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Novel long-chain neurotoxins from Bungarus candidus distinguish the two binding sites in muscle-type nicotinic acetylcholine receptors. Biochem J 2019; 476:1285-1302. [PMID: 30944155 DOI: 10.1042/bcj20180909] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2018] [Revised: 03/16/2019] [Accepted: 04/03/2019] [Indexed: 12/30/2022]
Abstract
αδ-Bungarotoxins, a novel group of long-chain α-neurotoxins, manifest different affinity to two agonist/competitive antagonist binding sites of muscle-type nicotinic acetylcholine receptors (nAChRs), being more active at the interface of α-δ subunits. Three isoforms (αδ-BgTx-1-3) were identified in Malayan Krait (Bungarus candidus) from Thailand by genomic DNA analysis; two of them (αδ-BgTx-1 and 2) were isolated from its venom. The toxins comprise 73 amino acid residues and 5 disulfide bridges, being homologous to α-bungarotoxin (α-BgTx), a classical blocker of muscle-type and neuronal α7, α8, and α9α10 nAChRs. The toxicity of αδ-BgTx-1 (LD50 = 0.17-0.28 µg/g mouse, i.p. injection) is essentially as high as that of α-BgTx. In the chick biventer cervicis nerve-muscle preparation, αδ-BgTx-1 completely abolished acetylcholine response, but in contrast with the block by α-BgTx, acetylcholine response was fully reversible by washing. αδ-BgTxs, similar to α-BgTx, bind with high affinity to α7 and muscle-type nAChRs. However, the major difference of αδ-BgTxs from α-BgTx and other naturally occurring α-neurotoxins is that αδ-BgTxs discriminate the two binding sites in the Torpedo californica and mouse muscle nAChRs showing up to two orders of magnitude higher affinity for the α-δ site as compared with α-ε or α-γ binding site interfaces. Molecular modeling and analysis of the literature provided possible explanations for these differences in binding mode; one of the probable reasons being the lower content of positively charged residues in αδ-BgTxs. Thus, αδ-BgTxs are new tools for studies on nAChRs.
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Zhang S, Gao B, Wang X, Zhu S. Loop Replacement Enhances the Ancestral Antibacterial Function of a Bifunctional Scorpion Toxin. Toxins (Basel) 2018; 10:toxins10060227. [PMID: 29867003 PMCID: PMC6024585 DOI: 10.3390/toxins10060227] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Accepted: 05/31/2018] [Indexed: 01/22/2023] Open
Abstract
On the basis of the evolutionary relationship between scorpion toxins targeting K+ channels (KTxs) and antibacterial defensins (Zhu S., Peigneur S., Gao B., Umetsu Y., Ohki S., Tytgat J. Experimental conversion of a defensin into a neurotoxin: Implications for origin of toxic function. Mol. Biol. Evol. 2014, 31, 546–559), we performed protein engineering experiments to modify a bifunctional KTx (i.e., weak inhibitory activities on both K+ channels and bacteria) via substituting its carboxyl loop with the structurally equivalent loop of contemporary defensins. As expected, the engineered peptide (named MeuTXKα3-KFGGI) remarkably improved the antibacterial activity, particularly on some Gram-positive bacteria, including several antibiotic-resistant opportunistic pathogens. Compared with the unmodified toxin, its antibacterial spectrum also enlarged. Our work provides a new method to enhance the antibacterial activity of bifunctional scorpion venom peptides, which might be useful in engineering other proteins with an ancestral activity.
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Affiliation(s)
- Shangfei Zhang
- Group of Peptide Biology and Evolution, State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, 1 Beichen West Road, Chaoyang District, Beijing 100101, China.
| | - Bin Gao
- Group of Peptide Biology and Evolution, State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, 1 Beichen West Road, Chaoyang District, Beijing 100101, China.
| | - Xueli Wang
- Group of Peptide Biology and Evolution, State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, 1 Beichen West Road, Chaoyang District, Beijing 100101, China.
| | - Shunyi Zhu
- Group of Peptide Biology and Evolution, State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, 1 Beichen West Road, Chaoyang District, Beijing 100101, China.
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Meng L, Xie Z, Zhang Q, Li Y, Yang F, Chen Z, Li W, Cao Z, Wu Y. Scorpion Potassium Channel-blocking Defensin Highlights a Functional Link with Neurotoxin. J Biol Chem 2016; 291:7097-106. [PMID: 26817841 DOI: 10.1074/jbc.m115.680611] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2015] [Indexed: 01/01/2023] Open
Abstract
The structural similarity between defensins and scorpion neurotoxins suggests that they might have evolved from a common ancestor. However, there is no direct experimental evidence demonstrating a functional link between scorpion neurotoxins and defensins. The scorpion defensin BmKDfsin4 from Mesobuthus martensiiKarsch contains 37 amino acid residues and a conserved cystine-stabilized α/β structural fold. The recombinant BmKDfsin4, a classical defensin, has been found to have inhibitory activity against Gram-positive bacteria such as Staphylococcus aureus, Bacillus subtilis, and Micrococcus luteusas well as methicillin-resistant Staphylococcus aureus Interestingly, electrophysiological experiments showed that BmKDfsin4,like scorpion potassium channel neurotoxins, could effectively inhibit Kv1.1, Kv1.2, and Kv1.3 channel currents, and its IC50value for the Kv1.3 channel was 510.2 nm Similar to the structure-function relationships of classical scorpion potassium channel-blocking toxins, basic residues (Lys-13 and Arg-19) of BmKDfsin4 play critical roles in peptide-Kv1.3 channel interactions. Furthermore, mutagenesis and electrophysiological experiments demonstrated that the channel extracellular pore region is the binding site of BmKDfsin4, indicating that BmKDfsin4 adopts the same mechanism for blocking potassium channel currents as classical scorpion toxins. Taken together, our work identifies scorpion BmKDfsin4 as the first invertebrate defensin to block potassium channels. These findings not only demonstrate that defensins from invertebrate animals are a novel type of potassium channel blockers but also provide evidence of a functional link between defensins and neurotoxins.
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Affiliation(s)
- Lanxia Meng
- From the State Key Laboratory of Virology, College of Life Sciences and
| | - Zili Xie
- From the State Key Laboratory of Virology, College of Life Sciences and
| | - Qian Zhang
- From the State Key Laboratory of Virology, College of Life Sciences and
| | - Yang Li
- From the State Key Laboratory of Virology, College of Life Sciences and
| | - Fan Yang
- From the State Key Laboratory of Virology, College of Life Sciences and
| | - Zongyun Chen
- From the State Key Laboratory of Virology, College of Life Sciences and
| | - Wenxin Li
- From the State Key Laboratory of Virology, College of Life Sciences and Center for BioDrug Research, Wuhan University, Wuhan 430072, China
| | - Zhijian Cao
- From the State Key Laboratory of Virology, College of Life Sciences and Center for BioDrug Research, Wuhan University, Wuhan 430072, China
| | - Yingliang Wu
- From the State Key Laboratory of Virology, College of Life Sciences and Center for BioDrug Research, Wuhan University, Wuhan 430072, China
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Martin-Eauclaire MF, Bosmans F, Céard B, Diochot S, Bougis PE. A first exploration of the venom of the Buthus occitanus scorpion found in southern France. Toxicon 2014; 79:55-63. [PMID: 24418174 DOI: 10.1016/j.toxicon.2014.01.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Revised: 12/20/2013] [Accepted: 01/01/2014] [Indexed: 11/28/2022]
Abstract
Even though Buthus occitanus scorpions are found throughout the Mediterranean region, a lack of distinctive characteristics has hampered their classification into different subspecies. Yet, stings from this particular scorpion family are reported each year to result in pain followed by various toxic symptoms. In order to determine the toxicity origin of the rare French B. occitanus Amoreux scorpion, we collected several specimens and studied their venom composition using a nano ultra high performance liquid chromatography and matrix assisted laser desorption/ionisation time-of-flight mass spectrometry (nano UHPLC/MALDI-TOF-MS) automated workflow combined with an enzyme-linked immunosorbent assay (ELISA) approach. Moreover, we compared this dataset to that obtained from highly lethal Androctonus australis and Androctonus mauretanicus scorpions collected in North Africa. As a result, we found that the B. occitanus Amoreux venom is toxic to mice, an observation that is most likely caused by venom components that inhibit voltage-gated sodium channel inactivation. Moreover, we identified similarities in venom composition between B. occitanus scorpions living in the South of France and other Buthidae collected in Morocco and Algeria. As such, the results of this study should be taken into consideration when treating stings from the B. occitanus species living in the South of France.
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Affiliation(s)
- Marie-France Martin-Eauclaire
- Aix Marseille Université, CNRS, CRN2M UMR7286, Faculté de Médecine, Campus Nord, CS80011, Bd Pierre Dramard, F-13344 Marseille Cedex 15, 13015 Marseille, France
| | - Frank Bosmans
- Department of Physiology, Johns Hopkins University-School of Medicine, Baltimore, MD 21205, USA; Solomon H. Snyder Department of Neuroscience, Johns Hopkins University-School of Medicine, Baltimore, MD 21205, USA
| | - Brigitte Céard
- Aix Marseille Université, CNRS, CRN2M UMR7286, Faculté de Médecine, Campus Nord, CS80011, Bd Pierre Dramard, F-13344 Marseille Cedex 15, 13015 Marseille, France
| | - Sylvie Diochot
- CNRS, IPMC UMR 6097, 06560, Sophia-Antipolis, Valbonne, France
| | - Pierre E Bougis
- Aix Marseille Université, CNRS, CRN2M UMR7286, Faculté de Médecine, Campus Nord, CS80011, Bd Pierre Dramard, F-13344 Marseille Cedex 15, 13015 Marseille, France.
