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Raymond S. Norton - One of the best experts on this subject based on the ideXlab platform.
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structural dynamics of the Potassium Channel Blocker shk srls analysis of 15n relaxation
Journal of Physical Chemistry B, 2015Co-Authors: Eva Meirovitch, Raymond S. Norton, Inbal Sher, Oren Tchaicheeyan, Jordan H ChillAbstract:The 35-residue ShK peptide binds with high affinity to voltage-gated Potassium Channels. The dynamics of the binding surface was studied recently with (microsecond to millisecond) 15N relaxation dispersion and (picosecond to nanosecond) 15N spin relaxation of the N–H bonds. Relaxation dispersion revealed microsecond conformational-exchange-mediated exposure of the functionally important Y23 side chain to the peptide surface. The spin relaxation parameters acquired at 14.1 and 16.45 T have been subjected to model-free (MF) analysis, which yielded a squared generalized order parameter, S2, of approximately 0.85 for virtually all of the N–H bonds. Only a “rigid backbone” evaluation could be inferred. We ascribe this limited information to the simplicity of MF in the context of challenging data. To improve the analysis, we apply the slowly relaxing local structure (SRLS) approach, which is a generalization of MF. SRLS describes N–H bond dynamics in ShK in terms of a local potential, u, ranging from 10 to 18.5...
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conformational flexibility in the binding surface of the Potassium Channel Blocker shk
ChemBioChem, 2014Co-Authors: Inbal Sher, Raymond S. Norton, Shihchieh Jeff Chang, Sandeep Chhabra, Arthur G Palmer, Jordan H ChillAbstract:ShK is a 35-residue peptide that binds with high affinity to human voltage-gated Potassium Channels through a conserved K-Y dyad. Here we have employed NMR measurements of backbone-amide (15)N spin-relaxation rates to investigate motions of the ShK backbone. Although ShK is rigid on the ps to ns timescale, increased linewidths observed for 11 backbone-amide (15)N resonances identify chemical or conformational exchange contributions to the spin relaxation. Relaxation dispersion profiles indicate that exchange between major and minor conformers occurs on the sub-millisecond timescale. Affected residues are mostly clustered around the central helix-kink-helix structure and the critical K22-Y23 motif. We suggest that the less structured minor conformer increases the exposure of Y23, known to contribute to binding affinity and selectivity, thereby facilitating its interaction with Potassium Channels. These findings have potential implications for the design of new Channel Blockers based on ShK.
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expression and isotopic labelling of the Potassium Channel Blocker shk toxin as a thioredoxin fusion protein in bacteria
Toxicon, 2012Co-Authors: Shih Chieh Chang, Michael W. Pennington, Christine Beeton, Charles A Galea, Eleanor W W Leung, Rajeev B Tajhya, Raymond S. NortonAbstract:The polypeptide toxin ShK is a potent Blocker of Kv1.3 Potassium Channels, which play a crucial role in the activation of human effector memory T-cells (TEM). Selective Blockers constitute valuable therapeutic leads for the treatment of autoimmune diseases mediated by TEM cells, such as multiple sclerosis, rheumatoid arthritis, and type-1 diabetes. We have established a recombinant peptide expression system in order to generate isotopically-labelled ShK and various ShK analogues for in-depth biophysical and pharmacological studies. ShK was expressed as a thioredoxin fusion protein in Escherichia coli BL21 (DE3) cells and purified initially by Ni2+ iminodiacetic acid affinity chromatography. The fusion protein was cleaved with enterokinase and purified to homogeneity by reverse-phase HPLC. NMR spectra of 15N-labelled ShK were similar to those reported previously for the unlabelled synthetic peptide, confirming that recombinant ShK was correctly folded. Recombinant ShK blocked Kv1.3 Channels with a Kd of 25 pM and inhibited the proliferation of human and rat T lymphocytes with a preference for TEM cells, with similar potency to synthetic ShK in all assays. This expression system also enables the efficient production of 15N-labelled ShK for NMR studies of peptide dynamics and of the interaction of ShK with Kv1.3 Channels.
