Gate Modulation Research Articles

452 Booting Up the Brain: Intracranial Electroencephalography Reveals Cognitive Network Dynamics During Anesthesia Emergence

INTRODUCTION: The dynamic interplay between several large-scale brain networks is thought to underlie human consciousness. The default mode network (DMN) governs internal thought during rest, the central executive network (CEN) drives goal-directed problem solving, and the salience network (SN) detects and integrates new stimuli during the transition between resting and cognitively active states. While scalp electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) have elucidated much about these networks in steady states, intracranial EEG (iEEG) dynamics during state transitions remain largely unclear. METHODS: Seven patients with medically refractory epilepsy underwent robot-assisted stereotactic placement of depth electrodes for epileptic focus localization. Recordings from 422 total iEEG contacts representing 49 distinct cognitive network nodes were obtained during anesthesia emergence. Local-field dynamics and Observer’s Assessment of Alertness/Sedation (OAAS) scale state were analyzed in 20s clips for complexity, functional connectivity (FC), and graph communicability metrics. RESULTS: Signal complexity as represented by mean multiscale sample entropy (MSE) of SN and DMN nodes increases significantly during emergence from anesthesia (P < 0.05), driven by a shift from low- to mid-frequency power in key nodes. Intermediate consciousness states demonstrated higher mean MSE and participation coefficient, representing early integrative network behavior, before reaching an optimal balance of segregation and integration at wakefulness. During emergence, between-network FC increased most strongly between SN and CEN nodes. Communicability of SN nodes increased during emergence, driven predominately by increasing communicability of right anterior insula. CONCLUSIONS: Intracranial electroencephalographic recording of brain activity during anesthesia emergence demonstrates a complex but quantifiable interplay of default mode, central executive, and salience network hubs. There may be a greater than previously understood role of right anterior insula in gating transitions in consciousness states.

Gate modulation drive and modeling of IGBT in MMC converters

The energy surplus caused by the alternating current (AC) system’s failure results in a severe overvoltage problem in Bai hetan-Jiangsu ±800 kV hybrid cascade direct current (DC) project. However, the insulated gate bipolar transistor’s (IGBT) off-state voltage is the crucial reason for the insufficient voltage capacity of modular multilevel converter (MMC). Therefore, analysis and suppression of the off-state overvoltage are of vital significance. The off-state model of IGBT in an MMC converter is established, and the process of IGBT’s turning off is analyzed. Then, based on the characteristics of IGBT’s off-state and traditional resistance switching strategy, the gate modulation drive strategy is proposed, and the equivalent topology of the MMC submodule with the strategy is established. Finally, MMC submodule models with gate modulation drive and resistance switching strategy, respectively, are built in simulation software, and two groups of data are compared under multiple groups of the control cycle and reference current slope given. The simulation results show that the gate modulation drive supresses the off-state overvoltage on IGBT better than the resistance switching strategy. Moreover, the shorter the control cycle and the less reference current slope, the better the overvoltage suppression.

Endothelial KCa channels: Novel targets to reduce atherosclerosis-driven vascular dysfunction.

Elevated levels of cholesterol in the blood can induce endothelial dysfunction, a condition characterized by impaired nitric oxide production and decreased vasodilatory capacity. Endothelial dysfunction can promote vascular disease, such as atherosclerosis, where macrophages accumulate in the vascular intima and fatty plaques form that impair normal blood flow in conduit arteries. Current pharmacological strategies to treat atherosclerosis mostly focus on lipid lowering to prevent high levels of plasma cholesterol that induce endothelial dysfunction and atherosclerosis. While this approach is effective for most patients with atherosclerosis, for some, lipid lowering is not enough to reduce their cardiovascular risk factors associated with atherosclerosis (e.g., hypertension, cardiac dysfunction, stroke, etc.). For such patients, additional strategies targeted at reducing endothelial dysfunction may be beneficial. One novel strategy to restore endothelial function and mitigate atherosclerosis risk is to enhance the activity of Ca2+-activated K+ (KCa) channels in the endothelium with positive gating modulator drugs. Here, we review the mechanism of action of these small molecules and discuss their ability to improve endothelial function. We then explore how this strategy could mitigate endothelial dysfunction in the context of atherosclerosis by examining how KCa modulators can improve cardiovascular function in other settings, such as aging and type 2 diabetes. Finally, we consider questions that will need to be addressed to determine whether KCa channel activation could be used as a long-term add-on to lipid lowering to augment atherosclerosis treatment, particularly in patients where lipid-lowering is not adequate to improve their cardiovascular health.

