Functional characterization of Helicobacter pylori 26695 sedoheptulose 7-phosphate isomerase encoded by hp0857 and its association with lipopolysaccharide biosynthesis and adhesion

High salt condition alters LPS synthesis and induces the emergence of drug resistance mutations in Helicobacter pylori

The burgeoning emergence of drug-resistant Helicobacter pylori strains poses a significant challenge to the clinical success of eradication therapies and is primarily attributed to mutations within drug-targeting genes that lead to antibiotic resistance. This study investigated the effect of high salt conditions on the occurrence of drug-resistance mutations in H. pylori. We found that high salt condition significantly amplifies the frequency of drug resistance mutations in H. pylori. This can be chiefly attributed to our discovery indicating that high salt concentration results in elevated reactive oxygen species (ROS) levels, initiating DNA damage within H. pylori. Mechanistically, high salt condition suppresses lipopolysaccharide (LPS) synthesis gene expression, inducing alterations in the LPS structure and escalating outer membrane permeability. This disruption of LPS synthesis attenuates the expression and activity of SodB, facilitates increased ROS levels, and consequently increases the drug resistance mutation frequency. Impairing LPS synthesis engenders a reduction in intracellular iron levels, leading to diminished holo-Fur activity and increased apo-Fur activity, which represses the expression of SodB directly. Our findings suggest a correlation between high salt intake and the emergence of drug resistance in the human pathogen H. pylori, implying that dietary choices affect the risk of emergence of antimicrobial resistance.IMPORTANCEDrug resistance mutations mainly contribute to the emergence of clinical antibiotic-resistant Helicobacter pylori, a bacterium linked to stomach ulcers and cancer. In this study, we explored how elevated salt conditions influence the emergence of drug resistance in H. pylori. We demonstrate that H. pylori exhibits an increased antibiotic resistance mutation frequency when exposed to a high salt environment. We observed an increase in reactive oxygen species (ROS) under high salt conditions, which can cause DNA damage and potentially lead to mutations. Moreover, our results showed that high salt condition alters the bacterium's lipopolysaccharide (LPS) synthesis, leading to a reduced expression of SodB in a Fur-dependent manner. This reduction, in turn, elevates ROS levels, culminating in a higher frequency of drug-resistance mutations. Our research underscores the critical need to consider environmental influences, such as diet and lifestyle, in managing bacterial infections and combating the growing challenge of antibiotic resistance.

Animal Models of Helicobacter pylori Infection and Vaccines: Current Status and Future Prospects

Helicobacter pylori infection causes chronic gastritis, ulcers, and gastric cancer, making it a threat to human health. Despite the use of antibiotic therapy, the global prevalence of H. pylori infection remains high, necessitating early eradication measures. Immunotherapy, especially vaccine development, is a promising solution in this direction, albeit the selection of an appropriate animal model is critical in efficient vaccine production. Accordingly, we conducted a literature, search and summarized the commonly used H. pylori strains, H. pylori infection-related animal models, and models for evaluating H. pylori vaccines. Based on factors such as the ability to replicate human diseases, strain compatibility, vaccine types, and eliciting of immune responses, we systematically compared the advantages and disadvantages of different animal models, to obtain the informed recommendations. In addition, we have proposed novel perspectives on H. pylori-related animal models to advance research and vaccine evaluation for the prevention and treatment of diseases such as gastric cancer.

