Insights from the redefinition of Helicobacter pylori lipopolysaccharide O-antigen and core-oligosaccharide domains

Chemical Synthesis of a Branched Nonasaccharide Fragment from Helicobacter pylori Lipopolysaccharide

A chemical synthesis of a unique nanosaccharide fragment from Helicobacter pylori lipopolysaccharide was achieved via a convergent glycosylation method. Challenges involved in the synthesis include the highly stereoselective construction of β-3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) and two 1,2-cis-glycosidic linkages, as well as the formation of a branched 2,7-disubstituted heptose subunit. Hydrogen-bond mediated aglycone delivery strategy and benzoyl-directing remote participation effect were employed, respectively, for the efficient generation of the desired β-Kdo glycoside and 1,2-cis-α-l-fucoside/d-glucoside. Moreover, the key branched framework was successfully established through a [(7 + 1) + 1] assembly approach involving the stepwise glycosylation of the heptasaccharide alcohol with two monosaccharide donors. The synthesized 1 containing a propylamine linker at the reducing end can be covalently bound to a carrier protein for further immunological studies.

Mechanism of Iron Ion Homeostasis in Intestinal Immunity and Gut Microbiota Remodeling

Iron is a vital trace element that plays an important role in humans and other organisms. It plays an active role in the growth, development, and reproduction of bacteria, such as Bifidobacteria. Iron deficiency or excess can negatively affect bacterial hosts. Studies have reported a major role of iron in the human intestine, which is necessary for maintaining body homeostasis and intestinal barrier function. Organisms can maintain their normal activities and regulate some cancer cells in the body by regulating iron excretion and iron-dependent ferroptosis. In addition, iron can modify the interaction between hosts and microorganisms by altering their growth and virulence or by affecting the immune system of the host. Lactic acid bacteria such as Lactobacillus acidophilus (L. acidophilus), Lactobacillus rhamnosus (L. rhamnosus), and Lactobacillus casei (L. casei) were reported to increase trace elements, protect the host intestinal barrier, mitigate intestinal inflammation, and regulate immune function. This review article focuses on the two aspects of the iron and gut and generally summarizes the mechanistic role of iron ions in intestinal immunity and the remodeling of gut microbiota.

Helicobacter pylori binds human Annexins via Lipopolysaccharide to interfere with Toll-like Receptor 4 signaling

Helicobacter pylori colonizes half of the global population and causes gastritis, peptic ulcer disease or gastric cancer. In this study, we were interested in human annexin (ANX), which comprises a protein family with diverse and partly unknown physiological functions, but with a potential role in microbial infections and possible involvement in gastric cancer. We demonstrate here for the first time that H. pylori is able to specifically bind ANXs. Binding studies with purified H. pylori LPS and specific H. pylori LPS mutant strains indicated binding of ANXA5 to lipid A, which was dependent on the lipid A phosphorylation status. Remarkably, ANXA5 binding almost completely inhibited LPS-mediated Toll-like receptor 4- (TLR4) signaling in a TLR4-specific reporter cell line. Furthermore, the interaction is relevant for gastric colonization, as a mouse-adapted H. pylori increased its ANXA5 binding capacity after gastric passage and its ANXA5 incubation in vitro interfered with TLR4 signaling. Moreover, both ANXA2 and ANXA5 levels were upregulated in H. pylori-infected human gastric tissue, and H. pylori can be found in close association with ANXs in the human stomach. Furthermore, an inhibitory effect of ANXA5 binding for CagA translocation could be confirmed. Taken together, our results highlight an adaptive ability of H. pylori to interact with the host cell factor ANX potentially dampening innate immune recognition.

