Membrane-Active Molecular Machines

Photo-Switchable Supramolecular Interactions Regulate K+ Transmembrane Transport and Cancer Cell Apoptosis

Natural channel proteins (NCPs) have numerous ion transport modes, but it remains a big challenge to replicate this trait by artificial ion transport systems. Herein, we present an azobenzene-incorporated single-chain random heteropolymers (RHPs)-derived biomimetic K+ channel P3, which can switch between three ion transport states ("ON," "Partially OFF," and "Totally OFF") in both liposomes and cancer cells. The conformational adjustments of P3 activated by light-modulating two groups of supramolecular interactions ((1) hydrogen bonding and π-π interactions; (2) host-guest interactions) realize these switches, resembling the protein mechanisms that govern activity. Underlying molecular mechanisms are the photoisomerization of azobenzene moieties in P3 and their complexation with β-cyclodextrin (β-CD), enabling the exploit of a "one stone (azobenzene moiety), two birds (supramolecular interactions)" strategy. Mechanistic investigations demonstrate that P3-induced substantial K+ efflux (a 50% drop within just 4 min) causes endoplasmic reticulum (ER) stress, intriguing Ca2+ sparks, enhanced reactive oxygen species (ROS), and finally severe mitochondria-dependent apoptosis. This NCP-like channel (P3) is expected to provide new opportunities for a deeper understanding of the internal mechanisms of NCPs, as well as for treating cancer and other diseases.

Artificial Ion Transporters as Potent Therapeutics for Channelopathies

Ion channels are essential for the selective transport of ions, playing a fundamental role in critical physiological processes. Dysfunctions in these channels, often arising from genetic mutations or environmental factors, give rise to a class of disorders collectively known as channelopathies. In recent years, artificial ion transporters have been developed to mimic the essential function of natural channels, offering potential therapeutic approaches for these conditions. Although significant progress has been made in improving the activity and selectivity of these synthetic transporters, their application in treating diseases associated with ion transport dysregulation remains in its infancy. This concept provides an overview of recent advancements in artificial ion transporters for treating channelopathies, while highlighting the key challenges and prospects in translating these developments into practical therapies.

Engineered Reactive Oxygen Species (ROS)-Responsive Artificial H+/Cl- Ion Channels for Targeted Cancer Treatment

Reactive oxygen species (ROS)-responsive ion channels regulate the ion flow across the membranes in response to alterations in the cellular redox state, playing a crucial role in cellular adaptation to oxidative stress. Despite their significance, replicating ROS-responsive functionality in artificial ion channels remains elusive. In this study, we introduce a novel class of artificial H+/Cl- ion channels activatable by elevated ROS levels in cancer cells. ROS-induced decaging of the phenylboronate group triggers the rapid release of the channel-forming units, leading to self-assembly of the H-bonded cascades facilitating the synergistic transport of H+ and Cl- ions, with H+/Cl- ion transport selectivity of 7.7. Upon activation, ROS-C-Cl exhibits significant apoptotic activity against human breast cancer cells, achieving an IC50 of 2.8 μM, comparable to that of paclitaxel. Exploiting the intrinsic oxidative microenvironment of cancer cells, along with the enhanced oxidative stress arising from H+/Cl- co-transport, ROS-C-Cl demonstrates exceptional selectivity in targeting cancer cells with a selectivity index of 10.2 over normal breast cells, outperforming that of paclitaxel by 19.4 folds.

Artificial Lithium Channels Built from Polymers with Intrinsic Microporosity

In sharp contrast to numerous artificial potassium channels developed over the past decade, the study of artificial lithium-transporting channels has remained limited. We demonstrate here the use of an interesting class of polymers with intrinsic microporosity (PIM) for constructing artificial lithium channels. These PIM-derived lithium channels show exceptionally efficient (γLi +>40 pS) and highly selective transport of Li+ ions, with selectivity factors of>10 against both Na+ and K+. By simply adjusting the initial reaction temperature, we can tune the transport property in a way that PIMs synthesized at initial reaction temperatures of 60 °C and 80 °C exhibit improved transport efficiency and selectivity, respectively, in the dioleoyl phosphatidylcholine membrane.