Global Multi-Attention UResNeXt for Semantic Segmentation of High-Resolution Remote Sensing Images

Semantic segmentation has played an essential role in remote sensing image interpretation for decades. Although there has been tremendous success in such segmentation with the development of deep learning in the field, several limitations still exist in the current encoder–decoder models. First, the potential interdependencies of the context contained in each layer of the encoder–decoder architecture are not well utilized. Second, multi-scale features are insufficiently used, because the upper-layer and lower-layer features are not directly connected in the decoder part. In order to solve those limitations, a global attention gate (GAG) module is proposed to fully utilize the interdependencies of the context and multi-scale features, and then a global multi-attention UResNeXt (GMAUResNeXt) module is presented for the semantic segmentation of remote sensing images. GMAUResNeXt uses GAG in each layer of the decoder part to generate the global attention gate (for utilizing the context features) and connects each global attention gate with the uppermost layer in the decoder part by using the Hadamard product (for utilizing the multi-scale features). Both qualitative and quantitative experimental results demonstrate that use of GAG in each layer lets the model focus on a certain pattern, which can help improve the effectiveness of semantic segmentation of remote sensing images. Compared with state-of-the-art methods, GMAUResNeXt not only outperforms MDCNN by 0.68% on the Potsdam dataset with respect to the overall accuracy but is also the MANet by 3.19% on the GaoFen image dataset. GMAUResNeXt achieves better performance and more accurate segmentation results than the state-of-the-art models.

Mutation of valine 53 at the interface between extracellular and transmembrane domains of the β2 principal subunit affects the GABAA receptor gating

GABAA receptors (gamma-aminobutyric acid type A receptors) are pentameric ligand-gated ion channels mediating inhibition in adult mammalian brains. Their static structure has been intensely studied in the past years but the underlying molecular activatory mechanisms remain obscure. The interface between extracellular and transmembrane domains has been recognized as a key player in the receptor gating. However, the role of the valine 53 in the β1-β2 loop of the principal subunit (β2) remains controversial showing differences compared to homologous residues in some cys-loop counterparts such as nAChR. To address the role of the β2V53 residue in the α1β2γ2L receptor gating, we performed high resolution macroscopic and single-channel recordings. To explore underlying molecular mechanisms a variety of substituting amino acids were investigated: Glutamate and Lysine (different electric charge), Alanine (aliphatic, larger than Valine) and Histidine (same residue as in homologous α1H55). We report that mutation of the β2V53 residue results in alterations of nearly all gating transitions including opening/closing, preactivation and desensitization. A dramatic gating impairment was observed for glutamate substitution (β2V53E) but β2V53K mutation had a weak effect. The impact of histidine substitution was also small while β2V53A markedly affected the receptor but to a smaller extent than β2V53E. Considering available structures in desensitized and bicuculline blocked shut states we propose that strongly detrimental effect of β2V53E mutation on receptor activation results from electrostatic interaction between the glutamate and β2K274 on the loop M2-M3 which stabilizes the receptor in the shut state. We conclude that β2V53 is strongly involved in mechanisms underlying the receptor gating.

