The structures of the lipooligosaccharide and capsule polysaccharide of Campylobacter jejuni genome sequenced strain NCTC 11168

A bifunctional Pasteurella multocida β1-3-galactosyl/N-acetylgalactosaminyltransferase (PmNatB) for the highly efficient chemoenzymatic synthesis of disaccharides

Glycosyltransferases are nature's key biocatalysts for the formation of glycosidic bonds. Discovery and characterization of new synthetically useful glycosyltransferases are critical for the development of efficient enzymatic and chemoenzymatic strategies for producing complex carbohydrates and glycoconjugates. Herein we report the identification of Pasteurella multocida PmNatB as a bifunctional single-catalytic-domain glycosyltransferase with both β1-3-galactosyltransferase and β1-3-N-acetylgalactosaminyltransferase activities. It is a novel glycosyltransferase for constructing structurally diverse GalNAcβ3Galα/βOR and Galβ3GalNAcα/βOR disaccharides in one-pot multienzyme systems with in situ generation of UDP-sugars.

Characterisation of a capsular polysaccharide from Moraxella nonliquefaciens CCUG 348T

Moraxella nonliquefaciens is a commensal of the human upper respiratory tract (URT) but on rare occasions is recovered in cases of ocular, septic and pulmonary infections. Hence there is interest in the pathogenic determinants of M. nonliquefaciens, of which outer membrane (OM) structures such as fimbriae and two capsular polysaccharide (CPS) structures, →3)-β-D-GalpNAc-(1→5)-β-Kdop-(2→ and →8)-α-NeuAc-(2→, have been reported in the literature. To further characterise its surface virulence factors, we isolated a novel CPS from M. nonliquefaciens type strain CCUG 348T. This structure was elucidated using NMR data obtained from CPS samples that were subjected to various degrees of mild acid hydrolysis. Together with GLC-MS data, the structure was resolved as a linear polymer composed of two GalfNAc residues consecutively added to Kdo, →3)-β-D-GalfNAc-(1→3)-α-D-GalfNAc-(1→5)-α-(8-OAc)Kdop-(2→. Supporting evidence for this material being CPS was drawn from the proposed CPS biosynthetic locus which encoded a potential GalfNAc transferase, a UDP-GalpNAc mutase for UDP-GalfNAc production and a putative CPS polymerase with predicted GalfNAc and Kdo transferase domains. This study describes a unique CPS composition reported in Moraxella spp. and offers genetic insights into the synthesis and expression of GalfNAc residues, which are rare in bacterial OM glycans.

Biosynthesis of UDP-α-N-Acetyl-d-mannosaminuronic Acid and CMP-β-N-Acetyl-d-neuraminic Acid for the Capsular Polysaccharides of Campylobacter jejuni

Campylobacter jejuni is a human pathogen and a leading cause of food poisoning in North America and Europe. The exterior surface of the bacterial cell wall is attached to a polymeric coat of sugar molecules known as the capsular polysaccharide (CPS) that helps protect the organism from the host immune response. The CPS is composed of a repeating sequence of common and unusual sugar residues. In the HS:11 serotype of C. jejuni, we identified two enzymes in the gene cluster for CPS formation that are utilized for the biosynthesis of UDP-α-N-acetyl-d-mannosaminuronic acid (UDP-ManNAcA). In the first step, UDP-α-N-acetyl-d-glucosamine (UDP-GlcNAc) is epimerized at C2 to form UDP-α-N-acetyl-d-mannosamine (UDP-ManNAc). This product is then oxidized by a NAD+-dependent C6-dehydrogenase to form UDP-ManNAcA. In the HS:6 serotype (C. jejuni strain 81116), we identified three enzymes that are required for the biosynthesis of CMP-β-N-acetyl-d-neuraminic acid (CMP-Neu5Ac). In the first step, UDP-GlcNAc is epimerized at C2 and subsequently hydrolyzed to form N-acetyl-d-mannosamine (ManNAc) with the release of UDP. This product is then condensed with PEP by N-acetyl-d-neuraminate synthase to form N-acetyl-d-neuraminic acid (Neu5Ac). In the final step, CMP-N-acetyl-d-neuraminic acid synthase utilizes CTP to convert this product into CMP-Neu5Ac. A bioinformatic analysis of these five enzymes from C. jejuni serotypes HS:11 and HS:6 identified other bacterial species that can produce UDP-ManNAcA or CMP-Neu5Ac for CPS formation.

Biosynthesis of Cytidine Diphosphate-6-d-Glucitol for the Capsular Polysaccharides of Campylobacter jejuni

Campylobacter jejuni is a Gram-negative pathogenic bacterium commonly found in chickens and is the leading cause of human diarrheal disease worldwide. The various serotypes of C. jejuni produce structurally distinct capsular polysaccharides (CPSs) on the exterior surfaces of the cell wall. The capsular polysaccharide from C. jejuni serotype HS:5 is composed of a repeating sequence of d-glycero-d-manno-heptose and d-glucitol-6-phosphate. We previously defined the pathway for the production of d-glycero-d-manno-heptose in C. jejuni. Here, we elucidate the biosynthetic pathway for the assembly of cytidine diphosphate (CDP)-6-d-glucitol by the combined action of two previously uncharacterized enzymes. The first enzyme catalyzes the formation of CDP-6-d-fructose from cytidine triphosphate (CTP) and d-fructose-6-phosphate. The second enzyme reduces CDP-6-d-fructose with NADPH to generate CDP-6-d-glucitol. Using sequence similarity network (SSN) and genome neighborhood network (GNN) analyses, we predict that these pairs of proteins are responsible for the biosynthesis of CDP-6-d-glucitol and/or CDP-d-mannitol in the lipopolysaccharides (LPSs) and capsular polysaccharides in more than 200 other organisms. In addition, high resolution X-ray structures of the second enzyme are reported, which provide novel insight into the manner in which an open-chain nucleotide-linked sugar is harbored in an active site cleft.

Effect of the polysaccharide capsule and its heptose on the resistance of Campylobacter jejuni to innate immune defenses

Campylobacter jejuni is a commensal in many animals but causes diarrhea in humans. Its polysaccharide capsule contributes to host colonization and virulence in a strain- and model-specific manner. We investigated if the capsule and its heptose are important for interactions of strain NCTC 11168 with various hosts and their innate immune defenses. We determined that they support bacterial survival in Drosophila melanogaster and enhance virulence in Galleria mellonella. We showed that the capsule had limited antiphagocytic activity in human and chicken macrophages, decreased adherence to chicken macrophages, and decreased intracellular survival in both macrophages. In contrast, the heptose increased uptake by chicken macrophages and supported adherence to human macrophages and survival within them. While the capsule triggered nitric oxide production in chicken macrophages, the heptose mitigated this and protected against nitrosative assault. Finally, the C. jejuni strain NCTC 11168 elicited strong cytokine production in both macrophages but quenched ROS production independently from capsule and heptose, and while the capsule and heptose did not protect against oxidative assault, they favored growth in biofilms under oxidative stress. This study shows that the wild-type capsule with its heptose is optimized to resist innate defenses in strain NCTC 11168 often via antagonistic effects of the capsule and its heptose.

