title: Amino acid substitution in alpha-helix 7 of Cry1Ac delta-endotoxin of Bacillus thuringiensis leads to enhanced toxicity to Helicoverpa armigera Hubner.
abstract: Insecticidal proteins or delta-endotoxins of Bacillus thuringiensis are highly toxic to a wide range of agronomically important pests. The toxins are formed of three structural domains. The N-terminal domain is a bundle of eight alpha-helices and is implicated in pore formation in insect midgut epithelial membranes. All the delta-endotoxins share a common hydrophobic motif of eight amino acids in alpha-helix 7. A similar motif is also present in fragment B of diphtheria toxin (DT). Site-directed mutagenesis of Cry1Ac delta-endotoxin of B. thuringiensis was carried out to substitute its hydrophobic motif with that of DT fragment B. The mutant toxin was shown to be more toxic to the larvae of Helicoverpa armigera (cotton bollworm) than the wild-type toxin. Voltage clamp analysis with planar lipid bilayers revealed that the mutant toxin opens larger ion channels and induces higher levels of conductance than the wild-type toxin.
authors.affiliation: National Research Centre for Plant Biotechnology, Indian Agricultural Research Institute, New Delhi.
authors.forename: A
authors.initials: A
authors.lastname: Chandra
authors.forename: P
authors.initials: P
authors.lastname: Ghosh
authors.forename: A D
authors.initials: AD
authors.lastname: Mandaokar
authors.forename: A K
authors.initials: AK
authors.lastname: Bera
authors.forename: R P
authors.initials: RP
authors.lastname: Sharma
authors.forename: S
authors.initials: S
authors.lastname: Das
authors.forename: P A
authors.initials: PA
authors.lastname: Kumar
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics*; D000818:Animals; D001413:Bacillus thuringiensis / Q000235:genetics*; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology / Q000633:toxicity*; D001427:Bacterial Toxins; D001681:Biological Assay; D004167:Diphtheria Toxin / Q000235:genetics; D004731:Endotoxins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology / Q000633:toxicity*; D006460:Hemolysin Proteins; D007814:Larva / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D008051:Lipid Bilayers / Q000737:chemistry; D009036:Moths / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000235:genetics; D017433:Protein Structure, Secondary
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004167:Diphtheria Toxin; D004731:Endotoxins; D006460:Hemolysin Proteins; D008051:Lipid Bilayers; D010446:Peptide Fragments; C039171:diphtheria toxin fragment B; C030956:insecticidal crystal protein, Bacillus Thuringiensis