TAILIEUCHUNG - Báo cáo Y học: Expanding the scorpion toxin a-KTX 15 family with AmmTX3 from Androctonus mauretanicus

Anovel toxin,AmmTX3 ( Da), was isolated fromthe venomof the scorpionAndroctonusmauretanicus. It showed 94% sequence homology with Aa1 fromAndroctonus aus-tralis and 91% with BmTX3 fromButhus martensiwhich, respectively,blockA-typeK + current incerebellumgranular cells and striatum cultured neurons. Binding and displace-ment experiments using rat brain synaptosomes showed that AmmTX3 and Aa1 competed effectively with 125 I-labelled sBmTX3 binding. | Eur. J. Biochem. 269 6037-6041 2002 FEBS 2002 doi Expanding the scorpion toxin a-KTX 15 family with AmmTX3 from Androctonus mauretanicus Helene Vacher1. Meriem Alami3. Marcel Crest2 Lourival D. Possani4. Pierre E Bouais1 I B and Marie-France Martin-Eauclaire1 1UMR 6560 CNRS and 2UMR 6150 CNRS Université de la Méditerranée Faculte de Medecine secteur Nord IFR Jean Roche Marseille France 3Institut Pasteur du Maroc Casablanca Morocco 4Biotechnology Institute UNAM Cuernavaca Mexico A novel toxin AmmTX3 Da was isolated from the venom of the scorpion Androctonus mauretanicus. It showed 94 sequence homology with Aa1 from Androctonus australis and 91 with BmTX3 from Buthus martensi which respectively block A-type K current in cerebellum granular cells and striatum cultured neurons. Binding and displacement experiments using rat brain synaptosomes showed that AmmTX3 and Aa1 competed effectively with 125I-labelled sBmTX3 binding. They fully inhibited the 125I-labelled sBmTX3 binding Ki values of pM and pM respectively demonstrating unambiguously that the three molecules shared the same target in rat brain. The specific binding parameters of 125I-labelled AmmTX3 for its site were determined at equilibrium Ki 66 pM Bmax 22 fmol per mg of protein . Finally patch-clamp experiments on striatal neurons in culture demonstrated that AmmTX3 was able to inhibit the A-type K current Ki 131 nM . Keywords scorpion toxins A-type potassium current striatum neurons patch clamp binding. An increasing number of toxins blocking the activity of K channels are isolated from various animal venoms and become key molecular probes for the characterization of these channels. They are usually small basic polypeptides between 30 and 70 amino acids cross-linked by three or four disulphide bridges reviewed in 1 . They recognize principally voltage-dependent Kv channels in particular Kv channels of the Kv1 family which generate sustained K current and some

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