Dataset Information

Analysis of the Salmonella regulatory network suggests involvement of SsrB and H-NS in ?(E)-regulated SPI-2 gene expression.

ABSTRACT: The extracytoplasmic functioning sigma factor ?(E) is known to play an essential role for Salmonella enterica serovar Typhimurium to survive and proliferate in macrophages and mice. However, its regulatory network is not well-characterized, especially during infection. Here we used microarray to identify genes regulated by ?(E) in Salmonella grown in three conditions: a nutrient-rich condition and two others that mimic early and late intracellular infection. We found that in each condition ?(E) regulated different sets of genes, and notably, several global regulators. When comparing nutrient-rich and infection-like conditions, large changes were observed in the expression of genes involved in Salmonella pathogenesis island (SPI)-1 type-three secretion system (TTSS), SPI-2 TTSS, protein synthesis, and stress responses. In total, the expression of 58% of Salmonella genes was affected by ?(E) in at least one of the three conditions. An important finding is that ?(E) up-regulates SPI-2 genes, which are essential for Salmonella intracellular survival, by up-regulating SPI-2 activator ssrB expression at the early stage of infection and down-regulating SPI-2 repressor hns expression at a later stage. Moreover, ?(E) is capable of countering the silencing of H-NS, releasing the expression of SPI-2 genes. This connection between ?(E) and SPI-2 genes, combined with the global regulatory effect of ?(E), may account for the lethality of rpoE-deficient Salmonella in murine infection.

SUBMITTER: Li J

PROVIDER: S-EPMC4322710 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Analysis of the Salmonella regulatory network suggests involvement of SsrB and H-NS in σ(E)-regulated SPI-2 gene expression.

Li Jie J Overall Christopher C CC Nakayasu Ernesto S ES Kidwai Afshan S AS Jones Marcus B MB Johnson Rudd C RC Nguyen Nhu T NT McDermott Jason E JE Ansong Charles C Heffron Fred F Cambronne Eric D ED Adkins Joshua N JN

Frontiers in microbiology 20150210

The extracytoplasmic functioning sigma factor σ(E) is known to play an essential role for Salmonella enterica serovar Typhimurium to survive and proliferate in macrophages and mice. However, its regulatory network is not well-characterized, especially during infection. Here we used microarray to identify genes regulated by σ(E) in Salmonella grown in three conditions: a nutrient-rich condition and two others that mimic early and late intracellular infection. We found that in each condition σ(E) ...[more]

PMID: 25713562

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Project description:In bacterial pathogenesis, virulence gene regulation is controlled by two-component regulatory systems. In Escherichia coli, the EnvZ/OmpR two-component system is best understood as regulating expression of outer membrane proteins, but in Salmonella enterica, OmpR activates transcription of the SsrA/B two-component system located on Salmonella pathogenicity island 2 (SPI-2). The response regulator SsrB controls expression of a type III secretory system in which effectors modify the vacuolar membrane and prevent its degradation via the endocytic pathway. Vacuolar modification enables Salmonella to survive and replicate in the macrophage phagosome and disseminate to the liver and spleen to cause systemic infection. The signals that activate EnvZ and SsrA are unknown but are related to the acidic pH encountered in the vacuole. Our previous work established that SsrB binds to regions of DNA that are AT-rich, with poor sequence conservation. Although SsrB is a major virulence regulator in Salmonella, very little is known regarding how it binds DNA and activates transcription. In the present work, we solved the structure of the C-terminal DNA binding domain of SsrB (SsrB(C)) by NMR and analyzed the effect of amino acid substitutions on function. We identified residues in the DNA recognition helix (Lys(179), Met(186)) and the dimerization interface (Val(197), Leu(201)) that are important for SsrB transcriptional activation and DNA binding. An essential cysteine residue in the N-terminal receiver domain was also identified (Cys(45)), and the effect of Cys(203) on dimerization was evaluated. Our results suggest that although disulfide bond formation is not required for dimerization, dimerization occurs upon DNA binding and is required for subsequent activation of transcription. Disruption of the dimer interface by a C203E substitution reduces SsrB activity. Modification of Cys(203) or Cys(45) may be an important mode of SsrB inactivation inside the host.

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Dataset Information

Analysis of the Salmonella regulatory network suggests involvement of SsrB and H-NS in ?(E)-regulated SPI-2 gene expression.

Publications

Analysis of the Salmonella regulatory network suggests involvement of SsrB and H-NS in σ(E)-regulated SPI-2 gene expression.

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