Identification of a new sialic acid-binding protein in Helicobacter pylori

How bacteria utilize sialic acid during interactions with the host: snip, snatch, dispatch, match and attach

N -glycolylneuraminic acid (Neu5Gc), and its precursor N-acetylneuraminic acid (Neu5Ac), commonly referred to as sialic acids, are two of the most common glycans found in mammals. Humans carry a mutation in the enzyme that converts Neu5Ac into Neu5Gc, and as such, expression of Neu5Ac can be thought of as a 'human specific' trait. Bacteria can utilize sialic acids as a carbon and energy source and have evolved multiple ways to take up sialic acids. In order to generate free sialic acid, many bacteria produce sialidases that cleave sialic acid residues from complex glycan structures. In addition, sialidases allow escape from innate immune mechanisms, and can synergize with other virulence factors such as toxins. Human-adapted pathogens have evolved a preference for Neu5Ac, with many bacterial adhesins, and major classes of toxin, specifically recognizing Neu5Ac containing glycans as receptors. The preference of human-adapted pathogens for Neu5Ac also occurs during biosynthesis of surface structures such as lipo-oligosaccharide (LOS), lipo-polysaccharide (LPS) and polysaccharide capsules, subverting the human host immune system by mimicking the host. This review aims to provide an update on the advances made in understanding the role of sialic acid in bacteria-host interactions made in the last 5-10 years, and put these findings into context by highlighting key historical discoveries. We provide a particular focus on 'molecular mimicry' and incorporation of sialic acid onto the bacterial outer-surface, and the role of sialic acid as a receptor for bacterial adhesins and toxins.

Sialic Acids as Receptors for Pathogens

Carbohydrates have long been known to mediate intracellular interactions, whether within one organism or between different organisms. Sialic acids (Sias) are carbohydrates that usually occupy the terminal positions in longer carbohydrate chains, which makes them common recognition targets mediating these interactions. In this review, we summarize the knowledge about animal disease-causing agents such as viruses, bacteria and protozoa (including the malaria parasite Plasmodium falciparum) in which Sias play a role in infection biology. While Sias may promote binding of, e.g., influenza viruses and SV40, they act as decoys for betacoronaviruses. The presence of two common forms of Sias, Neu5Ac and Neu5Gc, is species-specific, and in humans, the enzyme converting Neu5Ac to Neu5Gc (CMAH, CMP-Neu5Ac hydroxylase) is lost, most likely due to adaptation to pathogen regimes; we discuss the research about the influence of malaria on this trait. In addition, we present data suggesting the CMAH gene was probably present in the ancestor of animals, shedding light on its glycobiology. We predict that a better understanding of the role of Sias in disease vectors would lead to more effective clinical interventions.

Immunostimulatory and anti-allergic potential of novel heterotrimeric lectin from seeds of Zizyphus mauritiana Lam

Zizyphus mauritiana Lam. seeds (ZMS) have been used medicinally as sedative or hypnotic drugs in most of Asian countries. ZMS has significant benefits to the human health. Therefore, we have evaluated immunomodulatory effect of lectin extracted from these ZMSL in both in vitro and in vivo study. Anaphylaxis is a severe life-threatening allergic reaction and Arthus reaction is deposition of immune complex and complement system activation, so we hypothesized that if ZMSL can protect these severe allergic diseases. We have studied the effect of ZMSL on macrophages and Wistar albino rats and confirmed its protective effect against anaphylaxis and Arthus reaction. Results of this study suggest ZMSL have immunostimulatory and antiallergic activity.

Modification of Ganglioside Content of Human Gastric Epithelial Cell Membrane Decreases Helicobacter pylori Adhesion

BACKGROUND

In polarized cells, ganglioside location determines ganglioside function. Diet alters ganglioside content and composition in cell membranes. Ganglioside acts as a receptor for Helicobacter pylori. H pylori infects the stomach epithelium and may cause peptic ulcer disease and gastric cancer. The present study used purified gangliosides to modify the ganglioside composition of human gastric epithelial cells in vitro to reduce H pylori adhesion.

