Synthetic energy sensor AMPfret deciphers adenylate-dependent AMPK activation mechanism

Coenzyme Q10 protects keratinocytes against oxidation-induced energy stress as revealed by spatiotemporal analysis of cell energetics

Coenzyme Q10 (Q10) plays a critical role in cellular energy conversion within the mitochondrial respiratory chain and offers protective effects against oxidative and metabolic stress. In this study, we investigated the impact of Q10 on the spatio-temporal patterns of cellular energetics in keratinocyte-derived HaCaT cells, utilizing the genetically-encoded FRET sensor AMPfret. Engineered from the AMP-activated protein kinase (AMPK), this sensor leverages endogenous affinities of the kinase that evolved to detect energy stress, specifically decreases in ATP/ADP and ATP/AMP ratios that pose a threat to cell survival. We successfully established HaCaT cells stably expressing AMPfret, validated their functionality by inducing energy stress with 2-deoxy-D-glucose, and demonstrated that Q10, together with high glucose conditions in culture, can enhance cellular energetics compared to low glucose controls. We then employed AMPfret to analyze the spatio-temporal response of HaCaT keratinocytes to Luperox (tert-butyl peroxide), a potent organic prooxidant, in the presence of varying intracellular levels of Q10. Preloading cells with Q10 was protective, slowing the speed and reducing the extend of the energy stress response. In contrast, preincubation with Simvastatin, an inhibitor of the mevalonate Q10 biosynthesis pathway, depleted cellular Q10 levels, accelerated the onset of energy stress, and led to early cell death as compared to controls. Under all conditions, AMPfret revealed cell-to-cell heterogeneity in energy stress at baseline and in the response to Luperox. Overall, tracking changes in energy state in time and at single-cell level allows further insights into the beneficial role of Q10 in enhancing cellular bioenergetics in skin cells, and a potential role of AMPK in mediating responses to altered Q10 levels.

Visualize neuronal membrane cholesterol with split-fluorescent protein tagged YDQA sensor

Cholesterol is a major component of the cellular plasma membrane (PM), and its homeostasis is essential for brain health. Dysregulated cholesterol homeostasis has been strongly implicated in the pathogenesis of various neurological disorders, including Alzheimer's disease (AD). However, in vivo visualization of cholesterol has remained challenging, hindering a comprehensive understanding of AD pathology. In this study, we generated a new sensor combining the split-fluorescent protein tags with YDQA, a derivate of cholesterol-dependent cytolysin PFO. Through a series of validations in cell and C. elegans models, we demonstrate that the new sensor (name as sfPMcho) efficiently detects neuronal PM cholesterol. We further applied this sensor in 5X FAD and APOE KO mice models and revealed the cholesterol changes within neurons. PM cholesterol became sparse and locally aggregated in neuron bodies but significantly accumulated in nerve fibers. Collectively, this study provides a new tool for detecting neuronal PM cholesterol in vivo and uncovers cholesterol abnormalities in AD-related pathology at the cellular level. Further development based on this sensor or a similar strategy is to be expected.

Monitoring Cellular Energy Balance in Single Cells Using Fluorescent Biosensors for AMPK

5'-Adenosine monophosphate-activated protein kinase (AMPK) senses cellular metabolic status and reflects the balance between ATP production and ATP usage. This balance varies from cell to cell and changes over time, creating a need for methods that can capture cellular heterogeneity and temporal dynamics. Fluorescent biosensors for AMPK activity offer a unique approach to measure metabolic status nondestructively in single cells in real time. In this chapter, we provide a brief rationale for using live-cell biosensors to measure AMPK activity, survey the current AMPK biosensors, and discuss considerations for using this approach. We provide methodology for introducing AMPK biosensors into a cell line of choice, setting up experiments for live-cell fluorescent microscopy of AMPK activity, and calibrating the biosensors using immunoblot data.

