scholarly journals Epilepsy-associated mutations in the voltage sensor of KCNQ3 affect voltage dependence of channel opening

2018 ◽  
Vol 151 (2) ◽  
pp. 247-257 ◽  
Author(s):  
Rene Barro-Soria
Keyword(s):  
Unnatural Amino Acids ◽  
Molecular Mechanisms ◽  
Neuronal Excitability ◽  
Voltage Dependence ◽  
Therapeutic Potential ◽  
Voltage Sensor ◽  
Voltage Range ◽  
M Current ◽  
Channel Opening ◽  
Major Factors

One of the major factors known to cause neuronal hyperexcitability is malfunction of the potassium channels formed by KCNQ2 and KCNQ3. These channel subunits underlie the M current, which regulates neuronal excitability. Here, I investigate the molecular mechanisms by which epilepsy-associated mutations in the voltage sensor (S4) of KCNQ3 cause channel malfunction. Voltage clamp fluorometry reveals that the R230C mutation in KCNQ3 allows S4 movement but shifts the open/closed transition of the gate to very negative potentials. This results in the mutated channel remaining open throughout the physiological voltage range. Substitution of R230 with natural and unnatural amino acids indicates that the functional effect of the arginine residue at position 230 depends on both its positive charge and the size of its side chain. I find that KCNQ3-R230C is hard to close, but it is capable of being closed at strong negative voltages. I suggest that compounds that shift the voltage dependence of S4 activation to more positive potentials would promote gate closure and thus have therapeutic potential.

scholarly journals Domain IV voltage-sensor movement is both sufficient and rate limiting for fast inactivation in sodium channels

2013 ◽  
Vol 142 (2) ◽  
pp. 101-112 ◽  
Author(s):  
Deborah L. Capes ◽  
Marcel P. Goldschen-Ohm ◽  
Manoel Arcisio-Miranda ◽  
Francisco Bezanilla ◽  
Baron Chanda
Keyword(s):  
Sodium Channels ◽  
Voltage Sensor ◽  
Fast Inactivation ◽  
Voltage Range ◽  
Voltage Gated Sodium Channels ◽  
Channel Opening ◽  
The Individual ◽  
Electrical Impulses ◽  
Voltage Sensing Domain ◽  
Rate Limiting

Voltage-gated sodium channels are critical for the generation and propagation of electrical signals in most excitable cells. Activation of Na+ channels initiates an action potential, and fast inactivation facilitates repolarization of the membrane by the outward K+ current. Fast inactivation is also the main determinant of the refractory period between successive electrical impulses. Although the voltage sensor of domain IV (DIV) has been implicated in fast inactivation, it remains unclear whether the activation of DIV alone is sufficient for fast inactivation to occur. Here, we functionally neutralize each specific voltage sensor by mutating several critical arginines in the S4 segment to glutamines. We assess the individual role of each voltage-sensing domain in the voltage dependence and kinetics of fast inactivation upon its specific inhibition. We show that movement of the DIV voltage sensor is the rate-limiting step for both development and recovery from fast inactivation. Our data suggest that activation of the DIV voltage sensor alone is sufficient for fast inactivation to occur, and that activation of DIV before channel opening is the molecular mechanism for closed-state inactivation. We propose a kinetic model of sodium channel gating that can account for our major findings over a wide voltage range by postulating that DIV movement is both necessary and sufficient for fast inactivation.

