Complex O-acetylation in Legionella pneumophila serogroup 1 lipopolysaccharide. Evidence for two genes involved in 8-O-acetylation of legionaminic acid

Lipopolysaccharide of Legionella pneumophila Serogroup 1 Facilitates Interaction with Host Cells

Legionella pneumophila is the primary causative agent of Legionnaires' disease. The mutant-type strain interrupted in the ORF7 gene region responsible for the lipopolysaccharide biosynthesis of the L. pneumophila strain Heysham-1, lacking the O-acetyl groups attached to the rhamnose of the core part, showed a higher surface polarity compared with the wild-type strain. The measurement of excitation energy transfer between fluorophores located on the surface of bacteria and eukaryotic cells showed that, at an early stage of interaction with host cells, the mutant exhibited weaker interactions with Acanthamoeba castellanii cells and THP-1-derived macrophages. The mutant displayed reduced adherence to macrophages but enhanced adherence to A. castellanii, suggesting that the O-acetyl group of the LPS core region plays a crucial role in facilitating interaction with macrophages. The lack of core rhamnose O-acetyl groups made it easier for the bacteria to multiply in amoebae and macrophages. The mutant induced TNF-α production more strongly compared with the wild-type strain. The mutant synthesized twice as many ceramides Cer(t34:0) and Cer(t38:0) than the wild-type strain. The study showed that the internal sugars of the LPS core region of L. pneumophila sg 1 can interact with eukaryotic cell surface receptors and mediate in contacting and attaching bacteria to host cells as well as modulating the immune response to infection.

A novel fold for acyltransferase-3 (AT3) proteins provides a framework for transmembrane acyl-group transfer

Acylation of diverse carbohydrates occurs across all domains of life and can be catalysed by proteins with a membrane bound acyltransferase-3 (AT3) domain (PF01757). In bacteria, these proteins are essential in processes including symbiosis, resistance to viruses and antimicrobials, and biosynthesis of antibiotics, yet their structure and mechanism are largely unknown. In this study, evolutionary co-variance analysis was used to build a computational model of the structure of a bacterial O-antigen modifying acetyltransferase, OafB. The resulting structure exhibited a novel fold for the AT3 domain, which molecular dynamics simulations demonstrated is stable in the membrane. The AT3 domain contains 10 transmembrane helices arranged to form a large cytoplasmic cavity lined by residues known to be essential for function. Further molecular dynamics simulations support a model where the acyl-coA donor spans the membrane through accessing a pore created by movement of an important loop capping the inner cavity, enabling OafB to present the acetyl group close to the likely catalytic resides on the extracytoplasmic surface. Limited but important interactions with the fused SGNH domain in OafB are identified, and modelling suggests this domain is mobile and can both accept acyl-groups from the AT3 and then reach beyond the membrane to reach acceptor substrates. Together this new general model of AT3 function provides a framework for the development of inhibitors that could abrogate critical functions of bacterial pathogens.

Analysis of the Structure and Biosynthesis of the Lipopolysaccharide Core Oligosaccharide of Pseudomonas syringae pv. tomato DC3000

Lipopolysaccharide (LPS), the major component of the outer membrane of Gram-negative bacteria, is important for bacterial viability in general and host-pathogen interactions in particular. Negative charges at its core oligosaccharide (core-OS) contribute to membrane integrity through bridging interactions with divalent cations. The molecular structure and synthesis of the core-OS have been resolved in various bacteria including the mammalian pathogen Pseudomonas aeruginosa. A few core-OS structures of plant-associated Pseudomonas strains have been solved to date, but the genetic components of the underlying biosynthesis remained unclear. We conducted a comparative genome analysis of the core-OS gene cluster in Pseudomonas syringae pv. tomato (Pst) DC3000, a widely used model pathogen in plant-microbe interactions, within the P. syringae species complex and to other plant-associated Pseudomonas strains. Our results suggest a genetic and structural conservation of the inner core-OS but variation in outer core-OS composition within the P. syringae species complex. Structural analysis of the core-OS of Pst DC3000 shows an uncommonly high phosphorylation and presence of an O-acetylated sugar. Finally, we combined the results of our genomic survey with available structure information to estimate the core-OS composition of other Pseudomonas species.