The effect of altered pH growth conditions on the production, composition, and proteomes of Helicobacter pylori outer membrane vesicles

Gram-negative bacteria release outer membrane vesicles (OMVs) that contain cargo derived from their parent bacteria. Helicobacter pylori is a Gram-negative human pathogen that produces urease to increase the pH of the surrounding environment to facilitate colonization of the gastric mucosa. However, the effect of acidic growth conditions on the production and composition of H. pylori OMVs is unknown. In this study, we examined the production, composition, and proteome of H. pylori OMVs produced during acidic and neutral pH growth conditions. H. pylori growth in acidic conditions reduced the quantity and size of OMVs produced. Additionally, OMVs produced during acidic growth conditions had increased protein, DNA, and RNA cargo compared to OMVs produced during neutral conditions. Proteomic analysis comparing the proteomes of OMVs to their parent bacteria demonstrated significant differences in the enrichment of beta-lactamases and outer membrane proteins between bacteria and OMVs, supporting that differing growth conditions impacts OMV composition. We also identified differences in the enrichment of proteins between OMVs produced during different pH growth conditions. Overall, our findings reveal that growth of H. pylori at different pH levels is a factor that alters OMV proteomes, which may affect their subsequent functions.

Genomic and Transcriptomic Analyses Reveal Multiple Strategies for Vibrio parahaemolyticus to Tolerate Sub-Lethal Concentrations of Three Antibiotics

Vibrio parahaemolyticus can cause acute gastroenteritis, wound infections, and septicemia in humans. The overuse of antibiotics in aquaculture may lead to a high incidence of the multidrug-resistant (MDR) pathogen. Nevertheless, the genome evolution of V. parahaemolyticus in aquatic animals and the mechanism of its antibiotic tolerance remain to be further deciphered. Here, we investigated the molecular basis of the antibiotic tolerance of V. parahaemolyticus isolates (n = 3) originated from shellfish and crustaceans using comparative genomic and transcriptomic analyses. The genome sequences of the V. parahaemolyticus isolates were determined (5.0-5.3 Mb), and they contained 4709-5610 predicted protein-encoding genes, of which 823-1099 genes were of unknown functions. Comparative genomic analyses revealed a number of mobile genetic elements (MGEs, n = 69), antibiotic resistance-related genes (n = 7-9), and heavy metal tolerance-related genes (n = 2-4). The V. parahaemolyticus isolates were resistant to sub-lethal concentrations (sub-LCs) of ampicillin (AMP, 512 μg/mL), kanamycin (KAN, 64 μg/mL), and streptomycin (STR, 16 μg/mL) (p < 0.05). Comparative transcriptomic analyses revealed that there were significantly altered metabolic pathways elicited by the sub-LCs of the antibiotics (p < 0.05), suggesting the existence of multiple strategies for antibiotic tolerance in V. parahaemolyticus. The results of this study enriched the V. parahaemolyticus genome database and should be useful for controlling the MDR pathogen worldwide.

Potentiating Activity of GmhA Inhibitors on Gram-Negative Bacteria

Inhibition of the biosynthesis of bacterial heptoses opens novel perspectives for antimicrobial therapies. The enzyme GmhA responsible for the first committed biosynthetic step catalyzes the conversion of sedoheptulose 7-phosphate into d-glycero-d-manno-heptose 7-phosphate and harbors a Zn2+ ion in the active site. A series of phosphoryl- and phosphonyl-substituted derivatives featuring a hydroxamate moiety were designed and prepared from suitably protected ribose or hexose derivatives. High-resolution crystal structures of GmhA complexed to two N-formyl hydroxamate inhibitors confirmed the binding interactions to a central Zn2+ ion coordination site. Some of these compounds were found to be nanomolar inhibitors of GmhA. While devoid of HepG2 cytotoxicity and antibacterial activity of their own, they demonstrated in vitro lipopolysaccharide heptosylation inhibition in Enterobacteriaceae as well as the potentiation of erythromycin and rifampicin in a wild-type Escherichia coli strain. These inhibitors pave the way for a novel treatment of Gram-negative infections.

