Electrochemical Gradient Research Articles

A Well‐Coupled Supramolecular System Accelerates Photophosphorylation

AbstractSupramolecular assembly allows multiple chemical/bio‐components integrated as one system for cascade biochemical reactions. Herein the graphitic carbon nitrides (g‐C3N4) as photocatalyst trapped in a dipeptide hydrogel covering adenosine triphosphate (ATP) synthase accelerates the photophosphorylation through ATP synthesis. Self‐assembled N‐fluorenylmethoxycarbonyl diphenylalanine (Fmoc‐FF) as nanofibrils to allow g‐C3N4 nanosheets are embedded as a complex Fmoc‐FF/g‐C3N4 hydrogel. Fmoc‐FF gel exhibits good electronic coupling with g‐C3N4, which enables a photo‐induced proton generation. The transmembrane proton gradient can be established by ATP synthase‐lipid reconstituted on the surface of the Fmoc‐FF/g‐C3N4 hydrogel to enhance the ATP synthesis. It indicates that the Fmoc‐FF/g‐C3N4/ATP synthase‐lipid film can possess a longer‐term ATP production capability and allow repeated immersion for sustained ATP production. Such a hydrogel‐supported ATP synthesis platform is achieved by a procedure at a larger scale.

The chloroplast ATP synthase redox domain in Chlamydomonas reinhardtii eludes activity regulation for heterotrophic dark metabolism

To maintain CO2 fixation in the Calvin-Benson-Bassham cycle, multistep regulation of the chloroplast ATP synthase (CF1Fo) is crucial to balance the ATP output of photosynthesis with protection of the apparatus. A well-studied mechanism is thiol modulation; a light/dark regulation through reversible cleavage of a disulfide in the CF1Fo γ-subunit. The disulfide hampers ATP synthesis and hydrolysis reactions in dark-adapted CF1Fo from land plants by increasing the required transmembrane electrochemical proton gradient ([Formula: see text]). Here, we show in Chlamydomonas reinhardtii that algal CF1Fo is differently regulated in vivo. A specific hairpin structure in the γ-subunit redox domain disconnects activity regulation from disulfide formation in the dark. Electrochromic shift measurements suggested that the hairpin kept wild-type CF1Fo active, whereas the enzyme was switched off in algal mutant cells expressing a plant-like hairpin structure. The hairpin segment swap resulted in an elevated [Formula: see text] threshold to activate plant-like CF1Fo, increased by ~1.4 photosystem (PS) I charge separations. The resulting dark-equilibrated [Formula: see text] dropped in the mutants by ~2.7 PSI charge separation equivalents. Photobioreactor experiments showed no phenotypes in autotrophic aerated mutant cultures. In contrast, chlorophyll fluorescence measurements under heterotrophic dark conditions point to an altered dark metabolism in cells with the plant-like CF1Fo as the result of bioenergetic deviations from wild-type. Our results suggest that the lifestyle of C. reinhardtii requires a specific CF1Fo dark regulation that partakes in metabolic coupling between the chloroplast and acetate-fueled mitochondria.

Unique structural attributes of the PSI-NDH supercomplex in Physcomitrium patens.

Cyclic electron transport around photosystem I (PSI) is essential for the protection of the photosynthetic apparatus in plants under diverse light conditions. This process is primarily mediated by Proton Gradient Regulation 5 protein/Proton Gradient Regulation 5-like photosynthetic phenotype 1 protein (PGR5/PGRL1) and NADH dehydrogenase-like complex (NDH). In angiosperms, NDH interacts with two PSI complexes through distinct monomeric antennae, LHCA5 and LHCA6, which is crucial for its higher stability under variable light conditions. This interaction represents an advanced evolutionary stage and offers limited insight into the origin of the PSI-NDH supercomplex in evolutionarily older organisms. In contrast, the moss Physcomitrium patens (Pp), which retains the lhca5 gene but lacks the lhca6, offers a glimpse into an earlier evolutionary stage of the PSI-NDH supercomplex. Here we present structural evidence of the Pp PSI-NDH supercomplex formation by single particle electron microscopy, demonstrating the unique ability of Pp to bind a single PSI in two different configurations. One configuration closely resembles the angiosperm model, whereas the other exhibits a novel PSI orientation, rotated clockwise. This structural flexibility in Pp is presumably enabled by the variable incorporation of LHCA5 within PSI and is indicative of an early evolutionary adaptation that allowed for greater diversity at the PSI-NDH interface. Our findings suggest that this variability was reduced as the structural complexity of the NDH complex increased in vascular plants, primarily angiosperms. This study not only clarifies the evolutionary development of PSI-NDH supercomplexes but also highlights the dynamic nature of the adaptive mechanisms of plant photosynthesis.

