Cloning of Genes Encoding Scorpion Toxins: An Interpretative Review

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Abstract
Scorpion toxins (Stox) are polypeptides intensively investigated because they are excellent models to study protein-structure-function relationships and exquisite tools to access ion channel functions. Recently, techniques of molecular biology have been used to clone the genes encoding toxins specific for Na+-channels. Genes from scorpions of the genus Androctonus, Centruroides, Leiurus, Tityus and Bothus have been cloned and their nucleotide (nt) sequence determined. Data from complementary DNA (cDNA) cloning of Stox from the genus before mentioned and genomic cloning of Stox genes from scorpions of the genus Tityus and Androctonus have provided information for the deduction of the structure of the transcriptional units encoding toxin genes of these scorpions. It seems that transcription of these genomic regions generates pre messenger RNAs (pre-mRNAs) of approximately 800nt containing an intron of approximately 470nt, located within the region encoding the signal peptide. The processing of these pre-mRNAs originates a mature molecule of approximately 330 nt. The translation of the mRNAs give precursors of approximately 82–89 amino acid (aa) residues, which in some cases are processed at both amino- and carboxyl-terminus ends. At the amino terminus, a 18–21 aa signal peptide is released by a signal peptidase. At the C-terminus, basic residues (Lys or Arg) are eliminated by a carboxypeptidase. In some cases, the C-terminal residues are processed given rise to a final amidated aa. In this review, the information available on this subject is summarized and we also present an interpretive review of the main stox structure known, with the possible implications for their function on excitable cells.