scholarly journals An open state of a voltage-gated sodium channel involving a π-helix and conserved pore-facing Asparagine

2021 ◽  
Author(s):  
Koushik Choudhury ◽  
Marina Kasimova ◽  
Sarah McComas ◽  
Rebecca J Howard ◽  
Lucie Delemotte
Keyword(s):  
Functional Annotation ◽  
Drug Binding ◽  
Full Length ◽  
Structure Comparison ◽  
Detailed Model ◽  
Voltage Gated ◽  
Transient Nature ◽  
Activation Gate ◽  
Nav Channels ◽  
State Models

Voltage-gated sodium (Nav) channels play critical roles in propagating action potentials and otherwise manipulating ionic gradients in excitable cells. These channels open in response to membrane depolarization, selectively permeating sodium ions until rapidly inactivating. Structural characterization of the gating cycle in this channel family has proved challenging, particularly due to the transient nature of the open state. A structure from the bacterium Magnetococcus marinus Nav (NavMs) was initially proposed to be open, based on its pore diameter and voltage-sensor conformation. However, the functional annotation of this model, and the structural details of the open state, remain disputed. In this work, we used molecular modeling and simulations to test possible open-state models of NavMs. The full-length experimental structure, termed here the α-model, was consistently dehy-drated at the activation gate, indicating an inability to conduct ions. Based on a spontaneous transition observed in extended simulations, and sequence/structure comparison to other Nav channels, we built an alternative π-model featuring a helix transition and the rotation of a conserved asparagine residue into the activation gate. Pore hydration, ion permeation and state-dependent drug binding in this model were consistent with an open functional state. This work thus offers both a functional annotation of the full-length NavMS structure, and a detailed model for a stable Nav open state, with potential conservation in diverse ion-channel families.

scholarly journals Valproic acid interactions with the NavMs voltage-gated sodium channel

2019 ◽  
Vol 116 (52) ◽  
pp. 26549-26554 ◽  
Author(s):  
Geancarlo Zanatta ◽  
Altin Sula ◽  
Andrew J. Miles ◽  
Leo C. T. Ng ◽  
Rubben Torella ◽  
...  
Keyword(s):  
Valproic Acid ◽  
Sodium Channel ◽  
Sodium Channels ◽  
Anticonvulsant Drug ◽  
Drug Binding ◽  
Voltage Sensor ◽  
Full Length ◽  
Binding Studies ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels

Valproic acid (VPA) is an anticonvulsant drug that is also used to treat migraines and bipolar disorder. Its proposed biological targets include human voltage-gated sodium channels, among other membrane proteins. We used the prokaryotic NavMs sodium channel, which has been shown to be a good exemplar for drug binding to human sodium channels, to examine the structural and functional interactions of VPA. Thermal melt synchrotron radiation circular dichroism spectroscopic binding studies of the full-length NavMs channel (which includes both pore and voltage sensor domains), and a pore-only construct, undertaken in the presence and absence of VPA, indicated that the drug binds to and destabilizes the channel, but not the pore-only construct. This is in contrast to other antiepileptic compounds that have previously been shown to bind in the central hydrophobic core of the pore region of the channel, and that tend to increase the thermal stability of both pore-only constructs and full-length channels. Molecular docking studies also indicated that the VPA binding site is associated with the voltage sensor, rather than the hydrophobic cavity of the pore domain. Electrophysiological studies show that VPA influences the block and inactivation rates of the NavMs channel, although with lower efficacy than classical channel-blocking compounds. It thus appears that, while VPA is capable of binding to these voltage-gated sodium channels, it has a very different mode and site of action than other anticonvulsant compounds.

scholarly journals Probing the Cavity of the Slow Inactivated Conformation of Shaker Potassium Channels

2007 ◽  
Vol 129 (5) ◽  
pp. 403-418 ◽  
Author(s):  
Gyorgy Panyi ◽  
Carol Deutsch
Keyword(s):  
Potassium Channels ◽  
Binding Site ◽  
Conformational Change ◽  
Marked Decrease ◽  
Selectivity Filter ◽  
Slow Inactivation ◽  
Voltage Gated ◽  
Activation Gate ◽  
Shaker Potassium Channels

Slow inactivation involves a local rearrangement of the outer mouth of voltage-gated potassium channels, but nothing is known regarding rearrangements in the cavity between the activation gate and the selectivity filter. We now report that the cavity undergoes a conformational change in the slow-inactivated state. This change is manifest as altered accessibility of residues facing the aqueous cavity and as a marked decrease in the affinity of tetraethylammonium for its internal binding site. These findings have implications for global alterations of the channel during slow inactivation and putative coupling between activation and slow-inactivation gates.

scholarly journals Ca2+ entry through NaV channels generates submillisecond axonal Ca2+ signaling

