Nonconducting State Research Articles

Conformational equilibrium shift underlies altered K+ channel gating as revealed by NMR

The potassium ion (K+) channel plays a fundamental role in controlling K+ permeation across the cell membrane and regulating cellular excitabilities. Mutations in the transmembrane pore reportedly affect the gating transitions of K+ channels, and are associated with the onset of neural disorders. However, due to the lack of structural and dynamic insights into the functions of K+ channels, the structural mechanism by which these mutations cause K+ channel dysfunctions remains elusive. Here, we used nuclear magnetic resonance spectroscopy to investigate the structural mechanism underlying the decreased K+-permeation caused by disease-related mutations, using the prokaryotic K+ channel KcsA. We demonstrated that the conformational equilibrium in the transmembrane region is shifted toward the non-conductive state with the closed intracellular K+-gate in the disease-related mutant. We also demonstrated that this equilibrium shift is attributable to the additional steric contacts in the open-conductive structure, which are evoked by the increased side-chain bulkiness of the residues lining the transmembrane helix. Our results suggest that the alteration in the conformational equilibrium of the intracellular K+-gate is one of the fundamental mechanisms underlying the dysfunctions of K+ channels caused by disease-related mutations.

Origin of the hysteresis of magnetoconductance in a supramolecular spin-valve based on aTbPc2single-molecule magnet

We present a time-dependent microscopic model for Coulomb blockade transport through an experimentally realized supramolecular spin-valve device driven by an oscillating magnetic field, in which the $4f$-electron magnetic states of an array of $\mathrm{Tb}{\mathrm{Pc}}_{2}$ single-molecule magnets (SMMs) were observed to modulate a sequential tunneling current through an underlying substrate nanoconstriction. Our model elucidates the dynamical mechanism at the origin of the observed hysteresis loops of the magnetoconductance, a signature of the SMM-modulated spin-valve effect, in terms of a phonon-assisted multi-spin-reversal cascade relaxation process, which mediates the switching of the device between the two conductive all-parallel spin configurations of the SMM array. Moreover, our proposed model can explain the zero-bias giant magnetoresistive transport gap measured in this device, solely within the incoherent transport regime, consistently with the experimental observations, as opposed to previous interpretations invoking Fano-resonance conductance suppression within a coherent ballistic transport regime. Finally, according to the proposed Coulomb blockade scenario, the SMM-mediated giant magnetoresistance effect is predicted to increase with the number of SMMs aligned on the nanoconstriction surface, on account of the increased number of intermediate nonconducting spin-flip states intervening in the phonon-assisted multi-spin-reversal cascade relaxation process necessary to switch between the two conducting all-parallel SMM spin configurations.

Global alignment and assessment of TRP channel transmembrane domain structures to explore functional mechanisms.

The recent proliferation of published TRP channel structures provides a foundation for understanding the diverse functional properties of this important family of ion channel proteins. To facilitate mechanistic investigations, we constructed a structure-based alignment of the transmembrane domains of 120 TRP channel structures. Comparison of structures determined in the absence or presence of activating stimuli reveals similar constrictions in the central ion permeation pathway near the intracellular end of the S6 helices, pointing to a conserved cytoplasmic gate and suggesting that most available structures represent non-conducting states. Comparison of the ion selectivity filters toward the extracellular end of the pore supports existing hypotheses for mechanisms of ion selectivity. Also conserved to varying extents are hot spots for interactions with hydrophobic ligands, lipids and ions, as well as discrete alterations in helix conformations. This analysis therefore provides a framework for investigating the structural basis of TRP channel gating mechanisms and pharmacology, and, despite the large number of structures included, reveals the need for additional structural data and for more functional studies to establish the mechanistic basis of TRP channel function.

A Review on Different Single Electron Devices and Their Comparative Study

Single Electron Devices being one of the nanodevices offers reduced feature size and low power consumption along with unique characteristics. The principle of operation is established upon the quantum mechanical tunneling of a single or few electrons for device switching between conducting and non-conducting state. The present work is a detailed survey on the different Single Electron Devices such as Single Electron Box, Double Tunnel Junction, Single Electron Transistor and Single Electron Turnstile. An overall comparative study of them is also furnished here as a fragment of the study. Keywords: Single Electron Box; Double Tunnel Junction; Single electron transistor; Single Electron Turnstile. Cite this Article: Bidisha Das, Riya Bandyopadhyay, Anamika Saha, Promit Das, Arpita Ghosh. A Review on Different Single Electron Devices and Their Comparative Study. International Journal Digital Communication and Analog Signals . 2020; 6(2): 21–27p.