Open-Circuit Switch Fault Diagnosis and Accommodation of a Three-Level Interleaved Buck Converter for Electrolyzer Applications

This article proposes a novel open-circuit switch fault diagnosis method (FDM) for a three-level interleaved buck converter (TLIBC) in a hydrogen production system based on the water electrolysis process. The control algorithm is suitably modified to ensure the same hydrogen production despite the fault. The TLIBC enables the interfacing of the power source (i.e., low-carbon energy sources) and electrolyzer while driving the hydrogen production of the system in terms of current or voltage. On one hand, the TLIBC can guarantee a continuity of operation in case of power switch failures because of its interleaved architecture. On the other hand, the appearance of a power switch failure may lead to a loss of performance. Therefore, it is crucial to accurately locate the failure in the TLIBC and implement a fault-tolerant control strategy for performance purposes. The proposed FDM relies on the comparison of the shape of the input current and the pulse width modulation (PWM) gate signal of each power switch. Finally, an experimental test bench of the hydrogen production system is designed and realized to evaluate the performance of the developed FDM and fault-tolerant control strategy for TLIBC during post-fault operation. It is implemented with a real-time control based on a MicroLabBox dSPACE (dSPACE, Paderborn, Germany) platform combined with a TI C2000 microcontroller. The obtained simulation and experimental results demonstrate that the proposed FDM can detect open-circuit switch failures in one switching period and reconfigure the control law accordingly to ensure the same current is delivered before the failure.

Inkjet-Printed MoS2 Nanoplates on Flexible Substrates for High-Performance Field Effect Transistors and Gas Sensing Applications

Owing to the simplicity, scalability, and cost-efficiency, solution-processable two-dimensional (2D) semiconductors have attracted great interest in electronic applications, especially as the channel material for field-effect transistors (FETs). Inkjet printing is a lithography-free technique to achieve drop-on-demand patterning of solution-processable 2D ink. However, thus far, inkjet-printed 2D FETs exhibit limited performance due to the coffee-ring effect and consequent discontinuity of the printed 2D material films. Here, we report high-performance and flexible inkjet-printed MoS2 FETs with high mobilities and high on/off ratios and their gas sensing applications. By preparing high-quality MoS2 ink comprised of MoS2 nanoplates using electrochemical exfoliation and then applying a binary solvent comprised of 2-butanol and isopropanol, the obtained ink was printed to form a continuous and relatively uniform MoS2 film, and high-performance printed MoS2 FETs were demonstrated, with mobilities of 11 cm2 V–1 s–1 and on/off ratios of 106. Furthermore, low-voltage gate modulation was achieved by applying an ion gel gate, and robust electrical performance under tensile strain was observed for the ion gel-gated MoS2 FETs printed on flexible substrates. As the printed MoS2 film is abundant in edge sites and sulfur vacancies, we further demonstrated our MoS2 FETs as high-performance gas sensors with a limit of detection of 10 ppb for NO2 and 0.5 ppm for NH3, together with a fast recovery rate.

In silico analysis of the dynamic regulation of cardiac electrophysiology by Kv 11.1 ion-channel trafficking.

