Structural and Functional Insights into the C-terminal Fragment of Insecticidal Vip3A Toxin of Bacillus thuringiensis

Abstract

<jats:p>The vegetative insecticidal proteins (Vips) secreted by Bacillus thuringiensis are regarded as the new generation of insecticidal toxins because they have different insecticidal properties compared with commonly applied insecticidal crystal proteins (Cry toxins). Vip3A toxin, representing the vast majority of Vips, has been used commercially in transgenic crops and bio-insecticides. However, the lack of both structural information on Vip3A and a clear understanding of its insecticidal mechanism at the molecular level limits its further development and broader application. Here we present the first crystal structure of the C-terminal fragment of Vip3A toxin (Vip3Aa11200–789). Since all members of this insecticidal protein family are highly conserved, the structure of Vip3A provides unique insight into the general domain architecture and protein fold of the Vip3A family of insecticidal toxins. Our structural analysis reveals a four-domain organization, featuring a potential membrane insertion region, a receptor binding domain, and two potential glycan binding domains of Vip3A. In addition, cytotoxicity assays and insect bioassays show that the purified C-terminal fragment of Vip3Aa toxin alone have no insecticidal activity. Taken together, these findings provide insights into the mode of action of the Vip3A family of insecticidal toxins and will boost the development of Vip3A into more efficient bio-insecticides.</jats:p>

Current Insights on Vegetative Insecticidal Proteins (Vip) as Next Generation Pest Killers

“…Domain III comprises three β sheets potent for cell binding, along with domain II, persistent with previous results. In Vip3A, two CBM domains with different glycan binding pockets are found in C-terminal region, which forms domain IV and domain V [46]. This indicates a specificity in their binding capacity with glycan on the targeted cell surface.…”

Vegetative Insecticidal Protein (Vip): A Potential Contender From Bacillus thuringiensis for Efficient Management of Various Detrimental Agricultural Pests

“…The N-terminal of Vip3A protein as a signal peptide might be involved in the secretion of protein, structural maintenance, and insecticidal activity, and the maximum variability found at C-terminal is responsible for target specificity ( Zack et al, 2017 ; Chakrabarty et al, 2020 ). It was suggested that amino acid D199 to end (C-terminal core) represents the toxic core of Vip3Aa11 ( Jiang et al, 2020 ).…”

“…The first crystal structure of the C-terminal fragment of Vip3A (Vip3Aa11) toxic has been elucidated by Jiang et al (2020) . The structural analysis demonstrated the presence of four and five domains in activated Vip3A and protoxin Vip3A, respectively.…”

“…These crystal structures and proposed domain organization may be representative of all Vip3 proteins because of the high degree of sequence homology among more than 100 Vip3 proteins available in the bacterial pesticidal protein database ( Jiang et al, 2020 ; Núñez-Ramírez et al, 2020 ; Zheng et al, 2020 ).…”

Bacillus thuringiensis Toxins: Functional Characterization and Mechanism of Action

“…In the Special Issue, five papers analyze different aspects of its biology. They cover aspects ranging from its crystal structure [ 14 ] and structural–functional domain analyses [ 15 ] to different aspects in the mode of action, such as a study of a possible receptor (the alkaline phosphatase) in a resistant strain [ 16 ], the role of oligomerization in toxicity [ 17 ], and the study of intracellular events promoted by Vip3A intoxication in Spodoptera frugiperda Sf9 cells [ 18 ].…”