Mutagenesis of three surface-exposed loops of a Bacillus thuringiensis insecticidal toxin reveals residues important for toxicity, receptor recognition and possibly membrane insertion

Article Abstract:

Site-directed mutagenesis of 3 loops of a Bacillus thuringiensis insecticidal toxin shows four residues G439, Y367, R368, and R369 that have a function in receptor binding. The G312 change in loop 1 decreases toxicity without reducing reversible binding affinity. In loop 2, Y367 can be replaced by phenylalanine in the presence of arginine or lysine at position 368 without affecting toxicity or binding. The S438 in loop 3 has a role in toxicity and cannot be replaced by substituting threonine. Binding affinity is unaffected in G312 and S438 mutated strains, suggesting their involvement in membrane insertion and pore formation.

Mutagenesis

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Maximal toxicity of cloned CytA delta-endotoxin from Bacillus thuringiensis subsp. israelensis requires proteolytic processing from both the N- and C-termini

Article Abstract:

Proteinase K cleaves the N- and C-terminal of CytA toxin, produced by Bacillus thuringiensis subsp. israelensis, to increase the toxicity of CytA. Trypsin and gut extracts of Anopheles and Culex also cleave both the terminals. The cleavage occurs at Arg 25 of the N-terminal and the 225th residue of the C-terminal. The processing at the N-terminal is suppressed in the presence of DTT.

Endotoxins, Proteolysis

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Role of receptors in Bacillus thuringiensis crystal toxin activity

Article Abstract:

The physiology of binding of the cry proteins to the receptors in the insect cells and the insecticidal properties of these toxins from Bacillus thuringiensis are investigated.

Science & research, Causes of, Risk factors, Genetic aspects, Cell death, Microbial insecticides

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