Search results for "Hemolysin"
showing 10 items of 169 documents
A new gene superfamily of pathogen-response (repat) genes in Lepidoptera: Classification and expression analysis
2012
Repat (REsponse to PAThogens) genes were first identified in the midgut of Spodoptera exigua (Lepidoptera: Noctuidae) in response to Bacillus thuringiensis and baculovirus exposure. Since then, additional repat gene homologs have been identified in different studies. In this study the comprehensive larval transcriptome from S. exigua was analyzed for the presence of novel repat-homolog sequences. These analyses revealed the presence of at least 46 repat genes in S. exigua, establishing a new gene superfamily in this species. Phylogenetic analysis and studies of conserved motifs in these hypothetical proteins have allowed their classification in two main classes, αREPAT and βREPAT. Studies o…
Mannose phosphate isomerase isoenzymes in Plutella xylostella support common genetic bases of resistance to Bacillus thuringiensis toxins in Llpidopt…
2001
ABSTRACT A strong correlation between two mannose phosphate isomerase (MPI) isoenzymes and resistance to Cry1A toxins from Bacillus thuringiensis has been found in a Plutella xylostella population. MPI linkage to Cry1A resistance had previously been reported for a Heliothis virescens population. The fact that the two populations share similar biochemical, genetic, and cross-resistance profiles of resistance suggests the occurrence of homologous resistance loci in both species.
Genetic and Biochemical Characterization of Field-Evolved Resistance to Bacillus thuringiensis Toxin Cry1Ac in the Diamondback Moth, Plutella xyloste…
2004
ABSTRACT The long-term usefulness of Bacillus thuringiensis Cry toxins, either in sprays or in transgenic crops, may be compromised by the evolution of resistance in target insects. Managing the evolution of resistance to B. thuringiensis toxins requires extensive knowledge about the mechanisms, genetics, and ecology of resistance genes. To date, laboratory-selected populations have provided information on the diverse genetics and mechanisms of resistance to B. thuringiensis , highly resistant field populations being rare. However, the selection pressures on field and laboratory populations are very different and may produce resistance genes with distinct characteristics. In order to better…
Pore-forming toxins activate MAPK p38 by causing loss of cellular potassium.
2009
Mitogen activated protein kinase (MAPK) p38 has emerged as a survival protein in cells that are attacked by bacterial toxins forming small membrane pores. Activation of p38 by pore forming toxins (PFT) has been attributed to osmotic stress, but here we show that loss of K+ is likely to be the critical parameter. Several lines of evidence support this conclusion: first, osmoprotection did not prevent p38-phosphorylation in alpha-toxin-loaded cells. Second, treatment of cells with a K+ ionophore, or simple incubation in K+-free medium sufficed to cause robust p38-phosphorylation. Third, media containing high [K+] prevented p38-activation by Staphylococcus aureus alpha-toxin, Vibrio cholerae c…
Correct oligomerization is a prerequisite for insertion of the central molecular domain of staphylococcal α-toxin into the lipid bilayer
1995
Staphylococcal alpha-toxin is a primarily hydrophilic molecule that binds as a monomer to target membranes and then aggregates to form amphiphilic oligomers that represent water-filled transmembrane channels. Current evidence indicates that a region located in the center of the molecule inserts deeply into the bilayer. In the present study, we sought to determine whether membrane insertion was triggered by the oligomerization process, and whether insertion correlated with pore formation. Double mutants of alpha-toxin were prepared in which His-35 was replaced by Arg, and cysteine residues were introduced at positions 69, 130 and 186. Substitution of His-35 with Arg rendered the toxin molecu…
Mode of primary binding to target membranes and pore formation induced by Vibrio cholerae cytolysin (hemolysin).
1997
Vibrio cholerae cytolysin (VCC) is produced by many non-choleratoxigenic strains of V. cholerae, and possibly represents a relevant pathogenicity determinant of these bacteria. The protein is secreted as a pro-toxin that is proteolytically cleaved to yield the active toxin with a molecular mass of approximately 63 kDa. We here describe a simple procedure for preparative isolation of mature VCC from bacterial culture supernatants, and present information on its mode of binding and pore formation in biological membranes. At low concentrations, toxin monomers interact with a high-affinity binding site on highly susceptible rabbit erythrocytes. This as yet unidentified binding site is absent on…
Cholesterol Specificity of Some Heptameric β-Barrel Pore-Forming Bacterial Toxins: Structural and Functional Aspects
2010
Apart from the thiol-specific/cholesterol-dependent cytolysin family of toxins (see Chapter 20) there are a number of other unrelated bacterial toxins that also have an affinity for plasma membrane cholesterol. Emphasis is given here on the Vibrio cholerae cytolysin (VCC) and the cytolysins from related Vibrio species. The inhibition of the cytolytic activity of these toxins by prior incubation with extracellular cholesterol or low density lipoprotein emerges as a unifying feature, as does plasma membrane cholesterol depletion. Incubation of VCC with cholesterol produces a heptameric oligomer, which is not equivalent to the pre-pore since it is unable to penetrate the plasma membrane. In st…
Novel path to apoptosis: small transmembrane pores created by staphylococcal alpha-toxin in T lymphocytes evoke internucleosomal DNA degradation.
1994
Peripheral-blood human T lymphocytes were treated with Staphylococcus aureus alpha-toxin. Membrane permeabilization was assessed by measuring efflux of K+ and Rb+ and influx of Na+, Ca2+, and propidium iodide. Cellular ATP and [3H]thymidine incorporation following lectin stimulation were measured as parameters for cell viability. Internucleosomal cleavage characteristic of programmed cell death was assessed by agarose gel electrophoresis and by quantifying low-molecular-weight, [3H]thymidine-labeled DNA fragments. Nanomolar concentrations of alpha-toxin evoked protracted, irreversible ATP depletion in both activated and resting T lymphocytes. Toxin-damaged cells also lost their ability to i…
Cytocidal effects of Escherichia coli hemolysin on human T lymphocytes.
1993
Escherichia coli hemolysin is the prototype of a large family of pore-forming toxins produced by gram-negative organisms. Besides its known cytotoxic activities against granulocytes, monocytes, endothelial cells, and renal epithelial cells, we now demonstrate that the toxin potently kills human T lymphocytes. Evidence based on different and independent approaches indicates that lymphocidal activity is due to formation of transmembrane pores. Additionally, cells prestimulated with phytohemagglutinin respond to low doses of E. coli hemolysin with DNA fragmentation similar to that observed in cells undergoing programmed cell death. Kinetic considerations lead us to conclude that DNA degradatio…
Interferons increase cell resistance to Staphylococcal alpha-toxin.
2007
ABSTRACTMany bacterial pathogens, includingStaphylococcus aureus, use a variety of pore-forming toxins as important virulence factors. Staphylococcal alpha-toxin, a prototype β-barrel pore-forming toxin, triggers the release of proinflammatory mediators and induces primarily necrotic death in susceptible cells. However, whether host factors released in response to staphylococcal infections may increase cell resistance to alpha-toxin is not known. Here we show that prior exposure to interferons (IFNs) prevents alpha-toxin-induced membrane permeabilization, the depletion of ATP, and cell death. Moreover, pretreatment with IFN-α decreases alpha-toxin-induced secretion of interleukin 1β (IL-1β)…