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Hemitoxin (HTX) is a new K + channel blocker isolated from the venom of the Iranian scorpionHemiscorpius lepturus. It represents only 0.1% of the venom proteins, and displaces [ 125 I]a-dendrotoxin from its site on rat brain synaptosomes with an IC50value of 16 nm. | ỊFEBS Journal Hemitoxin the first potassium channel toxin from the venom of the Iranian scorpion Hemiscorpius lepturus Najet Srairi-Abid1 z Delavar Shahbazzadeh1 2 z Imen Chatti1 Saoussen Mlayah-Bellalouna1 Hafedh Mejdoub3 Lamia Borchani1 Rym Benkhalifa1 Abolfazl Akbari4 and Mohamed El Ayeb1 1 Laboratoire des Venins et Toxines Institut Pasteur de Tunis Tunisia 2 Biotechnology Department Institute Pasteur of Iran Tehran Iran 3 USCR Sequenceur de Proteines Faculte des Sciences de Sfax Tunisia 4 Razi Vaccine Serum Research Institute Karaj Iran Keywords Hemiscorpius lepturus hemitoxin K channel scorpion toxin structure-function relationships Correspondence N. Srairi-Abid Laboratoire des Venins et Toxines Institut Pasteur de Tunis 13 Place Pasteur Tunis BP-74 1002 Tunisia Fax 216 71 791 833 Tel 216 71 783 022 E-mail najet.abid@pasteur.rns.tn These authors contributed equally to this work Received 18 April2008 revised 28 June 2008 accepted 22 July 2008 doi 10.1111 j.1742-4658.2008.06607.x Hemitoxin HTX is a new K channel blocker isolated from the venom of the Iranian scorpion Hemiscorpius lepturus. It represents only 0.1 of the venom proteins and displaces 125I a-dendrotoxin from its site on rat brain synaptosomes with an IC50 value of 16 nM. The amino acid sequence of HTX shows that it is a 35-mer basic peptide with eight cysteine residues sharing 29-69 sequence identity with other K channel toxins especially with those of the aKTX6 family. A homology-based molecular model generated for HTX shows the characteristic a p-scaffold of scorpion toxins. The pairing of its disulfide bridges deduced from MS of trypsin-digested peptide is similar to that of classical four disulfide bridged scorpion toxins Cys1-Cys5 Cys2-Cys6 Cys3-Cys7 and Cys4-Cys8 . Although it shows the highest sequence similarity with maurotoxin HTX displays different affinities for Kv1 channel subtypes. It blocks rat Kv1.1 Kv1.2 and Kv1.3 channels expressed in Xenopus oocytes with IC50 values of 13 16 and 2
