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PubMed2003

Secretin of the enteropathogenic Escherichia coli type III secretion system requires components of the type III apparatus for assembly and localization.

At least 16 proteins are thought to be involved in forming the enteropathogenic Escherichia coli (EPEC) type III translocation apparatus which delivers virulence factors into host cells, yet their function and location have not been determined. A biochemical analysis was performed on three components: EscN, a predicted cytoplasmic ATPase; EscV, a predicted inner membrane protein; and EscC, a predicted outer membrane secretin. Wild-type EPEC and mutants constructed in these genes were fractionated by lysozyme treatment, ultracentrifugation, and selective detergent extraction. Fractionation revealed that the type III effectors Tir and EspB required a complete type III apparatus for any degree of export by EPEC, suggesting a continuous channel. Epitope-tagged EscC, EscV, and EscN were localized by fractionation, confirming computer modeling predictions for their location. Transcomplementation experiments revealed that localization of EscV and EscN was unaffected by mutations in other examined type III components. Remarkably, localization of EscC was altered in escV or escN mutants, where EscC accumulated in the periplasm. EscC was correctly localized in the escF needle component mutant, indicating that secretin localization is independent of needle formation. These data indicate that, contrary to previous indications, correct insertion and function of EscC secretin in the outer membrane depends not only on the sec-dependent secretion pathway but also on other type III apparatus components.

Adenosine Triphosphatases↗
PubMed1993

Construction of a model secretion system for oral streptococci.

A DNA fragment corresponding to the secretory domain from the Streptococcus mutans GS-5 gtfB gene, which encodes the putative 38-amino-acid signal peptide of the glucosyltransferase I (GTF-I) enzyme product, has been constructed. This fragment was fused with the alpha-amylase structural gene from alkalophilic Bacillus sp. strain 707. This hybrid gene as well as the intact amylase gene were introduced into an Escherichia coli-streptococcus shuttle vector consisting of three components: the E. coli replicon p15Aori from pACYC177, an erythromycin resistance gene from pAM beta-1, and the streptococcal replicon from pVA838. Transformation of the oral noncariogenic bacterium Streptococcus gordonii with the chimeric plasmid harboring the hybrid amylase gene resulted in strong extracellular amylase production. By contrast, transformants containing the intact amylase gene exhibited only trace amounts of amylase activity in culture fluids. Since the two signal peptide structures of the GTF-I enzyme and the Bacillus amylase are distinct from each other, these differences might result from the inability of S. gordonii to correctly process the Bacillus signal peptide. Furthermore, culture fluids from transformants of S. mutans as well as Streptococcus milleri harboring the hybrid amylase gene showed only weak amylase activity. Deletion of the gtfB, gtfC, or ftf gene from S. mutans GS-5 did not increase amylase secretion following transformation with the hybrid amylase gene. These results suggest that in contrast to S. gordonii, the inability of S. mutans and S. milleri to secrete hybrid amylase molecules could result from incorrect interaction of the secretory components of these organisms with amylase precursor molecules.

Amino Acid Sequence↗
PubMed2006

CagA protein secreted by the intact type IV secretion system leads to gastric epithelial inflammation in the Mongolian gerbil model.

Helicobacter pylori causes various gastro-duodenal diseases, including gastric cancer. The CagA protein, an H. pylori virulence factor, induces morphological changes in host cells and may be associated with the development of peptic ulcer and gastric carcinoma. The present study has analysed the role of CagA protein in the pathogenesis of H. pylori infection in the Mongolian gerbil model. Mongolian gerbils were challenged with wild-type H. pylori strain TN2, which has a functional cag pathogenicity island or isogenic mutants with disrupted cagA (DeltacagA) or cagE (DeltacagE) genes. They were sacrificed at 7, 13, and 25 weeks after inoculation. Pathological changes of the gastric mucosa were determined and apoptosis was assessed by the TUNEL assay. Immunohistochemistry for PCNA, phospho-IkappaBalpha, and phospho-Erk was also performed. All of the bacterial strains colonized the gerbil stomach at similar densities; however, the DeltacagA mutant induced milder gastritis than did the wild type. The extent of apoptosis and lymphoid follicle formation in the epithelium appeared to depend on intact cagA. The DeltacagA mutant induced less phosphorylation of IkappaBalpha and Erk, and less expression of interferon-gamma and interleukin-1beta mRNA in the epithelium than did the wild type. It is concluded that CagA protein may be essential for the induction of severe gastritis in the Mongolian gerbil model.