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analogs of the sea anemone Potassium Channel Blocker shk for the treatment of autoimmune diseases
Inflammation and Allergy - Drug Targets, 2011Co-Authors: Christine Beeton, Michael W. Pennington, Raymond S. NortonAbstract:CCR7- effector memory T (TEM) lymphocytes are involved in autoimmune diseases such as multiple sclerosis, type 1 diabetes mellitus and rheumatoid arthritis. These cells express Kv1.3 Potassium Channels that play a major role in their activation. Blocking these Channels preferentially inhibits the activation of CCR7- TEM cells, with little or no effects on CCR7+ naive and central memory T cells. Blockers of lymphocyte Kv1.3 Channels therefore show considerable potential as therapeutics for autoimmune diseases. ShK, a 35-residue polypeptide isolated from the Caribbean sea anemone Stichodactyla helianthus, blocks Kv1.3 Channels at picomolar concentrations. Although ShK was effective in treating rats with delayed type hypersensitivity and a model of multiple sclerosis, it lacks selectivity for Kv1.3 Channels over closely-related Kv1 Channels. Extensive mutagenesis studies combined with elucidation of the structure of ShK led to models of ShK docked with the Channel. This knowledge was valuable in the development of new ShK analogs with improved selectivity and increasing stability, which have proven efficacious in preventing and/or treating animal models of delayed type hypersensitivity, type 1 diabetes, rheumatoid arthritis, and multiple sclerosis without inducing generalized immunosuppression. They are currently undergoing further evaluation as potential immunomodulators for the treatment of autoimmune diseases.
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Designed peptide analogues of the Potassium Channel Blocker ShK toxin.
Biochemistry, 2001Co-Authors: Mark D. Lanigan, Michael W. Pennington, Yann Lefievre, Heiko Rauer, Raymond S. NortonAbstract:ShK toxin, a Potassium Channel Blocker from the sea anemone Stichodactyla helianthus, is a 35-residue polypeptide cross-linked by 3 disulfide bridges. In an effort to generate truncated peptidic analogues of this potent Channel Blocker, we have evaluated three analogues, one in which the native sequence was truncated and then stabilized by the introduction of additional covalent links (a non-native disulfide and two lactam bridges), and two in which non-native structural scaffolds stabilized by disulfide and/or lactam bridges were modified to include key amino acid residues from the native toxin. The effect of introducing a lactam bridge in the first helix of ShK toxin (to create cyclo14/18[Lys14,Asp18]ShK) was also examined to confirm that this modification was compatible with activity. All four analogues were tested in vitro for their ability to block Kv1.3 Potassium Channels in Xenopus oocytes, and their solution structures were determined using 1H NMR spectroscopy. The lactam bridge in full-length ShK...
Michael W. Pennington - One of the best experts on this subject based on the ideXlab platform.
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expression and isotopic labelling of the Potassium Channel Blocker shk toxin as a thioredoxin fusion protein in bacteria
Toxicon, 2012Co-Authors: Shih Chieh Chang, Michael W. Pennington, Christine Beeton, Charles A Galea, Eleanor W W Leung, Rajeev B Tajhya, Raymond S. NortonAbstract:The polypeptide toxin ShK is a potent Blocker of Kv1.3 Potassium Channels, which play a crucial role in the activation of human effector memory T-cells (TEM). Selective Blockers constitute valuable therapeutic leads for the treatment of autoimmune diseases mediated by TEM cells, such as multiple sclerosis, rheumatoid arthritis, and type-1 diabetes. We have established a recombinant peptide expression system in order to generate isotopically-labelled ShK and various ShK analogues for in-depth biophysical and pharmacological studies. ShK was expressed as a thioredoxin fusion protein in Escherichia coli BL21 (DE3) cells and purified initially by Ni2+ iminodiacetic acid affinity chromatography. The fusion protein was cleaved with enterokinase and purified to homogeneity by reverse-phase HPLC. NMR spectra of 15N-labelled ShK were similar to those reported previously for the unlabelled synthetic peptide, confirming that recombinant ShK was correctly folded. Recombinant ShK blocked Kv1.3 Channels with a Kd of 25 pM and inhibited the proliferation of human and rat T lymphocytes with a preference for TEM cells, with similar potency to synthetic ShK in all assays. This expression system also enables the efficient production of 15N-labelled ShK for NMR studies of peptide dynamics and of the interaction of ShK with Kv1.3 Channels.
