title: Binding of Bacillus thuringiensis subsp. israelensis Cry4Ba to Cyt1Aa has an important role in synergism.
abstract: Bacillus thuringiensis subsp. israelensis (Bti) produces at least four different crystal proteins that are specifically toxic to different mosquito species and that belong to two non-related family of toxins, Cry and Cyt named Cry4Aa, Cry4Ba, Cry11Aa and Cyt1Aa. Cyt1Aa enhances the activity of Cry4Aa, Cry4Ba or Cry11Aa and overcomes resistance of Culex quinquefasciatus populations resistant to Cry11Aa, Cry4Aa or Cry4Ba. Cyt1Aa synergized Cry11Aa by their specific interaction since single point mutants on both Cyt1Aa and Cry11Aa that affected their binding interaction affected their synergistic insecticidal activity. In this work we show that Cyt1Aa loop β6-αE K198A, E204A and β7 K225A mutants affected binding and synergism with Cry4Ba. In addition, site directed mutagenesis showed that Cry4Ba domain II loop α-8 is involved in binding and in synergism with Cyt1Aa since Cry4Ba SI303-304AA double mutant showed decreased binding and synergism with Cyt1Aa. These data suggest that similarly to the synergism between Cry11Aa and Cyt1Aa toxins, the Cyt1Aa also functions as a receptor for Cry4Ba explaining the mechanism of synergism between these two Bti toxins.
authors.affiliation: Instituto de Biotecnología, Universidad Nacional Autónoma de México. Apdo. postal 510-3, Cuernavaca 62250, Morelos, Mexico.
authors.forename: Pablo Emiliano
authors.initials: PE
authors.lastname: Cantón
authors.forename: Esmeralda Zanicthe
authors.initials: EZ
authors.lastname: Zanicthe Reyes
authors.forename: Iñigo
authors.initials: I
authors.lastname: Ruiz de Escudero
authors.forename: Alejandra
authors.initials: A
authors.lastname: Bravo
authors.forename: Mario
authors.initials: M
authors.lastname: Soberón
mesh_terms: D000330:Aedes / Q000187:drug effects; D000818:Animals; D001413:Bacillus thuringiensis / Q000235:genetics / Q000378:metabolism*; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D004731:Endotoxins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D006460:Hemolysin Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D007306:Insecticides / Q000378:metabolism* / Q000494:pharmacology; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding / Q000235:genetics / Q000502:physiology; D017433:Protein Structure, Secondary
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; D007306:Insecticides; C030956:insecticidal crystal protein, Bacillus Thuringiensis