Abstract
Bacillus thuringiensis (Bt) Vip3A proteins are important insecticidal proteins used for control of lepidopteran insects. However, the mode of action of Vip3A toxin is still unclear. In this study, the amino acid residue S164 in Vip3Aa was identified to be critical for the toxicity in Spodoptera litura. Results from substitution mutations of the S164 indicate that the insecticidal activity of Vip3Aa correlated with the formation of a >240 kDa complex of the toxin upon proteolytic activation. The >240 kDa complex was found to be composed of the 19 kDa and the 65 kDa fragments of Vip3Aa. Substitution of the S164 in Vip3Aa protein with Ala or Pro resulted in loss of the >240 kDa complex and loss of toxicity in Spodoptera litura. In contrast, substitution of S164 with Thr did not affect the >240 kDa complex formation, and the toxicity of the mutant was only reduced by 35%. Therefore, the results from this study indicated that formation of the >240 kDa complex correlates with the toxicity of Vip3Aa in insects and the residue S164 is important for the formation of the complex.
Highlights
The vegetative insecticidal proteins (VIPs) from Bacillus thuringiensis (Bt) have been used as important insecticidal proteins for control of insect pests [1,2,3]
Vip3Aa mutants with substitution of K152 or D154 with Ala were expressed as glutathione S-transferase (GST)-Vip3Aa-K152A and GST-Vip3Aa-D154A
Previous studies have indicated that proteolytic processing of Vip3A proteins in insect midgut is a key step to exert the insecticidal activity [3,13]
Summary
The vegetative insecticidal proteins (VIPs) from Bacillus thuringiensis (Bt) have been used as important insecticidal proteins for control of insect pests [1,2,3]. Vip toxins are divided into four families, including Vip, Vip, Vip and Vip4 [3]. Vip and Vip proteins act as binary toxins against some species of coleopteran and hemipteran insect [4,5]. 1 Vip protein has so far been identified but shows no activity in insects [6]. Vip proteins contain approximately 787 amino acid residues, showing no sequence homology with Vip, Vip and Vip proteins [3]. Vip proteins have a high insecticidal activity against a wide variety of lepidopteran pests [7]. Vip3A proteins do not share the binding sites with the Bt Cry proteins [8,9,10,11], so pyramiding Vip3A proteins and Cry proteins has been widely adopted in Bt-crops [12]
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