Molecular conformation of alpha-bungarotoxin as studied by nuclear magnetic resonance and circular dichroism.

We have examined the circular dichroism and nuclear magnetic resonance spectra of a long neurotoxin, alpha-bungarotoxin, over a wide range of pH values and temperatures, and under high salt conditions. The observations are interpreted partly in terms of the known crystal structure of this polypeptide. We support earlier findings of a greater degree of beta-sheet structure in solution than has been reported by X-ray crystallography and, importantly, the invariant residue associated with neurotoxicity, Trp29, is shown to be in a similar environment to that found in alpha-cobratoxin and LS III from Laticauda semifasciata. The implications of this observation for structure/function relationships are outlined.