Helicobacter pylori infection and Parkinson's Disease: etiology, pathogenesis and levodopa bioavailability

Parkinson's disease (PD), a neurodegenerative disorder with an unknown etiology, is primarily characterized by the degeneration of dopamine (DA) neurons. The prevalence of PD has experienced a significant surge in recent years. The unidentified etiology poses limitations to the development of effective therapeutic interventions for this condition. Helicobacter pylori (H. pylori) infection has affected approximately half of the global population. Mounting evidences suggest that H. pylori infection plays an important role in PD through various mechanisms. The autotoxin produced by H. pylori induces pro-inflammatory cytokines release, thereby facilitating the occurrence of central inflammation that leads to neuronal damage. Simultaneously, H. pylori disrupts the equilibrium of gastrointestinal microbiota with an overgrowth of bacteria in the small intestinal known as small intestinal bacterial overgrowth (SIBO). This dysbiosis of the gut flora influences the central nervous system (CNS) through microbiome-gut-brain axis. Moreover, SIBO hampers levodopa absorption and affects its therapeutic efficacy in the treatment of PD. Also, H. pylori promotes the production of defensins to regulate the permeability of the blood-brain barrier, facilitating the entry of harmful factors into the CNS. In addition, H. pylori has been found to induce gastroparesis, resulting in a prolonged transit time for levodopa to reach the small intestine. H. pylori may exploit levodopa to facilitate its own growth and proliferation, or it can inflict damage to the gastrointestinal mucosa, leading to gastrointestinal ulcers and impeding levodopa absorption. Here, this review focused on the role of H. pylori infection in PD from etiology, pathogenesis to levodopa bioavailability.

Quorum sensing autoinducers AHLs protect Shewanella baltica against phage infection

Quorum sensing (QS) plays an important role in phage-host interactions. Shewanella baltica can't produce the N-acyl-homoserine lactones (AHLs) signal molecules but can eavesdrop on exogenous AHLs through its LuxR receptor. However, no clear evidence exists regarding the involvement of AHLs-mediated QS systems in S. baltica in regulating phage infection. Here, we report that AHLs modulated the phage resistance of S. baltica OS155. Specifically, we characterized a S. baltica phage vB_Sb_QDWS and preliminarily identified that lipopolysaccharide (LPS) is an important receptor for phage vB_Sb_QDWS. AHLs could protect S. baltica against phage infection by decreasing LPS-mediated phage adsorption. The expression of genes galU and tkt, which are essential for LPS synthesis, down-regulated significantly in response to AHLs autoinducers. Our finding confirms the important roles of QS in virus-host interactions and would be helpful to develop novel phage strategies for food spoilage control.

Helicobacter pylori Modulates Heptose Metabolite Biosynthesis and Heptose-Dependent Innate Immune Host Cell Activation by Multiple Mechanisms

Heptose metabolites including ADP-d-glycero-β-d-manno-heptose (ADP-heptose) are involved in bacterial lipopolysaccharide and cell envelope biosynthesis. Recently, heptoses were also identified to have potent proinflammatory activity on human cells as novel microbe-associated molecular patterns. The gastric pathogenic bacterium Helicobacter pylori produces heptose metabolites, which it transports into human cells through its Cag type 4 secretion system. Using H. pylori as a model, we have addressed the question of how proinflammatory ADP-heptose biosynthesis can be regulated by bacteria. We have characterized the interstrain variability and regulation of heptose biosynthesis genes and the modulation of heptose metabolite production by H. pylori, which impact cell-autonomous proinflammatory human cell activation. HldE, a central enzyme of heptose metabolite biosynthesis, showed strong sequence variability between strains and was also variably expressed between strains. Amounts of gene transcripts in the hldE gene cluster displayed intrastrain and interstrain differences, were modulated by host cell contact and the presence of the cag pathogenicity island, and were affected by carbon starvation regulator A (CsrA). We reconstituted four steps of the H. pylori lipopolysaccharide (LPS) heptose biosynthetic pathway in vitro using recombinant purified GmhA, HldE, and GmhB proteins. On the basis of one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry, the structures of major reaction products were identified as β-d-ADP-heptose and β-heptose-1-monophosphate. A proinflammatory heptose-monophosphate variant was also identified for the first time as a novel cell-active product in H. pylori bacteria. Separate purified HldE subdomains and variant HldE allowed us to uncover additional strain variation in generating heptose metabolites. IMPORTANCE Bacterial heptose metabolites, intermediates of lipopolysaccharide (LPS) biosynthesis, are novel microbe-associated molecular patterns (MAMPs) that activate proinflammatory signaling. In the gastric pathogen Helicobacter pylori, heptoses are transferred into host cells by the Cag type IV secretion system, which is also involved in carcinogenesis. Little is known about how H. pylori, which is highly strain variable, regulates heptose biosynthesis and downstream host cell activation. We report here that the regulation of proinflammatory heptose production by H. pylori is strain specific. Heptose gene cluster activity is modulated by the presence of an active cag pathogenicity island (cagPAI), contact with human cells, and the carbon starvation regulator A. Reconstitution with purified biosynthesis enzymes and purified bacterial lysates allowed us to biochemically characterize heptose pathway products, identifying a heptose-monophosphate variant as a novel proinflammatory metabolite. These findings emphasize that the bacteria use heptose biosynthesis to fine-tune inflammation and also highlight opportunities to mine the heptose biosynthesis pathway as a potential therapeutic target against infection, inflammation, and cancer.

