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Apamin

The Experts below are selected from a list of 234 Experts worldwide ranked by ideXlab platform

Vincent Seutin – 1st expert on this subject based on the ideXlab platform

  • the interactions of Apamin and tetraethylammonium are differentially affected by single mutations in the pore mouth of small conductance calcium activated potassium sk channels
    Biochemical Pharmacology, 2013
    Co-Authors: Sebastien Dilly, Vincent Seutin, Fabian Philippart, Cedric Lamy, Sylvie Poncin, Dirk J Snyders, Jeanfrancois Liegeois

    Abstract:

    Abstract Valine residues in the pore region of SK2 (V366) and SK3 (V520) were replaced by either an alanine or a phenylalanine to evaluate the impact on the interactions with the allosteric blocker Apamin. Unlike TEA which showed high sensitivity to phenylalanine mutated channels, the binding affinity of Apamin to the phenylalanine mutants was strongly reduced. In addition, currents from phenylalanine mutants were largely resistant to block by Apamin. On the other hand, when the valine residue was replaced by an alanine residue, an increase of the binding affinity and the amount of block by Apamin was observed for alanine mutated SK2 channels, but not for mutated SK3 channels. Interestingly, the VA mutation reduced the sensitivity to TEA. In silico data confirmed these experimental results. Therefore, such mutations in the pore region of SK channels show that the three-dimensional structure of the SK tetramers can be disorganized in the outer pore region leading to reduced interaction of Apamin with its target.

  • crucial role of a shared extracellular loop in Apamin sensitivity and maintenance of pore shape of small conductance calcium activated potassium sk channels
    Proceedings of the National Academy of Sciences of the United States of America, 2011
    Co-Authors: Kate L. Weatherall, Vincent Seutin, Jeanfrancois Liegeois, Neil V. Marrion

    Abstract:

    Activation of small-conductance calcium (Ca2+)-dependent potassium (KCa2) channels (herein called “SK”) produces membrane hyperpolarization to regulate membrane excitability. Three subtypes (SK1–3) have been cloned and are distributed throughout the nervous system, smooth muscle, and heart. It is difficult to discern the physiological role of individual channel subtypes as most blockers or enhancers do not discriminate between subtypes. The archetypical blocker Apamin displays some selectivity between SK channel subtypes, with SK2 being the most sensitive, followed by SK3 and then SK1. Sensitivity of SK1 is species specific, with the human isoform being blocked by the toxin, whereas the rat is not. Mutation studies have identified residues within the outer pore that suggest Apamin blocks by an allosteric mechanism. Apamin also uses a residue within the S3–S4 extracellular loop to produce a high-sensitivity block. We have identified that a 3-amino acid motif within this loop regulates the shape of the channel pore. This motif is required for binding and block by Apamin, suggesting that a change in pore shape underlies allosteric block. This motif is absent in rat SK1, explaining why it is insensitive to block by Apamin. The overlapping distribution of SK channel subtype expression suggests that native heteromeric channels may be common. We show that the S3–S4 loop of one subunit overlaps the outer pore of the adjacent subunit, with Apamin interacting with both regions. This arrangement provides a unique binding site for each combination of SK subunits within a coassembled channel that may be targeted to produce blockers specific for heteromeric SK channels.

  • allosteric block of kca2 channels by Apamin
    Journal of Biological Chemistry, 2010
    Co-Authors: Cedric Lamy, Vincent Seutin, Kate L. Weatherall, Jeanfrancois Liegeois, Samuel J Goodchild, David E Jane, Neil V. Marrion

    Abstract:

    Abstract Activation of small conductance calcium-activated potassium (KCa2) channels can regulate neuronal firing and synaptic plasticity. They are characterized by their high sensitivity to the bee venom toxin Apamin, but the mechanism of block is not understood. For example, Apamin binds to both KCa2.2 and KCa2.3 with the same high affinity (KD ∼ 5 pm for both subtypes) but requires significantly higher concentrations to block functional current (IC50 values of ∼100 pm and ∼5 nm, respectively). This suggests that steps beyond binding are needed for channel block to occur. We have combined patch clamp and binding experiments on cell lines with molecular modeling and mutagenesis to gain more insight into the mechanism of action of the toxin. An outer pore histidine residue common to both subtypes was found to be critical for both binding and block by the toxin but not for block by tetraethylammonium (TEA) ions. These data indicated that Apamin blocks KCa2 channels by binding to a site distinct from that used by TEA, supported by a finding that the onset of block by Apamin was not affected by the presence of TEA. Structural modeling of ligand-channel interaction indicated that TEA binds deep within the channel pore, which contrasted with Apamin being modeled to interact with the channel outer pore by utilizing the outer pore histidine residue. This multidisciplinary approach suggested that Apamin does not behave as a classical pore blocker but blocks using an allosteric mechanism that is consistent with observed differences between binding affinity and potency of block.