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analogs of the sea anemone Potassium Channel Blocker shk for the treatment of autoimmune diseases
Inflammation and Allergy - Drug Targets, 2011Co-Authors: Christine Beeton, Michael W. Pennington, Raymond S. NortonAbstract:CCR7- effector memory T (TEM) lymphocytes are involved in autoimmune diseases such as multiple sclerosis, type 1 diabetes mellitus and rheumatoid arthritis. These cells express Kv1.3 Potassium Channels that play a major role in their activation. Blocking these Channels preferentially inhibits the activation of CCR7- TEM cells, with little or no effects on CCR7+ naive and central memory T cells. Blockers of lymphocyte Kv1.3 Channels therefore show considerable potential as therapeutics for autoimmune diseases. ShK, a 35-residue polypeptide isolated from the Caribbean sea anemone Stichodactyla helianthus, blocks Kv1.3 Channels at picomolar concentrations. Although ShK was effective in treating rats with delayed type hypersensitivity and a model of multiple sclerosis, it lacks selectivity for Kv1.3 Channels over closely-related Kv1 Channels. Extensive mutagenesis studies combined with elucidation of the structure of ShK led to models of ShK docked with the Channel. This knowledge was valuable in the development of new ShK analogs with improved selectivity and increasing stability, which have proven efficacious in preventing and/or treating animal models of delayed type hypersensitivity, type 1 diabetes, rheumatoid arthritis, and multiple sclerosis without inducing generalized immunosuppression. They are currently undergoing further evaluation as potential immunomodulators for the treatment of autoimmune diseases.
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Designed peptide analogues of the Potassium Channel Blocker ShK toxin.
Biochemistry, 2001Co-Authors: Mark D. Lanigan, Michael W. Pennington, Yann Lefievre, Heiko Rauer, Raymond S. NortonAbstract:ShK toxin, a Potassium Channel Blocker from the sea anemone Stichodactyla helianthus, is a 35-residue polypeptide cross-linked by 3 disulfide bridges. In an effort to generate truncated peptidic analogues of this potent Channel Blocker, we have evaluated three analogues, one in which the native sequence was truncated and then stabilized by the introduction of additional covalent links (a non-native disulfide and two lactam bridges), and two in which non-native structural scaffolds stabilized by disulfide and/or lactam bridges were modified to include key amino acid residues from the native toxin. The effect of introducing a lactam bridge in the first helix of ShK toxin (to create cyclo14/18[Lys14,Asp18]ShK) was also examined to confirm that this modification was compatible with activity. All four analogues were tested in vitro for their ability to block Kv1.3 Potassium Channels in Xenopus oocytes, and their solution structures were determined using 1H NMR spectroscopy. The lactam bridge in full-length ShK...
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Ionisation behaviour and solution properties of the Potassium‐Channel Blocker ShK toxin
European journal of biochemistry, 1998Co-Authors: Jane E. Tudor, Michael W. Pennington, Raymond S. NortonAbstract:The effects of pH, temperature and polypeptide concentration on the solution structure and side chain interactions of ShK toxin, a Potassium-Channel-blocking polypeptide from the sea anemone Stichodactyla helianthus, have been investigated by means of one-dimensional and two-dimensional 1H-NMR spectroscopy. Resonance assignments have been obtained for most protons in the molecule, and for the alpha and beta carbon atoms. The lack of concentration dependence of the 1H chemical shifts and linewidths indicates that self-association is not significant and cannot account for the sheet-like structure near the N terminus. The structure is stable to high temperature, showing little change even at 353 K. This stability allowed backbone-amide temperature coefficients to be interpreted, and the correlation of these values with hydrogen bonds observed in the structures and with solvent exchange rates is discussed. pKa values have been measured for Asp5, His19 and Tyr23, and the contributions to these pKa values from other residues investigated using the analogues R11Q (denoting substitution of Argll with Gln), R11E, H19K, K22A, Y23A and K30A. These results show that Asp5 (pKa 2.8) makes an electrostatic interaction with Lys30, which may be partially responsible for the importance of these side chains in the folding of synthetic toxin. The phenolic pKa of Tyr23 is reduced to 8.7 in the native toxin, as a result of interactions with the positively charged side chains of Arg11 and to a lesser extent Lys22. Several hydrogen bonds between the Arg11 guanidino group and the Tyr23 phenolic group are found in the solution structures. As these three residues are implicated in the tight binding of ShK toxin to the T-lymphocyte voltage-gated Potassium Channel Kv1.3, their close interactions should be taken into account in models of binding of this toxin to the pore and vestibule of this and other Potassium Channels.
