Gating Behavior Research Articles

The biophysical properties of TRIC-A and TRIC-B and their interactions with RyR2.

Trimeric intracellular cation channels (TRIC-A and TRIC-B) are thought to provide counter-ion currents to enable charge equilibration across the sarco/endoplasmic reticulum (SR) and nuclear membranes. However, there is also evidence that TRIC-A may interact directly with ryanodine receptor type 1 (RyR1) and 2 (RyR2) to alter RyR channel gating. It is therefore possible that the reverse is also true, where the presence of RyR channels is necessary for fully functional TRIC channels. We therefore coexpressed mouse TRIC-A or TRIC-B with mouse RyR2 in HEK293 cells to examine if after incorporating membrane vesicles from these cells into bilayers, the presence of TRIC affects RyR2 function, and to characterize the permeability and gating properties of the TRIC channels. Importantly, we used no purification techniques or detergents to minimize damage to TRIC and RyR2 proteins. We found that both TRIC-A and TRIC-B altered the gating behavior of RyR2 and its response to cytosolic Ca2+ but that TRIC-A exhibited a greater ability to stimulate the opening of RyR2. Fusing membrane vesicles containing TRIC-A or TRIC-B into bilayers caused the appearance of rapidly gating current fluctuations of multiple amplitudes. The reversal potentials of bilayers fused with high numbers of vesicles containing TRIC-A or TRIC-B revealed both Cl- and K+ fluxes, suggesting that TRIC channels are relatively non-selective ion channels. Our results indicate that the physiological roles of TRIC-A and TRIC-B may include direct, complementary regulation of RyR2 gating in addition to the provision of counter-ion currents of both cations and anions.

Modulation of Voltage-Gating and Hysteresis of Lysenin Channels by Cu2+ Ions.

The intricate voltage regulation presented by lysenin channels reconstituted in artificial lipid membranes leads to a strong hysteresis in conductance, bistability, and memory. Prior investigations on lysenin channels indicate that the hysteresis is modulated by multivalent cations which are also capable of eliciting single-step conformational changes and transitions to stable closed or sub-conducting states. However, the influence on voltage regulation of Cu2+ ions, capable of completely closing the lysenin channels in a two-step process, was not sufficiently addressed. In this respect, we employed electrophysiology approaches to investigate the response of lysenin channels to variable voltage stimuli in the presence of small concentrations of Cu2+ ions. Our experimental results showed that the hysteretic behavior, recorded in response to variable voltage ramps, is accentuated in the presence of Cu2+ ions. Using simultaneous AC/DC stimulation, we were able to determine that Cu2+ prevents the reopening of channels previously closed by depolarizing potentials and the channels remain in the closed state even in the absence of a transmembrane voltage. In addition, we showed that Cu2+ addition reinstates the voltage gating and hysteretic behavior of lysenin channels reconstituted in neutral lipid membranes in which lysenin channels lose their voltage-regulating properties. In the presence of Cu2+ ions, lysenin not only regained the voltage gating but also behaved like a long-term molecular memory controlled by electrical potentials.

Cascaded Logic Gates Based on High-Performance Ambipolar Dual-Gate WSe2 Thin Film Transistors.

Ambipolar dual-gate transistors based on low-dimensional materials, such as graphene, carbon nanotubes, black phosphorus, and certain transition metal dichalcogenides (TMDs), enable reconfigurable logic circuits with a suppressed off-state current. These circuits achieve the same logical output as complementary metal-oxide semiconductor (CMOS) with fewer transistors and offer greater flexibility in design. The primary challenge lies in the cascadability and power consumption of these logic gates with static CMOS-like connections. In this article, high-performance ambipolar dual-gate transistors based on tungsten diselenide (WSe2) are fabricated. A high on-off ratio of 108 and 106, a low off-state current of 100 to 300 fA, a negligible hysteresis, and an ideal subthreshold swing of 62 and 63 mV/dec are measured in the p- and n-type transport, respectively. We demonstrate cascadable and cascaded logic gates using ambipolar TMD transistors with minimal static power consumption, including inverters, XOR, NAND, NOR, and buffers made by cascaded inverters. A thorough study of both the control gate and the polarity gate behavior is conducted. The noise margin of the logic gates is measured and analyzed. The large noise margin enables the implementation of VT-drop circuits, a type of logic with reduced transistor number and simplified circuit design. Finally, the speed performance of the VT-drop and other circuits built by dual-gate devices is qualitatively analyzed. This work makes advancements in the field of ambipolar dual-gate TMD transistors, showing their potential for low-power, high-speed, and more flexible logic circuits.

