scholarly journals Variation of Two S3b Residues in KV4.1–4.3 Channels Underlies Their Different Modulations by Spider Toxin κ-LhTx-1

2021 ◽  
Vol 12 ◽  
Author(s):  
Zhen Xiao ◽  
Piao Zhao ◽  
Xiangyue Wu ◽  
Xiangjin Kong ◽  
Ruiwen Wang ◽  
...  
Keyword(s):  
Mutation Analysis ◽  
Voltage Dependence ◽  
Underlying Mechanism ◽  
Voltage Sensor ◽  
Action Mode ◽  
Gating Modifier ◽  
Peptide Toxin ◽  
Peptide Toxins ◽  
Key Residues ◽  
Animal Venoms

The naturally occurred peptide toxins from animal venoms are valuable pharmacological tools in exploring the structure-function relationships of ion channels. Herein we have identified the peptide toxin κ-LhTx-1 from the venom of spider Pandercetes sp (the Lichen huntsman spider) as a novel selective antagonist of the KV4 family potassium channels. κ-LhTx-1 is a gating-modifier toxin impeded KV4 channels’ voltage sensor activation, and mutation analysis has confirmed its binding site on channels’ S3b region. Interestingly, κ-LhTx-1 differently modulated the gating of KV4 channels, as revealed by toxin inhibiting KV4.2/4.3 with much more stronger voltage-dependence than that for KV4.1. We proposed that κ-LhTx-1 trapped the voltage sensor of KV4.1 in a much more stable resting state than that for KV4.2/4.3 and further explored the underlying mechanism. Swapping the non-conserved S3b segments between KV4.1(280FVPK283) and KV4.3(275VMTN278) fully reversed their voltage-dependence phenotypes in inhibition by κ-LhTx-1, and intensive mutation analysis has identified P282 in KV4.1, D281 in KV4.2 and N278 in KV4.3 being the key residues. Furthermore, the last two residues in this segment of each KV4 channel (P282/K283 in KV4.1, T280/D281 in KV4.2 and T277/N278 in KV4.3) likely worked synergistically as revealed by our combinatorial mutations analysis. The present study has clarified the molecular basis in KV4 channels for their different modulations by κ-LhTx-1, which have advanced our understanding on KV4 channels’ structure features. Moreover, κ-LhTx-1 might be useful in developing anti-arrhythmic drugs given its high affinity, high selectivity and unique action mode in interacting with the KV4.2/4.3 channels.

scholarly journals Mechanism of hERG inhibition by gating-modifier toxin, APETx1, deduced by functional characterization

2021 ◽  
Vol 22 (1) ◽  
Author(s):  
Kazuki Matsumura ◽  
Takushi Shimomura ◽  
Yoshihiro Kubo ◽  
Takayuki Oka ◽  
Naohiro Kobayashi ◽  
...  
Keyword(s):  
Potassium Channel ◽  
Resting State ◽  
Mutational Analysis ◽  
Functional Characterization ◽  
Structural Basis ◽  
Anthopleura Elegantissima ◽  
Gating Modifier ◽  
Peptide Toxin ◽  
Key Residues ◽  
Voltage Sensing Domain

Abstract Background Human ether-à-go-go-related gene potassium channel 1 (hERG) is a voltage-gated potassium channel, the voltage-sensing domain (VSD) of which is targeted by a gating-modifier toxin, APETx1. APETx1 is a 42-residue peptide toxin of sea anemone Anthopleura elegantissima and inhibits hERG by stabilizing the resting state. A previous study that conducted cysteine-scanning analysis of hERG identified two residues in the S3-S4 region of the VSD that play important roles in hERG inhibition by APETx1. However, mutational analysis of APETx1 could not be conducted as only natural resources have been available until now. Therefore, it remains unclear where and how APETx1 interacts with the VSD in the resting state. Results We established a method for preparing recombinant APETx1 and determined the NMR structure of the recombinant APETx1, which is structurally equivalent to the natural product. Electrophysiological analyses using wild type and mutants of APETx1 and hERG revealed that their hydrophobic residues, F15, Y32, F33, and L34, in APETx1, and F508 and I521 in hERG, in addition to a previously reported acidic hERG residue, E518, play key roles in the inhibition of hERG by APETx1. Our hypothetical docking models of the APETx1-VSD complex satisfied the results of mutational analysis. Conclusions The present study identified the key residues of APETx1 and hERG that are involved in hERG inhibition by APETx1. These results would help advance understanding of the inhibitory mechanism of APETx1, which could provide a structural basis for designing novel ligands targeting the VSDs of KV channels.