Enterobacterial Common Antigen: Synthesis and Function of an Enigmatic Molecule

The outer membrane (OM) of Gram-negative bacteria poses a barrier to antibiotic entry due to its high impermeability. Thus, there is an urgent need to study the function and biogenesis of the OM. In Enterobacterales, an order of bacteria with many pathogenic members, one of the components of the OM is enterobacterial common antigen (ECA). We have known of the presence of ECA on the cell surface of Enterobacterales for many years, but its properties have only more recently begun to be unraveled. ECA is a carbohydrate antigen built of repeating units of three amino sugars, the structure of which is conserved throughout Enterobacterales. There are three forms of ECA, two of which (ECAPG and ECALPS) are located on the cell surface, while one (ECACYC) is located in the periplasm. Awareness of the importance of ECA has increased due to studies of its function that show it plays a vital role in bacterial physiology and interaction with the environment. Here, we review the discovery of ECA, the pathways for the biosynthesis of ECA, and the interactions of its various forms. In addition, we consider the role of ECA in the host immune response, as well as its potential roles in host-pathogen interaction. Furthermore, we explore recent work that offers insights into the cellular function of ECA. This review provides a glimpse of the biological significance of this enigmatic molecule.

The Role of Legionella pneumophila Serogroup 1 Lipopolysaccharide in Host-Pathogen Interaction

The Legionella pneumophila TF3/1 mutant of the Corby strain, which possesses a point mutation in the active site of the O-acetyltransferase, synthesized the polysaccharide chain with a reduced degree of substitution with O-acetyl groups. The mutant did not produce a high-molecular-weight lipopolysaccharide (LPS) fraction above 12 kDa. The disturbances in LPS synthesis have an effect on the composition of other macromolecules (lipids and proteins), as indicated by differences in the infrared absorption spectra between the L. pneumophila Corby strain and its TF3/1 mutant. The wild-type strain contained less N⁺-CH₃ and C-N groups as well as more CH₃ groups than the mutant. The fatty acid composition showed that the wild type strain synthesized more branched acyl residues (a15:0, i16:0, and a17:0), a less unsaturated acid (16:1), and a straight-chain acid (18:0) than the mutant. The mutant synthesized approximately twice more a long-chain fatty acid (20:0) than the wild type. The main differences in the phospholipids between both strains were found in the classes of phosphatidylcholines and phosphatidylglycerols (PG). Substantial differences in the cell surface topography of these bacteria and their nanomechanical properties were shown by atomic force microscopy (AFM). The wild type strain had no undulated surface and produced numerous vesicles. In the case of the mutant type, the vesicles were not numerous, but there were grooves on the cell surface. The average roughness of the cell surface of the mutant was approximately twofold higher than in the wild-type strain. In turn, the wild-type strain exhibited much better adhesive properties than the mutant. The kinetic study of the interaction between the L. pneumophila strains and Acanthamoeba castellanii monitored by Förster resonance energy transfer revealed a pronounced difference, i.e., almost instantaneous and highly efficient binding of the L. pneumophila Corby strain to the amoeba surface, followed by penetration into the amoeba cells. This process was clearly not as efficient in the case of the mutant. The results point to LPS and, in particular, to the length of the polysaccharide fraction as an important L. pneumophila determinant involved in the process of adhesion to the host cell.

Exploration of the Sialic Acid World

Sialic acids are cytoprotectors, mainly localized on the surface of cell membranes with multiple and outstanding cell biological functions. The history of their structural analysis, occurrence, and functions is fascinating and described in this review. Reports from different researchers on apparently similar substances from a variety of biological materials led to the identification of a 9-carbon monosaccharide, which in 1957 was designated "sialic acid." The most frequently occurring member of the sialic acid family is N-acetylneuraminic acid, followed by N-glycolylneuraminic acid and O-acetylated derivatives, and up to now over about 80 neuraminic acid derivatives have been described. They appeared first in the animal kingdom, ranging from echinoderms up to higher animals, in many microorganisms, and are also expressed in insects, but are absent in higher plants. Sialic acids are masks and ligands and play as such dual roles in biology. Their involvement in immunology and tumor biology, as well as in hereditary diseases, cannot be underestimated. N-Glycolylneuraminic acid is very special, as this sugar cannot be expressed by humans, but is a xenoantigen with pathogenetic potential. Sialidases (neuraminidases), which liberate sialic acids from cellular compounds, had been known from very early on from studies with influenza viruses. Sialyltransferases, which are responsible for the sialylation of glycans and elongation of polysialic acids, are studied because of their significance in development and, for instance, in cancer. As more information about the functions in health and disease is acquired, the use of sialic acids in the treatment of diseases is also envisaged.