Simple and Accurate Model for the Propagation Delay in MCML Gates

In this article, we develop a simple and accurate model for evaluating the propagation delay in MOS Current-Mode Logic (MCML) gates. The model describes the behavior of MCML gates in a linear fashion despite the circuits themselves being non-linear. Indeed, we demonstrate that a linear model can be used, provided that, for each small-signal parameter, its average value calculated between the two different switching logic states is used. The proposed model is validated through simulations of MCML universal gates designed using modern nanometer processes. The model forecasts simulated values with an error lower than 4% and 20% in 65-nm standard CMOS and 28-nm Fully-Depleted Silicon-On-Insulator (FD-SOI), respectively.

Mice lacking Ptprd exhibit deficits in goal-directed behavior and female-specific impairments in sensorimotor gating.

Protein Tyrosine Phosphatase receptor type D (PTPRD) is a member of the protein tyrosine phosphatase family that mediates cell adhesion and synaptic specification. Genetic studies have linked Ptprd to several neuropsychiatric phenotypes, including Restless Leg Syndrome (RLS), opioid abuse disorder, and antipsychotic-induced weight gain. Genome-wide association studies (GWAS) of either pediatric obsessive-compulsive traits, or Obsessive-Compulsive Disorder (OCD), have identified loci near PTPRD as genome-wide significant, or strongly suggestive for this trait. We assessed Ptprd wild-type (WT), heterozygous (HT), and knockout (KO) mice for behavioral dimensions that are altered in OCD, including anxiety and exploration (open field test, dig test), perseverative behavior (splash-induced grooming, spatial d), sensorimotor gating (prepulse inhibition), and home cage goal-directed behavior (nest building). No effect of genotype was observed in any measure of the open field test, dig test, or splash test. However, Ptprd KO mice of both sexes showed impairments in nest building behavior. Finally, female, but not male, Ptprd KO mice showed deficits in prepulse inhibition, an operational measure of sensorimotor gating that is reduced in female, but not male, OCD patients. Our results indicate that constitutive lack of Ptprd may contribute to the development of certain domains that are altered OCD, including goal-directed behavior, and reduced sensorimotor gating specifically in females.

Strongly anisotropic ultrafast dynamic behavior of GaTe dominated by the tilted and flat bands

The anisotropic transport properties of gallium telluride (GaTe) have been reported by several experiments, giving rise to many debates recently. The anisotropic electronic band structure of GaTe shows the extreme difference between the flat band and tilted band in two distinct directions, - and - , and which we called as the mixed flat-tilted band (MFTB). Focusing on such two directions, the relaxation of photo-generated carriers has been studied using the non-adiabatic molecular dynamics (NAMD) method to investigate the anisotropic behavior of ultrafast dynamics. The results show that the relaxation lifetime is different in flat band direction and tilted band direction, which is evidence for the existence of anisotropic behavior of the ultrafast dynamic, and such anisotropic behavior comes from the different intensities of electron–phonon coupling of the flat band and tilted band. Furthermore, the ultrafast dynamic behavior is found to be affected strongly by spin–orbit coupling (SOC) and such anisotropic behavior of the ultrafast dynamic can be reversed by SOC. The tunable anisotropic ultrafast dynamic behavior of GaTe is expected to be detected in ultrafast spectroscopy experiments and it may provide a tunable application in nanodevice design. The results may also provide a reference for the investigation of MFTB semiconductors.

PI(4,5)P2 regulates the gating of NaV1.4 channels.

