title: Targeted mutagenesis of loop residues in the receptor-binding domain of the Bacillus thuringiensis Cry4Ba toxin affects larvicidal activity.
abstract: Loop residues in domain II of Bacillus thuringiensis Cry delta-endotoxins have been demonstrated to be involved in insecticidal specificity. In this study, selected residues in loops beta6-beta7 (S(387)SPS(390)), beta8-beta9 (S(410), N(411), T(413), T(415), E(417) and G(418)) and beta10-beta11 (D(454)YNS(457)) in domain II of the Cry4Ba mosquito-larvicidal protein were changed individually to alanine by PCR-based directed mutagenesis. All mutant toxins were expressed in Escherichia coli JM109 cells as 130-kDa protoxins at levels comparable to the wild type. Only E. coli cells that express the P389A, S410A, E417A, Y455A or N456A mutants exhibited a loss in toxicity against Aedes aegypti mosquito larvae of approximately 30% when compared to the wild type. In addition, E. coli cells expressing double mutants, S410A/E417A or Y455A/N456A, at wild-type levels revealed a significantly higher loss in larvicidal activity of approximately 70%. Similar to the wild-type protoxin, both double mutant toxins were structurally stable upon solubilisation and trypsin activation in carbonate buffer, pH 9.0. These results indicate that S(410) and E(417) in the beta8-beta9 loop, and Y(455) and N(456) in the beta10-beta11 loop are involved in larvicidal activity of the Cry4Ba toxin.
authors.affiliation: Laboratory of Molecular Biophysics and Structural Biochemistry, Institute of Molecular Biology and Genetics, Mahidol University, Salaya Campus, Nakornpathom 73170, Thailand.
authors.forename: Tipparat
authors.initials: T
authors.lastname: Tuntitippawan
authors.forename: Panadda
authors.initials: P
authors.lastname: Boonserm
authors.forename: Gerd
authors.initials: G
authors.lastname: Katzenmeier
authors.forename: Chanan
authors.initials: C
authors.lastname: Angsuthanasombat
mesh_terms: D000330:Aedes; D000818:Animals; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000633:toxicity*; D001427:Bacterial Toxins / Q000737:chemistry* / Q000235:genetics / Q000633:toxicity*; D004731:Endotoxins / Q000737:chemistry* / Q000235:genetics / Q000633:toxicity*; D004926:Escherichia coli; D006460:Hemolysin Proteins; D019476:Insect Proteins / Q000235:genetics / Q000633:toxicity*; D007814:Larva / Q000187:drug effects*; D016297:Mutagenesis, Site-Directed; D017433:Protein Structure, Secondary; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; C095416:Cry toxin receptors; D004731:Endotoxins; D006460:Hemolysin Proteins; D019476:Insect Proteins; D011956:Receptors, Cell Surface; C030956:insecticidal crystal protein, Bacillus Thuringiensis