Human Anti-Lipopolysaccharid (LPS) antibodies against Legionella with high species specificity

Legionella are Gram-negative bacteria that are ubiquitously present in natural and man-made water reservoirs. When humans inhale aerosolized water contaminated with Legionella, alveolar macrophages can be infected, which may lead to a life-threatening pneumonia called Legionnaires' disease. Due to the universal distribution of Legionella in water and their potential threat to human health, the Legionella concentration in water for human use must be strictly monitored, which is difficult since the standard detection still relies on lengthy cultivation and analysis of bacterial morphology. In this study, an antibody against L. pneumophila has been generated from the naïve human HAL antibody libraries by phage-display for the first time. The panning was performed on whole bacterial cells in order to select antibodies that bind specifically to the cell surface of untreated Legionella. The bacterial cell wall component lipopolysaccharide (LPS) was identified as the target structure. Specific binding to the important pathogenic L. pneumophila strains Corby, Philadelphia-1 and Knoxville was observed, while no binding was detected to seven members of the families Enterobacteriaceae, Pseudomonadaceae or Clostridiaceae. Production of this antibody in the recombinant scFv-Fc format using either a murine or a human Fc part allowed the set-up of a sandwich-ELISA for detection of Legionella cells. The scFv-Fc construct proved to be very stable, even when stored for several weeks at elevated temperatures. A sensitivity limit of 4,000 cells was achieved. The scFv-Fc antibody pair was integrated on a biosensor, demonstrating the specific and fast detection of L. pneumophila on a portable device. With this system, 10,000 Legionella cells were detected within 35 min. Combined with a water filtration/concentration system, this antibody may be developed into a promising reagent for rapid on-site Legionella monitoring.

Review: Conserved and variable structural features in the lipopolysaccharide of Pseudomonas aeruginosa

The review is devoted to recent progress in the structural elucidation of the lipopolysaccharide of the bacterium Pseudomonas aeruginosa, including O-antigen biological repeats, core oligosaccharide, and lipid A. Data on biosynthesis, genetics and serology of the lipopolysaccharide isolated from various P. aeruginosa O-serogroups are discussed in relation to the chemical structures.

Comparative Genomics Reveal That Host-Innate Immune Responses Influence the Clinical Prevalence of Legionella pneumophila Serogroups

Legionella pneumophila is the primary etiologic agent of legionellosis, a potentially fatal respiratory illness. Amongst the sixteen described L. pneumophila serogroups, a majority of the clinical infections diagnosed using standard methods are serogroup 1 (Sg1). This high clinical prevalence of Sg1 is hypothesized to be linked to environmental specific advantages and/or to increased virulence of strains belonging to Sg1. The genetic determinants for this prevalence remain unknown primarily due to the limited genomic information available for non-Sg1 clinical strains. Through a systematic attempt to culture Legionella from patient respiratory samples, we have previously reported that 34% of all culture confirmed legionellosis cases in Ontario (n = 351) are caused by non-Sg1 Legionella. Phylogenetic analysis combining multiple-locus variable number tandem repeat analysis and sequence based typing profiles of all non-Sg1 identified that L. pneumophila clinical strains (n = 73) belonging to the two most prevalent molecular types were Sg6. We conducted whole genome sequencing of two strains representative of these sequence types and one distant neighbour. Comparative genomics of the three L. pneumophila Sg6 genomes reported here with published L. pneumophila serogroup 1 genomes identified genetic differences in the O-antigen biosynthetic cluster. Comparative optical mapping analysis between Sg6 and Sg1 further corroborated this finding. We confirmed an altered O-antigen profile of Sg6, and tested its possible effects on growth and replication in in vitro biological models and experimental murine infections. Our data indicates that while clinical Sg1 might not be better suited than Sg6 in colonizing environmental niches, increased bloodstream dissemination through resistance to the alternative pathway of complement mediated killing in the human host may explain its higher prevalence.

