Structure-function studies on Taiwan cobra long neurotoxin homolog

A novel long neurotoxin homolog was purified from Naja naja atra (Taiwan co bra) venom using the combination of ion exchange chromatography and reverse phase high performance liquid chromatography. The determined protein seque nce was essentially the same as that deduced from the cDNA amplified by rev erse transcriptase-polymerase chain reaction. The long neurotoxin homolog e xhibited an activity that inhibited acetylcholine-induced muscle contractio ns, as with N. naja atra cobrotoxin. The degree of inhibition caused by the addition of long neurotoxin homolog was approximately 70% of that observed with the addition of cobrotoxin. Unlike the well-known short and long neur otoxins, this neurotoxin homolog contained two additional cysteine residues forming a disulfide linkage in the N-terminal region. Circular dichroism m easurement and computer models of the neurotoxin reveal that its secondary structure was not abundant in beta-sheet as noted with short and long neuro toxins. This less ordered structure may be associated with the lower activi ty noted with the long neurotoxin homolog, Together with the finding that t he known long neurotoxin homologs exclusively appear in the venoms of the N aja and Bungarus genera, the long neurotoxin homologs should represent an e volutionary branch from the long and short neurotoxins in the Elapidae fami ly. (C) 2000 Elsevier Science B.V. All rights reserved.