METHODS

A human gastric epithelial cell line (NCI-N87) was cultured with a ganglioside mix or with pure ganglioside (GM3 or GD3) at different concentrations (0-30 μg/mL) and ganglioside membrane content of gastric cells was determined after 48 hours. LC/triple quadrupole MS was used to analyse ganglioside concentration. H pylori was inoculated into the culture media of gastric cells previously treated with gangliosides GM3 or GD3 or a combination of GM3 and GD3.

RESULTS

GD3 and GM3 content increased in the plasma membrane in a dose-dependent manner. Gastric cells treated with GD3 showed more GM3 content than GD3 (P < 0.01). Ganglioside content was modified in the apical membrane, but GM3 and GD3 were also found in the basolateral membrane after treatments. Gastric cells treated with GM3, GD3 or the combination of GM3:GD3 decreased H pylori adhesion to gastric cells at all ganglioside concentrations tested by 80% compared with untreated gastric cells (P < 0.05).

CONCLUSIONS

These observations suggest that GD3 and GM3 present in the stomach lumen may be taken up into the apical gastric membrane and decrease H pylori adhesion to the epithelium.

Detection, purification and characterization of a lectin from freshwater green algae Spirogyra spp

Freshwater algae are rich sources of structurally biologically active metabolites, such as fatty acids, steroids, carotenoids and polysaccharides. Among these metabolites, lectins stand out. Lectins are proteins or glycoproteins of non-immune origin which bind to carbohydrates or glycoconjugates, without changing ligand structure. Many studies have reported on the use of Spirogyra spp. as effective bioindicators of heavy metals; however, reports on Spirogyra molecular bioprospecting are quite limited. Therefore, this study aimed to detect, isolate, purify and characterize a lectin present in the freshwater green algae Spirogyra. Presence of the lectin protein in the extract was detected by hemagglutination assays. Subsequently, the protein extract was subjected to a sugar inhibition assay to identify the lectin-specific carbohydrate. Following this, the extract was applied to a guar gum column to afford the pure lectin. The lectin was inhibited by N-acetyl-glucosamine and N-acetyl-beta-D-mannose, but more strongly by D-galactose. The apparent molecular mass of the purified lectin was evaluated by Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE). Electrophoretic analysis revealed a single protein band with an apparent molecular mass of 56 kDa. Thus, it could be concluded that a lectin was purified from Spirogyra spp.

Structural and functional aspects of the Helicobacter pylori secretome

Proteins secreted by Helicobacter pylori (H. pylori), an important human pathogen responsible for severe gastric diseases, are reviewed from the point of view of their biochemical characterization, both functional and structural. Despite the vast amount of experimental data available on the proteins secreted by this bacterium, the precise size of the secretome remains unknown. In this review, we consider as secreted both proteins that contain a secretion signal for the periplasm and proteins that have been detected in the external medium in in vitro experiments. In this way, H. pylori’s secretome appears to be composed of slightly more than 160 proteins, but this number must be considered very cautiously, not only because the definition of secretome itself is ambiguous but also because the included proteins were observed as secreted in in vitro experiments that were not representative of the environmental situation in vivo. The proteins that appear to be secreted can be grouped into different classes: enzymes (48 proteins), outer membrane proteins (43), components of flagella (11), members of the cytotoxic-associated genes pathogenicity island or other toxins (8 and 5, respectively), binding and transport proteins (9), and others (11). A final group, which includes 28 members, is represented by hypothetical uncharacterized proteins. Despite the large amount of data accumulated on the H. pylori secretome, a considerable amount of work remains to reach a full comprehension of the system at the molecular level.

