Electrostatic Switch Research Articles

Differential Behavior of Conformational Dynamics in Active and Inactive States of Cannabinoid Receptor 1.

Cannabinoid receptor 1 (CB1) is a G protein-coupled receptor that regulates critical physiological processes including pain, appetite, and cognition. Understanding the conformational dynamics of CB1 associated with transitions between inactive and active signaling states is imperative for developing targeted modulators. Using microsecond-level all-atom molecular dynamics simulations, we identified marked differences in the conformational ensembles of inactive and active CB1 in apo. The inactive state exhibited substantially increased structural heterogeneity and plasticity compared to the more rigidified active state in the absence of stabilizing ligands. Transmembrane helices TM3 and TM7 were identified as distinguishing factors modulating the state-dependent dynamics. TM7 displayed amplified fluctuations selectively in the inactive state simulations attributed to disruption of conserved electrostatic contacts anchoring it to surrounding helices in the active state. Additionally, we identified significant reorganizations in key salt bridge and hydrogen bond networks contributing to the CB1 activation/inactivation. For instance, D213-Y224 hydrogen bond and D184-K192 salt bridge showed marked rearrangements between the states. Collectively, these findings reveal the specialized role of TM7 in directing state-dependent CB1 dynamics through electrostatic switch mechanisms. By elucidating the intrinsic enhanced flexibility of inactive CB1, this study provides valuable insights into the conformational landscape enabling functional transitions. Our perspective advances understanding of CB1 activation mechanisms and offers opportunities for structure-based drug discovery targeting the state-specific conformational dynamics of this receptor.

Bioinformatic Study of Possible Acute Regulation of Acid Secretion in the Stomach

The gastric H+,K+-ATPase is an integral membrane protein which derives energy from the hydrolysis of ATP to transport H+ ions from the parietal cells of the gastric mucosa into the stomach in exchange for K+ ions. It is responsible for the acidic environment of the stomach, which is essential for digestion. Acid secretion is regulated by the recruitment of the H+,K+-ATPase from intracellular stores into the plasma membrane on the ingestion of food. The similar amino acid sequences of the lysine-rich N-termini α-subunits of the H+,K+- and Na+,K+-ATPases, suggests similar acute regulation mechanisms, specifically, an electrostatic switch mechanism involving an interaction of the N-terminal tail with the surface of the surrounding membrane and a modulation of the interaction via regulatory phosphorylation by protein kinases. From a consideration of sequence alignment of the H+,K+-ATPase and an analysis of its coevolution with protein kinase C and kinases of the Src family, the evidence points towards a phosphorylation of tyrosine-7 of the N-terminus by either Lck or Yes in all vertebrates except cartilaginous fish. The results obtained will guide and focus future experimental research.

High-reliability circular-contact RF MEMS switches in silicon hermetic package

This paper presents a highly reliable direct-contact electrostatic RF MEMS switch. To enhance the reliability, the contact structure of the switch is designed into a circular shape, and the bottom contact surface is covered by a hard metal Pt layer. In addition, a high resistance silicon cap is used for hermetic packaging of the switch structure. By theoretical calculation and FEM simulation, parameters of the switch structure as well as its packaging are co-designed and optimized. During fabrication, the circular contact structure is formed by a three-step etching process; and after fabrication, the silicon hermetic packaging is realized by epoxy bonding and multi-step dicing process. The measured insertion loss and isolation of the switch with package is −0.41@20 GHz, and −20.9@20 GHz. Due to the optimized design, the RF performance of the switch remains almost unchanged before and after packaging. The measured driving voltage is 50–60 V, and the ON/OFF switching time is 25 μs/5 μs. The lifetime test shows that the switch passes the 2.6 billion times hot switching at the working power of 25 dBm. Finally, the switch also shows good performances in package leak rate test.

The electrostatic basis of diacylglycerol pyrophosphate-protein interaction.