MTORC1 and 2 adrenergic regulation and function in brown adipose tissue.

Brown adipose tissue (BAT) thermogenesis results from the uncoupling of mitochondrial inner membrane proton gradient mediated by the uncoupling protein 1 (UCP-1), which is activated by lipolysis-derived fatty acids. Norepinephrine (NE) secreted by sympathetic innervation not only activates BAT lipolysis and UCP-1, but uniquely in brown adipocytes, promotes "futile" metabolic cycles and enhances BAT thermogenic capacity by increasing UCP-1 content, mitochondrial biogenesis and brown adipocyte hyperplasia. NE exerts these actions by triggering signaling in the canonical G protein coupled b adrenergic receptors, cAMP and protein kinase A (PKA) pathway which, in brown adipocyte, is under a complex and intricated crosstalk with important growth-promoting signaling pathways such as those of mechanistic target of rapamycin (mTOR) complexes 1 (mTORC1) and 2 (mTORC2). This article reviews evidence suggesting that mTOR complexes are modulated by and participate in the thermogenic, metabolic, and growth-promoting effects elicited by NE in BAT and discusses current gaps and future directions in this field of research.

Synthetic syntrophy for adenine nucleotide cross-feeding between metabolically active nanoreactors.

Living systems depend on continuous energy input for growth, replication and information processing. Cells use membrane proteins as nanomachines to convert light or chemical energy of nutrients into other forms of energy, such as ion gradients or adenosine triphosphate (ATP). However, engineering sustained fuel supply and metabolic energy conversion in synthetic systems is challenging. Here, inspired by endosymbionts that rely on the host cell for their nutrients, we introduce the concept of cross-feeding to exchange ATP and ADP between lipid-based compartments hundreds of nanometres in size. One population of vesicles enzymatically produces ATP in the mM concentration range and exports it. A second population of vesicles takes up this ATP to fuel internal reactions. The produced ADP feeds back to the first vesicles, and ATP-dependent reactions can be fuelled sustainably for up to at least 24 h. The vesicles are a platform technology to fuel ATP-dependent processes in a sustained fashion, with potential applications in synthetic cells and nanoreactors. Fundamentally, the vesicles enable studying non-equilibrium processes in an energy-controlled environment and promote the development and understanding of constructing life-like metabolic systems on the nanoscale.

Loss of the Na+/K+ cation pump CATP-1 suppresses nekl-associated molting defects.

