Ion Translocation Research Articles

Mechanisms of alamethicin ion channel inhibition by amiloride in zwitterionic tethered lipid bilayers

The effect of amiloride, an acid-sensing ion channel (ASIC) blocker, on the formation of alamethicin ion channels in tethered zwitterionic phospholipid bilayers was investigated using electrochemical impedance spectroscopy (EIS) and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). EIS measurements show a decrease in conductivity indicating that ion transported across the alamethicin-rich phospholipid membrane is inhibited by the presence of amiloride. The PM-IRRAS spectra indicate that amiloride has no effect on the secondary structure of the alamethicin peptide. The IR data suggests that amiloride does not block ion translocation through the alamethicin ion pore but prevents the insertion of alamethicin peptides into the biomembrane suppressing the formation of ion channels. The mechanism responsible for amiloride inhibition is explained in terms of the electrostatic interactions between the molecule and membrane surface. Amiloride is positively charged at physiological pH levels invoking a repulsive force on the positive pole of the alamethicin molecular dipole. These repulsive interactions prevent the insertion of the alamethicin peptides into the hydrophobic core of the lipid bilayer. The present paper offers a molecular view of the interactions that occur between amiloride, an ion channel inhibitor, with the lipids and ion channel forming peptides in model tBLMs.

The S. cerevisiae cation translocation protein Trk1 is functional without its “long hydrophilic loop” but LHL regulates cation translocation activity and selectivity

In Saccharomyces cerevisiae, K+-uptake under K+-limiting conditions is largely mediated by the cation translocation systems Trk1 and Trk2 belonging to the family of SKT proteins. They are related to two-transmembrane-domain (inward rectifying K-) channels but unlike the symmetrical tetrameric structure of K-channels, a single Trk contains four pore-forming domains (A-D) encoded on one polypeptide chain. Between domains A and B Trks contain large cytosolic regions dubbed “long hydrophilic loop” (LHL). LHLs are not homologous/similar to any other identified protein (domain) and also show little similarity between Trk1 and Trk2. Here we demonstrate that Trk1 is functional without LHL. However, in growth experiments NaCl sensitivity of Trk1[ΔLHL] expressing cells is increased under K+-limiting conditions compared to full-length Trk1. Non-invasive ion flux measurements showed that K+-influx through Trk1 and Trk1[ΔLHL] is decreased in the presence of surplus Na+ due to permeability of the proteins for both cations and competition between them. Trk1[ΔLHL] is less affected than full-length Trk1 because it is more selective for K+ over Na+. Furthermore, K+ re-uptake after starvation is delayed and decreased in Trk1[ΔLHL]. Thus, a role of LHL is regulating cation fluxes through Trk1 by (i) allowing also Na+ to pass if monovalent cations (mainly K+) are limiting and (ii) by accelerating/enhancing a switch from low to high affinity ion translocation. We propose that LHL could modulate Trk1 transport properties via direct influence on a transmembrane helix (M2A) which can switch between bent and straight conformation, thereby directly modifying the radius of the pore and selectivity filter.

Energy conservation in the gut microbe Methanomassiliicoccus luminyensis is based on membrane‐bound ferredoxin oxidation coupled to heterodisulfide reduction

