ToxR activates the virulence genes by tethering DNA to the membrane through versatile binding to multiple sites.

ToxR, a transmembrane one-component signal transduction factor, lies within a regulatory cascade that results in the expression of ToxT, toxin coregulated pilus, and cholera toxin. While ToxR has been extensively studied for its ability to activate or repress various genes in , here we present the crystal structures of the ToxR cytoplasmic domain bound to DNA at the and promoters. The structures confirm some predicted interactions, yet reveal other unexpected promoter interactions with implications for other potential regulatory roles for ToxR.

A Co-Association of Streptococcus mutans and Veillonella parvula/dispar in Root Caries Patients and Biofilms.

Root caries in geriatric patients is a growing problem as more people are maintaining their natural teeth into advanced age. We determined the levels of various bacterial species previously implicated in root caries disease or health using quantitative real-time PCR in a pilot study of 7 patients with 1 to 4 root caries lesions per person. Levels of 12 different species on diseased roots compared to healthy (contralateral control) roots were measured.

Complement evasion mechanisms of the systemic pathogens Yersiniae and Salmonellae.

Pathogens that colonize deep tissues and spread systemically encounter the innate host resistance mechanism of complement-mediated lysis and complement opsonization leading to engulfment and degradation by phagocytic cells. Yersinia and Salmonella species have developed numerous strategies to block the antimicrobial effects of complement. These include recruitment of complement regulatory proteins factor H, C4BP, and vitronectin (Vn) as well as interference in late maturation events such as assembly of C9 into the membrane attack complex that leads to bacterial lysis.

The wing of the ToxR winged helix-turn-helix domain is required for DNA binding and activation of toxT and ompU.

ToxR and TcpP, two winged helix-turn-helix (w-HTH) family transcription factors, co-activate expression of the toxT promoter in Vibrio cholerae. ToxT then directly regulates a number of genes required for virulence. In addition to co-activation of toxT, ToxR can directly activate the ompU promoter and repress the ompT promoter.

Ail provides multiple mechanisms of serum resistance to Yersinia pestis.

Ail, a multifunctional outer membrane protein of Yersinia pestis, confers cell binding, Yop delivery and serum resistance activities. Resistance to complement proteins in serum is critical for the survival of Y. pestis during the septicemic stage of plague infections.

Defining the Ail Ligand-Binding Surface: Hydrophobic Residues in Two Extracellular Loops Mediate Cell and Extracellular Matrix Binding To Facilitate Yop Delivery.

, the causative agent of plague, binds host cells to deliver cytotoxic Yop proteins into the cytoplasm that prevent phagocytosis and generation of proinflammatory cytokines. Ail is an eight-stranded β-barrel outer membrane protein with four extracellular loops that mediates cell binding and resistance to human serum. Following the deletion of each of the four extracellular loops that potentially interact with host cells, the Ail-Δloop 2 and Ail-Δloop 3 mutant proteins had no cell-binding activity while Ail-Δloop 4 maintained cell binding (the Ail-Δloop 1 protein was unstable).

Formation of an Intramolecular Periplasmic Disulfide Bond in TcpP Protects TcpP and TcpH from Degradation in Vibrio cholerae.

Unlabelled: TcpP and ToxR coordinately regulate transcription of toxT, the master regulator of numerous virulence factors in Vibrio cholerae. TcpP and ToxR are membrane-localized transcription factors, each with a periplasmic domain containing two cysteines. In ToxR, these cysteines form an intramolecular disulfide bond and a cysteine-to-serine substitution affects activity.

Yersinia pestis targets neutrophils via complement receptor 3.

Yersinia species display a tropism for lymphoid tissues during infection, and the bacteria select innate immune cells for delivery of cytotoxic effectors by the type III secretion system. Yet, the mechanism for target cell selection remains a mystery. Here we investigate the interaction of Yersinia pestis with murine splenocytes to identify factors that participate in the targeting process.

Ail proteins of Yersinia pestis and Y. pseudotuberculosis have different cell binding and invasion activities.

The Yersinia pestis adhesin Ail mediates host cell binding and facilitates delivery of cytotoxic Yop proteins. Ail from Y. pestis and Y.

ToxR recognizes a direct repeat element in the toxT, ompU, ompT, and ctxA promoters of Vibrio cholerae to regulate transcription.

ToxR facilitates TcpP-mediated activation of the toxT promoter in Vibrio cholerae, initiating a regulatory cascade that culminates in cholera toxin secretion and toxin coregulated pilus expression. ToxR binds a region from -104 to -68 of the toxT promoter, from which ToxR recruits TcpP to the TcpP-binding site from -53 to -38. To precisely define the ToxR-binding site within the toxT promoter, promoter derivatives with single-base-pair transversions spanning the ToxR-footprinted region were tested for transcription activation and DNA binding.

Ail protein binds ninth type III fibronectin repeat (9FNIII) within central 120-kDa region of fibronectin to facilitate cell binding by Yersinia pestis.

The Yersinia pestis adhesin molecule Ail interacts with the extracellular matrix protein fibronectin (Fn) on host cells to facilitate efficient delivery of cytotoxic Yop proteins, a process essential for plague virulence. A number of bacterial pathogens are known to bind to the N-terminal region of Fn, comprising type I Fn (FNI) repeats. Using proteolytically generated Fn fragments and purified recombinant Fn fragments, we demonstrated that Ail binds the centrally located 120-kDa fragment containing type III Fn (FNIII) repeats.

