[Role of lysines in the stability of a snake neurotoxin]

The effects of charge suppression at a single lysine residue on the energetics of thermal unfolding or unfolding with guanidinium chloride of erabutoxin b are studied by circular dichroism. It is shown that acylation of lysine 15, 47 or 51 has virtually no effect on the toxin stability. In contrast, abolition of the positive charge of lys-27, a residue involved in the "toxic" site of the molecule, substantially increases the toxin stability. This phenomenon is attributed to suppression of repulsive interactions occurring within the native toxin molecule between lys-27 and other positively charged groups.