Sequence characterization of a novel alpha-neurotoxin from the king cobra (Ophiophagus hannah) venom

Several postsynaptic neurotoxins (alpha-neurotoxins) with distinct pharmacological and biochemical properties were isolated and purified from the King cobra venom (Ophiophagus hannah) by employing sequentially preparative-scale cation-exchange chromatography on SP-Sephadex C-25 coupled with gel filtration and reversed-phase HPLC. The complete sequence of one neurotoxin was determined by N-terminal Edman degradation with the automatic pulsed-liquid phase sequencer on some peptide fragments generated from the endopeptidases, i.e. trypsin, S. aureus V8 protease and lysyl endopeptidase. This novel neurotoxin is a basic polypeptide of pI 9.05, consisting of 72 amino-acid residues with 10 cysteine residues. It is found to share about 60% sequence homology with Toxins a and b isolated from the same venom and the well established alpha-bungarotoxin, a major postsynaptic toxic ligand for acetylcholine receptor isolated from Bungarus multicinctus. The characterized alpha-neurotoxin molecules were also shown to bind specifically with nicotinic acetylcholine receptors of the electric eel, Torpedo californica.