The role of WlaRG, WlaTB and WlaTC in lipooligosaccharide synthesis by Campylobacter jejuni strain 81116

Molecular structures mediating adhesion of Campylobacter jejuni to abiotic and biotic surfaces

Microaerophilic, Gram-negative Campylobacter jejuni is the causative agent of campylobacteriosis, the most common bacterial gastrointestinal infection worldwide. Adhesion is the crucial first step in both infection or interaction with the host and biofilm formation, and is a critical factor for bacterial persistence. Here we describe the proteins and other surface structures that promote adhesion to various surfaces, including abiotic surfaces, microorganisms, and animal and human hosts. In addition, we provide insight into the distribution of adhesion proteins among strains from different ecological niches and highlight unexplored proteins involved in C. jejuni adhesion. Protein-protein, protein-glycan, and glycan-glycan interactions are involved in C. jejuni adhesion, with different factors contributing to adhesion to varying degrees under different circumstances. As adhesion is essential for survival and persistence, it represents an interesting target for C. jejuni control. Knowledge of the adhesion process is incomplete, as different molecular and functional aspects have been studied for different structures involved in adhesion. Therefore, it is important to strive for an integration of different approaches to obtain a clearer picture of the adhesion process on different surfaces and to consider the involvement of proteins, glycoconjugates, and polysaccharides and their cooperation.

Recent advances in microscale separation techniques for lipidome analysis

This review paper highlights the recent research on liquid-phase microscale separation techniques for lipidome analysis over the last 10 years, mainly focusing on capillary liquid chromatography (LC) and capillary electrophoresis (CE) coupled with mass spectrometry (MS). Lipids are one of the most important classes of biomolecules which are involved in the cell membrane, energy storage, signal transduction, and so on. Since lipids include a variety of hydrophobic compounds including numerous structural isomers, lipidomes are a challenging target in bioanalytical chemistry. MS is the key technology that comprehensively identifies lipids; however, separation techniques like LC and CE are necessary prior to MS detection in order to avoid ionization suppression and resolve structural isomers. Separation techniques using μm-scale columns, such as a fused silica capillary and microfluidic device, are effective at realizing high-resolution separation. Microscale separation usually employs a nL-scale flow, which is also compatible with nanoelectrospray ionization-MS that achieves high sensitivity. Owing to such analytical advantages, microscale separation techniques like capillary/microchip LC and CE have been employed for more than 100 lipidome studies. Such techniques are still being evolved and achieving further higher resolution and wider coverage of lipidomes. Therefore, microscale separation techniques are promising as the fundamental technology in next-generation lipidome analysis.

Virulence factors of foodborne pathogen Campylobacterjejuni

Campylobacter jejuni is a highly frequent cause of gastrointestinal foodborne disease in humans throughout the world. Disease outcomes vary from mild to severe diarrhea, and in rare cases the Guillain-Barré syndrome or reactive arthritis can develop as a post-infection complication. Transmission to humans usually occurs via the consumption of a range of foods, especially those associated with the consumption of raw or undercooked poultry meat, unpasteurized milk, and water-based environmental sources. When associated to food or water ingestion, the C. jejuni enters the human host intestine via the oral route and colonizes the distal ileum and colon. When it adheres and colonizes the intestinal cell surfaces, the C. jejuni is expected to express several putative virulence factors, which cause damage to the intestine either directly, by cell invasion and/or production of toxin(s), or indirectly, by triggering inflammatory responses. This review article highlights various C. jejuni characteristics - such as motility and chemotaxis - that contribute to the biological fitness of the pathogen, as well as factors involved in human host cell adhesion and invasion, and their potential role in the development of the disease. We have analyzed and critically discussed nearly 180 scientific articles covering the latest improvements in the field.

HldE Is Important for Virulence Phenotypes in Enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is one of the most common causes of diarrheal illness in third world countries and it especially affects children and travelers visiting these regions. ETEC causes disease by adhering tightly to the epithelial cells in a concerted effort by adhesins, flagella, and other virulence-factors. When attached ETEC secretes toxins targeting the small intestine host-cells, which ultimately leads to osmotic diarrhea. HldE is a bifunctional protein that catalyzes the nucleotide-activated heptose precursors used in the biosynthesis of lipopolysaccharide (LPS) and in post-translational protein glycosylation. Both mechanisms have been linked to ETEC virulence: Lipopolysaccharide (LPS) is a major component of the bacterial outer membrane and is needed for transport of heat-labile toxins to the host cells, and ETEC glycoproteins have been shown to play an important role for bacterial adhesion to host epithelia. Here, we report that HldE plays an important role for ETEC virulence. Deletion of hldE resulted in markedly reduced binding to the human intestinal cells due to reduced expression of colonization factor CFA/I on the bacterial surface. Deletion of hldE also affected ETEC motility in a flagella-dependent fashion. Expression of both colonization factors and flagella was inhibited at the level of transcription. In addition, the hldE mutant displayed altered growth, increased biofilm formation and clumping in minimal growth medium. Investigation of an orthogonal LPS-deficient mutant combined with mass spectrometric analysis of protein glycosylation indicated that HldE exerts its role on ETEC virulence both through protein glycosylation and correct LPS configuration. These results place HldE as an attractive target for the development of future antimicrobial therapeutics.