scholarly journals Peptide toxin blockers of voltage-sensitive K+ channels: inotropic effects on diaphragm

1999 ◽  
Vol 86 (3) ◽  
pp. 1009-1016 ◽  
Author(s):  
Erik van Lunteren ◽  
Michelle Moyer
Keyword(s):  
Inotropic Effects ◽  
Twitch Force ◽  
Voltage Gated ◽  
Blocking Voltage ◽  
Peptide Toxin ◽  
Peptide Toxins ◽  
Diaphragm In Vitro ◽  
Initial Force ◽  
Train Stimulation

Agents that block many types of K+ channels (e.g., the aminopyridines) have substantial inotropic effects in skeletal muscle. Specific blockers of ATP-sensitive and Ca2+-activated K+ channels, on the other hand, do not, or minimally, alter the force of nonfatigued muscle, consistent with a predominant role for voltage-gated K+ channels in regulating muscle force. To test this more directly, we examined the effects of peptide toxins, which in other tissues specifically block voltage-gated K+ channels, on rat diaphragm in vitro. Twitch force was increased in response to α-, β-, and γ-dendrotoxin and tityustoxin Kα (17 ± 6, 22 ± 5, 42 ± 14, and 13 ± 5%; P < 0.05, < 0.01, < 0.05, < 0.05, respectively) but not in response to δ-dendrotoxin or BSA (in which toxins were dissolved). Force during 20-Hz stimulation was also increased significantly by α-, β-, and γ-dendrotoxin and tityustoxin Kα. Among agents, increases in twitch force correlated with the degree to which contraction time was prolonged ( r = 0.88, P < 0.02). To determine whether inotropic effects could be maintained during repeated contractions, muscle strips underwent intermittent 20-Hz train stimulation for a duration of 2 min in presence or absence of γ-dendrotoxin. Force was significantly greater with than without γ-dendrotoxin during repetitive stimulation for the first 60 s of repetitive contractions. Despite the ∼55% higher value for initial force in the presence vs. absence of γ-dendrotoxin, the rate at which fatigue occurred was not accelerated by the toxin, as assessed by the amount of time over which force declined by 25 and 50%. These data suggest that blocking voltage-activated K+ channels may be a useful therapeutic strategy for augmenting diaphragm force, provided less toxic blockers of these channels can be found.

Inhibition of CFTR channels by a peptide toxin of scorpion venom

2004 ◽  
Vol 287 (5) ◽  
pp. C1328-C1341 ◽  
Author(s):  
Matthew D. Fuller ◽  
Zhi-Ren Zhang ◽  
Guiying Cui ◽  
Julia Kubanek ◽  
Nael A. McCarty
Keyword(s):  
Cystic Fibrosis ◽  
Single Channel ◽  
Genetic Disorders ◽  
Scorpion Venom ◽  
Burst Duration ◽  
Open Probability ◽  
Independent Manner ◽  
Peptide Toxin ◽  
Peptide Toxins ◽  
Block Mechanism

Peptide toxins have been valuable probes in efforts to identify amino acid residues that line the permeation pathway of cation-selective channels. However, no peptide toxins have been identified that interact with known anion-selective channels such as the cystic fibrosis transmembrane conductance regulator (CFTR). CFTR channels are expressed in epithelial cells and are associated with several genetic disorders, including cystic fibrosis and polycystic kidney disease. Several organic inhibitors have been used to investigate the structure of the Cl− permeation pathway in CFTR. However, investigations of the wider cytoplasmic vestibule have been hindered by the lack of a high-affinity blocker that interacts with residues in this area. In this study we show that venom of the scorpion Leiurus quinquestriatus hebraeus reversibly inhibits CFTR, in a voltage-independent manner, by decreasing single-channel mean burst duration and open probability only when applied to the cytoplasmic surface of phosphorylated channels. Venom was able to decrease burst duration and open probability even when CFTR channels were locked open by treatment with either vanadate or adenosine 5′-(β,γ-imido)triphosphate, and block was strengthened on reduction of extracellular Cl− concentration, suggesting inhibition by a pore-block mechanism. Venom had no effect on ATP-dependent macroscopic opening rate in channels studied by inside-out macropatches. Interestingly, the inhibitory activity was abolished by proteinase treatment. We conclude that a peptide toxin contained in the scorpion venom inhibits CFTR channels by a pore-block mechanism; these experiments provide the first step toward isolation of the active component, which would be highly valuable as a probe for CFTR structure and function.