Cardiac electrophysiology is regulated by continuous trafficking and internalization of ion channels occurring over minutes to hours. Kv 11.1 (also known as hERG) underlies the rapidly activating delayed-rectifier K+ current (IKr ), which plays a major role in cardiac ventricular repolarization. Experimental characterization of the distinct temporal effects of genetic and acquired modulators on channel trafficking and gating is challenging. Computer models are instrumental in elucidating these effects, but no currently available model incorporates ion-channel trafficking. Here, we present a novel computational model that reproduces the experimentally observed production, forward trafficking, internalization, recycling and degradation of Kv 11.1 channels, as well as their modulation by temperature, pentamidine, dofetilide and extracellular K+ . The acute effects of these modulators on channel gating were also incorporated and integrated with the trafficking model in the O'Hara-Rudy human ventricular cardiomyocyte model. Supraphysiological dofetilide concentrations substantially increased Kv 11.1 membrane levels while also producing a significant channel block. However, clinically relevant concentrations did not affect trafficking. Similarly, severe hypokalaemia reduced Kv 11.1 membrane levels based on long-term culture data, but had limited effect based on short-term data. By contrast, clinically relevant elevations in temperature acutely increased IKr due to faster kinetics, while after 24h, IKr was decreased due to reduced Kv 11.1 membrane levels. The opposite was true for lower temperatures. Taken together, our model reveals a complex temporal regulation of cardiac electrophysiology by temperature, hypokalaemia, and dofetilide through competing effects on channel gating and trafficking, and provides a framework for future studies assessing the role of impaired trafficking in cardiac arrhythmias. KEY POINTS: Kv 11.1 channels underlying the rapidly activating delayed-rectifier K+ current are important for ventricular repolarization and are continuously shuttled from the cytoplasm to the plasma membrane and back over minutes to hours. Kv 11.1 gating and trafficking are modulated by temperature, drugs and extracellular K+ concentration but experimental characterization of their combined effects is challenging. Computer models may facilitate these analyses, but no currently available model incorporates ion-channel trafficking. We introduce a new two-state ion-channel trafficking model able to reproduce a wide range of experimental data, along with the effects of modulators of Kv 11.1 channel functioning and trafficking. The model reveals complex dynamic regulation of ventricular repolarization by temperature, extracellular K+ concentration and dofetilide through opposing acute (millisecond) effects on Kv 11.1 gating and long-term (hours) modulation of Kv 11.1 trafficking. This in silico trafficking framework provides a tool to investigate the roles of acute and long-term processes on arrhythmia promotion and maintenance.

Dual Functional Conjugated Acetylenic Polymers: High-Efficacy Modulation for Organic Photoelectrochemical Transistors and Structural Evolution for Bioelectronic Detection.

Conjugated acetylenic polymers (CAPs) have emerged as a unique class of metal-free semiconductors with tunable electrical and optical properties yet their full potential remains largely unexplored. Organic bioelectronics is envisioned to create more opportunities for innovative biomedical applications. Herein, we report a poly(1,4-diethynylbenzene) (pDEB)/NiO gated enhancement-mode poly(ethylene dioxythiophene)-poly(styrene sulfonate) organic photoelectrochemical transistor (OPECT) and its structural evolution toward bioelectronic detection. pDEB was synthesized via copper-mediated Glaser polycondensation of DEB monomers on the NiO/FTO substrate, and the as-synthesized pDEB/NiO/FTO can efficiently modulate the enhancement-mode device with a high current gain. Linking with a sandwich immunoassay, the labeled alkaline phosphatase can catalyze sodium thiophosphate to generate H2S, which will react with the diacetylene group in pDEB through the Michael addition reaction, resulting in an altered molecular structure and thus the transistor response. Exemplified by HIgG as the model target, the developed biosensor achieves highly sensitive detection with a linear range of 70 fg mL-1-10 ng mL-1 and a low detection limit of 28.5 fg mL-1. This work features the dual functional CAP-gated OPECT, providing not only a novel gating module but also a structurally new rationale for bioelectronic detection.

Fuzzy neighbourhood neural network for high-resolution remote sensing image segmentation

ABSTRACT Remote sensing image segmentation plays an important role in many industrial-grade image processing applications. However, the problem of uncertainty caused by intraclass heterogeneity and interclass blurring is prevalent in high-resolution remote sensing images. Moreover, the complexity of information in high-resolution remote sensing images leads to a large amount of background information around objects. To solve this problem, a new fuzzy convolutional neural network is proposed in this paper. This network resolves the ambiguity and uncertainty of feature information by introducing a fuzzy neighbourhood module in the deep learning network structure. In addition, it adds a multi-attention gating module to highlight small object features and separate them from the complex background information to achieve fine segmentation of high-resolution remote sensing images. Experimental results on three different segmentation datasets suggest that the proposed method has higher segmentation accuracy and better performance than other deep learning networks, especially for complicated shadow information. Code will be provided in (https://github.com/tingtingqu/code).