Characterization of legionella lipopolysaccharide

The lipopolysaccharide(LPS) of Legionella spp. is an immuno-dominant antigen and the basis for Legionella pneumophila serogroup classification. The LPS shows a peculiar structure composed of a very hydrophobic lipid A acylated by long chain fatty acids and an O-antigen-specific chain consisting of homopolymeric legionaminic acid. In this chapter we describe a method for the isolation of LPS from L. pneumophila. In the first part we describe the chemical purification, in the second part we outline the application of monoclonal antibody (mAb) in Western blot and immuno-localization by indirect immunofluorescence. This report does not describe physico-chemical methods that analyze the structure of lipopolysaccharide entities.

Distribution of cepacian biosynthesis genes among environmental and clinical Burkholderia strains and role of cepacian exopolysaccharide in resistance to stress conditions

The genus Burkholderia includes strains pathogenic to animals and plants, bioremediators, or plant growth promoters. Genome sequence analyses of representative Burkholderia cepacia complex (Bcc) and non-Bcc strains for the presence of the bce-I gene cluster, directing the biosynthesis of the exopolysaccharide (EPS) cepacian, further extended this previously described cluster by another 9 genes. The genes in the bce-II cluster were named bceM to bceU and encode products putatively involved in nucleotide sugar precursor biosynthesis and repeat unit assembly, modification, and translocation across the cytoplasmic membrane. Disruption of the B. cepacia IST408 bceQ and bceR genes, encoding a putative repeat unit flippase and a glycosyltransferase, respectively, resulted in the abolishment of cepacian biosynthesis. A mutation in the bceS gene, encoding a putative acyltransferase, did not affect EPS production yield significantly but decreased its acetylation content by approximately 20%. Quantitative real-time reverse transcription-PCR experiments confirmed the induction of genes in the bce-I and bce-II clusters in a Burkholderia multivorans EPS producer clinical isolate in comparison to the level for its isogenic EPS-defective strain. Fourier Transform infrared spectroscopy analysis confirmed that the exopolysaccharide produced by 10 Burkholderia isolates tested was cepacian. The ability of Burkholderia strains to withstand desiccation and metal ion stress was higher when bacteria were incubated in the presence of 2.5 g/liter of cepacian, suggesting that this EPS plays a role in the survival of these bacteria by contributing to their ability to thrive in different environments.

Cj1123c (PglD), a multifaceted acetyltransferase from Campylobacter jejuni

Campylobacter jejuni produces both N- and O-glycosylated proteins. Because protein glycosylation contributes to bacterial virulence, a thorough characterization of the enzymes involved in protein glycosylation is warranted to assess their potential use as therapeutic targets and as glyco-engineering tools. We performed a detailed biochemical analysis of the molecular determinants of the substrate and acyl-donor specificities of Cj1123c (also known as PglD), an acetyltransferase of the HexAT superfamily involved in N-glycosylation of proteins. We show that Cj1123c has acetyl-CoA-dependent N-acetyltransferase activity not only on the UDP-4-amino-4,6-dideoxy-GlcNAc intermediate of the N-glycosylation pathway but also on the UDP-4-amino-4,6-dideoxy-AltNAc intermediate of the O-glycosylation pathway, implying functional redundancy between both pathways. We further demonstrate that, despite its somewhat relaxed substrate specificity for N-acetylation, Cj1123c cannot acetylate aminoglycosides, indicating a preference for sugar-nucleotide substrates. In addition, we show that Cj1123c can O-acetylate UDP-GlcNAc and that Cj1123c is very versatile in terms of acyl-CoA donors as it can use propionyl- and butyryl-CoA instead of acetyl-CoA. Finally, using structural information available for Cj1123c and related enzymes, we identify three residues (H125, G143, and G173) involved in catalysis and (or) acyl-donor specificity, opening up possibilities of tailoring the specificity of Cj1123c for the synthesis of novel sugars.