A Bittersweet Kiss of Gram-Negative Bacteria: The Role of ADP-Heptose in the Pathogenesis of Infection

Due to the global crisis caused by the dramatic rise of drug resistance among Gram-negative bacteria, there is an urgent need for a thorough understanding of the pathogenesis of infections of such an etiology. In light of the limited availability of new antibiotics, therapies aimed at host-pathogen interactions emerge as potential treatment modalities. Thus, understanding the mechanism of pathogen recognition by the host and immune evasion appear to be the key scientific issues. Until recently, lipopolysaccharide (LPS) was recognized as a major pathogen-associated molecular pattern (PAMP) of Gram-negative bacteria. However, recently, ADP-L-glycero-β-D-manno-heptose (ADP-heptose), an intermediate carbohydrate metabolite of the LPS biosynthesis pathway, was discovered to activate the hosts' innate immunity. Therefore, ADP-heptose is regarded as a novel PAMP of Gram-negative bacteria that is recognized by the cytosolic alpha kinase-1 (ALPK1) protein. The conservative nature of this molecule makes it an intriguing player in host-pathogen interactions, especially in the context of changes in LPS structure or even in its loss by certain resistant pathogens. Here, we present the ADP-heptose metabolism, outline the mechanisms of its recognition and the activation of its immunity, and summarize the role of ADP-heptose in the pathogenesis of infection. Finally, we hypothesize about the routes of the entry of this sugar into cytosol and point to emerging questions that require further research.

Genomic and Transcriptomic Analysis Reveal Multiple Strategies for the Cadmium Tolerance in Vibrio parahaemolyticus N10-18 Isolated from Aquatic Animal Ostrea gigas Thunberg

The waterborne Vibrio parahaemolyticus can cause acute gastroenteritis, wound infection, and septicemia in humans. Pollution of heavy metals in aquatic environments is proposed to link high incidence of the multidrug-resistant (MDR) pathogen. Nevertheless, the genome evolution and heavy metal tolerance mechanism of V. parahaemolyticus in aquatic animals remain to be largely unveiled. Here, we overcome the limitation by characterizing an MDR V. parahaemolyticus N10-18 isolate with high cadmium (Cd) tolerance using genomic and transcriptomic techniques. The draft genome sequence (4,910,080 bp) of V. parahaemolyticus N10-18 recovered from Ostrea gigas Thunberg was determined, and 722 of 4653 predicted genes had unknown function. Comparative genomic analysis revealed mobile genetic elements (n = 11) and heavy metal and antibiotic-resistance genes (n = 38 and 7). The bacterium significantly changed cell membrane structure to resist the Cd2+ (50 μg/mL) stress (p < 0.05). Comparative transcriptomic analysis revealed seven significantly altered metabolic pathways elicited by the stress. The zinc/Cd/mercury/lead transportation and efflux and the zinc ATP-binding cassette (ABC) transportation were greatly enhanced; metal and iron ABC transportation and thiamine metabolism were also up-regulated; conversely, propanoate metabolism and ribose and maltose ABC transportation were inhibited (p < 0.05). The results of this study demonstrate multiple strategies for the Cd tolerance in V. parahaemolyticus.