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ionisation behaviour and solution properties of the Potassium Channel Blocker shk toxin
FEBS Journal, 1998Co-Authors: Jane E. Tudor, Michael W. Pennington, Raymond S. NortonAbstract:The effects of pH, temperature and polypeptide concentration on the solution structure and side chain interactions of ShK toxin, a Potassium-Channel-blocking polypeptide from the sea anemone Stichodactyla helianthus, have been investigated by means of one-dimensional and two-dimensional 1H-NMR spectroscopy. Resonance assignments have been obtained for most protons in the molecule, and for the alpha and beta carbon atoms. The lack of concentration dependence of the 1H chemical shifts and linewidths indicates that self-association is not significant and cannot account for the sheet-like structure near the N terminus. The structure is stable to high temperature, showing little change even at 353 K. This stability allowed backbone-amide temperature coefficients to be interpreted, and the correlation of these values with hydrogen bonds observed in the structures and with solvent exchange rates is discussed. pKa values have been measured for Asp5, His19 and Tyr23, and the contributions to these pKa values from other residues investigated using the analogues R11Q (denoting substitution of Argll with Gln), R11E, H19K, K22A, Y23A and K30A. These results show that Asp5 (pKa 2.8) makes an electrostatic interaction with Lys30, which may be partially responsible for the importance of these side chains in the folding of synthetic toxin. The phenolic pKa of Tyr23 is reduced to 8.7 in the native toxin, as a result of interactions with the positively charged side chains of Arg11 and to a lesser extent Lys22. Several hydrogen bonds between the Arg11 guanidino group and the Tyr23 phenolic group are found in the solution structures. As these three residues are implicated in the tight binding of ShK toxin to the T-lymphocyte voltage-gated Potassium Channel Kv1.3, their close interactions should be taken into account in models of binding of this toxin to the pore and vestibule of this and other Potassium Channels.
Masataka Majima - One of the best experts on this subject based on the ideXlab platform.
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An ATP-sensitive Potassium Channel Blocker suppresses sodium-induced hypertension through increased secretion of urinary kallikrein
Hypertension Research, 2009Co-Authors: Yuji Kamata, Tomoe Fujita, Tetsuki Kato, Izumi Hayashi, Maya Kurosaka, Makoto Katori, Yoshikuni Fujita, Masataka MajimaAbstract:It is suggested that an ATP-sensitive Potassium Channel Blocker suppresses sodium-induced hypertension through increased secretion of urinary kallikrein. We reported that glibenclamide, an ATP-sensitive Potassium Channel Blocker, accelerated dose-dependent secretion of renal kallikrein in sliced kidney cortex and in vivo in rats. In vehicle-treated normal Brown- Norway-Kitasato (nBN-Ki) rats, the administration of glibenclamide increased urinary kallikrein secretion, but changed neither the systolic blood pressure nor the urinary sodium on low (0.3%) NaCl diets. Although on high (8%) NaCl diets, the systolic blood pressure of the nBN-Ki rats administrated glibenclamide was significantly lower ( P
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an atp sensitive Potassium Channel Blocker suppresses sodium induced hypertension through increased secretion of urinary kallikrein
Hypertension Research, 2009Co-Authors: Yuji Kamata, Tomoe Fujita, Tetsuki Kato, Izumi Hayashi, Maya Kurosaka, Makoto Katori, Yoshikuni Fujita, Masataka MajimaAbstract:It is suggested that an ATP-sensitive Potassium Channel Blocker suppresses sodium-induced hypertension through increased secretion of urinary kallikrein. We reported that glibenclamide, an ATP-sensitive Potassium Channel Blocker, accelerated dose-dependent secretion of renal kallikrein in sliced kidney cortex and in vivo in rats. In vehicle-treated normal Brown- Norway-Kitasato (nBN-Ki) rats, the administration of glibenclamide increased urinary kallikrein secretion, but changed neither the systolic blood pressure nor the urinary sodium on low (0.3%) NaCl diets. Although on high (8%) NaCl diets, the systolic blood pressure of the nBN-Ki rats administrated glibenclamide was significantly lower (P<0.05). The urinary levels of kallikrein and sodium of the nBN-Ki rats administrated glibenclamide were significantly increased (P<0.05, glibenclamide vs. vehicle). A similar result was obtained with a kidney-selective ATP-sensitive Potassium Blocker, N,N'-dicyclohexyl-4-morpholinecarboxamidine (U18177), in SD rats. Mutant kininogen-deficient Brown-Norway Katholiek (muBN-Ka) rats fed high (8%) NaCl diets showed an increase in urinary kallikrein levels, but showed neither hypotensive nor natriuretic actions by glibenclamide. A bradykinin B(2) receptor antagonist, 8-[3-[N-(E)-3-(6-acetamidopyridin-3-yl) acryloylglyycyl]-N-methylamino]-2,6-dichlorobenzyloxy]-2-methylquinoline (FR173657), which was administrated to SD rats, together with glibenclamide, abolished the hypotensive and natriuretic effects of glibenclamide in high-sodium (8%NaCl) hypertension, despite an accelerated secretion of urinary kallikrein. Therefore, these results indicate that glibenclamide, an ATP-sensitive Potassium Channel Blocker suppressed sodium-induced hypertension through sodium excretion from the kidney resulting from accelerated secretion of urinary kallikrein.
