Biological properties of loop-replaced mutants of Bacillus thuringiensis mosquitocidal Cry4Aa.
Cry4Aa produced by Bacillus thuringiensis subsp. israelensis (Bti) exhibits a specific toxicity to Anopheles, Aedes, and Culex larvae, which are vectors of serious diseases, and formulations of Bti are used worldwide for mosquito control. In general, domain II of the Cry toxin is believed to be important for target specificity, and three loops (loops 1, 2, and 3) in domain II have been studied extensively. In this report, to analyze the biological functions of loops 1, 2, and 3 of Cry4Aa, mutants were constructed in which one of the loops was replaced with either of the other two loops. A bioassay using Culex pipiens larvae revealed that the mosquitocidal activity was virtually lost upon replacement of loop2. The mutants in which loops 1 and/or 3 were replaced also showed decreased activity, but they still maintained some activities. This suggested that loop2, but not loops 1 and 3, was essential for the mosquitocidal activity of Cry4Aa. Proteolytic digestion revealed the involvement of loops in the stability of the Cry4Aa structure. No significant differences were observed in the amount of wild-type and mutant Cry4Aa bound to the BBMVs prepared from the C. pipiens larvae.
Howlader
Mohammad Tofazzal Hossain
MT
Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-Naka, Okayama-Shi, Okayama 700-8530, Japan.
Kagawa
Yasuhiro
Y
Sakai
Hiroshi
H
Hayakawa
Tohru
T
D000818:Animals; D001413:Bacillus thuringiensis / Q000235:genetics* / Q000378:metabolism; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000235:genetics / Q000494:pharmacology*; D001681:Biological Assay; D009033:Culicidae; D017931:DNA Primers / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D004731:Endotoxins / Q000235:genetics / Q000494:pharmacology*; D005818:Genetic Engineering; D005982:Glutathione Transferase / Q000378:metabolism; D006460:Hemolysin Proteins / Q000235:genetics / Q000494:pharmacology*; D009032:Mosquito Control; D009154:Mutation; D010572:Pest Control, Biological; D016133:Polymerase Chain Reaction
D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D017931:DNA Primers; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis; D005982:Glutathione Transferase