Methanomassiliicoccus luminyensis was originally isolated from human feces and belongs to the seventh order of methanogens, the Methanomassiliicoccales, which are only distantly related to other methanogenic archaea. The organism forms methane from the reduction of methylamines or methanol using molecular hydrogen as reductant. The energy-conserving system in M.luminyensis is unique and the enzymes involved in this process are not found in this combination in members of the other methanogenic orders. In this context our central question was how the organism is able to generate ATP. Energy transduction was dependent on a membrane-bound ferredoxin: heterodisulfide oxidoreductase composed of reduced ferredoxin as an electron donor, at least one protein in the membrane fraction and the heterodisulfide reductase HdrD, which reduced the electron acceptor CoM-S-S-CoB. Electron transfer of this respiratory chain proceeded with a rate of 145nmol reduced heterodisulfide min-1 ·mg-1 membrane protein. Methanomassiliicoccus luminyensis is the first example of a methanogenic archaeon that does not require Na+ ions for energy conservation. Only protons were used as coupling ions for the generation of the electrochemical ion gradient. The membrane-bound F420 H2 :phenazine oxidoreductase complex (without the electron input module FpoF) probably catalyzed the oxidation of reduced ferredoxin and potentially acted as primary proton pump in this electron transport system. In summary, the energy-conserving system of M.luminyensis possesses features found in the pathways of hydrogenotrophic and methylotrophic/aceticlastic methanogenesis. Consequently, the composition of the enzymes involved in ion translocation across the cytoplasmic membrane is different from all other methanogenic archaea.

Regulation of K+ Nutrition in Plants.

Modern agriculture relies on mineral fertilization. Unlike other major macronutrients, potassium (K+) is not incorporated into organic matter but remains as soluble ion in the cell sap contributing up to 10% of the dry organic matter. Consequently, K+ constitutes a chief osmoticum to drive cellular expansion and organ movements, such as stomata aperture. Moreover, K+ transport is critical for the control of cytoplasmic and luminal pH in endosomes, regulation of membrane potential, and enzyme activity. Not surprisingly, plants have evolved a large ensemble of K+ transporters with defined functions in nutrient uptake by roots, storage in vacuoles, and ion translocation between tissues and organs. This review describes critical transport proteins governing K+ nutrition, their regulation, and coordinated activity, and summarizes our current understanding of signaling pathways activated by K+ starvation.

Roles of the Hydrophobic Gate and Exit Channel in Vigna radiata Pyrophosphatase Ion Translocation

Membrane-embedded pyrophosphatase (M-PPase) hydrolyzes pyrophosphate to drive ion (H+ and/or Na+) translocation. We determined crystal structures and functions of Vigna radiata M-PPase (VrH+-PPase), the VrH+-PPase–2Pi complex and mutants at hydrophobic gate (residue L555) and exit channel (residues T228 and E225). Ion pore diameters along the translocation pathway of three VrH+-PPases complexes (Pi-, 2Pi- and imidodiphosphate-bound states) present a unique wave-like profile, with different pore diameters at the hydrophobic gate and exit channel, indicating that the ligands induced pore size alterations. The 2Pi-bound state with the largest pore diameter might mimic the hydrophobic gate open. In mutant structures, ordered waters detected at the hydrophobic gate among VrH+-PPase imply the possibility of solvation, and numerous waters at the exit channel might signify an open channel. A salt-bridge, E225–R562 is at the way out of the exit channel of VrH+-PPase; E225A mutant makes the interaction eliminated and reveals a decreased pumping ability. E225–R562 might act as a latch to regulate proton release. A water wire from the ion gate (R-D-K-E) through the hydrophobic gate and into the exit channel may reflect the path of proton transfer.

A Partially Closed State in Nhtmem16 Scramblase is Enabled by Lipid Tail Insertion into the Protein Groove

Ca2+-regulated TMEM16 proteins participate in key physiological processes such as ion transport and phospholipid scrambling. Studies of various members of the TMEM16 family have supported a functional role for the membrane-exposed groove in these proteins, showing that it can assist translocation of both ions and lipids by serving as a continuous conduit connecting the two leaflets of the membrane. The proposed mechanism of permeation involves gating of various regions of the groove through conformational rearrangements. Especially intriguing is the role of transmembrane helix 4 (TM4) that was seen in structural comparisons of the TMEM16A ion channel with TMEM16 scramblases to adopt different positions relative to the groove. To investigate the molecular mechanisms underlying the transitions between these different structural states we analyzed the dynamic properties of the nhTMEM16 scramblase with extensive atomistic molecular dynamics simulations. We found that occlusion of the groove by TM4 can occur in the Ca2+-bound state and is enabled by lipid tail penetration into the groove. Based on information about the relation between the dynamics of the scramblase and the conformational changes that facilitate lipid tail insertion into the groove, we identified a mutation in the nhTMEM16 that can stabilize the Ca2+-bound scramblase in the occluded conformation that is structurally similar to the Ca2+-bound form of the TMEM16A. These findings elucidate on how lipid-protein interactions can mechanistically drive formation of a functionally relevant state in nhTMEM16.