Structural insights into Ail-mediated adhesion in Yersinia pestis.

Ail is an outer membrane protein from Yersinia pestis that is highly expressed in a rodent model of bubonic plague, making it a good candidate for vaccine development. Ail is important for attaching to host cells and evading host immune responses, facilitating rapid progression of a plague infection. Binding to host cells is important for injection of cytotoxic Yersinia outer proteins.

The two faces of ToxR: activator of ompU, co-regulator of toxT in Vibrio cholerae.

ToxR of Vibrio cholerae directly activates the ompU promoter, but requires a second activator, TcpP to activate the toxT promoter. ompU encodes a porin, while toxT encodes the transcription factor, ToxT, which activates V. cholerae virulence genes including cholera toxin and the toxin co-regulated pilus.

Contributions of chaperone/usher systems to cell binding, biofilm formation and Yersinia pestis virulence.

Yersinia pestis genome sequencing projects have revealed six intact uncharacterized chaperone/usher systems with the potential to play roles in plague pathogenesis. We cloned each locus and expressed them in the Δfim Escherichia coli strain AAEC185 to test the assembled Y. pestis surface structures for various activities.

Three Yersinia pestis adhesins facilitate Yop delivery to eukaryotic cells and contribute to plague virulence.

To establish a successful infection, Yersinia pestis requires the delivery of cytotoxic Yops to host cells. Yops inhibit phagocytosis, block cytokine responses, and induce apoptosis of macrophages. The Y.

Identification of the TcpP-binding site in the toxT promoter of Vibrio cholerae and the role of ToxR in TcpP-mediated activation.

ToxR-dependent recruitment of TcpP to the toxT promoter facilitates toxT transcription in Vibrio cholerae, initiating a regulatory cascade that culminates in cholera toxin expression and secretion. Although TcpP usually requires ToxR to activate the toxT promoter, TcpP overexpression can circumvent the requirement for ToxR in this process. To define nucleotides critical for TcpP-dependent promoter recognition and activation, a series of toxT promoter derivatives with single-base-pair transversions spanning the TcpP-binding site were generated and used as plasmid-borne toxT-lacZ fusions, as DNA mobility shift targets, and as allelic replacements of the chromosomal toxT promoter.

Ail binding to fibronectin facilitates Yersinia pestis binding to host cells and Yop delivery.

Yersinia pestis, the causative agent of plague, evades host immune responses and rapidly causes disease. The Y. pestis adhesin Ail mediates host cell binding and is critical for Yop delivery.

Phosphoglucomutase of Yersinia pestis is required for autoaggregation and polymyxin B resistance.

Yersinia pestis, the causative agent of plague, autoaggregates within a few minutes of cessation of shaking when grown at 28 degrees C. To identify the autoaggregation factor of Y. pestis, we performed mariner-based transposon mutagenesis.

The Yersinia pestis autotransporter YapC mediates host cell binding, autoaggregation and biofilm formation.

YapC, a putative Yersinia pestis autotransporter protein, shows strong homology to the enterotoxigenic Escherichia coli adhesin TibA. As a potentially important surface protein of Y. pestis, we analysed YapC for several activities.

TcpH influences virulence gene expression in Vibrio cholerae by inhibiting degradation of the transcription activator TcpP.

Expression of toxT, the transcription activator of cholera toxin and pilus production in Vibrio cholerae, is the consequence of a complex cascade of regulatory events that culminates in activation of the toxT promoter by TcpP and ToxR, two membrane-localized transcription factors. Both are encoded in operons with genes whose products, TcpH and ToxS, which are also membrane localized, are hypothesized to control their activity. In this study we analyzed the role of TcpH in controlling TcpP function.

DNA binding and ToxR responsiveness by the wing domain of TcpP, an activator of virulence gene expression in Vibrio cholerae.

Virulence in Vibrio cholerae requires activation of toxT by two membrane-localized activators, TcpP and ToxR. We isolated 12 tcpP activation mutants that fell into two classes: class I mutants were inactive irrespective of the presence of ToxR, and class II mutants exhibited near wild-type activity when coexpressed with ToxR. Most class I mutants had lesions in the wing domain predicted by homology with the winged helix-turn-helix family of activators.

From motility to virulence: Sensing and responding to environmental signals in Vibrio cholerae.

Sensing its changing environment is key for Vibrio cholerae when making the transition from an aquatic lifestyle to one more suited to a human host. An inverse correlation between motility and virulence gene expression has been reported, with the NADH : ubiquinone oxidoreductase system which powers motility by generating a sodium-motive force, playing a pivotal role. Recent studies have demonstrated that bile inhibits activity of the transcription factor ToxT, a protein responsible for direct activation of numerous virulence gene promoters.

Membrane localization of the ToxR winged-helix domain is required for TcpP-mediated virulence gene activation in Vibrio cholerae.

ToxR is a bitopic membrane protein that controls virulence gene expression in Vibrio cholerae. Its cytoplasmic domain is homologous to the winged helix-turn-helix ('winged helix') DNA-binding/transcription activation domain found in a variety of prokaryotic and eukaryotic regulators, whereas its periplasmic domain is of ill-defined function. Several genes in V.