The conserved Caenorhabditis elegans protein kinases NEKL-2 and NEKL-3 regulate membrane trafficking and are required for larval molting. Through a forward genetic screen we identified a mutation in catp-1 as a suppressor of molting defects in synthetically lethal nekl-2; nekl-3 double mutants. catp-1 encodes a membrane-associated P4-type ATPase involved in Na+-K+ exchange. A previous study found that wild-type worms exposed to the nicotinic agonist dimethylphenylpiperazinium (DMPP) exhibited larval arrest and molting-associated defects, which were suppressed by inhibition of catp-1. By testing a spectrum catp-1 alleles, we found that resistance to DMPP toxicity and the suppression of nekl defects did not strongly correlate, suggesting key differences in the mechanism of catp-1-mediated suppression. Through whole genome sequencing of additional nekl-2; nekl-3 suppressor strains, we identified two additional coding-altering mutations in catp-1. However, neither mutation, when introduced into nekl-2; nekl-3 mutants using CRISPR, was sufficient to elicit robust suppression of molting defects, suggesting the involvement of other loci. Endogenously tagged CATP-1 was primarily expressed in epidermal cells within punctate structures located near the apical plasma membrane, consistent with a role in regulating cellular processes within the epidermis. Based on previous studies, we tested the hypothesis that catp-1 inhibition induces entry into the pre-dauer L2d stage, potentially accounting for the ability of catp-1 mutants to suppress nekl molting defects. However, we found no evidence that loss of catp-1 leads to entry into L2d. As such, loss of catp-1 may suppress nekl-associated and DMPP-induced defects by altering electrochemical gradients within membrane-bound compartments.

Accordion-Structured Hydrogel Battery Capable of Maintaining Ion Gradients for Extended Periods.

Inspired by the electric eel, biomimetic, biocompatible energy storage, and power generation technologies show promise for applications in portable and wearable electronic devices by mimicking the electric cell tandem structure of the electric eel and utilizing ionic gradients between hydrogel compartments to generate electricity. Previously, inspired by the unique morphology of the torpedo fish, an artificial flexible power source that can output a large current was introduced. This power source uses a hydrogel-infused paper hybrid to create, accordionize, and reconfigure arbitrary-sized gel films in series and parallel, and the power output of the flexible battery was significantly enhanced. However, maintaining the ionic gradient of hydrogel batteries during storage remains a challenge. Here, by borrowing the isolation properties of the accordion structure, we propose a unique paper accordion structure design to fabricate an Accordion-Structured Hydrogel Battery (ASHB). Pretreatment of hydrogel-injected paper strips improved storage stability and maintained the ionic gradient of hydrogel cells in the nonworking state, so that the cell's gradient retention time after the assembly is completed is increased by at least 30 h compared to stacking, and its per-cell operating voltage is still able to reach. The design also makes the assembly and use of flexible batteries more modular and holistic. In the future, it may be possible to power the cells with ions generated by the human body or the metabolites of living organisms, leading to the development of more efficient, sustainable, and eco-friendly power solutions.

Impact of laterally mobile surface charge on diffusiophoresis of hydrophobic rigid colloids

The diffusiophoresis of charged hydrophobic nanoparticles (NPs) governed by an imposed ionic concentration gradient is analysed. The main objective is to elucidate the impact of the laterally mobile adsorbed surface ions at the interface on the propulsion of the hydrophobic NPs in diffusiophoresis. In addition, the dielectric polarization due to the difference in dielectric constant between the NPs and the suspension medium is also considered. The mobile surface ions create a friction as well as an electric force at the hydrophobic surface, which leads to a modification of the slip velocity condition and the slip length. We obtain an exact numerical solution of the governing electrokinetic equations in their full form by adopting a control volume formulation. The numerical model is supplemented by analytical solutions derived based on the Debye–Hückel linearization. We find that the lateral mobility of the surface ions obstruct the coions to diffuse from the higher concentration side to the lower concentration side, which results in a repulsive force to the particle leading to the occurrence of a negative mobility. Based on the numerical results and analytical solutions, we have shown that for a fully mobile surface charge, the diffusiophoresis of a hydrophobic NP is identical to the diffusiophoresis of a liquid droplet whose viscosity is related to the slip length of the hydrophobic particle. We establish that the dielectric polarization enhances the velocity of a hydrophobic particle, which has potential applications in the practical context.

Closed-Loop and Precipitation-Free CO2 Capture Process Enabled by Electrochemical pH Gradient.

