Selectivity Filter Research Articles

Intrinsically dynamic mechanism within selectivity filter controls ion current through K2P2.1 channel

Intrinsically dynamic mechanism within selectivity filter controls ion current through K2P2.1 channel

Cryo-EM structures of KCa2.2 channels reveal the conformational changes in the selectivity filter induced by an inhibitor

Cryo-EM structures of KCa2.2 channels reveal the conformational changes in the selectivity filter induced by an inhibitor

A gate at the selectivity filter turns an inactivated Kv channel into a non-selective hyperpolarization activated channel

A gate at the selectivity filter turns an inactivated Kv channel into a non-selective hyperpolarization activated channel

From head to tail—atomistic mechanism of long-range coupling from the cytosolic sensor domain to the selectivity filter in TREK K2P channels

From head to tail—atomistic mechanism of long-range coupling from the cytosolic sensor domain to the selectivity filter in TREK K2P channels

Dynamic interplay of the proximal C-terminus and selectivity filter reveals gating and pharmacological modulation mechanisms in TREK K2P channels

Dynamic interplay of the proximal C-terminus and selectivity filter reveals gating and pharmacological modulation mechanisms in TREK K2P channels

Influence of the selectivity filter serine and threonine residues on the stability and conductivity of human small-conductance calcium-activated potassium channels

Influence of the selectivity filter serine and threonine residues on the stability and conductivity of human small-conductance calcium-activated potassium channels

Three-Minute Enantioselective Amino Acid Analysis by Ultra-High-Performance Liquid Chromatography Drift Tube Ion Mobility-Mass Spectrometry Using a Chiral Core-Shell Tandem Column Approach.

Fast liquid chromatography (LC) amino acid enantiomer separation of 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) derivatives using a chiral core-shell particle tandem column with weak anion exchange and zwitterionic-type quinine carbamate selectors in less than 3 min was achieved. Enantiomers of all AQC-derivatized proteinogenic amino acids and some isomeric ones (24 in total plus achiral glycine) were baseline separated (Rs > 1.5 except for glutamic acid with Rs = 1.3), while peaks of distinct amino acids and structural isomers (constitutional isomers and diastereomers of leucine and threonine) of the same configuration overlapped to various degrees. For this reason, drift tube ion mobility-mass spectrometry was added (i.e., LC-IM-MS) as an additional selectivity filter without extending run time. The IM separation dimension in combination with high-resolution demultiplexing enabled confirmation of threonine isomers (threonine, allo-threonine, homoserine), while leucine, isoleucine, and allo-isoleucine have almost identical collisional cross-section (DTCCSN2) values and added no selectivity to the partial LC separation. Density functional theory (DFT) calculations show that IM separation of threonine isomers was possible due to conformational stabilization by hydrogen bond formation between the hydroxyl side chain and the urea group. Generally, the CCSN2 of protonated ions increased uniformly with addition of the AQC label, while outliers could be explained by consideration of intramolecular interactions and additional structural analysis. Preliminary validation of the enantioselective LC-IM-MS method for quantitative analysis showed compliance of accuracy and precision with common limits in bioanalytical methods, and applicability to a natural lipopeptide and a therapeutic synthetic peptide could be demonstrated.

Phase retrieval from single-shot square wave fringe based on image denoising using deep learning.

Fringe-structured light measurement technology has garnered significant attention in recent years. To enhance measurement speed while maintaining a certain level of accuracy using binary fringe, this paper proposes a phase retrieval method with single-frame binary square wave fringe. The proposed method utilizes image denoising through deep learning to extract the phase, enabling the use of a trained image denoiser as a low-pass filter, which adaptively replaces the manual selection of the appropriate band-pass filter. The results demonstrate that this method achieves higher reconstruction accuracy than the traditional single-frame algorithm while preserving more object details.

Ionic Transistors.

Biological voltage-gated ion channels, which behave as life's transistors, regulate ion transport precisely and selectively through atomic-scale selectivity filters to sustain important life activities. By this inspiration, voltage-adaptable ionic transistors that use ions as signal carriers may provide an alternative information processing unit beyond solid-state electronic devices. This review provides a comprehensive overview of the first generation of biomimetic ionic transistors, including their operating mechanisms, device architecture development, and property characterizations. Despite its infancy, significant progress has been made in the applications of ionic transistors in fields such as DNA detection, drug delivery, and ionic circuits. Challenges and prospects of full exploitation of ionic transistors for a broad spectrum of practical applications are also discussed.

