Conformational stability of a snake cardiotoxin.

A snake cardiotoxin from the venom of the Formosan cobra, Naja naja atra, is a basic polypeptide. The protein can be denatured in 6.0 M guanidine hydrochloride or at elevated temperatures. Its conformation remains virtually the same in solvents of lower polarity than water such as 1, 2-ethanediol or 1-propanol and 1, 2-ethanediol (1:1 v/v). The circular dichroism spectrum is atypical in water in that the peptide chromophores show a small negative CD band at 214 nm and a large positive one at 195 nm. To some extent the CD pattern resembles that of the beta-form but differs in specific positions and magnitudes. Considering that the theoretical CD of the reverse beta-bend and the characteristics of model polypeptides in beta-form manifest a similar pattern, we suggest that cobra cardiotoxin is rich in beta structure including beta pleated-sheets and beta reverse-turns.