Kwankyu Park – 2nd expert on this subject based on the ideXlab platform

  • Therapeutic Effects of Apamin as a Bee Venom Component for Non-Neoplastic Disease.
    Toxins, 2020
    Co-Authors: Hyemin Gu, Kwankyu Park

    Abstract:

    Bee venom is a natural toxin produced by honeybees and plays an important role in defending bee colonies. Bee venom has several kinds of peptides, including melittin, Apamin, adolApamine, and mast cell degranulation peptides. Apamin accounts for about 2%-3% dry weight of bee venom and is a peptide neurotoxin that contains 18 amino acid residues that are tightly crosslinked by two disulfide bonds. It is well known for its pharmacological functions, which irreversibly block Ca2+-activated K+ (SK) channels. Apamin regulates gene expression in various signal transduction pathways involved in cell development. The aim of this study was to review the current understanding of Apamin in the treatment of apoptosis, fibrosis, and central nervous system diseases, which are the pathological processes of various diseases. Apamin‘s potential therapeutic and pharmacological applications are also discussed.

  • Apamin suppresses biliary fibrosis and activation of hepatic stellate cells
    International Journal of Molecular Medicine, 2017
    Co-Authors: Hyunjin An, Yoonyub Park, Kyung Duck Park, Kwankyu Park

    Abstract:

    : Cholestatic liver disease is characterized by the progressive destruction of biliary epithelial cells (BECs) followed by fibrosis, cirrhosis and liver failure. Activated hepatic stellate cells (HSCs) and portal fibroblasts are the major cellular effectors of enhanced collagen deposition in biliary fibrosis. Apamin, an 18 amino acid peptide neurotoxin found in apitoxin (bee venom), is known to block Ca2+-activated K+ channels and prevent carbon tetrachloride-induced liver fibrosis. In the present study, we aimed to ascertain whether Apamin inhibits biliary fibrosis and the proliferation of HSCs. Cholestatic liver fibrosis was established in mouse models with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) feeding. Cellular assays were performed on HSC-T6 cells (rat immortalized HSCs). DDC feeding led to increased hepatic damage and proinflammtory cytokine levels. Notably, Apamin treatment resulted in decreased liver injury and proinflammatory cytokine levels. Moreover, Apamin suppressed the deposition of collagen, proliferation of BECs and expression of fibrogenic genes in the DDC-fed mice. In HSCs, Apamin suppressed activation of HSCs by inhibiting the Smad signaling pathway. These data suggest that Apamin may be a potential therapeutic target in cholestatic liver disease.

  • Apamin inhibits tnf α and ifn γ induced inflammatory cytokines and chemokines via suppressions of nf κb signaling pathway and stat in human keratinocytes
    Pharmacological Reports, 2017
    Co-Authors: Hyunjin An, Kyung Duck Park, Migyeong Gwon, Hyemin Gu, Ji Y Park, Kwankyu Park

    Abstract:

    Abstract Background Atopic dermatitis (AD) is identified by an increase in infiltrations of several inflammatory cells including type 2 helper (Th2) lymphocytes. Th2-related chemokines such as thymus and activation-regulated chemokine (TARC/CCL17) and macrophage-derived chemokine (MDC/CCL22), and pro-inflammatory cytokines including interleukin (IL)-1β and IL-6 are considered to play a crucial role in AD. Tumor necrosis factor (TNF)-α- and interferon (IFN)-γ induce the inflammatory condition through production of TARC, MDC, IL-1β and IL-6, and activations of related transcription factors, such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and signal transducer and activator of transcription (STAT) in keratinocytes. Apamin, a peptide component of bee venom, has been reported its beneficial activities in various diseases. However, anti-inflammatory effects of Apamin on inflammatory condition in keratinocytes have not been explored. Therefore, the present study aimed to demonstrate the anti-inflammatory effect of Apamin on TNF-α- and IFN-γ-induced inflammatory condition in keratinocytes. Methods HaCaT was used as human keratinocytes cell line. Cell Counting Kit-8 was performed to measure a cytotoxicity of Apamin. The effects of Apamin on TNF-α-/IFN-γ-induced inflammatory condition were determined by real-time PCR and Western blot analysis. Further, NF-κB signaling pathways, STAT1, and STAT3 were analyzed by Western blot and immunofluorescence. Results Apamin ameliorated the inflammatory condition through suppression of Th2-related chemokines and pro-inflammatory cytokines. Further, Apamin down-regulated the activations of NF-κB signaling pathways and STATs in HaCaT cells. Conclusions These results suggest that Apamin has therapeutic effect on AD through improvement of inflammatory condition.

