Search results for "Hemolysi"
showing 10 items of 241 documents
Genetic variability of Spodoptera frugiperda Smith (Lepidoptera: Noctuidae) populations from Latin America is associated with variations in susceptib…
2006
ABSTRACT Bacillus thuringiensis strains isolated from Latin American soil samples that showed toxicity against three Spodoptera frugiperda populations from different geographical areas (Mexico, Colombia, and Brazil) were characterized on the basis of their insecticidal activity, crystal morphology, sodium dodecyl sulfate-polyacrylamide gel electrophoresis of parasporal crystals, plasmid profiles, and cry gene content. We found that the different S. frugiperda populations display different susceptibilities to the selected B. thuringiensis strains and also to pure preparations of Cry1B, Cry1C, and Cry1D toxins. Binding assays performed with pure toxin demonstrated that the differences in the …
Resistance to the Bacillus thuringiensis bioinsecticide in a field population of Plutella xylostella is due to a change in a midgut membrane receptor.
1991
The biochemical mechanism for resistance to Bacillus thuringiensis crystal proteins was studied in a field population of diamondback moths (Plutella xylostella) with a reduced susceptibility to the bioinsecticidal spray. The toxicity and binding characteristics of three crystal proteins [CryIA(b), CryIB, and CryIC] were compared between the field population and a laboratory strain. The field population proved resistant (greater than 200-fold compared with the laboratory strain) to CryIA(b), one of the crystal proteins in the insecticidal formulation. Binding studies showed that the two strains differ in a membrane receptor that recognizes CryIA(b). This crystal protein did not bind to the b…
Common receptor for Bacillus thuringiensis toxins Cry1Ac, Cry1Fa, and Cry1Ja in Helicoverpa armigera, Helicoverpa zea and Spodoptera exigua
2005
ABSTRACT Binding studies using 125 I-Cry1Ac and biotinylated Cry1Fa toxins indicate the occurrence of a common receptor for Cry1Ac, Cry1Fa, and Cry1Ja in Helicoverpa armigera , Helicoverpa zea , and Spodoptera exigua . Our results, along with previous binding data and the observed cases of cross-resistance, suggest that this pattern seems to be widespread among lepidopteran species.
Dynamic Antigen Presentation Patterns of Listeria monocytogenes-Derived CD8 T Cell Epitopes In Vivo
2001
Abstract Little information exists regarding the presentation of antigenic peptides in infected tissues. In this study the in vivo presentation of four different CD8 T cell epitopes of Listeria monocytogenes was monitored. Peptide presentation was measured by a new, highly sensitive, ex vivo Ag presentation assay that was based on the testing of freshly isolated cells from infected spleens with peptide-specific CD8 T cell lines in an IFN-γ-specific ELISPOT assay. Remarkably, the peptide presentation pattern of splenocytes and that of macrophages purified from spleens of L. monocytogenes-infected mice were different from those of in vitro infected macrophage-like cell lines. The in vivo Ag p…
Staphylococcal alpha-toxin, streptolysin-O, and Escherichia coli hemolysin: prototypes of pore-forming bacterial cytolysins.
1996
Staphylococcal alpha-toxin, streptolysin-O, and Escherichia coli hemolysin are well-studied prototypes of pore-forming bacterial cytotoxins. Each is produced as a water-soluble single-chain polypeptide that inserts into target membranes to form aqueous transmembrane pores. This review will compare properties of the three toxin prototypes, highlighting the similarities and also the differences in their structure, mode of binding, mechanism of pore formation, and the responses they elicit in target cells. Pore-forming toxins represent the most potent and versatile weapons with which invading microbes damage the host macroorganism.
Electrophysiological evidence for heptameric stoichiometry of ion channels formed by Staphylococcus aureus alpha-toxin in planar lipid bilayers.
2000
Staphylococcal alpha-toxin forms homo-oligomeric channels in lipid bilayers and cell membranes. Here, we report that electrophysiological monitoring of single-channel function using a derivatized cysteine substitution mutant allows accurate determination of the subunit stoichiometry of the oligomer in situ. The electrophysiological phenotype of channels formed in planar lipid bilayers with the cysteine replacement mutant I7C is equal to that of the wild type. When pores were formed with I7C, alterations of several channel properties were observed upon modification with SH reagents. Decreases in conductance then occurred that were seen only as negative voltage was applied. At the level of si…
Shared Binding Sites in Lepidoptera for Bacillus thuringiensis Cry1Ja and Cry1A Toxins
2001
ABSTRACT Bacillus thuringiensis toxins act by binding to specific target sites in the insect midgut epithelial membrane. The best-known mechanism of resistance to B. thuringiensis toxins is reduced binding to target sites. Because alteration of a binding site shared by several toxins may cause resistance to all of them, knowledge of which toxins share binding sites is useful for predicting cross-resistance. Conversely, cross-resistance among toxins suggests that the toxins share a binding site. At least two strains of diamondback moth ( Plutella xylostella ) with resistance to Cry1A toxins and reduced binding of Cry1A toxins have strong cross-resistance to Cry1Ja. Thus, we hypothesized that…
Variation in Susceptibility to Bacillus thuringiensis Toxins among Unselected Strains of Plutella xylostella
2001
ABSTRACT So far, the only insect that has evolved resistance in the field to Bacillus thuringiensis toxins is the diamondback moth ( Plutella xylostella ). Documentation and analysis of resistant strains rely on comparisons with laboratory strains that have not been exposed to B. thuringiensis toxins. Previously published reports show considerable variation among laboratories in responses of unselected laboratory strains to B. thuringiensis toxins. Because different laboratories have used different unselected strains, such variation could be caused by differences in bioassay methods among laboratories, genetic differences among unselected strains, or both. Here we tested three unselected st…
Interaction of Bacillus thuringiensis Toxins with Larval Midgut Binding Sites of Helicoverpa armigera (Lepidoptera: Noctuidae)
2004
ABSTRACT In 1996, Bt-cotton (cotton expressing a Bacillus thuringiensis toxin gene) expressing the Cry1Ac protein was commercially introduced to control cotton pests. A threat to this first generation of transgenic cotton is the evolution of resistance by the insects. Second-generation Bt-cotton has been developed with either new B. thuringiensis genes or with a combination of cry genes. However, one requirement for the “stacked” gene strategy to work is that the stacked toxins bind to different binding sites. In the present study, the binding of 125 I-labeled Cry1Ab protein ( 125 I-Cry1Ab) and 125 I-Cry1Ac to brush border membrane vesicles (BBMV) of Helicoverpa armigera was analyzed in com…
High Genetic Variability for Resistance to Bacillus thuringiensis Toxins in a Single Population of Diamondback Moth
2001
ABSTRACT The long-term benefit of insecticidal products based on Cry toxins, either in sprays or as transgenic crops, is threatened by the development of resistance by target pests. The models used to predict evolution of resistance to Cry toxins most often are monogenic models in which two alleles are used. Moreover, the high-dose/refuge strategy recommended for implementation with transgenic crops relies on the assumption that the resistance allele is recessive. Using selection experiments, we demonstrated the occurrence in a laboratory colony of diamondback moth of two different genes (either allelic or nonallelic) that confer resistance to Cry1Ab. At the concentration tested, resistance…