scholarly journals Voltage- and NADPH-dependence of electron currents generated by the phagocytic NADPH oxidase

2005 ◽  
Vol 388 (2) ◽  
pp. 485-491 ◽  
Author(s):  
Gábor L. PETHEŐ ◽  
Nicolas DEMAUREX
Keyword(s):  
Membrane Potential ◽  
Nadph Oxidase ◽  
Voltage Dependence ◽  
Intrinsic Property ◽  
Maximal Activity ◽  
Underlying Mechanism ◽  
Potential Range ◽  
Electron Current ◽  
Steady State Current ◽  
Voltage Dependent

The phagocytic NADPH oxidase generates superoxide by transferring electrons from cytosolic NADPH to extracellular O2. The activity of the oxidase at the plasma membrane can be measured as electron current (Ie), and the voltage dependence of Ie was recently reported to exhibit a strong rectification in human eosinophils, with the currents being nearly voltage independent at negative potentials. To investigate the underlying mechanism, we performed voltage-clamp experiments on inside-out patches from human eosinophils activated with PMA. Electron current was evoked by bath application of different concentrations of NADPH, whereas slow voltage ramps (0.8 mV/ms), ranging from −120 to 200 mV, were applied to obtain ‘steady-state’ current–voltage relationships (I–V). The amplitude of Ie recorded at −40 mV was minimal at 8 μM NADPH and saturated above 1 mM, with half-maximal activity (Km) observed at approx. 110 μM NADPH. Comparison of I–V values obtained at different NADPH concentrations revealed that the voltage-dependence of Ie is strongly influenced by the substrate concentration. Above 0.1 mM NADPH, Ie was markedly voltage-dependent and steeply decreased with depolarization within the physiological membrane potential range (−60 to 60 mV), the I–V curve strongly rectifying only below −100 mV. At lower NADPH concentrations the I–V curve was progressively shifted to more positive potentials and Ie became voltage-independent also within the physiological range. Consequently, the Km of the oxidase decreased by approx. 40% (from 100 to 60 μM) when the membrane potential increased from −60 to 60 mV. We concluded that the oxidase activity depends on both membrane potential and [NADPH], and that the shape of the Ie–V curve is influenced by the concentration of NADPH in the submillimolar range. The surprising voltage-independence of Ie reported in whole-cell perforated patch recordings was most likely due to substrate limitation and is not an intrinsic property of the oxidase.

scholarly journals Role of Charged Residues in the S1–S4 Voltage Sensor of BK Channels

2006 ◽  
Vol 127 (3) ◽  
pp. 309-328 ◽  
Author(s):  
Zhongming Ma ◽  
Xing Jian Lou ◽  
Frank T. Horrigan
Keyword(s):  
Voltage Dependence ◽  
Bk Channels ◽  
Bk Channel ◽  
Voltage Sensor ◽  
Voltage Gating ◽  
Voltage Sensing ◽  
Kv Channels ◽  
Gating Charge ◽  
Charged Residues ◽  
Sensor Activation