Selectivity filter conductance, rectification and fluctuations of subdomains—How can this all relate to the value of Hurst exponent in the dwell-times of ion channels states?

The Hurst effect in the signals describing ion channels’ activity has been known for many years. This effect is present in the experimental recordings of single-channel currents, but not only. The sequences of dwell times of functionally different channel states also exhibit long-range correlations. We have found that the memory effect within the dwell-time series is related to the coupling between the channel’s activation gate (AG) and selectivity filter (SF), which controls the ion conduction. In this work, we analyzed both the experimental data describing the activity of potassium channels of different types (e.g., BK, mitoBK, mitoTASK-3, mitoKv1.3, TREK-2-like channels) and the series generated according to our previously proposed Hurst effect model. The obtained results suggest that the strength of the allosteric cooperation between the AG and SF determines not only the conductance of the channel – which governs how often ions in SF move or remain blocked – but also modulates the correlations present in the dwell times when sampled with a suitably high sampling rate. Moreover, we found that rectification can interfere with this process, contributing to additional changes in correlations within the channel’s sojourns in subsequent states. Similarly, the correlations may be affected by processes proceeding at longer time scales, like interactions with the channel’s auxiliary domains or lipid surroundings.

Methods and Technologies for Supporting Knowledge Sharing within Learning Communities: A Systematic Literature Review

In an era marked by swift technological advancements and an escalating emphasis on collaborative learning, understanding effective methods and technologies for sharing knowledge is imperative to optimize educational outcomes. This study delves into the varied methods and technologies applied to facilitate and support knowledge sharing within learning communities. To achieve this, a systematic literature review was conducted, systematically collecting and scrutinizing pertinent literature. Employing automated searches, title-based selection, and reputation-based filters ensured the inclusion of high-quality studies. The chosen studies underwent a meticulous evaluation, considering factors like relevance, methodological robustness, and currency. The literature review unveiled a diverse array of methods and technologies employed in learning communities to facilitate effective knowledge sharing. The outcomes of this study offer a comprehensive snapshot of the existing literature, underscoring the significance of methods and technologies in supporting knowledge sharing within learning communities. By comprehending the strengths, challenges, and potential future trajectories, educators, researchers, and policymakers can make informed decisions to enhance the efficacy of knowledge sharing within learning communities.

Optimal design of solar/wind/battery and EV fed UPQC for power quality and power flow management using enhanced most valuable player algorithm

The behavior and performance of distribution systems have been significantly impacted by the presence of solar and wind based renewable energy sources (RES) and battery energy storage systems (BESS) based electric vehicle (EV) charging stations. This work designs the Unified Power Quality Conditioner (UPQC) through optimal selection of the active filter and PID Controller (PIDC) parameters using the enhanced most valuable player algorithm (EMVPA). The prime objective is to effectively address the power quality (PQ) challenges such as voltage distortions and total harmonic distortions (THD) of a distribution system integrated with UPQC, solar, wind, BESS and EV (U-SWBEV). The study also aims to manage the power flow between the RES, grid, EV, BESS, and consumer loads by artificial neuro-fuzzy interface system (ANFIS). Besides, this integration helps to have a reliable supply of electricity, efficient utilization of generated power, and effective fulfillment of the demand. The proposed scheme results in a THD of 4.5%, 2.26%, 4.09% and 3.98% for selected four distinct case studies with power factor to almost unity with an appropriate power sharing. Therefore, the study and results indicate that the ANFIS based power flow management with optimal design of UPQC addresses the PQ challenges and achieves the appropriate and effective sharing of power.

Modelling and Power Control of Wind Turbine Driving DFIG connected to the Utility Grid

In this paper, the modelling and power transfer control of the variable speed wind energy system are presented. Firstly, a Maximum Power Point Tracking (MPPT) method is developed in order to maximize the energy generation of wind system based on doubly fed induction generator (DFIG). Then, the control of both Rotor Side Converter (RSC) and Grid Side Converter (GSC) is studied and the design of a multivariable selective filter is presented. Finally, simulation of a 850 kW doubly fed induction generator wind system was performed in the Matlab / Simulink / SimPowerSystems environment

Molecular details of ruthenium red pore block in TRPV channels.