Jeanfrancois Liegeois – 3rd expert on this subject based on the ideXlab platform

  • the interactions of Apamin and tetraethylammonium are differentially affected by single mutations in the pore mouth of small conductance calcium activated potassium sk channels
    Biochemical Pharmacology, 2013
    Co-Authors: Sebastien Dilly, Vincent Seutin, Fabian Philippart, Cedric Lamy, Sylvie Poncin, Dirk J Snyders, Jeanfrancois Liegeois

    Abstract:

    Abstract Valine residues in the pore region of SK2 (V366) and SK3 (V520) were replaced by either an alanine or a phenylalanine to evaluate the impact on the interactions with the allosteric blocker Apamin. Unlike TEA which showed high sensitivity to phenylalanine mutated channels, the binding affinity of Apamin to the phenylalanine mutants was strongly reduced. In addition, currents from phenylalanine mutants were largely resistant to block by Apamin. On the other hand, when the valine residue was replaced by an alanine residue, an increase of the binding affinity and the amount of block by Apamin was observed for alanine mutated SK2 channels, but not for mutated SK3 channels. Interestingly, the VA mutation reduced the sensitivity to TEA. In silico data confirmed these experimental results. Therefore, such mutations in the pore region of SK channels show that the three-dimensional structure of the SK tetramers can be disorganized in the outer pore region leading to reduced interaction of Apamin with its target.

  • crucial role of a shared extracellular loop in Apamin sensitivity and maintenance of pore shape of small conductance calcium activated potassium sk channels
    Proceedings of the National Academy of Sciences of the United States of America, 2011
    Co-Authors: Kate L. Weatherall, Vincent Seutin, Jeanfrancois Liegeois, Neil V. Marrion

    Abstract:

    Activation of small-conductance calcium (Ca2+)-dependent potassium (KCa2) channels (herein called “SK”) produces membrane hyperpolarization to regulate membrane excitability. Three subtypes (SK1–3) have been cloned and are distributed throughout the nervous system, smooth muscle, and heart. It is difficult to discern the physiological role of individual channel subtypes as most blockers or enhancers do not discriminate between subtypes. The archetypical blocker Apamin displays some selectivity between SK channel subtypes, with SK2 being the most sensitive, followed by SK3 and then SK1. Sensitivity of SK1 is species specific, with the human isoform being blocked by the toxin, whereas the rat is not. Mutation studies have identified residues within the outer pore that suggest Apamin blocks by an allosteric mechanism. Apamin also uses a residue within the S3–S4 extracellular loop to produce a high-sensitivity block. We have identified that a 3-amino acid motif within this loop regulates the shape of the channel pore. This motif is required for binding and block by Apamin, suggesting that a change in pore shape underlies allosteric block. This motif is absent in rat SK1, explaining why it is insensitive to block by Apamin. The overlapping distribution of SK channel subtype expression suggests that native heteromeric channels may be common. We show that the S3–S4 loop of one subunit overlaps the outer pore of the adjacent subunit, with Apamin interacting with both regions. This arrangement provides a unique binding site for each combination of SK subunits within a coassembled channel that may be targeted to produce blockers specific for heteromeric SK channels.

  • allosteric block of kca2 channels by Apamin
    Journal of Biological Chemistry, 2010
    Co-Authors: Cedric Lamy, Vincent Seutin, Kate L. Weatherall, Jeanfrancois Liegeois, Samuel J Goodchild, David E Jane, Neil V. Marrion

    Abstract:

    Abstract Activation of small conductance calcium-activated potassium (KCa2) channels can regulate neuronal firing and synaptic plasticity. They are characterized by their high sensitivity to the bee venom toxin Apamin, but the mechanism of block is not understood. For example, Apamin binds to both KCa2.2 and KCa2.3 with the same high affinity (KD ∼ 5 pm for both subtypes) but requires significantly higher concentrations to block functional current (IC50 values of ∼100 pm and ∼5 nm, respectively). This suggests that steps beyond binding are needed for channel block to occur. We have combined patch clamp and binding experiments on cell lines with molecular modeling and mutagenesis to gain more insight into the mechanism of action of the toxin. An outer pore histidine residue common to both subtypes was found to be critical for both binding and block by the toxin but not for block by tetraethylammonium (TEA) ions. These data indicated that Apamin blocks KCa2 channels by binding to a site distinct from that used by TEA, supported by a finding that the onset of block by Apamin was not affected by the presence of TEA. Structural modeling of ligand-channel interaction indicated that TEA binds deep within the channel pore, which contrasted with Apamin being modeled to interact with the channel outer pore by utilizing the outer pore histidine residue. This multidisciplinary approach suggested that Apamin does not behave as a classical pore blocker but blocks using an allosteric mechanism that is consistent with observed differences between binding affinity and potency of block.