Random mutagenesis of Legionella pneumophila reveals genes associated with lipopolysaccharide synthesis and recognition by typing monoclonal antibodies

AIMS

To use random mutagenesis for the characterization of Legionella pneumophila lipopolysaccharide (LPS) components and serotypes.

METHODS AND RESULTS

Five strains belonging to different serogroups and/or monoclonal subgroups were mutagenized using a mini-Tn10 transposon. Exactly 11 819 mutants were checked for alterations in LPS using at least 11 monoclonal antibodies (mAbs) that define L. pneumophila serotypes. Among the mutants, five different mini-Tn10 insertions were identified. Four mutants originating from serogroup-1 did not lose their serogroup-specific epitope, but did sustain subtler changes that resulted in switches to different mAb subgroups. In contrast, a mutant from serogroup-6 lost its serogroup-specific epitope, while retaining a serogroup-cross-reacting epitope.

CONCLUSIONS

Random mutagenesis is a valuable tool for LPS epitope mapping. While some characteristics of L. pneumophila LPS can be altered, others appear resistant to mutagenesis. This underscores both the flexibility and rigidity of LPS architecture in L. pneumophila.

SIGNIFICANCE AND IMPACT OF THE STUDY

Losses of L. pneumophila LPS epitopes can result in new serotypes, changes that might escape detection by current DNA-based typing schemes. But, as the frequency of these changes is rare, based upon our observations, serotyping should remain an important tool for identifying L. pneumophila in water systems that are implicated in human infection.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update covering the period 2001-2002

This review is the second update of the original review on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates that was published in 1999. It covers fundamental aspects of the technique as applied to carbohydrates, fragmentation of carbohydrates, studies of specific carbohydrate types such as those from plant cell walls and those attached to proteins and lipids, studies of glycosyl-transferases and glycosidases, and studies where MALDI has been used to monitor products of chemical synthesis. Use of the technique shows a steady annual increase at the expense of older techniques such as FAB. There is an increasing emphasis on its use for examination of biological systems rather than on studies of fundamental aspects and method development and this is reflected by much of the work on applications appearing in tabular form.

Biosynthesis of CMP-N,N'-diacetyllegionaminic acid from UDP-N,N'-diacetylbacillosamine in Legionella pneumophila

Legionaminic acid is a nine-carbon alpha-keto acid that is similar in structure to other members of the sialic acid family that includes neuraminic acid and pseudaminic acid. It is found as a component of the lipopolysaccharide in several bacterial species and is perhaps best known for its presence in the O-antigen of the causative agent of Legionnaires' disease, Legionella pneumophila. In this work, the enzymes responsible for the biosynthesis and activation of N, N'-diacetyllegionaminic acid are identified for the first time. A cluster of three L. pneumophila genes bearing homology to known sialic acid biosynthetic genes ( neuA,B,C) were cloned and overexpressed in Escherichia coli. The NeuC homologue was found to be a hydrolyzing UDP- N, N'-diacetylbacillosamine 2-epimerase that converts UDP- N, N'-diacetylbacillosamine into 2,4-diacetamido-2,4,6-trideoxymannose and UDP. Stereochemical and isotopic labeling studies showed that the enzyme utilizes a mechanism involving an initial anti elimination of UDP to form a glycal intermediate and a subsequent syn addition of water to generate product. This is similar to the hydrolyzing UDP- N-acetylglucosamine 2-epimerase (NeuC) of sialic acid biosynthesis, but the L. pneumophila enzyme would not accept UDP-GlcNAc as an alternate substrate. The NeuB homologue was found to be a N, N'-diacetyllegionaminic acid synthase that condenses 2,4-diacetamido-2,4,6-trideoxymannose with phosphoenolpyruvate (PEP), although the in vitro activity of the recombinant enzyme (isolated as a MalE fusion protein) was very low. The synthase activity was dependent on the presence of a divalent metal ion, and the reaction proceeded via a C-O bond cleavage process, similar to the reactions catalyzed by the sialic acid and pseudaminic acid synthases. Finally, the NeuA homologue was shown to possess the CMP- N, N'-diacetyllegionaminic acid synthetase activity that generates the activated form of legionaminic acid used in lipopolysaccharide biosynthesis. Together, the three enzymes constitute a pathway that converts a UDP-linked bacillosamine derivative into a CMP-linked legionaminic acid derivative.