Structural modeling of peptide toxin-ion channel interactions using RosettaDock.

Voltage-gated ion channels play essential physiological roles in action potential generation and propagation. Peptidic toxins from animal venoms target ion channels and provide useful scaffolds for the rational design of novel channel modulators with enhanced potency and subtype selectivity. Despite recent progress in obtaining experimental structures of peptide toxin-ion channel complexes, structural determination of peptide toxins bound to ion channels in physiologically important states remains challenging. Here we describe an application of RosettaDock approach to the structural modeling of peptide toxins interactions with ion channels. We tested this approach on 10 structures of peptide toxin-ion channel complexes and demonstrated that it can sample near-native structures in all tested cases. Our approach will be useful for improving the understanding of the molecular mechanism of natural peptide toxin modulation of ion channel gating and for the structural modeling of novel peptide-based ion channel modulators.

Cortical and thalamic modulation of auditory gating in the posterior parietal cortex of awake mice.

Auditory gating (AG) is an adaptive mechanism for filtering out redundant acoustic stimuli to protect the brain against information overload. AG deficits have been found in many mental illnesses, including schizophrenia (SZ). However, the neural correlates of AG remain poorly understood. Here, we found that the posterior parietal cortex (PPC) shows an intermediate level of AG in auditory thalamocortical circuits, with a laminar profile in which the strongest AG is in the granular layer. Furthermore, AG of the PPC was decreased and increased by optogenetic inactivation of the medial dorsal thalamic nucleus (MD) and auditory cortex (AC), respectively. Optogenetically activating the axons from the MD and AC drove neural activities in the PPC without an obvious AG. These results indicated that AG in the PPC is determined by the integrated signal streams from the MD and AC in a bottom-up manner. We also found that a mouse model of SZ (postnatal administration of noncompetitive N-methyl-d-aspartate receptor antagonist) presented an AG deficit in the PPC, which may be inherited from the dysfunction of MD. Together, our findings reveal a neural circuit underlying the generation of AG in the PPC and its involvement in the AG deficit of SZ.

Potentiation of neuromuscular transmission by a small molecule calcium channel gating modifier improves motor function in a severe spinal muscular atrophy mouse model.

Spinal muscular atrophy (SMA) is a monogenic disease that clinically manifests as severe muscle weakness owing to neurotransmission defects and motoneuron degeneration. Individuals affected by SMA experience neuromuscular weakness that impacts functional activities of daily living. We have used a mouse model of severe SMA (SMNΔ7) to test whether a calcium channel gating modifier (GV-58), alone or in combination with a potassium channel antagonist (3,4-diaminopyridine; 3,4-DAP), can improve neuromuscular function in this mouse model. Bath application of GV-58 alone or in combination with 3,4-DAP significantly restored neuromuscular transmission to control levels in both a mildly vulnerable forearm muscle and a strongly vulnerable trunk muscle in SMNΔ7 mice at postnatal days 10-12. Similarly, acute subcutaneous administration of GV-58 to postnatal day 10 SMNΔ7 mice, alone or in combination with 3,4-DAP, significantly increased a behavioral measure of muscle strength. These data suggest that GV-58 may be a promising treatment candidate that could address deficits in neuromuscular function and strength and that the addition of 3,4-DAP to GV-58 treatment could aid in restoring function in SMA.

