Insect toxins, recombinant baculoviruses

However, other cells may respond differently to the toxin. In particular, platelets are able to resist the entry of pertussis toxin, either because they lack surface binding sites for the toxin B oligomer or because they are unable to internalize the bound toxin (Brass et al., 1990). PT-sensitive G proteins expressed in insect Sf9 cells (ovary cells from the insect Spodoptera frugiperda Sf9 cells are employed as an overexpression system for G proteins and other signal transduction components by infection with recombinant baculovirus) are also not modified by the toxin (Mulheron et al., 1994). 

Recombinant Baculoviruses Expressing Insect Toxins. The first attempt to modify a NPV for increased insecticidal activity was conducted by Carbonell et al 33) in which an insect-specific toxin (BelT) from the scorpion Buthus eupus was incorporated into the AcNPV genome. Although low levels of toxin expression were confirmed, the recombinant NPV did not result in quicker killing rates of host insects. Failure to improve killing activity may be due to an insufficient level of toxin expression by AcNPV, an incorrect sequence of toxin DNA, and/or insufficient or incorrect folding of the toxin following expression. 

It is well documented that certain arthropods produce neurotoxins, which are highly specific for insects. We selected the insect-selective neurotoxin, AalT, for expression in AcNPV primarily because AalT was the most thoroughly characterized of the insect-selective toxins isolated to date. This resource of information was instrumental in augmenting our toxicological characterization of the recombinant baculovirus expressing AalT. 

Another approach to improve the efficacy of recombinant baculoviruses includes the use of different promoters for expression of the foreign protein. Alternate promoters could lead to earlier or improved transcription, more stable messages, and/or improved translation. Tomalski and Miller (57) have recently reported the expression of the Pyemotes mite toxin by several different promoters. These included an early promoter, a late promoter, and two hybrid promoters derived of a late and a very late promoter sequence. The study indicated that expression of the mite toxin with one of the hybrid promoters resulted in slightly quicker kill and a reduction in feeding. Interestingly, the use of an early promoter did not result in larval paralysis suggesting that the levels of expressed toxin were not adequate to overcome the insect. However, this study should not discourage the use of earlier promoters, since a more potent toxin may provide more dramatic results (55). 

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