Metabolic Pathways for the Biosynthesis of Heptoses Used in the Construction of Capsular Polysaccharides in the Human Pathogen Campylobacter jejuni

Campylobacter jejuni is the leading cause of food poisoning in North America. The exterior surface of this bacterium is coated with a capsular polysaccharide (CPS) that consists of a repeating sequence of 2-5 different carbohydrates that is anchored to the outer membrane. Heptoses of various configurations are among the most common monosaccharides that have been identified within the CPS. It is currently thought that all heptose variations derive from the modification of GDP-d-glycero-α-d-manno-heptose (GMH). From the associated gene clusters for CPS biosynthesis, we have identified 20 unique enzymes with different substrate profiles that are used by the various strains and serotypes of C. jejuni to make six different stereoisomers of GDP-6-deoxy-heptose, four stereoisomers of GDP-d-glycero-heptoses, and two stereoisomers of GDP-3,6-dideoxy-heptoses starting from d-sedoheptulose-7-phosphate. The modification enzymes include a C4-dehydrogenase, a C4,6-dehydratase, three C3- and/or C5-epimerases, a C3-dehydratase, eight C4-reductases, two pyranose/furanose mutases, and four enzymes for the formation of GMH from d-sedoheptulose-7-phosphate. We have mixed these enzymes in different combinations to make novel GDP-heptose modifications, including GDP-6-hydroxy-heptoses, GDP-3-deoxy-heptoses, and GDP-3,6-dideoxy-heptoses.

Total Synthesis of Campylobacter jejuni NCTC11168 Capsular Polysaccharide via the Intramolecular Anomeric Protection Strategy

The infection of Campylobacter jejuni results in a significant diarrhea disease, which is highly fatal to young children in unindustrialized countries. Developing a new therapy is required due to increasing antibiotic resistance. Herein, we described a total synthesis of a C. jejuni NCTC11168 capsular polysaccharide repeating unit containing a linker moiety via an intramolecular anomeric protection (iMAP) strategy. This one-step 1,6-protecting method structured the challenging furanosyl galactosamine configuration, facilitated further concise regioselective protection, and smoothed the heptose synthesis. The tetrasaccharide was constructed in a [2 + 1 + 1] manner. The synthesis of this complicated CPS tetrasaccharide was completed in merely 28 steps, including the preparation of all the building blocks, construction of the tetrasaccharide skeleton, and functional group transformations.

Biosynthesis of 3,6-Dideoxy-heptoses for the Capsular Polysaccharides of Campylobacter jejuni

Campylobacter jejuni is the leading cause of food poisoning in the United States. Surrounding the exterior surface of this bacterium is a capsular polysaccharide (CPS) that helps protect the organism from the host immune system. The CPS is composed of a repeating sequence of common and unusual sugar residues, including relatively rare heptoses. In the HS:5 serotype, we identified four enzymes required for the biosynthesis of GDP-3,6-dideoxy-β-l-ribo-heptose. In the first step, GDP-d-glycero-α-d-manno-heptose is dehydrated to form GDP-6-deoxy-4-keto-α-d-lyxo-heptose. This product is then dehydrated by a pyridoxal phosphate-dependent C3-dehydratase to form GDP-3,6-dideoxy-4-keto-α-d-threo-heptose before being epimerized at C5 to generate GDP-3,6-dideoxy-4-keto-β-l-erythro-heptose. In the final step, a C4-reductase uses NADPH to convert this product to GDP-3,6-dideoxy-β-l-ribo-heptose. These results are at variance with the previous report of 3,6-dideoxy-d-ribo-heptose in the CPS from serotype HS:5 of C. jejuni. We also demonstrated that GDP-3,6-dideoxy-β-l-xylo-heptose is formed using the corresponding enzymes found in the gene cluster from serotype HS:11 of C. jejuni. The utilization of different C4-reductases from other serotypes of C. jejuni enabled the formation of GDP-3,6-dideoxy-α-d-arabino-heptose and GDP-3,6-dideoxy-α-d-lyxo-heptose.

Bifunctional Epimerase/Reductase Enzymes Facilitate the Modulation of 6-Deoxy-Heptoses Found in the Capsular Polysaccharides of Campylobacter jejuni

Campylobacter jejuni is a human pathogen and the leading cause of food poisoning in the United States and Europe. Surrounding the exterior surface of this bacterium is a capsular polysaccharide (CPS) that consists of a repeating sequence of common and unusual carbohydrate segments. At least 10 different heptose sugars have thus far been identified in the various strains of C. jejuni. The accepted biosynthetic pathway for the construction of the 6-deoxy-heptoses begins with the 4,6-dehydration of GDP-d-glycero-d-manno-heptose by a dehydratase, followed by an epimerase that racemizes C3 and/or C5 of the product GDP-6-deoxy-4-keto-d-lyxo-heptose. In the final step, a C4-reductase catalyzes the NADPH reduction of the resulting 4-keto product. However, in some strains and serotypes of C. jejuni, there are two separate C4-reductases with different product specificities in the gene cluster for CPS formation. Five pairs of these tandem C4-reductases were isolated, and the catalytic properties were ascertained. In four out of five cases, one of the two C4-reductases is able to catalyze the isomerization of C3 and C5 of GDP-6-deoxy-4-keto-d-lyxo-heptose, in addition to the catalysis of the reduction of C4, thus bypassing the requirement for a separate C3/C5-isomerase. In each case, the 3'-end of the gene for the first C4-reductase contains a poly-G tract of 8-10 guanine residues that may be used to control the expression and/or catalytic activity of either C4-reductase. The three-dimensional structure of the C4-reductase from serotype HS:15, which only does a reduction of C4, was determined to 1.45 Å resolution in the presence of NADPH and GDP.

Mouse models for bacterial enteropathogen infections: insights into the role of colonization resistance

Globally, enteropathogenic bacteria are a major cause of morbidity and mortality.1-3 Campylobacter, Salmonella, Shiga-toxin-producing Escherichia coli, and Listeria are among the top five most commonly reported zoonotic pathogens in the European Union.4 However, not all individuals naturally exposed to enteropathogens go on to develop disease. This protection is attributable to colonization resistance (CR) conferred by the gut microbiota, as well as an array of physical, chemical, and immunological barriers that limit infection. Despite their importance for human health, a detailed understanding of gastrointestinal barriers to infection is lacking, and further research is required to investigate the mechanisms that underpin inter-individual differences in resistance to gastrointestinal infection. Here, we discuss the current mouse models available to study infections by non-typhoidal Salmonella strains, Citrobacter rodentium (as a model for enteropathogenic and enterohemorrhagic E. coli), Listeria monocytogenes, and Campylobacter jejuni. Clostridioides difficile is included as another important cause of enteric disease in which resistance is dependent upon CR. We outline which parameters of human infection are recapitulated in these mouse models, including the impact of CR, disease pathology, disease progression, and mucosal immune response. This will showcase common virulence strategies, highlight mechanistic differences, and help researchers from microbiology, infectiology, microbiome research, and mucosal immunology to select the optimal mouse model.

Functional Characterization of a HAD Phosphatase Involved in Capsular Polysaccharide Biosynthesis in Campylobacter jejuni

Campylobacter jejuni is a Gram-negative, pathogenic bacterium found in the intestinal tracts of chickens and many other farm animals. C. jejuni infection results in campylobacteriosis, which can cause nausea, diarrhea, fever, cramps, and death. The surface of the bacterium is coated with a thick layer of sugar known as the capsular polysaccharide. This highly modified polysaccharide contains an unusual d-glucuronamide moiety in serotypes HS:2 and HS:19. Previously, we have demonstrated that a phosphorylated glucuronamide intermediate is synthesized in C. jejuni NCTC 11168 (serotype HS:2) by cumulative reactions of three enzymes: Cj1441, Cj1436/Cj1437, and Cj1438. Cj1441 functions as a UDP-d-glucose dehydrogenase to make UDP-d-glucuronate; then Cj1436 or Cj1437 catalyzes the formation of ethanolamine phosphate or S-serinol phosphate, respectively, and finally Cj1438 catalyzes amide bond formation using d-glucuronate and either ethanolamine phosphate or S-serinol phosphate. Here, we investigated the final d-glucuronamide-modifying enzyme, Cj1435. Cj1435 was shown to catalyze the hydrolysis of the phosphate esters from either the d-glucuronamide of ethanolamine phosphate or S-serinol phosphate. Kinetic constants for a range of substrates were determined, and the stereoselectivity of the enzyme for the hydrolysis of glucuronamide of S-serinol phosphate was established using 31P nuclear magnetic resonance spectroscopy. A bioinformatic analysis of Cj1435 reveals it to be a member of the HAD phosphatase superfamily with a unique DXXE catalytic motif.

