Mechanism of action of Bacillus thuringiensis toxins

Abstract

The selectivity of Bacillus thuringiensis toxins is determined both by the toxin structure and by factors inherent to the insect. These toxins contain distinct domains that appear to be functionally important in toxin binding to protein receptors in the midgut of susceptible insects, and the subsequent formation of a pore in the insect midgut epithelium. In this article features necessary for the insecticidal activity of these toxins are discussed. These include toxin structure, toxin processing in the insect midgut, the identification of toxin receptors in susceptible insects, and toxin pore formation in midgut cells. In addition a number of B. thuringiensis toxins act synergistically to exert their full insecticidal activity. This synergistic action is critical not only for expressing the insecticidal activity of these toxins, but could also play a role in delaying the onset of insect resistance.

Midgut GPI-anchored proteins with alkaline phosphatase activity from the cotton boll weevil (Anthonomus grandis) are putative receptors for the Cry1B protein of Bacillus thuringiensis

“…The best characterized among them is the APN receptor (Pacheco et al, 2009, Rajagopal et al, 2003Gill et al, 1995;Gill, 1995;Knight et al, 1994;Sangadala et al, 1994) and the cadherin-like receptor (Jurat-Fuentes and Adang, 2006;Flanagan et al, 2005;Zhang et al, 2005;Hua et al, 2004;Tsuda et al, 2003;Hara et al, 2003;Gahan et al, 2001;Valaitis et al, 2001;Nagamatsu et al, 1998a,b;Vadlamudi et al, 1995) identified in lepidopterans. In nematodes, glycolipids are believed to be involved in Cry toxin interaction (Griffitts et al, 2005).…”

Effects of Bacillus thuringiensis Cry1Ab Toxin on Mammalian Cells.

“…They reasoned that the initial toxic event is the formation of a small hole in the plasma membrane, impermeable to intracellular macromolecules. As ions and water enter the cell, a further breakdown of the stretched plasma membrane will occur, allowing progressively larger molecules to leak out of the cell [5][6][7]12]. In other words, experiments on tissue culture cells in the field of entomology clarified that Cry proteins have a fairly general capacity to form large nonspecific pores under certain conditions, including high Cry protein concentrations, long incubation times and relatively low pHs [18].…”

“…When this crystal is ingested by target insects, it develops an insecticidal activity due to partial digestion of the protoxin inside the midgut of the insect [7,18]. The insecticidal proteins in the crystal form two different families, Cry and Cyt, which have been classified on the basis of amino acid identity into more than 30 Cry subgroups and two Cyt subgroups [3].…”

THE EFFECT OF Bacillus thuringiensis TOXIN Cry1A.105 AND Cry2Ab2 ON THE SURVIVAL OF THE NON-TARGET PEST, Spodoptera litura (PENGARUH TOKSIN Bacillus thuringiensis Cry1A.105 DAN Cry2Ab2 TERHADAP KELANGSUNGAN HIDUP HAMA BUKAN SASARAN, Spodoptera litura)

“…The selectivity of Bt toxin is determined by toxin structure and other factors on the body of the target insects. The binding process of the toxin onto the receptor in the midgut can only be successful whenever they are compatible to each other (Gill, 1995).…”