Final Report Summary - VIPHASE (Mode of action of Bacillus thuringiensis VIP proteins in Helicoverpa armigera and Spodoptera exigua)
A polyclonal antibody raised in rabbit against Vip3Aa protoxin was produced. The quality of the antibody has been tested by Western blot analysis, and it was suitable for the detection of Vip3Aa and also other Vip3A proteins. It was very useful to confirm the presence of the Vip3A proteins in the different fractions obtained during the purification processes. It was also useful for preliminary studies of the Vip3A receptors and Vip3A mechanism of action at cellular level in progress in the host lab. Since in Spodoptera frugiperda the bioassays revealed a high toxicity in terms of mortality of Vip3Aa, Vip3Af and Vip3Ae proteins, we decided to investigate which step in the mode of action was responsible for the differences in mortality of these two closely related Spodoptera species. The activation with midgut juice crude extracts did not show differences in the activation profiles. The separation of serine-proteases was carried out by chromatographic techniques from the midgut juice of both species. The detailed study of the activation process by the different fractions with serine-protease activity in the two species is in progress.