tailieunhanh - Báo cáo khoa học: Phaiodotoxin, a novel structural class of insect-toxin isolated from the venom of the Mexican scorpion Anuroctonus phaiodactylus

Apeptide called phaiodotoxin was isolated from the venom of the scorpionAnuroctonus is lethal to crickets, but non toxic tomice at the doses assayed. It has 72 amino acid residues, with a molecular mass of 7971 atomic mass units. Its covalent structure was determined by Edman degradation and mass spectrometry; it contains four disul-fide-bridges, of which one of the pairs is formed between cysteine-7 and cysteine-8 (positions Cys63–Cys71). The other three pairs are formed between Cys13–Cys38, Cys23– Cys50 and Cys27–Cys52. . | Eur. J. Biochem. 271 4753-4761 2004 FEBS 2004 doi Phaiodotoxin a novel structural class of insect-toxin isolated from the venom of the Mexican scorpion Anuroctonus phaiodactylus Norma A. Valdez-Cruz1 Cesar V. F. Batista1 Fernando Z. Zamudio1 Frank Bosmans2 Jan Tytgat2 and Lourival D. Possani1 1 Department of Molecular Medicine and Bioprocesses Institute of Biotechnology National Autonomous University of Mexico Cuernavaca Mexico laboratory of Toxicology University of Leuven Leuven Belgium A peptide called phaiodotoxin was isolated from the venom of the scorpion Anuroctonus phaiodactylus. It is lethal to crickets but non toxic to mice at the doses assayed. It has 72 amino acid residues with a molecular mass of 7971 atomic mass units. Its covalent structure was determined by Edman degradation and mass spectrometry it contains four disul-fide-bridges of which one of the pairs is formed between cysteine-7 and cysteine-8 positions Cys63-Cys71 . The other three pairs are formed between Cys13-Cys38 Cys23-Cys50 and Cys27-Cys52. Comparative sequence analysis shows that phaiodotoxin belongs to the long-chain subfamily of scorpion peptides. Several genes coding for this peptide and similar ones were cloned by PCR using cDNA prepared from the RNA of venomous glands of this scor pion. Electrophysiological assays conducted with this toxin in several mammalian cell lines TE671 COS7 rat GH3 and cerebellum granular cells showed no effect on Na currents. However it shifts the voltage dependence of activation and inactivation of insect Na channels para tipE to more negative and positive potentials respectively. Therefore the window current is increased by 225 which is thought to be the cause of its toxicity toward insects. Phaiodotoxin is the first toxic peptide ever purified from a scorpion of the family Iuridae. Keywords Anuroctonus phaiodactylus disulfide bridges insect toxin Na -channel scorpion. Most of the biochemical work performed with scorpion