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Naomi AK Hanemaaijer ◽  
Marko A Popovic ◽  
Xante Wilders ◽  
Sara Grasman ◽  
Oriol Pavón Arocas ◽  
...  
Keyword(s):  
Calcium Channels ◽  
High Speed ◽  
Initial Segment ◽  
Hek 293 ◽  
Voltage Gated ◽  
Voltage Gated Calcium Channels ◽  
293 Cells ◽  
Axonal Initial Segment ◽  
Nav Channels ◽  
Activity Dependent

Calcium ions (Ca2+) are essential for many cellular signaling mechanisms and enter the cytosol mostly through voltage-gated calcium channels. Here, using high-speed Ca2+ imaging up to 20 kHz in the rat layer five pyramidal neuron axon we found that activity-dependent intracellular calcium concentration ([Ca2+]i) in the axonal initial segment was only partially dependent on voltage-gated calcium channels. Instead, [Ca2+]i changes were sensitive to the specific voltage-gated sodium (NaV) channel blocker tetrodotoxin. Consistent with the conjecture that Ca2+ enters through the NaV channel pore, the optically resolved ICa in the axon initial segment overlapped with the activation kinetics of NaV channels and heterologous expression of NaV1.2 in HEK-293 cells revealed a tetrodotoxin-sensitive [Ca2+]i rise. Finally, computational simulations predicted that axonal [Ca2+]i transients reflect a 0.4% Ca2+ conductivity of NaV channels. The findings indicate that Ca2+ permeation through NaV channels provides a submillisecond rapid entry route in NaV-enriched domains of mammalian axons.

scholarly journals Spider Knottin Pharmacology at Voltage-Gated Sodium Channels and Their Potential to Modulate Pain Pathways

Toxins ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 626 ◽  
Author(s):  
Yashad Dongol ◽  
Fernanda Caldas Cardoso ◽  
Richard J Lewis
Keyword(s):  
Chronic Pain ◽  
Sodium Channels ◽  
Structural Features ◽  
Voltage Gated ◽  
Subtype Selectivity ◽  
Voltage Gated Sodium Channels ◽  
Neuronal Signalling ◽  
Pain Pathways ◽  
Nav Channels ◽  
Chronic Pain Conditions

Voltage-gated sodium channels (NaVs) are a key determinant of neuronal signalling. Neurotoxins from diverse taxa that selectively activate or inhibit NaV channels have helped unravel the role of NaV channels in diseases, including chronic pain. Spider venoms contain the most diverse array of inhibitor cystine knot (ICK) toxins (knottins). This review provides an overview on how spider knottins modulate NaV channels and describes the structural features and molecular determinants that influence their affinity and subtype selectivity. Genetic and functional evidence support a major involvement of NaV subtypes in various chronic pain conditions. The exquisite inhibitory properties of spider knottins over key NaV subtypes make them the best lead molecules for the development of novel analgesics to treat chronic pain.

Pharmacological modulation of voltage-gated sodium (NaV) channels alters nociception arising from the female reproductive tract

Pain ◽  
2020 ◽  
Vol Publish Ahead of Print ◽  
Author(s):  
Joel Castro ◽  
Jessica Maddern ◽  
Andelain Erickson ◽  
Ashlee Caldwell ◽  
Luke Grundy ◽  
...  
Keyword(s):  
Reproductive Tract ◽  
Female Reproductive Tract ◽  
Voltage Gated ◽  
Pharmacological Modulation ◽  
Nav Channels

scholarly journals The hitchhiker’s guide to the voltage-gated sodium channel galaxy

2015 ◽  
Vol 147 (1) ◽  
pp. 1-24 ◽  
Author(s):  
Christopher A. Ahern ◽  
Jian Payandeh ◽  
Frank Bosmans ◽  
Baron Chanda
Keyword(s):  
Ion Selectivity ◽  
Current Understanding ◽  
Voltage Gated ◽  
Accessory Subunits ◽  
Genes Encoding ◽  
Nav Channels ◽  
Functional Symmetry ◽  
Electrical Signaling ◽  
And Behavior ◽  
Inherited Mutations