Transient receptor potential vanilloid (TRPV) channels play a critical role in calcium homeostasis, pain sensation, immunological response, and cancer progression. TRPV channels are blocked by ruthenium red (RR), a universal pore blocker for a wide array of cation channels. Here we use cryo-electron microscopy to reveal the molecular details of RR block in TRPV2 and TRPV5, members of the two TRPV subfamilies. In TRPV2 activated by 2-aminoethoxydiphenyl borate, RR is tightly coordinated in the open selectivity filter, blocking ion flow and preventing channel inactivation. In TRPV5 activated by phosphatidylinositol 4,5-bisphosphate, RR blocks the selectivity filter and closes the lower gate through an interaction with polar residues in the pore vestibule. Together, our results provide a detailed understanding of TRPV subfamily pore block, the dynamic nature of the selectivity filter and allosteric communication between the selectivity filter and lower gate.

High-Noise Grayscale Image Denoising Using an Improved Median Filter for the Adaptive Selection of a Threshold

Grayscale image processing is a key research area in the field of computer vision and image analysis, where image quality and visualization effects may be seriously damaged by high-density salt and pepper noise. A traditional median filter for noise removal may result in poor detail reservation performance under strong noise and the judgment performance of different noise characteristics has strong dependence and rather weak robustness. In order to reduce the effects of high-density salt and pepper noise on image quality when processing high-noise grayscale images, an improved two-dimensional maximum Shannon entropy median filter (TSETMF) is proposed for the adaptive selection of a threshold to enhance the filter performance while stably and effectively retaining the details of the images. The framework of the proposed improved TSETMF algorithm is designed in detail. The noise in images is filtered by means of automatically partitioning a window size, the threshold value of which is adaptively calculated using two-dimensional maximum Shannon entropy. The theoretical model is verified and analyzed through comparative experiments using three kinds of classical grayscale images. The experimental results demonstrate that the proposed improved TSETMF algorithm exhibits better processing performance than that of the traditional filter, with a higher suppression of high-density noise and denoising stability. This stronger ability while processing high-density noise is demonstrated by a higher peak signal-to-noise ratio (PSNR) of 24.97 dB with a 95% noise density located in the classical Lena grayscale image. The better denoising stability, with a noise density from 5% to 95%, is demonstrated by the minor decline in the PSNR of approximately 10.78% relative to a PSNR of 23.10 dB located in the classical Cameraman grayscale image. Furthermore, it can be advanced to promote higher noise filtering and stability for processing high-density salt and pepper noise in grayscale images.

Implementation of the Seeded Growth Method in Fabricating 3D‐Printed Nanocomposite Contact Lenses for Selective Transmission

Gold nanoparticles (GNPs) are useful materials that may be used in a variety of applications such as colorblindness management, drug delivery, and bacteria reduction. When incorporated with optical lenses, GNPs cause an absorption dip in the transmission spectra of the lenses. Out of the aforementioned medical applications, colorblindness management is the most benefited from such spectra absorption as it can potentially block problematic wavelengths that patients suffer from and hence manage their colorblindness, where color vision deficiency (CVD), also known as colorblindness, is a congenital ocular disorder that has no current cure, and patients suffering from it rely on wearable aids that enhance their color perception by filtering out the certain wavelengths. Herein, customized gold nanocomposite contact lenses are fabricated via additive manufacturing to filter selective transmission wavelengths in the range of 540 and 560 nm. To allow selective filtering, seed‐mediated synthesis of GNPs through nine growth steps is utilized to vary the GNPs’ size and plasmonic filtering properties. Thereafter, three contact lenses are fabricated with different GNPs concentrations and particle sizes. In the results of the study, it is indicated that the fabricated lenses can block certain wavelengths selectively while acquiring properties similar to commercially available eyewear.

A phenylalanine at the extracellular side of Kir1.1 facilitates potassium permeation