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.

scholarly journals Uncoupling Charge Movement from Channel Opening in Voltage-gated Potassium Channels by Ruthenium Complexes

2011 ◽  
Vol 286 (18) ◽  
pp. 16414-16425 ◽  
Author(s):  
Andrés Jara-Oseguera ◽  
Itzel G. Ishida ◽  
Gisela E. Rangel-Yescas ◽  
Noel Espinosa-Jalapa ◽  
José A. Pérez-Guzmán ◽  
...  
Keyword(s):  
Electromechanical Coupling ◽  
Voltage Dependence ◽  
Voltage Sensor ◽  
Delayed Rectifier ◽  
Charge Movement ◽  
Β Cells ◽  
Delayed Rectifier Current ◽  
Mechanism Of Inhibition ◽  
Channel Opening ◽  
Sensor Activation

The Kv2.1 channel generates a delayed-rectifier current in neurons and is responsible for modulation of neuronal spike frequency and membrane repolarization in pancreatic β-cells and cardiomyocytes. As with other tetrameric voltage-activated K+-channels, it has been proposed that each of the four Kv2.1 voltage-sensing domains activates independently upon depolarization, leading to a final concerted transition that causes channel opening. The mechanism by which voltage-sensor activation is coupled to the gating of the pore is still not understood. Here we show that the carbon-monoxide releasing molecule 2 (CORM-2) is an allosteric inhibitor of the Kv2.1 channel and that its inhibitory properties derive from the CORM-2 ability to largely reduce the voltage dependence of the opening transition, uncoupling voltage-sensor activation from the concerted opening transition. We additionally demonstrate that CORM-2 modulates Shaker K+-channels in a similar manner. Our data suggest that the mechanism of inhibition by CORM-2 may be common to voltage-activated channels and that this compound should be a useful tool for understanding the mechanisms of electromechanical coupling.

scholarly journals KCNE3 acts by promoting voltage sensor activation in KCNQ1

2015 ◽  
Vol 112 (52) ◽  
pp. E7286-E7292 ◽  
Author(s):  
Rene Barro-Soria ◽  
Marta E. Perez ◽  
H. Peter Larsson
Keyword(s):  
Electrostatic Interaction ◽  
Voltage Dependence ◽  
Voltage Sensor ◽  
Α Subunit ◽  
Voltage Range ◽  
Voltage Gated ◽  
Gate Opening ◽  
Channel Gate ◽  
Sensor Activation ◽  
Voltage Sensing Domain

KCNE β-subunits assemble with and modulate the properties of voltage-gated K+ channels. In the colon, stomach, and kidney, KCNE3 coassembles with the α-subunit KCNQ1 to form K+ channels important for K+ and Cl− secretion that appear to be voltage-independent. How KCNE3 subunits turn voltage-gated KCNQ1 channels into apparent voltage-independent KCNQ1/KCNE3 channels is not completely understood. Different mechanisms have been proposed to explain the effect of KCNE3 on KCNQ1 channels. Here, we use voltage clamp fluorometry to determine how KCNE3 affects the voltage sensor S4 and the gate of KCNQ1. We find that S4 moves in KCNQ1/KCNE3 channels, and that inward S4 movement closes the channel gate. However, KCNE3 shifts the voltage dependence of S4 movement to extreme hyperpolarized potentials, such that in the physiological voltage range, the channel is constitutively conducting. By separating S4 movement and gate opening, either by a mutation or PIP2 depletion, we show that KCNE3 directly affects the S4 movement in KCNQ1. Two negatively charged residues of KCNE3 (D54 and D55) are found essential for the effect of KCNE3 on KCNQ1 channels, mainly exerting their effects by an electrostatic interaction with R228 in S4. Our results suggest that KCNE3 primarily affects the voltage-sensing domain and only indirectly affects the gate.

scholarly journals Pore- and voltage sensor–targeted KCNQ openers have distinct state-dependent actions

2018 ◽  
Vol 150 (12) ◽  
pp. 1722-1734 ◽  
Author(s):  
Caroline K. Wang ◽  
Shawn M. Lamothe ◽  
Alice W. Wang ◽  
Runying Y. Yang ◽  
Harley T. Kurata
Keyword(s):  
Voltage Dependence ◽  
Drug Effects ◽  
Drug Binding ◽  
Voltage Sensor ◽  
Voltage Sensing ◽  
Channel Activation ◽  
M Current ◽  
State Dependent ◽  
Mechanistic Basis ◽  
Voltage Sensing Domain

