Reoxidation and renaturation studies on the main toxin of Naja naja samarensis

The main toxin of Naja naja samarensis is a very small and rigid protein (Mr 6850, 8 cysteines). When fully reduced, it regains its native conformation by a mechanism involving a rapid cysteine oxidation and a slower, less temperature-dependent disulfide exchange. In a native-like form of the protein we observed a population whose cysteines were incompletely reoxidized. When intermediates with blocked cysteines were incubated with oxidized and reduced glutathione, the percentage of native-like molecules increased. These findings suggest a multiple folding pathway.