title: Cadherin binding is not a limiting step for Bacillus thuringiensis subsp. israelensis Cry4Ba toxicity to Aedes aegypti larvae.
abstract: Bacillus thuringiensis subsp. israelensis produces three Cry toxins (Cry4Aa, Cry4Ba and Cry11Aa) that are active against Aedes aegypti larvae. The identification of the rate-limiting binding steps of Cry toxins that are used for insect control in the field, such as those of B. thuringiensis subsp. israelensis, should provide targets for improving insecticides against important insect pests. Previous studies showed that Cry11Aa binds to cadherin receptor fragment CR7-11 (cadherin repeats 7-11) with high affinity. Binding to cadherin has been proposed to facilitate Cry toxin oligomer formation. In the present study, we show that Cry4Ba binds to CR7-11 with 9-fold lower binding affinity compared with Cry11Aa. Oligomerization assays showed that Cry4Ba is capable of forming oligomers when proteolytically activated in vitro in the absence of the CR7-11 fragment in contrast with Cry11Aa that formed oligomers only in the presence of CR7-11. Pore-formation assays in planar lipid bilayers showed that Cry4Ba oligomers were proficient in opening ion channels. Finally, silencing the cadherin gene by dsRNA (double-stranded RNA) showed that silenced larvae were more tolerant to Cry11Aa in contrast with Cry4Ba, which showed similar toxic levels to those of control larvae. These findings show that cadherin binding is not a limiting step for Cry4Ba toxicity to A. aegypti larvae.
authors.affiliation: Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. postal 510-3, Cuernavaca 62250, Morelos, Mexico.
authors.forename: Claudia
authors.initials: C
authors.lastname: Rodríguez-Almazán
authors.forename: Esmeralda Z
authors.initials: EZ
authors.lastname: Reyes
authors.forename: Fernando
authors.initials: F
authors.lastname: Zúñiga-Navarrete
authors.forename: Carlos
authors.initials: C
authors.lastname: Muñoz-Garay
authors.forename: Isabel
authors.initials: I
authors.lastname: Gómez
authors.forename: Amy M
authors.initials: AM
authors.lastname: Evans
authors.forename: Supaporn
authors.initials: S
authors.lastname: Likitvivatanavong
authors.forename: Alejandra
authors.initials: A
authors.lastname: Bravo
authors.forename: Sarjeet S
authors.initials: SS
authors.lastname: Gill
authors.forename: Mario
authors.initials: M
authors.lastname: Soberón
mesh_terms: D000330:Aedes / Q000254:growth & development*; D000818:Animals; D001413:Bacillus thuringiensis / Q000378:metabolism*; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D015820:Cadherins / Q000378:metabolism*; D017931:DNA Primers; D004731:Endotoxins / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D006460:Hemolysin Proteins / Q000378:metabolism*; D011485:Protein Binding; D034622:RNA Interference; D020349:Surface Plasmon Resonance
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D015820:Cadherins; D017931:DNA Primers; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis