathway. To identify LPS components recognised by bladder epithelial cells, a bacterial lipid A mutant and LPS of different chemotypes were tested. Full interleukin 8 induction required hexa-acylated lipid A and was decreased by between 50% and 70% in the presence of O-antigen. Taken together, we propose that multiple independent pathways, which are organ- and cell-specifically expressed, mediate bacterial recognition and determine the outcome of innate responses to infection.

Two-dimensional NMR spectroscopy and structures of six lipid A species from Rhizobium etli CE3. Detection of an acyloxyacyl residue in each component and origin of the aminogluconate moiety

The chemical structures of six lipid A species (A, B, C, D-1, D-2, and E) purified from Rhizobium etli CE3 were investigated by one- and two-dimensional NMR spectroscopy. The R. etli lipid A subtypes each contain an unusual acyloxyacyl residue at position 2' as part of a conserved distal glucosamine moiety but differ in their proximal units. All R. etli lipid A species lack phosphate groups. However, they are derivatized with an alpha-linked galacturonic acid group at position 4', as shown by nuclear Overhauser effect spectroscopy. Component B, which had been not been reported in previous studies, features a beta, 1'-6 linked disaccharide of glucosamine acylated at positions 2, 3, 2', and 3' in a pattern that is typical of lipid A found in other Gram-negative bacteria. D-1 contains an acylated aminogluconate unit in place of the proximal glucosamine residue of B. C and E lack ester-linked beta-hydroxyacyl chains at position 3, as judged by their H-3 chemical shifts, and may be synthesized from B and D-1, respectively, by the R. etli 3-O-deacylase. D-2 is an isomer of D-1 that forms nonenzymatically by acyl chain migration. A may be an elimination product derived from D-1 during hydrolysis at 100 degrees C (pH 4.5), a step needed to release lipid A from lipopolysaccharide. Based on these findings, we propose a biosynthetic scheme for R. etli lipid A in which B is generated first by a variation of the E. coli pathway. The aminogluconate unit of D-1 could then be made from B by enzymatic oxidation of the proximal glucosamine. As predicted by our hypothesis, enzyme(s) can be demonstrated in extracts of R. etli that convert (14)C-labeled B to D-1.

Purification and mass spectrometry of six lipid A species from the bacterial endosymbiont Rhizobium etli. Demonstration of a conserved distal unit and a variable proximal portion

Lipid A of Rhizobium etli CE3 differs dramatically from that of other Gram-negative bacteria. Key features include the presence of an unusual C28 acyl chain, a galacturonic acid moiety at position 4', and an acylated aminogluconate unit in place of the proximal glucosamine. In addition, R. etli lipid A is reported to lack phosphate and acyloxyacyl residues. Most of these remarkable structural claims are consistent with our recent enzymatic studies. However, the proposed R. etli lipid A structure is inconsistent with the ability of the precursor (3-deoxy-D-manno-octulosonic acid)(2)-4'-(32)P-lipid IV(A) to accept a C28 chain in vitro (Brozek, K. A., Carlson, R. W., and Raetz, C. R. H. (1996) J. Biol. Chem. 271, 32126-32136). To re-evaluate the structure, CE3 lipid A was isolated by new chromatographic procedures. CE3 lipid A is now resolved into six related components. Aminogluconate is present in D-1, D-2, and E, whereas B and C contain the typical glucosamine disaccharide seen in lipid A of most other bacteria. All the components possess a peculiar acyloxyacyl moiety at position 2', which includes the ester-linked C28 chain. As judged by mass spectrometry, the distal glucosamine units of A through E are the same, but the proximal units are variable. As described in the accompanying article (Que, N. L. S., Ribeiro, A. A., and Raetz, C. R. H. (2000) J. Biol. Chem. 275, 28017-28027), the discovery of component B suggests a plausible enzymatic pathway for the biosynthesis of the aminogluconate residue found in species D-1, D-2, and E of R. etli lipid A. We suggest that the unusual lipid A species of R. etli might be essential during symbiosis with leguminous host plants.

