title: Functional characterizations of residues Arg-158 and Tyr-170 of the mosquito-larvicidal Bacillus thuringiensis Cry4Ba.
abstract: The insecticidal activity of Bacillus thuringiensis (Bt) Cry toxins involves toxin stabilization, oligomerization, passage across the peritrophic membrane (PM), binding to midgut receptors and pore-formation. The residues Arg-158 and Tyr-170 have been shown to be crucial for the toxicity of Bt Cry4Ba. We characterized the biological function of these residues. In mosquito larvae, the mutants R158A/E/Q (R158) could hardly penetrate the PM due to a significantly reduced ability to alter PM permeability; the mutant Y170A, however, could pass through the PM, but degraded in the space between the PM and the midgut epithelium. Further characterization by oligomerization demonstrated that Arg-158 mutants failed to form correctly sized high-molecular weight oligomers. This is the first report that Arg-158 plays a role in the formation of Cry4Ba oligomers, which are essential for toxin passage across the PM. Tyr-170, meanwhile, is involved in toxin stabilization in the toxic mechanism of Cry4Ba in mosquito larvae.
authors.affiliation: Bacterial Protein Toxin Research Cluster, Institute of Molecular Biosciences, Mahidol University, Nakhon-Pathom 73170, Thailand.
authors.forename: Somphob
authors.initials: S
authors.lastname: Leetachewa
authors.affiliation: Department of Protozoology, Faculty of Tropical Medicine, Mahidol University, Ratchathewi, Bangkok 10400, Thailand.
authors.forename: Saengduen
authors.initials: S
authors.lastname: Moonsom
authors.affiliation: Department of Tropical Pathology, Faculty of Tropical Medicine, Mahidol University, Ratchathewi, Bangkok 10400, Thailand.
authors.forename: Urai
authors.initials: U
authors.lastname: Chaisri
authors.affiliation: Department of Protozoology, Faculty of Tropical Medicine, Mahidol University, Ratchathewi, Bangkok 10400, Thailand.
authors.forename: Narumol
authors.initials: N
authors.lastname: Khomkhum
authors.affiliation: Faculty of Medical Technology, Western University, Kanchanaburi 71170, Thailand.
authors.forename: Nonglak
authors.initials: N
authors.lastname: Yoonim
authors.affiliation: Department of Entomology, New York State Agricultural Experiment Station, Cornell University, Geneva, NY 14456, USA.
authors.forename: Ping
authors.initials: P
authors.lastname: Wang
authors.affiliation: Bacterial Protein Toxin Research Cluster, Institute of Molecular Biosciences, Mahidol University, Nakhon-Pathom 73170, Thailand.
authors.forename: Chanan
authors.initials: C
authors.lastname: Angsuthanasombat
mesh_terms: D000330:Aedes / Q000187:drug effects*; D000818:Animals; D001120:Arginine / Q000378:metabolism*; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000737:chemistry* / Q000633:toxicity*; D002463:Cell Membrane Permeability / Q000187:drug effects; D004064:Digestive System / Q000187:drug effects; D004731:Endotoxins / Q000737:chemistry* / Q000633:toxicity*; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D006460:Hemolysin Proteins / Q000737:chemistry* / Q000633:toxicity*; D007814:Larva / Q000187:drug effects; D050505:Mutant Proteins / Q000737:chemistry / Q000633:toxicity; D011485:Protein Binding / Q000187:drug effects; D055503:Protein Multimerization / Q000187:drug effects; D055550:Protein Stability / Q000187:drug effects; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; D050505:Mutant Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis; D014443:Tyrosine; D001120:Arginine