title: Proteolytic processing of Bacillus thuringiensis Vip3A proteins by two Spodoptera species.
abstract: Vip3 proteins have been described to be secreted by Bacillus thuringiensis during the vegetative growth phase and to display a broad insecticidal spectrum against lepidopteran larvae. Vip3Aa protoxin has been reported to be significantly more toxic to Spodoptera frugiperda than to Spodoptera exigua and differences in the midgut processing have been proposed to be responsible. In contrast, we have found that Vip3Ae is essentially equally toxic against these two species. Proteolysis experiments were performed to study the stability of Vip3A proteins to peptidase digestion and to see whether the differences found could explain differences in toxicity against these two Spodoptera species. It was found that activation of the protoxin form and degradation of the 62kDa band took place at lower concentrations of trypsin when using Vip3Aa than when using Vip3Ae. The opposite effect was observed for chymotrypsin. Vip3Aa and Vip3Ae protoxins were effectively processed by midgut content extracts from the two Spodoptera species and the proteolytic activation did not produce a peptidase resistant core under these in vitro conditions. Digestion experiments performed with S. frugiperda chromatography-purified digestive serine peptidases showed that the degradation of the Vip3A toxins active core is mainly due to the action of cationic chymotrypsin-like peptidase. Although the digestion patterns of Vip3A proteins do not always correlate with toxicity, the peptidase stability of the 62kDa core is in agreement with intraspecific differences of toxicity of the Vip3Aa protein.
authors: Departamento de Genética, Facultad de CC. Biológicas, Universidad de Valencia, Burjassot, Spain.
authors: Silvia
authors: S
authors: Caccia
authors: Departamento de Genética, Facultad de CC. Biológicas, Universidad de Valencia, Burjassot, Spain.
authors: Maissa
authors: M
authors: Chakroun
authors: Departamento de Genética, Facultad de CC. Biológicas, Universidad de Valencia, Burjassot, Spain.
authors: Konstantin
authors: K
authors: Vinokurov
authors: Departamento de Genética, Facultad de CC. Biológicas, Universidad de Valencia, Burjassot, Spain. Electronic address: juan.ferre@uv.es.
authors: Juan
authors: J
authors: Ferré
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism* / Q000494:pharmacology*; D004064:Digestive System / Q000201:enzymology*; D007306:Insecticides / Q000378:metabolism; D007814:Larva / Q000187:drug effects* / Q000378:metabolism*; D010572:Pest Control, Biological; D012697:Serine Endopeptidases / Q000378:metabolism; D013045:Species Specificity; D018411:Spodoptera / Q000187:drug effects* / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D007306:Insecticides; C447139:Vip3A protein, Bacillus thuringiensis; D012697:Serine Endopeptidases
keywords: Midgut peptidases; Mode of action; Serine peptidases; Spodoptera exigua; Spodoptera frugiperda; Vegetative insecticidal proteins