Product Specificity of C4-Reductases in the Biosynthesis of GDP-6-Deoxy-Heptoses during Capsular Polysaccharide Formation in Campylobacter jejuni

Campylobacter jejuni is the leading cause of food poisoning in the United States and Europe. A capsular polysaccharide that coats the exterior of the bacterium helps evade the host immune system. At least 33 different strains of C. jejuni have been identified, and the chemical structures of 12 different capsular polysaccharides (CPSs) have been characterized from various serotypes. Thus far, 10 different heptose sugars have been found in the chemically characterized CPSs, and each of these are currently thought to originate from the modification of GDP-d-glycero-d-manno-heptose by the successive action of 4,6-dehydratase (or C4-dehydrogenase), C3- or C3/C5-epimerase, and C4-reductase. Within the sequenced strains of C. jejuni, we have identified 25 different C4-reductases that cluster into nine groups at a sequence identity of >90%. Eight of the proteins from seven different clusters were purified, and their product profiles were determined with GDP-6-deoxy-4-keto-heptose substrates using NMR and ESI mass spectrometry. The isolated products included GDP-6-deoxy-l-gluco-heptose (serotype HS:2), GDP-6-deoxy-l-galacto-heptose (serotype HS:42), GDP-6-deoxy-l-gulo-heptose (serotype HS:15), GDP-6-deoxy-d-ido-heptose (serotypes HS:3, HS:4, and HS:33), GDP-6-deoxy-d-manno-heptose (serotype HS:53), and GDP-6-deoxy-d-altro-heptose (serotype HS:23/36). Based on these observations, the product specificity can be reliably predicted for 14 additional C4-reductases from C. jejuni. The remaining three C4-reductases are highly likely to be required for the biosynthesis of 3,6-dideoxy-heptose products.

In-cell NMR: Why and how?

NMR spectroscopy has been applied to cells and tissues analysis since its beginnings, as early as 1950. We have attempted to gather here in a didactic fashion the broad diversity of data and ideas that emerged from NMR investigations on living cells. Covering a large proportion of the periodic table, NMR spectroscopy permits scrutiny of a great variety of atomic nuclei in all living organisms non-invasively. It has thus provided quantitative information on cellular atoms and their chemical environment, dynamics, or interactions. We will show that NMR studies have generated valuable knowledge on a vast array of cellular molecules and events, from water, salts, metabolites, cell walls, proteins, nucleic acids, drugs and drug targets, to pH, redox equilibria and chemical reactions. The characterization of such a multitude of objects at the atomic scale has thus shaped our mental representation of cellular life at multiple levels, together with major techniques like mass-spectrometry or microscopies. NMR studies on cells has accompanied the developments of MRI and metabolomics, and various subfields have flourished, coined with appealing names: fluxomics, foodomics, MRI and MRS (i.e. imaging and localized spectroscopy of living tissues, respectively), whole-cell NMR, on-cell ligand-based NMR, systems NMR, cellular structural biology, in-cell NMR… All these have not grown separately, but rather by reinforcing each other like a braided trunk. Hence, we try here to provide an analytical account of a large ensemble of intricately linked approaches, whose integration has been and will be key to their success. We present extensive overviews, firstly on the various types of information provided by NMR in a cellular environment (the "why", oriented towards a broad readership), and secondly on the employed NMR techniques and setups (the "how", where we discuss the past, current and future methods). Each subsection is constructed as a historical anthology, showing how the intrinsic properties of NMR spectroscopy and its developments structured the accessible knowledge on cellular phenomena. Using this systematic approach, we sought i) to make this review accessible to the broadest audience and ii) to highlight some early techniques that may find renewed interest. Finally, we present a brief discussion on what may be potential and desirable developments in the context of integrative studies in biology.

Bacterial glycosylation, it’s complicated

Each microbe has the ability to produce a wide variety of sugar structures that includes some combination of glycolipids, glycoproteins, exopolysaccharides and oligosaccharides. For example, bacteria may synthesize lipooligosaccharides or lipopolysaccharides, teichoic and lipoteichoic acids, N- and O-linked glycoproteins, capsular polysaccharides, exopolysaccharides, poly-N-acetylglycosamine polymers, peptidoglycans, osmoregulated periplasmic glucans, trehalose or glycogen, just to name a few of the more broadly distributed carbohydrates that have been studied. The composition of many of these glycans are typically dissimilar from those described in eukaryotes, both in the seemingly endless repertoire of sugars that microbes are capable of synthesizing, and in the unique modifications that are attached to the carbohydrate residues. Furthermore, strain-to-strain differences in the carbohydrate building blocks used to create these glycoconjugates are the norm, and many strains possess additional mechanisms for turning on and off transferases that add specific monosaccharides and/or modifications, exponentially contributing to the structural heterogeneity observed by a single isolate, and preventing any structural generalization at the species level. In the past, a greater proportion of research effort was directed toward characterizing human pathogens rather than commensals or environmental isolates, and historically, the focus was on microbes that were simple to grow in large quantities and straightforward to genetically manipulate. These studies have revealed the complexity that exists among individual strains and have formed a foundation to better understand how other microbes, hosts and environments further transform the glycan composition of a single isolate. These studies also motivate researchers to further explore microbial glycan diversity, particularly as more sensitive analytical instruments and methods are developed to examine microbial populations in situ rather than in large scale from an enriched nutrient flask. This review emphasizes many of these points using the common foodborne pathogen Campylobacter jejuni as the model microbe.

C3- and C3/C5-Epimerases Required for the Biosynthesis of the Capsular Polysaccharides from Campylobacter jejuni

Campylobacter jejuni is a human pathogen and one of the leading causes of food poisoning in Europe and the United States. The outside of the bacterium is coated with a capsular polysaccharide that assists in the evasion of the host immune system. Many of the serotyped strains of C. jejuni contain a 6-deoxy-heptose moiety that is biosynthesized from GDP-d-glycero-d-manno-heptose by the successive actions of a 4,6-dehydratase, a C3/C5-epimerase, and a C4-reductase. We identified 18 different C3/C5-epimerases that could be clustered together into three groups at a sequence identity of >89%. Four of the enzymes from the largest cluster (from serotypes HS:3, HS:10, HS:23/36, and HS:41) were shown to only catalyze the epimerization at C3. Three enzymes from the second largest cluster (HS:2, HS:15, and HS:42) were shown to catalyze the epimerization at C3 and C5. Enzymes from the third cluster were not characterized. The three-dimensional structures of the epimerases from serotypes HS:3, HS:23/36, HS:15, and HS:41 were determined to resolutions of 1.5-1.9 Å. The overall subunit architecture places these enzymes into the diverse "cupin" superfamily. Within X-ray coordinate error, the immediate regions surrounding the active sites are identical, suggesting that factors extending farther out may influence product outcome. The X-ray crystal structures are consistent with His-67 and Tyr-134 acting as general acid/base catalysts for the epimerization of C3 and/or C5. Two amino acid changes (A76V/C136L) were enough to convert the C3-epimerase from serotype HS:3 to one that could now catalyze the epimerization at both C3 and C5.

