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At least 685 records · Page 38Linked to original sources
PubMed2005

Coevolution between nonhomologous but functionally similar proteins and their conserved partners in the Legionella pathogenesis system.

Legionella pneumophila, the causative agent of Legionnaires' disease, and other pathogenic Legionella species multiply inside protozoa and human macrophages by using the intracellular multiplication (Icm)/defect in organelle trafficking (Dot) type-IV secretion system. The IcmQ protein, which possesses pore-forming activity, and IcmR, which regulates the IcmQ activity, are two essential components of this system. Analysis of the region expected to contain these two genes from 29 Legionella species revealed the presence of a conserved icmQ gene and a large hypervariable gene family [functional homologues of icmR (fir) genes], located at the icmR genomic position. Although hypervariable in their sequence, the fir genes from all 29 Legionella species were found, together with their corresponding icmQ genes, to function similarly during infection. In addition, all FIR proteins we examined were found to interact with their corresponding IcmQ proteins. Detailed bioinformatic, biochemical, and genetic analysis of the interaction between the variable FIR proteins and conserved IcmQ proteins revealed that their interaction depends on a variable region located between two conserved domains of IcmQ. This variable region was also found to be critical for IcmQ self-interaction, and the region probably coevolved with the corresponding FIR protein. A FIR-IcmQ pair was also found in Coxiella burnetii, the only known non-Legionella bacterium that contains an Icm/Dot system, indicating the significance of this protein pair for the function of this type-IV secretion system. We hypothesize that this gene variation, which is probably mediated by positive selection, plays an important role in the evolutionary arms race between the protozoan host cell and the pathogen.

Acanthamoeba castellanii↗
PubMed1990

The mechanism of secretion of hemolysin and other polypeptides from gram-negative bacteria.

In the secretion of polypeptides from Gram-negative bacteria, the outer membrane constitutes a specific barrier which has to be circumvented. In the majority of systems, secretion is a two-step process, with initial export to the periplasm involving an N-terminal signal sequence. Transport across the outer membrane then involves a variable number of ancillary polypeptides including both periplasmic and outer membrane. While such ancillary proteins are probably specific for each secreted protein, the mechanism of movement across the outer membrane is unknown. In contrast to these systems, secretion of the E. coli hemolysin (HlyA) has several distinctive features. These include a novel targeting signal located within the last 50 or so C-terminal amino acids, the absence of any periplasmic intermediates in transfer, and a specific membrane-bound translocator, HlyB, with important mammalian homologues such as P-glycoprotein (Mdr) and the cystic fibrosis protein. In this review we discuss the nature of the HlyA targeting signal, the structure and function of HlyB, and the probability that HlyA is secreted directly to the medium through a trans-envelope complex composed of HlyB and HlyD.

Amino Acid Sequence↗
PubMed2000

Yersinia enterocolitica-mediated translocation of defined fusion proteins to the cytosol of mammalian cells results in peptide-specific MHC class I-restricted antigen presentation.

Yersinia enterocolitica delivers a set of effector proteins [Yersinia outer proteins (Yop)] into the cytosol of target cells to modulate host cell signal transduction pathways required for the extracellular survival of the bacterium. Secretion and subsequent translocation of Yop across the eukaryotic cell membrane are achieved via a type III secretion system. About 50 - 100 amino acids of the N terminus of Yop are required for chaperone-directed secretion and translocation. In this study, it is demonstrated by immunoblot analysis of Yersinia-infected cultured epithelial cells that one ot these proteins, YopE, can serve as a molecular carrier to deliver protein fragments of the heterologous p60 antigen of Listeria monocytogenes into the cytosol of target cells. T cell activation assays revealed that the observed type III-mediated antigen translocation led to a p60 peptide-specific MHC class I-restricted antigen presentation. Efficient translocation and antigen presentation were strictly dependent on the co-localized expression of hybrid YopE-p60 proteins and the YopE-specific chaperone SycE. These results suggest that the Yersinia type III secretion system may serve as an attractive tool for antigen delivery in Yersinia-based live vaccines to induce cellular immune responses.

Animals↗
PubMed2006

Interactions between peptidoglycan and the ExeAB complex during assembly of the type II secretin of Aeromonas hydrophila.