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Characterization of the first K+ channel blockers from the venom of the Moroccan scorpion Buthus occitanus Paris. Toxicon 2013; 75:168-76. [DOI: 10.1016/j.toxicon.2013.03.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Revised: 02/27/2013] [Accepted: 03/06/2013] [Indexed: 11/22/2022]
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Martin-Eauclaire MF, Granjeaud S, Belghazi M, Bougis PE. Achieving automated scorpion venom mass fingerprinting (VMF) in the nanogram range. Toxicon 2013; 69:211-8. [DOI: 10.1016/j.toxicon.2013.03.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2012] [Revised: 02/11/2013] [Accepted: 03/01/2013] [Indexed: 10/27/2022]
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Bergeron ZL, Bingham JP. Scorpion toxins specific for potassium (K+) channels: a historical overview of peptide bioengineering. Toxins (Basel) 2012. [PMID: 23202307 PMCID: PMC3509699 DOI: 10.3390/toxins4111082] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Scorpion toxins have been central to the investigation and understanding of the physiological role of potassium (K+) channels and their expansive function in membrane biophysics. As highly specific probes, toxins have revealed a great deal about channel structure and the correlation between mutations, altered regulation and a number of human pathologies. Radio- and fluorescently-labeled toxin isoforms have contributed to localization studies of channel subtypes in expressing cells, and have been further used in competitive displacement assays for the identification of additional novel ligands for use in research and medicine. Chimeric toxins have been designed from multiple peptide scaffolds to probe channel isoform specificity, while advanced epitope chimerization has aided in the development of novel molecular therapeutics. Peptide backbone cyclization has been utilized to enhance therapeutic efficiency by augmenting serum stability and toxin half-life in vivo as a number of K+-channel isoforms have been identified with essential roles in disease states ranging from HIV, T-cell mediated autoimmune disease and hypertension to various cardiac arrhythmias and Malaria. Bioengineered scorpion toxins have been monumental to the evolution of channel science, and are now serving as templates for the development of invaluable experimental molecular therapeutics.
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Affiliation(s)
- Zachary L Bergeron
- Department of Molecular Biosciences and Bioengineering, College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa, Honolulu, HI 96822, USA.
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Potassium Channels Blockers from the Venom of Androctonus mauretanicus mauretanicus. J Toxicol 2012; 2012:103608. [PMID: 22685457 PMCID: PMC3362950 DOI: 10.1155/2012/103608] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2012] [Accepted: 03/16/2012] [Indexed: 01/09/2023] Open
Abstract
K+ channels selectively transport K+ ions across cell membranes and play a key role in regulating the physiology of excitable and nonexcitable cells. Their activation allows the cell to repolarize after action potential firing and reduces excitability, whereas channel inhibition increases excitability. In eukaryotes, the pharmacology and pore topology of several structural classes of K+ channels have been well characterized in the past two decades. This information has come about through the extensive use of scorpion toxins. We have participated in the isolation and in the characterization of several structurally distinct families of scorpion toxin peptides exhibiting different K+ channel blocking functions. In particular, the venom from the Moroccan scorpion Androctonus mauretanicus mauretanicus provided several high-affinity blockers selective for diverse K+ channels (SKCa, Kv4.x, and Kv1.x K+ channel families). In this paper, we summarize our work on these toxin/channel interactions.
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Dai H, Yin S, Li T, Cao Z, Ji Y, Wu Y, Li W. Recombinant expression, purification, and characterization of scorpion toxin BmαTX14. Protein Expr Purif 2012; 82:325-31. [PMID: 22343065 DOI: 10.1016/j.pep.2012.02.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2011] [Revised: 02/01/2012] [Accepted: 02/02/2012] [Indexed: 12/19/2022]
Abstract
Long-chain and cysteine-rich scorpion toxins exhibit various pharmacological profiles for different voltage-gated sodium channel subtypes. However, the exploration of toxin structure-function relationships has progressed slowly due to the difficulty of obtaining synthetic or recombinant peptides. We now report that we have established an effective expression and purification approach for the novel scorpion toxin BmαTX14. BmαTX14 was over-expressed as inclusion bodies in Escherichia coli. The insoluble pellet was successfully transformed into active peptide by using a refolding procedure. One-step purification by reverse-phase HPLC was sufficient to generate chromatographically pure peptide. The yield of recombinant toxin reached 4mg from 1L LB medium. The pharmacological data further showed that BmαTX14 selectively inhibited the fast inactivation of mNa(v)1.4 (EC(50)=82.3±15.7nM) rather than that of rNa(v)1.2 (EC(50)>30μM), which indicates that BmαTX14 is a new α-like toxin. This work enables further structural, functional, and pharmacological studies of BmαTX14 and similar toxins.
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Affiliation(s)
- Hui Dai
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, PR China
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Abbas N, Rosso JP, Céard B, Belghazi M, Lebrun R, Bougis PE, Martin-Eauclaire MF. Characterization of three "Birtoxin-like" toxins from the Androctonus amoreuxi scorpion venom. Peptides 2011; 32:911-9. [PMID: 21335045 DOI: 10.1016/j.peptides.2011.02.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2010] [Revised: 02/07/2011] [Accepted: 02/09/2011] [Indexed: 12/19/2022]
Abstract
The venom of the North African scorpion Androctonus amoreuxi (Aam) was analyzed using a combination of gel filtration, C18 reverse phase HPLC together with mass spectrometry analysis and bioassays. Three novel Birtoxin-like (BTX-L) peptides of 58 amino acid residues comprising three disulfide bridges were isolated and chemically characterized. One peptide, AamBTX-L3, induced serious toxic symptoms in mice and was lethal at nanogram quantities using intracerebroventricular injection. The three BTX-L peptides were tested in competition experiments on rat brain synaptosomes against the (125)I-labeled "classical" α- and β-toxins of reference, as well as with the (125)I-KTX, a voltage-gated potassium channel blocker. Only AamBTX-L3 was able to prevent the equilibrium binding of the β-toxin (125)I-Css IV to its receptor site 4 with a IC(50) value of 189 nM. Even if previous electrophysiological data allowed the classification of other BTX-L peptides among the β-type toxins, this report clearly shows that AamBTX-L3 is pharmacologically a β-toxin, which recognizes the voltage-gated Na(+) (Na(v)) channels from central mammalian neurons. In order to uncover the residues functionally essential for interaction between the AamBTX-L3 with the putative receptor site of (125)I-Css IV on Na(v)1.2, molecular models of the three novel Aam BTX-L molecules were made and their surfaces were compared to the already described Css IV biologically interactive surfaces. A hypothesis is given that in BTX-L3, three residues found in the α-helix play a key role during target binding.
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Affiliation(s)
- Najwa Abbas
- CNRS UMR6231, CRN2M, Université de la Méditerranée, Faculté de Médecine secteur Nord, CS80011, Bd Pierre Dramard, F-13344 Marseille Cedex 15, France
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Zhu S, Gao B, Aumelas A, del Carmen Rodríguez M, Lanz-Mendoza H, Peigneur S, Diego-Garcia E, Martin-Eauclaire MF, Tytgat J, Possani LD. MeuTXKβ1, a scorpion venom-derived two-domain potassium channel toxin-like peptide with cytolytic activity. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2010; 1804:872-83. [DOI: 10.1016/j.bbapap.2009.12.017] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2009] [Revised: 12/22/2009] [Accepted: 12/23/2009] [Indexed: 11/24/2022]
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Pentelute BL, Mandal K, Gates ZP, Sawaya MR, Yeates TO, Kent SBH. Total chemical synthesis and X-ray structure of kaliotoxin by racemic protein crystallography. Chem Commun (Camb) 2010; 46:8174-6. [DOI: 10.1039/c0cc03148h] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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13
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Legros C, Guette C, Martin-Eauclaire MF, Goyffon M, Tortajada J. Affinity capture using chimeric membrane proteins bound to magnetic beads for rapid ligand screening by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2009; 23:745-755. [PMID: 19204930 DOI: 10.1002/rcm.3939] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
The rapid and specific detection of therapeutically important ligands in complex mixtures, that may bind to membrane proteins, remains challenging for many research laboratories and pharmaceutical industries. Through its use in the development of screening assays, mass spectrometry (MS) is currently experiencing a period of tremendous expansion. In the study presented here, we took advantage of the remarkable stability properties of a bacterial membrane protein, the KcsA K+ channel, produced in E. coli and purified as a tetrameric protein in the presence of a detergent. This membrane protein can subserve as a molecular template to display the pore-forming region of human K+ channels, which are considered as targets in the search for inhibitory ligands. The engineered chimeric proteins were linked to metal-bound magnetic beads, for the screening of complex peptide mixtures, such as that of scorpion venoms. The affinity-captured scorpion toxins were eluted prior to matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS), and to nano-electrospray ionization tandem mass QqTOF mass spectrometry (MS/MS) analysis. The de novo sequence of the toxins was deduced by combining the MS/MS fragmentation of the reduced form (up to the 33 first residues) and the trypsin digest peptides of the native toxins. This affinity-capture screening assay led to the isolation and characterization of potent and specific ligands of the human K+ channel, Kv1.3. The affinity-capture procedure is fast and reproducible. When linked to magnetic beads, the chimeric membrane protein can be re-used several times without losing any of its selectivity or specificity. This assay also benefits from the fact that it requires minimal amounts of animal venoms or complex mixtures, which can be expensive or difficult to procure.
