scholarly journals The α-Helix 4 Residue, Asn135, Is Involved in the Oligomerization of Cry1Ac1 and Cry1Ab5 Bacillus thuringiensis Toxins

2001 ◽  
Vol 67 (12) ◽  
pp. 5715-5720 ◽  
Author(s):  
Natalie J. Tigue ◽  
Juliette Jacoby ◽  
David J. Ellar
Keyword(s):  
Bacillus Thuringiensis ◽  
Membrane Vesicles ◽  
Wild Type ◽  
Cell Plasma Membrane ◽  
Structural Domains ◽  
Cell Plasma ◽  
Α Helix ◽  
Domain I ◽  
Mutant Toxin ◽  
Made In

ABSTRACT The insecticidal Cry toxins produced by the bacteriumBacillus thuringiensis are comprised of three structural domains. Domain I, a seven-helix bundle, is thought to penetrate the insect epithelial cell plasma membrane through a hairpin composed of α-helices 4 and 5, followed by the oligomerization of four hairpin monomers. The α-helix 4 has been proposed to line the lumen of the pore, whereas some residues in α-helix 5 have been shown to be responsible for oligomerization. Mutation of the Cry1Ac1 α-helix 4 amino acid Asn135 to Gln resulted in the loss of toxicity toManduca sexta, yet binding was still observed. In this study, the equivalent mutation was made in the Cry1Ab5 toxin, and the properties of both wild-type and mutant toxin counterparts were analyzed. Both mutants appeared to bind to M. sextamembrane vesicles, but they were not able to form pores. The ability of both N135Q mutants to oligomerize was also disrupted, providing the first evidence that a residue in α-helix 4 can contribute to toxin oligomerization.

scholarly journals Role of Bacillus thuringiensis Toxin Domains in Toxicity and Receptor Binding in the Diamondback Moth

1999 ◽  
Vol 65 (5) ◽  
pp. 1900-1903 ◽  
Author(s):  
V. Ballester ◽  
F. Granero ◽  
R. A. de Maagd ◽  
D. Bosch ◽  
J. L. Ménsua ◽  
...  
Keyword(s):  
Bacillus Thuringiensis ◽  
Receptor Binding ◽  
Diamondback Moth ◽  
Membrane Vesicles ◽  
Binding Assays ◽  
Structural Domains ◽  
Specificity Of Binding ◽  
Domain Iii ◽  
Domain I

ABSTRACT The toxic fragment of Bacillus thuringiensis crystal proteins consists of three distinct structural domains. There is evidence that domain I is involved in pore formation and that domain II is involved in receptor binding and specificity. It has been found that, in some cases, domain III is also important in determining specificity. Furthermore, involvement of domain III in binding has also been reported recently. To investigate the role of toxin domains in the diamondback moth (Plutella xylostella), we used hybrid toxins with domain III substitutions among Cry1C, Cry1E, and Cry1Ab. Neither Cry1E nor G27 (a hybrid with domains I and II from Cry1E and domain III from Cry1C) was toxic, whereas Cry1C and F26 (the reciprocal hybrid) were equally toxic. H04 (a hybrid with domains I and II from Cry1Ab and domain III from Cry1C) showed toxicity that was of a similar level as that of Cry1Ab and significantly higher than that of Cry1C. Binding assays with 125I-Cry1C showed that Cry1C and F26 competed for the same binding sites on midgut membrane vesicles, whereas Cry1E, G27, and H04 did not bind to these sites. Our results show that, in contrast to findings in other insects for the toxins and hybrids used here, toxin specificity as well as specificity of binding to membrane vesicles in the diamondback moth is mediated by domain II (and/or I) and not by domain III.

scholarly journals Mutations in the Bacillus thuringiensis Cry1Ca toxin demonstrate the role of domains II and III in specificity towards Spodoptera exigua larvae

2004 ◽  
Vol 384 (3) ◽  
pp. 507-513 ◽  
Author(s):  
Salvador HERRERO ◽  
Joel GONZÁLEZ-CABRERA ◽  
Juan FERRÉ ◽  
Petra L. BAKKER ◽  
Ruud A. de MAAGD
Keyword(s):  
Bacillus Thuringiensis ◽  
Spodoptera Exigua ◽  
Brush Border Membrane ◽  
Specific Activity ◽  
Membrane Vesicles ◽  
Wild Type ◽  
Oligomeric Form ◽  
Specific Receptors ◽  
Domain Iii