Comparative genomic analysis of East Asian and non-Asian Helicobacter pylori strains identifies rapidly evolving genes

Helicobacter pylori infection is a risk factor for the development of gastric adenocarcinoma, a disease that has a high incidence in East Asia. Genes that are highly divergent in East Asian H. pylori strains compared to non-Asian strains are predicted to encode proteins that differ in functional activity and could represent novel determinants of virulence. To identify such proteins, we undertook a comparative analysis of sixteen H. pylori genomes, selected equally from strains classified as East Asian or non-Asian. As expected, the deduced sequences of two known virulence determinants (CagA and VacA) are highly divergent, with 77% and 87% mean amino acid sequence identities between East Asian and non-Asian groups, respectively. In total, we identified 57 protein sequences that are highly divergent between East Asian and non-Asian strains, but relatively conserved within East Asian strains. The most highly represented functional groups are hypothetical proteins, cell envelope proteins and proteins involved in DNA metabolism. Among the divergent genes with known or predicted functions, population genetic analyses indicate that 86% exhibit evidence of positive selection. McDonald-Kreitman tests further indicate that about one third of these highly divergent genes, including cagA and vacA, are under diversifying selection. We conclude that, similar to cagA and vacA, most of the divergent genes identified in this study evolved under positive selection, and represent candidate factors that may account for the disproportionately high incidence of gastric cancer associated with East Asian H. pylori strains. Moreover, these divergent genes represent robust biomarkers that can be used to differentiate East Asian and non-Asian H. pylori strains.

Glycoconjugates play a key role in Campylobacter jejuni Infection: interactions between host and pathogen

Glycan based interactions between host and pathogen are critical in many bacterial and viral diseases. Glycan interactions range from initial receptor based adherence to protecting the infective agent from the host’s immune response through molecular mimicry. Campylobacter jejuni is an ideal model for studying the role of glycans in host–pathogen interactions, as well as the role of bacterial surface glycoconjugates in infection. Using glycan array analysis, C. jejuni has been shown to interact with a wide range of host glycoconjugates. Mannose and sialic acid residues appear to play a role in initial interactions between host and pathogen following environmental exposure, whereas fucose and galactose based interactions are likely to be required for prolonged colonization. Other studies have highlighted potential decoy receptor type interactions between host’s intestinal mucins and C. jejuni, demonstrating the importance of host glycoproteins as defense against C. jejuni infection as well as the role for glycoconjugates found in human breast milk in protection of breast feeding infants from infection with C. jejuni. C. jejuni can produce N- and O-linked glycoproteins, capsular polysaccharide (CPS) and/or lipooligosaccharide (LOS) which results in C. jejuni presenting its own diverse sugar coated displays on the cell surface. Bacterial glycans play an important and versatile role in infection and disease. Of these, the best understood is the molecular mimicry of human gangliosides presented by C. jejuni’s LOS and its link to the onset of autoimmune neuropathies such as the Guillain Barrè syndrome (GBS). However, the role of glycoconjugates presented by C. jejuni extends beyond expression of sialylated ganglioside structures involved in initiation of GBS. Expression of surface glycans by C. jejuni may also relate to the ability of this organism to interact with the glycoproteins for initial host–pathogen interactions and continued infectivity.

Alzheimer's Disease: APP, Gamma Secretase, APOE, CLU, CR1, PICALM, ABCA7, BIN1, CD2AP, CD33, EPHA1, and MS4A2, and Their Relationships with Herpes Simplex, C. Pneumoniae, Other Suspect Pathogens, and the Immune System

Alzheimer's disease susceptibility genes, APP and gamma-secretase, are involved in the herpes simplex life cycle, and that of other suspect pathogens (C. pneumoniae, H. pylori, C. neoformans, B. burgdorferri, P. gingivalis) or immune defence. Such pathogens promote beta-amyloid deposition and tau phosphorylation and may thus be causative agents, whose effects are conditioned by genes. The antimicrobial effects of beta-amyloid, the localisation of APP/gamma-secretase in immunocompetent dendritic cells, and gamma secretase cleavage of numerous pathogen receptors suggest that this network is concerned with pathogen disposal, effects which may be abrogated by the presence of beta-amyloid autoantibodies in the elderly. These autoantibodies, as well as those to nerve growth factor and tau, also observed in Alzheimer's disease, may well be antibodies to pathogens, due to homology between human autoantigens and pathogen proteins. NGF or tau antibodies promote beta-amyloid deposition, neurofibrillary tangles, or cholinergic neuronal loss, and, with other autoantibodies, such as anti-ATPase, are potential agents of destruction, whose formation is dictated by sequence homology between pathogen and human proteins, and thus by pathogen strain and human genes. Pathogen elimination in the ageing population and removal of culpable autoantibodies might reduce the incidence and offer hope for a cure in this affliction.