Transmembrane Delivery of an Aryl Azopyrazole Photo-switchable Ion Transporter Relay

Stimuli-responsive synthetic ionophores allow for spatial and temporal control over ion transport, with promise for applications in targeted therapy. Relay transporters have emerged as a new class of ion transporters - these are anchored carriers that sit in both leaflets of the bilayer and mediate transport across the membrane by passing ions between them. The relays are themselves membrane impermeable, and so must be incorporated into the membrane during vesicle preparation. Here we show that relay transporters can be delivered to both sides of the membrane of vesicles using a synthetic flippase. By incorporating an aryl azopyrazole photo-switch into the movable arm of the relay transporters the ion transport activity can be very efficiently and reversibly switched between off and on states. This control is achieved by extension and contraction of their movable arms via photo-isomerization of the central aryl azopyrazole moiety, hence modulating the ability of the relays to pass ions across the membrane.

Uncovering the epigenetic regulatory clues of PRRT1 in Alzheimer's disease: a strategy integrating multi-omics analysis with explainable machine learning

BACKGROUND

Alzheimer's disease (AD) is a complex neurodegenerative disorder with a largely unexplored epigenetic landscape.

OBJECTIVE

This study employs an innovative approach that integrates multi-omics analysis and explainable machine learning to explore the epigenetic regulatory mechanisms underlying the epigenetic signature of PRRT1 implicated in AD.

METHODS

Through comprehensive DNA methylation and transcriptomic profiling, we identified distinct epigenetic signatures associated with gene PRRT1 expression in AD patient samples compared to healthy controls. Utilizing interpretable machine learning models and ELMAR analysis, we dissected the complex relationships between these epigenetic signatures and gene expression patterns, revealing novel regulatory elements and pathways. Finally, the epigenetic mechanisms of these genes were investigated experimentally.

RESULTS

This study identified ten epigenetic signatures, constructed an interpretable AD diagnostic model, and utilized various bioinformatics methods to create an epigenomic map. Subsequently, the ELMAR R package was used to integrate multi-omics data and identify the upstream transcription factor MAZ for PRRT1. Finally, experiments confirmed the interaction between MAZ and PRRT1, which mediated apoptosis and autophagy in AD.

CONCLUSION

This study adopts a strategy that integrates bioinformatics analysis with molecular experiments, providing new insights into the epigenetic regulatory mechanisms of PRRT1 in AD and demonstrating the importance of explainable machine learning in elucidating complex disease mechanisms.

Aromatic foldamer-derived transmembrane transporters

This review is the first to focus on transmembrane transporters derived from aromatic foldamers, with most studies reported over the past decade. These foldamers have made significant strides in mimicking the essential functions of natural ion channel proteins. With their aromatic backbones rigidified by intramolecular hydrogen bonds or differential repulsive forces, this innovative family of molecules stands out for its structural diversity and functional adaptability. They achieve efficient and selective ion and molecule transport across lipid bilayers via carefully designed helical structures and tunable large cavities. Recent developments in this field highlight the transformative potential of foldamers in therapeutic applications and biomaterial engineering. Key advances include innovative molecular engineering strategies that enable highly selective ion transport by fine-tuning structural and functional attributes. Specific modifications to macrocyclic or helical foldamer structures have allowed precise control over ion selectivity and transport efficiency, with notable selectivity for K+, Li+, H+ and water molecules. Although challenges remain, future directions may focus on more innovative molecular designs, optimizing synthetic methods, improving membrane transport properties, integrating responsive designs that adapt to environmental stimuli, and fostering interdisciplinary collaborations. By emphasizing the pivotal role of aromatic foldamers in modern chemistry, this review aims to inspire further development, offering new molecular toolboxes and strategies to address technological and biological challenges in chemistry, biology, medicine, and materials science.