Molecular and in silico typing of the lipooligosaccharide biosynthesis gene cluster in Campylobacter jejuni and Campylobacter coli

The extensive genetic variation in the lipooligosaccharide (LOS) core biosynthesis gene cluster has led to the development of a classification system; with 8 classes (I-VIII) for Campylobacter coli (C. coli) LOS region and with 23 classes (A-W) or four groups (1–4) for Campylobacter jejuni (C. jejuni) LOS region. PCR based LOS locus type identification for C. jejuni clinical isolates from a UK hospital as well as in silico LOS locus analysis for C. jejuni and C. coli genome sequences from GenBank was carried out to determine the frequencies of various LOS genotypes in C. jejuni and C. coli. Analysis of LOS gene content in 60 clinical C. jejuni isolates and 703 C. jejuni genome sequences revealed that class B (Group 1) was the most abundant LOS class in C. jejuni. The hierarchy of C. jejuni LOS group prevalence (group 1 > group 2 > group 3 > group 4) as well as the hierarchy of the frequency of C. jejuni LOS classes present within the group 1 (B > C > A > R > M > V), group 2 (H/P > O > E > W), group 3 (F > K > S) and group 4 (G > L) was identified. In silico analysis of LOS gene content in 564 C. coli genome sequences showed class III as the most abundant LOS locus type in C. coli. In silico analysis of LOS gene content also identified three novel LOS types of C. jejuni and previously unknown LOS biosynthesis genes in C. coli LOS locus types I, II, III, V and VIII. This study provides C. jejuni and C. coli LOS loci class frequencies in a smaller collection of C. jejuni clinical isolates as well as within the larger, worldwide database of C. jejuni and C. coli.

Discovery and Functional Characterization of a Clandestine ATP-Dependent Amidoligase in the Biosynthesis of the Capsular Polysaccharide from Campylobacter jejuni

Campylobacter jejuni is a Gram-negative, pathogenic bacterium that is commensal in poultry. Infection of C. jejuni leads to campylobacteriosis, the leading cause of gastroenteritis worldwide. Coating the surface of C. jejuni is a thick layer of sugar molecules known as the capsular polysaccharide (CPS). The CPS of C. jejuni NCTC 11168 (HS:2) is composed of a repeating unit of d-glycero-l-gluco-heptose, d-glucuronate, d-N-acetyl-galactosamine, and d-ribose. The glucuronate is further amidated with either ethanolamine or serinol, but it is unknown how this new amide bond is formed. Sequence similarity networks were used to identify a candidate enzyme for amide bond formation during the biosynthesis of the CPS of C. jejuni. The C-terminal domain of Cj1438 was shown to catalyze amide bond formation using MgATP and d-glucuronate in the presence of either ethanolamine phosphate or (S)-serinol phosphate. Product formation was verified using ³¹P NMR spectroscopy and ESI mass spectrometry, and the kinetic constants determined using a coupled enzyme assay by measuring the rate of ADP formation. This work represents the first functional characterization of an ATP-dependent amidoligase in the formation of amide bonds in the biosynthetic pathway for the assembly of the CPS in C. jejuni.

Improving Chicken Responses to Glycoconjugate Vaccination Against Campylobacter jejuni

Campylobacter jejuni is a common cause of diarrheal disease worldwide. Human infection typically occurs through the ingestion of contaminated poultry products. We previously demonstrated that an attenuated Escherichia coli live vaccine strain expressing the C. jejuni N-glycan on its surface reduced the Campylobacter load in more than 50% of vaccinated leghorn and broiler birds to undetectable levels (responder birds), whereas the remainder of the animals was still colonized (non-responders). To understand the underlying mechanism, we conducted three vaccination and challenge studies using 135 broiler birds and found a similar responder/non-responder effect. Subsequent genome-wide association studies (GWAS), analyses of bird sex and levels of vaccine-induced IgY responses did not correlate with the responder versus non-responder phenotype. In contrast, antibodies isolated from responder birds displayed a higher Campylobacter-opsonophagocytic activity when compared to antisera from non-responder birds. No differences in the N-glycome of the sera could be detected, although minor changes in IgY glycosylation warrant further investigation. As reported before, the composition of the microbiota, particularly levels of OTU classified as Clostridium spp., Ruminococcaceae and Lachnospiraceae are associated with the response. Transplantation of the cecal microbiota of responder birds into new birds in combination with vaccination resulted in further increases in vaccine-induced antigen-specific IgY responses when compared to birds that did not receive microbiota transplants. Our work suggests that the IgY effector function and microbiota contribute to the efficacy of the E. coli live vaccine, information that could form the basis for the development of improved vaccines targeted at the elimination of C. jejuni from poultry.

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.

Reduced Infection Efficiency of Phage NCTC 12673 on Non-Motile Campylobacter jejuni Strains Is Related to Oxidative Stress

Campylobacter jejuni is a Gram-negative foodborne pathogen that causes diarrheal disease and is associated with severe post-infectious sequelae. Bacteriophages (phages) are a possible means of reducing Campylobacter colonization in poultry to prevent downstream human infections. However, the factors influencing phage-host interactions must be better understood before this strategy can be predictably employed. Most studies have focused on Campylobacter phage binding to the host surface, with all phages classified as either capsule- or flagella-specific. Here we describe the characterization of a C. jejuni phage that requires functional flagellar glycosylation and motor genes for infection, without needing the flagella for adsorption to the cell surface. Through phage infectivity studies of targeted C. jejuni mutants, transcriptomic analysis of phage-resistant mutants, and genotypic and phenotypic analysis of a spontaneous phage variant capable of simultaneously overcoming flagellar gene dependence and sensitivity to oxidative stress, we have uncovered a link between oxidative stress, flagellar motility, and phage infectivity. Taken together, our results underscore the importance of understanding phage-host interactions beyond the cell surface and point to host oxidative stress state as an important and underappreciated consideration for future phage-host interaction studies.

Functional Characterization of Two PLP-Dependent Enzymes Involved in Capsular Polysaccharide Biosynthesis from Campylobacter jejuni

Campylobacter jejuni is a Gram-negative, pathogenic bacterium that causes campylobacteriosis, a form of gastroenteritis. C. jejuni is the most frequent cause of food-borne illness in the world, surpassing Salmonella and E. coli. Coating the surface of C. jejuni is a layer of sugar molecules known as the capsular polysaccharide that, in C. jejuni NCTC 11168, is composed of a repeating unit of d-glycero-l-gluco-heptose, d-glucuronic acid, d-N-acetyl-galactosamine, and d-ribose. The d-glucuronic acid moiety is further amidated with either serinol or ethanolamine. It is unknown how these modifications are synthesized and attached to the polysaccharide. Here, we report the catalytic activities of two previously uncharacterized, pyridoxal phosphate (PLP)-dependent enzymes, Cj1436 and Cj1437, from C. jejuni NCTC 11168. Using a combination of mass spectrometry and nuclear magnetic resonance, we determined that Cj1436 catalyzes the decarboxylation of l-serine phosphate to ethanolamine phosphate. Cj1437 was shown to catalyze the transamination of dihydroxyacetone phosphate to (S)-serinol phosphate in the presence of l-glutamate. The probable routes to the ultimate formation of the glucuronamide substructures in the capsular polysaccharides of C. jejuni are discussed.

