Newly discovered protein mechanism will help develop more effective biopesticides

Yolanda Bel, Patricia Casino, Joan Ferré i Juan José Huesa

A team from Valencia University has taken part in research that will improve plague control in agriculture.

A research team of Valencia University, ERI Biotecmed, along with researchers from the Centre for Biological Research (CIB) of the Spanish National Research Council (CSIC) and the rare disease CIBER, CIBERERE-ISCIII, have proved, for the first time, the structure of insecticidal protein Vip3Aa, as well as the changes experienced to go from its inactive structure (‘protoxin’) to its active structure (‘toxin’). The results of this work have been published in journal Nature Communications.

Reveal the mechanism of activation of the insecticidal protein Vip3A that will help develop more effective biopesticides

Vip3Aa is an insecticidal protein secreted by bacterium Bacillus thuringiensis that has effective action against a broad spectrum of lepidoptera insects. Today, it is used in ecological and conventional crops as a spray biopesticide (Bt insecticides), as well as in transgenic crops protected against the attack of insects (Bt crops). However, the mechanism that induced the insecticidal action of Vip3Aa remained unknown.

“Our contribution helps understand how Vip3 proteins act to destroy the epithelial cells of the midgut of insect larvae, which ultimately lead to their death,” explain Joan Ferré and Yolanda Bel, researchers of Valencia University.

This project presents a turning point in the study of the insecticidal action of Vip3Aa and opens the door to the development of new biotechnological applications, such as protein engineering, which make it possible to produce more stable proteins and with greater activity in order to control agricultural plagues.

“It is worth noting that this is the first structure of a protein, at atomic resolution, obtained through electronic cryo-electron microscopy at Valencia University, a new technique that is gaining traction and has a lot to offer together with crystallography,” says Patricia Casino, ‘Ramón y Cajal’ researcher at Valencia University.

Structural study of protein Vip3A

The study conducted makes it possible to view the structure of insecticidal protein Vip3Aa, as well as the changes experienced to go from its inactive structure (‘protoxin’) to its active structure (‘toxin’).

The structural study conducted shows that the protoxin is a tetramer of pyramidal structure, where the N-terminal region sticks out and creates a ray of twisted helixes, and the C-terminal region stretches out in the opposite direction, revealing a branched appearance. The protoxin has a cleavage site exposed to the solvent that is recognised by proteases, which cause a cut that will facilitate the transformation of protoxin into toxin. This process entails a dramatic restructuring of the N-terminal region and gives way to the creation of a parallel coiled coil of four helixes with the appearance of a needle. This needle, of almost 160 Å, is long enough to penetrate the insect’s membrane and contribute to the toxic effect. Although for some time it has been known that the proteins of the Vip3 family are found in a solution in the form of a tetramer, there had never before been a structural image of the changes that led from the protoxin structure to the active form. Thus, now it is understood how the Vip3 proteins work to destroy insect larvae. This paper will enable the development of new biotechnological applications to produce more stable insecticides in order to control agricultural plagues.

Article of reference:

Núñez-Ramírez R, Huesa J, Bel Y, Ferré J, Casino P* and Arias-Palomo* E.

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

doi: 10.1038/s41467-020-17758-5