Variations in Electroosmotic Flow Outside Glass Nanopores with Species of Monovalent Cation

Nanopores are an important technology in molecular sensing systems. Their behaviour is strongly affected by flow characteristics that are not well understood. Utilising a novel 3 dimensional combination optical tweezers and capillary nanopore measurement system, we have measured flow behaviour outside conical glass nanopores as a function of species of group 1 cation. We present a full 3 dimensional flow field about the nanopore. We use this 3 dimensional measurement system to find the flow force as a function of distance from the pore, allowing us to determine the momentum flux for each salt condition. We find strong salt dependence on the strength of momentum flux from the nanopore. Additionally we find previously reported voltage dependent flow reversal to be dictated by salt species. For a subset of species we observe EOF in the expected direction as predicted by classical electrokinetic theory, while for others the direction of the flow is reversed. We present a model explaining the observed behaviour. These data and corresponding model are key to understanding ion transport, fluid flow and translocation dynamics in voltage driven nanopore systems.

Kinetic and thermodynamic insights into sodium ion translocation through the μ-opioid receptor from molecular dynamics and machine learning analysis

The differential modulation of agonist and antagonist binding to opioid receptors (ORs) by sodium (Na+) has been known for decades. To shed light on the molecular determinants, thermodynamics, and kinetics of Na+ translocation through the μ-OR (MOR), we used a multi-ensemble Markov model framework combining equilibrium and non-equilibrium atomistic molecular dynamics simulations of Na+ binding to MOR active or inactive crystal structures embedded in an explicit lipid bilayer. We identify an energetically favorable, continuous ion pathway through the MOR active conformation only, and provide, for the first time: i) estimates of the energy differences and required timescales of Na+ translocation in inactive and active MORs, ii) estimates of Na+-induced changes to agonist binding validated by radioligand measurements, and iii) testable hypotheses of molecular determinants and correlated motions involved in this translocation, which are likely to play a key role in MOR signaling.

Towards an Understanding of the Molecular Basis of Nickel Hyperaccumulation in Plants.

Metal hyperaccumulation is a rare and fascinating phenomenon, whereby plants actively accumulate high concentrations of metal ions in their above-ground tissues. Enhanced uptake and root-to-shoot translocation of specific metal ions coupled with an increased capacity for detoxification and sequestration of these ions are thought to constitute the physiological basis of the hyperaccumulation phenotype. Nickel hyperaccumulators were the first to be discovered and are the most numerous, accounting for some seventy-five percent of all known hyperaccumulators. However, our understanding of the molecular basis of the physiological processes underpinning Ni hyperaccumulation has lagged behind that of Zn and Cd hyperaccumulation, in large part due to a lack of genomic resources for Ni hyperaccumulators. The advent of RNA-Seq technology, which allows both transcriptome assembly and profiling of global gene expression without the need for a reference genome, has offered a new route for the analysis of Ni hyperaccumulators, and several such studies have recently been reported. Here we review the current state of our understanding of the molecular basis of Ni hyperaccumulation in plants, with an emphasis on insights gained from recent RNA-Seq experiments, highlight commonalities and differences between Ni hyperaccumulators, and suggest potential future avenues of research in this field.

Current Scenario of Pb Toxicity in Plants: Unraveling Plethora of Physiological Responses.