Animals↗
PubMed2006

Function and distribution of EspG2, a type III secretion system effector of enteropathogenic Escherichia coli.

The enteropathogenic Escherichia coli (EPEC) effector protein EspG, like the Shigella effector VirA, functions through disruption of the host cell microtubule network. Reports have differed as to whether the EspG homologue, EspG2, is also responsible for microtubule disruption. In this study we show that following translocation, EspG2 and VirA are localised under adherent bacteria and able to restore the microtubule disruption phenotype to an espG/espG2 double EPEC mutant. The espG/espG2 double mutant produced A/E lesions similar to wild-type EPEC on human intestinal in vitro organ cultures. Determining the distribution of espG and espG2 among clinical EPEC isolates revealed two different types of espG (espG alpha and espG beta) and espG2 (intact and pseudo genes), which were associated with specific EPEC serotypes and closely followed the EPEC lineage. This investigation has established a role for EspG2 in the disruption of the microtubule network and associated different espG and espG2 types with different groups of EPEC.

Caco-2 Cells↗
PubMed2003

Interaction between the IncHI1 plasmid R27 coupling protein and type IV secretion system: TraG associates with the coiled-coil mating pair formation protein TrhB.

Assemblies of plasmid-encoded proteins direct the conjugative transfer of plasmid DNA molecules between bacteria. These include the membrane-associated mating pair formation (Mpf) complex necessary for pilus production and the cytoplasmic relaxosome required for DNA processing. The proposed link between these distinct protein complexes is the coupling protein (the TraG family of proteins). Interactions between the coupling protein and relaxosome components have been previously characterized and we document here, for the first time, a direct interaction between the coupling protein and an Mpf protein. Using the adenylate cyclase bacterial two-hybrid (BTH) system, we present in vivo evidence that the IncHI1 plasmid R27-encoded proteins TraG and TrhB interact. This interaction was verified through a co-immunoprecipitation reaction. We have also been able to delineate the interaction domain of TrhB to TraG by showing a positive interaction using the first 220 amino acids of TrhB (452 aa). TrhB has a proline-rich domain from amino acids 135-173 which may serve to facilitate protein interactions and/or periplasmic extension. TrhB self association was detected using far-Western, co-immunoprecipitation, and also BTH analysis, which was used to define the homotypic interaction domain, comprising a predicted coiled-coil region at residues 77-124 of TrhB. These data support a model in which the coupling protein interacts with an Mpf component to target the transferring DNA strand held by the relaxosome to the transmembrane Mpf complex.

Biological Transport↗
PubMed2000

Sinorhizobium fredii USDA257, a cultivar-specific soybean symbiont, carries two copies of y4yA and y4yB, two open reading frames that are located in a region that encodes the type III protein secretion system.

Sinorhizobium fredii USDA257 forms nitrogen-fixing nodules on primitive soybean (Glycine max) cultivar Peking but fails to nodulate the improved cultivar McCall. Cultivar specificity is governed by a plasmid-borne locus, nolXBTUV. By DNA sequence analysis, we have identified two open reading frames, y4yA and y4yB, immediately downstream of nolX. Northern (RNA) blot analysis indicated that the expression of both y4yA and y4yB is inducible by isoflavonoids, and an intact copy of nolX is required. Two copies each of y4yA and y4yB are present in S. fredii USDA257, one on the sym plasmid (y4yAsp and y4yBsp), and the other on the chromosome (y4yAc and y4yBc). The cultivar-nonspecific strain USDA191 lacks y4yAc and y4yBc. Introduction of y4yAc plus y4yBc from USDA257 into USDA191 did not influence the ability of the latter strain to nodulate McCall soybean plants. Unlike nolX, the inactivation of y4yAsp and y4yBsp of USDA257 did not extend the host range of this strain. A double mutant, in which both the plasmid and chromosomal copies of y4yA and y4yB were mutated, had no observable effect on symbiotic ability of USDA257. The y4yAsp and y4yBsp mutants did not influence flavonoid-dependent extracellular protein production. Rhizobium sp. strain NGR234 and S. saheli USDA4893 both contain sequences similar to S. fredii USDA257 y4yAsp and y4yBsp; however, Bradyrhizobium spp., the traditional soybean symbionts, lack these genes.

Amino Acid Sequence↗
PubMed1993

Continuous systemic secretion of a lysosomal enzyme by genetically modified mouse skin fibroblasts.