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. exigua were determined for all toxins. Compared with Cry1Ca, the affinity of mutant pPB19 was slightly affected (2-fold lower), whereas the affinity of the mutants with an altered domain III (pPB20 and pPB21) was approx. 8-fold lower. Activation of Cry1Ca protoxin by incubation with S. exigua or M. sexta BBMV revealed the transient formation of an oligomeric form of Cry1Ca. The presence of this oligomeric form was tested in the activation of the different Cry1Ca mutants, and we found that those mutated in domain II (pPB19 and pPB21) could not generate the oligomeric form when activated by S. exigua BBMV. In contrast, when oligomerization was tested using BBMV prepared from M. sexta, all of the Cry1Ca mutants showed the formation of a similar oligomeric form as did the wild-type toxin. Our results show how modification of insect specificity can be achieved by manipulation of different parts of the toxin structure involved in different steps of the mode of action of B. thuringiensis toxins.

Two Phases Of Ferricyanide Reductase Activity In Ehrlich Cell Plasma Membranes

1992 ◽  
Vol 47 (11-12) ◽  
pp. 929-931 ◽  
Author(s):  
Antonio del Castillo-Olivares ◽  
Javier Márquez ◽  
Ignacio Núñez de Castro ◽  
Miguel Angel Medina
Keyword(s):  
Plasma Membrane ◽  
Plasma Membranes ◽  
Reductase Activity ◽  
Membrane Vesicles ◽  
Plasma Membrane Vesicles ◽  
Cell Plasma Membrane ◽  
Ferricyanide Reductase ◽  
Ehrlich Cell ◽  
Cell Plasma ◽  
Two Phases

Ehrlich cell plasma membrane vesicles have a ferricyanide reductase activity that shows two phases. These two phases were kinetically characterized. Evidence is presented for a differential effect of trypsin on both phases

scholarly journals Rearrangement of N-Terminal α-Helices of Bacillus thuringiensis Cry1Ab Toxin Essential for Oligomer Assembly and Toxicity

Toxins ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 647
Author(s):  
Sabino Pacheco ◽  
Jean Piere Jesus Quiliche ◽  
Isabel Gómez ◽  
Jorge Sánchez ◽  
Mario Soberón ◽  
...  
Keyword(s):  
Bacillus Thuringiensis ◽  
Conformational Changes ◽  
Membrane Integrity ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Membrane Vesicles ◽  
Insect Midgut ◽  
Cry Proteins ◽  
Cry1ab Toxin ◽  
Domain I

Cry proteins produced by Bacillus thuringiensis are pore-forming toxins that disrupt the membrane integrity of insect midgut cells. The structure of such pore is unknown, but it has been shown that domain I is responsible for oligomerization, membrane insertion and pore formation activity. Specifically, it was proposed that some N-terminal α-helices are lost, leading to conformational changes that trigger oligomerization. We designed a series of mutants to further analyze the molecular rearrangements at the N-terminal region of Cry1Ab toxin that lead to oligomer assembly. For this purpose, we introduced Cys residues at specific positions within α-helices of domain I for their specific labeling with extrinsic fluorophores to perform Föster resonance energy transfer analysis to fluorescent labeled Lys residues located in Domains II–III, or for disulfide bridges formation to restrict mobility of conformational changes. Our data support that helix α-1 of domain I is cleaved out and swings away from the toxin core upon binding with Manduca sexta brush border membrane vesicles. That movement of helix α-2b is also required for the conformational changes involved in oligomerization. These observations are consistent with a model proposing that helices α-2b and α-3 form an extended helix α-3 necessary for oligomer assembly of Cry toxins.

scholarly journals Structure of the Functional Form of the Mosquito Larvicidal Cry4Aa Toxin from Bacillus thuringiensis at a 2.8-Angstrom Resolution

2006 ◽  
Vol 188 (9) ◽  
pp. 3391-3401 ◽  
Author(s):  
Panadda Boonserm ◽  
Min Mo ◽  
Chanan Angsuthanasombat ◽  
Julien Lescar
Keyword(s):  
Bacillus Thuringiensis ◽  
Functional Form ◽  
Membrane Insertion ◽  
Carbohydrate Binding ◽  
Putative Receptor ◽  
Mosquito Cells ◽  
Carbohydrate Binding Proteins ◽  
Α Helix ◽  
Domain Iii ◽  
Domain I

