Molecular architecture and activation of the insecticidal protein Vip3Aa from Bacillus thuringiensis

Abstract

Bacillus thuringiensis Vip3 (Vegetative Insecticidal Protein 3) toxins are widely used in biotech crops to control Lepidopteran pests. These proteins are produced as inactive protoxins that need to be activated by midgut proteases to trigger cell death. However, little is known about their three-dimensional organization and activation mechanism at the molecular level. Here, we have determined the structures of the protoxin and the protease-activated state of Vip3Aa at 2.9 Å using cryo-electron microscopy. The reconstructions show that the protoxin assembles into a pyramid-shaped tetramer with the C-terminal domains exposed to the solvent and the N-terminal region folded into a spring-loaded apex that, after protease activation, drastically remodels into an extended needle by a mechanism akin to that of influenza haemagglutinin. These results provide the molecular basis for Vip3 activation and function, and serves as a strong foundation for the development of more efficient insecticidal proteins.

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

“…After trypsinization, all four monomers stay connected, and no conformational change takes place in domains II to V. Three N-terminal α helices form a parallel four helix coiled coil, which forms a long dipole to lodge the ions in its cavity. Its dimension has the ability to form pores in the lipid bilayer [47].…”

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

“…Thus, this architecture revealed that tetramer of Vip3 protoxin assembled into pyramid shape having N-terminal apex and core, and C-terminal exposed toward solvents (Núñez-Ramírez et al, 2020). The structure-comparison analysis of Vip3A and Vip3B revealed that both proteins have similar tetrameric organization shares a significant similarity between domains I, II, and III and the analogous relationship between the flexible domains IV and V as they are responsible for exposing of glycan-binding side toward solvent (Núñez-Ramírez et al, 2020;Zheng et al, 2020).…”

“…Recently, another new high-resolution 3D-structures of complete protoxin and activated Vip3Aa protein conformations were analyzed through Cryo-electron microscopy at 2.9 Å by Núñez-Ramírez et al (2020). The domain organization of protoxin Vip3 revealed five domains in the protoxin (Figure 4), which are following: Domain I (1-199aa): It is composed of highly curved four (α1-α4) helices that look like pyramid apex and validated as protease cleavage site.…”

Nutrient conditions determine the localization of Bacillus thuringiensis Vip3Aa protein in the mother cell compartment

“…However, thus far no resistance to Vip proteins has been reported (Tabashnik and Carrière, 2017; Tabashnik and Carrière, 2020). Although Cry and Vip toxins affect the same cells in the larval midgut tissue, these proteins have no structural homology and bind to different receptors in the larval midgut (Lee et al ., 2003; Wang et al ., 2018; Núñez‐Ramírez et al ., 2020), and no cross‐resistance has been observed between these two proteins (Carrière et al ., 2015; Chakroun et al ., 2016a,b).…”