Biological properties of loop-replaced mutants of Bacillus thuringiensis mosquitocidal Cry4Aa

Mohammad Tofazzal Hossain Howlader, Yasuhiro Kagawa, Hiroshi Sakai, Tohru Hayakawa

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)179-183
Number of pages5
JournalJournal of Bioscience and Bioengineering
Issue number3
Publication statusPublished - Sept 2009


  • Bacillus thuringiensis
  • Cry4Aa
  • Culex pipiens
  • Genetic engineering
  • Loop replaced mutants
  • Mosquitocidal toxicity

ASJC Scopus subject areas

  • Biotechnology
  • Bioengineering
  • Applied Microbiology and Biotechnology


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