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Affiliation(s)
- Christian Legros
- Laboratoire Analyse et Modélisation pour la Biologie et l'Environnement (LAMBE), Université d'Evry Val d'Essonne, CNRS UMR 8587, Bd F. Mitterrand, 91025 Evry, France.
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Abbas N, Belghazi M, Abdel-Mottaleb Y, Tytgat J, Bougis PE, Martin-Eauclaire MF. A new Kaliotoxin selective towards Kv1.3 and Kv1.2 but not Kv1.1 channels expressed in oocytes. Biochem Biophys Res Commun 2008; 376:525-30. [DOI: 10.1016/j.bbrc.2008.09.033] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2008] [Accepted: 09/05/2008] [Indexed: 01/02/2023]
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New analysis of the toxic compounds from the Androctonus mauretanicus mauretanicus scorpion venom. Toxicon 2008; 51:835-52. [DOI: 10.1016/j.toxicon.2007.12.012] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2007] [Revised: 12/10/2007] [Accepted: 12/14/2007] [Indexed: 11/23/2022]
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16
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Legros C, Martin-Eauclaire MF, Pongs O, Bougis PE. Toxin binding to chimeric K+ channels immobilised on a solid nitrocellulose support. Biochem Biophys Res Commun 2006; 353:1086-90. [PMID: 17198678 DOI: 10.1016/j.bbrc.2006.12.156] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2006] [Accepted: 12/20/2006] [Indexed: 09/30/2022]
Abstract
In this work, we used a panel prokaryote/eukaryote K+ channel chimeras to generate K+ channel arrays. Their behaviour in solution was compared with that when spotted on a nitrocellulose-supported film and their responses to selective high affinity ligands, including polypeptide toxins and TEA, were studied.
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Affiliation(s)
- Christian Legros
- ZMNH, Universität Hamburg, Zentrum für Molekulare Neurobiologie, Institut für Neurale Signalverarbeitung, Falkenried 94, 20251 Hamburg, Germany
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Martin-Eauclaire MF, Ceard B, Bosmans F, Rosso JP, Tytgat J, Bougis PE. New “Birtoxin analogs” from Androctonus australis venom. Biochem Biophys Res Commun 2005; 333:524-30. [PMID: 15963953 DOI: 10.1016/j.bbrc.2005.05.148] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2005] [Accepted: 05/23/2005] [Indexed: 11/16/2022]
Abstract
From the venom of the scorpion Androctonus australis, we have isolated a new bioactive polypeptide termed AaBTX-L1. When tested on the insect voltage-gated Na(+) channel (para) of the fruit fly, this toxin was able to induce a clear shift in activation (V(1/2)), resulting in the opening of the channel at more negative membrane potentials. Furthermore, AaBTX-L1 was totally devoid of toxicity when injected into mice intracerebroventricularly and did not compete with radiolabeled voltage-gated K(+) and Na(+) channel toxins in binding experiments on rat brain synaptosomes. Using its N-terminal amino acid sequence to design degenerate primers, several clones were amplified by PCR from the A. australis venom gland cDNA library. As a consequence, seven full oligonucleotide sequences encoding "long-chain" polypeptides with only three disulfide bridges have been cloned for the first time and are described here. Remarkably, they share high similarity with the anti-insect toxin Birtoxin from Parabuthus transvaalicus.
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Affiliation(s)
- Marie-France Martin-Eauclaire
- CNRS FRE 2738, Ingénierie des Protéines, Faculté de Médecine secteur Nord, Institut Jean Roche, Université de la Méditerranée, Bd Pierre Dramard, 13916 Marseille 20, France.
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Mouhat S, Visan V, Ananthakrishnan S, Wulff H, Andreotti N, Grissmer S, Darbon H, De Waard M, Sabatier JM. K+ channel types targeted by synthetic OSK1, a toxin from Orthochirus scrobiculosus scorpion venom. Biochem J 2005; 385:95-104. [PMID: 15588251 PMCID: PMC1134677 DOI: 10.1042/bj20041379] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
OSK1 (alpha-KTx3.7) is a 38-residue toxin cross-linked by three disulphide bridges that was initially isolated from the venom of the Asian scorpion Orthochirus scrobiculosus. OSK1 and several structural analogues were produced by solid-phase chemical synthesis, and were tested for lethality in mice and for their efficacy in blocking a series of 14 voltage-gated and Ca2+-activated K+ channels in vitro. In the present paper, we report that OSK1 is lethal in mice by intracerebroventricular injection, with a LD50 (50% lethal dose) value of 2 microg/kg. OSK1 blocks K(v)1.1, K(v)1.2, K(v)1.3 channels potently and K(Ca)3.1 channel moderately, with IC50 values of 0.6, 5.4, 0.014 and 225 nM respectively. Structural analogues of OSK1, in which we mutated positions 16 (Glu16-->Lys) and/or 20 (Lys20-->Asp) to amino acid residues that are conserved in all other members of the alpha-KTx3 toxin family except OSK1, were also produced and tested. Among the OSK1 analogues, [K16,D20]-OSK1 (OSK1 with Glu16-->Lys and Lys20-->Asp mutations) shows an increased potency on K(v)1.3 channel, with an IC50 value of 0.003 nM, without loss of activity on K(Ca)3.1 channel. These data suggest that OSK1 or [K16,D20]-OSK1 could serve as leads for the design and production of new immunosuppressive drugs.
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Affiliation(s)
- Stéphanie Mouhat
- *Laboratoire Cellpep S.A., 13-15 Rue Ledru-Rollin, 13015 Marseille, France
| | - Violeta Visan
- †Universität Ulm, Albert Einstein Allee 11, 89081 Ulm, Germany
| | - S. Ananthakrishnan
- ‡Department of Medical Pharmacology and Toxicology, University of California, Davis, CA 95616, U.S.A
| | - Heike Wulff
- ‡Department of Medical Pharmacology and Toxicology, University of California, Davis, CA 95616, U.S.A
| | - Nicolas Andreotti
- *Laboratoire Cellpep S.A., 13-15 Rue Ledru-Rollin, 13015 Marseille, France
| | | | - Hervé Darbon
- §AFMB, CNRS UPR 9039, 31 Chemin Joseph Aiguier, 13402 Marseille, France
| | - Michel De Waard
- ∥INSERM U607, CEA, 17 Rue des Martyrs, 38054 Grenoble Cedex 09, France
| | - Jean-Marc Sabatier
- *Laboratoire Cellpep S.A., 13-15 Rue Ledru-Rollin, 13015 Marseille, France
- ¶CNRS FRE 2738, Boulevard Pierre Dramard, 13916 Marseille Cedex 20, France
- To whom correspondence should be addressed (email )
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19
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Yu K, Fu W, Liu H, Luo X, Chen KX, Ding J, Shen J, Jiang H. Computational simulations of interactions of scorpion toxins with the voltage-gated potassium ion channel. Biophys J 2005; 86:3542-55. [PMID: 15189853 PMCID: PMC1304258 DOI: 10.1529/biophysj.103.039461] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Based on a homology model of the Kv1.3 potassium channel, the recognitions of the six scorpion toxins, viz. agitoxin2, charybdotoxin, kaliotoxin, margatoxin, noxiustoxin, and Pandinus toxin, to the human Kv1.3 potassium channel have been investigated by using an approach of the Brownian dynamics (BD) simulation integrating molecular dynamics (MD) simulation. Reasonable three-dimensional structures of the toxin-channel complexes have been obtained employing BD simulations and triplet contact analyses. All of the available structures of the six scorpion toxins in the Research Collaboratory for Structural Bioinformatics Protein Data Bank determined by NMR were considered during the simulation, which indicated that the conformations of the toxin significantly affect both the molecular recognition and binding energy between the two proteins. BD simulations predicted that all the six scorpion toxins in this study use their beta-sheets to bind to the extracellular entryway of the Kv1.3 channel, which is in line with the primary clues from the electrostatic interaction calculations and mutagenesis results. Additionally, the electrostatic interaction energies between the toxins and Kv1.3 channel correlate well with the binding affinities (-logK(d)s), R(2) = 0.603, suggesting that the electrostatic interaction is a dominant component for toxin-channel binding specificity. Most importantly, recognition residues and interaction contacts for the binding were identified. Lys-27 or Lys-28, residues Arg-24 or Arg-25 in the separate six toxins, and residues Tyr-400, Asp-402, His-404, Asp-386, and Gly-380 in each subunit of the Kv1.3 potassium channel, are the key residues for the toxin-channel recognitions. This is in agreement with the mutation results. MD simulations lasting 5 ns for the individual proteins and the toxin-channel complexes in a solvated lipid bilayer environment confirmed that the toxins are flexible and the channel is not flexible in the binding. The consistency between the results of the simulations and the experimental data indicated that our three-dimensional models of the toxin-channel complex are reasonable and can be used as a guide for future biological studies, such as the rational design of the blocking agents of the Kv1.3 channel and mutagenesis in both toxins and the Kv1.3 channel. Moreover, the simulation result demonstrates that the electrostatic interaction energies combined with the distribution frequencies from BD simulations might be used as criteria in ranking the binding configuration of a scorpion toxin to the Kv1.3 channel.