Voltage-gated sodium (NaV) channels are densely expressed in most excitable cells and activate in response to depolarization, causing a rapid influx of Na+ ions that initiates the action potential. The voltage-dependent activation of NaV channels is followed almost instantaneously by fast inactivation, setting the refractory period of excitable tissues. The gating cycle of NaV channels is subject to tight regulation, with perturbations leading to a range of pathophysiological states. The gating properties of most ion channels are regulated by the membrane phospholipid, phosphatidylinositol (4,5) bisphosphate (PI(4,5)P2). However, it is not known whether PI(4,5)P2 modulates the activity of NaV channels. Here, we utilize optogenetics to activate specific, membrane-associated phosphoinositide (PI)-phosphatases that dephosphorylate PI(4,5)P2 while simultaneously recording NaV1.4 channel currents. We show that dephosphorylating PI(4,5)P2 left-shifts the voltage-dependent gating of NaV1.4 to more hyperpolarized membrane potentials, augments the late current that persists after fast inactivation, and speeds the rate at which channels recover from fast inactivation. These effects are opposed by exogenous diC8PI(4,5)P2. We provide evidence that PI(4,5)P2 is a negative regulator that tunes the gating behavior of NaV1.4 channels.

A reversible and selective chromogenic thiazole tagged chemosensor for Hg2+in aqueous medium: Crystal structure, theoretical investigations and real sample analysis

A novel thiazole tagged Schiff base chemosensor, (E)-N'-((2-aminothiazol-5-yl)methylene)-2-hydroxybenzohydrazide (ATH) has been synthesized in excellent yield by a simple one pot method and characterized by single crystal X-ray diffraction and spectroscopic techniques. The sensing ability of ATH was determined for detection of Hg2+ ions in the presence of different metal ions in aqueous medium. It behaves as an extremely selective and sensitive chromogenic sensor for naked-eye detection of Hg2+ ions with a colour change from colourless to yellow due to ligand to metal charge transfer. Remarkably, the binding constant (Ka) and limit of detection (LOD) for ATHHg2+ complex were found as 1.75 × 104M −1 and 8.85 × 10−7 M, respectively. The Job's plot indicated that the stoichiometric ratio of ATH to Hg2+ is 1:1. The binding mechanism was established based on FT-IR, 1H NMR titration, mass spectrometry and density functional theory studies. The chemosensor exhibited an excellent colorimetric property in 7.0–12.0 pH range. The chemosensor was found to be reversible and reusable in the presence of CN− ions with logic gate behaviour. Further, the chemosensor was utilized to sense Hg2+ ions in tap and Ganga river water samples.

Ligand sensitivity of type-1 inositol 1,4,5-trisphosphate receptor is enhanced by the D2594K mutation

Inositol 1,4,5-trisphosphate receptor (IP3R) and ryanodine receptor (RyR) are homologous cation channels that mediate release of Ca2+ from the endoplasmic/sarcoplasmic reticulum (ER/SR) and thereby are involved in many physiological processes. In previous studies, we determined that when the D2594 residue, located at or near the gate of the IP3R type 1, was replaced by lysine (D2594K), a gain of function was obtained. This mutant phenotype was characterized by increased IP3 sensitivity. We hypothesized the IP3R1-D2594 determines the ligand sensitivity of the channel by electrostatically affecting the stability of the closed and open states. To test this possibility, the relationship between the D2594 site and IP3R1 regulation by IP3, cytosolic, and luminal Ca2+ was determined at the cellular, subcellular, and single-channel levels using fluorescence Ca2+ imaging and single-channel reconstitution. We found that in cells, D2594K mutation enhances the IP3 ligand sensitivity. Single-channel IP3R1 studies revealed that the conductance of IP3R1-WT and -D2594K channels is similar. However, IP3R1-D2594K channels exhibit higher IP3 sensitivity, with substantially greater efficacy. In addition, like its wild type (WT) counterpart, IP3R1-D2594K showed a bell-shape cytosolic Ca2+-dependency, but D2594K had greater activity at each tested cytosolic free Ca2+ concentration. The IP3R1-D2594K also had altered luminal Ca2+ sensitivity. Unlike IP3R1-WT, D2594K channel activity did not decrease at low luminal Ca2+ levels. Taken together, our functional studies indicate that the substitution of a negatively charged residue by a positive one at the channels’ pore cytosolic exit affects the channel’s gating behavior thereby explaining the enhanced ligand-channel’s sensitivity.