Helicobacter pylori employs a general protein glycosylation system for the modification of outer membrane adhesins

Helicobacter pylori infection is associated with the development of several gastric diseases including gastric cancer. To reach a long-term colonization in the host stomach, H. pylori employs multiple outer membrane adhesins for binding to the gastric mucosa. However, due to the redundancy of adhesins that complement the adhesive function of bacteria, targeting each individual adhesin alone usually achieves nonideal outcomes for preventing bacterial adhesion. Here, we report that key adhesins AlpA/B and BabA/B in H. pylori are modified by glycans and display a two-step molecular weight upshift pattern from the cytoplasm to the inner membrane and from the inner membrane to the outer membrane. Nevertheless, this upshift pattern is missing when the expression of some enzymes related to lipopolysaccharide (LPS) biosynthesis, including the LPS O-antigen assembly and ligation enzymes WecA, Wzk, and WaaL, is disrupted, indicating that the underlying mechanisms and the involved enzymes for the adhesin glycosylation are partially shared with the LPS biosynthesis. Loss of the adhesin glycosylation not only reduces the protease resistance and the stability of the tested adhesins but also changes the adhesin-binding ability. In addition, mutations in the LPS biosynthesis cause a significant reduction in bacterial adhesion in the in vitro cell-line model. The current findings reveal that H. pylori employs a general protein glycosylation system related to LPS biosynthesis for adhesin modification and its biological significance. The enzymes required for adhesin glycosylation rather than the adhesins themselves are potentially better drug targets for preventing or treating H. pylori infection.

The Effects of HP0044 and HP1275 Knockout Mutations on the Structure and Function of Lipopolysaccharide in Helicobacter pylori Strain 26695

Helicobacter pylori infection is associated with several gastric diseases, including gastritis, peptic ulcer, gastric adenocarcinoma and mucosa-associated lymphatic tissue (MALT) lymphoma. Due to the prevalence and severeness of H. pylori infection, a thorough understanding of this pathogen is necessary. Lipopolysaccharide, one of the major virulence factors of H. pylori, can exert immunomodulating and immunostimulating functions on the host. In this study, the HP0044 and HP1275 genes were under investigation. These two genes potentially encode GDP-D-mannose dehydratase (GMD) and phosphomannomutase (PMM)/phosphoglucomutase (PGM), respectively, and are involved in the biosynthesis of fucose. HP0044 and HP1275 knockout mutants were generated; both mutants displayed a truncated LPS, suggesting that the encoded enzymes are not only involved in fucose production but are also important for LPS construction. In addition, these two gene knockout mutants exhibited retarded growth, increased surface hydrophobicity and autoaggregation as well as being more sensitive to the detergent SDS and the antibiotic novobiocin. Furthermore, the LPS-defective mutants also had significantly reduced bacterial infection, adhesion and internalization in the in vitro cell line model. Moreover, disruptions of the HP0044 and HP1275 genes in H. pylori altered protein sorting into outer membrane vesicles. The critical roles of HP0044 and HP1275 in LPS biosynthesis, bacterial fitness and pathogenesis make them attractive candidates for drug inventions against H. pylori infection.