Oriented triplex DNA as a synthetic receptor for transmembrane signal transduction

Signal transduction across biological membranes enables cells to detect and respond to diverse chemical or physical signals, and replicating these complex biological processes through synthetic methods is of significant interest in synthetic biology. Here we present an artificial signal transduction system using oriented cholesterol-tagged triplex DNA (TD) as synthetic receptors to transmit and amplify signals across lipid bilayer membranes through H+-mediated TD conformational transitions from duplex to triplex. An auxiliary sequence, complementary to the third strand of the TD, ensures a controlled and preferred outward orientation of cholesterol-tagged TD on membranes. Upon external H+ stimuli, the conformational change triggers the translocation of the third strand from the outer to the inner membrane leaflet, resulting in effective transmembrane signal transduction. This mechanism enables fluorescence resonance energy transfer (FRET), selective photocleavage, catalytic signal amplification, and logic gate modulation within vesicles. Our findings demonstrate that these TD-based receptors mimic the functional dynamics of natural G protein-coupled receptors (GPCRs), providing a foundation for advanced applications in biosensing, cell signaling modulation, and targeted drug delivery systems.

Highly Selective Artificial K+ Transporters Reverse Liver Fibrosis In Vivo

Liver fibrosis is a life-threatening disease that currently lacks clinically effective therapeutic agents. Given the close correlation between dysregulated intracellular K+ homeostasis and the progression of liver fibrosis, developing artificial K+ transporters mimicking the essential function of their natural counterparts in regulating intracellular K+ levels might offer an appealing yet unexplored treatment strategy. Here, we present an unconventional class of artificial K+ transporters involving the "motional" collaboration between two K+ transporter molecules. In particular, 6C6 exhibits an impressive EC50 value of 0.28 μM (i.e., 0.28 mol % relative to lipid) toward K+ and an exceptionally high K+/Na+ selectivity of 15.5, representing one of the most selective artificial K+ transporters reported to date. Most importantly, our study demonstrates, for the first time, the potential therapeutic effect of K+-selective artificial ion transporters in reversing liver fibrosis both in vitro and in vivo.

Light-Powered Propeller-like Transporter for Boosted Transmembrane Ion Transport

Membrane-active molecular machines represent a recently emerging, yet important line of expansion in the field of artificial transmembrane transporters. Their hitherto demonstrated limited types (molecular swing, ion fishers, shuttlers, rotors, etc.) certainly call for new inspiring developments. Here, we report a very first motorized ion-transporting carrier-type transporter, i.e., a modularly tunable, light-powered propeller-like transporter derived from Feringa's molecular motor for consistently boosting transmembrane ion transport under continuous UV light irradiation. Based on the EC50 values, the molecular propeller-mediated ion transport activities under UV light irradiation for 300 s are 2.31, 1.74, 2.29, 2.80, and 2.92 times those values obtained without irradiation for Li+, Na+, K+, Rb+, and Cs+ ions, respectively, with EC50 value as low as 0.71 mol % for K+ ion under light irradiation.

Synthetic cation channel: reconstructing the ion permeation pathway of TRPA1 in an artificial system

A novel artificial cation channel was developed by rebuilding the ion permeation pathway of the natural channel protein (TRPA1) in a synthetic system. This tubular molecule can effectively embed into lipid bilayers and form transmembrane channels, thereby mediating cation transport. Furthermore, due to its carboxyl-modified ion permeation pathway, the transport activity of this artificial channel can be modulated by the pH of the buffer solution.

Length dependent reversible off-on activation of photo-switchable relay anion transporters

A homologous series of azobenzene-derived photo-switchable ion relay transporters is reported. We reveal that both the length and geometry of the relay strongly affect transport rate, allowing the relative activity of the E and Z isomers to be reversed and hence the wavelengths of light used for on and off switching to be exchanged.

Supramolecular cage-mediated cargo transport

A steady stream of material transport based on carriers and channels in living systems plays an extremely important role in normal life activities. Inspired by nature, researchers have extensively applied supramolecular cages in cargo transport because of their unique three-dimensional structures and excellent physicochemical properties. In this review, we will focus on the development of supramolecular cages as carriers and channels for cargo transport in abiotic and biological systems over the past fifteen years. In addition, we will discuss future challenges and potential applications of supramolecular cages in substance transport.

