Agrotis segetum midgut putative receptor of Bacillus thuringiensis vegetative insecticidal protein Vip3Aa16 differs from that of Cry1Ac toxin

• Vip3Aa16 toxin is active against Agrotis segetum with an LC50 of about 86.27 ng/cm2.
• Larvae midgut proteases activated the Vip3Aa16 protoxin to a 62 kDa core toxin.
• Vip3Aa16 recognizes receptor of 65 kDa Cry1Ac binds to a 120 kDa protein.
• Cry1Ac binding to the BBMV did not inhibit the binding of Vip3Aa16 and vice versa.
• Extensive damage was detected in the midgut cells of Vip3Aa16 treated larvae.

Considering the fact that Agrotis segetum is one of the most pathogenic insects to vegetables and cereals in the world, particularly in Africa, the mode of action of Vip3Aa16 of Bacillus thuringiensis BUPM95 and Cry1Ac of the recombinant strain BNS3Cry-(pHTcry1Ac) has been examined in this crop pest. A. segetum proteases activated the Vip3Aa16 protoxin (90 kDa) yielding three bands of about 62, 45, 22 kDa and the activated form of the toxin was active against this pest with an LC50 of about 86 ng/cm2. To be active against A. segetum, Cry1Ac protoxin was activated to three close bands of about 60–65 kDa. Homologous and heterologous competition binding experiments demonstrated that Vip3Aa16 bound specifically to brush border membrane vesicles (BBMV) prepared from A. segetum midgut and that it does not inhibit the binding of Cry1Ac. Moreover, BBMV protein blotting experiments showed that the receptor of Vip3Aa16 toxin in A. segetum midgut differs from that of Cry1Ac. In fact, the latter binds to a 120 kDa protein whereas the Vip3Aa16 binds to a 65 kDa putative receptor. The midgut histopathology of Vip3Aa16 fed larvae showed vacuolization of the cytoplasm, brush border membrane lysis, vesicle formation in the goblet cells and disintegration of the apical membrane. The distinct binding properties and the unique protein sequence of Vip3Aa16 support its use as a novel insecticidal agent to control the crop pest A. segetum.

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