title: Definition of the alpha-KTx15 subfamily.
abstract: Three novel scorpion toxins, Aa1 from Androctonus australis, BmTX3 from Buthus martensi and AmmTX3 from Androctonus mauretanicus were shown able to selectively block A-type K+ currents in cerebellum granular cells or cultured striatum neurons from rat brain. In electrophysiology experiments, the transient A-current completely disappeared when 1 microM of the toxins was applied to the external solution whereas the sustained K+ current was unaffected. The three toxins shared high sequence homologies (more than 94%) and constituted a new 'short-chain' scorpion toxin subfamily: alpha-KTx15. Monoiododerivative of 125I-sBmTX3 specifically bound to rat brain synaptosomes. Under equilibrium binding conditions, maximum binding was 14 fmol/mg of protein and the dissociation constant (Kd) was 0.21 nM. This Kd value was confirmed by kinetic experiments (kon = 6.0 x 10(6) M(-1) s(-1) and koff = 6.0 x 10(-4) s(-1)). Competitions with AmmTX3 and Aa1 with 125I-sBmTX3 bound to its receptor on rat brain synaptosomes showed that they fully inhibited the 125I-sBmTX3 binding (Ki values of 20 and 44 pM, respectively), demonstrating unambiguously that the three molecules shared the same target in rat brain. A panel of toxins described as specific ligands for different K+, Na+ and Ca2+ channels were not able to displace 125I-sBmTX3 from its binding site. Thus, 125I-sBmTX3 is a new ligand for a still unidentified target in rat brain. In autoradiography, the distribution of 125I-sBmTX3 binding sites in the adult rat brain indicated a high density of 125I-sBmTX3 receptors in the striatum, hippocampus, superior colliculus, and cerebellum.
authors.affiliation: CNRS UMR 6560, Institut Federatif de Recherche Jean Roche, Faculté de Médecine Nord, Université de la Méditerranée, Bd Pierre Dramard, 13916 Marseille cedex 20, France.
authors.forename: Hélène
authors.initials: H
authors.lastname: Vacher
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Prestipino
authors.forename: Marcel
authors.initials: M
authors.lastname: Crest
authors.forename: Marie France
authors.initials: MF
authors.lastname: Martin-Eauclaire
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D007457:Iodine Radioisotopes / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D008969:Molecular Sequence Data; D009474:Neurons / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism*; D012604:Scorpion Venoms / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D012605:Scorpions / Q000737:chemistry*; D016415:Sequence Alignment; D013329:Structure-Activity Relationship; D013574:Synaptosomes / Q000378:metabolism
chemical_list: C471416:AmmTX3 protein, Androctonus mauretanicus; D007457:Iodine Radioisotopes; D008024:Ligands; D015221:Potassium Channels; D012604:Scorpion Venoms; C418406:TX3 toxin, Buthus martensii