Carbon dioxide (CO2) capture is a crucial negative-emission technology for the mitigation of climate change and global warming. The urgent need of combating climate change motivates the research and development of economical, effective and environmentally benign processes for CO2 capture. Herein, we design and report a flow cell for the CO2 capture from air or flue gas in a precipitate-free and closed-loop manner. No ion-exchange membrane is used in the electrolyser. The water electrolysis produces acidic solution near the anode and alkaline solution near the cathode, while generating valuable hydrogen and oxygen byproducts. The dilute CO2 in air or flue gas is captured by the alkaline solution, which is then mixed with the acidic solution to release the concentrated CO2. The process operates in a cyclic manner as driven by the water electrolysis and the mechanical pumping. No precipitation of calcium carbonate is involved for fixing CO2, which may simplify the separation process and minimizing the materials loss. The simple process enabled by electrochemical pH gradient shows promise for efficient CO2 capture on both small and large scales.

An effector protein of Fusarium graminearum targets chloroplasts and suppresses cyclic photosynthetic electron flow.

Chloroplasts are important photosynthetic organelles that regulate plant immunity, growth, and development. However, the role of fungal secretory proteins in linking the photosystem to the plant immune system remains largely unknown. Our systematic characterization of 17 chloroplast-targeting secreted proteins of Fusarium graminearum indicated that Fg03600 is an important virulence factor. Fg03600 translocation into plant cells and accumulation in chloroplasts depended on its chloroplast transit peptide. Fg03600 interacted with the wheat (Triticum aestivum L.) proton gradient regulation 5-like protein 1 (TaPGRL1), a part of the cyclic photosynthetic electron transport chain, and promoted TaPGRL1 homo-dimerization. Interestingly, TaPGRL1 also interacted with ferredoxin (TaFd), a chloroplast ferredoxin protein that transfers cyclic electrons to TaPGRL1. TaFd competed with Fg03600 for binding to the same region of TaPGRL1. Fg03600 expression in plants decreased cyclic electron flow (CEF) but increased the production of chloroplast-derived reactive oxygen species (ROS). Stably silenced TaPGRL1 impaired resistance to Fusarium head blight (FHB) and disrupted CEF. Overall, Fg03600 acts as a chloroplast-targeting effector to suppress plant CEF and increase photosynthesis-derived ROS for FHB development at the necrotrophic stage by promoting homo-dimeric TaPGRL1 or competing with TaFd for TaPGRL1 binding.

Reduction in mitochondrial ATP synthesis mimics the effect of low glucose in depolarizing neurons from the subpostremal nucleus of the solitary tract of rats.

Neurons of the subpostremal nucleus of the solitary tract (NTS) respond to changes in extracellular glucose with alterations in membrane potential with both depolarization and hyperpolarization. From 5 mM glucose, a rapid shift to 0.5 mM glucose produces a membrane depolarization by an unknown mechanism in most neurons. However, the mechanism involved in this response needs to be known. Here, we investigated if the low glucose-induced depolarization could be mimicked by reducing ATP synthesis and possible mediators of this effect. We showed that applying the mitochondrial uncoupler CCCP (1 µM) reproduced the effects of low glucose depolarizing the membrane, generating an inward current, and decreasing membrane resistance. On the other hand, activation of AMPK did not alter these parameters. To test if low glucose and CCCP could depolarize the membrane by affecting the ionic gradient, we inhibited the electrogenic Na/K pump with 10 µM of ouabain. We observed a similar membrane depolarization but not a decrease in membrane resistance. We conclude that perfusion of neurons of the subpostremal NTS with a low glucose solution depolarizes the membrane by probably reducing intracellular ATP, but not by activating AMPK or decreasing the ionic gradient across the membrane.

