Bacillus thuringiensis subsp. israelensis Cyt1Aa synergizes Cry11Aa toxin by functioning as a membrane-bound receptor

Abstract

Bacillus thuringiensis subsp. israelensis produces crystal proteins, Cry (4Aa, 4Ba, 10Aa, and 11Aa) and Cyt (1Aa and 2Ba) proteins, toxic to mosquito vectors of human diseases. Cyt1Aa overcomes insect resistance to Cry11Aa and Cry4 toxins and synergizes the toxicity of these toxins. However, the molecular mechanism of synergism remains unsolved. Here, we provide evidence that Cyt1Aa functions as a receptor of Cry11Aa. Sequential-binding analysis of Cyt1Aa and Cry11Aa revealed that Cyt1Aa binding to Aedes aegypti brush border membrane vesicles enhanced the binding of biotinylated-Cry11Aa. The Cyt1Aa-and Cry11Aa-binding epitopes were mapped by means of the yeast two-hybrid system, peptide arrays, and heterologous competition assays with synthetic peptides. Two exposed regions in Cyt1Aa, loop ␤6-␣E and part of ␤7, bind Cry11Aa. On the other side, Cry11Aa binds Cyt1Aa proteins by means of domain II-loop ␣8 and ␤-4, which are also involved in midgut receptor interaction. Characterization of single-point mutations in Cry11Aa and Cyt1Aa revealed key Cry11Aa (S259 and E266) and Cyt1Aa (K198, E204 and K225) residues involved in the interaction of both proteins and in synergism. Additionally, a Cyt1Aa loop ␤6-␣E mutant (K198A) with enhanced synergism to Cry11Aa was isolated. Data provided here strongly indicates that Cyt1Aa synergizes or suppresses resistance to Cry11Aa toxin by functioning as a membrane-bound receptor. Bacillus thuringiensis subsp. israelensis is a highly effective pathogenic bacterium because it produces a toxin and also its functional receptor, promoting toxin binding to the target membrane and causing toxicity.receptor interaction ͉ binding epitopes ͉ insect resistance ͉ mode of action

Comparison the Effect of Fungi (Beauveria bassiana) and Bacteria Bacillus thuringiensis (israelensis) on a Cumulative Mortality of Culex Quinquefasciatus (Diptera: Culicidae)

“…First larva instar is more susceptible to Bti than other instars (Mulla et al, 1990) this depend on mechanism of action of Bti toxin which consist a multistage process, ingestion cry protein by larvae with feeding, solubilisation of cry in midgut which have alkaline medium, proteolytic activation in the insecticidal solubilised protein, apical microvillus membrane of epithelial midgut cell walls have a receptors which bind with toxin, changing in shape allowing toxin insertion into the membrane, toxins doing pores in the cell membrane, because of that osmotic balance disruption and cells swell then burst, thus larva stops feeding. Most larva die in few hours of ingestion (Marrone and Macintosh, 1993;Perez et al, 2005). The result of this search agree with Mario and Montserrat (2012) and Ben-Dov (2014) so it is important to choose the stronger microorganism pathogenic to kill insects (pests) then stopping vector disease with no harmful effect on environment.…”

Retargeting of the Bacillus thuringiensis toxin Cyt2Aa against hemipteran insect pests

“…S1). Loop 6 was not selected for modification due to its role in potentiation of Cry toxin action (17) whereas the remaining six loops are not involved in protein production and folding (18). Two sets of modified Cyt2Aa were constructed, by addition of GBP3.1 to each Cyt2Aa loop [Cyt2Aa-GBP3.1-addition-Loopn (CGALn)] or by substitution of amino acids in each Cyt2Aa loop with GBP3.1 (CGSLn).…”

Modelos caracterizando a interação entre as toxinas da família Cry1A de Bacillus thuringiensis e o receptor BT-R1 de Manduca sexta

“…& Bravo, A., 2013). Além disso, algumas toxinas Cyt agem em sinergia com outras toxinas de Bt e aumentam sua atividade inseticida, podendo inclusive atuar como um receptor e suprimir resistências de insetos (Perez, C. et al, 2005;Soberon, M., LopezDiaz, J.A. & Bravo, A., 2013;Yu, X. et al, 2012;Zhang, B. et al, 2006).…”