Characterization of the dTDP-Fuc3N and dTDP-Qui3N biosynthetic pathways in Campylobacter jejuni 81116

The Gram-negative bacterium Campylobacter jejuni 81116 (Penner serotype HS:6) has a class E lipooligosaccharide (LOS) biosynthesis locus containing 19 genes, which encode for 11 putative glycosyltransferases, 1 lipid A acyltransferase and 7 enzymes thought to be involved in the biosynthesis of dideoxyhexosamine (ddHexN) moieties. Although the LOS outer core structure of C. jejuni 81116 is still unknown, recent mass spectrometry analyses suggest that it contains acetylated forms of two ddHexN residues. For this investigation, five of the genes encoding enzymes reportedly involved in the biosyntheses of these sugar residues were examined, rmlA, rmlB, wlaRA, wlaRB and wlaRG. Specifically, these genes were cloned and expressed in Escherichia coli, and the corresponding enzymes were purified and tested for biochemical activity. Here we present data demonstrating that RmlA functions as a glucose-1-phosphate thymidylyltransferase and that RmlB is a thymidine diphosphate (dTDP)-glucose 4,6-dehydratase. We also show, through nuclear magnetic resonance spectroscopy and mass spectrometry analyses, that WlaRG, when utilized in coupled assays with either WlaRA or WlaRB and dTDP-4-keto-6-deoxyglucose, results in the production of either dTDP-3-amino-3,6-dideoxy-d-galactose (dTDP-Fuc3N) or dTDP-3-amino-3,6-dideoxy-d-glucose (dTDP-Qui3N), respectively. In addition, the X-ray crystallographic structures of the 3,4-ketoisomerases, WlaRA and WlaRB, were determined to 2.14 and 2.0 Å resolutions, respectively. Taken together, the data reported herein demonstrate that C. jejuni 81116 utilizes five enzymes to synthesize dTDP-Fuc3N or dTDP-Qui3N and that WlaRG, an aminotransferase, can function on sugars with differing stereochemistry about their C-4' carbons. Importantly, the data reveal that C. jejuni 81116 has the ability to synthesize two isomeric ddHexN forms.

Genetic diversity of the O antigens of Proteus species and the development of a suspension array for molecular serotyping

Proteus species are well-known opportunistic pathogens frequently associated with skin wound and urinary tract infections in humans and animals. O antigen diversity is important for bacteria to adapt to different hosts and environments, and has been used to identify serotypes of Proteus isolates. At present, 80 Proteus O-serotypes have been reported. Although the O antigen structures of most Proteus serotypes have been identified, the genetic features of these O antigens have not been well characterized. The O antigen gene clusters of Proteus species are located between the cpxA and secB genes. In this study, we identified 55 O antigen gene clusters of different Proteus serotypes. All clusters contain both the wzx and wzy genes and exhibit a high degree of heterogeneity. Potential functions of O antigen-related genes were proposed based on their similarity to genes in available databases. The O antigen gene clusters and structures were compared, and a number of glycosyltransferases were assigned to glycosidic linkages. In addition, an O serotype-specific suspension array was developed for detecting 31 Proteus serotypes frequently isolated from clinical specimens. To our knowledge, this is the first comprehensive report to describe the genetic features of Proteus O antigens and to develop a molecular technique to identify different Proteus serotypes.

Structural investigation on WlaRG from Campylobacter jejuni: A sugar aminotransferase

Campylobacter jejuni is a Gram-negative bacterium that represents a leading cause of human gastroenteritis worldwide. Of particular concern is the link between C. jejuni infections and the subsequent development of Guillain-Barré syndrome, an acquired autoimmune disorder leading to paralysis. All Gram-negative bacteria contain complex glycoconjugates anchored to their outer membranes, but in most strains of C. jejuni, this lipoglycan lacks the O-antigen repeating units. Recent mass spectrometry analyses indicate that the C. jejuni 81116 (Penner serotype HS:6) lipoglycan contains two dideoxyhexosamine residues, and enzymological assay data show that this bacterial strain can synthesize both dTDP-3-acetamido-3,6-dideoxy-d-glucose and dTDP-3-acetamido-3,6-dideoxy-d-galactose. The focus of this investigation is on WlaRG from C. jejuni, which plays a key role in the production of these unusual sugars by functioning as a pyridoxal 5'-phosphate dependent aminotransferase. Here, we describe the first three-dimensional structures of the enzyme in various complexes determined to resolutions of 1.7 Å or higher. Of particular significance are the external aldimine structures of WlaRG solved in the presence of either dTDP-3-amino-3,6-dideoxy-d-galactose or dTDP-3-amino-3,6-dideoxy-d-glucose. These models highlight the manner in which WlaRG can accommodate sugars with differing stereochemistries about their C-4' carbon positions. In addition, we present a corrected structure of WbpE, a related sugar aminotransferase from Pseudomonas aeruginosa, solved to 1.3 Å resolution.