Evolution of carbohydrate antigens--microbial forces shaping host glycomes?

Many glycans show remarkably discontinuous distribution across evolutionary lineages. These differences play major roles when organisms belonging to different lineages interact as host-pathogen or host-symbiont. Certain lineage-specific glycans have become important signals for multicellular host organisms, which use them as molecular signatures of their pathogens and symbionts through recognition by a toolkit of innate defense molecules. In turn, pathogens have evolved to exploit host lineage-specific glycans and are constantly shaping the glycomes of their hosts. These interactions take place in the face of numerous critical endogenous functions played by glycans within host organisms. Whether due to simple evolutionary divergence or adaptive changes under natural selection resulting from endogenous functional requirements, once different lineages elaborate on differential glycomes these mutual differences provide opportunities for host exploitation and/or pathogen defense between lineages. Such phylogenetic molecular recognition mechanisms will augment and likely contribute to the maintenance of lineage-specific differences in glycan repertoires.

O acetylation of the enterobacterial common antigen polysaccharide is catalyzed by the product of the yiaH gene of Escherichia coli K-12

The carbohydrate component of the enterobacterial common antigen (ECA) of Escherichia coli K-12 occurs primarily as a water-soluble cyclic polysaccharide located in the periplasm (ECA(CYC)) and as a phosphoglyceride-linked linear polysaccharide located on the cell surface (ECA(PG)). The polysaccharides of both forms are comprised of the amino sugars N-acetyl-D-glucosamine (GlcNAc), N-acetyl-D-mannosaminuronic acid (ManNAcA), and 4-acetamido-4,6-dideoxy-D-galactose (Fuc4NAc). These amino sugars are linked to one another to form trisaccharide repeat units with the structure -->3-alpha-D-Fuc4NAc-(1-->4)-beta-D-ManNAcA-(1-->4)-alpha-D-GlcNAc-(1-->. The hydroxyl group in the 6 position of the GlcNAc residues of both ECA(CYC) and ECA(PG) are nonstoichiometrically esterified with acetyl groups. Random transposon insertion mutagenesis of E. coli K-12 resulted in the generation of a mutant defective in the incorporation of O-acetyl groups into both ECA(CYC) and ECA(PG). This defect was found to be due to an insertion of the transposon into the yiaH locus, a putative gene of unknown function located at 80.26 min on the E. coli chromosomal map. Bioinformatic analyses of the predicted yiaH gene product indicate that it is an integral inner membrane protein that is a member of an acyltransferase family of enzymes found in a wide variety of organisms. The results of biochemical and genetic experiments presented here strongly support the conclusion that yiaH encodes the O-acetyltransferase responsible for the incorporation of O-acetyl groups into both ECA(CYC) and ECA(PG). Accordingly, we propose that this gene be designated wecH.

Membrane vesicles shed by Legionella pneumophila inhibit fusion of phagosomes with lysosomes

When cultured in broth to the transmissive phase, Legionella pneumophila infects macrophages by inhibiting phagosome maturation, whereas replicative-phase cells are transported to the lysosomes. Here we report that the ability of L. pneumophila to inhibit phagosome-lysosome fusion correlated with developmentally regulated modifications of the pathogen's surface, as judged by its lipopolysaccharide profile and by its binding to a sialic acid-specific lectin and to the hydrocarbon hexadecane. Likewise, the composition of membrane vesicles shed by L. pneumophila was developmentally regulated, based on binding to the lectin and to the lipopolysaccharide-specific monoclonal antibody 3/1. Membrane vesicles were sufficient to inhibit phagosome-lysosome fusion by a mechanism independent of type IV secretion, since only approximately 25% of beads suspended with or coated by vesicles from transmissive phase wild type or dotA secretion mutants colocalized with lysosomal probes, whereas approximately 75% of beads were lysosomal when untreated or presented with vesicles from the L. pneumophila letA regulatory mutant or E. coli. As observed previously for L. pneumophila infection of mouse macrophages, vesicles inhibited phagosome-lysosome fusion only temporarily; by 10 h after treatment with vesicles, macrophages delivered approximately 72% of ingested beads to lysosomes. Accordingly, in the context of the epidemiology of the pneumonia Legionnaires' disease and virulence mechanisms of Leishmania and Mycobacteria, we discuss a model here in which L. pneumophila developmentally regulates its surface composition and releases vesicles into phagosomes that inhibit their fusion with lysosomes.