TIFA has dual functions in Helicobacter pylori-induced classical and alternative NF-κB pathways

Helicobacter pylori infection constitutes one of the major risk factors for the development of gastric diseases including gastric cancer. The activation of nuclear factor‐kappa‐light‐chain‐enhancer of activated B cells (NF‐κB) via classical and alternative pathways is a hallmark of H. pylori infection leading to inflammation in gastric epithelial cells. Tumor necrosis factor receptor‐associated factor (TRAF)‐interacting protein with forkhead‐associated domain (TIFA) was previously suggested to trigger classical NF‐κB activation, but its role in alternative NF‐κB activation remains unexplored. Here, we identify TRAF6 and TRAF2 as binding partners of TIFA, contributing to the formation of TIFAsomes upon H. pylori infection. Importantly, the TIFA/TRAF6 interaction enables binding of TGFβ‐activated kinase 1 (TAK1), leading to the activation of classical NF‐κB signaling, while the TIFA/TRAF2 interaction causes the transient displacement of cellular inhibitor of apoptosis 1 (cIAP1) from TRAF2, and proteasomal degradation of cIAP1, to facilitate the activation of the alternative NF‐κB pathway. Our findings therefore establish a dual function of TIFA in the activation of classical and alternative NF‐κB signaling in H. pylori‐infected gastric epithelial cells.

Helicobacter pylori GmhB enzyme involved in ADP-heptose biosynthesis pathway is essential for lipopolysaccharide biosynthesis and bacterial virulence

Helicobacter pylori infection is linked to serious gastric-related diseases including gastric cancer. However, current therapies for treating H. pylori infection are challenged by the increased antibiotic resistance of H. pylori. Therefore, it is in an urgent need to identify novel targets for drug development against H. pylori infection. In this study, HP0860 gene from H. pylori predicted to encode a D-glycero-D-manno-heptose-1,7-bisphosphate phosphatase (GmhB) involved in the synthesis of ADP-L-glycero-D-manno-heptose for the assembly of lipopolysaccharide (LPS) in the inner core region was cloned and characterized. We reported HP0860 protein is monomeric and functions as a phosphatase by converting D-glycero-D-manno-heptose-1,7-bisphosphate into D-glycero-D-manno-heptose-1-phosphate with a preference for the β-anomer over the α-anomer of sugar phosphate substrates. Subsequently, a HP0860 knockout mutant and its complementary mutant were constructed and their phenotypic properties were examined. HP0860 knockout mutant contained both mature and immature forms of LPS and could still induce significant IL-8 secretion after gastric AGS cell infection, suggesting other enzymatic activities in HP0860 knockout mutant might be able to partially compensate for the loss of HP0860 activity. In addition, HP0860 knockout mutant was much more sensitive to antibiotic novobiocin, had decreased adherence abilities, and caused less classic hummingbird phenotype on the infected AGS cells, indicating H. pylori lacking HP0860 is less virulent. Furthermore, the disruption of HP0860 gene altered the sorting of cargo proteins into outer membrane vesicles (OMVs). The above findings confirm the importance of HP0860 in LPS core biosynthesis and shed light on therapeutic intervention against H. pylori infection.

Structural and functional characterization of M. tuberculosis sedoheptulose- 7-phosphate isomerase, a critical enzyme involved in lipopolysaccharide biosynthetic pathway

