NMR-based structural analysis of the complete rough-type lipopolysaccharide isolated from Capnocytophaga canimorsus

Amelioration of autophagy and inflammatory signaling pathways via α-lipoic acid, burdock and bee pollen versus lipopolysaccharide-induced insulin resistance in murine model

Lipopolysaccharide (LPS) has previously been implicated in insulin resistance by generating an innate immune response and activating inflammatory cascades. Many studies have discovered a relationship between high levels of serum LPS and the advancement of diabetic microvascular problems, indicating that LPS may play a role in the control of critical signaling pathways connected to insulin resistance. The current study focused on signaling pathways linked to insulin resistance and explored probable mechanisms of LPS-induced insulin resistance in a murine model. It next looked at the effects of burdock, bee pollen, and -lipoic acid on LPS-induced inflammation and autoimmune defects in rats. LPS intoxication was induced via ip injection for one week in a dose of 10 mg/kg followed by α-lipoic acid, Burdock and bee pollen in an oral treatment for one month. Following that, biochemical and molecular studies were performed. The RNA expression of the regulating genes STAT5A and PTEN was measured. In addition, ATF-4 and CHOP as autophagy biomarkers were also subjected to mRNA quantification. The results demonstrated a considerable improvement in the -lipoic acid, Burdock, and bee pollen treated groups via modifying oxidative stress indicators as well as molecular ones. Furthermore, glucose concentration in serum and α-amylase were also improved upon treatment with the superiority of α-lipoic acid for modulating all estimated parameters. In conclusion: the results declared in the current study suggested that α-lipoic acid could regulate insulin resistance signaling pathways induced by LPS intoxication.

PplD is a de-N-acetylase of the cell wall linkage unit of streptococcal rhamnopolysaccharides

The cell wall of the human bacterial pathogen Group A Streptococcus (GAS) consists of peptidoglycan decorated with the Lancefield group A carbohydrate (GAC). GAC is a promising target for the development of GAS vaccines. In this study, employing chemical, compositional, and NMR methods, we show that GAC is attached to peptidoglycan via glucosamine 1-phosphate. This structural feature makes the GAC-peptidoglycan linkage highly sensitive to cleavage by nitrous acid and resistant to mild acid conditions. Using this characteristic of the GAS cell wall, we identify PplD as a protein required for deacetylation of linkage N-acetylglucosamine (GlcNAc). X-ray structural analysis indicates that PplD performs catalysis via a modified acid/base mechanism. Genetic surveys in silico together with functional analysis indicate that PplD homologs deacetylate the polysaccharide linkage in many streptococcal species. We further demonstrate that introduction of positive charges to the cell wall by GlcNAc deacetylation protects GAS against host cationic antimicrobial proteins.

Shortening the Lipid A Acyl Chains of Bordetella pertussis Enables Depletion of Lipopolysaccharide Endotoxic Activity

Whooping cough, or pertussis, is an acute respiratory infectious disease caused by the Gram-negative bacterium Bordetella pertussis. Whole-cell vaccines, which were introduced in the fifties of the previous century and proved to be effective, showed considerable reactogenicity and were replaced by subunit vaccines around the turn of the century. However, there is a considerable increase in the number of cases in industrialized countries. A possible strategy to improve vaccine-induced protection is the development of new, non-toxic, whole-cell pertussis vaccines. The reactogenicity of whole-cell pertussis vaccines is, to a large extent, derived from the lipid A moiety of the lipopolysaccharides (LPS) of the bacteria. Here, we engineered B. pertussis strains with altered lipid A structures by expressing genes for the acyltransferases LpxA, LpxD, and LpxL from other bacteria resulting in altered acyl-chain length at various positions. Whole cells and extracted LPS from the strains with shorter acyl chains showed reduced or no activation of the human Toll-like receptor 4 in HEK-Blue reporter cells, whilst a longer acyl chain increased activation. Pyrogenicity studies in rabbits confirmed the in vitro assays. These findings pave the way for the development of a new generation of whole-cell pertussis vaccines with acceptable side effects.