Elucidating the pH gating mechanism of Helicobacter pyloris urea channel UreI.

Over 50% of the world population suffer from chronic gastric infection with Helicobacter pyloris which is linked to peptic ulcer disease and stomach cancer. Yet, the efficacy of the common therapy including antibiotics is decreasing. An alternative drug target could be H. pyloris pH gatedinner-membrane urea channel UreI, which is pivotal for the survival of the pathogen in the acidic environment of the human stomach. However, despite in vivo studies and high-resolution structures in the open and closed state, HpUreIs gating mechanism is still elusive. Using yeast complementation assays, we tested (i) homologues urea channels, (ii) point mutations of charged residues also on the cytoplasmic side, and (iii) variants carrying changes at the periplasmic side at the N- and C-terminus as well as in periplasmic loop 1 (PL1). The functionality and pH gating behaviour of these constructs are compared to the wild type protein in the physiological relevant pH range from 4.0 to 7.0. Our in vivo studies are guided and accompanied by an extensive sequence- and structure-based analysis of homologues urea channels. The results question the hypothesis of PL1 and PL2 constituting the main pH-sensor of HpUreI but confirm the importance of the N- and C-terminus in the pH gating mechanism. For example, additional amino acids at the C-terminus provoke a urea impermeable HpUreI, emphasizing its importance for the stability of the open state. Furthermore, the urea channels from Helicobacter hepaticus and Streptococcus salivarius, lacking such extensive periplasmic loops, show similar pH dependence as HpUreI. Overall, yeast complementation assays are an cost-effective tool for testing qualitative differences in protein variant activity for a broad range of solutes.

Gating transitions in the MthK potassium channel.

Potassium channels form one of the most ubiquitous classes of proteins and are found across all forms of life. Permeation of ions through potassium channels is controlled in different ways, most notably at the lower gate and at the selectivity filter. Here, we focus on the MthK channel, an archaeal calcium-gated potassium channel that has seen wide use as a model system. Particularly, binding of Ca2+ ions opens full-length MthK, possibly also triggering the allosteric coupling between the filter and the gate. To understand the gating behavior in more detail, we apply molecular dynamics (MD) simulations, with and without applied voltage, combined with essential dynamics sampling. This is enabled by the recent availability of both closed and open conformations.

Selective colorimetric signaling of mercury (II) ions using a quinoline-based probe with INHIBIT logic gate behavior and test strip

Selective colorimetric signaling of mercury (II) ions using a quinoline-based probe with INHIBIT logic gate behavior and test strip

Cu(II)-Triggered Ion Channel Properties of a 2,2'-Bipyridine-Modified Amphotericin B.

The development of stimuli-responsive synthetic channels that open and close in response to physical and chemical changes in the surrounding environment has attracted attention because of their potential bioapplications such as sensing, drug release, antibiotics, and molecular manipulation tools to control membrane transport in cells. Metal coordination is ideal as a stimulus for stimuli-responsive channels because it allows for reversible gating behavior through the addition and removal of metal ions and fine-tuning of channel structure through coordination geometry defined by the type of the metal ion and ligand. We have previously reported on transition metal-ion dependent ion permeability control of Amphotericin B (AmB) modified with a metal coordination site, 2,2'-bipyridine ligand (bpy-AmB). AmB is one of the polyene macrolide antibiotics, and it is known that the interaction between AmB and ergosterol molecules is required for AmB channel formation. In contrast, the Cu2+ coordination to the bpy moiety of bpy-AmB induces formation of Ca2+ ion-permeable channels in the ergosterol-free POPC membrane. However, the details of bpy-AmB properties such as channel stability, ion selectivity, pore size, and the effect of ergosterol on channel formation remain unclear. Here, we investigate bpy-AmB channels triggered by transition metal coordination in POPC or ergosterol-containing POPC liposomes using an HPTS assay, electrophysiological measurements, and time-resolved UV-vis spectral measurements. These analyses reveal that bpy-AmB channels triggered by Cu2+ ions are more stable and have larger pore sizes than the original AmB channels and enable efficient permeation of various cations. We believe that our channel design will lead to the construction of metal coordination-triggered synthetic ion channels.