Carbohydrate mediated bacterial adhesion

In the process of adhesion, bacteria often carry proteins on their surface, adhesins, that bind to specific components of tissue cells or the extracellular matrix. In many cases these components are carbohydrate structures. The carbohydrate binding specificities of many bacteria have been uncovered over the years. The design and synthesis of inhibitors of bacterial adhesion has the potential to create new therapeutics for the prevention and possibly treatment of bacterial infections. Unfortunately, the carbohydrate structures often bind only weakly to the adhesion proteins, although drug design approaches can improve the situation. Furthermore, in some cases linking carbohydrates covalently together, to create so-called multivalent systems, can also significantly enhance the inhibitory potency. Besides adhesion inhibition as a potential therapeutic strategy, the adhesion proteins can also be used for detection. Novel methods to do this are being developed. These include the use of microarrays and glyconanoparticles. New developments in these areas are discussed.

Identification of S-nitrosylation of proteins of Helicobacter pylori in response to nitric oxide stress

Innate and adaptive immune responses are activated in humans when Helicobacter pylori invades the gastric mucosa. Nitric oxide (NO) and reactive nitrogen species are important immune effectors, which can exert their functions through oxidation and S-nitrosylation of proteins. S-nitrosoglutathione and sodium nitroprus-side were used as NO donors and H. pylori cells were incubated with these compounds to analyze the inhibitory effect of NO. The suppressing effect of NO on H. pylori has been shown in vitro. Furthermore, the proteins modified by S-nitrosylation in H. pylori were identified through the biotin switch method in association with matrix-assisted laser desorption ionization/time-of-flight tandem mass spectrometry (MALDI-TOF-MS/MS). Five S-nitrosylated proteins identified were a chaperone and heat-shock protein (GroEL), alkyl hydroperoxide reductase (TsaA), urease alpha subunit (UreA), HP0721, and HP0129. Importantly, S-nitrosylation of TsaA and UreA were confirmed using purified recombinant proteins. Considering the importance of these enzymes in antioxidant defenses, adherence, and colonization, NO may exert its antibacterial actions by targeting enzymes through S-nitrosylation. Identification of protein S-nitrosylation may contribute to an understanding of the antibacterial actions of NO. Our findings provide an insight into potential targets for the development of novel therapeutic agents against H. pylori infection.

Large molecules as anti-adhesive compounds against pathogens

Anti-adhesive compounds are potential prophylactic tools in alternative treatment regimes against bacterial infection, as bacterial adhesion is commonly mediated by carbohydrate-protein interactions between surface adhesions of microorganisms and the host cell. The use of exogenous polyvalent, high-molecular carbohydrates and tannin-like plant-derived compounds should antagonize the adhesive interaction. A range of carbohydrates and carbohydrate- and proanthocyanidin-enriched plant extracts were screened for potential anti-adhesive effects against Helicobacter pylori, Campylobacter jejuni, Porphyromonas gingivalis and Candida albicans in different in-situ assays on primary tissue. The adhesion of H. pylori on human stomach tissue was effectively blocked by glucuronic acid-enriched polysaccharides from immature okra fruits (Abelmoschus esculentus). These compounds also had strong in-vitro effects against C. jejuni (inhibition up to 80%), but were ineffective in an in-vivo study in infected chicken broilers due to metabolism in the gastrointestinal system. Polysaccharides from Glycyrrhizia glabra, also enriched with glucuronic acid, showed strong anti-adhesive properties against H. pylori and P. gingivalis (inhibition 60–70%). Pelargonium sidoides extract, containing mainly polymeric proanthocyanidins, was effective against H. pylori in a dose-dependent manner. Due to the multifunctional adhesive strategy of C. albicans, no effective compounds were detected against this yeast. Structure-activity relationships are presented and the potential in-vivo use of carbohydrate-based anti-adhesives is discussed.

