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Mlayah-Bellalouna S, Dufour M, Mabrouk K, Mejdoub H, Carlier E, Othman H, Belghazi M, Tarbe M, Goaillard JM, Gigmes D, Seagar M, El Ayeb M, Debanne D, Srairi-Abid N. AaTX1, from Androctonus australis scorpion venom: purification, synthesis and characterization in dopaminergic neurons. Toxicon 2014; 92:14-23. [PMID: 25240295 DOI: 10.1016/j.toxicon.2014.09.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Revised: 07/21/2014] [Accepted: 09/09/2014] [Indexed: 10/24/2022]
Abstract
We have purified the AaTX1 peptide from the Androctonus australis (Aa) scorpion venom, previously cloned and sequenced by Legros and collaborators in a venom gland cDNA library from Aa scorpion. AaTX1 belongs to the α-Ktx15 scorpion toxins family (αKTx15-4). Characterized members of this family share high sequence similarity and were found to block preferentially IA-type voltage-dependent K(+) currents in rat cerebellum granular cells in an irreversible way. In the current work, we studied the effects of native AaTX1 (nAaTX1) using whole-cell patch-clamp recordings of IA current in substantia nigra pars compacta dopaminergic neurons. At 250 nM, AaTX1 induces 90% decrease in IA current amplitude. Its activity was found to be comparable to that of rAmmTX3 (αKTx15-3), which differs by only one conserved (R/K) amino acid in the 19th position suggesting that the difference between R19 and K19 in AaTX1 and AmmTX3, respectively, may not be critical for the toxins' effects. Molecular docking of both toxins with Kv4.3 channel is in agreement with experimental data and suggests the implication of the functional dyade K27-Y36 in toxin-channel interactions. Since AaTX1 is not highly abundant in Aa venom, it was synthesized as well as AmmTX3. Synthetic peptides, native AaTX1 and rAmmTX3 peptides showed qualitatively the same pharmacological activity. Overall, these data identify a new biologically active toxin that belongs to a family of peptides active on Kv4.3 channel.
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Affiliation(s)
- Saoussen Mlayah-Bellalouna
- Institut Pasteur de Tunis, Laboratoire des Venins et biomolécules thérapeutiques LR11IPT08, Tunis 1002, Tunisia
| | - Martial Dufour
- INSERM UMR_S 1072, Unité de Neurobiologie des canaux Ioniques et de la Synapse (UNIS), Faculté de Médecine - Secteur Nord, Aix Marseille Université, 51, Bd Pierre Dramard, 13015 Marseille, France
| | - Kamel Mabrouk
- Aix Marseille Université, Institut de Chimie Radicalaire ICR, UMR 7273, Equipe CROPS, Site St Jérôme, Avenue Escadrille Normandie Niémen, Case 542, 13397 Marseille Cedex 20, France
| | - Hafedh Mejdoub
- USCR séquenceur de protéines, faculté des sciences de Sfax, Route de Soukra, Km 3.5, BP 1171, 3000 Sfax, Tunisia
| | - Edmond Carlier
- INSERM UMR_S 1072, Unité de Neurobiologie des canaux Ioniques et de la Synapse (UNIS), Faculté de Médecine - Secteur Nord, Aix Marseille Université, 51, Bd Pierre Dramard, 13015 Marseille, France
| | - Houcemeddine Othman
- Institut Pasteur de Tunis, Laboratoire des Venins et biomolécules thérapeutiques LR11IPT08, Tunis 1002, Tunisia
| | - Maya Belghazi
- CRN2M UMR 7286, Plate Forme de Recherche en Neurosciences - CAPM, Faculté de Médecine-secteur Nord Aix Marseille Université, 51 bd Pierre Dramard, 13015 Marseille, France
| | - Marion Tarbe
- Aix Marseille Université, Institut de Chimie Radicalaire ICR, UMR 7273, Equipe CROPS, Site St Jérôme, Avenue Escadrille Normandie Niémen, Case 542, 13397 Marseille Cedex 20, France
| | - Jean Marc Goaillard
- INSERM UMR_S 1072, Unité de Neurobiologie des canaux Ioniques et de la Synapse (UNIS), Faculté de Médecine - Secteur Nord, Aix Marseille Université, 51, Bd Pierre Dramard, 13015 Marseille, France