Neuronal Glutamatergic Network Electrically Wired with Silent But Activatable Gap Junctions.

It is widely assumed that electrical synapses in the mammalian brain, especially between interneurons, underlie neuronal synchrony. In the hippocampus, principal cells also establish electrical synapses with each other and have also been implicated in network oscillations, whereby the origin of fast electrical activity has been attributed to ectopic spikelets and dendro-dendritic or axo-axonal gap junctions. However, if electrical synapses were in axo-dendritic connections, where chemical synapses occur, the synaptic events would be mixed, having an electrical component preceding the chemical one. This type of communication is less well studied, mainly because it is not easily detected. Moreover, a possible scenario could be that an electrical synapse coexisted with a chemical one, but in a nonconductive state; hence, it would be considered inexistent. Could chemical synapses have a quiescent electrical component? If so, can silent electrical synapses be activated to be detected? We addressed this possibility, and we here report that, indeed, the connexin-36-containing glutamatergic mossy fiber synapses of the rat hippocampus express previously unrecognized electrical synapses, which are normally silent. We reveal that these synapses are pH sensitive, actuate in vitro and in vivo, and that the electrical signaling is bidirectional. With the simultaneous recording of hundreds of cells, we could reveal the existence of an electrical circuit in the hippocampus of adult rats of either sex consisting of principal cells where the nodes are interregional glutamatergic synapses containing silent but ready-to-use gap junctions.SIGNIFICANCE STATEMENT In this work, we present a series of experiments, both in vitro and in vivo, that reveal previously unrecognized silent pH-sensitive electrical synapses coexisting in one of the best studied glutamatergic synapses of the brain, the mossy fiber synapse of the hippocampus. This type of connectivity underlies an "electrical circuit" between two substructures of the adult rat hippocampus consisting of principal cells where the nodes are glutamatergic synapses containing silent but ready-to-use gap junctions. Its identification will allow us to explore the participation of such a circuit in physiological and pathophysiological functions and will provide valuable conceptual tools to understanding computational and regulatory mechanisms that may underlie network activity.

Protonation state of the selectivity filter of bacterial voltage-gated sodium channels is modulated by ions.

The selectivity filter (SF) of bacterial voltage-gated sodium channels consists of four glutamate residues arranged in a C4 symmetry. The protonation state population of this tetrad is unclear. To address this question, we simulate the pore domain of bacterial voltage-gated sodium channel of Magnetococcus sp. (Nav Ms) through constant pH methodology in explicit solvent and free energy perturbation calculations. We find that at physiological pH the fully deprotonated as well as singly and doubly protonated states of the SF appear feasible, and that the calculated pKa decreases with each additional bound ion, suggesting that a decrease in the number of ions in the pore can lead to protonation of the SF. Previous molecular dynamics simulations have suggested that protonation can lead to a decrease in the conductance, but no pKa calculations were performed. We confirm a decreased ionic population of the pore with protonation, and also observe structural symmetry breaking triggered by protonation; the SF of the deprotonated channel is closest to the C4 symmetry observed in crystal structures of the open state, while the SF of protonated states display greater levels of asymmetry which could lead to transition to the inactivated state which possesses a C2 symmetry in the crystal structure. We speculate that the decrease in the number of ions near the mouth of the channel, due to either random fluctuations or ion depletion due to conduction, could be a self-regulatory mechanism resulting in a nonconducting state that functionally resembles inactivated states.

Reduced graphene oxide resistance in composites with polystyrene of different molecular masses

Multi-layered reduced graphene oxide after UV-perforation (RGOp) flakes of large areas, some of them up to 1 mm in diameter, have been produced on polystyrene surface during special precipitation method of RGOp/polystyrene composites from benzene solution. For this, composites on the base of polystyrenes of different molecular masses: 4500 Da; 6000 Da; 9000 Da; and 45,000 Da were synthesized. Very low resistances at the room temperature for some RGOp flakes deposited from benzene-petroleum ether solution of composite of 9000 Da molecular mass were obtained. The absolute values of measured resistances turned out to be almost 3 orders lower than copper resistance. This result can be related to formation a high conductive phase in the reduced graphene oxide bilayer inclusions. In the case of RGOp flakes produced from our highest molecular mass polystyrene composite (45,000 Da) resistance was high and varying from semiconducting values to non-conductive state.