Naphthalene Diimide-Based Metallacage as an Artificial Ion Channel for Chloride Ion Transport

Developing synthetic molecular devices for controlling ion transmembrane transport is a promising research field in supramolecular chemistry. These artificial ion channels provide models to study ion channel diseases and have huge potential for therapeutic applications. Compared with self-assembled ion channels constructed by intermolecular weak interactions between smaller molecules or cyclic compounds, metallacage-based ion channels have well-defined structures and can exist as single components in the phospholipid bilayer. A naphthalene diimide-based artificial chloride ion channel is constructed through efficient subcomponent self-assembly and its selective ion transport activity in large unilamellar vesicles and the planar lipid bilayer membrane by fluorescence and ion-current measurements is investigated. Molecular dynamics simulations and density functional theory calculations show that the metallacage spans the entire phospholipid bilayer as an unimolecular ion transport channel. This channel transports chloride ions across the cell membrane, which disturbs the ion balance of cancer cells and inhibits the growth of cancer cells at low concentrations.

Redox-Regulated Synthetic Channels: Enabling Reversible Ion Transport by Modulating the Ion-Permeation Pathway

Natural redox-regulated channel proteins often utilize disulfide bonds as redox sensors for adaptive regulation of channel conformations in response to diverse physiological environments. In this study, we developed novel synthetic ion channels capable of reversibly switching their ion-transport capabilities by incorporating multiple disulfide bonds into artificial systems. X-ray structural analysis and electrophysiological experiments demonstrated that these disulfide-bridged molecules possess well-defined tubular cavities and can be efficiently inserted into lipid bilayers to form artificial ion channels. More importantly, the disulfide bonds in these molecules serve as redox-tunable switches to regulate the formation and disruption of ion-permeation pathways, thereby achieving a transition in the transmembrane transport process between the ON and OFF states.

Molecular machines working at interfaces: physics, chemistry, evolution and nanoarchitectonics

As a post-nanotechnology concept, nanoarchitectonics combines nanotechnology with advanced materials science. Molecular machines made by assembling molecular units and their organizational bodies are also products of nanoarchitectonics. They can be regarded as the smallest functional materials. Originally, studies on molecular machines analyzed the average properties of objects dispersed in solution by spectroscopic methods. Researchers' playgrounds partially shifted to solid interfaces, because high-resolution observation of molecular machines is usually done on solid interfaces under high vacuum and cryogenic conditions. Additionally, to ensure the practical applicability of molecular machines, operation under ambient conditions is necessary. The latter conditions are met in dynamic interfacial environments such as the surface of water at room temperature. According to these backgrounds, this review summarizes the trends of molecular machines that continue to evolve under the concept of nanoarchitectonics in interfacial environments. Some recent examples of molecular machines in solution are briefly introduced first, which is followed by an overview of studies of molecular machines and similar supramolecular structures in various interfacial environments. The interfacial environments are classified into (i) solid interfaces, (ii) liquid interfaces, and (iii) various material and biological interfaces. Molecular machines are expanding their activities from the static environment of a solid interface to the more dynamic environment of a liquid interface. Molecular machines change their field of activity while maintaining their basic functions and induce the accumulation of individual molecular machines into macroscopic physical properties molecular machines through macroscopic mechanical motions can be employed to control molecular machines. Moreover, research on molecular machines is not limited to solid and liquid interfaces; interfaces with living organisms are also crucial.

Light-controllable cell-membrane disturbance for intracellular delivery

Highly polar and charged molecules, such as oligonucleotides, face significant barriers in crossing the cell membrane to access the cytoplasm. To address this problem, we developed a light-triggered twistable tetraphenylethene (TPE) derivative, TPE-C-N, to facilitate the intracellular delivery of charged molecules through an endocytosis-independent pathway. The central double bond of TPE in TPE-C-N is planar in the ground state but becomes twisted in the excited state. Under light irradiation, this planar-to-twisted structural change induces continuous cell membrane disturbances. Such disturbance does not lead to permanent damage to the cell membrane. TPE-C-N significantly enhanced the intracellular delivery of negatively charged molecules under light irradiation when endocytosis was inhibited through low-temperature treatment, confirming the endocytosis-independent nature of this delivery method. We have successfully demonstrated that the TPE-C-N-mediated light-controllable method can efficiently promote the intracellular delivery of charged molecules, such as peptides and oligonucleotides, with molecular weights ranging from 1000 to 5000 Da.