The Bacterial Product Violacein Exerts an Immunostimulatory Effect Via TLR8

Violacein, an indole-derived, purple-colored natural pigment isolated from Chromobacterium violaceum has shown multiple biological activities. In this work, we studied the effect of violacein in different immune cell lines, namely THP-1, MonoMac 6, ANA-1, Raw 264.7 cells, as well as in human peripheral blood mononuclear cells (PBMCs). A stimulation of TNF-α production was observed in murine macrophages (ANA-1 and Raw 264.7), and in PBMCs, IL-6 and IL-1β secretion was detected. We obtained evidence of the molecular mechanism of activation by determining the mRNA expression pattern upon treatment with violacein in Raw 264.7 cells. Incubation with violacein caused activation of pathways related with an immune and inflammatory response. Our data utilizing TLR-transfected HEK-293 cells indicate that violacein activates the human TLR8 (hTLR8) receptor signaling pathway and not human TLR7 (hTLR7). Furthermore, we found that the immunostimulatory effect of violacein in PBMCs could be suppressed by the specific hTLR8 antagonist, CU-CPT9a. Finally, we studied the interaction of hTLR8 with violacein in silico and obtained evidence that violacein could bind to hTLR8 in a similar fashion to imidazoquinoline compounds. Therefore, our results indicate that violacein may have some potential in contributing to future immune therapy strategies.

Capnocytophaga canimorsus as Cause of Fatal Sepsis

A rare consequence of dog bites is the infection with Capnocytophaga canimorsus, and only a few cases have been documented. We describe a 41-year-old, formerly healthy woman who died from septic shock and multiorgan failure. It is the first case of a young individual without obvious immunosuppression.

Effects of ozonation on the activity of endotoxin and its inhalation toxicity in reclaimed water

Aerosolized reclaimed water can cause inflammatory responses in lung after inhalation, and endotoxin has been identified as the main inducer. Since the effects of disinfection treatments on endotoxins had conflicting results, this study explored the changes of endotoxin activity and inflammation inducing ability of reference endotoxin, gram-negative bacteria solutions and reclaimed water after ozonation respectively, and found that LAL assay based endotoxin activity and mouse inhalation exposure based inflammation examination had inconsistent results. The excessive ozone could not remove the endotoxin activity, but was able to reduce the inflammation inducing ability of free endotoxin. When treating on gram-negative strains, ozone first released the cell-bound endotoxin and caused the dramatic increase of endotoxin activity. But for the inflammatory response, despite the rapid increase at the very beginning, it immediately dropped back with further ozonation. The endotoxin aggregate size was proposed as a key regulator of the toxicity of endotoxin, which was modified by ozone oxidation. In real reclaimed water, insufficient ozone significantly enhanced the inflammatory response, but when the ozone dosages were large enough, the inflammation could be drawn back to the original level, which was consistent with the observations from pure endotoxin and bacteria. This work demonstrates that the endotoxin activity cannot predict the endotoxin-induced toxicity of ozone treated water, and low dosage of ozone treatment may even increase the health risk of reclaimed water.

Bactericidal/Permeability-Increasing Protein Is an Enhancer of Bacterial Lipoprotein Recognition

Adequate perception of immunologically important pathogen-associated molecular patterns like lipopolysaccharide and bacterial lipoproteins is essential for efficient innate and adaptive immune responses. In the context of Gram-negative infection, bactericidal/permeability-increasing protein (BPI) neutralizes endotoxic activity of lipopolysaccharides, and thus prohibits hyperactivation. So far, no immunological function of BPI has been described in Gram-positive infections. Here, we show a significant elevation of BPI in Gram-positive meningitis and, surprisingly, a positive correlation between BPI and pro-inflammatory markers like TNFα. To clarify the underlying mechanisms, we identify BPI ligands of Gram-positive origin, specifically bacterial lipopeptides and lipoteichoic acids, and determine essential structural motifs for this interaction. Importantly, the interaction of BPI with these newly defined ligands significantly enhances the immune response in peripheral blood mononuclear cells (PBMCs) mediated by Gram-positive bacteria, and thereby ensures their sensitive perception. In conclusion, we define BPI as an immune enhancing pattern recognition molecule in Gram-positive infections.

Solid State NMR Studies of Intact Lipopolysaccharide Endotoxin

Lipopolysaccharides (LPS) are complex glycolipids forming the outside layer of Gram-negative bacteria. Their hydrophobic and heterogeneous nature greatly hampers their structural study in an environment similar to the bacterial surface. We have studied LPS purified from E. coli and pathogenic P. aeruginosa with long O-antigen polysaccharides assembled in solution as vesicles or elongated micelles. Solid-state NMR with magic-angle spinning permitted the identification of NMR signals arising from regions with different flexibilities in the LPS, from the lipid components to the O-antigen polysaccharides. Atomic scale data on the LPS enabled the study of the interaction of gentamicin antibiotic bound to P. aeruginosa LPS, for which we could confirm that a specific oligosaccharide is involved in the antibiotic binding. The possibility to study LPS alone and bound to a ligand when it is assembled in membrane-like structures opens great prospects for the investigation of proteins and antibiotics that specifically target such an important molecule at the surface of Gram-negative bacteria.