H. pylori is very well adapted to its natural habitat, the human gastric mucosa. For this purpose, the bacterium has evolved a number of highly specific virulence factors, such as the cag-type IV secretion system, vacuolating cytotoxin A (VacA) or secreted gamma-glutamyl transpeptidase. An important function of these bacterial factors is to manipulate the host immune response to enable a chronic H. pylori infection. The present work identifies a new player in this process. Here, we have discovered that H. pylori, as well as several other bacterial species, can bind human annexins (ANX), suggesting a more widespread phenomenon. We show that H. pylori specifically binds ANXA5 via lipid A. The interaction is strictly dependent on calcium and modulated by the phosphorylation status of lipid A. Notably, ANXA5 binding strongly inhibits LPS-mediated Toll-like receptor 4 (TLR4) signal transduction, suggesting that H. pylori exploits ANXs binding to avoid its recognition by this important receptor of the innate immune system. The study thus provides novel molecular and mechanistic insights into a further strategy of H. pylori to successfully evade recognition by the host.

Small RNA mediated gradual control of lipopolysaccharide biosynthesis affects antibiotic resistance in Helicobacter pylori

The small, regulatory RNA RepG (Regulator of polymeric G-repeats) regulates the expression of the chemotaxis receptor TlpB in Helicobacter pylori by targeting a variable G-repeat in the tlpB mRNA leader. Here, we show that RepG additionally controls lipopolysaccharide (LPS) phase variation by also modulating the expression of a gene (hp0102) that is co-transcribed with tlpB. The hp0102 gene encodes a glycosyltransferase required for LPS O-chain biosynthesis and in vivo colonization of the mouse stomach. The G-repeat length defines a gradual (rather than ON/OFF) control of LPS biosynthesis by RepG, and leads to gradual resistance to a membrane-targeting antibiotic. Thus, RepG-mediated modulation of LPS structure might impact host immune recognition and antibiotic sensitivity, thereby helping H. pylori to adapt and persist in the host.

The small RNA RepG modulates expression of chemotaxis receptor TlpB in Helicobacter pylori by targeting a length-variable G-repeat in the tlpB mRNA. Here, Pernitzsch et al. show that RepG also gradually controls lipopolysaccharide biosynthesis, antibiotic susceptibility, and in-vivo colonization of the stomach, by regulating a gene that is co-transcribed with tlpB.

Immune response and immune escape mechanism in Helicobacter pylori infection

Helicobacter pylori (H. pylori) is a Gram-negative bacterium which is parasitic on the surface of the gastric mucosa, and it is a causative agent in the development of chronic gastritis, gastric and duodenal peptic ulcer, gastric adenocarcinoma, and lymphoid tissue lymphoma associated with the gastric mucosa. After H. pylori infection, the bacterium is first recognized by the pattern recognition receptors of immune cells, which in turn causes the innate immune and adaptive immune responses, but these responses are usually insufficient to eliminate bacterial infections. H. pylori can evade the identification and clearance by the immune system by modifying and attenuating the immunogenicity of its pathogen-associated molecular patterns, regulating the immune responses of innate immune cells and T cells, and leading to persistent infection. A thorough understanding of the immune response and immune escape mechanism in H. pylori infection is of great significance for eliminating H. pylori infection and controlling the occurrence of H. pylori infection-related diseases.

Lipopolysaccharide Structural Differences between Western and Asian Helicobacter pylori Strains

Recent structural analysis of the lipopolysaccharide (LPS) isolated from Helicobacter pylori G27 wild-type and O-antigen ligase mutant resulted in the redefinition of the core-oligosaccharide and O-antigen domains. The short core-oligosaccharide (Glc–Gal–Hep-III–Hep-II–Hep-I–KDO) and its attached trisaccharide (Trio, GlcNAc–Fuc–Hep) appear to be highly conserved structures among H. pylori strains. The G27 LPS contains a linear glucan–heptan linker between the core-Trio and distal Lewis antigens. This linker domain was commonly identified in Western strains. In contrast, out of 12 partial LPS structures of Asian strains, none displayed the heptan moiety, despite the presence of Lewis antigens. This raises the question of how Lewis antigens are attached to the Trio, and whether the LPS structure of Asian strains contain another linker. Of note, a riban was identified as a linker in LPS of the mouse-adapted SS1 strain, suggesting that alternative linker structures can occur. In summary, additional full structural analyses of LPS in Asian strains are required to assess the presence or absence of an alternative linker in these strains. It will also be interesting to study the glucan-heptan linker moieties in pathogenesis as H. pylori infections in Asia are usually more symptomatic than the ones presented in the Western world.