Lead (Pb) is an extremely toxic metal for all living forms including plants. It enters plants through roots from soil or soil solution. It is considered as one of the most eminent examples of anthropogenic environmental pollutant added in environment through mining and smelting of lead ores, coal burning, waste from battery industries, leaded paints, metal plating, and automobile exhaust. Uptake of Pb in plants is a nonselective process and is driven by H+/ATPases. Translocation of Pb metal ions occurs by apoplastic movement resulting in deposition of metal ions in the endodermis and is further transported by symplastic movement. Plants exposed to high concentration of Pb show toxic symptoms due to the overproduction of reactive oxygen species (ROS) through Fenton-Haber-Weiss reaction. ROS include superoxide anion, hydroxyl radical, and hydrogen peroxide, which reach to macro- and micro-cellular levels in the plant cells and cause oxidative damage. Plant growth and plethora of biochemical and physiological attributes including plant growth, water status, photosynthetic efficiency, antioxidative defense system, phenolic compounds, metal chelators, osmolytes, and redox status are adversely influenced by Pb toxicity. Plants respond to toxic levels of Pb in varied ways such as restricted uptake of metal, chelation of metal ions to the root endodermis, enhancement in activity of antioxidative defense, alteration in metal transporters expression, and involvement of plant growth regulators.

Phytotoxicity of chromium and nickel in early stage of ontogenetic development of corn

The data on phytotoxicity of the combined action of chromium and nickel ions on maize hybrids Premiya 190 MV and Euro 401 SV in laboratory vegetation experiments have been analyzed. Plants were grown during 6 days in vegetation vessels at the temperature of 26–27°C on standard Hogland-Snyder’s nutrient medium, with the illumination of 15,000 lux for 16 hours per day and the aeration of nutrient medium. Then chromium and nickel compounds were added into the growth vessels. The effect of the combined action of aqueous solutions of chromium (III) and nickel (II) sulfates was studied in the following variants of the experiment: control (distilled water); 1MPC Ni2++1MPC Cr3+; 10MPC Ni2++ 1MPC Cr3+; 1MPC Ni2++10MPC Cr3+; 10MPC Ni2++10MPC Cr3+ (MPC – maximum permissible concentration). In the experiments, it was assumed that MPC of Cr is 6 mg/l and MPC of Ni is 4 mg/l. Then, after 24 and 72 hours of applying of chromium and nickel solutions, the length of the main root and the height of the aerial part and their weight were measured, and the root index value was calculated. Analysis of the data showed that the inhibitory effect of chromium and nickel ions on the growth of plant of hybrid Premiya 190 MV was 1.4 times less than that for plants of Euro 401 SV hybrid. At 72 hours of plant growth with a minimum concentration of chromium on the background of maximum nickel, the growth inhibition of main root of plants of hybrid Premiya 190 MV was 27%, while at the maximum concentration of chromium on the background of the minimum nickel content – 19.4%. For hybrid Euro 401 SV more effective inhibition of root growth was found: in the variant with the maximum nickel on the background of minimum chromium – by 54.6%, and at the maximum chromium content – by 40%. At the same time, it was found that chromium and nickel ions in minimal concentrations stimulated the main root growth by 16–17 % in Premiya 190 MV, whereas in Euro 401 SV – suppressed by 33%. In general, the similar effects were observed for the production of weight of root system. Most significantly, this effect was revealed in the Euro 401 SV hybrid. Reducing the weight of wet and dry mass of this hybrid plants at the maximum nickel content was 50 and 28%, whereas at the maximum concentration of chromium it was 40 and 20% respectively. The obtained results indicate both the greater negative effect of chromium ions on maize plants and the lower metal tolerance of Euro 401 SV hybrid seedlings compared to the Premiya 190 MV at joint influence of chromium and nickel. The results allow to state that in maize plants at the early stages of their ontogenetic development, there is a greater up to 15% negative effect of nickel ions than chromium on the root and aerial part growth, formation of wet and dry weight. Combined action of chromium and nickel ions shows a greater phytotoxic effect on the root system development than on the aerial parts of plants. This effect is, most likely, due to the functioning of the anatomical, physiological and biochemical barrier mechanisms in the root-leaf system with respect to the excessive translocation of metal ions that cause inhibiting effects.

