Molecular cloning and nucleotide sequence analysis of a cDNA encoding the main β‐neurotoxin from the venom of the South American scorpion Tityus serrulatus

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Abstract
A cDNA encoding the main Tityus serrulatus β‐neurotoxin was isolated from a venom gland cDNA library by using an oligonucleotide probe. The amino acid sequence deduced from the cDNA nucleotide sequence indicated that the toxin is the processed product of a precursor containing: (i) a signal peptide of 20 residues: (ii) the amino acid sequence of the mature toxin: and (iii) an extra Gly‐Lys‐Lys tail at the C‐terminal end before the termination codon. Thus, in addition to the removal of the signal peptide by a signal peptidase, the generation of the mature toxin requires both a post‐translational cleavage by a carboxypeptidase specific for basic residues and the action of an α‐amidating enzyme. These results also show that the biosynthetic pathway for β‐toxins of ‘New World’ scorpion venoms is similar to that already described for α‐toxins of ‘Old World’ scorpion venoms.