Dendrotoxins
 
The venom of the Dendroaspsis mamba snakes contains several toxins, termed dendrotoxins, which bind with nanomolar affinities to voltage-dependent potassium channels and facilitate neurotransmitter release because they prolong membrane depolarization. Their polypeptide chains consist of 57 to 60 amino acid residues, with three disulfide bonds and folding closely similar to that of BPTI-type inhibitors of serine proteinases. A short amino-terminal 3₁₀-helix is followed by a two-stranded b-sheet and a short COOH-terminal a-helix (1). Dendrotoxins provide yet another example of a stable protein module that has been readapted during the course of evolution to perform a different biological function.
References
1. J.-M. Lancelin et al. (1994) Struc. Biol. 1, 246–250.