Comportamento hidráulico de registros utilizados em instalações hidráulicas prediais

ABSTRACT This study was developed with the objective of evaluating the steady-state hydraulic behavior of gate, ball, and pressure valves with nominal diameters of ½” and ¾”, which are widely used in building water supply networks in Brazil. For this purpose, tests were performed to determine the head loss in ten different valves in four openings with five replicates. A hydraulic head loss testing apparatus was set up in a pipeline network that allowed for the control, monitoring, and acquisition of data. Mean values of the K coefficient of the minor head loss and the equivalent length were estimated for the conditions evaluated. The results were analyzed using box plots, correlation, principal components analysis, and hierarchical clustering. In general, the gate valves showed lower head loss for all the relative openings considered, while the pressure valves showed the greatest head loss. Of the clusters formed, for the second group, there was a predominance of treatments with pressure valves, which showed similarity in terms of the values of the hydraulic variables due to the geometry and construction of the valves.

Conformational Dynamics of Loop L3 in OmpF: Implications toward Antibiotic Translocation and Voltage Gating.

In the present work, we delineate the molecular mechanism of a bulky antibiotic permeating through a bacterial channel and uncover the role of conformational dynamics of the constriction loop in this process. Using the temperature accelerated sliced sampling approach, we shed light onto the dynamics of the L3 loop, in particular the F118 to S125 segment, at the constriction regions of the OmpF porin. We complement the findings with single channel electrophysiology experiments and applied-field simulations, and we demonstrate the role of hydrogen-bond stabilization in the conformational dynamics of the L3 loop. A molecular mechanism of permeation is put forward wherein charged antibiotics perturb the network of stabilizing hydrogen-bond interactions and induce conformational changes in the L3 segment, thereby aiding the accommodation and permeation of bulky antibiotic molecules across the constriction region. We complement the findings with single channel electrophysiology experiments and demonstrate the importance of the hydrogen-bond stabilization in the conformational dynamics of the L3 loop. The generality of the present observations and experimental results regarding the L3 dynamics enables us to identify this L3 segment as the source of gating. We propose a mechanism of OmpF gating that is in agreement with previous experimental data that showed the noninfluence of cysteine double mutants that tethered the L3 tip to the barrel wall on the OmpF gating behavior. The presence of similar loop stabilization networks in porins of other clinically relevant pathogens suggests that the conformational dynamics of the constriction loop is possibly of general importance in the context of antibiotic permeation through porins.

Cardiac sodium channel complexes and arrhythmia: structural and functional roles of the β1 and β3 subunits.

In cardiac myocytes, the voltage-gated sodium channel NaV 1.5 opens in response to membrane depolarisation and initiates the action potential. The NaV 1.5 channel is typically associated with regulatory β-subunits that modify gating and trafficking behaviour. These β-subunits contain a single extracellular immunoglobulin (Ig) domain, a single transmembrane α-helix and an intracellular region. Here we focus on the role of the β1 and β3 subunits in regulating NaV 1.5. We catalogue β1 and β3 domain specific mutations that have been associated with inherited cardiac arrhythmia, including Brugada syndrome, long QT syndrome, atrial fibrillation and sudden death. We discuss how new structural insights into these proteins raises new questions about physiological function.

Conformational motions and ligand-binding underlying gating and regulation in IP3R channel

Inositol-1,4,5-trisphosphate receptors (IP3Rs) are activated by IP3 and Ca2+ and their gating is regulated by various intracellular messengers that finely tune the channel activity. Here, using single particle cryo-EM analysis we determined 3D structures of the nanodisc-reconstituted IP3R1 channel in two ligand-bound states. These structures provide unprecedented details governing binding of IP3, Ca2+ and ATP, revealing conformational changes that couple ligand-binding to channel opening. Using a deep-learning approach and 3D variability analysis we extracted molecular motions of the key protein domains from cryo-EM density data. We find that IP3 binding relies upon intrinsic flexibility of the ARM2 domain in the tetrameric channel. Our results highlight a key role of dynamic side chains in regulating gating behavior of IP3R channels. This work represents a stepping-stone to developing mechanistic understanding of conformational pathways underlying ligand-binding, activation and regulation of the channel.