Stabilizing Genetically Unstable Simple Sequence Repeats in the Campylobacter jejuni Genome by Multiplex Genome Editing: a Reliable Approach for Delineating Multiple Phase-Variable Genes

Hypermutable simple sequence repeats (SSRs) are major drivers of phase variation in Campylobacter jejuni. The presence of multiple SSR-mediated phase-variable genes encoding enzymes that modify surface structures, including capsular polysaccharide (CPS) and lipooligosaccharide (LOS), generates extreme cell surface diversity within bacterial populations, thereby promoting adaptation to selective pressures in host environments. Therefore, genetically controlling SSR-mediated phase variation can be important for achieving stable and reproducible research on C. jejuni. Here, we show that natural "cotransformation" is an effective method for C. jejuni genome editing. Cotransformation is a trait of naturally competent bacteria that causes uptake/integration of multiple different DNA molecules, which has been recently adapted to multiplex genome editing by natural transformation (MuGENT), a method for introducing multiple mutations into the genomes of these bacteria. We found that cotransformation efficiently occurred in C. jejuni. To examine the feasibility of MuGENT in C. jejuni, we "locked" different polyG SSR tracts in strain NCTC11168 (which are located in the biosynthetic CPS/LOS gene clusters) into either the ON or OFF configurations. This approach, termed "MuGENT-SSR," enabled the generation of all eight edits within 2 weeks and the identification of a phase-locked strain with a highly stable type of Penner serotyping, a CPS-based serotyping scheme. Furthermore, extensive genome editing of this strain by MuGENT-SSR identified a phase-variable gene that determines the Penner serotype of NCTC11168. Thus, MuGENT-SSR provides a platform for genetic and phenotypic engineering of genetically unstable C. jejuni, making it a reliable approach for elucidating the mechanisms underlying phase-variable expression of specific phenotypes. IMPORTANCE Campylobacter jejuni is the leading bacterial cause of foodborne gastroenteritis in developed countries and occasionally progresses to the autoimmune disease Guillain-Barré syndrome. A relatively large number of hypermutable simple sequence repeat (SSR) tracts in the C. jejuni genome markedly decreases its phenotypic stability through reversible changes in the ON or OFF expression states of the genes in which they reside, a phenomenon called phase variation. Thus, controlling SSR-mediated phase variation can be important for achieving stable and reproducible research on C. jejuni. In this study, we developed a feasible and effective approach for genetically manipulate multiple SSR tracts in the C. jejuni genome using natural cotransformation, a trait of naturally transformable bacterial species that causes the uptake and integration of multiple different DNA molecules. This approach will greatly help to improve the genetic and phenotypic stability of C. jejuni to enable diverse applications in research and development.

Progress toward the Development of Glycan-Based Vaccines against Campylobacteriosis

As one of the main causes of bacterial diarrhea and a major risk factor for triggering Guillain-Barré autoimmune syndrome, campylobacteriosis, that is, Campylobacter spp. infections, represents a major health issue worldwide. There is thus a pressing need for developing an effective and broad-coverage campylobacteriosis vaccine. Campylobacter jejuni, an encapsulated, multidrug resistant Gram-negative bacterium, expresses virulence-associated capsular polysaccharides (CPSs), which constitute exquisite targets for the design of glycoconjugate vaccines. In that context, synthetic carbohydrate chemistry acts as a crucial enabling technology for the preparation of homogeneous constructs while allowing antigenic epitopes to be deciphered and probed at the molecular level. This review aims at covering recent developments in CPS-based campylobacteriosis vaccines as well as in the total syntheses of C. jejuni-related mono- and oligosaccharide mimics.

Biosynthesis of d-glycero-l-gluco-Heptose in the Capsular Polysaccharides of Campylobacter jejuni

Campylobacter jejuni is the leading cause of food poisoning in the United States and Europe. The exterior cell surface of C. jejuni is coated with a capsular polysaccharide (CPS) that is essential for the maintenance and integrity of the bacterial cell wall and evasion of the host immune response. The identity and sequences of the monosaccharide components of the CPS are quite variable and dependent on the specific strain of C. jejuni. It is currently thought that the immediate precursor for the multiple variations found in the heptose moieties of the C. jejuni CPS is GDP-d-glycero-α-d-manno-heptose. In C. jejuni NCTC 11168, the heptose moiety is d-glycero-l-gluco-heptose. It has previously been shown that Cj1427 catalyzes the oxidation of GDP-d-glycero-α-d-manno-heptose to GDP-d-glycero-4-keto-α-d-lyxo-heptose using α-ketoglutarate as a cosubstrate. Cj1430 was now demonstrated to catalyze the double epimerization of this product at C3 and C5 to form GDP-d-glycero-4-keto-β-l-xylo-heptose. Cj1428 subsequently catalyzes the stereospecific reduction of this GDP-linked heptose by NADPH to form GDP-d-glycero-β-l-gluco-heptose. The three-dimensional crystal structure of Cj1430 was determined to a resolution of 1.85 Å in the presence of bound GDP-d-glycero-β-l-gluco-heptose, a product analogue. The structure shows that it belongs to the cupin superfamily. The three-dimensional crystal structure of Cj1428 was solved in the presence of NADPH to a resolution of 1.50 Å. Its fold places it into the short-chain dehydrogenase/reductase superfamily. Typically, members in this family display a characteristic signature sequence of YXXXK, with the conserved tyrosine serving a key role in catalysis. In Cj1428, this residue is a phenylalanine.

Synthesis of an Exhaustive Library of Naturally Occurring Galf-Manp and Galp-Manp Disaccharides. Toward Fingerprinting According to Ring Size by Advanced Mass Spectrometry-Based IM-MS and IRMPD

Nature offers a huge diversity of glycosidic derivatives. Among numerous structural modulations, the nature of the ring size of hexosides may induce significant differences on both biological and physicochemical properties of the glycoconjugate of interest. On this assumption, we expect that small disaccharides bearing either a furanosyl entity or a pyranosyl residue would give a specific signature, even in the gas phase. On the basis of the scope of mass spectrometry, two analytical techniques to register those signatures were considered, i.e., the ion mobility (IM) and the infrared multiple photon dissociation (IRMPD), in order to build up cross-linked databases. d-Galactose occurs in natural products in both tautomeric forms and presents all possible regioisomers when linked to d-mannose. Consequently, the four reducing Galf-Manp disaccharides as well as the four Galp-Manp counterparts were first synthesized according to a highly convergent approach, and IM-MS and IRMPD-MS data were second collected. Both techniques used afforded signatures, specific to the nature of the connectivity between the two glycosyl entities.

Genome-wide screening of vaccine targets prioritization and reverse vaccinology aided design of peptides vaccine to enforce humoral immune response against Campylobacter jejuni

Campylobacter jejuni, gram-negative bacteria, is an infectious agent of foodborne disease-causing bloody diarrhea, abdominal pain, fever, Guillain-Barré syndrome (GBS) and Miller Fisher syndrome in humans. Campylobacter spp. with multidrug resistance to fluoroquinolones, tetracycline, and erythromycin are reported. Hence, an effective vaccine candidate would provide long-term immunity against C. jejuni infections. Thus, we used a subtractive proteomics pipeline to prioritize essential proteins, which impart a critical role in virulence, replication and survival. Five proteins, i.e. Single-stranded DNA-binding protein, UPF0324 membrane protein Cj0999c, DNA translocase FtsK, 50S ribosomal protein L22, and 50S ribosomal protein L1 were identified as virulent proteins and selected for vaccine designing. We reported that the multi-epitopes subunit vaccine based on CTL, HTL and B-cell epitopes combination possess strong antigenic properties and associates no allergenic reaction. Further investigation revealed that the vaccine interacts with the immune receptor (TLR-4) and triggered the release of primary and secondary immune factors. Moreover, the CAI and GC contents obtained through codon optimization were reported to be 0.93 and 53% that confirmed a high expression in the selected vector. The vaccine designed in this study needs further scientific consensus and will aid in managing C. jejuni infections.