Sarcasm Detection Base on Adaptive Incongruity Extraction Network and Incongruity Cross-Attention

Sarcasm is a linguistic phenomenon indicating a difference between literal meanings and implied intentions. It is commonly used on blogs, e-commerce platforms, and social media. Numerous NLP tasks, such as opinion mining and sentiment analysis systems, are hampered by its linguistic nature in detection. Traditional techniques concentrated mostly on textual incongruity. Recent research demonstrated that the addition of commonsense knowledge into sarcasm detection is an effective new method. However, existing techniques cannot effectively capture sentence “incongruity” information or take good advantage of external knowledge, resulting in imperfect detection performance. In this work, new modules are proposed for maximizing the utilization of the text, the commonsense knowledge, and their interplay. At first, we propose an adaptive incongruity extraction module to compute the distance between each word in the text and commonsense knowledge. Two adaptive incongruity extraction modules are applied to text and commonsense knowledge, respectively, which can obtain two adaptive incongruity attention matrixes. Therefore, each of the words in the sequence receives a new representation with enhanced incongruity semantics. Secondly, we propose the incongruity cross-attention module to extract the incongruity between the text and the corresponding commonsense knowledge, thereby allowing us to pick useful commonsense knowledge in sarcasm detection. In addition, we propose an improved gate module as a feature fusion module of text and commonsense knowledge, which determines how much information should be considered. Experimental results on publicly available datasets demonstrate the superiority of our method in achieving state-of-the-art performance on three datasets as well as enjoying improved interpretability.

Gated Region-Refine pose transformer for human pose estimation

Implementing the transformer for global fusion is a novel and efficient method for pose estimation. Although the computational complexity of modeling dense attention can be significantly reduced by pruning possible human tokens, the accuracy of pose estimation still suffers from the problem of high overlap of candidate regions and severe background noise. Moreover, the undifferentiated fusion of features from different views also leads to a sizeable effective information loss. To address these challenges, we propose a Gated Region-Refine Pose Transformer (GRRPT) for human pose estimation. The proposed GRRPT can obtain the general area of the human body from the coarse-grained tokens and then embed it into the fine-grained ones to extract more details of the joints. Experimental results on COCO demonstrate that performing the Multi-Resolution Attention mechanism learns more refined candidate regions and improves accuracy. Furthermore, we design a Fusion Gate module consisting of two gates to pixel-wise select valid information from the auxiliary views, which significantly alleviates information redundancy. Finally, we evaluate the effectiveness of our method on Human3.6M and our dataset FDU-Motion and achieve state-of-the-art performance.

Mapping the binding site of NS309, a superagonistic positive gating modulator for the calcium-activated potassium channel KCa3.1.

The intermediate-conductance Ca2+-activated K+ channel KCa3.1 is expressed in erythrocytes, vascular endothelial cells, and immune cells. KCa3.1 is involved in a wide variety of disease pathologies, suggesting that both positive and negative gating modulators would be of interest as pharmacological tools and potential drugs. NS309 is the most potent positive gating modulator for KCa3.1, with an EC50 of 75 nM, and interestingly, it is capable of increasing channel activity even at saturating calcium concentrations. However, its binding site is currently unknown. Previous X-ray crystallographic and solution-state NMR studies suggested that NS309 was binding between calmodulin's N-lobe and the C-terminal region of the calmodulin binding domain and interacting with residues M51 and R372. Unfortunately, the crystal dimer used in these studies was later found to be an artifact and disproved when the full-length crystal structure of KCa3.1 was published in 2018. This full-length structure suggested that the “real” binding site for positive gating modulators was located within the interface between calmodulin's N-lobe and the S4-S5 linker, a hypothesis we have now confirmed via site-directed mutagenesis and whole-cell patch clamp. In addition, we have also been investigating a second binding pocket between the distal end of the S4-S5 intracellular loop and the S6 transmembrane segment (a site highlighted by Schroedinger's SiteMap software). And while NS309 does not seem to be binding in this second pocket, several mutations within this pocket cause the channel to become hypersensitive to calcium, indicating that this pocket could serve as another functional binding site for positive gating channel modulators.

