The pre-pore from Bacillus thuringiensis Cry1Ab toxin is necessary to induce insect death in Manduca sexta

Jiménez-Juárez, Nuria; Muñóz-Garay, Carlos; Gómez, Isabel; Gill, Sarjeet S.; Soberón, Mário; Bravo, Alejandra

doi:10.1016/j.peptides.2007.09.026

Cited by 26 publications

(18 citation statements)

References 47 publications

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“…The observed increased Cry1Fa oligomer formation in the presence of SfCad and MsCad agrees with the reported correlation between increased formation of toxin oligomers and enhanced activity of toxin binding cadherin fragments (33,37). However, unlike the Cry1Ab oligomers that are stable in M. sexta BBMVs (20), the Cry1Fa oligomers observed here were transient and disappeared in the presence of S. frugiperda BBMVs. It is possible that the Cry1Fa oligomers observed without BBMVs were present in BBMVs but were unstable under our BBMV solubilization conditions.…”

Section: Discussionsupporting

confidence: 91%

Differential Protection of Cry1Fa Toxin against Spodoptera frugiperda Larval Gut Proteases by Cadherin Orthologs Correlates with Increased Synergism

Rahman

Abdullah

Ambati

et al. 2012

Appl Environ Microbiol

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The Cry proteins produced by Bacillus thuringiensis (Bt) are the most widely used biopesticides effective against a range of crop pests and disease vectors. Like chemical pesticides, development of resistance is the primary threat to the long-term efficacy of Bt toxins. Recently discovered cadherin-based Bt Cry synergists showed the potential to augment resistance management by improving efficacy of Cry toxins. However, the mode of action of Bt Cry synergists is thus far unclear. Here we elucidate the mechanism of cadherin-based Cry toxin synergism utilizing two cadherin peptides, Spodoptera frugiperda Cad (SfCad) and Manduca sexta Cad (MsCad), which differentially enhance Cry1Fa toxicity to Spodoptera frugiperda neonates. We show that differential SfCad-and MsCad-mediated protection of Cry1Fa toxin in the Spodoptera frugiperda midgut correlates with differential Cry1Fa toxicity enhancement. Both peptides exhibited high affinity for Cry1Fa toxin and an increased rate of Cry1Fa-induced pore formation in S. frugiperda. However, only SfCad bound the S. frugiperda brush border membrane vesicle and more effectively prolonged the stability of Cry1Fa toxin in the gut, explaining higher Cry1Fa enhancement by this peptide. This study shows that cadherin fragments may enhance B. thuringiensis toxicity by at least two different mechanisms or a combination thereof: (i) protection of Cry toxin from protease degradation in the insect midgut and (ii) enhancement of pore-forming ability of Cry toxin. Bacillus thuringiensis (Bt) Cry toxins are a family of bacterial pore-forming proteins that are highly toxic to a range of crop pests and disease vectors. Cry proteins are produced as crystals during the sporulation phase. Crystals are ingested, solubilized in the gut lumen to protoxin, and activated by host gut proteases. Activated toxin crosses the peritrophic matrix (PM) and binds cadherin, which is the primary high-affinity receptor for Cry1 toxins on the apical border of midgut microvilli. A current model postulates that toxin interaction with cadherin causes a conformational change in toxin allowing a specific proteolytic cleavage and formation of a prepore toxin oligomer. Evidence suggests that the prepore oligomer has increased affinity for secondary glycosylphosphatidylinositol (GPI)-anchored receptors, such as aminopeptidases (APNs) or alkaline phosphatases (ALPs) localized in lipid rafts. Oligomers insert into the membrane and disrupt membrane integrity by forming lytic pores, which lead directly to insect mortality or indirectly to mortality due to septicemia (5,7,21,45). A recent modification to the pore formation model described above proposes that activated toxin monomers first bind to abundant low-affinity APN receptors before binding to high-affinity cadherin receptors, which results in toxin oligomerization (32). In contrast to the pore formation model, the cell-signaling model (54) proposes that binding of activated toxin monomers to cadherin activates an intracellular signaling pathway, which ultimately results ...

