[Structural changes in wild-type Cry3A delta-endotoxin and its mutants in ethyl alcohol solutions at pH 2-2.5]

The methods of circular dichroism, scanning microcalorimetry, electron microscopy, and proteolysis were used to study the ability of wild-type Cry3A-delta-endotoxin and three mutant toxins with cysteine substitutions in helices alpha3 and alpha4 (domain I) to form oligomeric structures in acidic alcohol solutions that reproduce the premembrane environment. At pH 2-2.2 and 20% ethanol, the mutant toxins with single substitutions E132C (alpha3) and E160C (alpha4), as well as the double mutant E132C/S160C with a cysteine bridge connecting helices alpha3 and alpha4, form short linear oligomers specific for Cry3A with a high content of the beta-structure and enhanced sensitivity to proteolysis with pepsin. The data obtained show that the formation of oligomeric structures of this type does not require any divergence of helices alpha3 and alpha4 in domain I of the Cry3A toxin. It has been demonstrated that, at higher pH values in 20% solution of ethanol, the proteins studied are in a metastable state, and their ability to form oligomeric structures depends on temperature.