Crop Biotech Update

Scientists Report Two Distinct Pre-pores Involved in Cry1Ab Toxicity

January 29, 2014

The crystal proteins from common soil bacterium Bacillus thuringiensis are insecticidal pore forming toxins. Isabel Gómez and colleagues at Universidad Nacional Autonoma de Mexico reported that two distinct functional pre-pores of Cry1Ab are formed not after binding of the protoxin or the protease-activated toxin to the cadherin-receptor, but before membrane-insertion. Both pre-pores are active causing the formation of pore, although with varied characteristics, and contribute to insecticidal function.

Furthermore, the researchers analyzed the oligomerization of the mutant Cry1AbMod protein. The mutant eradicates different insect populations resistant to Cry toxins, but lost effectiveness against susceptible insects. They found that the Cry1AbMod-protoxin efficiently induces oligomerization, and not the activated Cry1AbMod-toxin, explaining the loss of potency of Cry1AbMod against susceptible insects. The results of the study are relevant for the future control of insects resistant to Cry proteins. The researchers propose that not only different insect-targets could have different receptors, but also different midgut proteases that would influence the rate of protoxin/toxin activation.

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