Characterization of the genome from Geobacter anodireducens, a strain with enhanced current production in bioelectrochemical systems.

Geobacter anodireducens is unique in that it can generate high current densities in bioelectrochemical systems (BES) operating under high salt conditions. This ability is important for the development of BES treating high salt wastewater and microbial desalination cells. Therefore, the genome of G. anodireducens was characterized to identify proteins that might allow this strain to survive in high salt BES. Comparison to other Geobacter species revealed that 81 of its 87 c-type cytochromes had homologs in G. soli and G. sulfurreducens. Genes coding for many extracellular electron transfer proteins were also detected, including the outer membrane c-type cytochromes OmcS and OmcZ and the soluble c-type cytochrome PgcA. G. anodireducens also appears to have numerous membrane complexes involved in the translocation of protons and sodium ions and channels that provide protection against osmotic shock. In addition, it has more DNA repair genes than most Geobacter species, suggesting that it might be able to more rapidly repair DNA damage caused in high salt and low pH anode environments. Although this genomic analysis provides invaluable insight into mechanisms used by G. anodireducens to survive in high salt BES, genetic, transcriptomic, and proteomic studies will need to be done to validate their roles.

Biogenesis of the Insulin Secretory Granule in Health and Disease.

The secretory granules of pancreatic beta cells are specialized organelles responsible for the packaging, storage and secretion of the vital hormone insulin. The insulin secretory granules also contain more than 100 other proteins including the proteases involved in proinsulin-to insulin conversion, other precursor proteins, minor co-secreted peptides, membrane proteins involved in cell trafficking and ion translocation proteins essential for regulation of the intragranular environment. The synthesis, transport and packaging of these proteins into nascent granules must be carried out in a co-ordinated manner to ensure correct functioning of the granule. The process is regulated by many circulating nutrients such as glucose and can change under different physiological states. This chapter discusses the various processes involved in insulin granule biogenesis with a focus on the granule composition in health and disease.

HgII -Mediated TlI -to-TlIII Oxidation in Dynamic PbII /Tl Porphyrin Complexes.

Compared with their purely organic counterparts, molecular switches that are based on metal ion translocations have been underexplored, and more particularly, it remains challenging to control the translocation of several particles in multisite receptors. Recently, bimetallic complexes that undergo double translocation processes have been developed with bis-strapped porphyrin ligands. To implement a redox control for these systems, we have investigated the formation of heterobimetallic lead/thallium complexes, with thallium in the +I and +III oxidation states. Two different complexes were characterized: 1) a PbII /TlI complex, in which both metal ions interact with the N-core on its different sides, and 2) a PbII /TlIII complex with TlIII selectively bound to the N-core and PbII selectively bound to the strap opposite to TlIII . These two complexes undergo interconversion between their two degenerate forms (same coordination of the metal ions but on opposite sides) by different intra or intermolecular translocation pathways. In addition, conversion of the PbII /TlI complex into its PbII /TlIII counterpart was achieved by addition of a stoichiometric amount of HgII salt as a sacrificial electron acceptor. These results further contribute to the elaboration of devices that feature redox-controlled compartmentalized double translocations.

Ion-Ion Repulsions and Charge-Shielding Effects Dominate the Permeation Mechanism through the OmpF Porin Channel.

OmpF is a wide channel bacterial porin frequently employed to study selective ionic translocation. The cationic preference of this porin is mainly determined by electrostatic forces between the translocated ion and the protein and the formation of ion pairs (e.g., K+···Cl-) being previously pointed as the main cause to favor the cationic transport through the constriction zone. Hybrid quantum mechanics/molecular mechanics-molecular dynamics simulations, which have provided polarization-containing potentials of mean force profiles for different permeation scenarios, reveal significant new insights related with the ion translocation mechanism. Results show that the permeation is dominated by electrostatic interactions, which in turn affect ion-protein interactions at the constriction zone. However, it is observed that ion flow is favored by ion-ion repulsions and, in a lesser extent, by charge-shielding effects, instead of the previously pointed ionic pair formation.