The activation of large conductance Ca2+-activated (BK) potassium channels is weakly voltage dependent compared to Shaker and other voltage-gated K+ (KV) channels. Yet BK and KV channels share many conserved charged residues in transmembrane segments S1–S4. We mutated these residues individually in mSlo1 BK channels to determine their role in voltage gating, and characterized the voltage dependence of steady-state activation (Po) and IK kinetics (τ(IK)) over an extended voltage range in 0–50 μM [Ca2+]i. mSlo1 contains several positively charged arginines in S4, but only one (R213) together with residues in S2 (D153, R167) and S3 (D186) are potentially voltage sensing based on the ability of charge-altering mutations to reduce the maximal voltage dependence of PO. The voltage dependence of PO and τ(IK) at extreme negative potentials was also reduced, implying that the closed–open conformational change and voltage sensor activation share a common source of gating charge. Although the position of charged residues in the BK and KV channel sequence appears conserved, the distribution of voltage-sensing residues is not. Thus the weak voltage dependence of BK channel activation does not merely reflect a lack of charge but likely differences with respect to KV channels in the position and movement of charged residues within the electric field. Although mutation of most sites in S1–S4 did not reduce gating charge, they often altered the equilibrium constant for voltage sensor activation. In particular, neutralization of R207 or R210 in S4 stabilizes the activated state by 3–7 kcal mol−1, indicating a strong contribution of non–voltage-sensing residues to channel function, consistent with their participation in state-dependent salt bridge interactions. Mutations in S4 and S3 (R210E, D186A, and E180A) also unexpectedly weakened the allosteric coupling of voltage sensor activation to channel opening. The implications of our findings for BK channel voltage gating and general mechanisms of voltage sensor activation are discussed.

scholarly journals Structural basis for voltage-sensor trapping of the cardiac sodium channel by a deathstalker scorpion toxin

2020 ◽  
Author(s):  
Daohua Jiang ◽  
Lige Tonggu ◽  
Tamer M. Gamal El-Din ◽  
Richard Banh ◽  
Régis Pomès ◽  
...  
Keyword(s):  
Ion Pairs ◽  
Voltage Sensor ◽  
Structural Basis ◽  
Fast Inactivation ◽  
Toxin Binding ◽  
Cardiac Sodium Channel ◽  
Activated State ◽  
Nav Channels ◽  
Gating Modifier ◽  
Voltage Sensing Domain

AbstractVoltage-gated sodium (NaV) channels initiate action potentials in excitable cells, and their function is altered by potent gating-modifier toxins. The α-toxin LqhIII from the deathstalker scorpion inhibits fast inactivation of cardiac NaV1.5 channels with IC50=11.4 nM. Here we reveal the structure of LqhIII bound to NaV1.5 at 3.3 Å resolution by cryo-EM. LqhIII anchors on top of voltage-sensing domain IV, wedged between the S1-S2 and S3-S4 linkers, which traps the gating charges of the S4 segment in a unique intermediate-activated state stabilized by four ion-pairs. This conformational change is propagated inward to weaken binding of the fast inactivation gate and favor opening the activation gate. However, these changes do not permit Na+ permeation, revealing why LqhIII slows inactivation of NaV channels but does not open them. Our results provide important insights into the structural basis for gating-modifier toxin binding, voltage-sensor trapping, and fast inactivation of NaV channels.

scholarly journals PIP2 mediates functional coupling and pharmacology of neuronal KCNQ channels

2017 ◽  
Vol 114 (45) ◽  
pp. E9702-E9711 ◽  
Author(s):  
Robin Y. Kim ◽  
Stephan A. Pless ◽  
Harley T. Kurata
Keyword(s):  
Conformational Changes ◽  
Neuronal Excitability ◽  
Voltage Dependence ◽  
Voltage Sensor ◽  
Functional Coupling ◽  
Voltage Sensing ◽  
Kcnq Channels ◽  
C Terminus ◽  
Hyperpolarizing Shift ◽  
State Ionic

Retigabine (RTG) is a first-in-class antiepileptic drug that suppresses neuronal excitability through the activation of voltage-gated KCNQ2–5 potassium channels. Retigabine binds to the pore-forming domain, causing a hyperpolarizing shift in the voltage dependence of channel activation. To elucidate how the retigabine binding site is coupled to changes in voltage sensing, we used voltage-clamp fluorometry to track conformational changes of the KCNQ3 voltage-sensing domains (VSDs) in response to voltage, retigabine, and PIP2. Steady-state ionic conductance and voltage sensor fluorescence closely overlap under basal PIP2 conditions. Retigabine stabilizes the conducting conformation of the pore and the activated voltage sensor conformation, leading to dramatic deceleration of current and fluorescence deactivation, but these effects are attenuated upon disruption of channel:PIP2 interactions. These findings reveal an important role for PIP2 in coupling retigabine binding to altered VSD function. We identify a polybasic motif in the proximal C terminus of retigabine-sensitive KCNQ channels that contributes to VSD–pore coupling via PIP2, and thereby influences the unique gating effects of retigabine.

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