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Affiliation(s)
- Kunqian Yu
- Center for Drug Discovery and Design, State Key Laboratory of New Drug Research, Shanghai Institute of Materia Medica, Shanghai, Republic of China
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20
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Bessone R, Martin-Eauclaire MF, Crest M, Mourre C. Heterogeneous competition of Kv1 channel toxins with kaliotoxin for binding in rat brain: autoradiographic analysis. Neurochem Int 2004; 45:1039-47. [PMID: 15337303 DOI: 10.1016/j.neuint.2004.05.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2003] [Accepted: 05/12/2004] [Indexed: 11/24/2022]
Abstract
The alpha-subunits of Kv1 channels display characteristic distributions and restricted co-assembly in mammalian brain. The heterogeneous composition of Kv1 channels has made it difficult to use specific toxins to label brain structures. We used autoradiography to analyse the competitive behaviour of three Kv1 channel toxins--alpha-dendrotoxin, kaliotoxin, and mast cell degranulating peptide--for binding to kaliotoxin binding sites in various brain structures. IC(50) varied considerably between brain regions (by up to three orders of magnitude) for each ligand. alpha-dendrotoxin and kaliotoxin competed equally in some regions and to different extents in others, identifying two types of structure. Mast cell degranulating peptide competed with (125)I-kaliotoxin less efficiently than alpha-dendrotoxin and kaliotoxin, in all regions. Thus, differences in the capacity of these three toxins to bind to kaliotoxin binding sites provide evidence of major differences in the composition of the Kv1 channels constituting the kaliotoxin binding sites.
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Affiliation(s)
- Richard Bessone
- ITIS, CNRS-UMR 6150, IFR Jean Roche, Faculté de Médecine de Marseille, Université de la Méditerranée, Boulevard Pierre Dramard 13916 Marseille, France
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21
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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.
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Affiliation(s)
- Hélène Vacher
- 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
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22
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Vacher H, Martin-Eauclaire MF. Antigenic polymorphism of the "short" scorpion toxins able to block K+ channels. Toxicon 2004; 43:447-53. [PMID: 15051409 DOI: 10.1016/j.toxicon.2004.02.016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2003] [Accepted: 02/10/2004] [Indexed: 11/16/2022]
Abstract
BmTX3 is a toxin recently characterised from the venom of the Chinese scorpion Buthus martensi Karch, which specifically blocks a transient A-type K+ current in striatum neurons in culture and binds to rat brain synaptosomes with high affinity. With Aa1 and AmmTX3, it belongs to the new alpha-KTx15 subfamily from "short-chain" scorpion toxins, which specifically block different types of K+ channels. Here, a highly specific polyclonal antiserum was raised in rabbit against a C-terminal deleted BmTX3 analogue (BmTX-del YP). Using liquid-phase radioimmunoassay, we have studied its selectivity for the toxins from the alpha-KTx15 subfamily. We have also demonstrated that no/or poor cross-reactivity was observed with a panel of "short-chain" scorpion toxins representative of other structurally different subfamilies. These results suggest that a wide antigenic polymorphism, similar to that previously observed for "long-chain" scorpion toxins acting as modulators of voltage-activated Na+ channels, is also the rule for the "short-chain" scorpion toxins able to block K+ channels.
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Affiliation(s)
- Hélène Vacher
- CNRS FRE 2738, Laboratoire de Biochimie, Institut Jean Roche, Faculté de Médecine Nord, Université de la Méditerranée, Boulevard Pierre Dramard, 13916 Marseille cedex 20, France
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23
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M'Barek S, Fajloun Z, Cestèle S, Devaux C, Mansuelle P, Mosbah A, Jouirou B, Mantegazza M, Van Rietschoten J, El Ayeb M, Rochat H, Sabatier JM, Sampieri F. First chemical synthesis of a scorpion α-toxin affecting sodium channels: The Aah I toxin ofAndroctonus australis hector. J Pept Sci 2004; 10:666-77. [PMID: 15568681 DOI: 10.1002/psc.582] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Aah I is a 63-residue alpha-toxin isolated from the venom of the Buthidae scorpion Androctonus australis hector, which is considered to be the most dangerous species. We report here the first chemical synthesis of Aah I by the solid-phase method, using a Fmoc strategy. The synthetic toxin I (sAah I) was renatured in DMSO-Tris buffer, purified and subjected to thorough analysis and comparison with the natural toxin. The sAah I showed physico-chemical (CD spectrum, molecular mass, HPLC elution), biochemical (amino-acid composition, sequence), immunochemical and pharmacological properties similar to those of the natural toxin. The synthetic toxin was recognized by a conformation-dependent monoclonal anti-Aah I antibody, with an IC50 value close to that for the natural toxin. Following intracerebroventricular injection, the synthetic and the natural toxins were similarly lethal to mice. In voltage-clamp experiments, Na(v) 1.2 sodium channel inactivation was inhibited by the application of sAah I or of the natural toxin in a similar way. This work describes a simple protocol for the chemical synthesis of a scorpion alpha-toxin, making it possible to produce structural analogues in time.
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Affiliation(s)
- Sarrah M'Barek
- FRE 2738 CNRS-Université de la Méditerranée, Laboratoire de Biochimie and Laboratoire International Associé d'lngénierie Biomoleculaire, IFR Jean Roche, Faculté de Médecine Nord, Bd Pierre Dramard, 13916 Marseille, France
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24
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Pimenta AMC, Mansuelle P, Diniz CR, Martin-Eauclaire MF. Covalent structure and some pharmacological features of native and cleaved alpha-KTx12-1, a four disulfide-bridged toxin from Tityus serrulatus venom. J Pept Sci 2003; 9:132-40. [PMID: 12630699 DOI: 10.1002/psc.440] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A toxin with four disulfide bridges from Tityus serrulatus venom was able to compete with 125I-kaliotoxin on rat brain synaptosomal preparations, with an IC50 of 46 nM. The obtained amino acid sequence and molecular mass are identical to the previously described butantoxin. Enzymatic cleavages in the native peptide followed by mass spectrometry peptide mapping analysis were used to determine the disulfide bridge pattern of alpha-KTx12-1. Also, after the cleavage of the first six N-terminal residues, including the unusual disulfide bridge which forms an N-terminus ring, the potency of the cleaved peptide was found to decrease about 100 fold compared with the native protein.
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Affiliation(s)
- A M C Pimenta
- Laboratoire de Biochimie, Ingénierle des Protéines, UMR 6560, IFR Jean Roche, Bd Pierre Dramard, 13916 Marseille Cedex 20, France.
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25
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Legros C, Schulze C, Garcia ML, Bougis PE, Martin-Eauclaire MF, Pongs O. Engineering-specific pharmacological binding sites for peptidyl inhibitors of potassium channels into KcsA. Biochemistry 2002; 41:15369-75. [PMID: 12484776 DOI: 10.1021/bi026264a] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The bacterial potassium channel, KcsA, can be modified to express a high-affinity receptor site for the scorpion toxin kaliotoxin (KTX) by substituting subregion I in the P region of KcsA with the one present in the human voltage-gated potassium channel Kv1.3 [Legros, C., Pollmann, V., Knaus, H. G., Farrell, A. M., Darbon, H., Bougis, P. E., Martin-Eauclaire, M. F., and Pongs, O. (2000) J. Biol. Chem. 275, 16918-16924]. This approach opened the way to investigate whether sequence differences in subregion I of Kv1 channels correlate with the distinct pharmacological profiles of peptide inhibitors. A panel of six chimeras between KcsA and human Kv1.1-6 were constructed, expressed in Escherichia coli, purified to homogeneity, and assessed in filter binding assays using either monoiodo-tyrosine-KTX ([(125)I]KTX) or monoiodo-tyrosine-hongotoxin(1)(A19Y/Y37F) ([(125)I]HgTX(1)(A19Y/Y37F)). The KcsA-Kv1.X chimeras were found to have lower affinities for these ligands than the corresponding mammalian Kv1.X channels, indicating that other parts of the channels may contribute to binding or that subtle structural differences exist between these channels. The properties of the KcsA-Kv1.X chimeras were also characterized in surface plasmon resonance experiments. KcsA-Kv1.3 chimeras were immobilized on the surface of a sensor chip for determining, in real time, binding of the peptides. KTX binding properties to immobilized KcsA-Kv1.3 chimera were similar to those determined by filtration techniques. Taken together, our results demonstrate that the pharmacological profile of peptide toxins can be incorporated into KcsA-Kv1.X chimeras containing the subregion I of the corresponding mammalian Kv1.X channels. This innovative approach may facilitate the high-throughput screening of ligand libraries aimed at the discovery of novel potassium channel modulators.
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Affiliation(s)
- Christian Legros
- Institut für Neurale Signalverarbeitung, ZMNH, Universität Hamburg, Martinistrasse 52, D-20246 Hamburg, Germany.
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26
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Vacher H, Alami M, Crest M, Possani LD, Bougis PE, Martin-Eauclaire MF. Expanding the scorpion toxin alpha-KTX 15 family with AmmTX3 from Androctonus mauretanicus. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:6037-41. [PMID: 12473099 DOI: 10.1046/j.1432-1033.2002.03294.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A novel toxin, AmmTX3 (3823.5 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 19.5 pm and 44.2 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 (Kd = 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).