Aeromonas hydrophila transports extracellular protein toxins via the type II secretion system, an export mechanism comprised of numerous proteins that spans both the inner and outer membranes. Two components of this secretion system, ExeA and ExeB, form a complex in the inner membrane that functions to locate and/or assemble the ExeD secretin in the outer membrane. In the studies reported here, two-codon insertion mutagenesis of exeA revealed that an insertion at amino acid 495 in the C-terminal region of ExeA did not alter ExeAB complex formation yet completely abrogated its involvement in ExeD secretin assembly and thus rendered the bacteria secretion negative. In silico analysis of protein motifs with similar amino acid profiles revealed that this amino acid is located within a putative peptidoglycan (PG) binding motif in the periplasmic domain of ExeA. Substitution mutations of three highly conserved amino acids in the motif were constructed. In cells expressing each of these mutants, the ability to assemble the ExeD secretin or secrete aerolysin was lost, while ExeA retained the ability to form a complex with ExeB. In in vivo cross-linking experiments, wild-type ExeA could be cross-linked to PG, whereas the three substitution mutants of ExeA could not. These data indicate that PG binding and/or remodelling plays a role in the function of the ExeAB complex during assembly of the ExeD secretin.

Aeromonas hydrophila↗
PubMed2003

CesD2 of enteropathogenic Escherichia coli is a second chaperone for the type III secretion translocator protein EspD.

Enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli are extracellular pathogens that employ a type III secretion system to export translocator and effector proteins, proteins which facilitates colonization of the mucosal surface of the intestine via formation of attaching and effacing (A/E) lesions. The genes encoding the proteins for A/E lesion formation are located on a pathogenicity island, termed the locus of enterocyte effacement (LEE), which contains eae encoding intimin as well as the type III secretion system and effector genes. Many type III secreted proteins are stabilized and maintained in a secretion-competent conformation in the bacterial cytosol by specific chaperone proteins. Three type III chaperones have been described thus far within the EPEC LEE region: CesD, for the translocator proteins EspB and EspD; CesT, for the effector proteins Tir and Map; and CesF, for EspF. In this study we report the characterization of CesD2 (previously Orf27), a second LEE-encoded chaperone for EspD. We show specific CesD2-EspD protein interaction which appears to be necessary for proper EspD secretion in vitro and pathogenesis in vivo as demonstrated in the A/E-lesion-forming mouse pathogen Citrobacter rodentium.

Amino Acid Sequence↗
PubMed1998

S. typhimurium encodes an activator of Rho GTPases that induces membrane ruffling and nuclear responses in host cells.

S. typhimurium stimulates signaling pathways leading to membrane ruffling, actin cytoskeleton rearrangements, and nuclear responses. The stimulation requires a protein secretion system (type III) that translocates bacterial proteins into the host cell. We show that SopE, a substrate of this secretion system, stimulates cytoskeletal reorganization and JNK activation in a CDC42- and Rac-1-dependent manner. A lambda gt11 cDNA library screen for proteins that interact with SopE identified Rac-1 and CDC42. Furthermore, purified SopE was shown to stimulate GDP/GTP nucleotide exchange in several Rho GTPases in vitro, including Rac-1 and CDC42. These findings establish a paradigm for microbial stimulation of cellular responses in which the pathogen induces signaling events by directly engaging the signaling machinery within the host cell.

Animals↗
PubMed2002

Quorum sensing Escherichia coli regulators B and C (QseBC): a novel two-component regulatory system involved in the regulation of flagella and motility by quorum sensing in E. coli.