FRET-Based Sensor for Measuring Adenine Nucleotide Binding to AMPK

AMP-activated protein kinase (AMPK) has evolved to detect a critical increase in cellular AMP/ATP and ADP/ATP concentration ratios as a signal for limiting energy supply. Such energy stress then leads to AMPK activation and downstream events that maintain cellular energy homeostasis. AMPK activation by AMP, ADP, or pharmacological activators involves a conformational switch within the AMPK heterotrimeric complex. We have engineered an AMPK-based sensor, AMPfret, which translates the activating conformational switch into a fluorescence signal, based on increased fluorescence resonance energy transfer (FRET) between donor and acceptor fluorophores. Here we describe how this sensor can be used to analyze direct AMPK activation by small molecules in vitro using a fluorimeter, or to estimate changes in the energy state of cells using standard fluorescence or confocal microscopy.

Higher AMPK activation in mouse oxidative compared with glycolytic muscle does not correlate with LKB1 or CaMKKβ expression

AMP-activated protein kinase (AMPK) is an energy-sensing serine/threonine kinase involved in metabolic regulation. It is phosphorylated by the upstream liver kinase B1 (LKB1) or calcium/calmodulin-dependent kinase kinase 2 (CaMKKβ). In cultured cells, AMPK activation correlates with LKB1 activity. The phosphorylation activates AMPK, shifting metabolism toward catabolism and promoting mitogenesis. In muscles, inactivity reduces AMPK activation, shifting the phenotype of oxidative muscles toward a more glycolytic profile. Here, we compared the basal level of AMPK activation in glycolytic and oxidative muscles and analyzed whether this relates to LKB1 or CaMKKβ. Using Western blotting, we assessed AMPK expression and phosphorylation in soleus, gastrocnemius (GAST), extensor digitorum longus (EDL), and heart from C57BL6J mice. We also assessed LKB1 and CaMKKβ expression, and CaMKKβ activity in tissue homogenates. AMPK activation was higher in oxidative (soleus and heart) than in glycolytic muscles (gastrocnemius and EDL). This correlated with AMPK α1-isoform expression, but not LKB1 and CaMKKβ. LKB1 expression was sex dependent and lower in male than female muscles. CaMKKβ expression was very low in skeletal muscles and did not phosphorylate AMPK in muscle lysates. The higher AMPK activation in oxidative muscles is in line with the fact that activated AMPK maintains an oxidative phenotype. However, this could not be explained by LKB1 and CaMKKβ. These results suggest that the regulation of AMPK activation is more complex in muscle than in cultured cells. As AMPK has been proposed as a therapeutic target for several diseases, future research should consider AMPK isoform expression and localization, and energetic compartmentalization.NEW & NOTEWORTHY It is important to understand how AMP-activated kinase, AMPK, is regulated, as it is a potential therapeutic target for several diseases. AMPK is activated by liver kinase B1, LKB1, and calcium/calmodulin-dependent kinase kinase 2, CaMKKβ. In cultured cells, AMPK activation correlates with LKB1 expression. In contrast, we show that AMPK-activation was higher in oxidative than glycolytic muscle, without correlating with LKB1 or CaMKKβ expression. Thus, AMPK regulation is more complex in highly compartmentalized muscle cells.

Autophagy and cancer therapy

Autophagy is an intracellular degradation process that sequesters cytoplasmic components in double-membrane vesicles known as autophagosomes, which are degraded upon fusion with lysosomes. This pathway maintains the integrity of proteins and organelles while providing energy and nutrients to cells, particularly under nutrient deprivation. Deregulation of autophagy can cause genomic instability, low protein quality, and DNA damage, all of which can contribute to cancer. Autophagy can also be overactivated in cancer cells to aid in cancer cell survival and drug resistance. Emerging evidence indicates that autophagy has functions beyond cargo degradation, including roles in tumor immunity and cancer stem cell survival. Additionally, autophagy can also influence the tumor microenvironment. This feature warrants further investigation of the role of autophagy in cancer, in which autophagy manipulation can improve cancer therapies, including cancer immunotherapy. This review discusses recent findings on the regulation of autophagy and its role in cancer therapy and drug resistance.