Ultrastretchable Conductive Elastomers with a Low Percolation Threshold for Printed Soft Electronics.

Stretchable conductors are required for next-generation soft electronics. Achieving both high electrical conductivity and high stretchability in conductors composed of elastomers and conductive fillers, however, is challenging. Here, a generic, versatile strategy is reported for producing ultrastretchable conductors exhibiting both superior electrical conductivity (>103 S/cm) and stretchability (>1600%). This is achieved by adding small amounts of immiscible secondary fluid into silver (Ag)-filled inks. Capillary forces in these ternary systems induce the self-assembly of conductive particle networks at a low percolation threshold (6-7 vol %), cutting silver consumption by more than 2/3 compared to conventional conductive elastomers. Ag-filled polydimethylsiloxane exhibits superior cyclic durability sustaining 100% tensile strain for 1000 cycles with only a minor loss of conductivity. Ag-filled thermoplastic polyurethane displays unprecedented reversibility with nonretarded switching from conductive to nonconductive states during repeated stretching up to 200% strain. Patterned strain sensors and conductive wirings were 3D-printed to demonstrate the technical feasibility.

The Mechanism of Dedoping PEDOT:PSS by Aliphatic Polyamines.

Poly(3,4-ethylenedioxythiophene) blended with polystyrenesulfonate and poly(styrenesulfonic acid), PEDOT:PSS, has found widespread use in organic electronics. Although PEDOT:PSS is commonly used in its doped electrically conducting state, the ability to efficiently convert PEDOT:PSS to its undoped nonconducting state is of interest for a wide variety of applications ranging from biosensors to organic neuromorphic devices. Exposure to aliphatic monoamines, acting as an electron donor and Brønsted–Lowry base, has been reported to be partly successful, but monoamines are unable to fully dedope PEDOT:PSS. Remarkably, some—but not all—polyamines can dedope PEDOT:PSS very efficiently to very low conductivity levels, but the exact chemical mechanism involved is not understood. Here, we study the dedoping efficacy of 21 different aliphatic amines. We identify the presence of two or more primary amines, which can participate in an intramolecular reaction, as the key structural motif that endows polyamines with high PEDOT:PSS dedoping strength. A multistep reaction mechanism, involving sequential electron transfer and deprotonation steps, is proposed that consistently explains the experimental results. Finally, we provide a simple method to convert the commonly used aqueous PEDOT:PSS dispersion into a precursor formulation that forms fully dedoped PEDOT:PSS films after spin coating and subsequent thermal annealing.

Extremely Potent Block of Bacterial Voltage-Gated Sodium Channels by µ-Conotoxin PIIIA.

µ-Conotoxin PIIIA, in the sub-picomolar, range inhibits the archetypal bacterial sodium channel NaChBac (NavBh) in a voltage- and use-dependent manner. Peptide µ-conotoxins were first recognized as potent components of the venoms of fish-hunting cone snails that selectively inhibit voltage-gated skeletal muscle sodium channels, thus preventing muscle contraction. Intriguingly, computer simulations predicted that PIIIA binds to prokaryotic channel NavAb with much higher affinity than to fish (and other vertebrates) skeletal muscle sodium channel (Nav 1.4). Here, using whole-cell voltage clamp, we demonstrate that PIIIA inhibits NavBac mediated currents even more potently than predicted. From concentration-response data, with [PIIIA] varying more than 6 orders of magnitude (10−12 to 10−5 M), we estimated an IC50 = ~5 pM, maximal block of 0.95 and a Hill coefficient of 0.81 for the inhibition of peak currents. Inhibition was stronger at depolarized holding potentials and was modulated by the frequency and duration of the stimulation pulses. An important feature of the PIIIA action was acceleration of macroscopic inactivation. Docking of PIIIA in a NaChBac (NavBh) model revealed two interconvertible binding modes. In one mode, PIIIA sterically and electrostatically blocks the permeation pathway. In a second mode, apparent stabilization of the inactivated state was achieved by PIIIA binding between P2 helices and trans-membrane S5s from adjacent channel subunits, partially occluding the outer pore. Together, our experimental and computational results suggest that, besides blocking the channel-mediated currents by directly occluding the conducting pathway, PIIIA may also change the relative populations of conducting (activated) and non-conducting (inactivated) states.

Electrical stimulation of cell growth and neurogenesis using conductive and nonconductive microfibrous scaffolds.