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Affiliation(s)
- Hélène Vacher
- UMR 6560 CNRS and UMR 6150 CNRS, Université de la Méditerranée, Faculté de Médecine secteur Nord, IFR Jean Roche, Marseille, France
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27
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Huys I, Dyason K, Waelkens E, Verdonck F, van Zyl J, du Plessis J, Müller GJ, van der Walt J, Clynen E, Schoofs L, Tytgat J. Purification, characterization and biosynthesis of parabutoxin 3, a component of Parabuthus transvaalicus venom. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:1854-65. [PMID: 11952787 DOI: 10.1046/j.1432-1033.2002.02833.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A novel peptidyl inhibitor of voltage-gated K+ channels, named parabutoxin 3 (PBTx3), has been purified to homogeneity from the venom of Parabuthus transvaalicus. This scorpion toxin contains 37 residues, has a mass of 4274 Da and displays 41% identity with charybdotoxin (ChTx, also called 'alpha-KTx1.1'). PBTx3 is the tenth member (called 'alpha-KTx1.10') of subfamily 1 of K+ channel-blocking peptides known thus far. Electrophysiological experiments using Xenopus laevis oocytes indicate that PBTx3 is an inhibitor of Kv1 channels (Kv1.1, Kv1.2, Kv1.3), but has no detectable effects on Kir-type and ERG-type channels. The dissociation constants (Kd) for Kv1.1, Kv1.2 and Kv1.3 channels are, respectively, 79 microm, 547 nm and 492 nm. A synthetic gene encoding a PBTx3 homologue was designed and expressed as a fusion protein with the maltose-binding protein (MBP) in Escherichia coli. The recombinant protein was purified from the bacterial periplasm compartment using an amylose affinity resin column, followed by a gel filtration purification step and cleavage by factor Xa (fXa) to release the recombinant toxin peptide (rPBTx3). After final purification and refolding, rPBTx3 was shown to be identical to the native PBTx3 with respect to HPLC retention time, mass spectrometric analysis and functional properties. The three-dimensional structure of PBTx3 is proposed by homology modelling to contain a double-stranded antiparallel beta sheet and a single alpha-helix, connected by three disulfide bridges. The scaffold of PBTx3 is homologous to most other alpha-KTx scorpion toxins.
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Affiliation(s)
- Isabelle Huys
- Laboratory of Toxicology, University of Leuven, Leuven, Belgium
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28
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Wicher D, Walther C, Wicher C. Non-synaptic ion channels in insects--basic properties of currents and their modulation in neurons and skeletal muscles. Prog Neurobiol 2001; 64:431-525. [PMID: 11301158 DOI: 10.1016/s0301-0082(00)00066-6] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Insects are favoured objects for studying information processing in restricted neuronal networks, e.g. motor pattern generation or sensory perception. The analysis of the underlying processes requires knowledge of the electrical properties of the cells involved. These properties are determined by the expression pattern of ionic channels and by the regulation of their function, e.g. by neuromodulators. We here review the presently available knowledge on insect non-synaptic ion channels and ionic currents in neurons and skeletal muscles. The first part of this article covers genetic and structural informations, the localization of channels, their electrophysiological and pharmacological properties, and known effects of second messengers and modulators such as neuropeptides or biogenic amines. In a second part we describe in detail modulation of ionic currents in three particularly well investigated preparations, i.e. Drosophila photoreceptor, cockroach DUM (dorsal unpaired median) neuron and locust jumping muscle. Ion channel structures are almost exclusively known for the fruitfly Drosophila, and most of the information on their function has also been obtained in this animal, mainly based on mutational analysis and investigation of heterologously expressed channels. Now the entire genome of Drosophila has been sequenced, it seems almost completely known which types of channel genes--and how many of them--exist in this animal. There is much knowledge of the various types of channels formed by 6-transmembrane--spanning segments (6TM channels) including those where four 6TM domains are joined within one large protein (e.g. classical Na+ channel). In comparison, two TM channels and 4TM (or tandem) channels so far have hardly been explored. There are, however, various well characterized ionic conductances, e.g. for Ca2+, Cl- or K+, in other insect preparations for which the channels are not yet known. In some of the larger insects, i.e. bee, cockroach, locust and moth, rather detailed information has been established on the role of ionic currents in certain physiological or behavioural contexts. On the whole, however, knowledge of non-synaptic ion channels in such insects is still fragmentary. Modulation of ion currents usually involves activation of more or less elaborate signal transduction cascades. The three detailed examples for modulation presented in the second part indicate, amongst other things, that one type of modulator usually leads to concerted changes of several ion currents and that the effects of different modulators in one type of cell may overlap. Modulators participate in the adaptive changes of the various cells responsible for different physiological or behavioural states. Further study of their effects on the single cell level should help to understand how small sets of cells cooperate in order to produce the appropriate output.
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Affiliation(s)
- D Wicher
- Sächsische Akademie der Wissenschaften zu Leipzig, Arbeitsgruppe Neurohormonale Wirkungsmechanismen, Erbertstr. 1, 07743, Jena, Germany.
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29
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Vacher H, Romi-Lebrun R, Mourre C, Lebrun B, Kourrich S, Masméjean F, Nakajima T, Legros C, Crest M, Bougis PE, Martin-Eauclaire MF. A new class of scorpion toxin binding sites related to an A-type K+ channel: pharmacological characterization and localization in rat brain. FEBS Lett 2001; 501:31-6. [PMID: 11457451 DOI: 10.1016/s0014-5793(01)02620-5] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A 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 microM 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 x 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.
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Affiliation(s)
- H Vacher
- UMR 6560 CNRSUniversité de la Mediterranée, Faculté de Médecine Nord, Marseille, France
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30
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Garcia ML, Gao Y, McManus OB, Kaczorowski GJ. Potassium channels: from scorpion venoms to high-resolution structure. Toxicon 2001; 39:739-48. [PMID: 11137531 DOI: 10.1016/s0041-0101(00)00214-2] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Affiliation(s)
- M L Garcia
- Department of Membrane Biochemistry and Biophysics, Merck Research Laboratories, P.O. Box 2000, Rahway, NJ 07065, USA.
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31
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Kourrich S, Mourre C, Soumireu-Mourat B. Kaliotoxin, a Kv1.1 and Kv1.3 channel blocker, improves associative learning in rats. Behav Brain Res 2001; 120:35-46. [PMID: 11173083 DOI: 10.1016/s0166-4328(00)00356-9] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Olfactory associative learning was used to investigate the involvement of Kv channels containing Kv1.1 and Kv1.3 alpha-subunits in learning and memory. Kaliotoxin (KTX), a specific inhibitor of these Kv channels, was injected intracerebroventricularly in the rat brain, at a dose of 10 ng that did not disturb the rats' locomotor activity or drinking behaviour. In the first paradigm (odour-reward training), KTX improved learning but not information consolidation. Moreover, KTX increased the long-term retrieval of an odour-reward association tested by a reversal test 1 month after the odour-reward training. The second paradigm (successive odour-pair training) tested reference memory. The first session was an acquisition session where the rats learned a new odour-discrimination problem with the same procedure. The second was a retention session held 24 h later to test retrieval of the learned information. KTX injected before the acquisition or retention session improved performance, but no effect was found when KTX was injected immediately after acquisition. We showed that these effects were not due to the action of KTX on attention processes. Thus, these results suggest that the blockage of Kv1.1 or Kv1.3 channels by KTX facilitates cognitive processes as learning, in particular in a reference representation.
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Affiliation(s)
- S Kourrich
- Laboratoire de Neurobiologie des Comportements, UMR 6562, CNRS-Université de Provence, IBHOP, Traverse Susini, 13388 Cedex 13, Marseille, France
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32
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Beeton C, Barbaria J, Giraud P, Devaux J, Benoliel AM, Gola M, Sabatier JM, Bernard D, Crest M, Béraud E. Selective blocking of voltage-gated K+ channels improves experimental autoimmune encephalomyelitis and inhibits T cell activation. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2001; 166:936-44. [PMID: 11145670 DOI: 10.4049/jimmunol.166.2.936] [Citation(s) in RCA: 148] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Kaliotoxin (KTX), a blocker of voltage-gated potassium channels (Kv), is highly selective for Kv1.1 and Kv1.3. First, Kv1.3 is expressed by T lymphocytes. Blockers of Kv1.3 inhibit T lymphocyte activation. Second, Kv1.1 is found in paranodal regions of axons in the central nervous system. Kv blockers improve the impaired neuronal conduction of demyelinated axons in vitro and potentiate the synaptic transmission. Therefore, we investigated the therapeutic properties of KTX via its immunosuppressive and symptomatic neurological effects, using experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. The T line cells used to induce adoptive EAE were myelin basic protein (MBP)-specific, constitutively contained mRNA for Kv1.3. and expressed Kv1.3. These channels were shown to be blocked by KTX. Activation is a crucial step for MBP T cells to become encephalitogenic. The addition of KTX during Ag-T cell activation led to a great reduction in the MBP T cell proliferative response, in the production of IL-2 and TNF, and in Ca(2+) influx. Furthermore, the addition of KTX during T cell activation in vitro led a decreased encephalitogenicity of MBP T cells. Moreover, KTX injected into Lewis rats impaired T cell function such as the delayed-type hypersensitivity. Lastly, the administration of this blocker of neuronal and lymphocyte channels to Lewis rats improved the symptoms of EAE. We conclude that KTX is a potent immunosuppressive agent with beneficial effects on the neurological symptoms of EAE.