Crystal structure of a GDP-6-OMe-4-keto-L-xylo-heptose reductase from Campylobacter jejuni

Carbohydrates play a major role in infection strategies of various enteric pathogens. In Campylobacter jejuni, the most common cause of gastroenteritis, uniquely modified heptoses found in surface carbohydrates are synthesized by specific pathways. Owing to the importance of such pathways for the infectious potential of pathogens and/or their virulence, these biosynthesis pathways present potential targets for therapeutic intervention. Here, we determined the crystal structure of GDP-6-OMe-4-keto-L-xylo-heptose reductase (MlghC), an enzyme within the L-gluco-heptose synthesis pathway of C. jejuni strain NCTC 11168. This enzyme lacks the canonical tyrosine residue of the conserved catalytic Ser-Lys-Tyr triad commonly found among functionally related reductases. Despite adopting the overall two-domain fold shared with other short-chain dehydrogenase/reductase family members, subtle structural differences in the interface between the cofactor- and substrate-binding domains explain the absence of epimerase activity and different substrate specificity of this reductase. Modeling of the product-bound complex based on the crystal structure presented here suggests that a tyrosine residue unique to MlghC replaces the missing canonical residue of the catalytic triad.

Heptose-containing bacterial natural products: structures, bioactivities, and biosyntheses

Covering: up to 2020Glycosylated natural products hold great potential as drugs for the treatment of human and animal diseases. Heptoses, known as seven-carbon-chain-containing sugars, are a group of saccharides that are rarely observed in natural products. Based on the structures of the heptoses, the heptose-containing natural products can be divided into four groups, characterized by heptofuranose, highly-reduced heptopyranose, d-heptopyranose, and l-heptopyranose. Many of them possess remarkable biological properties, including antibacterial, antifungal, antitumor, and pain relief activities, thereby attracting great interest in biosynthesis and chemical synthesis studies to understand their construction mechanisms and structure-activity relationships. In this review, we summarize the structural properties, biological activities, and recent progress in the biosynthesis of bacterial natural products featuring seven-carbon-chain-containing sugars. The biosynthetic origins of the heptose moieties are emphasized.

Functional and Structural Characterization of the UDP-Glucose Dehydrogenase Involved in Capsular Polysaccharide Biosynthesis from Campylobacter jejuni

Campylobacter jejuni is a pathogenic organism that can cause campylobacteriosis in children and adults. Most commonly, campylobacter infection is brought on by consumption of raw or undercooked poultry, unsanitary drinking water, or pet feces. Surrounding the C. jejuni bacterium is a coat of sugar molecules known as the capsular polysaccharide (CPS). The capsular polysaccharide can be very diverse among the different strains of C. jejuni, and this diversity is considered important for evading the host immune system. Modifications to the CPS of C. jejuni NCTC 11168 include O-methylation, phosphoramidylation, and amidation of glucuronate with either serinol or ethanolamine. The enzymes responsible for amidation of glucuronate are currently unknown. In this study, Cj1441, an enzyme expressed from the CPS biosynthetic gene cluster in C. jejuni NCTC 11168, was shown to catalyze the oxidation of UDP-α-d-glucose into UDP-α-d-glucuronic acid with NAD⁺ as the cofactor. No amide products were found in an attempt to determine whether the putative thioester intermediate formed during the oxidation of UDP-glucose by Cj1441 could be captured in the presence of added amines. The three-dimensional crystal structure of Cj1441 was determined in the presence of NAD⁺ and UDP-glucose bound in the active site of the enzyme (Protein Data Bank entry 7KWS). A more thorough bioinformatic analysis of the CPS gene cluster suggests that the amidation activity is localized to the t-terminal half of Cj1438, a bifunctional enzyme that is currently annotated as a sugar transferase.

Campylobacter sp.: Pathogenicity factors and prevention methods-new molecular targets for innovative antivirulence drugs?

Infections caused by bacterial species from the genus Campylobacter are one of the four main causes of strong diarrheal enteritis worldwide. Campylobacteriosis, a typical food-borne disease, can range from mild symptoms to fatal illness. About 550 million people worldwide suffer from campylobacteriosis and lethality is about 33 million p.a. This review summarizes the state of the current knowledge on Campylobacter with focus on its specific virulence factors. Using this knowledge, multifactorial prevention strategies can be implemented to reduce the prevalence of Campylobacter in the food chain. In particular, antiadhesive strategies with specific adhesion inhibitors seem to be a promising concept for reducing Campylobacter bacterial load in poultry production. Antivirulence compounds against bacterial adhesion to and/or invasion into the host cells can open new fields for innovative antibacterial agents. Influencing chemotaxis, biofilm formation, quorum sensing, secretion systems, or toxins by specific inhibitors can help to reduce virulence of the bacterium. In addition, the unusual glycosylation of the bacterium, being a prerequisite for effective phase variation and adaption to different hosts, is yet an unexplored target for combating Campylobacter sp. Plant extracts are widely used remedies in developing countries to combat infections with Campylobacter. Therefore, the present review summarizes the use of natural products against the bacterium in an attempt to stimulate innovative research concepts on the manifold still open questions behind Campylobacter towards improved treatment and sanitation of animal vectors, treatment of infected patients, and new strategies for prevention. KEY POINTS: • Campylobacter sp. is a main cause of strong enteritis worldwide. • Main virulence factors: cytolethal distending toxin, adhesion proteins, invasion machinery. • Strong need for development of antivirulence compounds.

Functional Characterization of Cj1427, a Unique Ping-Pong Dehydrogenase Responsible for the Oxidation of GDP-d-glycero-α-d-manno-heptose in Campylobacter jejuni

The capsular polysaccharides (CPS) of Campylobacter jejuni contain multiple heptose residues with variable stereochemical arrangements at C3-C6. The immediate precursor to all of these possible variations is currently believed to be GDP-d-glycero-α-d-manno-heptose. Oxidation of this substrate at C4 enables subsequent epimerization reactions at C3-C5 that can be coupled to the dehydration/reduction at C5/C6. However, the enzyme responsible for the critical oxidation of C4 from GDP-d-glycero-α-d-manno-heptose has remained elusive. The enzyme Cj1427 from C. jejuni NCTC 11168 was shown to catalyze the oxidation of GDP-d-glycero-α-d-manno-heptose to GDP-d-glycero-4-keto-α-d-lyxo-heptose in the presence of α-ketoglutarate using mass spectrometry and nuclear magnetic resonance spectroscopy. At pH 7.4, the apparent kcat is 0.6 s-1, with a value of kcat/Km of 1.0 × 104 M-1 s-1 for GDP-d-glycero-α-d-manno-heptose. α-Ketoglutarate is required to recycle the tightly bound NADH nucleotide in the active site of Cj1427, which does not dissociate from the enzyme during catalysis.

