The effect of delta-endotoxin from Bacillus thuringiensis var. tenebrionison phospholipid vesicles

The effects of delta-endotoxin from Bacillus thuringiensis var. tenebrionis and its 53-kDa and 49-kDa fragments on phospholipid vesicles were studied by scanning microcalorimetry and electron microscopy. At pH 3.0, a decrease in transition temperature of both the protein and phospholipid was registe red, as well as a diminished enthalpy of protein transition. As shown by el ectron micrographs, under these conditions, the interaction between delta-e ndotoxin or its 53-kDa and 49-kDa fragments and phospholipid vesicles resul ts in destruction of the latter. Taking into account that the 53-kDa fragme nt lacks four N-terminal alpha-helices (14 kDa) and that three N-terminal a lpha-helices (11 kDa) as well as 56 C-terminal amino acids (7 kDa) are abse nt from the 49-kDa fragment, it is suggested that the active unit responsib le for toxic functions is not larger than 46 kDa. The current study shows t hat B. thuringiensis delta-endotoxins can destroy phospholipid vesicles con taining no specific receptors.