Concentration-Driven Evolution of Adaptive Artificial Ion Channels or Nanopores with Specific Anticancer Activities

In nature, ceramides are a class of sphingolipids possessing a unique ability to self-assemble into protein-permeable channels with intriguing concentration-dependent adaptive channel cavities. However, within the realm of artificial ion channels, this interesting phenomenon is scarcely represented. Herein, we report on a novel class of adaptive artificial channels, Pn-TPPs, based on PEGylated cholic acids bearing triphenylphosphonium (TPP) groups as anion binding motifs. Interestingly, the molecules self-assemble into chloride ion channels at low concentrations while transforming into small molecule-permeable nanopores at high concentrations. Moreover, the TPP groups endow the molecules with mitochondria-targeting properties, enabling them to selectively drill holes on the mitochondrial membrane of cancer cells and subsequently trigger the caspase 9 apoptotic pathway. The anticancer efficacies of Pn-TPPs correlate with their abilities to form nanopores. Significantly, the most active ensembles formed by P5-TPP exhibits impressive anticancer activity against human liver cancer cells, with an IC50 value of 3.8 μM. While demonstrating similar anticancer performance to doxorubicin, P5-TPP exhibits a selectivity index surpassing that of doxorubicin by a factor of 16.8.

Non-Covalently Stapled H+ /Cl- Ion Channels Activatable by Visible Light for Targeted Anticancer Therapy

The development of stimuli-responsive artificial H+ /Cl- ion channels, capable of specifically disturbing the intracellular ion homeostasis of cancer cells, presents an intriguing opportunity for achieving high selectivity in cancer therapy. Herein, we describe a novel family of non-covalently stapled self-assembled artificial channels activatable by biocompatible visible light at 442 nm, which enables the co-transport of H+ /Cl- across the membrane with H+ /Cl- transport selectivity of 6.0. Upon photoirradiation of the caged C4F-L for 10 min, 90 % of ion transport efficiency can be restored, giving rise to a 10.5-fold enhancement in cytotoxicity against human colorectal cancer cells (IC50 =8.5 μM). The mechanism underlying cancer cell death mediated by the H+ /Cl- channels involves the activation of the caspase 9 apoptosis pathway as well as the scarcely reported disruption of the autophagic processes. In the absence of photoirradiation, C4F-L exhibits minimal toxicity towards normal intestine cells, even at a concentration of 200 μM.

Artificial transmembrane potassium transporters: designs, functions, mechanisms and applications

Potassium channels represent the most prevalent class of ion channels, exerting regulatory control over numerous vital biological processes, including muscle contraction, neurotransmitter release, cell proliferation, and apoptosis. The seamless integration of astonishing functions into a sophisticated structure, as seen in these protein channels, inspires the chemical community to develop artificial versions, gearing toward simplifying their structure while replicating their key functions. In particular, over the past ten years or so, a number of elegant artificial potassium transporters have emerged, demonstrating high selectivity, high transport efficiency or unprecedented transport mechanisms. In this review, we will provide a detailed exposition of these artificial potassium transporters that are derived from a single molecular backbone or self-assembled from multiple components, with their respective structural designs, channel functions, transport mechanisms and biomedical applications thoroughly reviewed.

