Search results for "Bacterial Toxin"
showing 10 items of 192 documents
A guide to the use of pore-forming toxins for controlled permeabilization of cell membranes
1993
Depending on the size of the pores one wishes to produce in plasma membranes, the choice will probably fall on one of the three toxins discussed above. S. aureus alpha-toxin should be tried first when pores of 1-1.5 nm diameter are required. This is generally the case when Ca2+ and nucleotide dependence of a given process is being studied. If alpha-toxin does not work, this is probably due to the fact that the toxin either does not produce pores, or that the pores are too small. In this case, high concentrations of alpha-toxin should be tried. If this still does not work, we recommend the use of HlyA. When very large pores are to be created, e.g. for introduction of antibodies into the cell…
Mutations in the Bacillus thuringiensis Cry1Ca toxin demonstrate the role of domains II and III in specificity towards Spodoptera exigua larvae
2004
Several mutants of the Bacillus thuringiensis Cry1Ca toxin affected with regard to specific activity towards Spodoptera exigua were studied. Alanine was used to replace single residues in loops 2 and 3 of domain II (mutant pPB19) and to replace residues 541– 544 in domain III (mutant pPB20). Additionally, a Cry1Ca mutant combining all mutations was constructed (mutant pPB21). Toxicity assays showed a marked decrease in toxicity against S. exigua for all mutants, while they retained their activity against Manduca sexta, confirming the importance of these residues in determining insect specificity. Parameters for binding to the specific receptors in BBMV (brush border membrane vesicles) of S.…
Proteome response of Tribolium castaneum larvae to Bacillus thuringiensis toxin producing strains.
2012
Susceptibility of Tribolium castaneum (Tc) larvae was determined against spore-crystal mixtures of five coleopteran specific and one lepidopteran specific Bacillus thuringiensis Cry toxin producing strains and those containing the structurally unrelated Cry3Ba and Cry23Aa/Cry37Aa proteins were found toxic (LC(50) values 13.53 and 6.30 µg spore-crystal mixture/µL flour disc, respectively). Using iTRAQ combined with LC-MS/MS allowed the discovery of seven novel differentially expressed proteins in early response of Tc larvae to the two active spore-crystal mixtures. Proteins showing a statistically significant change in treated larvae compared to non-intoxicated larvae fell into two major cat…
Interaction of Heparins and Dextran Sulfates with a Mesoscopic Protein Nanopore
2009
A mechanism of how polyanions influence the channel formed by Staphylococcus aureus alpha-hemolysin is described. We demonstrate that the probability of several types of polyanions to block the ion channel depends on the presence of divalent cations and the polyanion molecular weight and concentration. For heparins, a 10-fold increase in molecular weight decreases the half-maximal inhibitory concentration, IC(50), nearly 10(4)-fold. Dextran sulfates were less effective at blocking the channel. The polyanions are significantly more effective at reducing the conductance when added to the trans side of this channel. Lastly, the effectiveness of heparins on the channel conductance correlated wi…
Tyrosine-phosphorylation-dependent and Rho-protein-mediated control of cellular phosphatidylinositol 4,5-bisphosphate levels
1998
The polyphosphoinositide PtdIns(4,5)P2, best known as a substrate for phospholipase C isozymes, has recently been recognized to be involved in a variety of other cellular processes. The aim of this study was to examine whether the cellular levels of this versatile phospholipid are controlled by tyrosine phosphorylation. The studies were performed in human embryonic kidney (HEK)-293 cells stably expressing the M3 muscarinic acetylcholine receptor. Inhibition of tyrosine phosphatases by pervanadate induced an up-to-approx.-2.5-fold increase in the total cellular level of PtdIns(4,5)P2, which was both time- and concentration-dependent. In contrast, the tyrosine kinase inhibitors, genistein and…
A role for Rho in receptor- and G protein-stimulated phospholipase C Reduction in phosphatidylinositol 4,5-bisphosphate by Clostridium difficile toxi…
1996
Receptors coupled to heterotrimeric guanine nucleotide-binding proteins (G proteins) activate phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2)-hydrolyzing phospholipase C (PLC) enzymes by activated alpha of free beta gamma subunits of the relevant G proteins. To study whether low molecular weight G proteins of the Rho family are involved in receptor signaling to PLC, we examined the effect of Clostridium difficile toxin B, which glucosylates and thereby inactivates Rho proteins, on the regulation of PLC activity in human embryonic kidney (HEK) cells stably expressing the m3 muscarinic acetylcholine receptor (mAChR) subtype. Toxin B treatment of HEK cells did not affect basal PLC activi…
Restoration of Clostridium difficile toxin-B-inhibited phospholipase D by phosphatidylinositol 4,5-bisphosphate.
1996
Receptor signalling to phospholipase D (PLD) in human embryonic kidney (HEK) cells stably expressing the m3 muscarinic acetylcholine receptor apparently involves Rho proteins. Since phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] has been recognized as an essential cofactor for PLD activity and since activated Rho proteins have been reported to stimulate the synthesis of PtdIns(4,5)P2, we studied whether in HEK cells PLD activity is regulated by PtdIns(4,5)P2 and, in particular, whether PtdIns(4,5)P2 can restore PLD activity inhibited by Clostridium difficile toxin B, which inactivates Rho proteins. Addition of MgATP to permeabilized HEK cells increased basal PLD activity and potentia…
Control of cellular phosphatidylinositol 4,5-bisphosphate levels by adhesion signals and Rho GTPases in NIH 3T3 fibroblasts
2000
The involvement of small GTPases of the Rho family in the control of phosphoinositide metabolism by adhesion signals was examined in NIH 3T3 fibroblasts. Abrogation of adhesion signals by detachment of cells from their substratum resulted in a time-dependent decrease in the cellular level of PtdIns(4,5)P2 by approximately 50%. This effect could be mimicked by treatment of adherent cells with Clostridium difficile toxin B and toxin B-1470, which inhibit specific subsets of Rho and Ras GTPases. Detachment of cells that had been pretreated with the clostridial toxins did not cause a further reduction in PtdIns(4,5)P2 levels, suggesting that the target GTPases are integrated into the control of…
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…