Pore Bacillus thuringiensis toxin

Prince, R. C., 1990. At least one Bacillus thuringiensis toxin forms ion-selecdve pores in membranes. Trends in Biochemical Sciences 15 2-3. 

Interestingly, certain other pore-forming toxins possess helix-bundle motifs that may participate in channel formation, in a manner similar to that proposed for colicin la. For example, the S-endotoxui produced by Bacillus thuringiensis is toxic to Coleoptera insects (beetles) and is composed of three domains, including a seven-helix bundle, a three-sheet domain, and a /3-sandwich. In the seven-helix bundle, helix 5 is highly hydrophobic, and the other six helices are amphipathic. In solution (Figure 10.32), the six amphipathic... 

The bacterium Bacillus thuringiensis forms an internal crystal that contains a number of insecticidal protein toxins. When eaten by the insect, the crystal dissolves in the midgut, the toxin mixture is released, and the proteins are cleaved into active forms. The toxins bind specifically to midgut cells and assemble a pore that leads to disintegration of the cells, gut paralysis, and death. B. thuringiensis strains have toxins specific for caterpillars, beetles, or flies. They have little or no effect on mammals. 

Structural and functional studies of a synthetic peptide that mimics a proposed membrane inserting segment of a Bacillus thuringiensis delta-endotoxin have been conducted. An NMR study of a methanol solution of a synthetic 31-mer peptide corresponding to the sequence of a putative pore-forming segment of the CrylA(c) toxin showed that the peptide exists as an a-helix. Hie peptide forms discrete, characterizable channels in planar lipid bilayers. It is possible that this helix is a component of the transmembrane pore formed by Bacillus thuringiensis delta-endotoxins in vivo. 

Gazit, E., N. Burshtein, D.J. Ellar, T. Sawyer, and Y. Shai. 1997. Bacillus thuringiensis cytolytic toxin associates specifically with its synthetic helices A and C in the membrane bound state. Implications for the assembly of oligomeric transmembrane pores. Biochemistry 36 15546-15554. 

Jurat-Fuentes, J.L., F.L. Gould, and M.J. Adang. 2000. High levels of resistance and cross-resistance to Bacillus thuringiensis Cryl toxins in Heliothis virescens are due to reduced toxin binding and pore formation. Resist.Pest Manag. Newslett. 11 23-24. 

Soberon, M., R.V. Perez, M.E. Nunez-Valdez, A. Lorence, 1. Gomez, J. Sanchez, and A. Bravo. 2000. Evidence for intermolecular interaction as a necessary step for pore-formation activity and toxicity of Bacillus thuringiensis CrylAb toxin. FEMS Microb. Lett. 191 221-225. 

Tran, L.B., V. Vachon, J-L. Schwartz, and R. Laprade. 2001. Differential effects of pH on the pore-forming properties of Bacillus thuringiensis insecticidal crystal toxins. Appl. Environ. Microbiol. 67 4488-4494. 

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