Crystal structure of insecticidal δ-endotoxin from Bacillus thuringiensis at 2.5 Å resolution

Abstract

The structure of the delta-endotoxin from Bacillus thuringiensis subsp. tenebrionis that is specifically toxic to Coleoptera insects (beetle toxin) has been determined at 2.5 A resolution. It comprises three domains which are, from the N- to C-termini, a seven-helix bundle, a three-sheet domain, and a beta sandwich. The core of the molecule encompassing all the domain interfaces is built from conserved sequence segments of the active delta-endotoxins. Therefore the structure represents the general fold of this family of insecticidal proteins. The bundle of long, hydrophobic and amphipathic helices is equipped for pore formation in the insect membrane, and regions of the three-sheet domain are probably responsible for receptor binding.

Cytotoxicity of Bacillus thuringiensis Cry1Ab toxin depends on specific binding of the toxin to the cadherin receptor BT-R1 expressed in insect cells

“…Most significantly, incorporation of Cry1Ab oligomers into cell membrane does not result in the formation of lytic pores and, therefore, argues against the 'pore-formation model' postulated previously. [22][23][24][25] In the pore-forming model of Cry toxin action, the toxin monomers are considered precursors to oligomeric assembly. 21,25 The formation of toxin oligomer also has been postulated to be the result of the interaction of monomers that were bound to the cadherin receptor.…”

“…In other words, Cry toxin action was believed to involve the formation of lytic pores that are the result of assembly of toxin molecules as oligomers in membrane. [22][23][24][25] However, there is no definitive correlation between the association of Cry toxin oligomer complexes and toxic action. Studies of mutated Cry toxin proteins have shown that neither the toxin oligomer complex nor commensurate changes in membrane vesicle permeability correlate directly with toxicity.…”

Employing phage display to study the mode of action of Bacillus thuringiensis Cry toxins

“…The three dimensional structures of six Cry toxins with different insect specificities have been solved [2,3,9,15,22,26]. These toxins are composed of three domains -domain I, a seven α-helix bundle involved in membrane insertion, oligomer formation and pore formation [4]; domain II, a three anti-parallel β-sheets packed around a hydrophobic core in a "beta-prism" involved in receptor interaction [4]; and domain III, a β-sandwich of two antiparallel β-sheets also involved in receptor interaction [4].…”

Transgenics in groundnut (Arachis hypogaea L.) expressing cry1AcF gene for resistance to Spodoptera litura (F.)

“…Further, an alternative to gene pyramiding would be to use synthetic genes of multiple efficacies. Cry proteins share a common three domain structure (Li et al 1991). In simple words, hybrid (Synthetic) toxins produced through inclusion of a domain from another toxin results in increased potency of the fused protein by the shift in receptor binding (Bosch et al 1994).…”