Circular dichroism of elapidae protein toxins.

The effect of temperature variation on the circular dichroic spectra of four Elapid snake toxins (one short neurotoxin, two long neurotoxins and one cytotoxin) was determined and the results compared. The three neurotoxins have in common a delicately balanced conformation which can be perturbed independently of the predominant secondary structuring. Despite the many differences in sequence between long and short neurotoxins, the nature of this balance seems to be the same in both types and it is considered to involve an equilibrium between two defined conformers. Such properties could not be discerned in the cytotoxin studied, but related work suggests that they could nevertheless be present in some cases. In terms of global structure, long neurotoxins may have a greater proportion of 'random chain' inherent than short neurotoxins, the latter having extensive beta-sheet. The important feature of all toxins is deemed to be a conformational freedom defined by the secondary structuring and characteristic disulphide bridge formation. Possible relevance to toxicity of such a property is discussed.