Phosphatidic acid (PA) is an anionic lipid with a simple phosphate headgroup that recruits multiple proteins for its diverse functional roles in all eukaryotes. Its charge, shape and Electrostatic Hydrogen bond switch mechanism forms the basis of its interaction with membrane components. PA is phosphorylated to Diacylglycerol pyrophosphate (DGPP) in many signaling events in plants, yeast, and some parasites. DGPP has a pyrophosphate headgroup with similar ionization properties to PA, except that its charge at any given physiological pH is higher. The synthesis of DGPP in the signaling cascade potentially alters membrane dynamics and properties due to the differences in the physicochemical parameters between the two lipids. Thus, DGPP is expected to differ from PA in its interaction with membrane components. However, the overall effect on the biophysical properties of DGPP's interactions with proteins and ions are unexplored. In this study, we investigated the effect of the interactions of DGPP with model peptides KALP23 and WALP23 by 31P MAS NMR spectroscopy. In addition, we also analyzed the effect of DGPP with two positively charged lipids, dioleoyl trimethylammonium propane (DOTAP) and ethyl -phosphatidylcholine (EtPC) as well as with Magnesium and Calcium cations. Results from this study highlight a unique model for DGPP-protein interactions and has important implications in how DGPP interacts with membrane components in the signaling pathway.

Involvement of alpha-subunit N-termini in the mechanism and regulation of the Na+,K+- and H+,K+-ATPases.

The cytoplasmic lysine-rich N-termini of the Na+,K+- and H+,K+-ATPases have been designated as R domains because of their possible role in regulation of ion pumping activity. Prior to the publication of any crystal structures of either protein, it was suggested, based on mutagenesis studies, that regulation of the Na+,K+-ATPase could involve the formation and breakage of a salt bridge between Lys30 of the N-terminus and Glu233 in the first M2-M3 cytoplasmic loop of the alpha subunit. In structural studies of the Na+,K+-ATPase, the N-terminus has never been able to be resolved, probably because it is intrinsically disordered. Nevertheless, after theoretically predicting the N-terminus conformation, and adding it to the structure, the distance between residues Lys30 and Glu233 makes it doubtful that a direct long-lived interaction between them is involved in pump regulation. As an alternative hypothesis, we propose that regulation could occur via an interaction of the positively charged lysine residues of the N-terminus with negatively charged lipid headgroups (notably phosphatidylserine) on the cytoplasmic surface of the surrounding membrane, and that such an interaction could potentially be regulated by an electrostatic switch mechanism, whereby serine and tyrosine residues of the N-terminus are phosphorylated by protein kinases. Phosphorylation of these residues would decrease the positive charge of the N-terminus, allowing its release from the membrane. Experimental and theoretical data will be presented which support this hypothesis.

Bioinformatic Analysis of Na+, K+-ATPase Regulation through Phosphorylation of the Alpha-Subunit N-Terminus.

The Na+, K+-ATPase is an integral membrane protein which uses the energy of ATP hydrolysis to pump Na+ and K+ ions across the plasma membrane of all animal cells. It plays crucial roles in numerous physiological processes, such as cell volume regulation, nutrient reabsorption in the kidneys, nerve impulse transmission, and muscle contraction. Recent data suggest that it is regulated via an electrostatic switch mechanism involving the interaction of its lysine-rich N-terminus with the cytoplasmic surface of its surrounding lipid membrane, which can be modulated through the regulatory phosphorylation of the conserved serine and tyrosine residues on the protein's N-terminal tail. Prior data indicate that the kinases responsible for phosphorylation belong to the protein kinase C (PKC) and Src kinase families. To provide indications of which particular enzyme of these families might be responsible, we analysed them for evidence of coevolution via the mirror tree method, utilising coevolution as a marker for a functional interaction. The results obtained showed that the most likely kinase isoforms to interact with the Na+, K+-ATPase were the θ and η isoforms of PKC and the Src kinase itself. These theoretical results will guide the direction of future experimental studies.

Event-driven MEMS vibration sensor: Integration of triboelectric nanogenerator and low-frequency switch