Quorum sensing is a cell-to-cell signalling mechanism in which bacteria secrete hormone-like compounds called autoinducers. When these auto-inducers reach a certain threshold concentration, they interact with bacterial transcriptional regulators, thereby regulating gene expression. Enterohaemorrhagic Escherichia coli (EHEC) O157:H7 as well as E. coli K-12 produces the autoinducer-2 (AI-2), which is synthesized by the product of the luxS gene, and previous work from our laboratory has shown that genes encoding the EHEC type III secretion system were activated by quorum sensing. Recently, by hybridizing an E. coli K-12 gene array with cDNA synthesized from RNA extracted from EHEC strain 86-24 and its isogenic luxS mutant, we observed that other potential virulence-associated factors, such as genes encoding the expression and assembly of flagella, motility and chemotaxis, were also activated by quorum sensing. The array data also indicated that several genes encoding putative E. coli regulators were controlled by quorum sensing. In this report, we describe a two-component system regulated by quorum sensing that shares homology with Salmonella typhimurium PmrAB, which we have named quorum sensing E. coli regulator B and C (QseBC). The qseBC genes, previously identified only as open reading frames b3025 and b3026, are organized in an operon in the E. coli chromosome, with qseB encoding the response regulator and qseC the sensor kinase. We confirmed the regulation of qseBC by quorum sensing using qseB::lacZ transcriptional fusions and characterized the phenotypes of an isogenic qseC mutation in EHEC. This mutant expressed less flagellin and had reduced motility compared with the wild-type and complemented strains. Transcription of flhD, fliA, motA and fliC::lacZ fusions was decreased in the qseC mutant, suggesting that qseBC is a transcriptional regulator of flagella genes. A qseC mutant was also generated in E. coli K-12 strain MC1000 that showed the same phenotypes as the EHEC mutant, indicating that qseBC regulates flagella and motility by quorum sensing in both EHEC and K-12. QseBC activates transcription of flhDC, which is the master regulator for the flagella and motility genes and, in the absence of flhD, QseBC failed to activate the transcription of fliA. Motility of a luxS, but not of a qseC, mutant can be restored by providing AI-2 exogenously as preconditioned media, suggesting that the qseC mutant is unable to respond to AI-2. However, QseC has no effect on the expression of other quorum sensing-controlled genes such as those encoding for the type III secretion system. These data indicate that QseBC is one component of the quorum-sensing regulatory cascade in both EHEC and K-12 that is involved in the regulation of flagella and motility genes, but that additional regulators in this cascade remain to be characterized.

DNA-Binding Proteins↗
PubMed2004

Protein secretion in Legionella pneumophila and its relation to virulence.

Protein secretion is a universal process of fundamental importance for various aspects of cell physiology including the infection of a host organism by a bacterial pathogen. Many Gram-negative pathogens export virulence-associated proteins across one or two cell membranes to their place of action using a wide plethora of secretory pathways with the objective of infecting the host. For Legionella pneumophila, a facultative intracellular, human pathogen which is ubiquitously found in natural and artificial aquatic environments, two major secretory pathways known to be involved in virulence have been described. These are the PilD-dependent Lsp type II secretion pathway and the type IV secretion system encoded by the dot/icm genes. In addition, a second type IV system, with high sequence similarity to the Agrobacterium tumefaciens VirB system for conjugal transfer of oncogenic DNA, is present. Albeit dispensable for intracellular growth, this type IV system is important for efficient host cell infection at lower temperatures. Further more, evidence exists for the presence of at least one type I secretion system in L. pneumophila as well as for the presence of a twin arginine dependent translocation (Tat) pathway. This is a recently detected, signal peptide-dependent, secretion pathway complementary to the well-known Sec-dependent pathway for protein transport across the cytoplasmic membrane.

Bacterial Proteins↗
PubMed2002

Regulation of flagellar assembly.

Research on the molecular mechanism of bacterial flagellar assembly has been an ongoing study that spans three decades. Early work showed that regulation of flagellar gene transcription was coupled to the assembly process. Recent advances in the understanding of the regulation of flagellar assembly have shown that translational and post-translational regulation also plays a significant role in flagellar assembly. In both Salmonella and Caulobacter crescentus, translational regulation influences the secretion of the anti-sigma(28) factor FlgM and the flagellin fljK, respectively. Post-translational regulatory mechanisms also control the length of the hook and the ability of the type III secretion system to discriminate between middle and late secretion substrates. The flagellum provides a model system for understanding how gene regulation functions to ensure the efficient assembly of a complex structure and fundamental mechanisms common to all type III secretion systems.

Bacterial Proteins↗
PubMed2001

A Salmonella inositol polyphosphatase acts in conjunction with other bacterial effectors to promote host cell actin cytoskeleton rearrangements and bacterial internalization.