Structural analysis of the lipopolysaccharide from Chlamydophila psittaci strain 6BC

The lipopolysaccaride of Chlamydophila psittaci 6BC was isolated from tissue culture-grown elementary bodies using a modified phenol/water procedure followed by extraction with phenol/chloroform/light petroleum. Compositional analyses indicated the presence of 3-deoxy-Dmanno-oct-2-ulosonic acid, GlcN, organic bound phosphate and fatty acids in a molar ratio of approximately 3. 3 : 2 : 1.8 : 4.6. Deacylated lipopolysaccharide was obtained after successive microscale treatment with hydrazine and potassium hydroxide, and was then separated by high performance anion-exchange chromatography into two major fractions, the structures of which were determined by 600 MHz NMR spectroscopy as alpha-Kdo-(2-->8)-alpha-Kdo-(2-->4)-alpha-Kdo-(2-->6)-beta-D-GlcpN -(1 -->6)-alpha-D-GlcpN 1,4'-bisphosphate and alpha-Kdo-(2-->4)-[alpha-Kdo-(2-->8)]-alpha-Kdo-(2-->4)-alpha-Kdo-(2- ->6)-beta-D-GlcpN-(1-->6)-alpha-D-GlcpN 1,4'-bisphosphate. The distribution of fatty acids in lipid A was determined by compositional analyses and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry experiments on lipid A and de-O-acylated lipid A. It was shown that the carbohydrate backbone of lipid A is replaced by a complex mixture of fatty acids, including long-chain and branched (R)-configured 3-hydroxy fatty acids, the latter being exclusively present in an amide linkage.

Cutting edge: repurification of lipopolysaccharide eliminates signaling through both human and murine toll-like receptor 2

Toll-like receptor (TLR) 2 has recently been associated with cellular responses to numerous microbial products, including LPS and bacterial lipoproteins. However, many preparations of LPS contain low concentrations of highly bioactive contaminants described previously as "endotoxin protein," suggesting that these contaminants could be responsible for the TLR2-mediated signaling observed upon LPS stimulation. To test this hypothesis, commercial preparations of LPS were subjected to a modified phenol re-extraction protocol to eliminate endotoxin protein. While it did not influence the ability to stimulate cells from wild-type mice, repurification eliminated the ability of LPS to activate cells from C3H/HeJ (Lpsd) mice. Additionally, only cell lines transfected with human TLR4, but not human or murine TLR2, acquired responsiveness to both re-extracted LPS and to a protein-free, synthetic preparation of lipid A. These results suggest that neither human nor murine TLR2 plays a role in LPS signaling in the absence of contaminating endotoxin protein.

Structure of the lipid A of Bordetella hinzii ATCC 51730

Bordetella hinzii has recently been isolated from immunocompromised human hosts. The structure of the lipid A of its endotoxin was investigated using chemical analyses, nuclear magnetic resonnance (NMR), gas liquid chromatography/mass spectrometry (GC/MS), plasma desorption mass spectrometry (PDMS) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The lipid A contains the classical bisphosphorylated beta-(1-->6)-linked D-glucosamine disaccharide with hydroxytetradecanoic acid (C14OH) in amide linkages. The lipid A components of B. pertussis, B. bronchiseptica, and B. parapertussis all differ in their acylation pattern but share a residue of tetradecanoyl-3-hydroxytetradecanoic acid in amide linkage at the C-2' position. However, in the B. hinzii species, the tetradecanoic acid (C14) is stoichiometrically replaced by a 2-hydroxytetradecanoic acid (2-C14OH). In the few reported examples of a hydroxylated fatty acid in this position, the substitutions were only partial. The B. hinzii lipid A differs from that of B. pertussis also by replacement of the hydroxydecanoic acid (C10OH) by hydroxydodecanoic acid (C12OH) and by the presence of a hexadecanoic acid (C16) to give a sixth fatty acid. The lipid A was heterogeneous, being composed of three major molecular species: tetra-, penta- and hexaacylated. The fatty acids in ester linkage were localized by PDMS of the native and alkali-treated lipid A. The lipid A components isolated from the O-chain-linked lipopolysaccharides (LPSs) were shown to be more acylated than those from the O-chain-free LPSs.