A new method to visualize the Helicobacter pylori-associated Lewis(b)-binding adhesin utilizing SDS-digested freeze-fracture replica labeling

Topology of the outer-membrane secretin PilQ from Neisseria meningitidis

Neisseria meningitidis is the causative agent of epidemic meningococcal meningitis and septicaemia. Type IV pili are surface organelles that mediate a variety of functions, including adhesion, twitching motility, and competence for DNA binding and uptake in transformation. The secretin PilQ is required for type IV pilus expression at the cell surface, and forms a dodecameric cage-like macromolecular complex in the meningococcal outer membrane. PilQ-null mutants are devoid of surface pili, and prevailing evidence suggests that the PilQ complex facilitates extrusion and retraction of type IV pili across the outer membrane. Defining the orientation of the meningococcal PilQ complex in the membrane is a prerequisite for understanding the structure-function relationships of this important protein in pilus biology. In order to begin to define the topology of the PilQ complex in the outer membrane, polyhistidine insertions in N- and C-terminal regions of PilQ were constructed, and their subcellular locations examined. Notably, the insertion epitopes at residues 205 and 678 were located within the periplasm, whereas residue 656 was exposed at the outer surface of the outer membrane. Using electron microscopy with Ni-NTA gold labelling, it was demonstrated that the insertion at residue 205 within the N-terminus mapped to a site on the arm-like features of the 3D structure of the PilQ multimer. Interestingly, mutation of the same region gave rise to an increase in vancomycin permeability through the PilQ complex. The results yield novel information on the PilQ N-terminal location and function in the periplasm, and reveal a complex organization of the membrane-spanning secretin in vivo.

Assessing the interaction between Helicobacter pylori and human neutrophils by freeze-fracture replica labeling

We recently introduced a freeze-fracture replica labeling method adapted to studies of bacterial envelopes. This report describes a further development of this detergent-digested freeze-fracture replica labeling technique, thus more exactly the conception of this explicit methodology for visualization of bacteria-host cell interactions. Our experimental model employs human neutrophils and the gastric pathogenic bacterium Helicobacter pylori. The phagocytic process performed by the neutrophils represents a crucial element of the host defense system against invading microorganisms, and by so doing, it allows direct observation of the interplay between bacteria and host cells at an ultrastructural level. The here launched methodology can be used as a tool to investigate the events taking place between pathogenic microbes and phagocytes, as well as for pinpoint targeting of other cell-cell communications in the field of cell biology.

Helicobacter pylori binds to CD74 on gastric epithelial cells and stimulates interleukin-8 production

The pathogenesis associated with Helicobacter pylori infection requires consistent contact with the gastric epithelium. Although several cell surface receptors have been suggested to play a role in adhesion, the bacterium-host interactions that elicit host responses are not well defined. This study investigated the interaction of H. pylori with the class II major histocompatibility complex (MHC)-associated invariant chain (Ii; CD74), which was found to be highly expressed by gastric epithelial cells. Bacterial binding was increased when CD74 surface expression was increased by gamma interferon (IFN-gamma) treatment or by fibroblast cells transfected with CD74, while binding was decreased by CD74 blocking antibodies, enzyme cleavage of CD74, and CD74-coated bacteria. H. pylori was also shown to bind directly to affinity-purified CD74 in the absence of class II MHC. Cross-linking of CD74 and the engagement of CD74 were verified to stimulate IL-8 production by unrelated cell lines expressing CD74 in the absence of class II MHC. Increased CD74 expression by cells increased IL-8 production in response to H. pylori, and agents that block CD74 decreased these responses. The binding of H. pylori to CD74 presents a novel insight into an initial interaction of H. pylori with the gastric epithelium that leads to upregulation of inflammatory responses.

srf-3, a mutant of Caenorhabditis elegans, resistant to bacterial infection and to biofilm binding, is deficient in glycoconjugates

srf-3 is a mutant of C. elegans that is resistant to infection by Microbacterium nematophilum and to binding of the biofilm produced by Yersinia pseudotuberculosis and Yersinia pestis. Recently, SRF-3 was characterized as a nucleotide sugar transporter of the Golgi apparatus occurring exclusively in hypodermal seam cells, pharyngeal cells, and spermatheca. Based on the above observations, we hypothesized that srf-3 may have altered glyconjugates that may enable the mutant nematode to grow unaffected in the presence of the above pathogenic bacteria. Following analyses of N- and O-linked glycoconjugates of srf-3 and wild type nematodes using a combination of enzymatic degradation, permethylation, and mass spectrometry, we found in srf-3 a 65% reduction of acidic O-linked glycoconjugates containing glucuronic acid and galactose as well as a reduction of N-linked glycoconjugates containing galactose and fucose. These results are consistent with the specificity of SRF-3 for UDP-galactose and strongly suggest that the above glycoconjugates play an important role in allowing adhesion of M. nematophilum or Y. pseudotuberculosis biofilm to wild type C. elegans. Furthermore, because seam cells as well as pharyngeal cells secrete their glycoconjugates to the cuticle and surrounding surfaces, the results also demonstrate the critical role of these cells and their secreted glycoproteins in nematode-bacteria interactions and offer a mechanistic basis for strategies to block such recognition processes.

Expression and localization of alpha- and beta-carbonic anhydrase in Helicobacter pylori

Helicobacter pylori, the causative agent of peptic ulcer disease, expresses two different forms of the zinc-containing enzyme carbonic anhydrase (CA) (alpha and beta), catalyzing the reversible hydration of CO(2). Presumably, the high CO(2) requirement of H. pylori implies an important role for this enzyme in the bacterial physiology. In this paper, expression of the CAs has been analyzed in three different strains of the bacterium, 26695, J99 and 17.1, and appears to be independent of CO(2) concentration in the investigated range (0.1-10%). Presence of the potent and highly specific CA inhibitor, acetazolamide, in the medium does not seem to inhibit bacterial growth at the given sulfonamide concentration. Moreover, the localization and distribution of the alpha-CA was analyzed by immunonegative staining, while SDS-digested freeze-fracture immunogold labelling was used for the beta-form of the enzyme. The latter method has the advantage of allowing assessment of protein localization to distinct cell compartments and membrane structures. The resulting electron microscopy images indicate a localization of the beta-CA in the cytosol, on the cytosolic side of the inner membrane and on the outer membrane facing the periplasmic space. The alpha-enzyme was found attached to the surface of the bacterium.