Ion channels encoded by KCNQ2-5 generate a prominent K+ conductance in the central nervous system, referred to as the M current, which is controlled by membrane voltage and PIP2. The KCNQ2-5 voltage-gated potassium channels are targeted by a variety of activating compounds that cause negative shifts in the voltage dependence of activation. The underlying pharmacology of these effects is of growing interest because of possible clinical applications. Recent studies have revealed multiple binding sites and mechanisms of action of KCNQ activators. For example, retigabine targets the pore domain, but several compounds have been shown to influence the voltage-sensing domain. An important unexplored feature of these compounds is the influence of channel gating on drug binding or effects. In the present study, we compare the state-dependent actions of retigabine and ICA-069673 (ICA73, a voltage sensor–targeted activator). We assess drug binding to preopen states by applying drugs to homomeric KCNQ2 channels at different holding voltages, demonstrating little or no association of ICA73 with resting states. Using rapid solution switching, we also demonstrate that the rate of onset of ICA73 correlates with the voltage dependence of channel activation. Retigabine actions differ significantly, with prominent drug effects seen at very negative holding voltages and distinct voltage dependences of drug binding versus channel activation. Using similar approaches, we investigate the mechanistic basis for attenuation of ICA73 actions by the voltage-sensing domain mutation KCNQ2[A181P]. Our findings demonstrate different state-dependent actions of pore- versus voltage sensor–targeted KCNQ channel activators, which highlight that subtypes of this drug class operate with distinct mechanisms.

scholarly journals Characterization of Synthetic Tf2 as a NaV1.3 Selective Pharmacological Probe

Biomedicines ◽  
2020 ◽  
Vol 8 (6) ◽  
pp. 155
Author(s):  
Mathilde R. Israel ◽  
Thomas S. Dash ◽  
Stefanie N. Bothe ◽  
Samuel D. Robinson ◽  
Jennifer R. Deuis ◽  
...  
Keyword(s):  
Neuropathic Pain ◽  
Neuronal Excitability ◽  
Voltage Dependence ◽  
Scorpion Toxins ◽  
Intraplantar Injection ◽  
Voltage Gated ◽  
Channel Opening ◽  
Excitatory Activity ◽  
Target Activity

NaV1.3 is a subtype of the voltage-gated sodium channel family. It has been implicated in the pathogenesis of neuropathic pain, although the contribution of this channel to neuronal excitability is not well understood. Tf2, a β-scorpion toxin previously identified from the venom of Tityus fasciolatus, has been reported to selectively activate NaV1.3. Here, we describe the activity of synthetic Tf2 and assess its suitability as a pharmacological probe for NaV1.3. As described for the native toxin, synthetic Tf2 (1 µM) caused early channel opening, decreased the peak current, and shifted the voltage dependence of NaV1.3 activation in the hyperpolarizing direction by −11.3 mV, with no activity at NaV1.1, NaV1.2, and NaV1.4-NaV1.8. Additional activity was found at NaV1.9, tested using the hNav1.9_C4 chimera, where Tf2 (1 µM) shifted the voltage dependence of activation by −6.3 mV. In an attempt to convert Tf2 into an NaV1.3 inhibitor, we synthetized the analogue Tf2[S14R], a mutation previously described to remove the excitatory activity of related β-scorpion toxins. Indeed, Tf2[S14R](10 µM) had reduced excitatory activity at NaV1.3, although it still caused a small −5.8 mV shift in the voltage dependence of activation. Intraplantar injection of Tf2 (1 µM) in mice caused spontaneous flinching and swelling, which was not reduced by the NaV1.1/1.3 inhibitor ICA-121431 nor in NaV1.9-/- mice, suggesting off-target activity. In addition, despite a loss of excitatory activity, intraplantar injection of Tf2[S14R](10 µM) still caused swelling, providing strong evidence that Tf2 has additional off-target activity at one or more non-neuronal targets. Therefore, due to activity at NaV1.9 and other yet to be identified target(s), the use of Tf2 as a selective pharmacological probe may be limited.

