Amino acid sequence of two neurotoxins from the venom of the Egyptian black snake (Walterinnesia aegyptia).

The venom of the Egyptian black snake Walterinnesia aegyptia contains at least three toxins, which act postsynaptically to block the neuromuscular transmission of isolated rat phrenic nerve-diaphragm and chicken biventer cervicis muscle. The complete amino acid sequence of the two toxins, W-III and W-IV, consisting of 62 amino acid residues, was elucidated by Edman degradation of fragments obtained after Staphylococcus aureus protease and prolylpeptidase digestion. Although the toxins exhibit close structural homology to other short-chain postsynaptic neurotoxins from Elapidae venoms, toxin IV is unique by having a free SH-group (cysteine) at position 16. In position 35 of W-III, which is located at the tip of the central loop, threonine is replaced by lysine, which may alter the interaction of the toxin with the acetylcholine receptor, since the toxin is seven times less lethal than toxin W-IV.