Elucidating endotoxin-biomolecule interactions with FRET: extending the frontiers of their supramolecular complexation

Endotoxin has been one of the topical chemical contaminants of major concern to researchers, especially in the field of bioprocessing. This major concern of researchers stems from the fact that the presence of Gram-negative bacterial endotoxin in intracellular products is unavoidable and requires complex downstream purification steps. For instance, endotoxin interacts with recombinant proteins, peptides, antibodies and aptamers and these interactions have formed the foundation for most biosensors for endotoxin detection. It has become imperative for researchers to engineer reliable means/techniques to detect, separate and remove endotoxin, without compromising the quality and quantity of the end-product. However, the underlying mechanism involved during endotoxin-biomolecule interaction is still a gray area. The use of quantitative molecular microscopy that provides high resolution of biomolecules is highly promising, hence, may lead to the development of improved endotoxin detection strategies in biomolecule preparation. Förster resonance energy transfer (FRET) spectroscopy is one of the emerging most powerful tools compatible with most super-resolution techniques for the analysis of molecular interactions. However, the scope of FRET has not been well-exploited in the analysis of endotoxin-biomolecule interaction. This article reviews endotoxin, its pathophysiological consequences and the interaction with biomolecules. Herein, we outline the common potential ways of using FRET to extend the current understanding of endotoxin-biomolecule interaction with the inference that a detailed understanding of the interaction is a prerequisite for the design of strategies for endotoxin identification and removal from protein milieus.

The redefinition of Helicobacter pylori lipopolysaccharide O-antigen and core-oligosaccharide domains

Helicobacter pylori lipopolysaccharide promotes chronic gastric colonisation through O-antigen host mimicry and resistance to mucosal antimicrobial peptides mediated primarily by modifications of the lipid A. The structural organisation of the core and O-antigen domains of H. pylori lipopolysaccharide remains unclear, as the O-antigen attachment site has still to be identified experimentally. Here, structural investigations of lipopolysaccharides purified from two wild-type strains and the O-antigen ligase mutant revealed that the H. pylori core-oligosaccharide domain is a short conserved hexasaccharide (Glc-Gal-DD-Hep-LD-Hep-LD-Hep-KDO) decorated with the O-antigen domain encompassing a conserved trisaccharide (-DD-Hep-Fuc-GlcNAc-) and variable glucan, heptan and Lewis antigens. Furthermore, the putative heptosyltransferase HP1284 was found to be required for the transfer of the third heptose residue to the core-oligosaccharide. Interestingly, mutation of HP1284 did not affect the ligation of the O-antigen and resulted in the attachment of the O-antigen onto an incomplete core-oligosaccharide missing the third heptose and the adjoining Glc-Gal residues. Mutants deficient in either HP1284 or O-antigen ligase displayed a moderate increase in susceptibility to polymyxin B but were unable to colonise the mouse gastric mucosa. Finally, mapping mutagenesis and colonisation data of previous studies onto the redefined organisation of H. pylori lipopolysaccharide revealed that only the conserved motifs were essential for colonisation. In conclusion, H. pylori lipopolysaccharide is missing the canonical inner and outer core organisation. Instead it displays a short core and a longer O-antigen encompassing residues previously assigned as the outer core domain. The redefinition of H. pylori lipopolysaccharide domains warrants future studies to dissect the role of each domain in host-pathogen interactions. Also enzymes involved in the assembly of the conserved core structure, such as HP1284, could be attractive targets for the design of new therapeutic agents for managing persistent H. pylori infection causing peptic ulcers and gastric cancer.

Evidence for a LOS and a capsular polysaccharide in Capnocytophaga canimorsus

Capnocytophaga canimorsus is a dog’s and cat’s oral commensal which can cause fatal human infections upon bites or scratches. Infections mainly start with flu-like symptoms but can rapidly evolve in fatal septicaemia with a mortality as high as 40%. Here we present the discovery of a polysaccharide capsule (CPS) at the surface of C. canimorsus 5 (Cc5), a strain isolated from a fulminant septicaemia. We provide genetic and chemical data showing that this capsule is related to the lipooligosaccharide (LOS) and probably composed of the same polysaccharide units. A CPS was also found in nine out of nine other strains of C. canimorsus. In addition, the genomes of three of these strains, sequenced previously, contain genes similar to those encoding CPS biosynthesis in Cc5. Thus, the presence of a CPS is likely to be a common property of C. canimorsus. The CPS and not the LOS confers protection against the bactericidal effect of human serum and phagocytosis by macrophages. An antiserum raised against the capsule increased the killing of C. canimorsus by human serum thus showing that anti-capsule antibodies have a protective role. These findings provide a new major element in the understanding of the pathogenesis of C. canimorsus.