Thiadiazole Functionalized Salicylaldehyde-Schiff Base as a pH-responsive and chemo-reversible "Turn-Off" fluorescent probe for selective cu (II) detection: Logic Gate Behaviour and Molecular Docking Studies.

A novel thiadiazole functionalized schiff base chemoreceptor (E)-2,4-dichloro-6-(((5-mercapto-1,3,4-thiadiazol-2-yl)imino)methyl)phenol (SB-1) has been synthesized and characterized spectroscopically by using various techniques. Its photophysical behaviour was scanned towards a variety of metal ions in mixed aqueous media. The chemosensor (SB-1) displayed excellent selectivity towards Cu2+ ion through fluorescent diminishment (turn-off phenomenon). Colorimetric analyses showed a rapid colour change from yellow to dark red under visible light upon addition of Cu2+ ions. Interestingly, the original yellow colour reappeared back instantly after the addition of EDTA2- anions, thus confirming the reversible nature of SB-1. Competitive experiments validated no interference from the other co-existing metal ions in the recognition process of SB-1 towards Cu2+ ion. Job's plot confirmed 1:1 binding stoichiometry between SB-1 and Cu2+ ion with the binding constant value of 3.87 × 104M- 1. The limit of detection was determined to be 1.01 × 10- 7M suggesting good sensitivity of SB-1 towards Cu2+ ions. Furthermore, pH-dependent UV-Vis spectral behaviour of SB-1 confirmed that it could act as an effective optical pH-sensor for highly acidic environment as well. Portable nature of probe SB-1 was explored by fabricating "easy-to-use" paper test strips, which allow robust and rapid detection of Cu2+ ions. Based on the multi-responsive properties of SB-1, a 'NOR' logic gate was constructed by applying Cu2+ and EDTA2- as chemical inputs (ln1: Cu2+, ln2: EDTA2-) while emission intensity observed at 560nm was considered as output signal (O1). DFT optimized geometries confirmed that chemosensor SB-1 exists in Azo form (Enol form) in its ground state. Molecular docking of the SB-1 and its copper complex, into the binding site of TRK protein tyrosine kinase (PDB: 1t46) was also carried out to explore their biological activity and their potential use as TRK inhibitors.

Rectified Janus nanopores: new vitality for ionic diodes

Gated nanopores have gained tremendous attention in various fundamental and applied studies. A recent article by Siwy et al. proposes the use of ion concentration as a simple way to tune the gating behavior of Janus nanopores, which opens up a new frontier for ion-based devices.

Colitis-associated intestinal microbiota regulates brain glycine and host behavior in mice

Inflammatory bowel diseases (IBD) are chronic and relapsing inflammatory disorders of the gastrointestinal tract with complex etiology and no strategies for complete cure. IBD are often complicated by mental disorders like anxiety and depression, indicating substantial shifts in the microbiota gut-brain axis. However, the mechanisms connecting IBD to mental diseases are still under debate. Here we use Muc2 knockout mouse model of chronic colitis to uncouple the effects of the intestinal microbiota on host behavior from chronic inflammation in the gut. Muc2 knockout male mice exhibit high exploratory activity, reduced anxiety-related behaviors, impaired sensorimotor gating, and altered social preference towards males and females. Microbial transfer to wild-type mice via littermate co-housing shows that colitis-associated microbiota rather than inflammation per se defines behavioral features in Muc2 colitis model. Metagenomic profiling and combination of antibiotic treatments revealed that bacterial species Akkermansia muciniphila is associated with the behavioral phenotype in mutants, and that its intestinal abundance correlates with social preference towards males. Metabolomic analysis together with pharmacological inhibition of Gly and NMDA receptors helped us to determine that brain glycine is responsible for the behavioral phenotype in Muc2 mice. Blood and brain metabolic profiles suggest that microbiota-dependent changes in choline metabolism might be involved in regulation of central glycine neurotransmission. Taken together, our data demonstrates that colitis-associated microbiota controls anxiety, sensorimotor gating and social behavior via metabolic regulation of the brain glycinergic system, providing new venues to combat neurological complications of IBD.