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Section: Discussionsupporting

confidence: 91%

Differential Protection of Cry1Fa Toxin against Spodoptera frugiperda Larval Gut Proteases by Cadherin Orthologs Correlates with Increased Synergism

Rahman

Abdullah

Ambati

et al. 2012

Appl Environ Microbiol

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“…Soberon et al (25) provide an explanation for how cadherin fragments are involved in Cry1Ab toxicity. The CR12 fragment induces the formation of a prepore Cry1Ab oligomer, a critical step in the intoxication process (16), and the enhancement of Cry1A toxicity by the CR12 fragment is correlated with oligomer formation (21). We do not know if the Cry3A toxins function in a similar manner, but our data suggest this possibility.…”

Section: Discussionmentioning

confidence: 99%

Enhancement ofBacillus thuringiensisCry3Aa and Cry3Bb Toxicities to Coleopteran Larvae by a Toxin-Binding Fragment of an Insect Cadherin

Park¹,

Abdullah

Taylor

et al. 2009

Appl Environ Microbiol

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The Cry3Aa and Cry3Bb insecticidal proteins of Bacillus thuringiensis are used in biopesticides and transgenic crops to control larvae of leaf-feeding beetles and rootworms. Cadherins localized in the midgut epithelium are identified as receptors for Cry toxins in lepidopteran and dipteran larvae. Previously, we discovered that a peptide of a toxin-binding cadherin expressed in Escherichia coli functions as a synergist for Cry1A toxicity against lepidopteran larvae and Cry4 toxicity against dipteran larvae. Here we report that the fragment containing the three most C-terminal cadherin repeats (CR) from the cadherin of the western corn rootworm binds toxin and enhances Cry3 toxicity to larvae of naturally susceptible species. The cadherin fragment (CR8 to CR10 [CR8-10]) of western corn rootworm Diabrotica virgifera virgifera was expressed in E. coli as an inclusion body. By an enzyme-linked immunosorbent microplate assay, we demonstrated that the CR8-10 peptide binds ␣-chymotrypsin-treated Cry3Aa and Cry3Bb toxins at high affinity (11.8 nM and 1.4 nM, respectively). Coleopteran larvae ingesting CR8-10 inclusions had increased susceptibility to Cry3Aa or Cry3Bb toxin. The Cry3 toxin-enhancing effect of CR8-10 was demonstrated for Colorado potato beetle Leptinotarsa decemlineata, southern corn rootworm Diabrotica undecimpunctata howardi, and western corn rootworm. The extent of Cry3 toxin enhancement, which ranged from 3-to 13-fold, may have practical applications for insect control. Cry3-containing biopesticides that include a cadherin fragment could be more efficacious. And Bt corn (i.e., corn treated with B. thuringiensis to make it resistant to pests) coexpressing Cry3Bb and CR8-10 could increase the functional dose level of the insect toxic activity, reducing the overall resistance risk.

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“…It was proposed that the observed structure is the prepore of actinoporins. Prepores were observed in many ␤-PFT (4) and were proposed also for some ␣-PFT (5,29).…”

mentioning

confidence: 85%

Membrane Damage by an α-Helical Pore-forming Protein, Equinatoxin II, Proceeds through a Succession of Ordered Steps

Rojko

Kristan

Viero

et al. 2013

Journal of Biological Chemistry

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Background: Actinoporins are pore-forming toxins that damage cellular membranes by ␣-helices. Results: An engineered mutant of actinoporin equinatoxin II reveals sequential steps during pore formation. Conclusion: Pore formation is composed of a succession of ordered steps: fast membrane binding followed by the N-terminal region association with the membrane and oligomerization. Significance: Equinatoxin II pore formation does not require stable prepore intermediate as is often found in other poreforming toxins.

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The pre-pore from Bacillus thuringiensis Cry1Ab toxin is necessary to induce insect death in Manduca sexta

Cited by 26 publications

References 47 publications

Differential Protection of Cry1Fa Toxin against Spodoptera frugiperda Larval Gut Proteases by Cadherin Orthologs Correlates with Increased Synergism

Differential Protection of Cry1Fa Toxin against Spodoptera frugiperda Larval Gut Proteases by Cadherin Orthologs Correlates with Increased Synergism

Enhancement ofBacillus thuringiensisCry3Aa and Cry3Bb Toxicities to Coleopteran Larvae by a Toxin-Binding Fragment of an Insect Cadherin

Membrane Damage by an α-Helical Pore-forming Protein, Equinatoxin II, Proceeds through a Succession of Ordered Steps

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