"Rules of Engagement" of Protein-Glycoconjugate Interactions: A Molecular View Achievable by using NMR Spectroscopy and Molecular Modeling

Understanding the dynamics of protein-ligand interactions, which lie at the heart of host-pathogen recognition, represents a crucial step to clarify the molecular determinants implicated in binding events, as well as to optimize the design of new molecules with therapeutic aims. Over the last decade, advances in complementary biophysical and spectroscopic methods permitted us to deeply dissect the fine structural details of biologically relevant molecular recognition processes with high resolution. This Review focuses on the development and use of modern nuclear magnetic resonance (NMR) techniques to dissect binding events. These spectroscopic methods, complementing X-ray crystallography and molecular modeling methodologies, will be taken into account as indispensable tools to provide a complete picture of protein-glycoconjugate binding mechanisms related to biomedicine applications against infectious diseases.

Inhibition of lipopolysaccharide induced acute inflammation in lung by chlorination

Lipopolysaccharide (LPS, also called endotoxin) is a pro-inflammatory constituent of gram negative bacteria and cyanobacteria, which causes a potential health risk in the process of routine urban application of reclaimed water, such as car wash, irrigation, scenic water refilling, etc. Previous studies indicated that the common disinfection treatment, chlorination, has little effect on endotoxin activity removal measured by Limulus amebocyte lysate (LAL) assay. However, in this study, significant decrease of acute inflammatory effects was observed in mouse lung, while LAL assay still presented a moderate increase of endotoxin activity. To explore the possible mechanisms, the nuclear magnetic resonance (NMR) results showed the chlorination happened in alkyl chain of LPS molecules, which could affect the interaction between LPS and LPS-binding protein. Also the size of LPS aggregates was found to drop significantly after treatment, which could be another results of chlorination caused polarity change. In conclusion, our observation demonstrated that chlorination is effective to reduce the LPS induced inflammation in lung, and it is recommended to use health effect-based methods to assess risk removal of water treatment technologies.

Modification of the 1-Phosphate Group during Biosynthesis of Capnocytophaga canimorsus Lipid A

Capnocytophaga canimorsus, a commensal bacterium of dog's mouth flora causing severe infections in humans after dog bites or scratches, has a lipopolysaccharide (LPS) (endotoxin) with low-inflammatory lipid A. In particular, it contains a phosphoethanolamine (P-Etn) instead of a free phosphate group at the C-1 position of the lipid A backbone, usually present in highly toxic enterobacterial Gram-negative lipid A. Here we show that the C. canimorsus genome comprises a single operon encoding a lipid A 1-phosphatase (LpxE) and a lipid A 1 P-Etn transferase (EptA). This suggests that lipid A is modified during biosynthesis after completing acylation of the backbone by removal of the 1-phosphate and subsequent addition of an P-Etn group. As endotoxicity of lipid A is known to depend largely on the degree of unsubstituted or unmodified phosphate residues, deletion of lpxE or eptA led to mutants lacking the P-Etn group, with consequently increased endotoxicity and decreased resistance to cationic antimicrobial peptides (CAMP). Consistent with the proposed sequential biosynthetic mechanism, the endotoxicity and CAMP resistance of a double deletion mutant of lpxE-eptA was similar to that of a single lpxE mutant. Finally, the proposed enzymatic activities of LpxE and EptA based on sequence similarity could be successfully validated by mass spectrometry (MS)-based analysis of lipid A isolated from the corresponding deletion mutant strains.

Novel structural features of the immunocompetent ceramide phospho-inositol glycan core from Trichomonas vaginalis

The ceramide phosphoinositol glycan core (CPI-GC) of the lipophosphoglycan of Trichomonas vaginalis is a major virulent factor of this common genitourinary parasite. While its carbohydrate composition has been reported before, its structure has remained largely unknown. We isolated the glycan portions of CPI-GC by nitrous acid deamination and hydrofluoric acid treatment and investigated their structures by methylation analysis and 1- and 2-D NMR. We found that the α-anomer of galactose is a major constituent of CPI-GC. The β-anomer was found exclusively at the non-reducing end of CPI-GC side chains. Furthermore the data showed that the rhamnan backbone is more complex than previously thought and that the inositol residue at the reducing end is linked to a 4-linked α-glucuronic acid (GlcA) residue. This appears to be the most striking and novel feature of this GPI-anchor type molecule.