Conformational rearrangements in the second voltage sensor domain switch PIP2- and voltage-gating modes in two-pore channels

Two-pore channels (TPCs) are activated by phosphatidylinositol bisphosphate (PIP2) binding to domain I and/or by voltage sensing in domain II (DII). Little is known about how these two stimuli are integrated, and how each TPC subtype achieves its unique preference. Here, we show that distinct conformations of DII-S4 in the voltage-sensor domain determine the two gating modes. DII-S4 adopts an intermediate conformation, and forced stabilization in this conformation was found to result in a high PIP2-dependence in primarily voltage-dependent TPC3. In TPC2, which is PIP2-gated and nonvoltage-dependent, a stabilized intermediate conformation does not affect the PIP2-gated currents. These results indicate that the intermediate state represents the PIP2-gating mode, which is distinct from the voltage-gating mode in TPCs. We also found in TPC2 that the tricyclic antidepressant desipramine induces DII-S4-based voltage dependence and that naringenin, a flavonoid, biases the mode preference from PIP2-gating to desipramine-induced voltage gating. Taken together, our study on TPCs revealed an unprecedented mode-switching mechanism involving conformational changes in DII-S4, and its active role in integrating voltage and PIP2 stimuli.

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.

The single residue K12 governs highly sensitive voltage gating of the voltage-dependent anion channel.

The voltage-dependent anion channel (VDAC) has emerged as a key player in mitochondrial bioenergetics. As the main pathway for calcium and mitochondrial metabolites, such as ATP and ADP, to cross the mitochondrial outer membrane, VDAC is central to maintenance of mitochondrial homeostasis. It is thus unsurprising that VDAC is implicated in nearly every mitochondria-related pathology, including cardiovascular disease, cancers, and neurodegeneration. Despite decades of research, the relatively uncomplicated structure of VDAC—a β-barrel with an internal broken α-helical belt—has hampered efforts to elucidate its functional mechanisms. Unlike other β-barrel channels, such as bacterial porins and toxins, VDAC transitions to low-conducting states, or “gates”, at relatively low voltages, less than 30 mV. In VDAC's gated state, metabolite transport is suppressed and calcium transport enhanced; thus, gating is one means by which VDAC may regulate fluxes across the mitochondrial membrane. In this talk, I will describe computational and experimental efforts that have led to identification of K12 as a key residue that is responsible for the exquisite sensitivity to voltage of its gating process [JACS 2022, 144(32) 14564-14577, DOI:10.1021/jacs.2c03316]. K12 is bistable; its motions between two widely separated positions along the pore axis enhance the fluctuations of the β-barrel and augment the likelihood of gating. These results are confirmed by single channel electrophysiology of various K12 mutants, which show a dramatic reduction of the frequency of voltage-induced gating transitions. The crystallographic structure of the K12E mutant is similar to the wild type; however, 60 µs of atomistic MD simulations using the K12E mutant structure show restricted motion of the mutated residue 12, due to enhanced connectivity with neighboring residues, and diminished amplitude of barrel motions. We conclude that β-barrel fluctuations, governed particularly by residue K12, drive VDAC gating transitions.

Nicotinic acetylcholine receptor structural pharmacology and gating transitions.

Our lab focuses on using structural and functional approaches to understand signaling by ligand-gated ion channels in the nervous system. A major emphasis is on understanding nicotinic receptor pharmacology from a structural perspective. Here I will present some of our recent work using the muscle-type nicotinic receptor from the Torpedo ray as a structurally tractable reference for the human receptor at the neuromuscular junction. I will focus on how toxins from animals and plants, as well as drugs used in the clinic, act on the receptor, and how we can use this information to understand state transitions that underlie ion channel gating. These studies have revealed a new class of allosteric site at the junction of the extracellular and transmembrane domains that small molecules can leverage to modulate channel desensitization. Our findings suggest that stabilizing a desensitized-like non-conducting state, through this allosteric site, is an important alternative mechanism for antagonizing the receptor.