Abstract
Since the first X-ray structure of Cry3Aa was revealed in 1991, numerous structures of B. thuringiensis toxins have been determined and published. In recent years, functional studies on the mode of action and resistance mechanism have been proposed, which notably promoted the developments of biological insecticides and insect-resistant transgenic crops. With the exploration of known pore-forming toxins (PFTs) structures, similarities between PFTs and B. thuringiensis toxins have provided great insights into receptor binding interactions and conformational changes from water-soluble to membrane pore-forming state of B. thuringiensis toxins. This review mainly focuses on the latest discoveries of the toxin working mechanism, with the emphasis on structural related progress. Based on the structural features, B. thuringiensis Cry, Cyt and parasporin toxins could be divided into three categories: three-domain type α-PFTs, Cyt toxin type β-PFTs and aerolysin type β-PFTs. Structures from each group are elucidated and discussed in relation to the latest data, respectively.
Highlights
Bacillus thuringiensis, as a Gram-positive soil bacterium, is a member of the B. cereus group that includes five other species: B. cereus, B. anthracis, B. mycoides, B. pseudomycoides, andB. weihenstephanensi
PFTs are classified as two main groups: α-pore-forming toxins (α-PFTs) and β-pore-forming toxins (β-PFTs)
In this review, according to the similarities of known or predicted structures between B. thuringiensis toxins and PFTs, we describe Cry, Cyt and parasporin toxins as three categories based on structural features: three-domain type α-PFTs, Cyt toxin type β-PFTs and aerolysin type β-PFTs
Summary
As a Gram-positive soil bacterium, is a member of the B. cereus group that includes five other species: B. cereus, B. anthracis, B. mycoides, B. pseudomycoides, and. Cry toxin is described as: a parasporal inclusion (Crystal) protein from B. thuringiensis that exhibits toxic effects to a target organism, or any protein that has obvious sequence similarity to a known Cry toxin [10]. PFTs is a major category of membrane-damaging toxins, which could penetrate target cell membrane in a water-soluble form and generate pores, eventually leading to cell death [20,21]. By their transmembrane structure, PFTs are classified as two main groups: α-pore-forming toxins (α-PFTs) and β-pore-forming toxins (β-PFTs). Structural features of these three categories, similarities to the PFTs and structure-related functional progress are elucidated in detail
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