Alexander A Vassilevski - One of the best experts on this subject based on the ideXlab platform.
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c terminal residues in small Potassium Channel Blockers odk1 and osk3 from scorpion venom fine tune the selectivity
Biochimica et Biophysica Acta, 2017Co-Authors: Steve Peigneur, Jan Tytgat, Alexey I Kuzmenkov, Anton O Chugunov, Valentin M Tabakmakher, Roman G Efremov, Eugene V Grishin, Alexander A VassilevskiAbstract:We report isolation, sequencing, and electrophysiological characterization of OSK3 (α-KTx 8.8 in Kalium and Uniprot databases), a Potassium Channel Blocker from the scorpion Orthochirus scrobiculosus venom. Using the voltage clamp technique, OSK3 was tested on a wide panel of 11 voltage-gated Potassium Channels expressed in Xenopus oocytes, and was found to potently inhibit Kv1.2 and Kv1.3 with IC50 values of ~331nM and ~503nM, respectively. OdK1 produced by the scorpion Odontobuthus doriae differs by just two C-terminal residues from OSK3, but shows marked preference to Kv1.2. Based on the charybdotoxin-Potassium Channel complex crystal structure, a model was built to explain the role of the variable residues in OdK1 and OSK3 selectivity.
Steve Peigneur - One of the best experts on this subject based on the ideXlab platform.
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Protein surface topography as a tool to enhance the selective activity of a Potassium Channel Blocker.
Journal of Biological Chemistry, 2019Co-Authors: Antonina A. Berkut, Steve Peigneur, Anton O Chugunov, Valentin M Tabakmakher, Konstantin S. Mineev, Nikolay A. Krylov, Peter B. Oparin, Alyona F. Lihonosova, Ekaterina V. Novikova, Alexander S. ArsenievAbstract:: Tk-hefu is an artificial peptide designed based on the α-hairpinin scaffold, which selectively blocks voltage-gated Potassium Channels Kv1.3. Here we present its spatial structure resolved by NMR spectroscopy and analyze its interaction with Channels using computer modeling. We apply protein surface topography to suggest mutations and increase Tk-hefu affinity to the Kv1.3 Channel isoform. We redesign the functional surface of Tk-hefu to better match the respective surface of the Channel pore vestibule. The resulting peptide Tk-hefu-2 retains Kv1.3 selectivity and displays ∼15 times greater activity compared with Tk-hefu. We verify the mode of Tk-hefu-2 binding to the Channel outer vestibule experimentally by site-directed mutagenesis. We argue that scaffold engineering aided by protein surface topography represents a reliable tool for design and optimization of specific ion Channel ligands.
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c terminal residues in small Potassium Channel Blockers odk1 and osk3 from scorpion venom fine tune the selectivity
Biochimica et Biophysica Acta, 2017Co-Authors: Steve Peigneur, Jan Tytgat, Alexey I Kuzmenkov, Anton O Chugunov, Valentin M Tabakmakher, Roman G Efremov, Eugene V Grishin, Alexander A VassilevskiAbstract:We report isolation, sequencing, and electrophysiological characterization of OSK3 (α-KTx 8.8 in Kalium and Uniprot databases), a Potassium Channel Blocker from the scorpion Orthochirus scrobiculosus venom. Using the voltage clamp technique, OSK3 was tested on a wide panel of 11 voltage-gated Potassium Channels expressed in Xenopus oocytes, and was found to potently inhibit Kv1.2 and Kv1.3 with IC50 values of ~331nM and ~503nM, respectively. OdK1 produced by the scorpion Odontobuthus doriae differs by just two C-terminal residues from OSK3, but shows marked preference to Kv1.2. Based on the charybdotoxin-Potassium Channel complex crystal structure, a model was built to explain the role of the variable residues in OdK1 and OSK3 selectivity.