Finding the E-channel proton loading sites by calculating the ensemble of protonation microstates

The aerobic electron transfer chain builds a proton gradient by proton coupled electron transfer reactions through a series of proteins. Complex I is the first enzyme in the sequence. Here transfer of two electrons from NADH to quinone yields four protons pumped from the membrane N- (negative, higher pH) side to the P- (positive, lower) side. Protons move through three linear antiporter paths, with a few amino acids and waters providing the route; and through the E-channel, a complex of competing paths, with clusters of interconnected protonatable residues.Proton loading sites (PLS) transiently bind protons as they are transported from N- to P-compartments. PLS can be individual residues or extended clusters of residues. The program MCCE uses Monte Carlos sampling to analyze the E-channel proton binding in equilibrium with individual Molecular Dynamics snapshots from trajectories of Thermus thermuphillus Complex I in the apo, quinone and quinol bound states. At pH 7, the five E-channel subunits (Nqo4, Nqo7, Nqo8, Nqo10, and Nqo11) take >25,000 protonation microstates, each with different residues protonated. The microstate explosion is tamed by analyzing interconnected clusters of residues along the proton transfer paths. A proton is bound and released from a cluster of five coupled residues on the protein N-side and to six coupled residues in the protein center. Loaded microstates bind protons to sites closer to the P-side in the forward pumping direction. MCCE microstate analysis identifies strongly coupled proton binding amongst individual residues in the two PLS clusters.

Nernst Equilibrium, Rectification, and Saturation: Insights into Ion Channel Behavior

The dissipation of electrochemical gradients through ion channels plays a central role in biology. Herein we use voltage responsive kinetic models of ion channels to explore how electrical and chemical potentials differentially influence ion transport properties. These models demonstrate how electrically driven flux is greater than the Nernstian equivalent chemically driven flux, yet still perfectly cancels when the two gradients oppose each other. We find that the location and relative stability of ion binding sites dictates rectification properties by shifting the location of the most voltage sensitive transitions. However, these rectification properties invert when bulk concentrations increase relative to the binding site stabilities, moving the rate limiting steps from uptake into a relatively empty channel to release from an ion-blocked full channel. Additionally, the origin of channel saturation is shown to depend on the free energy of uptake relative to bulk concentrations. Collectively these insights provide framework for interpreting and predicting how channel properties manifest in electrochemical transport behavior.

The Pivotal Function of SLC16A1 and SLC16A1-AS1 in Cancer Progress: Molecular Pathogenesis and Prognosis.

More than 300 membranes make up the SLC family of transporters, utilizing an ion gradient or electrochemical potential difference to move their substrates across biological membranes. The SLC16 gene family contains fourteen members. Proton-linked transportation of monocarboxylates can be promoted by the transporters MCT1, which the SLC16A1 gene family encodes. Glycolysis is constitutively up-regulated in cancer cells, and the amount of lactate produced as a result is correlated with prognosis. Further speaking, SLC16A1 plays an essential role in controlling the growth and spread of tumors, according to mounting evidence. Additionally, LncRNAs are the collective term for all genes that produce RNA transcripts longer than 200 nucleotides but do not convert into proteins. It has steadily developed into a hub for research, offering an innovative approach to tumor study as technology related to molecular biology advances. The growing study has uncovered SLC16A1-AS1, an RNA that acts as an antisense to SLC16A1, which is erroneously expressed in various types of cancers. Therefore, we compiled the most recent information on the physiological functions and underlying processes of SLC16A1 and the LncRNA SLC16A1-AS1 during tumor development to explore their impact on cancer treatment and prognosis. We compiled the most recent information on the physiological functions and underlying processes of SLC16A1 and the LncRNA SLC16A1-AS1 during tumor development to explore their impact on cancer treatment and prognosis. Relevant studies were retrieved and collected through the PubMed system. After determining SLC16A1 and SLC16A1-AS1 as the research object, we found a close relationship between SLC16A1 and tumorigenesis as well as the influencing factors through the analysis of the research articles. SLC16A1 regulates lactate chemotaxis while uncovering SLC16A1- AS1 as an antisense RNA acting through multiple pathways; they affect the metabolism of tumor cells and have an impact on the prognosis of patients with various cancers.