M. tuberculosis GmhA enzyme catalyzes the isomerization of D-sedoheptulose 7-phosphate into D-glycero-D-α-manno-heptose-7-phosphate in GDP-D-glycero-α-D-manno-heptose biosynthetic pathway. The D-glycero-α-D-manno-heptose is a major constituent of lipopolysaccharide and contributes to virulence and antibiotic resistance to mycobacteria. In current study, we have performed the structural and biochemical analysis of M. tuberculosis GmhA, the first enzyme involved in D-sedoheptulose 7-phosphate isomerization in GDP-D-α-D-heptose biosynthetic pathway. The MtbGmhA enzyme exits as tetramer and small angle X-ray scattering analysis also yielded tetrameric envelope in solution. The MtbGmhA enzyme binds to D-sedoheptulose 7-phosphate with K_m ~ 0.31 ± 0.06 mM^-1 and coverts it to D-glycero-D-α-manno-heptose-7-phosphate with catalytic efficiency (k_cat/K_m) ~ 1.45 mM^-1 s^-1. The residues involved in D-sedoheptulose 7-phosphate and Zn²⁺ binding were identified using modeled MtbGmhA + D-sedoheptulose 7-phosphate + Zn²⁺ structure. To understand the role in catalysis, six site directed mutants of MtbGmhA were generated, which showed significant decrease in catalytic activity. The circular dichroism analysis showed ~ 46% α-helix, ~ 19% β-sheet and ~ 35% random coil structures of MtbGmhA enzyme and melting temperature ~ 53.5 °C. Small angle X-ray scattering analysis showed the tetrameric envelope, which fitted well with modeled MtbGmhA tetramer in closed conformation. The MtbGmhA dynamics involved in D-sedoheptulose 7-phosphate and Zn²⁺ binding was identified using dynamics simulation and showed enhanced stability in presence of these ligands. Our biochemical data and structural knowledge have provided insight into mechanism of action of MtbGmhA enzyme, which can be targeted for novel antibiotics development against M. tuberculosis.

Chemical synthesis of human trefoil factor 1 (TFF1) and its homodimer provides novel insights into their mechanisms of action

TFF1 is a key peptide for gastrointestinal protection and repair. Its molecular mechanism of action remains poorly understood with synthetic intractability a recognised bottleneck. Here we describe the synthesis of TFF1 and its homodimer and their interactions with mucins and Helicobacter pylori. Synthetic access to TFF1 is an important milestone for probe and therapeutic development.

Direct Genetic and Enzymatic Evidence for Oxidative Cyclization in Hygromycin B Biosynthesis

Hygromycin B is an aminoglycoside antibiotic with a structurally distinctive orthoester linkage. Despite its long history of use in industry and in the laboratory, its biosynthesis remains poorly understood. We show here, by in-frame gene deletion in vivo and detailed enzyme characterization in vitro, that formation of the unique orthoester moiety is catalyzed by the α-ketoglutarate- and non-heme iron-dependent oxygenase HygX. In addition, we identify HygF as a glycosyltransferase adding UDP-hexose to 2-deoxystreptamine, HygM as a methyltransferase responsible for N-3 methylation, and HygK as an epimerase. These experimental results and bioinformatic analyses allow a detailed pathway for hygromycin B biosynthesis to be proposed, including the key oxidative cyclization reactions.

TIFA Signaling in Gastric Epithelial Cells Initiates the cag Type 4 Secretion System-Dependent Innate Immune Response to Helicobacter pylori Infection

