Genomic organization of the KTX2 gene, encoding a `short' scorpion toxin active on K+ channels

AbstractA single intron of 87 bp, close to the region encoding the C-terminal part of the signal peptide, was found in the gene of the `short' scorpion toxin kaliotoxin 2 of Androctonus australis acting on various types of K+ channels. Its A+T content was particularly high (up to 86%). By walking and ligation-mediated PCR, the promoter sequences of the kaliotoxin 2 gene of Androctonus australis were studied. The transcription unit of the gene is 390 bp long. Consensus sequences were identified. The genes of `short' scorpion toxins active on K+ channels are organized similarly to those of the `long' scorpion toxins active on Na+ channels and not like those of structurally related insect defensins, which are intronless

Functional Properties and Toxin Pharmacology of a Dorsal Root Ganglion Sodium Channel Viewed through its Voltage Sensors

The voltage-activated sodium (Nav) channel Nav1.9 is expressed in dorsal root ganglion (DRG) neurons where it is believed to play an important role in nociception. Progress in revealing the functional properties and pharmacological sensitivities of this non-canonical Nav channel has been slow because attempts to express this channel in a heterologous expression system have been unsuccessful. Here, we use a protein engineering approach to dissect the contributions of the four Nav1.9 voltage sensors to channel function and pharmacology. We define individual S3b–S4 paddle motifs within each voltage sensor, and show that they can sense changes in membrane voltage and drive voltage sensor activation when transplanted into voltage-activated potassium channels. We also find that the paddle motifs in Nav1.9 are targeted by animal toxins, and that these toxins alter Nav1.9-mediated currents in DRG neurons. Our results demonstrate that slowly activating and inactivating Nav1.9 channels have functional and pharmacological properties in common with canonical Nav channels, but also show distinctive pharmacological sensitivities that can potentially be exploited for developing novel treatments for pain

Toxines et Transferts ioniques

Collection Rencontres en Toxinologie, ISSN 1760-6004 ; http://sfet.asso.fr/international/images/stories/SFET/pdf/Ebook-RT19-2011-signets.pdfInternational audienc

A new class of scorpion toxin binding sites related to an A-type K+ channel: pharmacological characterization and localization in rat brain

AbstractA new scorpion toxin (3751.8 Da) was isolated from the Buthus martensi venom, sequenced and chemically synthesized (sBmTX3). The A-type current of striatum neurons in culture completely disappeared when 1 μM sBmTX3 was applied (Kd=54 nM), whereas the sustained K+ current was unaffected. 125I-sBmTX3 specifically bound to rat brain synaptosomes (maximum binding=14 fmol mg−1 of protein, Kd=0.21 nM). A panel of toxins yet described as specific ligands for K+ channels were unable to compete with 125I-sBmTX3. A high density of 125I-sBmTX3 binding sites was found in the striatum, hippocampus, superior colliculus, and cerebellum in the adult rat brain

La diversité des toxines de scorpions et leur intérêt dans la recherche biologique et pharmacologique ((purification et caractérisation chimique, pharmacologique et immunologique des toxines de scorpion présentant des problèmes de santé publique au Moyen Orient et leurs implications pharmacologiques))

Les scorpions du genre Androctonus, comme Androctonus australis en Algérie et en Tunisieou Androctonus mauretanicus au Maroc, sont responsables d environ 100.000 piqûres par ansur l ensemble du Maghreb, suivies de 1 % de décès. Ils posent un réel problème de santépublique. Les toxines alpha modulant les canaux sodium voltage-activés (Nav) sontresponsables de 80 à 90% de l activité létale des venins d Androctonus australis etmauretanicus. Cependant, certaines petites molécules sont aussi capables de bloquer lefonctionnement d autres types de canaux ioniques, en particulier des canaux potassiumvoltage-activés (Kv).Au cours de cette thèse, nous avons isolé et caractérisé les composants du venind Androctonus amoreuxi, scorpion largement distribué en Afrique du Nord et au Moyen-Orient, mais qui n avait jusqu ici fait l objet d aucune etude rigoureuse. Nous avons identifiéles constituants impliqués dans la toxicité du venin et précisé leurs propriétéspharmacologiques et immunologiques, ainsi que l effet qu elles induisent enélectrophysiologie sur des canaux Nav et Kv clonés exprimés dans l ovocyte de Xenope.Nous avons recherché de nouveaux membres d une famille de toxines récemment isolées, lesBirtoxines-like, et interprété leur polymorphisme biologique par la modélisation de leursstructures 3D. Enfin, nous avons mené à bien un programme portant sur les effetsantinociceptifs des toxines de scorpion chez la souris. Cela nous a permis de proposer uneexplication qui fait intervenir le système opiacé et la contre-irritation . L effet des toxinesreconnues analgésiques a ensuite été testé en électrophysiologie sur des neuronesnocicepteurs.The North African scorpion Androctonus australis in Algeria and Tunisia, or Androctonusmauretanicus in Morocco, are responsible of about 100.000 stings each year in Maghreb,followed by 1% of death. Small toxins modulating voltage-gated sodium channels (Nav),named alpha , are responsible of 80 to 90% of the total lethal activity from the Androctonusaustralis and mauretanicus venoms. However, smaller molecules are also able to block thefunctioning of another type of ionic channels, in particular, the voltage-gated potassiumchannels (Kv).During this thesis, we have isolated and characterized the compounds of the venom fromAndroctonus amoreuxi, a scorpion widely found in North Africa and Middle East, but neverseriously studied so far. We have identified the constituents implicated in the toxicity anddefined their immunological and pharmacological properties, as well as theirelectrophysiological effects on cloned Nav and Kv channels expressed in Xenopus oocytes.We also have looked for recently characterized new molecules, the Birtoxins-like, and tried toexplain their large biological polymorphism by 3D structural models. At last, we haveevaluated the antinociceptifs effects of scorpion toxins in mice. We have proposed that theantalgic effects observed after administration of scorpion toxins are partly due to a counterirritation phenomenon, which implicates the activation of an endogenous opioid system. The analgesic toxins have been further tested in electrophysiology on DRG neurons.AIX-MARSEILLE2-Bib.electronique (130559901) / SudocSudocFranceF