ABSTRACT The Cry4Aa δ-endotoxin from Bacillus thuringiensis is toxic to larvae of Culex, Anopheles, and Aedes mosquitoes, which are vectors of important human tropical diseases. With the objective of designing modified toxins with improved potency that could be used as biopesticides, we determined the structure of this toxin in its functional form at a resolution of 2.8 Å. Like other Cry δ-endotoxins, the activated Cry4Aa toxin consists of three globular domains, a seven-α-helix bundle responsible for pore formation (domain I) and the following two other domains having structural similarities with carbohydrate binding proteins: a β-prism (domain II) and a plant lectin-like β-sandwich (domain III). We also studied the effect on toxicity of amino acid substitutions and deletions in three loops located at the surface of the putative receptor binding domain II of Cry4Aa. Our results indicate that one loop is an important determinant of toxicity, presumably through attachment of Cry4Aa to the surface of mosquito cells. The availability of the Cry4Aa structure should guide further investigations aimed at the molecular basis of the target specificity and membrane insertion of Cry endotoxins.

scholarly journals Key Residues of Bacillus Thuringiensis Cry2Ab for Oligomerization and Pore-Formation Activity

2021 ◽  
Author(s):  
Zhi-Zhen Pan ◽  
Lian Xu ◽  
Bo Liu ◽  
Qing-Xi Chen ◽  
Yu-Jing Zhu
Keyword(s):  
Bacillus Thuringiensis ◽  
Insecticidal Activity ◽  
Mode Of Action ◽  
Pore Formation ◽  
Wild Type ◽  
Cry Toxins ◽  
Key Residues ◽  
Domain I ◽  
First Time

Abstract As a pore-forming toxin, oligomerization and pore-formation were both required for the mode of action of Cry toxins. Previous studies revealed that Domain I helices α4-α5 were involved in oligomerization of Cry2Ab, while the active residues in charge of Cry2Ab aggregation remained ambiguous. In present studies, we built 20 Cry2Ab alanine mutants site directed in helices α4-α5 and demonstrated that mutants N151A, T152A, F157A, L183A, L185A and I188A blocked the assembly of 250 kDa oligomers, suggesting that those residues were key residues for Cry2Ab oligomerization. As expected, those variants severely reduced the insecticidal activity against P. xylostella which was similar to our previous reports. Furthermore, we found that the pore-forming activities of non-oligomerization mutants sharply decreased compared to wild-type Cry2Ab. Taken together, our data comprehensively identified key residues for Cry2Ab for the first time and emphasized that oligomerization was closely related to insecticidal activity and pore-forming activity in Cry2Ab.

scholarly journals Mutations in Domain I Interhelical Loops Affect the Rate of Pore Formation by the Bacillus thuringiensis Cry1Aa Toxin in Insect Midgut Brush Border Membrane Vesicles

2009 ◽  
Vol 75 (12) ◽  
pp. 3842-3850 ◽  
Author(s):  
Geneviève Lebel ◽  
Vincent Vachon ◽  
Gabrielle Préfontaine ◽  
Frédéric Girard ◽  
Luke Masson ◽  
...  
Keyword(s):  
Bacillus Thuringiensis ◽  
Conformational Changes ◽  
Brush Border ◽  
Pore Formation ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Thiol Group ◽  
Brush Border Membrane Vesicles ◽  
Site Directed Mutagenesis ◽  
Domain I

ABSTRACT Pore formation in the apical membrane of the midgut epithelial cells of susceptible insects constitutes a key step in the mode of action of Bacillus thuringiensis insecticidal toxins. In order to study the mechanism of toxin insertion into the membrane, at least one residue in each of the pore-forming-domain (domain I) interhelical loops of Cry1Aa was replaced individually by cysteine, an amino acid which is normally absent from the activated Cry1Aa toxin, using site-directed mutagenesis. The toxicity of most mutants to Manduca sexta neonate larvae was comparable to that of Cry1Aa. The ability of each of the activated mutant toxins to permeabilize M. sexta midgut brush border membrane vesicles was examined with an osmotic swelling assay. Following a 1-h preincubation, all mutants except the V150C mutant were able to form pores at pH 7.5, although the W182C mutant had a weaker activity than the other toxins. Increasing the pH to 10.5, a procedure which introduces a negative charge on the thiol group of the cysteine residues, caused a significant reduction in the pore-forming abilities of most mutants without affecting those of Cry1Aa or the I88C, T122C, Y153C, or S252C mutant. The rate of pore formation was significantly lower for the F50C, Q151C, Y153C, W182C, and S252C mutants than for Cry1Aa at pH 7.5. At the higher pH, all mutants formed pores significantly more slowly than Cry1Aa, except the I88C mutant, which formed pores significantly faster, and the T122C mutant. These results indicate that domain I interhelical loop residues play an important role in the conformational changes leading to toxin insertion and pore formation.

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