Conformation of snake toxic polypeptides studied by a method of prediction and circular dichroism.

Short and long neurotoxins as well as cardiotoxins belong to three distinct families of homologous toxic polypeptides extracted from cobra venoms. A study of their conformation was undertaken by using the method of Chou and Fasman for prediction of secondary structures of proteins. To improve the reliability of this method, an averaging scheme was developed. The data obtained showed that all toxins have a predominant trend for beta-sheet nucleation. Moreover, predicted beta-sheet strands fitted well those actually observed from X-ray data. Thus, it seems that all toxins share similarities in their secondary structure. This proposition was supported by a comparative study of the CD spectra of a set of toxins. Nevertheless, the present data suggest also that each type of toxins possesses localized structural individualities which might be responsible for the biological and/or immunological specificities.