Molecular Spies in Action: Genetically Encoded Fluorescent Biosensors Light up Cellular Signals

Cellular function is controlled through intricate networks of signals, which lead to the myriad pathways governing cell fate. Fluorescent biosensors have enabled the study of these signaling pathways in living systems across temporal and spatial scales. Over the years there has been an explosion in the number of fluorescent biosensors, as they have become available for numerous targets, utilized across spectral space, and suited for various imaging techniques. To guide users through this extensive biosensor landscape, we discuss critical aspects of fluorescent proteins for consideration in biosensor development, smart tagging strategies, and the historical and recent biosensors of various types, grouped by target, and with a focus on the design and recent applications of these sensors in living systems.

Compartmentalization in cardiomyocytes modulates creatine kinase and adenylate kinase activities

Intracellular molecules are transported by motor proteins or move by diffusion resulting from random molecular motion. Cardiomyocytes are packed with structures that are crucial for function, but also confine the diffusional spaces, providing cells with a means to control diffusion. They form compartments in which local concentrations are different from the overall, average concentrations. For example, calcium and cyclic AMP are highly compartmentalized, allowing these versatile second messengers to send different signals depending on their location. In energetic compartmentalization, the ratios of AMP and ADP to ATP are different from the average ratios. This is important for the performance of ATPases fuelling cardiac excitation-contraction coupling and mechanical work. A recent study suggested that compartmentalization modulates the activity of creatine kinase and adenylate kinase in situ. This could have implications for energetic signaling through, for example, AMP-activated kinase. It highlights the importance of taking compartmentalization into account in our interpretation of cellular physiology and developing methods to assess local concentrations of AMP and ADP to enhance our understanding of compartmentalization in different cell types.

Enhancing Therapeutic Efficacy in Cancer Treatment: Integrating Nanomedicine with Autophagy Inhibition Strategies

The complicated stepwise lysosomal degradation process known as autophagy is in charge of destroying and eliminating damaged organelles and defective cytoplasmic components. This mechanism promotes metabolic adaptability and nutrition recycling. Autophagy functions as a quality control mechanism in cells that support homeostasis and redox balance under normal circumstances. However, the role of autophagy in cancer is controversial because, mostly depending on the stage of the tumor, it may either suppress or support the disease. While autophagy delays the onset of tumors and slows the dissemination of cancer in the early stages of tumorigenesis, numerous studies demonstrate that autophagy promotes the development and spread of tumors as well as the evolution and development of resistance to several anticancer drugs in advanced cancer stages. In this Review, we primarily emphasize the therapeutic role of autophagy inhibition in improving the treatment of multiple cancers and give a broad overview of how its inhibition modulates cancer responses. There have been various attempts to inhibit autophagy, including the use of autophagy inhibitor drugs, gene silencing therapy (RNA interference), and nanoparticles. In this Review, all these topics are thoroughly covered and illustrated by recent studies and field investigations.

Next-Generation Genetically Encoded Fluorescent Biosensors Illuminate Cell Signaling and Metabolism

Genetically encoded fluorescent biosensors have revolutionized the study of cell signaling and metabolism, as they allow for live-cell measurements with high spatiotemporal resolution. This success has spurred the development of tailor-made biosensors that enable the study of dynamic phenomena on different timescales and length scales. In this review, we discuss different approaches to enhancing and developing new biosensors. We summarize the technologies used to gain structural insights into biosensor design and comment on useful screening technologies. Furthermore, we give an overview of different applications where biosensors have led to key advances over recent years. Finally, we give our perspective on where future work is bound to make a large impact.