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MESH Headings
- Adoptive Transfer
- Animals
- Antigens/pharmacology
- Calcium/antagonists & inhibitors
- Calcium/metabolism
- Cell Line
- Encephalomyelitis, Autoimmune, Experimental/drug therapy
- Encephalomyelitis, Autoimmune, Experimental/immunology
- Encephalomyelitis, Autoimmune, Experimental/prevention & control
- Epitopes, T-Lymphocyte/immunology
- Female
- Guinea Pigs
- Humans
- Hypersensitivity, Delayed/immunology
- Hypersensitivity, Delayed/prevention & control
- Immunosuppressive Agents/pharmacology
- Injections, Subcutaneous
- Interleukin-2/antagonists & inhibitors
- Interleukin-2/biosynthesis
- Intracellular Fluid/drug effects
- Intracellular Fluid/metabolism
- Ion Channel Gating/drug effects
- Ion Channel Gating/immunology
- Jurkat Cells
- Kv1.3 Potassium Channel
- Lymphocyte Activation/drug effects
- Lymphocyte Activation/immunology
- Mice
- Myelin Basic Protein/antagonists & inhibitors
- Myelin Basic Protein/immunology
- Myelin Basic Protein/pharmacology
- Patch-Clamp Techniques
- Potassium Channel Blockers
- Potassium Channels/biosynthesis
- Potassium Channels/genetics
- Potassium Channels, Voltage-Gated
- RNA, Messenger/biosynthesis
- Rats
- Rats, Inbred Lew
- Scorpion Venoms/administration & dosage
- Scorpion Venoms/pharmacology
- T-Lymphocytes/drug effects
- T-Lymphocytes/immunology
- T-Lymphocytes/metabolism
- T-Lymphocytes/transplantation
- Tumor Necrosis Factor-alpha/antagonists & inhibitors
- Tumor Necrosis Factor-alpha/biosynthesis
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Affiliation(s)
- C Beeton
- Laboratoire d'Immunologie, Faculté de Médecine, Université de la Méditerranée, Unité de Formation et de Recherche de Médecine, Université de la Méditerranée, 13385 Marseille Cedex 5, France
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33
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Tricaud N, Marchot P, Martin-Eauclaire MF. On the kaliotoxin and dendrotoxin binding sites on rat brain synaptosomes. Toxicon 2000; 38:1749-58. [PMID: 10858514 DOI: 10.1016/s0041-0101(00)00104-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The toxic polypeptides alpha-, beta-, gamma- and delta-dendrotoxin (DTX), known to be potent blockers of voltage-dependent potassium channels of the Kv1 family, were purified from the venom of the green mamba Dendroaspis angusticeps. Their binding behaviour to synaptosomal membranes of rat brain was analysed and compared with that of kaliotoxin (KTX), in a competition assay using [(125)I] KTX. alpha-DTX and delta-DTX were found to compete with radioiodinated-KTX (IC(50) of 8 pM and 0.2 nM respectively), whereas gamma-DTX did not. Several minor components that competed with radioiodinated-KTX binding were identified and characterised chemically and biologically.
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Affiliation(s)
- N Tricaud
- Laboratoire de Biochimie, CNRS UMR 6560, Ingénierie des Protéines, Faculté de Médecine secteur Nord, Institut Fédératif de Recherche Jean Roche, Université de la Méditérranée, Boulevard Pierre-Dramard, Marseille, France
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34
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Srairi-Abid N, Mansuelle P, Mejri T, Karoui H, Rochat H, Sampieri F, El Ayeb M. Purification, characterization and molecular modelling of two toxin-like proteins from the Androctonus australis Hector venom. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:5614-20. [PMID: 10951222 DOI: 10.1046/j.1432-1327.2000.01632.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Two toxin-like proteins (AahTL1 and AahTL3) were purified from the venom of the scorpion Androctonus australis Hector (Aah). AahTL1 and AahTL3 are the first non toxic proteins cross-reacting with AahI toxins group which indicates that these proteins can be used as a model of vaccins. In order to study structure-function relationships, their complete amino-acid sequences (66 residues) were determined, by automated Edman degradation. They show more than 50% of similarity with both AahI and AahIII antimammal toxins. Three-dimensional structural models of AahTL1 and AahTL3 constructed by homology suggest that the two proteins are structurally similar to antimammal scorpion alpha-toxins specific to voltage dependent Na+ channels. The models showed also that amino-acid changes between potent Aah toxins and both AahTL1 and AahTL3 disrupt the electrostatic potential gradient at their surface preventing their interaction with the receptor, which may explain their non toxicity.
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Affiliation(s)
- N Srairi-Abid
- Laboratoire des Venins et Toxines, Institut Pasteur de Tunis, Tunisia.
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35
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Legros C, Pollmann V, Knaus HG, Farrell AM, Darbon H, Bougis PE, Martin-Eauclaire MF, Pongs O. Generating a high affinity scorpion toxin receptor in KcsA-Kv1.3 chimeric potassium channels. J Biol Chem 2000; 275:16918-24. [PMID: 10828071 DOI: 10.1074/jbc.275.22.16918] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The crystal structure of the bacterial K(+) channel, KcsA (Doyle, D. A., Morais, C. J., Pfuetzner, R. A., Kuo, A., Gulbis, J. M., Cohen, S. L., Chait, B. T., and MacKinnon, R. (1998) Science 280, 69-77), and subsequent mutagenesis have revealed a high structural conservation from bacteria to human (MacKinnon, R., Cohen, S. L., Kuo, A., Lee, A., and Chait, B. T. (1998) Science 280, 106-109). We have explored this conservation by swapping subregions of the M1-M2 linker of KcsA with those of the S5-S6 linker of the human Kv-channel Kv1.3. The chimeric K(+) channel constructs were expressed in Escherichia coli, and their multimeric state was analyzed after purification. We used two scorpion toxins, kaliotoxin and hongotoxin 1, which bind specifically to Kv1.3, to analyze the pharmacological properties of the KcsA-Kv1.3 chimeras. The results demonstrate that the high affinity scorpion toxin receptor of Kv1.3 could be transferred to KcsA. Our biochemical studies with purified KcsA-Kv1.3 chimeras provide direct chemical evidence that a tetrameric channel structure is necessary for forming a functional scorpion toxin receptor. We have obtained KcsA-Kv1.3 chimeras with kaliotoxin affinities (IC(50) values of approximately 4 pm) like native Kv1.3 channels. Furthermore, we show that a subregion of the S5-S6 linker may be an important determinant of the pharmacological profile of K(+) channels. Using available structural information on KcsA and kaliotoxin, we have developed a structural model for the complex between KcsA-Kv1.3 chimeras and kaliotoxin to aid future pharmacological studies of K(+) channels.
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Affiliation(s)
- C Legros
- Institut für Neurale Signalverarbeitung, Zentrum für Molekulare Neurobiologie Hamburg, Universität Hamburg, D-20246 Hamburg, Germany
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36
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Lew A, Chamberlin AR. Human T-cell Kv1.3 potassium channel blockers: new strategies for immunosuppression. Expert Opin Ther Pat 2000. [DOI: 10.1517/13543776.10.6.905] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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37
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Carlier E, Avdonin V, Geib S, Fajloun Z, Kharrat R, Rochat H, Sabatier JM, Hoshi T, De Waard M. Effect of maurotoxin, a four disulfide-bridged toxin from the chactoid scorpion Scorpio maurus, on Shaker K+ channels. THE JOURNAL OF PEPTIDE RESEARCH : OFFICIAL JOURNAL OF THE AMERICAN PEPTIDE SOCIETY 2000; 55:419-27. [PMID: 10888198 DOI: 10.1034/j.1399-3011.2000.00715.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Maurotoxin is a 34-residue toxin isolated from the venom of the Tunisian chactoid scorpion Scorpio maurus palmatus and contains four disulfide bridges that are normally found in long-chain toxins of 60-70 amino acid residues, which affect voltage-gated sodium channels. However, despite the unconventional disulfide-bridge pattern of maurotoxin, the conformation of this toxin remains similar to that of other toxins acting on potassium channels. Here, we analyzed the effects of synthetic maurotoxin on voltage-gated Shaker potassium channels (ShB) expressed in Xenopus oocytes. Maurotoxin produces a strong, but reversible, inhibition of the ShB K+ current with an IC50 of 2 nM. Increasing concentrations of the toxin induce a progressively higher block at saturating concentrations. At nonsaturating concentrations of the toxin (5-20 nM), the channel block appears slightly more pronounced at threshold potentials suggesting that the toxin may have a higher affinity for the closed state of the channel. At the single channel level, the toxin does not modify the unitary current amplitude, but decreases ensemble currents by increasing the number of depolarizing epochs that failed to elicit any opening. A point mutation of Lys23 to alanine in maurotoxin produces a 1000-fold reduction in the IC50 of block by the toxin suggesting the importance of this charged residue for the interaction with the channel. Maurotoxin does not affect K+ currents carried by Kir2.3 channels in oocytes or Na+ currents carried by the alphaIIa channel expressed in CHO cells.