Lysosomal enzymes secreted or externally supplied into the extracellular medium can be internalized by cells and targeted to lysosomes after binding to specific membrane receptors. This process allows for the replacement of the missing enzyme activity in deficient cells. Using a retroviral vector, we have introduced the human beta-glucuronidase cDNA into primary mouse skin fibroblasts. The genetically modified cells were then engrafted into neo-organs that had been previously implanted into the peritoneal cavity of syngeneic recipient mice. The hypervascularized structures, made of collagen and basic fibroblast growth factor-coated synthetic fibers embedded into extracellular matrix gel, allowed in vivo survival of engrafted fibroblasts that expressed the human beta-glucuronidase cDNA for at least 3 months. The human enzyme was detected in the liver, lung, and spleen of experimental animals, but became undetectable after removal of the neo-organ. This observation indicated that the human enzyme was secreted into the serum and then captured by distant organs. The use of genetically modified fibroblasts implanted into neo-organs may, therefore, represent a convenient approach to enzyme replacement therapy in lysosomal storage diseases.

3T3 Cells↗
PubMed2005

A pH-dependent conformational change in EspA, a component of the Escherichia coli O157:H7 type III secretion system.

pH-Dependent structural changes for Escherichia coli O157:H7 EspA were characterized by CD, 8-anilino-2-naphthyl sulfonic acid (ANS) fluorescence, and sedimentation equilibrium ultracentrifugation. Far- and near-UV CD spectra, recorded between pH 2.0 and 7.0, indicate that the protein has significant amounts of secondary and tertiary structures. An increase in ANS fluorescence intensity (in the presence of EspA) was observed at acidic pH; whereas, no increased ANS fluorescence was observed at pH 7.0. These results suggest the presence of a partially unfolded state. Interestingly, urea-induced unfolding transitions, monitored by far-UV CD spectroscopy, showed that the protein is destabilized at pH 2.0 as compared with EspA at neutral pH. Although increased ANS fluorescence was observed at pH 3.0, the urea-induced unfolding curve is similar to that found at pH 7.0. This result suggests the presence, at pH 3.0, of an ordered, but partially unfolded state, which differs from typical molten globule. The results of analytical ultracentrifugation and infrared spectroscopy indicate that EspA molecules associate at pH 7.0, suggesting the formation of short filamentous oligomers containing alpha-helical structures, whereas the protein tend to form nonspecific aggregates containing intermolecular beta-sheets at pH 2.0. Our experiments indicate that EspA has the potential to spontaneously form filamentous oligomers at neutral pH; whereas the protein is partially unfolded, assuming different conformations, at acidic pH.

Amino Acid Sequence↗
PubMed1998

Cell-contact-stimulated formation of filamentous appendages by Salmonella typhimurium does not depend on the type III secretion system encoded by Salmonella pathogenicity island 1.

The formation of filamentous appendages on Salmonella typhimurium has been implicated in the triggering of bacterial entry into host cells (C. C. Ginocchio, S. B. Olmsted, C. L. Wells, and J. E. Galán, Cell 76:717-724, 1994). We have examined the roles of cell contact and Salmonella pathogenicity island 1 (SPI1) in appendage formation by comparing the surface morphologies of a panel of S. typhimurium strains adherent to tissue culture inserts, to cultured epithelial cell lines, and to murine intestine. Scanning electron microscopy revealed short filamentous appendages 30 to 50 nm in diameter and up to 300 nm in length on many wild-type S. typhimurium bacteria adhering to both cultured epithelial cells and to murine Peyer's patch follicle-associated epithelia. Wild-type S. typhimurium adhering to cell-free culture inserts lacked these filamentous appendages but sometimes exhibited very short appendages which might represent a rudimentary form of the cell contact-stimulated filamentous appendages. Invasion-deficient S. typhimurium strains carrying mutations in components of SPI1 (invA, invG, sspC, and prgH) exhibited filamentous appendages similar to those on wild-type S. typhimurium when adhering to epithelial cells, demonstrating that formation of these appendages is not itself sufficient to trigger bacterial invasion. When adhering to cell-free culture inserts, an S. typhimurium invG mutant differed from its parent strain in that it lacked even the shorter surface appendages, suggesting that SPI1 may be involved in appendage formation in the absence of epithelia. Our data on S. typhimurium strains in the presence of cells provide compelling evidence that SPI1 is not an absolute requirement for the formation of the described filamentous appendages. However, appendage formation is controlled by PhoP/PhoQ since a PhoP-constitutive mutant very rarely possessed such appendages when adhering to any of the cell types examined.

Animals↗