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bcstx3 is a founder of a novel sea anemone toxin family of Potassium Channel Blocker
FEBS Journal, 2013Co-Authors: Diego J B Orts, Yehu Moran, Camila Takeno Cologna, Bruno Madio, Daniela Praher, Loic Quinton, Jose Eduardo P W Bicudo, Steve Peigneur, Edwin De Pauw, Jan TytgatAbstract:Sea anemone venoms have become a rich source of peptide toxins which are invaluable tools for studying the structure and functions of ion Channels. In this work, BcsTx3, a toxin found in the venom of a Bunodosoma caissarum (population captured at the Saint Peter and Saint Paul Archipelago, Brazil) was purified and biochemically and pharmacologically characterized. The pharmacological effects were studied on 12 different subtypes of voltage-gated Potassium Channels (KV1.1–KV1.6; KV2.1; KV3.1; KV4.2; KV4.3; hERG and Shaker IR) and three cloned voltage-gated sodium Channel isoforms (NaV1.2, NaV1.4 and BgNaV1.1) expressed in Xenopus laevis oocytes. BcsTx3 shows a high affinity for Drosophila Shaker IR Channels over rKv1.2, hKv1.3 and rKv1.6, and is not active on NaV Channels. Biochemical characterization reveals that BcsTx3 is a 50 amino acid peptide crosslinked by four disulfide bridges, and sequence comparison allowed BcsTx3 to be classified as a novel type of sea anemone toxin acting on KV Channels. Moreover, putative toxins homologous to BcsTx3 from two additional actiniarian species suggest an ancient origin of this newly discovered toxin family.
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novel Potassium Channel Blocker venom peptides from mesobuthus gibbosus scorpiones buthidae
Toxicon, 2012Co-Authors: Elia Diegogarcia, Steve Peigneur, Jan Tytgat, Sarah Debaveye, Eveline Gheldof, Figen CaliskanAbstract:In the present study, we report for the first time, the molecular, biochemical and electrophysiological characterization of the components present in the soluble venom from Mesobuthus gibbosus (Brulle, 1832). According to the epidemiological and clinical situation of scorpion envenomation cases M. gibbosus scorpion is one of the most important health-threatening species of Turkey. Despite the medical importance reported for M. gibbosus, there is no additional information on toxin peptides and venom components to clarify the toxic effect of the M. gibbosus sting. Biochemical characterization of the venom was performed using different protocols and techniques following a bioassay-guided strategy (HPLC, mass spectrometry and Edman degradation sequencing). Venom fractions were tested in electrophysiological assays on a panel of six K+ Channels (Kv1.1–1.6) by using the two-electrode voltage clamp technique. Three new α-KTx peptides were found and called MegKTx1, MegKTx2 and MegKTx3 (M. gibbosus, K+ Channel toxin number 1–3). A cDNA library from the telson was constructed and specific screening of transcripts was performed. Biochemical and molecular characterization of MegKTx peptides and transcripts shows a relation with toxins of three different α-KTx subfamilies (α-KTx3.x, α-KTx9.x and α-KTx16.x).
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a potent Potassium Channel Blocker from mesobuthus eupeus scorpion venom
Biochimie, 2010Co-Authors: Bin Gao, Steve Peigneur, Jan Tytgat, Shunyi ZhuAbstract:Abstract Scorpion venom-derived peptidyl toxins are valuable pharmacological tools for investigating the structure–function relationship of ion Channels. Here, we report the purification, sequencing and functional characterization of a new K + Channel Blocker (MeuKTX) from the venom of the scorpion Mesobuthus eupeus . Effects of MeuKTX on ten cloned Potassium Channels in Xenopus oocytes were evaluated using two-electrode voltage-clamp recordings. MeuKTX is the orthologue of BmKTX (α-KTx3.6), a known Kv1.3 Blocker from the scorpion Mesobuthus martensii , and classified as α-KTx3.13. MeuKTX potently blocks rKv1.1, rKv1.2 and hKv1.3 Channels with 50% inhibitory concentration (IC 50 ) of 203.15 ± 4.06 pM, 8.92 ± 2.3 nM and 171 ± 8.56 pM, respectively, but does not affect rKv1.4, rKv1.5, hKv3.1, rKv4.3, and hERG Channels even at 2 μM concentration. At this high concentration, MeuKTX is also active on rKv1.6 and Shaker IR. Our results also demonstrate that MeuKTX and BmKTX have the same Channel spectrum and similar pharmacological potency. Analysis of the structure–function relationships of α-KTx3 subfamily toxins allows us to recognize several key sites which may be useful for designing toxins with improved activity on hKv1.3, an attractive target for T-cell mediated autoimmune diseases.