41 research outputs found

    An ATP-binding cassette-type cysteine transporter in Campylobacter jejuni inferred from the structure of an extracytoplasmic solute receptor protein

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    Campylobacter jejuni is a Gram-negative food-borne pathogen associated with gastroenteritis in humans as well as cases of the autoimmune disease Guillain Barre syndrome. C. jejuni is asaccharolytic because it lacks an active glycolytic pathway for the use of sugars as a carbon source. This suggests an increased reliance on amino acids as nutrients and indeed the genome sequence of this organism indicates the presence of a number of amino acid uptake systems. Cj0982, also known as CjaA, is a putative extracytoplasmic solute receptor for one such uptake system as well as a major surface antigen and vaccine candidate. The crystal structure of Cj0982 reveals a two-domain protein with density in the enclosed cavity between the domains that clearly defines the presence of a bound cysteine ligand. Fluorescence titration experiments were used to demonstrate that Cj0982 binds cysteine tightly and specifically with a K-d of similar to 10(-7) M consistent with a role as a receptor for a high- affinity transporter. These data imply that Cj0982 is the binding protein component of an ABC-type cysteine transporter system and that cysteine uptake is important in the physiology of C. jejuni

    Human exploration of space: A review of NASA's 90-day study and alternatives

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    The National Research Council (NRC) examines the NASA Report of the 90-Day Study on Human Exploration of the Moon and Mars, and alternative concepts. Included in this paper, prepared for the National Space Council, are the answers to a challenging set of questions posed by the Vice President. Concerns addressed include: the appropriate pace, the scope of human exploration, the level of long-term support required, the technology development available and needed, the feasibility of long-duration human spaceflight in a low-gravity environment, scientific objectives, and other considerations such as costs and risks

    Vibrio cholerae vexH Encodes a Multiple Drug Efflux Pump That Contributes to the Production of Cholera Toxin and the Toxin Co-Regulated Pilus

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    The resistance-nodulation-division (RND) efflux systems are ubiquitous transporters that function in antimicrobial resistance. Recent studies showed that RND systems were required for virulence factor production in Vibrio cholerae. The V. cholerae genome encodes six RND efflux systems. Three of the RND systems (VexB, VexD, and VexK) were previously shown to be redundant for in vitro resistance to bile acids and detergents. A mutant lacking the VexB, VexD, and VexK RND pumps produced wild-type levels of cholera toxin (CT) and the toxin co-regulated pilus (TCP) and was moderately attenuated for intestinal colonization. In contrast, a RND negative mutant produced significantly reduced amounts of CT and TCP and displayed a severe colonization defect. This suggested that one or more of the three uncharacterized RND efflux systems (i.e. VexF, VexH, and VexM) were required for pathogenesis. In this study, a genetic approach was used to generate a panel of V. cholerae RND efflux pump mutants in order to determine the function of VexH in antimicrobial resistance, virulence factor production, and intestinal colonization. VexH contributed to in vitro antimicrobial resistance and exhibited a broad substrate specificity that was redundant with the VexB, VexD, and VexK RND efflux pumps. These four efflux pumps were responsible for in vitro antimicrobial resistance and were required for virulence factor production and intestinal colonization. Mutation of the VexF and/or VexM efflux pumps did not affect in vitro antimicrobial resistance, but did negatively affect CT and TCP production. Collectively, our results demonstrate that the V. cholerae RND efflux pumps have redundant functions in antimicrobial resistance and virulence factor production. This suggests that the RND efflux systems contribute to V. cholerae pathogenesis by providing the bacterium with protection against antimicrobial compounds that are present in the host and by contributing to the regulated expression of virulence factors

    Small Molecule Control of Virulence Gene Expression in Francisella tularensis

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    In Francisella tularensis, the SspA protein family members MglA and SspA form a complex that associates with RNA polymerase (RNAP) to positively control the expression of virulence genes critical for the intramacrophage growth and survival of the organism. Although the association of the MglA-SspA complex with RNAP is evidently central to its role in controlling gene expression, the molecular details of how MglA and SspA exert their effects are not known. Here we show that in the live vaccine strain of F. tularensis (LVS), the MglA-SspA complex works in concert with a putative DNA-binding protein we have called PigR, together with the alarmone guanosine tetraphosphate (ppGpp), to regulate the expression of target genes. In particular, we present evidence that MglA, SspA, PigR and ppGpp regulate expression of the same set of genes, and show that mglA, sspA, pigR and ppGpp null mutants exhibit similar intramacrophage growth defects and are strongly attenuated for virulence in mice. We show further that PigR interacts directly with the MglA-SspA complex, suggesting that the central role of the MglA and SspA proteins in the control of virulence gene expression is to serve as a target for a transcription activator. Finally, we present evidence that ppGpp exerts its effects by promoting the interaction between PigR and the RNAP-associated MglA-SspA complex. Through its responsiveness to ppGpp, the contact between PigR and the MglA-SspA complex allows the integration of nutritional cues into the regulatory network governing virulence gene expression

    Current concept of abdominal sepsis : WSES position paper

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    Current concept of abdominal sepsis: WSES position paper

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    Second Thoughts on Colonial Historians and American Indians

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    Coming to Terms with Early America

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    Ambience/Stimuli

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    Andrews elaborates on the premise of an exhibition of ten "works" illustrative of the artists' "creative urge" and representative of the process involved in producing a finished work. Includes artist's statements and biographical notes. 13 bibl. ref
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