Large Sequence Diversity within the Biosynthesis Locus and Common Biochemical Features of Campylobacter coli Lipooligosaccharides

Despite the importance of lipooligosaccharides (LOSs) in the pathogenicity of campylobacteriosis, little is known about the genetic and phenotypic diversity of LOS in Campylobacter coli In this study, we investigated the distribution of LOS locus classes among a large collection of unrelated C. coli isolates sampled from several different host species. Furthermore, we paired C. coli genomic information and LOS chemical composition for the first time to investigate possible associations between LOS locus class sequence diversity and biochemical heterogeneity. After identifying three new LOS locus classes, only 85% of the 144 isolates tested were assigned to a class, suggesting higher genetic diversity than previously thought. This genetic diversity is at the basis of a completely unexplored LOS structural heterogeneity. Mass spectrometry analysis of the LOSs of nine isolates, representing four different LOS classes, identified two features distinguishing C. coli LOS from that of Campylobacter jejuni 2-Amino-2-deoxy-d-glucose (GlcN)-GlcN disaccharides were present in the lipid A backbone, in contrast to the β-1'-6-linked 3-diamino-2,3-dideoxy-d-glucopyranose (GlcN3N)-GlcN backbone observed in C. jejuni Moreover, despite the fact that many of the genes putatively involved in 3-acylamino-3,6-dideoxy-d-glucose (Quip3NAcyl) were apparently absent from the genomes of various isolates, this rare sugar was found in the outer core of all C. coli isolates. Therefore, regardless of the high genetic diversity of the LOS biosynthesis locus in C. coli, we identified species-specific phenotypic features of C. coli LOS that might explain differences between C. jejuni and C. coli in terms of population dynamics and host adaptation.

IMPORTANCE

Despite the importance of C. coli to human health and its controversial role as a causative agent of Guillain-Barré syndrome, little is known about the genetic and phenotypic diversity of C. coli LOSs. Therefore, we paired C. coli genomic information and LOS chemical composition for the first time to address this paucity of information. We identified two species-specific phenotypic features of C. coli LOS, which might contribute to elucidating the reasons behind the differences between C. jejuni and C. coli in terms of population dynamics and host adaptation.

Impact of Campylobacter jejuni cj0268c knockout mutation on intestinal colonization, translocation, and induction of immunopathology in gnotobiotic IL-10 deficient mice

Background

Although Campylobacter jejuni infections have a high prevalence worldwide and represent a significant socioeconomic burden, the underlying molecular mechanisms of induced intestinal immunopathology are still not well understood. We have recently generated a C. jejuni mutant strain NCTC11168::cj0268c, which has been shown to be involved in cellular adhesion and invasion. The immunopathological impact of this gene, however, has not been investigated in vivo so far.

Methodology/Principal Findings

Gnotobiotic IL-10 deficient mice were generated by quintuple antibiotic treatment and perorally infected with C. jejuni mutant strain NCTC11168::cj0268c, its complemented version (NCTC11168::cj0268c-comp-cj0268c), or the parental strain NCTC11168. Kinetic analyses of fecal pathogen loads until day 6 post infection (p.i.) revealed that knockout of cj0268c did not compromise intestinal C. jejuni colonization capacities. Whereas animals irrespective of the analysed C. jejuni strain developed similar clinical symptoms of campylobacteriosis (i.e. enteritis), mice infected with the NCTC11168::cj0268c mutant strain displayed significant longer small as well as large intestinal lengths indicative for less distinct C. jejuni induced pathology when compared to infected control groups at day 6 p.i. This was further supported by significantly lower apoptotic and T cell numbers in the colonic mucosa and lamina propria, which were paralleled by lower intestinal IFN-γ and IL-6 concentrations at day 6 following knockout mutant NCTC11168::cj0268c as compared to parental strain infection. Remarkably, less intestinal immunopathology was accompanied by lower IFN-γ secretion in ex vivo biopsies taken from mesenteric lymphnodes of NCTC11168::cj0268c infected mice versus controls.

Conclusion/Significance

We here for the first time show that the cj0268c gene is involved in mediating C. jejuni induced immunopathogenesis in vivo. Future studies will provide further deep insights into the immunological and molecular interplays between C. jejuni and innate immunity in human campylobacteriosis.