Minimizing Interfacial Recombination in 1.8 eV Triple-Halide Perovskites for 27.5% Efficient All-Perovskite Tandems

All-perovskite tandem solar cells show great potential to enable the highest performance at reasonable costs for a viable market entry in the near future. In particular, wide-bandgap (WBG) perovskites with higher open-circuit voltage (VOC ) are essential to further improve the tandem solar cells' performance. Here, a new 1.8 eV bandgap triple-halide perovskite composition in conjunction with a piperazinium iodide (PI) surface treatment is developed. With structural analysis, it is found that the PI modifies the surface through a reduction of excess lead iodide in the perovskite and additionally penetrates the bulk. Constant light-induced magneto-transport measurements are applied to separately resolve charge carrier properties of electrons and holes. These measurements reveal a reduced deep trap state density, and improved steady-state carrier lifetime (factor 2.6) and diffusion lengths (factor 1.6). As a result, WBG PSCs achieve 1.36 V VOC , reaching 90% of the radiative limit. Combined with a 1.26 eV narrow bandgap (NBG) perovskite with a rubidium iodide additive, this enables a tandem cell with a certified scan efficiency of 27.5%.

Genetically encoded ATP and NAD(P)H biosensors: potential tools in metabolic engineering

To date, many metabolic engineering tools and strategies have been developed, including tools for cofactor engineering, which is a common strategy for bioproduct synthesis. Cofactor engineering is used for the regulation of pyridine nucleotides, including NADH/NAD+ and NADPH/NADP+, and adenosine triphosphate/adenosine diphosphate (ATP/ADP), which is crucial for maintaining redox and energy balance. However, the intracellular levels of NADH/NAD+, NADPH/NADP+, and ATP/ADP cannot be monitored in real time using traditional methods. Recently, many biosensors for detecting, monitoring, and regulating the intracellular levels of NADH/NAD+, NADPH/NADP+, and ATP/ADP have been developed. Although cofactor biosensors have been mainly developed for use in mammalian cells, the potential application of cofactor biosensors in metabolic engineering in bacterial and yeast cells has received recent attention. Coupling cofactor biosensors with genetic circuits is a promising strategy in metabolic engineering for optimizing the production of biochemicals. In this review, we focus on the development of biosensors for NADH/NAD+, NADPH/NADP+, and ATP/ADP and the potential application of these biosensors in metabolic engineering. We also provide critical perspectives, identify current research challenges, and provide guidance for future research in this promising field.

Research development of porphyrin-based metal-organic frameworks: targeting modalities and cancer therapeutic applications

Porphyrins are naturally occurring organic molecules that have attracted widespread attention for their potential in the field of biomedical research. Porphyrin-based metal-organic frameworks (MOFs) that utilize porphyrin molecules as organic ligands have gained attention from researchers due to their excellent results as photosensitizers in tumor photodynamic therapy (PDT). Additionally, MOFs hold significant promise and potential for other tumor therapeutic approaches due to their tunable size and pore size, excellent porosity, and ultra-high specific surface area. Active delivery of nanomaterials via targeted molecules for tumor therapy has demonstrated greater accumulation, lower drug doses, higher therapeutic efficacy, and reduced side effects relative to passive targeting through the enhanced permeation and retention effect (EPR). This paper presents a comprehensive review of the targeting methods employed by porphyrin-based MOFs in tumor targeting therapy over the past few years. It further discusses the applications of porphyrin-based MOFs for targeted cancer therapy through various therapeutic methods. The objective of this paper is to provide a valuable reference and source of ideas for targeted therapy using porphyrin-based MOF materials and to inspire further exploration of their potential in the field of cancer therapy.

An initiator-free and solvent-free in-situ self-catalyzed crosslinked polymer electrolyte for all-solid-state lithium-metal batteries