Myricetin and myricitrin indirectly and directly increases uncoupling protein-1 mRNA expression in C3H10T1/2 beige adipocytes

In thermogenic brown and beige adipocytes, the proton gradient formed by energy derived from nutrients such as lipids and carbohydrates is consumed by uncoupling protein-1 (UCP-1), resulting in thermogenesis without ATP production in the mitochondria. Accordingly, increased UCP-1 expression represents a crucial aspect of dietary management for individuals with overweight and obesity. Myricetin and its glycoside, myricitrin, are food-derived flavonoids that possess various beneficial effects. This is the first study to examine the effects of myricetin and myricitrin on the inflammation-inhibited expression of Ucp-1 using a modified cell-based assay with conditioned medium (CM). The CM derived from lipopolysaccharide (LPS)-activated RAW264.7 macrophages was observed to inhibit the Ucp-1 expression induced by adrenergic stimulation in 10T1/2 adipocytes. Conversely, the CM derived from activated macrophages treated with myricetin or myricitrin reversed this inhibition of Ucp-1 expression. Subsequently, the direct effects of both the compounds on basal and adrenaline-induced expression of Ucp-1 were investigated. In contrast to a previous report, myricetin and myricitrin did not increase the basal Ucp-1 mRNA expression in 10T1/2 adipocytes when treated during the differentiation-promoting period. However, we have found for the first time that both compounds enhanced the adrenergic sensitivity of 10T1/2 adipocytes when treated during the differentiation-inducing period. These results indicate that myricetin and myricitrin have indirect effects on inflammation-induced suppression and direct effects on adrenergic sensitivity, suggesting a novel mechanism that both compounds increase Ucp-1 expression in vivo by both indirect and direct effects, rather than by affecting basal expression.

Evolution of a biological thermocouple by adaptation of cytochrome c oxidase in a subterrestrial metazoan, Halicephalobus mephisto

In this study, we report a biological temperature-sensing electrical regulator in the cytochrome c oxidase of the Devil Worm, Halicephalobus mephisto. This extremophile metazoan was isolated 1.3 km underground in a South African goldmine, where it adapted to heat and potentially to hypoxia, making its mitochondrial sequence a likely target of adaptational change. We obtained the complete mitochondrial genome sequence of this organism and show through dN/dS analysis evidence of positive selection in H. mephisto cytochrome c oxidase subunits. Seventeen of these positively selected amino acid substitutions were located in proximity to the H- and K-pathway proton channels of the complex. Surprisingly, the H. mephisto cytochrome c oxidase completely shuts down at low temperatures (20 °C), leading to a 4.8-fold reduction in the transmembrane proton gradient (ΔΨm) compared to optimal temperature (37 °C). Direct measurement of oxygen consumption found a corresponding 4.6-fold drop at 20 °C compared to 37 °C. Correspondingly, the lifecycle of H. mephisto takes four times longer at low temperature than at higher. This elegant evolutionary adaptation creates a finely-tuned mitochondrial temperature sensor, allowing this ectothermic organism to maximize its reproductive success across varying environmental temperatures.

Osmotic energy conversion in serpentinite-hosted deep-sea hydrothermal vents

Cells harvest energy from ionic gradients by selective ion transport across membranes, and the same principle is recently being used for osmotic power generation from salinity gradients at ocean-river interfaces. Common to these ionic gradient conversions is that they require intricate nanoscale structures. Here, we show that natural submarine serpentinite-hosted hydrothermal vent (HV) precipitates are capable of converting ionic gradients into electrochemical energy by selective transport of Na+, K+, H+, and Cl-. Layered hydroxide nanocrystals are aligned radially outwards from the HV fluid channels, constituting confined nanopores that span millimeters in the HV wall. The nanopores change the surface charge depending on adsorbed ions, allowing the mineral to function as a cation- and anion-selective ion transport membrane. Our findings indicate that chemical disequilibria originating from flow and concentration gradients in geologic environments generate confined nanospaces which enable the spontaneous establishment of osmotic energy conversion.

A Well-Coupled Supramolecular System Accelerates Photophosphorylation.