The Campylobacter jejuni Cj0268c protein is required for adhesion and invasion in vitro

Adherence of Campylobacter jejuni to its particular host cells is mediated by several pathogen proteins. We screened a transposon-based mutant library of C. jejuni in order to identify clones with an invasion deficient phenotype towards Caco2 cells and detected a mutant with the transposon insertion in gene cj0268c. In vitro characterization of a generated non-random mutant, the mutant complemented with an intact copy of cj0268c and parental strain NCTC 11168 confirmed the relevance of Cj0268c in the invasion process, in particular regarding adherence to host cells. Whereas Cj0268c does not impact autoagglutination or motility of C. jejuni, heterologous expression in E. coli strain DH5α enhanced the potential of the complemented E. coli strain to adhere to Caco2 cells significantly and, thus, indicates that Cj0268c does not need to interact with other C. jejuni proteins to develop its adherence-mediating phenotype. Flow cytometric measurements of E. coli expressing Cj0268c indicate a localization of the protein in the periplasmic space with no access of its C-terminus to the bacterial surface. Since a respective knockout mutant possesses clearly reduced resistance to Triton X-100 treatment, Cj0268c contributes to the stability of the bacterial cell wall. Finally, we could show that the presence of cj0268c seems to be ubiquitous in isolates of C. jejuni and does not correlate with specific clonal groups regarding pathogenicity or pathogen metabolism.

Assessment of glycan interactions of clinical and avian isolates of Campylobacter jejuni

BACKGROUND

Campylobacter jejuni strain 11168 was demonstrated to have a broad specificity for eukaryotic surface glycosylation using glycan array analysis. The initial screen indicated that sialic acid and mannose are important binding partners after environmental stress, while galactose and fucose structures are likely to be involved in persistent infection.

RESULTS

In this broader study, five additional human/clinical isolates and six chicken isolates were fully assessed to determine their glycan binding capacity using an extended glycan array. C. jejuni 11168 was rescreened here due to the presence of glycoaminoglycan (GAG) and other structures that were not available on our previous glycan array. The current array analysis of additional C. jejuni strains confirmed the growth condition dependent differences in glycan binding that was previously observed for C. jejuni 11168. We noted strain to strain variations, particularly for the human isolates C. jejuni 520 and 81116 and the chicken isolate C. jejuni 331, with the majority of differences observed in galactose, mannose and GAG binding. Chicken isolates were found to bind to a broader range of glycans compared to the human isolates, recognising branched mannose and carageenan (red seaweed) glycans. Glycan array data was confirmed using cell-based lectin inhibition assays with the fucose (UEA-I) and mannose (ConA) binding lectins.

CONCLUSIONS

This study confirms that all C. jejuni strains tested bind to a broad range of glycans, with the majority of strains (all except 81116) altering recognition of sialic acid and mannose after environmental stress. Galactose and fucose structures were bound best by all strains when C. jejuni was grown under host like conditions confirming the likelihood of these structures being involved in persistent infection.

Structure of a sugar N-formyltransferase from Campylobacter jejuni

The O-antigens, which are components of the outer membranes of Gram-negative bacteria, are responsible for the wide species variations seen in nature and are thought to play a role in bacterial virulence. They often contain unusual dideoxysugars such as 3,6-dideoxy-3-formamido-d-glucose (Qui3NFo). Here, we describe a structural and functional investigation of the protein C8J_1081 from Campylobacter jejuni 81116, which is involved in the biosynthesis of Qui3NFo. Specifically, the enzyme, hereafter referred to as WlaRD, catalyzes the N-formylation of dTDP-3,6-dideoxy-3-amino-d-glucose (dTDP-Qui3N) using N(10)-formyltetrahydrofolate as the carbon source. For this investigation, seven X-ray structures of WlaRD, in complexes with various dTDP-linked sugars and cofactors, were determined to resolutions of 1.9 Å or better. One of the models, with bound N(10)-formyltetrahydrofolate and dTDP, represents the first glimpse of an N-formyltransferase with its natural cofactor. Another model contains the reaction products, tetrahydrofolate and dTDP-Qui3NFo. In combination, the structures provide snapshots of the WlaRD active site before and after catalysis. On the basis of these structures, three amino acid residues were targeted for study: Asn 94, His 96, and Asp 132. Mutations of any of these residues resulted in a complete loss of enzymatic activity. Given the position of His 96 in the active site, it can be postulated that it functions as the active site base to remove a proton from the sugar amino group as it attacks the carbonyl carbon of the N-10 formyl group of the cofactor. Enzyme assays demonstrate that WlaRD is also capable of utilizing dTDP-3,6-dideoxy-3-amino-d-galactose (dTDP-Fuc3N) as a substrate, albeit at a much reduced catalytic efficiency.