Antimicrobial peptides activate the Rcs regulon through the outer membrane lipoprotein RcsF.

Salmonella enterica species are exposed to envelope stresses due to their environmental and infectious lifestyles. Such stresses include amphipathic cationic antimicrobial peptides (CAMPs), and resistance to these peptides is an important property for microbial virulence for animals. Bacterial mechanisms used to sense and respond to CAMP-induced envelope stress include the RcsFCDB phosphorelay, which contributes to survival from polymyxin B exposure.

The PhoQ histidine kinases of Salmonella and Pseudomonas spp. are structurally and functionally different: evidence that pH and antimicrobial peptide sensing contribute to mammalian pathogenesis.

The PhoQ sensor kinase is essential for Salmonella typhimurium virulence for animals, and a homologue exists in the environmental organism and opportunistic pathogen Pseudomonas aeruginosa. S. typhimurium PhoQ (ST-PhoQ) is repressed by millimolar concentrations of divalent cations and activated by antimicrobial peptides and at acidic pH.

Activation of the bacterial sensor kinase PhoQ by acidic pH.

The Salmonellae PhoQ sensor kinase senses the mammalian phagosome environment to activate a transcriptional program essential for virulence. The PhoQ periplasmic domain binds divalent cations, forming bridges with inner membrane phospholipids to maintain PhoQ repression. PhoQ also binds and is activated by cationic antimicrobial peptides.

Cytoplasmic flagellin activates caspase-1 and secretion of interleukin 1beta via Ipaf.

Macrophages respond to Salmonella typhimurium infection via Ipaf, a NACHT-leucine-rich repeat family member that activates caspase-1 and secretion of interleukin 1beta. However, the specific microbial salmonella-derived agonist responsible for activating Ipaf is unknown. We show here that cytosolic bacterial flagellin activated caspase-1 through Ipaf but was independent of Toll-like receptor 5, a known flagellin sensor.

Metal bridges between the PhoQ sensor domain and the membrane regulate transmembrane signaling.

Bacterial histidine kinases respond to environmental stimuli by transducing a signal from an extracytosolic sensor domain to a cytosolic catalytic domain. Among them, PhoQ promotes bacterial virulence and is tightly repressed by the divalent cations such as calcium and magnesium. We have determined the crystal structure of the PhoQ sensor domain from Salmonella typhimurium in the Ca2+-bound state, which reveals a highly negatively charged surface that is in close proximity to the inner membrane.

Recognition of antimicrobial peptides by a bacterial sensor kinase.

PhoQ is a membrane bound sensor kinase important for the pathogenesis of a number of Gram-negative bacterial species. PhoQ and its cognate response regulator PhoP constitute a signal-transduction cascade that controls inducible resistance to host antimicrobial peptides. We show that enzymatic activity of Salmonella typhimurium PhoQ is directly activated by antimicrobial peptides.

Comparison of the PhoPQ regulon in Escherichia coli and Salmonella typhimurium.

The PhoPQ two-component system acts as a transcriptional regulator that responds to Mg(2+) starvation both in Escherichia coli and Salmonella typhimurium (Garcia et al. 1996; Kato et al. 1999).

LPS, TLR4 and infectious disease diversity.

Innate immune receptors recognize microorganism-specific motifs. One such receptor-ligand complex is formed between the mammalian Toll-like receptor 4 (TLR4)-MD2-CD14 complex and bacterial lipopolysaccharide (LPS). Recent research indicates that there is significant phylogenetic and individual diversity in TLR4-mediated responses.

Escherichia coli Hsp31 functions as a holding chaperone that cooperates with the DnaK-DnaJ-GrpE system in the management of protein misfolding under severe stress conditions.

Escherichia coli Hsp31 is a homodimeric protein that exhibits chaperone activity in vitro and is a representative member of a recently recognized family of heat shock proteins (Hsps). To gain insights on Hsp31 cellular function, we deleted the hchA gene from the MC4100 chromosome and combined the resulting null allele with lesions in other cytoplasmic chaperones. Although the hchA mutant only exhibited growth defects when cultivated at 48 degrees C, loss of Hsp31 had a strong deleterious effect on the ability of cells to survive and recover from transient exposure to 50 degrees C, and led to the enhanced aggregation of a subset of host proteins at this temperature.

Regulation of Salmonella typhimurium virulence gene expression by cationic antimicrobial peptides.

Cationic antimicrobial peptides (CAMP) represent a conserved and highly effective component of innate immunity. During infection, the Gram-negative pathogen Salmonella typhimurium induces different mechanisms of CAMP resistance that promote pathogenesis in animals. This study shows that exposure of S.

Reconstitution of a disulfide isomerization system.

Isomerization of disulfide bonds is vital for the proper folding of proteins that possess multiple disulfides. In prokaryotes, the catalytic pathway responsible for disulfide isomerization involves thioredoxin, thioredoxin reductase, and the DsbC, DsbG, and DsbD proteins. To be active as isomerases, DsbC and DsbG must be kept reduced.

Identification of the ubiquinone-binding domain in the disulfide catalyst disulfide bond protein B.

Disulfide bond (Dsb) formation is catalyzed in the periplasm of prokaryotes by the Dsb proteins. DsbB, a key enzyme in this process, generates disulfides de novo by using the oxidizing power of quinones. To explore the mechanism of this newly described enzymatic activity, we decided to study the ubiquinone-protein interaction and identify the ubiquinone-binding domain in DsbB by cross-linking to photoactivatable quinone analogues.