Molecular Mechanisms and Therapeutic Potential of miR-493 in Cancer

2019 ◽  
Vol 29 (6) ◽  
pp. 521-528
Author(s):  
Lingli Huang ◽  
Lingwei Huang ◽  
Ziwei Li ◽  
Qing Wei
Keyword(s):  
Molecular Mechanisms ◽  
Therapeutic Potential

Neuroprotective Effects of Ellagic Acid in Alzheimer's Disease: Focus on Underlying Molecular Mechanisms of Therapeutic Potential

2020 ◽  
Vol 26 ◽  
Author(s):  
Nimra Javaid ◽  
Muhammad Ajmal Shah ◽  
Azhar Rasul ◽  
Zunera Chauhdary ◽  
Uzma Saleem ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Ellagic Acid ◽  
Molecular Mechanisms ◽  
Neurodegenerative Disorder ◽  
Therapeutic Potential ◽  
Neuronal Cell Death ◽  
Neuronal Cell ◽  
Acetylcholinesterase Activity ◽  
Neuroprotective Effects

: Neurodegeneration is a multifactorial process involved the different cytotoxic pathways that lead towards neuronal cell death. Alzheimer’s disease (AD) is a persistent neurodegenerative disorder that normally has a steady onset yet later on it worsens. The documented evidence of AD neuropathology manifested the neuro-inflammation, increased reactive oxygen, nitrogen species and decreased antioxidant protective process; mitochondrial dysfunction as well as increased level of acetylcholinesterase activity. Moreover, enhanced action of proteins leads towards neural apoptosis which have a vital role in the degeneration of neurons. The inability of commercial therapeutic options to treat AD with targeting single mechanism leads the attraction towards organic drugs. Ellagic acid is a dimer of gallic acid, latest studies expressed that ellagic acid can initiate the numerous cell signaling transmission and decrease the progression of disorders, involved in the degeneration of neurons. The influential property of ellagic acid to protect the neurons in neurodegenerative disorders is due to its antioxidant effect, iron chelating and mitochondrial protective effect. The main goal of this review is to critically analyze the molecular mode of action of ellagic acid against neurodegeneration.

Classic and Novel Signaling Pathways Involved in Cancer: Targeting the NF-κB and Syk Signaling Pathways

2019 ◽  
Vol 14 (3) ◽  
pp. 219-225 ◽  
Author(s):  
Cong Tang ◽  
Guodong Zhu
Keyword(s):  
Cancer Therapy ◽  
Tyrosine Kinase ◽  
Signaling Pathways ◽  
Molecular Mechanisms ◽  
Therapeutic Potential ◽  
Cell Receptor ◽  
Transmembrane Receptors ◽  
Biological Responses ◽  
Different Types

The nuclear factor kappa B (NF-κB) consists of a family of transcription factors involved in the regulation of a wide variety of biological responses. Growing evidence support that NF-κB plays a major role in oncogenesis as well as its well-known function in the regulation of immune responses and inflammation. Therefore, we made a review of the diverse molecular mechanisms by which the NF-κB pathway is constitutively activated in different types of human cancers and the potential role of various oncogenic genes regulated by this transcription factor in cancer development and progression. We also discussed various pharmacological approaches employed to target the deregulated NF-κB signaling pathway and their possible therapeutic potential in cancer therapy. Moreover, Syk (Spleen tyrosine kinase), non-receptor tyrosine kinase which mediates signal transduction downstream of a variety of transmembrane receptors including classical immune-receptors like the B-cell receptor (BCR), which can also activate the inflammasome and NF-κB-mediated transcription of chemokines and cytokines in the presence of pathogens would be discussed as well. The highlight of this review article is to summarize the classic and novel signaling pathways involved in NF-κB and Syk signaling and then raise some possibilities for cancer therapy.

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