A central feature of Salmonella pathogenicity is the bacterium's ability to enter into non-phagocytic cells. Bacterial internalization is the consequence of cellular responses characterized by Cdc42- and Rac-dependent actin cytoskeleton rearrangements. These responses are triggered by the co-ordinated function of bacterial proteins delivered into the host cell by a specialized protein secretion system termed type III. We report here that SopB, a Salmonella inositol polyphosphatase delivered to the host cell by this secretion system, mediates actin cytoskeleton rearrangements and bacterial entry in a Cdc42-dependent manner. SopB exhibits overlapping functions with two other effectors of bacterial entry, the Rho family GTPase exchange factors SopE and SopE2. Thus, Salmonella strains deficient in any one of these proteins can enter into cells at high efficiency, whereas a strain lacking all three effectors is completely defective for entry. Consistent with an important role for inositol phosphate metabolism in Salmonella-induced cellular responses, a catalytically defective mutant of SopB failed to stimulate actin cytoskeleton rearrangements and bacterial entry. Furthermore, bacterial infection of intestinal cells resulted in a marked increase in Ins(1,4,5,6)P4, a consumption of InsP5 and the activation of phospholipase C. In agreement with the in vivo findings, purified SopB specifically dephosphorylated InsP5 to Ins(1,4,5,6)P4 in vitro. Surprisingly, the inositol phosphate fluxes induced by Salmonella were not caused exclusively by SopB. We show that the SopB-independent inositol phosphate fluxes are the consequence of the SopE-dependent activation of an endogenous inositol phosphatase. The ability of Salmonella to stimulate Rho GTPases signalling and inositol phosphate metabolism through alternative mechanisms is an example of the remarkable ability of this bacterial pathogen to manipulate host cellular functions.

Actins↗
PubMed2004

Inhibition of MAPK signaling pathways by VopA from Vibrio parahaemolyticus.

During infection, bacterial pathogens utilize a type III secretion system to inject effectors into the cytoplasm of a target cell where they disrupt the defense system of the host cell. Vibrio parahaemolyticus, a causative agent of gastroenteritis endemic in Southeast Asia, has a type III secretion system that encodes a novel member of the YopJ-like protein effector family, VopA (Vibrio outer protein A). Our studies revealed that Vibrio VopA encodes an evolutionarily conserved activity that is extremely potent and requires an intact catalytic site to abrogate signaling pathways in a manner distinct from that of other YopJ-like effectors. We observed that VopA efficiently inhibits the MAPK signaling pathways but not the NFkappaB pathway in mammalian cells. When expressed in yeast, VopA induces a growth arrest phenotype and also blocks yeast MAPK signaling pathways. Our observations provide insight into the immense diversity of targets utilized by YopJ-like effectors to manipulate eukaryotic signaling machineries that are important for the response and survival of the host cell during infection and/or symbiosis.

Amino Acid Sequence↗
PubMed1997

Involvement of mitogen-activated protein kinase pathways in the nuclear responses and cytokine production induced by Salmonella typhimurium in cultured intestinal epithelial cells.

Central to the pathogenesis of Salmonella typhimurium is its ability to engage the host cell in a two-way biochemical interaction. As a consequence of this interaction, a dedicated protein secretion system, termed type III, is activated in these bacteria and directs the translocation of signaling proteins into the host cell. Secretion of these proteins stimulates host cell signal transduction pathways that lead to a variety of cellular responses. An important feature of S. typhimurium pathogenesis is the induction of a profound inflammatory response in the intestinal epithelium. In this report, we show that S. typhimurium induces host cell signal transduction pathways that lead to the activation of the transcription factors NF-kappaB and AP-1, resulting in the production of proinflammatory cytokines such as IL-8. We also show that S. typhimurium infection of cultured intestinal epithelial cells results in the activation of the mitogen-activated protein (MAP) kinases ERK, JNK, and p38. Induction of these signaling pathways and the synthesis of IL-8 was strictly dependent on the function of the invasion-associated type III protein secretion system encoded by S. typhimurium. Pretreatment of cells with the highly specific p38 MAP kinase inhibitor SB 203580 prevented S. typhimurium-induced IL-8 production. These results indicate that the inflammatory response induced by S. typhimurium may be due to the specific stimulation of MAP kinase signaling pathways leading to nuclear responses.

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed1988

Yeast beta-glucanases: a complex system of secreted enzymes.