Helicobacter pylori is a bacterial pathogen that colonizes the human stomach, causing inflammation which, in some cases, leads to gastric ulcers and cancer. The clinical outcome of infection depends on a complex interplay of bacterial, host genetic, and environmental factors. Although H. pylori is recognized by both the innate and adaptive immune systems, this rarely results in bacterial clearance. Gastric epithelial cells are the first line of defense against H. pylori and alert the immune system to bacterial presence. Cytosolic delivery of proinflammatory bacterial factors through the cag type 4 secretion system (cag-T4SS) has long been appreciated as the major mechanism by which gastric epithelial cells detect H. pylori Classically attributed to the peptidoglycan sensor NOD1, recent work has highlighted the role of NOD1-independent pathways in detecting H. pylori; however, the bacterial and host factors involved have remained unknown. Here, we show that bacterially derived heptose-1,7-bisphosphate (HBP), a metabolic precursor in lipopolysaccharide (LPS) biosynthesis, is delivered to the host cytosol through the cag-T4SS, where it activates the host tumor necrosis factor receptor-associated factor (TRAF)-interacting protein with forkhead-associated domain (TIFA)-dependent cytosolic surveillance pathway. This response, which is independent of NOD1, drives robust NF-κB-dependent inflammation within hours of infection and precedes NOD1 activation. We also found that the CagA toxin contributes to the NF-κB-driven response subsequent to TIFA and NOD1 activation. Taken together, our results indicate that the sequential activation of TIFA, NOD1, and CagA delivery drives the initial inflammatory response in gastric epithelial cells, orchestrating the subsequent recruitment of immune cells and leading to chronic gastritis.IMPORTANCEH. pylori is a globally prevalent cause of gastric and duodenal ulcers and cancer. H. pylori antibiotic resistance is rapidly increasing, and a vaccine remains elusive. The earliest immune response to H. pylori is initiated by gastric epithelial cells and sets the stage for the subsequent immunopathogenesis. This study revealed that host TIFA and H. pylori-derived HBP are critical effectors of innate immune signaling that account for much of the inflammatory response to H. pylori in gastric epithelial cells. HBP is delivered to the host cell via the cag-T4SS at a time point that precedes activation of the previously described NOD1 and CagA inflammatory pathways. Manipulation of the TIFA-driven immune response in the host and/or targeting of ADP-heptose biosynthesis enzymes in H. pylori may therefore provide novel strategies that may be therapeutically harnessed to achieve bacterial clearance.

Helicobacter pylori modulates host cell responses by CagT4SS-dependent translocation of an intermediate metabolite of LPS inner core heptose biosynthesis

Highly virulent Helicobacter pylori cause proinflammatory signaling inducing the transcriptional activation and secretion of cytokines such as IL-8 in epithelial cells. Responsible in part for this signaling is the cag pathogenicity island (cagPAI) that codetermines the risk for pathological sequelae of an H. pylori infection such as gastric cancer. The Cag type IV secretion system (CagT4SS), encoded on the cagPAI, can translocate various molecules into cells, the effector protein CagA, peptidoglycan metabolites and DNA. Although these transported molecules are known to contribute to cellular responses to some extent, a major part of the cagPAI-induced signaling leading to IL-8 secretion remains unexplained. We report here that biosynthesis of heptose-1,7-bisphosphate (HBP), an important intermediate metabolite of LPS inner heptose core, contributes in a major way to the H. pylori cagPAI-dependent induction of proinflammatory signaling and IL-8 secretion in human epithelial cells. Mutants defective in the genes required for synthesis of HBP exhibited a more than 95% reduction of IL-8 induction and impaired CagT4SS-dependent cellular signaling. The loss of HBP biosynthesis did not abolish the ability to translocate CagA. The human cellular adaptor TIFA, which was described before to mediate HBP-dependent activity in other Gram-negative bacteria, was crucial in the cagPAI- and HBP pathway-induced responses by H. pylori in different cell types. The active metabolite was present in H. pylori lysates but not enriched in bacterial supernatants. These novel results advance our mechanistic understanding of H. pylori cagPAI-dependent signaling mediated by intracellular pattern recognition receptors. They will also allow to better dissect immunomodulatory activities by H. pylori and to improve the possibilities of intervention in cagPAI- and inflammation-driven cancerogenesis.

The Cag Type IV secretion system, which contributes to inflammation and cancerogenesis during chronic infection, is one of the major virulence and fitness factors of the bacterial gastric pathogen Helicobacter pylori. Up to now, the mechanisms leading to cagPAI-dependent signal transduction and cytokine secretion were not completely understood. We report here that HBP, an intermediate metabolite in LPS core heptose biosynthesis, is translocated into host cells dependent on the CagT4SS, and is a major factor leading to the activation of cellular responses. This response is connected to the human cellular adaptor protein TIFA. The knowledge of this specific response pathway is a major advance in understanding CagT4SS-dependent signaling and will enable us to understand better how H. pylori modulates the immune response repertoire in its human host.