The cDNA encoding a variant of α bungarotoxin was cloned from the venom glands of Bungarus multicinctus by RT PCR.The deduced protein precursor contained a 21 amino acid signal peptide and a following 74 amino acid mature protein.The signal peptide is very similar to those of short chain neurotoxins,κ neurotoxins and cardiotoxins.The amino acid sequence of the mature protein is identical to α bungarotoxin (V31),a minor variant of α bungarotoxin identified by protein sequencing technique.Furthermore,the cDNA encoding the deletion precursor of α bungarotoxin was also cloned.By use of pMAL p2,the variant was overexpressed in E coli as a soluble fusion protein and purified by sepharose 6B amylose affinity chromatography,which was confirmed by western blotting with the antisera agai nst α bungarotoxin.The recombinant variant was achieved after digestion by factor X a.It displayed about 1/6 in vivo toxicity of natural α bungarotoxin.The successful cloning and functional expression of α bungarotoxin provided a basis for the future study of structure function of long neurotoxins.