The effect of exogenous electrical stimulation on cell viability, attachment, growth, and neurogenesis was examined using PC12 cells in microfibrous viscose-rayon scaffolds immersed in culture medium. The scaffolds were applied either in their nonconductive state or after coating the fibres with 200 nm of gold to give a scaffold sheet resistivity of (13 ± 1.3) Ω square-1. The cells were treated for 12 days using direct current electrical stimulation of 2 h per day. No cytotoxic effects were observed when up to 500 mV (8.3 mV mm-1) was applied to the scaffolds without gold, or when up to 100 mV (1.7 mV mm-1) was applied to the scaffolds with gold. Compared with unstimulated cells, whereas electrical stimulation significantly enhanced cell growth and attachment in the nonconductive scaffolds without gold, similar effects were not found for the conductive scaffolds with gold. Neural differentiation in the presence of nerve growth factor was improved by electrical stimulation in both scaffolds; however, neurite development and the expression of key differentiation markers were greater in the nonconductive scaffolds without gold than in the scaffolds with gold. Application of the same current to scaffolds with and without gold led to much higher levels of neurogenesis in the scaffolds without gold. This work demonstrates that substantial benefits in terms of cell growth and neural differentiation can be obtained using electric fields exerted across nonconductive microfibrous scaffolds, and that this approach to electrical stimulation can be more effective than when the stimulus is applied to cells on conductive scaffolds.

Cell Junction Proteins-Mimetic Artificial Nanochannel System: Basic Logic Gates Implemented by Nanofluidic Diodes.

Inspired by communication modes of cell junction proteins, an artificial bichannel nanofluidic diode system was constructed and investigated to implement basic "AND" and "OR" logic gates in different connection modes. Input conditions were set as conducting and nonconducting states of each nanofluidic diode unit. Output results were set as response current of the system at rated voltage. Besides, nanofluidic diodes with different ionic permeabilities were connected in multiple modes, and different logic operation results were obtained. This novel logic device based on nanofluidic diodes provided a new approach to establish diverse stimuli-responsive signal processing networks and has prospect to obtain nanofluidic diode intelligence chips by integrating in large scale.

Minimum breakdown parameters through H2, He, N2 and Ar gases

The gas discharge plasma has attracted the attention of scientists and technologists because it is a source of electrons and ions beams which are needed and used in several applications and modern instruments. Minimum breakdown voltage of the cylindrical coaxial virtual cathode oscillator is investigated on Nitrogen (N2), Argon (Ar), Helium (He) and Hydrogen (H2) through different anode transparencies. The study includes the effect of secondary electron emission on the minimum breakdown voltage (Vb)min and the product of gas pressure P and inter-electrode distance d, Pdmin. The changes in the minimum breakdown voltage with the gas pressure are studied where pressure is the main factor of electric discharge. Paschen curve is studied through electric discharge for Ar and H2 by using different anode transparencies. This study aims to understand the parameters that can affect the minimum voltage (Vb)min at which the gas transfers from a non-conducting state to a conducting state. The study is carried out on a cylindrical coaxial vircator for different gases and different anode transparencies.

Molecular Mechanism of Depolarization-Dependent Inactivation in W366F Mutant of Kv1.2.

Voltage-gated potassium channels play crucial roles in regulating membrane potential. They are activated by membrane depolarization, allowing the selective permeation of K+ ions across the plasma membrane, and enter a nonconducting state after lasting depolarization, a process known as inactivation. Inactivation in voltage-activated potassium channels occurs through two distinct mechanisms, N-type and C-type inactivation. C-type inactivation is caused by conformational changes in the extracellular mouth of the channel, whereas N-type inactivation is elicited by changes in the cytoplasmic mouth of the protein. The W434F-mutated Shaker channel is known as a nonconducting mutant and is in a C-type inactivation state at a depolarizing membrane potential. To clarify the structural properties of C-type inactivated protein, we performed molecular dynamics simulations of the wild-type and W366F (corresponding to W434F in Shaker) mutant of the Kv1.2-2.1 chimera channel. The W366F mutant was in a nearly nonconducting state with a depolarizing voltage and recovered from inactivation with a reverse voltage. Our simulations and three-dimensional reference interaction site model analysis suggested that structural changes in the selectivity filter upon membrane depolarization trap K+ ions around the inner mouth of the selectivity filter and prevent ion permeation. This pore restriction is involved in the molecular mechanism of C-type inactivation.

Closed-Locked and Apo-Resting State Structures of the Human α7 Nicotinic Receptor: A Computational Study.