The complement of glucan-hydrolysing enzymes produced by yeast species is considered to be relevant to morphogenesis, since this polysaccharide is the major structural component of the yeast cell wall. beta-glucanase systems of different species consist of both 1,3-beta- and 1,6-beta-hydrolases, which exert their action by either an exo- or an endo-splitting mechanism. The diversity of beta-glucanase systems, even among related species, is striking. The enzymes are produced for export, and the active forms of some of them seem to be generated upon secretion. Genetic approaches and the cloning of the glucanase genes are being used to clarify the biological role of the different enzymes. These also offer a possibility for genetic analysis of the functions related to cell wall dynamics with potential applications in biotechnology.

Gene Expression Regulation, Fungal↗
PubMed2003

Pseudomonas syringae exchangeable effector loci: sequence diversity in representative pathovars and virulence function in P. syringae pv. syringae B728a.

Pseudomonas syringae is a plant pathogen whose pathogenicity and host specificity are thought to be determined by Hop/Avr effector proteins injected into plant cells by a type III secretion system. P. syringae pv. syringae B728a, which causes brown spot of bean, is a particularly well-studied strain. The type III secretion system in P. syringae is encoded by hrp (hypersensitive response and pathogenicity) and hrc (hrp conserved) genes, which are clustered in a pathogenicity island with a tripartite structure such that the hrp/hrc genes are flanked by a conserved effector locus and an exchangeable effector locus (EEL). The EELs of P. syringae pv. syringae B728a, P. syringae strain 61, and P. syringae pv. tomato DC3000 differ in size and effector gene composition; the EEL of P. syringae pv. syringae B728a is the largest and most complex. The three putative effector proteins encoded by the P. syringae pv. syringae B728a EEL--HopPsyC, HopPsyE, and HopPsyV--were demonstrated to be secreted in an Hrp-dependent manner in culture. Heterologous expression of hopPsyC, hopPsyE, and hopPsyV in P. syringae pv. tabaci induced the hypersensitive response in tobacco leaves, demonstrating avirulence activity in a nonhost plant. Deletion of the P. syringae pv. syringae B728a EEL strongly reduced virulence in host bean leaves. EELs from nine additional strains representing nine P. syringae pathovars were isolated and sequenced. Homologs of avrPphE (e.g., hopPsyE) and hopPsyA were particularly common. Comparative analyses of these effector genes and hrpK (which flanks the EEL) suggest that the EEL effector genes were acquired by horizontal transfer after the acquisition of the hrp/hrc gene cluster but before the divergence of modern pathovars and that some EELs underwent transpositions yielding effector exchanges or point mutations producing effector pseudogenes after their acquisition.

Bacterial Proteins↗
PubMed2005

Brucella lipopolysaccharide acts as a virulence factor.

Brucella is a facultative intracellular bacterium responsible for brucellosis. Virulence factors involved in Brucella replication and Brucella's strategies to circumvent the immune response are under investigation. VirB proteins that form the type IV secretion system and that are involved in intracellular replication are considered as one of Brucella's virulence factors. In addition to this secretion system, bacterial outer membrane components have also been described as being implicated in Brucella survival in the host. For example, this bacterium possesses an unconventional non-endotoxic lipopolysaccharide that confers resistance to anti-microbial attacks and modulates the host immune response. These properties make lipopolysaccharide an important virulence factor for Brucella survival and replication in the host.

Animals↗
PubMed2004

Identification of host-specific colonization factors of Salmonella enterica serovar Typhimurium.

The severity of infections caused by Salmonella enterica serovar Typhimurium varies depending on the host species. Numerous virulence genes have been identified in S. Typhimurium, largely from studies in mice, but their roles in infections of other species remain unclear. In the most comprehensive survey of its kind, through the use of signature-tagged mutagenesis of S. Typhimurium we have identified mutants that were unable to colonize calf intestines, mutants unable to colonize chick intestines and mutants unable to colonize both species. The type three secretion systems encoded on Salmonella pathogenicity islands (SPIs) 1 and 2 were required for efficient colonization of cattle. However, disruption of these secretion systems only caused a minor defect in S. Typhimurium colonization of chicks. Transposon insertions in SPI-4 compromised S. Typhimurium colonization of cattle, but not chicks. This is the first data confirming a role for SPI-4 in pathogenesis. We have also been able to ascribe a role in colonization for cell surface polysaccharides, cell envelope proteins, and many 'housekeeping' genes and genes of unknown function. We conclude that S. Typhimurium uses different strategies to colonize calves and chicks. This has major implications for vaccine design.

Animals↗