Molecular Machines For The Control Of Transmembrane Transport

Nature embeds some of its molecular machinery, including ion pumps, within lipid bilayer membranes. This has inspired chemists to attempt to develop synthetic analogues to exploit membrane confinement and transmembrane potential gradients, much like their biological cousins. In this perspective, we outline the various strategies by which molecular machines─molecular systems in which a nanomechanical motion is exploited for function─have been designed to be incorporated within lipid membranes and utilized to mediate transmembrane ion transport. We survey molecular machines spanning both switches and motors, those that act as mobile carriers or that are anchored within the membrane, mechanically interlocked molecules, and examples that are activated in response to external stimuli.

Photoswitchable Calixarene Activators for Controlled Peptide Transport across Lipid Membranes

Supramolecular synthetic transporters are crucial to understand and activate the passage across lipid membranes of hydrophilic effector molecules. Herein, we introduce photoswitchable calixarenes for the light-controlled transport activation of cationic peptide cargos across model lipid bilayers and inside living cells. Our approach was based on rationally designed p-sulfonatocalix[4]arene receptors equipped with a hydrophobic azobenzene arm, which recognize cationic peptide sequences at the nM range. Activation of membrane peptide transport is confirmed, in synthetic vesicles and living cells, for calixarene activators featuring the azobenzene arm in the E configuration. Therefore, this method allows the modulation of the transmembrane transport of peptide cargos upon Z-E photoisomerization of functionalized calixarenes using 500 nm visible light. These results showcase the potential of photoswitchable counterion activators for the light-triggered delivery of hydrophilic biomolecules and pave the way for potential applications in remotely controlled membrane transport and photopharmacology applications of hydrophilic functional biomolecules.

Molecular Complementarity of Proteomimetic Materials for Target-Specific Recognition and Recognition-Mediated Complex Functions

As biomolecules essential for sustaining life, proteins are generated from long chains of 20 different α-amino acids that are folded into unique 3D structures. In particular, many proteins have molecular recognition functions owing to their binding pockets, which have complementary shapes, charges, and polarities for specific targets, making these biopolymers unique and highly valuable for biomedical and biocatalytic applications. Based on the understanding of protein structures and microenvironments, molecular complementarity can be exhibited by synthesizable and modifiable materials. This has prompted researchers to explore the proteomimetic potentials of a diverse range of materials, including biologically available peptides and oligonucleotides, synthetic supramolecules, inorganic molecules, and related coordination networks. To fully resemble a protein, proteomimetic materials perform the molecular recognition to mediate complex molecular functions, such as allosteric regulation, signal transduction, enzymatic reactions, and stimuli-responsive motions; this can also expand the landscape of their potential bio-applications. This review focuses on the recognitive aspects of proteomimetic designs derived for individual materials and their conformations. Recent progress provides insights to help guide the development of advanced protein mimicry with material heterogeneity, design modularity, and tailored functionality. The perspectives and challenges of current proteomimetic designs and tools are also discussed in relation to future applications.

Halogen bonding relay and mobile anion transporters with kinetically controlled chloride selectivity

Selective transmembrane transport of chloride over competing proton or hydroxide transport is key for the therapeutic application of anionophores, but remains a significant challenge. Current approaches rely on enhancing chloride anion encapsulation within synthetic anionophores. Here we report the first example of a halogen bonding ion relay in which transport is facilitated by the exchange of ions between lipid-anchored receptors on opposite sides of the membrane. The system exhibits non-protonophoric chloride selectivity, uniquely arising from the lower kinetic barrier to chloride exchange between transporters within the membrane, compared to hydroxide, with selectivity maintained across membranes with different hydrophobic thicknesses. In contrast, we demonstrate that for a range of mobile carriers with known high chloride over hydroxide/proton selectivity, the discrimination is strongly dependent on membrane thickness. These results demonstrate that the selectivity of non-protonophoric mobile carriers does not arise from ion binding discrimination at the interface, but rather through a kinetic bias in transport rates, arising from differing membrane translocation rates of the anion-transporter complexes.

A K+-selective channel with a record-high K+/Na+ selectivity of 20.1

For compounds each containing a phenylalanine moiety with its two ends amidated to have a 15-crown-5 unit and an alkyl chain, a simple tuning of the alkyl chain length delivered a K⁺-selective channel with a record-high K⁺/Na⁺ selectivity of 20.1.