Linear polymer (e.g. polyethylene oxide, PEO) based electrolytes have been widely studied due to their flexibility and relatively good contact against electrodes. However, the linear polymers are prone to crystallization at room temperature and melting at moderate temperature, restricting their application in lithium metal batteries. To address these problems, a self-catalyzed crosslinked polymer electrolyte (CPE) was designed and prepared by the reaction of poly (ethylene glycol diglycidyl ether) (PEGDGE) and polyoxypropylenediamine (PPO) with only the bistrifluoromethanesulfonimide lithium salt (LiTFSI) added and with no any initiators. LiTFSI catalyzed the reaction by reducing the activation energy to form a crosslinked network structure, which was identified by calculation, NMR and FTIR. The as-prepared CPE has high resilience and a low glass transition temperature (Tg = -60 °C). Meanwhile, the solvent-free in-situ polymerization technique has been adopted in the assembly of the CPE with electrodes to decrease the interfacial impedance greatly and improve the ionic conductivity to 2.05 × 10^-5 S cm^-1 and 2.55 × 10^-4 S cm^-1 at room temperature and 75 °C, respectively. As a result, the in-situ LiFeO₄/CPE/Li battery exhibits outstanding thermal and electrochemical stability at 75 °C. Our work has proposed an initiator-free and solvent-free in-situ self-catalyzed strategy of preparing high performance crosslinked solid polymer electrolytes.

Mitochondrial Modulators: The Defender

Mitochondria are widely considered the "power hub" of the cell because of their pivotal roles in energy metabolism and oxidative phosphorylation. However, beyond the production of ATP, which is the major source of chemical energy supply in eukaryotes, mitochondria are also central to calcium homeostasis, reactive oxygen species (ROS) balance, and cell apoptosis. The mitochondria also perform crucial multifaceted roles in biosynthetic pathways, serving as an important source of building blocks for the biosynthesis of fatty acid, cholesterol, amino acid, glucose, and heme. Since mitochondria play multiple vital roles in the cell, it is not surprising that disruption of mitochondrial function has been linked to a myriad of diseases, including neurodegenerative diseases, cancer, and metabolic disorders. In this review, we discuss the key physiological and pathological functions of mitochondria and present bioactive compounds with protective effects on the mitochondria and their mechanisms of action. We highlight promising compounds and existing difficulties limiting the therapeutic use of these compounds and potential solutions. We also provide insights and perspectives into future research windows on mitochondrial modulators.

Spatial regulation of AMPK signaling revealed by a sensitive kinase activity reporter

AMP-activated protein kinase (AMPK) is a master regulator of cellular energetics which coordinates metabolism by phosphorylating a plethora of substrates throughout the cell. But how AMPK activity is regulated at different subcellular locations for precise spatiotemporal control over metabolism is unclear. Here we present a sensitive, single-fluorophore AMPK activity reporter (ExRai AMPKAR), which reveals distinct kinetic profiles of AMPK activity at the mitochondria, lysosome, and cytoplasm. Genetic deletion of the canonical upstream kinase liver kinase B1 (LKB1) results in slower AMPK activity at lysosomes but does not affect the response amplitude at lysosomes or mitochondria, in sharp contrast to the necessity of LKB1 for maximal cytoplasmic AMPK activity. We further identify a mechanism for AMPK activity in the nucleus, which results from cytoplasmic to nuclear shuttling of AMPK. Thus, ExRai AMPKAR enables illumination of the complex subcellular regulation of AMPK signaling.

Iron phthalocyanine on Au(111) is a "non-Landau" Fermi liquid

The paradigm of Landau’s Fermi liquid theory has been challenged with the finding of a strongly interacting Fermi liquid that cannot be adiabatically connected to a non-interacting system. A spin-1 two-channel Kondo impurity with anisotropy D has a quantum phase transition between two topologically different Fermi liquids with a peak (dip) in the Fermi level for D < D_c (D > D_c). Extending this theory to general multi-orbital problems with finite magnetic field, we reinterpret in a unified and consistent fashion several experimental studies of iron phthalocyanine molecules on Au(111) that were previously described in disconnected and conflicting ways. The differential conductance shows a zero-bias dip that widens when the molecule is lifted from the surface (reducing the Kondo couplings) and is transformed continuously into a peak under an applied magnetic field. We reproduce all features and propose an experiment to induce the topological transition.

