Cyt2Aa1 is a cytolytic protein produced by Bacillus thuringiensis subsp. kyushuensis. Penetration of the toxin into membranes has been studied to learn more about membrane-insertion mechanisms and transmembrane-pore formation. The haemolysis assay of Cyt2Aa1 showed a steep and sigmoidal dose–response curve, indicating that toxin aggregation or oligomerization is required for pore formation. Studies of the effect of temperature on pore formation and fluorimetric studies of acrylodan-labelled toxin suggest that toxin inserts into the membrane before oligomerizing to form a pore. Low temperature neither inhibited membrane binding nor closed pores that have been formed, but markedly inhibited oligomerization of the toxin molecules. When toxin-treated red blood cells at 4 °C were transferred to a toxin-free solution at 37 °C, no significant increase in haemolysis was observed. This result suggests that membrane-bound toxin could not diffuse laterally and interact with other molecules to form a pore. From these results, we propose that Cyt2Aa1 binds and inserts into the membrane as a monomer. Oligomerization occurs when toxin molecules have bound in close proximity to each other and pores are formed from large oligomers.
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Research Article| August 15 2003
Investigation of the pore-forming mechanism of a cytolytic δ-endotoxin from Bacillus thuringiensis
Boonhiang PROMDONKOY 1
∗National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, 113 Phaholyothin Road, Klong 1, Klong Luang, Pathumthani 12120, Thailand
1To whom correspondence should be addressed (e-mail firstname.lastname@example.org).
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Boonhiang PROMDONKOY, David J. ELLAR; Investigation of the pore-forming mechanism of a cytolytic δ-endotoxin from Bacillus thuringiensis. Biochem J 15 August 2003; 374 (1): 255–259. doi: https://doi.org/10.1042/bj20030437
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