A haemagglutinin from the medicinal fungus Cordyceps militaris

There are only a few reports on agglutinins from ascomycete and medicinal fungi. An HA (haemagglutinin), with an N-terminal amino acid sequence different from those of known lectins, was isolated in the present study from dried fruiting bodies of the medicinal ascomycete fungus Cordyceps militaris. The purification protocol consisted of affinity chromatography, ion-exchange chromatography and gel filtration. The haemagglutinating activity of the HA could not be inhibited by simple sugars or heparin, and was stable over the pH range 2–13 and up to 60°C. Chemical modification of tryptophan and tyrosine residues had no effect. The HA exhibited some antiproliferative activity towards hepatoma (HepG2) cells and inhibited HIV-1 reverse transcriptase (IC50=10 μM). However, it did not exhibit antifungal activity, mitogenic activity towards splenocytes, nitric oxide-inducing activity towards macrophages or RNase activity. The results of the present study add to the meagre information pertaining to agglutinins from ascomycete and medicinal mushrooms. It is revealed in this study that C. militaris HA differs from other ascomycete mushroom HAs in a variety of biochemical characteristics.

Helicobacter pylori protein response to human bile stress

The ability of Helicobacter pylori to tolerate bile is likely to be important for its colonization and survival in the gastrointestinal tract of humans. As bile can be acidified after reflux into the low pH of the human stomach, the inhibitory effect of fresh human bile with normal appearance on H. pylori before and after acidification was tested first. The results showed that acidification of bile attenuated its inhibitory activity towards H. pylori. Next, the protein profiles of H. pylori under human bile and acidified bile stress were obtained by two-dimensional electrophoresis. Protein spots with differential expression were identified using tandem matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The results showed that the changes in proteomic profiles under bile and acidified bile stress were similar when compared with that of normal H. pylori. Expression of 28 proteins was found to be modulated, with the majority being induced during bile or acidified bile exposure. These proteins included molecular chaperones, proteins involved in iron storage, chemotaxis protein, enzymes related to energy metabolism and flagellar protein. These results indicate that H. pylori responds to bile and acidified bile stress through multiple mechanisms involving many signalling pathways.

To activate or not to activate: distinct strategies used by Helicobacter pylori and Francisella tularensis to modulate the NADPH oxidase and survive in human neutrophils

Neutrophils accumulate rapidly at sites of infection, and the ability of these cells to phagocytose and kill microorganisms is an essential component of the innate immune response. Relatively few microbial pathogens are able to evade neutrophil killing. Herein, we describe the novel strategies used by Helicobacter pylori and Francisella tularensis to disrupt neutrophil function, with a focus on assembly and activation of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase.

Gastroesophageal reflux disease leads to major alterations in lectin-binding in the columnar epithelium of the gastroesophageal junction

OBJECTIVE

Chronic gastritis and esophagitis are associated with changes in glycosylation patterns. Lectins are carbohydrate-binding proteins that are used as sensitive tools in the analysis of glycosylation patterns. The aim was to investigate the binding patterns of lectins UEA-I, DBA, HPA and PNA at the squamocolumnar junction in relation to the existence of gastroesophageal reflux disease (GERD) and Helicobacter pylori (H. pylori) infection.

MATERIAL AND METHODS

Eighty-eight patients with either dyspeptic or gastroesophageal reflux-related symptoms were included in the study and stratified into four subgroups based on the presence of GERD and H. pylori infection. The binding patterns of lectins were examined immunohistochemically at the squamocolumnar junction, in squamous (SE) and columnar-lined epithelium (CLE). Staining patterns of lectins were semiquantitatively evaluated using an immunohistochemical score; data were analyzed using the non-parametric Mann-Whitney U-test.

