Active form of dipteran-specific insecticidal protein cryllA produced by Bacillus thuringiensis subsp. israelensis

The nucleotide sequence of the cry11A gene from Bacillus thuringiensis subsp. israelensis strain HD522 was analyzed and the molecular characterization of CryllA toxin was done. The 70-kDa CryllA protoxin was processed in vitro into 36- and 32-kDa fragments by trypsin and into 34- and 32-kDa fragments by gut proteases from C. pipiens. These two processed fragments are associated together to form the heterodimer. The results of the binding assay with BBMV and the bioassay toward C. pipiens larvae suggested that the heterodimer was biologically as active as the non-digested CryllA toxin and the intramolecular cleavage did not promote the insecticidal activity. These results suggested that a probable complex of the 36- or 34-kDa and 32-kDa fragments was also one of the possible active forms of Cry11A, and that the biological functions of CryllA was not essentially affected by the intramolecular cleavage of the 70-kDa protein.