Supramolecular assembly allows multiple chemical/bio-components integrated as one system for cascade biochemical reactions. Herein the graphitic carbon nitrides (g-C3N4) as photocatalyst trapped in a dipeptide hydrogel covering adenosine triphosphate (ATP) synthase accelerates the photophosphorylation through ATP synthesis. Self-assembled N-fluorenylmethoxycarbonyl diphenylalanine (Fmoc-FF) as nanofibrils to allow g-C3N4 nanosheets are embedded as a complex Fmoc-FF/g-C3N4 hydrogel. Fmoc-FF gel exhibits good electronic coupling with g-C3N4, which enables a photo-induced proton generation. The transmembrane proton gradient can be established by ATP synthase-lipid reconstituted on the surface of the Fmoc-FF/g-C3N4 hydrogel to enhance the ATP synthesis. It indicates that the Fmoc-FF/g-C3N4/ATP synthase-lipid film can possess a longer-term ATP production capability and allow repeated immersion for sustained ATP production. Such a hydrogel-supported ATP synthesis platform is achieved by a procedure at a larger scale.

Versatile Ultrahigh‐Output Bilayer Hydrogel for Electricity Generation and Passive Cooling

AbstractThe gradient concentration in nature has garnered significant attention as a promising source for energy harvesting. Researchers have explored various methods to harness electricity from gradient‐concentration‐induced flows, including evaporation‐driven nanogenerators and humidity‐gradient‐based power generators. However, their low current and power density are the main obstacles toward practical applications. Herein, a Bilayer Hydrogel Electricity Generator (BHEG) is presented to enable efficient energy harvesting through the synergy between ion gradient concentration and galvanic effects. A BHEG unit employing identical materials for both electrodes demonstrates an open‐circuit voltage of 0.7 V and a short‐circuit current of 4.34 mA—surpassing the currently reported average by over 73 times—and achieves a maximum power density of 72.2 mW m−2. Moreover, another BHEG unit using Zn─C electrode materials exhibit an open‐circuit voltage of 1.86 V and a short‐circuit current of 92 mA. Furthermore, the versatility of the BHEG extends beyond power generation, effectively providing passive thermal management for electronics, resulting in a maximum temperature reduction of ≈20 °C. Consequently, the study contributes insights into the design and fabrication of efficient hydrogel‐based power generators, providing a promising avenue for leveraging natural‐flow‐induced energy for various applications.

Alternating access of a bacterial homolog of neurotransmitter: sodium symporters determined from AlphaFold2 ensembles and DEER spectroscopy

Neurotransmitter:sodium symporters (NSSs) play critical roles in neural signaling by regulating neurotransmitter uptake into cells powered by sodium electrochemical gradients. Bacterial NSSs orthologs, including MhsT from Bacillus halodurans, have emerged as model systems to understand the structural motifs of alternating access in NSSs and the extent of conservation of these motifs across the family. Here, we apply a computational/experimental methodology to illuminate the conformational landscape of MhsT alternating access. Capitalizing on our recently developed method, Sampling Protein Ensembles and Conformational Heterogeneity with AlphaFold2 (SPEACH_AF), we derived clusters of MhsT models spanning the transition from inward-facing to outward-facing conformations. Systematic application of double electron-electron resonance (DEER) spectroscopy revealed ligand-dependent movements of multiple structural motifs that underpin MhsT's conformational cycle. Remarkably, comparative DEER analysis in detergent micelles and lipid nanodiscs highlights the profound effect of the environment on the energetics of conformational changes. Through experimentally derived selection of collective variables, we present a model of ion and substrate-powered transport by MhsT consistent with the conformational cycle derived from DEER. Our findings not only advance the understanding of MhsT's function but also uncover motifs of conformational dynamics conserved within the broader context of the NSS family and within the LeuT-fold class of transporters. Importantly, our methodological blueprint introduces an approach that can be applied across a diverse spectrum of transporters to describe their conformational landscapes.