ABSTRACT The Kir1.1 (ROMK) family of weak inward rectifiers controls K secretion in the renal CCT and K recycling in the renal TALH. A single point mutant of the inward rectifier, F127V-Kir1.1b was used to investigate the K transition between the selectivity filter and the outer mouth of the channel. We hypothesize that normally an aromatic Phe at the external entryway of Kir1.1b facilitates outward K secretion. We tested this by replacing F127-Kir1.1b with a small aliphatic Val. Results indicate that removal of the Phe at 127 suppresses outward currents that normally contribute to K secretion. Results with the F127V mutant could be explained by increased polyamine block and/or a decrease in the avidity of Kir1.1 for K ions near the outer mouth of the channel. The latter is supported by F127V-Kir1.1b having a lower affinity (Km = 33 mM) for K than wild-type Kir1.1b (Km = 7 mM) during external K elevation. Conversely, chelation of K with 18-Crown-6 ether reduced K conductance faster in F127V (half-time = 6s) than in wt-Kir1.1b (half-time = 120s), implying that F127V is less hospitable to external K. In other experiments, positive membrane potentials gated the F127V mutant channel closed at physiological levels of external Ca, possibly by electrostatically depleting K adjacent to the membrane, suggesting that the Phe residue is critical for outward K secretion at physiological Ca. We speculate that the avidity of wt-Kir1.1b for external K could result from a cation-Pi interaction between K and the aromatic F127.

Water inside the Selectivity Filter of a K+ Ion Channel: Structural Heterogeneity, Picosecond Dynamics, and Hydrogen Bonding.

Water inside biological ion channels regulates the key properties of these proteins, such as selectivity, ion conductance, and gating. In this article, we measure the picosecond spectral diffusion of amide I vibrations of an isotope-labeled KcsA potassium channel using two-dimensional infrared (2D IR) spectroscopy. By combining waiting time (100-2000 fs) 2D IR measurements of the KcsA channel including 13C18O isotope-labeled Val76 and Gly77 residues with molecular dynamics simulations, we elucidated the site-specific dynamics of water and K+ ions inside the selectivity filter of KcsA. We observe inhomogeneous 2D line shapes with extremely slow spectral diffusion. Our simulations quantitatively reproduce the experiments and show that water is the only component with any appreciable dynamics, whereas K+ ions and the protein are essentially static on a picosecond timescale. By analyzing simulated and experimental vibrational frequencies, we find that water in the selectivity filter can be oriented to form hydrogen bonds with adjacent or nonadjacent carbonyl groups with the reorientation timescales being three times slower and comparable to that of water molecules in liquid, respectively. Water molecules can reside in the cavity sufficiently far from carbonyls and behave essentially like "free" gas-phase-like water with fast reorientation times. Remarkably, no interconversion between these configurations was observed on a picosecond timescale. These dynamics are in stark contrast with liquid water, which remains highly dynamic even in the presence of ions at high concentrations.

Asymmetric contribution of a selectivity filter gate in triggering inactivation of CaV1.3 channels.

Voltage-dependent and Ca2+-dependent inactivation (VDI and CDI, respectively) of CaV channels are two biologically consequential feedback mechanisms that fine-tune Ca2+ entry into neurons and cardiomyocytes. Although known to be initiated by distinct molecular events, how these processes obstruct conduction through the channel pore remains poorly defined. Here, focusing on ultrahighly conserved tryptophan residues in the interdomain interfaces near the selectivity filter of CaV1.3, we demonstrate a critical role for asymmetric conformational changes in mediating VDI and CDI. Specifically, mutagenesis of the domain III-IV interface, but not others, enhanced VDI. Molecular dynamics simulations demonstrate that mutations in distinct selectivity filter interfaces differentially impact conformational flexibility. Furthermore, mutations in distinct domains preferentially disrupt CDI mediated by the N- versus C-lobes of CaM, thus uncovering a scheme of structural bifurcation of CaM signaling. These findings highlight the fundamental importance of the asymmetric arrangement of the pseudotetrameric CaV pore domain for feedback inhibition.

A Novel Frequency and Positive Sequence Detector for Utility Applications and Power Quality Analysis.

Based on multi-dimensional representation and vector calculus definitions, this paper proposes two novel and quite simple algorithms for utility applications and power quality analysis. The first one is a synchronizing procedure, based on a digital PLL (Phase Locked Loop). Its design and dynamic behavior are analyzed for single and three-phase systems. The second one is a positive sequence detector, which uses the proposed PLL to ensure that the positive sequence components can be calculated even under distorted waveform conditions or frequency variations. Since it is not based on Fortescue’s classical decomposition and no special input filtering are needed, its dynamic response may be as fast as one fundamental cycle. In order to validate the proposed models, simulations are shown and experimental results were obtained by means of a DSP-based system and a prototype of Power Quality Monitor. Furthermore, the PLL algorithm was implemented in a selective active filter to confirm the expectations in a closed-loop application.