Differential inductions of TNF-alpha and IGTP, IIGP by structurally diverse classic and non-classic lipopolysaccharides

The innate immune system recognizes microbes by characteristic molecules like the Gram-negative lipopolysaccharide (LPS). Lipid A (the LPS bioactive moiety) signals through toll-like receptors (TLRs) to induce pro-inflammatory molecules and small GTPases of the p47 family involved in intracellular pathogen control. We tested TNF-alpha and p47-GTPase induction in macrophages using classical LPSs [lipid As with glucosamine backbones, ester- and amide-linked C14:0(3-OH) and C12 to C16 in acyloxyacyl groups] of wild type and mutant Escherichia coli and Yersinia species and non-classical LPSs [lipid As with diaminoglucose, ester-linked 3-OH-fatty acids and C28:0(27-OH) and C23:0(29-OH) in acyloxyacyl groups] of plant endosymbionts (Rhizobium), intracellular pathogens (Brucella and Legionella) and phylogenetically related opportunistic bacteria (Ochrobactrum). Classical but not non-classical LPSs efficiently induced TNF-alpha, IIGP and IGTP p47-GTPase expression. Remarkably, the acyloxyacyl groups in classical LPSs necessary to efficiently induce TNF-alpha were not necessary to induce p47-GTPases, suggesting that different aspects of lipid A are involved in this differential induction. This was confirmed by using PPDM2, a non-endotoxic lipid A-structurally related synthetic glycolipid. Despite their different bioactivity, all types of LPSs signalled through TLR-4 and not through TLR-2. However, whereas TNF-alpha induction was myeloid differentiation factor 88 (MyD88)-dependent, that of p47-GTPases occurred via a MyD88-independent pathway. These observations show that different aspects of the LPS pathogen-associated molecular pattern may be triggering different signalling pathways linked to the same TLR. They also reinforce the hypothesis that non-classical lipid As act as virulence factors by favouring the escape from the innate immune system.

The group B streptococcal sialic acid O-acetyltransferase is encoded by neuD, a conserved component of bacterial sialic acid biosynthetic gene clusters

Nearly two dozen microbial pathogens have surface polysaccharides or lipo-oligosaccharides that contain sialic acid (Sia), and several Sia-dependent virulence mechanisms are known to enhance bacterial survival or result in host tissue injury. Some pathogens are also known to O-acetylate their Sias, although the role of this modification in pathogenesis remains unclear. We report that neuD, a gene located within the Group B Streptococcus (GBS) Sia biosynthetic gene cluster, encodes a Sia O-acetyltransferase that is itself required for capsular polysaccharide (CPS) sialylation. Homology modeling and site-directed mutagenesis identified Lys-123 as a critical residue for Sia O-acetyltransferase activity. Moreover, a single nucleotide polymorphism in neuD can determine whether GBS displays a "high" or "low" Sia O-acetylation phenotype. Complementation analysis revealed that Escherichia coli K1 NeuD also functions as a Sia O-acetyltransferase in GBS. In fact, NeuD homologs are commonly found within Sia biosynthetic gene clusters. A bioinformatic approach identified 18 bacterial species with a Sia biosynthetic gene cluster that included neuD. Included in this list are the sialylated human pathogens Legionella pneumophila, Vibrio parahemeolyticus, Pseudomonas aeruginosa, and Campylobacter jejuni, as well as an additional 12 bacterial species never before analyzed for Sia expression. Phylogenetic analysis shows that NeuD homologs of sialylated pathogens share a common evolutionary lineage distinct from the poly-Sia O-acetyltransferase of E. coli K1. These studies define a molecular genetic approach for the selective elimination of GBS Sia O-acetylation without concurrent loss of sialylation, a key to further studies addressing the role(s) of this modification in bacterial virulence.