| | - Didier Gigmes
- Aix Marseille Université, Institut de Chimie Radicalaire ICR, UMR 7273, Equipe CROPS, Site St Jérôme, Avenue Escadrille Normandie Niémen, Case 542, 13397 Marseille Cedex 20, France
| | - Michael Seagar
- INSERM UMR_S 1072, Unité de Neurobiologie des canaux Ioniques et de la Synapse (UNIS), Faculté de Médecine - Secteur Nord, Aix Marseille Université, 51, Bd Pierre Dramard, 13015 Marseille, France
| | - Mohamed El Ayeb
- Institut Pasteur de Tunis, Laboratoire des Venins et biomolécules thérapeutiques LR11IPT08, Tunis 1002, Tunisia
| | - Dominique Debanne
- INSERM UMR_S 1072, Unité de Neurobiologie des canaux Ioniques et de la Synapse (UNIS), Faculté de Médecine - Secteur Nord, Aix Marseille Université, 51, Bd Pierre Dramard, 13015 Marseille, France
| | - Najet Srairi-Abid
- Institut Pasteur de Tunis, Laboratoire des Venins et biomolécules thérapeutiques LR11IPT08, Tunis 1002, Tunisia.
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Abstract
The cAMP fluorescent probe FlCRhR was used to monitor changes in intracellular cAMP concentration ([cAMP]i) in isolated frog ventricular myocytes. The probe was introduced into the cell through a patch pipette which allowed simultaneous recording of the whole-cell L-type Ca2+ current (ICa). Ratiometric imaging was used to monitor [cAMP]i changes in response to the beta-adrenergic agonist isoprenaline (ISO) or to the direct adenylyl cyclase activator forskolin (FSK). FlCRhR fluorescence was distributed in the cytosol in a striated pattern, with high fluorescence in the I-bands and low fluorescence in the A-bands. This pattern of distribution was mimicked by fluorescein dextran, another high molecular weight fluorescent molecule, and was therefore likely to be due to anisotropic diffusion of the probe in the cytosol due to the hindrance generated by sarcomeric proteins in the A-bands. Introduction of FlCRhR into the cell induced a small approximately 70% stimulatory effect on basal ICa, attenuating about 2-fold a subsequent response of ICa to 1-10 microM ISO (from 400 to 200%). Brief (10 s) application of a saturating concentration of ISO (1-20 microM) to the cell induced a transient increase in both ICa and [cAMP]i. However, the [cAMP]i transient was approximately 2-fold shorter in duration than the ICa transient, i.e. ICa was still strongly enhanced when [cAMP]i had already returned to control level. This indicates that hydrolysis of cAMP by phosphodiesterases is not a rate limiting step in the recovery of ICa from ISO stimulation. When the application of ISO was maintained, ICa and [cAMP]i responses followed a similar time course, with a half-maximal response at approximately 60 s. This suggests that activation of Ca2+ channels by cAMP-dependent protein kinase occurs on a much faster time scale than the rise in [cAMP]i. When the cells were exposed to FSK (13 microM), both responses of ICa and [cAMP]i were approximately 2-fold slower than with ISO. This demonstrates that the slower response of ICa to FSK is due to a slower rise in [cAMP]i rather than to some inhibitory effect of FSK on ICa or to a direct or priming effect of the stimulatory G protein Gs on Ca2+ channels. Simultaneous measurements of [cAMP]i and ICa changes in intact cardiac myocytes opens the way to dissect the temporal sequence of events in the cAMP cascade mediating the response of the heart to a large number of hormones and inotropic agents.
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Affiliation(s)
- J M Goaillard
- Laboratoire de Neurobiologie Cellulaire, CNRS UMR7624, Universite Paris VI, F-75005 Paris, France
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