Eukaryotic voltage-gated sodium (Nav) channels contribute to the rising phase of action potentials and served as an early muse for biophysicists laying the foundation for our current understanding of electrical signaling. Given their central role in electrical excitability, it is not surprising that (a) inherited mutations in genes encoding for Nav channels and their accessory subunits have been linked to excitability disorders in brain, muscle, and heart; and (b) Nav channels are targeted by various drugs and naturally occurring toxins. Although the overall architecture and behavior of these channels are likely to be similar to the more well-studied voltage-gated potassium channels, eukaryotic Nav channels lack structural and functional symmetry, a notable difference that has implications for gating and selectivity. Activation of voltage-sensing modules of the first three domains in Nav channels is sufficient to open the channel pore, whereas movement of the domain IV voltage sensor is correlated with inactivation. Also, structure–function studies of eukaryotic Nav channels show that a set of amino acids in the selectivity filter, referred to as DEKA locus, is essential for Na+ selectivity. Structures of prokaryotic Nav channels have also shed new light on mechanisms of drug block. These structures exhibit lateral fenestrations that are large enough to allow drugs or lipophilic molecules to gain access into the inner vestibule, suggesting that this might be the passage for drug entry into a closed channel. In this Review, we will synthesize our current understanding of Nav channel gating mechanisms, ion selectivity and permeation, and modulation by therapeutics and toxins in light of the new structures of the prokaryotic Nav channels that, for the time being, serve as structural models of their eukaryotic counterparts.

scholarly journals Evidence for a Deep Pore Activation Gate in Small Conductance Ca2+-activated K+ Channels

2007 ◽  
Vol 130 (6) ◽  
pp. 601-610 ◽  
Author(s):  
Andrew Bruening-Wright ◽  
Wei-Sheng Lee ◽  
John P. Adelman ◽  
James Maylie
Keyword(s):  
Cysteine Residue ◽  
Selectivity Filter ◽  
K Channel ◽  
Homologous Region ◽  
Sk Channels ◽  
Voltage Gated ◽  
Kv Channels ◽  
Substituted Cysteine Accessibility ◽  
Activation Gate ◽  
Small Conductance

Small conductance calcium-gated potassium (SK) channels share an overall topology with voltage-gated potassium (Kv) channels, but are distinct in that they are gated solely by calcium (Ca2+), not voltage. For Kv channels there is strong evidence for an activation gate at the intracellular end of the pore, which was not revealed by substituted cysteine accessibility of the homologous region in SK2 channels. In this study, the divalent ions cadmium (Cd2+) and barium (Ba2+), and 2-aminoethyl methanethiosulfonate (MTSEA) were used to probe three sites in the SK2 channel pore, each intracellular to (on the selectivity filter side of) the region that forms the intracellular activation gate of voltage-gated ion channels. We report that Cd2+ applied to the intracellular side of the membrane can modify a cysteine introduced to a site (V391C) just intracellular to the putative activation gate whether channels are open or closed. Similarly, MTSEA applied to the intracellular side of the membrane can access a cysteine residue (A384C) that, based on homology to potassium (K) channel crystal structures (i.e., the KcsA/MthK model), resides one amino acid intracellular to the glycine gating hinge. Cd2+ and MTSEA modify with similar rates whether the channels are open or closed. In contrast, Ba2+ applied to the intracellular side of the membrane, which is believed to block at the intracellular end of the selectivity filter, blocks open but not closed channels when applied to the cytoplasmic face of rSK2 channels. Moreover, Ba2+ is trapped in SK2 channels when applied to open channels that are subsequently closed. Ba2+ pre-block slows MTSEA modification of A384C in open but not in closed (Ba2+-trapped) channels. The findings suggest that the SK channel activation gate resides deep in the vestibule of the channel, perhaps in the selectivity filter itself.

scholarly journals Ionic selectivity and thermal adaptations within the voltage-gated sodium channel family of alkaliphilic Bacillus

eLife ◽  
2014 ◽  
Vol 3 ◽  
Author(s):  
Paul G DeCaen ◽  
Yuka Takahashi ◽  
Terry A Krulwich ◽  
Masahiro Ito ◽  
David E Clapham
Keyword(s):  
Divalent Cations ◽  
Ion Selectivity ◽  
Resting Membrane Potential ◽  
Na Channel ◽  
Ph Homeostasis ◽  
Ionic Selectivity ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Nav Channels ◽  
Alkaliphilic Bacillus

Entry and extrusion of cations are essential processes in living cells. In alkaliphilic prokaryotes, high external pH activates voltage-gated sodium channels (Nav), which allows Na+ to enter and be used as substrate for cation/proton antiporters responsible for cytoplasmic pH homeostasis. Here, we describe a new member of the prokaryotic voltage-gated Na+ channel family (NsvBa; Non-selective voltage-gated, Bacillus alcalophilus) that is nonselective among Na+, Ca2+ and K+ ions. Mutations in NsvBa can convert the nonselective filter into one that discriminates for Na+ or divalent cations. Gain-of-function experiments demonstrate the portability of ion selectivity with filter mutations to other Bacillus Nav channels. Increasing pH and temperature shifts their activation threshold towards their native resting membrane potential. Furthermore, we find drugs that target Bacillus Nav channels also block the growth of the bacteria. This work identifies some of the adaptations to achieve ion discrimination and gating in Bacillus Nav channels.

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