Structural Analysis of Cj1427, an Essential NAD-Dependent Dehydrogenase for the Biosynthesis of the Heptose Residues in the Capsular Polysaccharides of Campylobacter jejuni

Many strains of Campylobacter jejuni display modified heptose residues in their capsular polysaccharides (CPS). The precursor heptose was previously shown to be GDP-d-glycero-α-d-manno-heptose, from which a variety of modifications of the sugar moiety have been observed. These modifications include the generation of 6-deoxy derivatives and alterations of the stereochemistry at C3-C6. Previous work has focused on the enzymes responsible for the generation of the 6-deoxy derivatives and those involved in altering the stereochemistry at C3 and C5. However, the generation of the 6-hydroxyl heptose residues remains uncertain due to the lack of a specific enzyme to catalyze the initial oxidation at C4 of GDP-d-glycero-α-d-manno-heptose. Here we reexamine the previously reported role of Cj1427, a dehydrogenase found in C. jejuni NTCC 11168 (HS:2). We show that Cj1427 is co-purified with bound NADH, thus hindering catalysis of oxidation reactions. However, addition of a co-substrate, α-ketoglutarate, converts the bound NADH to NAD⁺. In this form, Cj1427 catalyzes the oxidation of l-2-hydroxyglutarate back to α-ketoglutarate. The crystal structure of Cj1427 with bound GDP-d-glycero-α-d-manno-heptose shows that the NAD(H) cofactor is ideally positioned to catalyze the oxidation at C4 of the sugar substrate. Additionally, the overall fold of the Cj1427 subunit places it into the well-defined short-chain dehydrogenase/reductase superfamily. The observed quaternary structure of the tetrameric enzyme, however, is highly unusual for members of this superfamily.

Biosynthesis of GDP-d-glycero-α-d-manno-heptose for the Capsular Polysaccharide of Campylobacter jejuni

The capsular polysaccharide (CPS) structure of Campylobacter jejuni contributes to its robust fitness. Many strains contain heptose moieties in their CPS units. The precursor heptose is GDP-d-glycero-α-d-manno-heptose; modifications to the stereochemistry at C3-C6 as well as additions of methyl and phosphoramidate groups lend to the hypervariability of the C. jejuni CPS structures. Synthesis of GDP-d-glycero-α-d-manno-heptose has been described previously, but using enzymes from Aneurinibacillus thermoaerophilus DSM 10155. Here we describe the complete synthesis of GDP-d-glycero-α-d-manno-heptose using enzymes from C. jejuni NTCC 11168: Cj1152 and Cj1423-Cj1425. Our results yield kinetic parameters for these enzymes and outline a successful strategy for milligram-gram scale synthesis of GDP-d-glycero-α-d-manno-heptose. This achievement is critical for the characterization of other carbohydrate tailoring enzymes, which are expected to utilize GDP-d-glycero-α-d-manno-heptose for the biosynthesis of more complex carbohydrates in the CPS of C. jejuni.

Campylobacter jejuni: collective components promoting a successful enteric lifestyle

Campylobacter jejuni is the leading cause of bacterial diarrhoeal disease in many areas of the world. The high incidence of sporadic cases of disease in humans is largely due to its prevalence as a zoonotic agent in animals, both in agriculture and in the wild. Compared with many other enteric bacterial pathogens, C. jejuni has strict growth and nutritional requirements and lacks many virulence and colonization determinants that are typically used by bacterial pathogens to infect hosts. Instead, C. jejuni has a different collection of factors and pathways not typically associated together in enteric pathogens to establish commensalism in many animal hosts and to promote diarrhoeal disease in the human population. In this Review, we discuss the cellular architecture and structure of C. jejuni, intraspecies genotypic variation, the multiple roles of the flagellum, specific nutritional and environmental growth requirements and how these factors contribute to in vivo growth in human and avian hosts, persistent colonization and pathogenesis of diarrhoeal disease.

Natural Products Containing 'Rare' Organophosphorus Functional Groups

Phosphorous-containing molecules are essential constituents of all living cells. While the phosphate functional group is very common in small molecule natural products, nucleic acids, and as chemical modification in protein and peptides, phosphorous can form P⁻N (phosphoramidate), P⁻S (phosphorothioate), and P⁻C (e.g., phosphonate and phosphinate) linkages. While rare, these moieties play critical roles in many processes and in all forms of life. In this review we thoroughly categorize P⁻N, P⁻S, and P⁻C natural organophosphorus compounds. Information on biological source, biological activity, and biosynthesis is included, if known. This review also summarizes the role of phosphorylation on unusual amino acids in proteins (N- and S-phosphorylation) and reviews the natural phosphorothioate (P⁻S) and phosphoramidate (P⁻N) modifications of DNA and nucleotides with an emphasis on their role in the metabolism of the cell. We challenge the commonly held notion that nonphosphate organophosphorus functional groups are an oddity of biochemistry, with no central role in the metabolism of the cell. We postulate that the extent of utilization of some phosphorus groups by life, especially those containing P⁻N bonds, is likely severely underestimated and has been largely overlooked, mainly due to the technological limitations in their detection and analysis.

Spectroscopic diagnostic for the ring-size of carbohydrates in the gas phase: furanose and pyranose forms of GalNAc

Hexoses are sparingly found in nature in the furanose form (5-membered ring).

Substrate Specificity and Chemical Mechanism for the Reaction Catalyzed by Glutamine Kinase

Campylobacter jejuni, a leading cause of gastroenteritis worldwide, has a unique O-methyl phosphoramidate (MeOPN) moiety attached to its capsular polysaccharide. Investigations into the biological role of MeOPN have revealed that it contributes to the pathogenicity of C. jejuni, and this modification is important for the colonization of C. jejuni. Previously, the reactions catalyzed by four enzymes (Cj1418-Cj1415) from C. jejuni that are required for the biosynthesis of the phosphoramidate modification have been elucidated. Cj1418 (l-glutamine kinase) catalyzes the formation of the initial phosphoramidate bond with the ATP-dependent phosphorylation of the amide nitrogen of l-glutamine. Here we show that Cj1418 catalyzes the phosphorylation of l-glutamine through a three-step reaction mechanism via the formation of covalent pyrophosphorylated ( Enz-X-P_β-P_γ) and phosphorylated ( Enz-X-P_β) intermediates. In the absence of l-glutamine, the enzyme was shown to catalyze a positional isotope exchange (PIX) reaction within β-[¹⁸O₄]-ATP in support of the formation of the Enz-X-P_β-P_γintermediate. In the absence of ATP, the enzyme was shown to catalyze a molecular isotope exchange (MIX) reaction between l-glutamine phosphate and [¹⁵N-amide]-l-glutamine in direct support of the Enz-X-P_βintermediate. The active site nucleophile has been identified as His-737 based on the lack of activity of the H737N mutant and amino acid sequence comparisons. The enzyme was shown to also catalyze the phosphorylation of d-glutamine, γ-l-glutamyl hydroxamate, γ-l-glutamyl hydrazide, and β-l-aspartyl hydroxamate, in addition to l-glutamine.