Survey of the year 2001 commercial optical biosensor literature

We have assembled references of 700 articles published in 2001 that describe work performed using commercially available optical biosensors. To illustrate the technology's diversity, the citation list is divided into reviews, methods and specific applications, as well as instrument type. We noted marked improvements in the utilization of biosensors and the presentation of kinetic data over previous years. These advances reflect a maturing of the technology, which has become a standard method for characterizing biomolecular interactions.

Epitope mapping of the O-chain polysaccharide of Legionella pneumophila serogroup 1 lipopolysaccharide by saturation-transfer-difference NMR spectroscopy

Two modifications of 5-acetimidoylamino-7-acetamido-3,5,7,9-tetradeoxy-D-glycero-D-galacto-non-2-ulosonic acid (5-N-acetimidoyl-7-N-acetyllegionaminic acid) in the O-chain polysaccharide (OPS) of the Legionella pneumophila serogroup 1 lipopolysaccharide (LPS) concern N-methylation of the 5-N-acetimidoyl group in legionaminic acid. Both N-methylated substituents, the (N,N-dimethylacetimidoyl) amino and acetimidoyl(N-methyl)amino group, could be allocated to one single legionaminic acid residue in the long- and middle-chain OPS, respectively. Using mutants devoid of N-methylated legionaminic acid derivatives, it could be shown that N-methylation of legionaminic acid correlated with the expression of the mAb 2625 epitope. In the present study we investigated the binding of the LPS-specific monoclonal antibody mAb 2625 to isolated OPS with surface-plasmon-resonance biomolecular interaction analysis and saturation-transfer-difference (STD) NMR spectroscopy in order to map the mAb 2625 epitope on a molecular level. It could be demonstrated that the binding affinity of the N-methylated legionaminic acid derivatives was independent from the size of the isolated OPS molecular species. In addition, STD NMR spectroscopic studies with polysaccharide ligands with an average molecular mass of up to 14 kDa revealed that binding was mainly mediated via the N-methylated acetimidoylamino group and via the closely located 7-N-acetyl group of the respective legionaminic acid residue, thus indicating these derivatives to represent the major epitope of mAb 2625.

N-Methylation in polylegionaminic acid is associated with the phase-variable epitope of Legionella pneumophila serogroup 1 lipopolysaccharide. Identification of 5-(N,N-dimethylacetimidoyl)amino and 5-acetimidoyl(N-methyl)amino-7-acetamido-3,5,7,9-tetradeoxynon-2-ulosonic acid in the O-chain polysaccharide

Previously, a phase-variable epitope was detected in the virulent wild-type strain RC1 of Legionella pneumophila serogroup 1 subgroup OLDA using a lipopolysaccharide-specific monoclonal antibody, mAb 2625 [Lüneberg, E., Zähringer, U., Knirel, Y. A., Steinmann, D., Hartmann, M., Steinmetz, I., Rohde, M., Kohl, J. & Frosch, M. (1998) J.Exp. Med. 188, 49-60]. In the present study, an isogenic mutant strain, termed 5215, was constructed by deletion of genes involved in the biosynthesis of the mAb 2625 epitope. Mutant 5215 was as virulent as the parental wild-type RC1 but did not bind mAb 2625. The two strains showed no difference in the core oligosaccharide and lipid A but in the O-chain polysaccharide structure, which is a homopolymer of 5-acetimidoylamino-7-acetamido-3,5,7,9-tetradeoxy-d-glycero-d-galacto-non-2-ulosonic acid (a derivative of legionaminic acid). NMR spectroscopic studies revealed a hitherto unknown modification of bacterial polysaccharides in the wild-type strain, namely N-methylation of the 5-acetimidoylamino group on a single legionaminic acid residue that is located, most likely, proximal to the core oligosaccharide. Two major N-methylated substituents, the (N,N-dimethylacetimidoyl)amino and acetimidoyl(N-methyl) amino groups, could be allocated to the long- and middle-chain O-polysaccharide species, respectively. N-Methylation of legionaminic acid that was absent from the isogenic mutant 5215 and from the spontaneous phase variant 811, correlated with the presence of the mAb 2625 epitope.