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Affiliation(s)
- E Carlier
- Laboratoire de Neurobiologie des Canaux Ioniques, Institut Fédératif Jean Roche, INSERM U464, Marseille, France
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38
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Lecomte C, Ben Khalifa R, Martin-Eauclaire MF, Kharrat R, El Ayeb M, Darbon H, Rochat H, Crest M, Sabatier JM. Maurotoxin and the Kv1.1 channel: voltage-dependent binding upon enantiomerization of the scorpion toxin disulfide bridge Cys31-Cys34. THE JOURNAL OF PEPTIDE RESEARCH : OFFICIAL JOURNAL OF THE AMERICAN PEPTIDE SOCIETY 2000; 55:246-54. [PMID: 10727107 DOI: 10.1034/j.1399-3011.2000.00170.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Maurotoxin (MTX) is a 34-amino acid polypeptide cross-linked by four disulfide bridges that has been isolated from the venom of the scorpion Scorpio maurus palmatus and characterized. Maurotoxin competed with radiolabeled apamin and kaliotoxin for binding to rat brain synaptosomes and blocked K+ currents from Kv1 channel subtypes expressed in Xenopus oocytes. Structural characterization of the synthetic toxin identified half-cystine pairings at Cys3-Cys24, Cys9-Cys29, Cys13-Cys19 and Cys31-Cys34 This disulfide bridge pattern is unique among known scorpion toxins, particularly the existence of a C-terminal '14-membered disulfide ring' (i.e. cyclic domain 31-34), We therefore studied structure-activity relationships by investigating the structure and pharmacological properties of synthetic MTX peptides either modified at the C-terminus ¿i.e. MTX(1-29), [Abu31,34]-MTX and [Cys31,34, Tyr32]D-MTX) or mimicking the cyclic C-terminal domain [i.e. MTX(31-34)]. Unexpectedly, the absence of a disulfide bridge Cys31-Cys34 in [Abu 31,34]-MTX and MTX(1-29) resulted in MTX-unrelated half-cystine pairings of the three remaining disulfide bridges for the two analogs, which is likely to be responsible for their inactivity against Kv1 channel subtypes. Cyclic MTX(31-34) was also biologically inactive. [Cys31,34, Tyr32]D-MTX, which had a 'native', MTX-related, disulfide bridge organization, but a D-residue-induced reorientation of the C-terminal disulfide bridge, was potent at blocking the Kv1.1 channel. This peptide-induced Kv1.1 blockage was voltage-dependent (a property not observed for MTX), maximal in the low depolarization range and associated with on-rate changes in ligand binding. Thus, the cyclic C-terminal domain of MTX seems to be crucial for recognition of Kv1.3, and to a lesser extent, Kv1.2 channels and it may contribute to the stabilization and strength of the interaction between the toxin and the Kv1.1 channel.
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Affiliation(s)
- C Lecomte
- Laboratoire de Biochimie, CNRS UMR 6560, IFR Jean Roche, Faculté de Médecine Nord, Marseille, France.
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39
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Meki A, Mansuelle P, Laraba-Djebari F, Oughideni R, Rochat H, Martin-Eauclaire MF. KTX3, the kaliotoxin from Buthus occitanus tunetanus scorpion venom: one of an extensive family of peptidyl ligands of potassium channels. Toxicon 2000; 38:105-11. [PMID: 10669015 DOI: 10.1016/s0041-0101(99)00137-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
A new ligand of the K+ channels sensitive to KTX was purified from the venom of Buthus occitanus tunetanus, using two steps of high-performance-liquid-chromatography and by following its ability to compete with [125I]-KTX for binding to the KTX receptor on rat brain synaptosomes. Amino-acid analysis, amino acid sequencing and mass spectroscopy defined this new ligand. KTX3, as a 37-amino acid peptide, with three disulfide bridges. Its sequence shares 76% identity with KTX. The main differences between the two peptides are in the N-terminal region and the residue position 34 located in the region involved in channel recognition. These differences may explain the 5-fold lower binding affinity of KTX3, IC50=50 pM, than KTX to rat brain synaptosomes. Specific antibodies raised against KTX (1-37) were not able to recognize KTX3.
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Affiliation(s)
- A Meki
- Laboratoire de Biochimie, Ingénierie des Protéines, UMR 6560 du Centre National de la Recherche Scientifique, Faculté de Médecine Nord, Institut Fédératif Jean Roche, Université de la Méditérranée, Marseille, France
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40
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Meir A, Ginsburg S, Butkevich A, Kachalsky SG, Kaiserman I, Ahdut R, Demirgoren S, Rahamimoff R. Ion channels in presynaptic nerve terminals and control of transmitter release. Physiol Rev 1999; 79:1019-88. [PMID: 10390521 DOI: 10.1152/physrev.1999.79.3.1019] [Citation(s) in RCA: 220] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The primary function of the presynaptic nerve terminal is to release transmitter quanta and thus activate the postsynaptic target cell. In almost every step leading to the release of transmitter quanta, there is a substantial involvement of ion channels. In this review, the multitude of ion channels in the presynaptic terminal are surveyed. There are at least 12 different major categories of ion channels representing several tens of different ion channel types; the number of different ion channel molecules at presynaptic nerve terminals is many hundreds. We describe the different ion channel molecules at the surface membrane and inside the nerve terminal in the context of their possible role in the process of transmitter release. Frequently, a number of different ion channel molecules, with the same basic function, are present at the same nerve terminal. This is especially evident in the cases of calcium channels and potassium channels. This abundance of ion channels allows for a physiological and pharmacological fine tuning of the process of transmitter release and thus of synaptic transmission.
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Affiliation(s)
- A Meir
- Department of Physiology and the Bernard Katz Minerva Centre for Cell Biophysics, Hebrew University Hadassah Medical School, Jerusalem, Israel
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41
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Rauer H, Grissmer S. The effect of deep pore mutations on the action of phenylalkylamines on the Kv1.3 potassium channel. Br J Pharmacol 1999; 127:1065-74. [PMID: 10455250 PMCID: PMC1566106 DOI: 10.1038/sj.bjp.0702599] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
We investigated the action of the phenylalkylamines verapamil and N-methyl-verapamil on the Kv1.3 potassium channel using the whole-cell configuration of the patch-clamp technique. Our goal was to identify their binding as a prerequisite for using the phenylalkylamines as small, well-defined molecular probes, not only to expand the structural findings made with peptide toxins or by crystallization, but also to use them as lead compounds for the generation of more potent and therefore more specific K+ channel modulators. Competition experiments with charybdotoxin, known to interact with external residues of Kv1.3, showed no interaction with verapamil. The internal application of quarternary N-methyl-verapamil in combination with verapamil suggested competition for the same internal binding site. Verapamil affinity was decreased 6 fold by a mutation (M395V) in a region of the internal pore which forms part of the internal tetraethylammonium (TEA+) binding site, although mutations at neighbouring residues (T396 and T397) were without effect. Modification of C-type inactivation by mutations in the internal pore suggest that this region participates in the inactivation process. The action of phenylalkylamines and local anaesthetics on L-type Ca2+ channels and Na channels, respectively, and verapamil on Kv1.3 indicate very similar blocking mechanisms. This might allow the use of these compounds as molecular probes to map the internal vestibule of all three channel types.
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Affiliation(s)
- Heiko Rauer
- Department of Physiology and Biophysics, University of California, Irvine, Irvine, California, CA 92697-4560, U.S.A
| | - Stephan Grissmer
- Department of Applied Physiology, University of Ulm, Albert-Einstein-Allee 11, 89075 Ulm, Germany
- Author for correspondence:
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42
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Martin-Eauclaire MF, Legros C, Bougis PE, Rochat H. Les toxines des venins de scorpion. ACTA ACUST UNITED AC 1999. [DOI: 10.1016/s0924-4204(99)80035-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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43
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Canto J, Fernandez Y, Pons M, Giralt E, Perez JJ. Molecular dynamics study of kaliotoxin in water. Int J Biol Macromol 1999; 24:1-9. [PMID: 10077265 DOI: 10.1016/s0141-8130(98)00070-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Kaliotoxin (KTX), a potassium channel blocker found in the venom of the scorpion Androctonous Mauretanicus is a 38 residue polypeptide with a well defined structure consisting of a alpha-helix and a three strand antiparallel beta-sheet interconnected by three disulfide bonds. Although the 3D structure has been determined by NMR, there is a number of features, mainly concerning the conformation and flexibility of the side chains, but also the long range order in the peptide and its fluctuations, that may have escaped the experimental study. These questions are now being addressed using molecular dynamics (MD) simulations. Accordingly, the present work reports the analysis of a 430 ps molecular dynamics trajectory of the polypeptide soaked with 4700 TIP3 water molecules inside a 56 A box. MD calculations were performed with periodic boundary conditions. Analysis of the conformational space sampled by each of the residues along the trajectory, suggests a special behavior of Pro17 and Lys19 both located on the helix. Furthermore, analysis of the relative movements of the secondary structure elements indicates that the alpha-helix and beta-sheets fluctuate in a correlated motion, preserving the tertiary structure of the polypeptide along the trajectory. Finally, analysis of the charge distribution was also examined. The direction of the dipole moment, computed from the center of masses appears to be an interesting feature of the structure probably related to the biological function of the molecule.