Triboelectric-nano-generator (TENG) is able to produce a very small current and a large voltage compared to piezoelectric or electromagnetic generators. The large voltages from the TENGs are suitable for operating MEMS devices without external AC or DC generators. Producing micro-sized TENG using MEMS fabrication process enables integration of them with MEMS sensors and actuators. This combination is useful because the required voltage for driving MEMS is obtained from the motion of the event that is being measured. In this work, an event-driven vibration sensor is introduced which actuates a switch as the frequency or amplitude of the vibration exceeds a desired threshold. Using CMOS micromachining, a 1.5 mm × 1.5 mm TENG in contact-separation (CS) mode is fabricated to convert ambient vibrations to a voltage generated between a conductive aluminum layer and a dielectric Polyimide layer. The large generated voltage between the electrodes can operate a low-frequency electrostatic MEMS switch. Two events are able to produce the resonant dynamic pull-in needed to close the switch. Event one is when the input amplitude exceeds the dynamic pull-in threshold which is called acceleration sensitive mode. Event two is when the frequency of the vibration exceeds a specified threshold. An electromechanical model for the MEMS switch part of the vibration sensor is also presented. Results show that MEMS-TENG is able to supply the MEMS switch in the frequency sensitive and acceleration sensitive modes with a good signal-to-noise-ratio, sensitivity, and accuracy.

Manipulation of tissue factor-mediated basal PAR-2 signalling on macrophages determines sensitivity for IFNγ responsiveness and significantly modifies the phenotype of murine DTH.

BackgroundTissue factor (TF) generates proteases that can signal through PAR-1 and PAR-2. We have previously demonstrated PAR-1 signalling primes innate myeloid cells to be exquisitely sensitive to interferon-gamma (IFNγ). In this work we explored how TF mediated PAR-2 signalling modulated responsiveness to IFNγ and investigated the interplay between PAR-1/-2 signalling on macrophages.MethodologyWe characterised how TF through PAR-2 influenced IFNγ sensitivity in vitro using PCR and flow cytometry. and how it influenced oxazolone-induced delayed type hypersensitivity (DTH) responses in vivo. We investigated how basal signalling through PAR-2 influenced PAR-1 signalling using a combination of TF-inhibitors and PAR-1 &-2 agonists and antagonists. Finally, we investigated whether this system could be targeted therapeutically using 3-mercaptopropionyl-F-Cha-Cha-RKPNDK (3-MP), which has actions on both PAR-1 and -2.ResultsTF delivered a basal signal through PAR-2 that upregulated SOCS3 expression and blunted M1 polarisation after IFNγ stimulation, opposing the priming achieved by signalling through PAR-1. PAR-1 and -2 agonists or antagonists could be used in combination to modify this basal signal in vitro and in vivo. 3-MP, by virtue of its PAR-2 agonist properties was superior to agents with only PAR-1 antagonist properties at reducing M1 polarisation induced by IFNγ and suppressing DTH. Tethering a myristoyl electrostatic switch almost completely abolished the DTH response.ConclusionsTF-mediated signalling through PARs-1 and -2 act in a homeostatic way to determine how myeloid cells respond to IFNγ. 3-MP, an agent that simultaneously inhibits PAR-1 whilst delivering a PAR-2 signal, can almost completely abolish immune responses dependent on M1 polarisation, particularly if potency is enhanced by targeting to cell membranes; this has potential therapeutic potential in multiple diseases.

Electrostatic Forces Mediate the Specificity of RHO GTPase-GDI Interactions.

Three decades of research have documented the spatiotemporal dynamics of RHO family GTPase membrane extraction regulated by guanine nucleotide dissociation inhibitors (GDIs), but the interplay of the kinetic mechanism and structural specificity of these interactions is as yet unresolved. To address this, we reconstituted the GDI-controlled spatial segregation of geranylgeranylated RHO protein RAC1 in vitro. Various biochemical and biophysical measurements provided unprecedented mechanistic details for GDI function with respect to RHO protein dynamics. We determined that membrane extraction of RHO GTPases by GDI occurs via a 3-step mechanism: (1) GDI non-specifically associates with the switch regions of the RHO GTPases; (2) an electrostatic switch determines the interaction specificity between the C-terminal polybasic region of RHO GTPases and two distinct negatively-charged clusters of GDI1; (3) a non-specific displacement of geranylgeranyl moiety from the membrane sequesters it into a hydrophobic cleft, effectively shielding it from the aqueous milieu. This study substantially extends the model for the mechanism of GDI-regulated RHO GTPase extraction from the membrane, and could have implications for clinical studies and drug development.