RESULTS

The presence of GERD led to significant changes in lectin-binding patterns. Lectin-binding was significantly reduced for UEA-I (p<0.0001), DBA (p<0.0001), PNA (p<0.01) and DBA (p<0.05) in CLE and SE of patients with GERD, respectively. H. pylori infection was associated with reduced PNA and DBA binding to the deep glandular mucosa of CLE (p<0.05) and surface SE (p<0.05), respectively.

CONCLUSIONS

Distinct and complex changes in lectin-staining patterns are most prominent in CLE of patients with GERD. The functional relevance of changes in the glycosylation patterns needs further investigation.

Phagocytosis and persistence of Helicobacter pylori

Helicobacter pylori is a spiral-shaped, flagellated, microaerophilic Gram-negative bacterium that colonizes the gastric epithelium of humans. All persons infected with H. pylori have gastritis, and some will develop severe disease such as peptic ulcers or gastric cancer. A characteristic feature of this infection is the pronounced accumulation of phagocytes, particularly neutrophils, in the gastric mucosa. H. pylori thrives in a phagocyte-rich environment, and we describe here how this organism uses an array of novel virulence factors to manipulate chemotaxis, phagocytosis, membrane trafficking and the respiratory burst as a means to evade elimination by the innate immune response.

Intervention with bacterial adhesion by multivalent carbohydrates

Bacterial adhesion is often a prelude to infection. In many cases, this process is governed by protein-carbohydrate interactions. Intervention at this early stage of infection is a conceptually highly attractive alternative to conventional antibiotics that are increasingly prone to resistance. The lack of high-affinity inhibitors of adhesion has proven to be a hurdle for further exploitation of this concept; however, new developments indicate a positive change. Structure-based design at the monovalent level and also evaluation of glycodendrimers and glycopolymers have yielded structures of high affinity. In addition to the development of inhibitors, topics of this review include available structural information of adhesion proteins, carbohydrate specificities of the various pathogens and their adhesion proteins. Other new developments aimed at affecting bacterial adhesion and the use of the adhesins for bacterial detection are also discussed.

Helicobacter pylori: present status and future prospects in Japan

The discovery of Helicobacter pylori has already changed the natural history of peptic ulcer disease, with most patients being cured at their first presentation. Similarly, the incidence of gastric cancer and other diseases related to H. pylori are likely to be greatly reduced in the near future. Isolation of the spiral intragastric bacterium H. pylori totally reversed the false dogma that the stomach was sterile, and it taught us that chronic infectious disease can still exist in modern society. Helicobacter pylori's unique location, persistence, and evasion of the immune system offer important insights into the pathophysiology of the gut. Also, the fact that it was overlooked for so long encourages us to think "outside the box" when investigating other diseases with obscure etiologies. We should consider such provocative scientific ideas as bridges to the future disease control.

Interactions between gastric epithelial stem cells and Helicobacter pylori in the setting of chronic atrophic gastritis

Chronic atrophic gastritis (ChAG), a Helicobacter pylori-associated risk factor for the development of gastric cancer, involves loss of acid-producing parietal cells. Recent studies in gnotobiotic mouse models of ChAG have shown that parietal cell loss results in amplification of multi- and oligo-potential gastric stem cells that express sialylated glycan receptors recognized by H. pylori adhesins. Moreover, H. pylori resides within a subset of these stem cells. Studies of the transcriptomes of gastric stem cells, harvested directly from the stomachs of uninfected mice, using laser capture microdissection, suggest that they have the ability to complement some of the metabolic needs of H. pylori. These findings indicate that proliferating and non-proliferating gastric stem cells provide a habitat that could support H. pylori persistence in a gastric ecosystem that has lost its acid barrier to colonization by environmental, oral and intestinal microbes. One consequence to the host might be an increased risk of tumorigenesis.