Caractérisation pharmacologique d'un courant potassium de type A bloqué par une nouvelle famille de toxines de scorpions

Ces travaux de thèse ont permis d'identifier une nouvelle sous-famille (appelée a-KTx15) de toxines de scorpions, actives sur le courant K+ de type A des neurones de striatum en culture. Ces toxines, BmTX3 (du scorpion Buthus martensii Karch), et AmmTX3 (du scorpion Androctonus mauritanicus), sont sélectives et possèdent une très haute affinité pour leur cible, qu'elles inhibent par occlusion du pore. La distribution de leur cible dans le cerveau de rat est très hétérogène avec peu de régions présentant de fortes densités: le caudete putamen, les cellules en grain de cervelet, l'hippocampe, le colliculus supérieur et le thalamus. Lors de l'ontogénèse, ce canal cible garde la même distribution, seule sa densité évolue nettement. Ce canal est aussi présent dans le coeur de rat adulte au niveau des noeuds sinoauriculaire et auriculoventriculaire. A ce jour, il est certain que ce canal cible ne correspond pas aux canaux K+, Kv1.4 et Kv3.4, mais semble s'apparenter aux canaux Kv4AIX-MARSEILLE2-BU Méd/Odontol. (130552103) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

The myth of scorpion suicide: are scorpions insensitive to their own venom?

International audienceThe resistance of the scorpion Androctonus australis to its own venom, as well as to the venom of other species, was investigated. A comparison of the electrical and pharmacological properties of muscle and nerve fibres from Androctonus australis with those from the crayfish Procambarus clarkii enabled us to understand the lack of effect of scorpion venom (110-180 microg ml-1) and purified toxins, which are active on voltage-gated Na+ and K+ channels, Ca2+-activated K+ channels, on scorpion tissues. Voltage-clamp experiments showed that peptide K+ channel blockers from scorpion and snake have no effect on currents in muscle and nerve fibres from either scorpions or crayfish. The scorpion toxin kaliotoxin (KTX), a specific blocker of Kv1.1 and Kv1.3 K+ channels, had no effect on muscle fibres of A. australis (2 micromol l-1) or P. clarkii (400 nmol l-1). Similarly, charybdotoxin (ChTX) had no effect on the muscle fibres of A. australis (10 micromol l-1) or P. clarkii (200 nmol l-1) and neither did the snake toxin dendrotoxin (DTX) at concentrations of 100 nmol l-1 in A. australis and 200 nmol l-1 in P. clarkii. These three toxins (KTX, ChTX and DTX) did not block K+ currents recorded from nerve fibres in P. clarkii. The pharmacology of the K+ channels in these two arthropods did not conform to that previously described for K+ channels in other species. Current-clamp experiments clearly indicated that the venom of A. australis (50 microg ml-1) had no effect on the shape of the action potential recorded from nerve cord axons from A. australis. At a concentration of 50 microg ml-1, A. australis venom greatly prolonged the action potential in the crayfish giant axon. The absence of any effect of the anti-mammal -toxin AaH II (100 nmol l-1) and the anti-insect toxin AaH IT1 (100 nmol l-1) on scorpion nerve fibres revealed strong pharmacological differences between the voltage-gated Na+ channels of scorpion and crayfish. We conclude that the venom from A. australis is pharmacologically inactive on K+ channels and on voltage-sensitive Na+ channels from this scorpion