Sequence characterization of venom toxins from Thailand cobra

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Abstract
Several toxins with distinct pharmacological properties were isolated from the venom of Thailand cobra (Naja naja siamensis) by cation-exchange chromatography. Two neurotoxins and one basic toxin with cardiotoxic activity were further purified and sequenced. The neurotoxins characterized were closely similar to the previously reported long- and short-chain neurotoxins. The complete sequences of one minor neurotoxin and one cardiotoxin analogue were determined with the automatic protein sequencer in non-stop single runs of Edman degradation coupled with C-terminal sequence determination with carboxypeptidase digestion. The minor neurotoxin consists of 62 amino-acid residues with 8 cysteine residues and is found to be almost identical to cobrotoxin, a major toxic component of Formosa corbra (Naja naja atra). The sequence comparison of the 60-residue cardiotoxin with other reported cytotoxins of snake venoms indicates that 8 cysteine residues at the positions 3, 14, 21, 38, 42, 53, 54, and 59 are invariant among all sequences, with only two conservative changes at other positions along the sequence. The upshot of this report exemplified the facile sequence analysis of venom toxins by the application of pulsed-liquid phase protein sequencer and also revealed new analogues of a minor neurotoxin and one major cardiotoxin reported previously on the same species of Thailand cobra.