Nicotinic acetylcholine receptors, belonging to the Cys-loop superfamily of ligand-gated ion channels (LGICs), are membrane proteins present in neurons and at neuromuscular junctions. They are responsible for signal transmission, and their function is regulated by neurotransmitters, agonists, and antagonists drugs. A detailed knowledge of their conformational transition in response to ligand binding is critical to understanding the basis of ligand-receptor interaction, in view of new pharmacological approaches to control receptor activity. However, the scarcity of experimentally derived structures of human channels makes this perspective extremely challenging. To contribute overcoming this issue, we have recently reported structural models for the open and the desensitized states of the human α7 nicotinic receptor. Here, we provide all-atom structural models of the same receptor in two different nonconductive states. The first structure, built via homology modeling and relaxed with extensive Molecular Dynamics simulations, represents the receptor bound to the natural antagonist α-conotoxin ImI. After comparison with available experimental data and computational models of other eukaryotic LGICs, we deem it consistent with the "closed-locked" state. The second model, obtained with simulations from the spontaneous relaxation of the open, agonist-bound α7 structure after ligand removal, recapitulates the characteristics of the apo-resting state of the receptor. These results add to our previous work on the active and desensitized state conformations, contributing to the structural characterization of the conformational landscape of the human α7 receptor and suggesting benchmarks to discriminate among conformations found in experiments or in simulations of LGICs. In particular key interactions at the interface between the extracellular domain and the transmembrane domain are identified, that could be critical to the α7 receptor function.

Slc7a5 regulates Kv1.2 channels and modifies functional outcomes of epilepsy-linked channel mutations

Kv1.2 is a prominent voltage-gated potassium channel that influences action potential generation and propagation in the central nervous system. We explored multi-protein complexes containing Kv1.2 using mass spectrometry followed by screening for effects on Kv1.2. We report that Slc7a5, a neutral amino acid transporter, has a profound impact on Kv1.2. Co-expression with Slc7a5 reduces total Kv1.2 protein, and dramatically hyperpolarizes the voltage-dependence of activation by −47 mV. These effects are attenuated by expression of Slc3a2, a known binding partner of Slc7a5. The profound Slc7a5-mediated current suppression is partly explained by a combination of gating effects including accelerated inactivation and a hyperpolarizing shift of channel activation, causing channels to accumulate in a non-conducting state. Two recently reported Slc7a5 mutations linked to neurodevelopmental delay exhibit a localization defect and have attenuated effects on Kv1.2. In addition, epilepsy-linked gain-of-function Kv1.2 mutants exhibit enhanced sensitivity to Slc7a5.

Analysis of the technology to manufacture a high-temperature microstrip superconductive device for the electromagnetic protection of receivers

Technological features of the process of manufacturing a high-speed high-temperature superconducting microstrip protective device which can reduce in a picosecond period (the time of switching or operation speed) the incoming power from the antenna-feeder path and the power passing through it to a level safe for sensitive semiconductor elements of the receiver (preventing current destruction of p-n junction). The study enables determination of the features and conditions for the use of modern technological methods for creating a superconducting microstrip protective device taking into account influence of the substrate material, superconductor and contacts and the method of their connection on the switching properties of superconducting films of the proposed protective device. The switching properties of superconducting films include speed of phase transition of a film from a superconducting to a nonconducting state. To determine degree of material influence on switching properties, it was proposed to use the following: lattice parameter, thermal expansion coefficient of materials, degree of interaction of molecular structures of the contacting surfaces, probability of local defects on the surface (nonconducting zones). The study outlines basic conditions (methods of film deposition, applying a certain superconducting film (YBCO) on the chosen substrate) which should be met in order to create an operable protective device. The study results make it possible to assess the degree of influence of contact materials and the method of deposition (of both film on the substrate and contacts on the film) on microstructure and switching properties of the superconducting protective device. Such results can be used in synthesis of high-temperature superconducting devices for protecting receiver elements from current destruction of their p–n junctions

Rational synthesis of a polymerizable fullerene–aniline derivative: study of photophysical, morphological and photovoltaic properties $$^{\S }$$ §