Electrostatic switch of magnetic anisotropy in the composite with iron-metal granule and barium-titanate matrix

This work investigates electrostatic switch of magnetic anisotropy in the composite with iron-metal granule and barium-titanate matrix theoretically. As the spontaneous polarization is switched downward or upward in barium-titanate matrix, the parallel or perpendicular magnetizing is preferred in iron-metal granule respectively. This demagnetizing anisotropy originates from the long-range electrostatic interaction in matrix body, which induces the inharmonic magnetic moment on granule surface. The effects of position bias and composite size are delicately studied. The cross-section map displays distorted electric polarization in barium-titanate matrix, and demagnetizing energy gradient in iron-metal granule. This work predicts the electrostatic switch of magnetic anisotropy in metal/oxide composite, which would develop the integrated device and functional material.

Multi-scale ensemble properties of the Escherichia coli RNA degradosome.

In organisms from all domains of life, multi-enzyme assemblies play central roles in defining transcript lifetimes and facilitating RNA-mediated regulation of gene expression. An assembly dedicated to such roles, known as the RNA degradosome, is found amongst bacteria from highly diverse lineages. About a fifth of the assembly mass of the degradosome of Escherichia coli and related species is predicted to be intrinsically disordered – a property that has been sustained for over a billion years of bacterial molecular history and stands in marked contrast to the high degree of sequence variation of that same region. Here, we characterize the conformational dynamics of the degradosome using a hybrid structural biology approach that combines solution scattering with ad hoc ensemble modelling, cryo-electron microscopy, and other biophysical methods. The E. coli degradosome can form punctate bodies in vivo that may facilitate its functional activities, and based on our results, we propose an electrostatic switch model to account for the propensity of the degradosome to undergo programmable puncta formation.

Analytical modelling, design optimisation and numerical simulation of a variable width cantilever beam MEMS switch

ABSTRACT Pull-in potential of electrostatic actuation ohmic cantilever beam type RF MEMS switch is lowered by reducing stiffness constant of its cantilever beam. However, this design objective is highly interlinked to major criteria like its mechanical, RF performance parameters, materials used and fabrication constraints. The purpose of this study is to address the design methodology of such interdisciplinary complex phenomenon to obtain global optimum solution. A variable width cantilever beam design is proposed to lower its pull-in potential. The design optimisation methodology adopted in this study uses analytical model of stiffness constant, major interlinked criteria based on cantilever beam profile and geometric dimensions of the switch. This methodology is further identified as a multivariable constraint optimisation problem to be solved using evolutionary optimisation algorithm for various geometric dimensions of the switch. 3-D modelling, simulation of the optimised device for pull-in potential, mechanical and RF performance parameters is carried out using CAD tools. The results obtained from simulation and analytical models are in agreement. The proposed optimised design opens a new avenue in RF MEMS switch design as it satisfies additional essential performance parameters compared to the results of previous published designs concluding significance of design optimisation methodology adopted in this work.

Role of Electrostatic Hotspots in the Selectivity of Complement Control Proteins Toward Human and Bovine Complement Inhibition.

Poxviruses are dangerous pathogens, which can cause fatal infection in unvaccinated individuals. The causative agent of smallpox in humans, variola virus, is closely related to the bovine vaccinia virus, yet the molecular basis of their selectivity is currently incompletely understood. Here, we examine the role of the electrostatics in the selectivity of the smallpox protein SPICE and vaccinia protein VCP toward the human and bovine complement protein C3b, a key component of the complement immune response. Electrostatic calculations, in-silico alanine-scan and electrostatic hotspot analysis, as introduced by Kieslich and Morikis (PLoS Comput. Biol. 2012), are used to assess the electrostatic complementarity and to identify sites resistant to local perturbation where the electrostatic potential is likely to be evolutionary conserved. The calculations suggest that the bovine C3b is electrostatically prone to selectively bind its VCP ligand. On the other hand, the human isoform of C3b exhibits a lower electrostatic complementarity toward its SPICE ligand. Yet, the human C3b displays a highly preserved electrostatic core, which suggests that this isoform could be less selective in binding different ligands like SPICE and the human Factor H. This is supported by experimental cofactor activity assays revealing that the human C3b is prone to bind both SPICE and Factor H, which exhibit diverse electrostatic properties. Additional investigations considering mutants of SPICE and VCP that revert their selectivity reveal an “electrostatic switch” into the central modules of the ligands, supporting the critical role of the electrostatics in the selectivity. Taken together, these evidences provide insights into the selectivity mechanism of the complement regulator proteins encoded by the variola and vaccinia viruses to circumvent the complement immunity and exert their pathogenic action. These fundamental aspects are valuable for the development of novel vaccines and therapeutic strategies.