Modeling ion permeation in wild-type and mutant human α7 nachr ion channels

Molecular dynamics simulations of wild type and two mutant (T248F and L251T) human [Formula: see text]7 nicotinic acetylcholine receptors (nAChR) have been performed. The channel transmembrane domains were modeled from the closed channel structure from torpedo ray (PDB ID 2BG9) and embedded in DPPC lipid bilayers, surrounded by physiological saline solution. An external electric field was used to obtain stable open channel structures. The adaptive biasing force (ABF) method was used to obtain potential of mean force (PMF) profiles for Na[Formula: see text] ion translocation through the wild type and mutant receptors. Based on the geometry and PMF profiles, the channel gate was found to be at one of the two hydrophobic conserved regions (V249-L251) near the lower end of the channel. The L251T mutation reduced the energetic barrier by 1.9[Formula: see text]kcal/mol, consistent with a slight increase in the channel radius in the bottleneck region. On the other hand, the T248F mutation caused a significant decrease in the channel radius (0.4 Å) and a substantial increase of 3.9[Formula: see text]kcal/mol in the energetic barrier. Ion permeation in all three structures was compared and found to be consistent with barrier height values. Using an external field in an incrementally increasing manner was found to be an effective way to obtain stable open, conducting channel structures.

Encapsulation versus Self-Aggregation toward Highly Selective Artificial K+ Channels.

Natural ion-channel proteins allow ion transport across cell membranes at rates very close to those for ionic diffusion in water. Among them, naturalKcsA K+ channels present high transport rates and total selectivity for K+ cations, rejecting all other cations. Most of the reported artificial ion channels cannot reach this type of activity because of their low selectivity. Several synthetic channels have been designed to mimic the natural KcSA channels, but those presenting an important K+/Na+ selectivity are limited. High-selectivity issues are determinant for the performance of natural protein channels, but they have been not considered as determinant in controlling the transport activity of the artificial ion channels. This Account discusses the last developments of artificial supramolecular carriers or channels that selectivelytransport K+ cations against other cations. Mimicking the complex structures of protein channels is an important research area. These studies are related to such adaptive biomimetic systems that can self-select their functions, with a specific emphasis on artificial superstructures enabling K+ transport like in the natural ones. Alternatively, it is more than interesting to synthetically construct only the active key structures of protein filters or gates that give the chemical selectivity or lead us to describe their dynamic role in the ion pumping and translocation along the channel. Several self-assembled macrocyclic channels are presented here. The macrocyclic binding sites may selectively encapsulate the K+ cations or form aggregated H-bonded central pores of self-assembled macrocycles that coordinate the K+ cations as hydrating water molecules in aqueous solution, compensating for the energetic cost of cation dehydration. These macrocyclic channels are responsive in the presence of K+ cations, even when a large excess of Na+ is present. From the mechanistic point of view, these systems express a synergistic dynamic feature: addition of K+ cations drives the selection and emergence of specific ion channels that selectively conduct the K+ cations that promoted the formation of channel superstructures in the first place. These highly permeable and K+-selective artificial channels may be considered as simple primitive biomimetic alternatives of natural KcsA channels that may find interesting applications in chemical separations, selective sensing, and biomedical materials.