This paper describes the synthesis of a polymerizable, aniline appended fullerene derivative, 3-aminobenzyl-phenyl- $$\hbox {C}_{61}$$ -butyrate (PCBAn) and its corresponding polymer (P-PCBAn), and detailed photophysical and morphological analysis towards application as an acceptor in polymer solar cells (BHJ-PSCs). The poly-3-aminobenzyl-phenyl- $$\hbox {C}_{61}$$ -butyrate (P-PCBAn), having a substituted polyaniline (PANI) skeletal structure, was synthesized via $$\hbox {FeCl}_{3}$$ oxidative polymerisation of PCBA in its non-conducting leucoemaraldine state. HOMO and LUMO energies estimated using optical and electrochemical techniques revealed upshifted LUMO levels for PCBAn ( $$-$$ 3.68 eV, $$\Delta \hbox {E} = 0.1$$ eV) and P-PCBAn ( $$-$$ 3.66 eV, $$\Delta \hbox {E} = 0.12$$ eV) compared to the parental fullerene derivative, PCBM ( $$-$$ 3.78 eV). The morphologies of PCBAn and P-PCBAn individually and in polymer blends with P3HT were investigated using AFM and TEM analysis, which showed nanoflake-like aggregates for P3HT/PCBAn and a favourable interconnected nanonetwork structure for P3HT/P-PCBAn. The wide angle X-ray scattering (WAXS) studies of PCBAn films drop-cast from THF/water (3:7) mixture and P-PCBAn films drop-cast from 1,2-dichlorobenzene exhibited plane reflections of lamellar mesophases with d-spacing of 3.4 nm and 3 nm for PCBAn and P-PCBAn, respectively. The fluorescence quenching experiments with P3HT indicated efficient electron transfer from P3HT to P-PCBAn when compared to PCBAn. The fabrication of an inverted BHJ-PSC device using PCBAn and P-PCBAn as an acceptor in combination with P3HT showed PCE of 0.9% and 1.1%, respectively, showing considerable enhancement in the case of the polymeric acceptor. The polymeric acceptor and the rational design strategy used here could open up new opportunities in the PSC device fabrication. Ref.: Ms. No. JCSC-D-18-001042 SYNOPSIS Synthesis of a polymerizable, aniline appended fullerene derivative, 3-aminobenzyl-phenyl- $$\hbox {C}_{61}$$ -butyrate (PCBAn) and its corresponding polymer, and detailed photophysical and morphological analysis towards application as acceptor in polymer solar cells (BHJ-PSCs) are reported. The results suggest bicontinuous interpenetrating network and better charge transport properties for P3HT:P-PCBAn polymer blend compared to P3HT:PCBAn.

Implications for the impairment of the rapid channel closing of Proteomonas sulcata anion channelrhodopsin 1 at high Cl\u2212 concentrations

Natural anion channelrhodopsins (ACRs) have recently received increased attention because of their effectiveness in optogenetic manipulation for neuronal silencing. In this study, we focused on Proteomonas sulcata ACR1 (PsuACR1), which has rapid channel closing kinetics and a rapid recovery to the initial state of its anion channel function that is useful for rapid optogenetic control. To reveal the anion concentration dependency of the channel function, we investigated the photochemical properties of PsuACR1 using spectroscopic techniques. Recombinant PsuACR1 exhibited a Cl− dependent spectral red-shift from 531 nm at 0.1 mM to 535 nm at 1000 mM, suggesting that it binds Cl− in the initial state with a Kd of 5.5 mM. Flash-photolysis experiments revealed that the photocycle was significantly changed at high Cl− concentrations, which led not only to suppression of the accumulation of the M-intermediate involved in the Cl− non-conducting state but also to a drastic change in the equilibrium state of the other photo-intermediates. Because of this, the Cl− conducting state is protracted by one order of magnitude, which implies an impairment of the rapid channel closing of PsuACR1 in the presence of high concentrations of Cl−.

Single-particle cryo-EM structure of a voltage-activated potassium channel in lipid nanodiscs.

Voltage-activated potassium (Kv) channels open to conduct K+ ions in response to membrane depolarization, and subsequently enter non-conducting states through distinct mechanisms of inactivation. X-ray structures of detergent-solubilized Kv channels appear to have captured an open state even though a non-conducting C-type inactivated state would predominate in membranes in the absence of a transmembrane voltage. However, structures for a voltage-activated ion channel in a lipid bilayer environment have not yet been reported. Here we report the structure of the Kv1.2-2.1 paddle chimera channel reconstituted into lipid nanodiscs using single-particle cryo-electron microscopy. At a resolution of ~3 Å for the cytosolic domain and ~4 Å for the transmembrane domain, the structure determined in nanodiscs is similar to the previously determined X-ray structure. Our findings show that large differences in structure between detergent and lipid bilayer environments are unlikely, and enable us to propose possible structural mechanisms for C-type inactivation.