Electrostatic switch of magnetic core-shell in 0-3 type LSMO/PZT composite film**Project supported by the Science Foundation of North University of China (Grant No. 2017026), the Applied Basic Research Foundation of Shanxi Province, China (Grant No. 201801D221143), the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi, China (Grant No. 2019L0535), and the National Natural Science Foundation of China

By dispersing La1 – xSrxMnO3 (LSMO) granule into PbZrxTi1 – xO3 (PZT) matrix, the 0-3 type LSMO/PZT composite film is synthesized through chemical solution method. The asymmetry of the top and bottom electrodes introduces novel electrostatic screening on LSMO/PZT interface. As electric polarization is switched between upward and downward orientations, the evolution of exchange bias, diode transport, and magnetoresistance is observed. The result implies the electrostatic switch of magnetic core-shell in the present film. In detail, as the spontaneous polarization is upward or downward in the PZT matrix, the ferromagnetic/antiferromagnetic or ferromagnetic/ferromagnetic core-shell structure is formed in LSMO granule, respectively. This work would develop a novel device for spintronics and metamaterial.

Dielectric Transfer Process for 3D Printed Metal Microsystems

This paper deals with the fabrication and unconstrained dielectric transfer of 3D printed metal components demonstrated using an electrostatic micro switch. The use of micro laser sintering (MLS) to print micro-electro-mechanical systems (MEMS) enables a new MEMS fabrication capability able to bypass conventional high-cost fabrication processes for low-volume prototypes. To demonstrate the above mentioned technology, this paper presents the fabrication of a one-piece 3D printed metal component consisting of electrodes and sacrificial metal frames from bronze powder. A method to transfer this component onto the target substrate, removal of sacrificial metal frame for electrical isolation, electrostatic device actuation, and characterization of the dielectric isolation are presented in detail. [2020-0162]

Regression of Atherosclerosis in ApoE-/- Mice Via Modulation of Monocyte Recruitment and Phenotype, Induced by Weekly Dosing of a Novel "Cytotopic" Anti-Thrombin Without Prolonged Anticoagulation.

BackgroundAnticoagulants induce atherosclerosis regression in animal models but exploiting this clinically is limited by bleeding events. Here we test a novel thrombin inhibitor, PTL060, comprising hirulog covalently linked to a synthetic myristoyl electrostatic switch to tether to cell membranes.Methods and ResultsApoE−/− mice were fed chow or high‐fat diets, before transplantation of congenic aortic segments or injection of PTL060, parental hirulog, control saline, or labeled CD11b positive cells. Aortic transplants from transgenic mice expressing anticoagulants on endothelium did not develop atherosclerosis. A single intravenous injection of PTL060, but not hirulog inhibited atheroma development by >50% compared with controls when assessed 4 weeks later. Mice had prolonged bleeding times for only one seventh of the time that PTL060 was biologically active. Repeated weekly injections of PTL060 but not hirulog caused regression of atheroma. We dissected 2 contributory mechanisms. First, the majority of CCR2+ (C‐C chemokine receptor type 2+) monocytes recruited into plaques expressed CCR7 (C‐C chemokine receptor type 7), ABCA1 (ATP‐binding cassette transporter – 1), and interleukin‐10 in PTL060 mice, a phenotype seen in <20% of CCR2+ recruits in controls. Second, after several doses, there was a significant reduction in monocyte recruits, the majority of which were CCR2‐negative with a similar regression‐associated phenotype. Regression equivalent to that induced by intravenous PTL060 was induced by adoptive transfer of CD11b+ cells pre‐coated with PTL060.ConclusionsCovalent linkage of a myristoyl electrostatic switch onto hirulog in PTL060 uncouples the pharmacodynamic effects on hemostasis and atherosclerosis, such that plaque regression, mediated predominantly via effects on monocytes, is accompanied by only transient anticoagulation.