Only a subset of C. canimorsus strains is dangerous for humans

Capnocytophaga canimorsus are gram-negative bacteria living as commensals in the mouth of dogs and cats. C. canimorsus cause rare but life-threatening generalized infections in humans that have been in contact with a dog or a cat. Over the last years we collected 105 C. canimorsus strains from different geographical origins and from severe human infections or healthy dogs. All these strains were analyzed by 16S rDNA sequencing and a phylogenetic tree revealed two main groups of bacteria instead of one with no relation to the geographical origin. This branching was confirmed by the whole-genome sequencing of 10 strains, supporting the evidence of a new Capnocytophaga species in dogs. Interestingly, 19 out of 19 C. canimorsus strains isolated from human infections belonged to the same species. Furthermore, most strains from this species could grow in heat-inactivated human serum (HIHS) (40/46 tested), deglycosylate IgM (48/66) and were cytochrome-oxidase positive (60/66) while most strains from the other species could not grow in HIHS (22/23 tested), could not deglycosylate IgM (33/34) and were cytochrome-oxidase negative (33/34). Here, we propose to call Capnocytophaga canis (Latin: dog) the novel, presumably less virulent dog-hosted Capnocytophaga species and to keep the name C. canimorsus for the species including human pathogens.

A lectin S-domain receptor kinase mediates lipopolysaccharide sensing in Arabidopsis thaliana

The sensing of microbe-associated molecular patterns (MAMPs) triggers innate immunity in animals and plants. Lipopolysaccharide (LPS) from Gram-negative bacteria is a potent MAMP for mammals, with the lipid A moiety activating proinflammatory responses via Toll-like receptor 4 (TLR4). Here we found that the plant Arabidopsis thaliana specifically sensed LPS of Pseudomonas and Xanthomonas. We isolated LPS-insensitive mutants defective in the bulb-type lectin S-domain-1 receptor-like kinase LORE (SD1-29), which were hypersusceptible to infection with Pseudomonas syringae. Targeted chemical degradation of LPS from Pseudomonas species suggested that LORE detected mainly the lipid A moiety of LPS. LORE conferred sensitivity to LPS onto tobacco after transient expression, which demonstrated a key function in LPS sensing and indicated the possibility of engineering resistance to bacteria in crop species.

Glycan-foraging systems reveal the adaptation of Capnocytophaga canimorsus to the dog mouth

Capnocytophaga canimorsus is known to form two kinds of cells on blood agar plates (coccoid and bacillary), evoking phase variation. When grown in coculture with animal cells these bacteria appeared only as bacilli, but in the presence of vancomycin they were round, indicating that coccoid shapes likely result from weakening of the peptidoglycan layer. Polysaccharide utilization locus 5 (PUL5) and sialidase mutant bacteria, unable to retrieve glycans from glycoproteins, grew less than wild-type bacteria and also appeared polymorphic unless GlcNAc was added, suggesting that C. canimorsus is unable to synthesize GlcNAc, an essential component of peptidoglycan. Accordingly, a genome analysis was conducted and revealed that C. canimorsus strain 5 lacks the GlmM and GlmU enzymes, which convert glucosamine into GlcNAc. Expression of the Escherichia coli GlmM together with the acetyltransferase domain of GlmU allowed PUL5 mutant bacteria to grow normally, indicating that C. canimorsus is a natural auxotroph that relies on GlcNAc harvested from the host N-glycoproteins for peptidoglycan synthesis. Mucin, a heavily O-glycosylated protein abundant in saliva, also rescued growth and the shape of PUL5 mutant bacteria. Utilization of mucin was found to depend on Muc, a Sus-like system encoded by PUL9. Contrary to all known PUL-encoded systems, Muc cleaves peptide bonds of mucin rather than glycosidic linkages. Thus, C. canimorsus has adapted to build its peptidoglycan from the glycan-rich dog’s mouth glycoproteins.

Capnocytophaga canimorsus is a bacterium that lives as a commensal in the dog mouth and causes severe infections in humans. In vitro, it forms two kinds of cells (coccoid and bacillary), evoking phase variation. Here, we show that cell rounding likely results from weakening of the peptidoglycan layer due to a shortage of N-acetylglucosamine (GlcNAc). C. canimorsus cannot synthesize GlcNAc because of the lack of key enzymes. In its niche, the dog mouth, C. canimorsus retrieves GlcNAc by foraging glycans from salivary mucin and N-linked glycoproteins through two different apparatuses, Muc and Gpd, both of which are related to the Bacteroides starch utilization system. The Muc system is peculiar in the sense that the enzyme of the complex is a protease and not a glycosylhydrolase, as it cleaves peptide bonds in order to capture glycan chains. This study provides a molecular genetic demonstration for the complex adaptation of C. canimorsus to its ecological niche, the oral cavity of dogs.