A potential gain-of-function variant of SLC9A6 leads to endosomal alkalinization and neuronal atrophy associated with Christianson Syndrome

Loss-of-function mutations in the recycling endosomal (Na+,K+)/H+ exchanger gene SLC9A6/NHE6 result in overacidification and dysfunction of endosomal-lysosomal compartments, and cause a neurodevelopmental and degenerative form of X-linked intellectual disability called Christianson Syndrome (CS). However, knowledge of the disease heterogeneity of CS is limited. Here, we describe the clinical features and underlying molecular and cellular mechanisms associated with a CS patient carrying a de novo missense variant (p.Gly218Arg; G218R) of a conserved residue in its ion translocation domain that results in a potential gain-of-function. The patient manifested several core symptoms typical of CS, including pronounced cognitive impairment, mutism, epilepsy, ataxia and microcephaly; however, deterioration of motor function often observed after the first decade of life in CS children with total loss of SLC9A6/NHE6 function was not evident. In transfected non-neuronal cells, complex glycosylation and half-life of the G218R were significantly decreased compared to the wild-type transporter. This correlated with elevated ubiquitination and partial proteasomal-mediated proteolysis of G218R. However, a major fraction was delivered to the plasma membrane and endocytic pathways. Compared to wild-type, G218R-containing endosomes were atypically alkaline and showed impaired uptake of recycling endosomal cargo. Moreover, instead of accumulating in recycling endosomes, G218R was redirected to multivesicular bodies/late endosomes and ejected extracellularly in exosomes rather than progressing to lysosomes for degradation. Attenuated acidification and trafficking of G218R-containing endosomes were also observed in transfected hippocampal neurons, and correlated with diminished dendritic branching and density of mature mushroom-shaped spines and increased appearance of filopodia-like protrusions. Collectively, these findings expand our understanding of the genetic diversity of CS and further elucidate a critical role for SLC9A6/NHE6 in fine-tuning recycling endosomal pH and cargo trafficking, processes crucial for the maintenance of neuronal polarity and mature synaptic structures.

Role of the Interaction Motif in Maintaining the Open Gate of an Open Sodium Channel

Voltage-gated sodium channels undergo transitions between open, closed, and inactivated states, enabling regulation of the translocation of sodium ions across membranes. A recently published crystal structure of the full-length prokaryotic NavMs crystal structure in the activated open conformation has revealed the presence of a novel motif consisting of an extensive network of salt bridges involving residues in the voltage sensor, S4-S5 linker, pore, and C-terminal domains. This motif has been proposed to be responsible for maintaining an open conformation that enables ion translocation through the channel. In this study, we have used long-time molecular dynamics calculations without artificial restraints to demonstrate that the interaction network of full-length NavMs indeed prevents a rapid collapse and closure of the gate, in marked difference to earlier studies of the pore-only construct in which the gate had to be restrained to remain open. Interestingly, a frequently discussed “hydrophobic gating” mechanism at nanoscopic level is also observed in our simulations, in which the discontinuous water wire close to the gate region leads to an energetic barrier for ion conduction. In addition, we demonstrate the effects of in silico mutations of several of the key residues in the motif on the open channel’s stability and functioning, correlating them with existing functional studies on this channel and homologous disease-associated mutations in human sodium channels; we also examine the effects of truncating/removing the voltage sensor and C-terminal domains in maintaining an open gate.

Polymerization driven monomer passage through monolayer chemical vapour deposition graphene

Mass transport through graphene is receiving increasing attention due to the potential for molecular sieving. Experimental studies are mostly limited to the translocation of protons, ions, and water molecules, and results for larger molecules through graphene are rare. Here, we perform controlled radical polymerization with surface-anchored self-assembled initiator monolayer in a monomer solution with single-layer graphene separating the initiator from the monomer. We demonstrate that neutral monomers are able to pass through the graphene (via native defects) and increase the graphene defects ratio (Raman ID/IG) from ca. 0.09 to 0.22. The translocations of anionic and cationic monomers through graphene are significantly slower due to chemical interactions of monomers with the graphene defects. Interestingly, if micropatterned initiator-monolayers are used, the translocations of anionic monomers apparently cut the graphene sheet into congruent microscopic structures. The varied interactions between monomers and graphene defects are further investigated by quantum molecular dynamics simulations.