Reliability of RF MEMS switches at cryogenic (liquid He) temperatures

This paper reports on the reliability of RF MEMS switches operating in a cryogenic (<6 K) environment while monitoring the repeatability of their contact resistance (Rc) over time. Series DC-contact switches were actuated with a bipolar waveform then checked for stiction every 100 thousand contacts, and after every million cycles Rc was measured 100 times. Device lifetimes were limited to under 10 million contacts. The dominant failure mechanism is believed to be charging of the substrate underneath the electrostatic MEMS switch leading to permanent hold down of the device.

Multifunctional Self-Powered Switch toward Delay-Characteristic Sensors.

With the development of the internet of things (IoT) and 5th generation communication technology, construction of smart cities is making a great progress. However, the IoT system needs millions of sensing nodes; therefore, it is rather challenging to power various sensors. Here, we design an electrostatic force-based switch (EFS) that can work as either an optical or an electrical switch. The EFS provides a method to directly detect or control high-voltage electrical systems with delay characteristics. Advantages of the EFS include self-contained delay characteristics, ease of fabrication, low cost, and high stability, especially when used in combination with the triboelectric nanogenerator (TENG) to realize self-powered sensors. Based on the self-powered sensor, a mechanical motion-sensing system is built with high sensitivity and active response to the mechanical trigger. This study proposes a multifunctional self-powered switch, which realizes a high-voltage delay control system and can also combine with the TENG to expand the application of self-powered smart sensing systems.

Charge Neutralization Tunes Dynamic Arrest of Initially Disordered Reflectin Proteins

The intrinsically disordered reflectin proteins fill the reflective Bragg lamellae of iridescent cells in squid. In vivo, phosphorylation of the cationic reflectins leads to protein condensation and hierarchical assembly, driving osmotic dehydration of the lamellae and causing enhancement of intensity and tuning of the color of reflected light. In vitro, purified monomeric reflectin protein can be driven to cyclably and tunably assemble by pH‐neutralization or addition of salt, forming spheres of low polydispersity and reproducible size. Analysis of reflectin assembly by dynamic light scattering, x‐ray scattering, and transmission electron microscopy shows that the calibration between charge‐neutralization and assembly size is enabled by the rapid dynamic arrest of particle growth, as controlled by an electrostatic switch spatially distributed across the reflectin chain. Confocal microscopy of fluorescently labeled micron‐sized reflectin assemblies shows that they exhibit internal dynamics that rapidly slow following assembly, suggesting that assembly occurs through a transient liquid‐liquid phase separation that undergoes gelation to form stable protein‐dense condensates. Electron paramagnetic resonance (EPR) analysis shows the initially disordered reflectin monomers form ordered secondary structure that may be critical in the arrest of growth and stabilization of particles. These results provide new insights into the assembly of these unique intrinsically disordered proteins and the biophotonic systems they form, and suggest pathways for the creation of novel tunable biomaterials.Support or Funding InformationThis research was supported by the U.S. Department of Energy, U.S. Army Research Office, and Institute for Collaborative Biotechnologies.

The C2A domain of synaptotagmin is an essential component of the calcium sensor for synaptic transmission.

The synaptic vesicle protein, synaptotagmin, is the principle Ca2+ sensor for synaptic transmission. Ca2+ influx into active nerve terminals is translated into neurotransmitter release by Ca2+ binding to synaptotagmin's tandem C2 domains, triggering the fast, synchronous fusion of multiple synaptic vesicles. Two hydrophobic residues, shown to mediate Ca2+-dependent membrane insertion of these C2 domains, are required for this process. Previous research suggested that one of its tandem C2 domains (C2B) is critical for fusion, while the other domain (C2A) plays only a facilitatory role. However, the function of the two hydrophobic residues in C2A have not been adequately tested in vivo. Here we show that these two hydrophobic residues are absolutely required for synaptotagmin to trigger vesicle fusion. Using in vivo electrophysiological recording at the Drosophila larval neuromuscular junction, we found that mutation of these two key C2A hydrophobic residues almost completely abolished neurotransmitter release. Significantly, mutation of both hydrophobic residues resulted in more severe deficits than those seen in synaptotagmin null mutants. Thus, we report the most severe phenotype of a C2A mutation to date, demonstrating that the C2A domain is absolutely essential for synaptotagmin's function as the electrostatic switch.