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Affiliation(s)
- J Canto
- Departament d'Enginyeria Quimica, UPC ETS d'Enginyers Industrials, Barcelona, Spain
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44
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Ali SA, Stoeva S, Schütz J, Kayed R, Abassi A, Zaidi ZH, Voelter W. Purification and primary structure of low molecular mass peptides from scorpion (Buthus sindicus) venom. Comp Biochem Physiol A Mol Integr Physiol 1998; 121:323-32. [PMID: 10048185 DOI: 10.1016/s1095-6433(98)10140-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The primary structures of four low molecular mass peptides (Bs 6, 8, 10 and 14) from scorpion Buthus sindicus were elucidated via combination of Edman degradation and matrix-assisted laser desorption ionization mass spectrometry. Bs 8 and 14 are cysteine-rich, thermostable peptides composed of 35-36 residues with molecular weights of 3.7 and 3.4 kDa, respectively. These peptides show close sequence homologies (55-78%) with other scorpion chlorotoxin-like short-chain neurotoxins (SCNs) containing four intramolecular disulfide bridges. Despite the sequence variation between these two peptides (37% heterogeneity) their general structural organization is very similar as shown by their clearly related circular dichroism spectra. Furthermore, Bs6 is a minor component, composed of 38 residues (4.1 kDa) containing six half-cystine residues and having close sequence identities (40-80%) with charybdotoxin-like SCNs containing three disulfide bridges. The non-cysteinic, bacic and thermolabile Bs10 is composed of 34 amino acid residues (3.7 kDa), and belongs to a new class of peptides, with no sequence resemblance to any other so far reported sequence isolated from scorpions. Surprisingly, Bs10 shows some limited sequence analogy with oocyte zinc finger proteins. Results of these studies are discussed with respect to their structural similarities within the scorpion LCNs, SCNs and other biologically active peptides.
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Affiliation(s)
- S A Ali
- International Centre for Chemical Sciences, University of Karachi, Pakistan.
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45
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Lauth X, Nesin A, Briand JP, Roussel JP, Hetru C. Isolation, characterization and chemical synthesis of a new insect defensin from Chironomus plumosus (Diptera). INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 1998; 28:1059-1066. [PMID: 9887520 DOI: 10.1016/s0965-1748(98)00101-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Injection of low doses of bacteria into the aquatic larvae of the dipteran insect Chironomus plumosus induces the appearance in their hemolymph of a potent antibacterial activity. We have isolated two 36-residue peptides from this hemolymph which are active against Gram-positive bacteria. The peptides are novel members of the insect defensin family and their sequences present marked differences with those of insect defensins isolated from other dipteran species. We have developed a method for efficient renaturation of this cysteine-rich molecule and obtained a highly pure synthetic Chironomus defensin.
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Affiliation(s)
- X Lauth
- UPR 9022, CNRS, Réponse Immunitaire et Développement chez les Insectes, Institut de Biologie Moléculaire et Cellulaire, Strasbourg, France
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46
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Olamendi-Portugal T, Gómez-Lagunas F, Gurrola GB, Possani LD. Two similar peptides from the venom of the scorpion Pandinus imperator, one highly effective blocker and the other inactive on K+ channels. Toxicon 1998; 36:759-70. [PMID: 9655636 DOI: 10.1016/s0041-0101(97)00163-3] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Two novel peptides, named Pi4 and Pi7, were purified from the venom of the scorpion Pandinus imperator, and their primary structures were determined. These peptides have 38 amino acids residues, compacted by four disulfide bridges, instead of the normal three found in most K+-channel specific toxins. Both peptides contain 25 identical amino acid residues in equivalent positions (about 66% identity), including all eight half-cystines. Despite the fact that their C-terminal sequence comprising amino acid residues 27 to 37 are highly conserved (10 out of 11 amino acids are identical), Pi4 blocks completely and reversibly Shaker B K+ -channels (a Kv1.1 sub-family type of channel) at 100nM concentration, whereas Pi7 is absolutely inactive at this concentration. Similar effects were observed in binding and displacement experiments to rat brain synaptosomal membranes using 125I-Noxiustoxin, a well known K+-channel specific toxin. In this preparation Pi4 displaces the binding of radiolabeled Noxiustoxin with Ic50 in the order of 10 nM, whereas Pi7 is ineffective at same concentration. Comparative analysis of Pi4 and Pi7 sequences with those obtained by site directed mutagenesis of Charybdotoxin, another very well studied K -channel blocking toxin, shows that the substitution of lysine (in Pi4) for arginine (in Pi7) at position 26, might be one of the important 'point mutations' responsible for such impressive variation in blocking properties of both toxins, here described.
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Affiliation(s)
- T Olamendi-Portugal
- Department of Molecular Recognition and Structural Biology, Institute of Biotechnology, Universidad Nacional Autonoma de Mexico, Cuernavaca
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47
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Lecomte C, Sabatier JM, Van Rietschoten J, Rochat H. Synthetic peptides as tools to investigate the structure and pharmacology of potassium channel-acting short-chain scorpion toxins. Biochimie 1998; 80:151-4. [PMID: 9587672 DOI: 10.1016/s0300-9084(98)80021-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
In the last decade, numerous polypeptide toxins acting on ion channels have been isolated and characterized from diverse scorpion venoms. These toxins are useful pharmacological probes to study ion-specific channel proteins because they interact selectively with these channels and modulate their activities. Since low amounts of natural toxins can be isolated from scorpion venoms, the chemical synthesis approach is extremely useful to produce larger quantities of toxins and toxin analogs. This report is a succinct overview of the possibilities offered by the chemical synthesis to investigate pharmacological and structural properties of these compounds.
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Affiliation(s)
- C Lecomte
- Laboratoire de Biochimie, Ingéniérie des Protéines, CNRS UMR 6560, IFR Jean Roche, Faculté de Médecine Nord, Marseille, France
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48
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Romi-Lebrun R, Lebrun B, Martin-Eauclaire MF, Ishiguro M, Escoubas P, Wu FQ, Hisada M, Pongs O, Nakajima T. Purification, characterization, and synthesis of three novel toxins from the Chinese scorpion Buthus martensi, which act on K+ channels. Biochemistry 1997; 36:13473-82. [PMID: 9354615 DOI: 10.1021/bi971044w] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Three novel toxins belonging to the scorpion K+ channel-inhibitor family were purified to homogeneity from the venom of the Chinese scorpion Buthus martensi. They have been identified according to their molecular mass (3800-4300 Da) and their neurotoxicity in mice and characterized as 37-amino acid peptides. One of them shows 81-87% sequence identity with members of the kaliotoxin group (named BmKTX), whereas the other two, named BmTX1 and BmTX2, show 65-70% identity with toxins of the charybdotoxin group. Their chemical synthesis by the Fmoc methodology allowed us to show that BmKTX, unlike BmTX1 and BmTX2, possesses an amidated C-terminal extremity. Toxicity assays in vivo established that they are lethal neurotoxic agents in mice (LD50s of 40-95 ng per mouse). Those toxins proved to be potent inhibitors of the voltage-gated K+ channels, as they were able to compete with [125I]kaliotoxin for its binding to rat brain synaptosomes (IC50s of 0.05-1 nM) and to block the cloned voltage-gated K+ channel Kv1.3 from rat brain, expressed in Xenopus oocytes (IC50s of 0.6-1.6 nM). BmTX1 and BmTX2 were also shown to compete with [125I]charybdotoxin for its binding to the high-conductance Ca2+-activated K+ channels present on bovine aorta sarcolemmal membranes (IC50s of 0.3-0.6 nM). These new sequences show multipoint mutations when compared to the other related scorpion K+ channel toxins and should prove to be useful probes for studying the diverse family of K+ channels.
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Affiliation(s)
- R Romi-Lebrun
- Suntory Institute for Bioorganic Research, Mishima-Gun, Shimamoto-Cho, Wakayamadai 1-1-1, Osaka 618, Japan
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Legros C, Feyfant E, Sampieri F, Rochat H, Bougis PE, Martin-Eauclaire MF. Influence of a NH2-terminal extension on the activity of KTX2, a K+ channel blocker purified from Androctonus australis scorpion venom. FEBS Lett 1997; 417:123-9. [PMID: 9395089 DOI: 10.1016/s0014-5793(97)01177-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
A cDNA encoding a short polypeptide blocker of K+ channels, kaliotoxin 2 (KTX2), from the venom of the North African scorpion Androctonus australis was expressed in the periplasmic space of Escherichia coli. KTX2 was produced as a fusion protein with the maltose binding protein followed by the recognition site for factor Xa or enterokinase preceding the first amino acid residue of the toxin. The fully refolded recombinant KTX2 (rKTX2) was obtained (0.15-0.30 mg/l of culture) and was indistinguishable from the native toxin according to chemical and biological criteria. An N-extended analogue of KTX2 exhibiting three additional residues was also expressed. This analogue had 1000-fold less affinity for the 125I-kaliotoxin binding site on rat brain synaptosomes than KTX2. Conformational models of KTX2 and its mutant were designed by amino acid replacement using the structure of agitoxin 2 from Leiurus quinquestriatus as template, to try to understand the decrease in affinity for the receptor.
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Affiliation(s)
- C Legros
- Laboratoire de Biochimie, Ingénierie des Protéines, UMR 6560 du Centre National de la Recherche Scientifique, Institut Fédératif Jean Roche, Faculté de Médecine Nord, Marseille, France
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Gairí M, Romi R, Fernández I, Rochat H, Martin-Eauclaire MF, Van Rietschoten J, Pons M, Giralt E. 3D structure of kaliotoxin: is residue 34 a key for channel selectivity? J Pept Sci 1997. [DOI: 10.1002/(sici)1099-1387(199707)3:4<314::aid-psc117>3.0.co;2-e] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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