Cytidine Diphosphoramidate Kinase: An Enzyme Required for the Biosynthesis of the O-Methyl Phosphoramidate Modification in the Capsular Polysaccharides of Campylobacter jejuni

Campylobacter jejuni, a leading cause of gastroenteritis, produces a capsular polysaccharide that is derivatized with a unique O-methyl phosphoramidate (MeOPN) modification. This modification contributes to serum resistance and invasion of epithelial cells. Previously, the first three biosynthetic steps for the formation of MeOPN were elucidated. The first step is catalyzed by a novel glutamine kinase (Cj1418), which catalyzes the adenosine triphosphate (ATP)-dependent phosphorylation of the amide nitrogen of l-glutamine. l-Glutamine phosphate is used by cytidine triphosphate (CTP):phosphoglutamine cytidylyltransferase (Cj1416) to displace pyrophosphate from CTP to generate cytidine diphosphate (CDP)-l-glutamine, which is then hydrolyzed by γ-glutamyl-CDP-amidate hydrolase (Cj1417) to form cytidine diphosphoramidate (CDP-NH₂). Here, we show that Cj1415 catalyzes the ATP-dependent phosphorylation of CDP-NH₂ to form 3'-phospho-cytidine-5'-diphosphoramidate. Cj1415 will also catalyze the phosphorylation of adenosine diphosphoramidate (ADP-NH₂) and uridine diphosphoramidate (UDP-NH₂) but at significantly reduced rates. It is proposed that Cj1415 be named cytidine diphosphoramidate kinase.

Phase Variable Expression of a Single Phage Receptor in Campylobacter jejuni NCTC12662 Influences Sensitivity Toward Several Diverse CPS-Dependent Phages

Campylobacter jejuni NCTC12662 is sensitive to infection by many Campylobacter bacteriophages. Here we used this strain to investigate the molecular mechanism behind phage resistance development when exposed to a single phage and demonstrate how phase variable expression of one surface component influences phage sensitivity against many diverse C. jejuni phages. When C. jejuni NCTC12662 was exposed to phage F207 overnight, 25% of the bacterial cells were able to grow on a lawn of phage F207, suggesting that resistance develops at a high frequency. One resistant variant, 12662R, was further characterized and shown to be an adsorption mutant. Plaque assays using our large phage collection showed that seven out of 36 diverse capsular polysaccharide (CPS)-dependent phages could not infect 12662R, whereas the remaining phages formed plaques on 12662R with reduced efficiencies. Analysis of the CPS composition of 12662R by high-resolution magic angle spinning nuclear magnetic resonance (HR-MAS NMR) showed a diminished signal for O-methyl phosphoramidate (MeOPN), a phase variable modification of the CPS. This suggested that the majority of the 12662R population did not express this phase variable modification in the CPS, indicating that MeOPN serves as a phage receptor in NCTC12662. Whole genome analysis of 12662R showed a switch in the length of the phase variable homopolymeric G tract of gene 06810, encoding a putative MeOPN-transferase located in the CPS locus, resulting in a non-functional protein. To confirm the role of 06810 in phage resistance development of NCTC12662, a 06810 knockout mutant in NCTC12662 was constructed and analyzed by HR-MAS NMR demonstrating the absence of MeOPN in the CPS of the mutant. Plaque assays using NCTC12662Δ06810 demonstrated that seven of our CPS-dependent Campylobacter phages are dependent on the presence of MeOPN for successful infection of C. jejuni, whereas the remaining 29 phages infect independently of MeOPN, although with reduced efficiencies. Our data indicate that CPS-dependent phages uses diverse mechanisms for their initial interaction with their C. jejuni host.

Biosynthesis of Nucleoside Diphosphoramidates in Campylobacter jejuni

Campylobacter jejuni is a pathogenic Gram-negative bacterium and a leading cause of food-borne gastroenteritis. C. jejuni produces a capsular polysaccharide (CPS) that contains a unique O-methyl phosphoramidate modification (MeOPN). Recently, the first step in the biosynthetic pathway for the assembly of the MeOPN modification to the CPS was elucidated. It was shown that the enzyme Cj1418 catalyzes the phosphorylation of the amide nitrogen of l-glutamine to form l-glutamine phosphate. In this investigation, the metabolic fate of l-glutamine phosphate was determined. The enzyme Cj1416 catalyzes the displacement of pyrophosphate from MgCTP by l-glutamine phosphate to form CDP-l-glutamine. The enzyme Cj1417 subsequently catalyzes the hydrolysis of CDP-l-glutamine to generate cytidine diphosphoramidate and l-glutamate. The structures of the two novel intermediates, CDP-l-glutamine and cytidine diphosphoramidate, were confirmed by ³¹P nuclear magnetic resonance spectroscopy and mass spectrometry. It is proposed that the enzyme Cj1416 be named CTP:phosphoglutamine cytidylyltransferase and that the enzyme Cj1417 be named γ-glutamyl-CDP-amidate hydrolase.

Discovery of a Glutamine Kinase Required for the Biosynthesis of the O-Methyl Phosphoramidate Modifications Found in the Capsular Polysaccharides of Campylobacter jejuni

Bacterial capsular polysaccharides (CPS) are complex carbohydrate structures that play a role in the overall fitness of the organism. Campylobacter jejuni, known for being a major cause of bacterial gastroenteritis worldwide, produces a CPS with a unique O-methyl phosphoramidate (MeOPN) modification on specific sugar residues. The formation of P-N bonds in nature is relatively rare, and the pathway for the assembly of the phosphoramidate moiety in the CPS of C. jejuni is unknown. In this investigation we discovered that the initial transformation in the biosynthetic pathway for the MeOPN modification of the CPS involves the direct phosphorylation of the amide nitrogen of l-glutamine with ATP by the catalytic activity of Cj1418. The other two products are AMP and inorganic phosphate. The l-glutamine-phosphate product was characterized using 31P NMR spectroscopy and mass spectrometry. We suggest that this newly discovered enzyme be named l-glutamine kinase.

The biofilm matrix of Campylobacter jejuni determined by fluorescence lectin-binding analysis

Campylobacter jejuni is responsible for the most common bacterial foodborne gastroenteritis. Despite its fastidious growth, it can survive harsh conditions through biofilm formation. In this work, fluorescence lectin-binding analysis was used to determine the glycoconjugates present in the biofilm matrix of two well-described strains. Screening of 72 lectins revealed strain-specific patterns with six lectins interacting with the biofilm matrix of both strains. The most common sugar moiety contained galactose and N-acetylgalactosamine. Several lectins interacted with N-acetylglucosamine and sialic acid, probably originated from the capsular polysaccharides, lipooligosaccharides and N-glycans of C. jejuni. In addition, glycoconjugates containing mannose and fucose were detected within the biofilm, which have not previously been found in the C. jejuni envelope. Detection of thioflavin T and curcumin highlighted the presence of amyloids in the cell envelope without association with specific cell appendages. The lectins ECA, GS-I, HMA and LEA constitute a reliable cocktail to detect the biofilm matrix of C. jejuni.

A Flagellar Glycan-Specific Protein Encoded by Campylobacter Phages Inhibits Host Cell Growth

We previously characterized a carbohydrate binding protein, Gp047, derived from lytic Campylobacter phage NCTC 12673, as a promising diagnostic tool for the identification of Campylobacter jejuni and Campylobacter coli. We also demonstrated that this protein binds specifically to acetamidino-modified pseudaminic acid residues on host flagella, but the role of this protein in the phage lifecycle remains unknown. Here, we report that Gp047 is capable of inhibiting C. jejuni growth both on solid and liquid media, an activity, which we found to be bacteriostatic. The Gp047 domain responsible for bacterial growth inhibition is localized to the C-terminal quarter of the protein, and this activity is both contact- and dose-dependent. Gp047 gene homologues are present in all Campylobacter phages sequenced to date, and the resulting protein is not part of the phage particle. Therefore, these results suggest that either phages of this pathogen have evolved an effector protein capable of host-specific growth inhibition, or that Campylobacter cells have developed a mechanism of regulating their growth upon sensing an impending phage threat.