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

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.