Single molecules on metal surfaces are paradigmatic systems for the study of many-body phenomena. Here, the authors show that several spectroscopic experiments on iron phthalocyanine on Au(111) surface can be described in a unified way in terms of a strongly interacting topologically non-trivial (non-Landau) Fermi liquid.

Protein kinase sensors: an overview of new designs for visualizing kinase dynamics in single plant cells

Protein kinase dynamics play key roles in regulation of cell differentiation, growth, development and in diverse cell signaling networks. Protein kinase sensors enable visualization of protein kinase activity in living cells and tissues in time and space. These sensors have therefore become important and powerful molecular tools for investigation of diverse kinase activities and can resolve long-standing and challenging biological questions. In the present Update, we review new advanced approaches for genetically encoded protein kinase biosensor designs developed in animal systems together with the basis of each biosensor's working principle and components. In addition, we review recent first examples of real time plant protein kinase activity biosensor development and application. We discuss how these sensors have helped to resolve how stomatal signal transduction in response to elevated CO2 merges with abscisic acid signaling downstream of a resolved basal SnRK2 kinase activity in guard cells. Furthermore, recent advances, combined with the new strategies described in this Update, can help deepen the understanding of how signaling networks regulate unique functions and responses in distinct plant cell types and tissues and how different stimuli and signaling pathways can interact.

Crosstalk between Autophagy and Inflammatory Processes in Cancer

Inflammation is an adaptive response to tissue injury, which is a critical process in order to restore tissue functionality and homeostasis. The association between inflammation and cancer has been a topic of interest for many years, not only inflammatory cells themselves but also the chemokines and cytokines they produce, which affect cancer development. Autophagy is an intracellular self-degradative process providing elimination of damaged or dysfunctional organelles under stressful conditions such as nutrient deficiency, hypoxia, or chemotherapy. Interestingly, the signaling pathways that are involved in cancer-associated inflammation may regulate autophagy as well. These are (1) the toll-like receptor (TLR) signaling cascade, (2) the reactive oxygen species (ROS) signaling pathway, (3) the inflammatory cytokine signaling pathway, and (4) the IκB kinase (IKK)/Nuclear factor-κB (NF-κB) signaling axis. Moreover, the studies on the context-specific functions of autophagy during inflammatory responses in cancer will be discussed here. On that basis, we focus on autophagy inhibitors and activators regulating inflammatory process in cancer as useful candidates for enhancing anticancer effects. This review summarizes how the autophagic process regulates these key inflammatory processes and vice versa in various cancers.

Low-temperature supercritical dehydroxylation for achieving an ultra-low subthreshold swing of thin-film transistors

Thin-film transistors (TFTs) have been widely used in the increasingly advanced field of displays. However, it remains a challenge for TFTs to overcome the poor subthreshold swing in the fast switching and high-speed applications. Here, we provide a solution to the above-mentioned challenge via supercritical dehydroxylation, which combines a low temperature, environmentally friendly supercritical fluid technology with a CaCl₂ treatment. An embedded structure of amorphous indium gallium zinc oxide (a-IGZO) TFTs with double-layer high-k dielectric containing Ta₂O₅ and SiO₂ layers was first manufactured. The subthreshold swing of the fabricated TFTs treated with supercritical dehydroxylation was optimized to an ultra-low value of 72.7 mV dec^-1. Moreover, other key figures of merits including threshold voltage, on/off ratio and field effect mobility all improved after the supercritical dehydroxylation. The bandgap of the gate dielectric material increased due to the supercritical dehydroxylation verified by the current conduction mechanism. Besides, numerous material analyses further confirmed that owing to the supercritical dehydroxylation the dominant dehydration reactions can effectively repair the defects introduced in the device manufacture. The ultra-low subthreshold swing with optimized electrical performances can be achieved via the low-temperature supercritical dehydroxylation treatment, enabling its promising potential in realizing ultra-fast and low power electronics.

Natural compounds against cytotoxic drug-induced cardiotoxicity: A review on the involvement of PI3K/Akt signaling pathway

Cardiotoxicity is a critical concern in the use of several cytotoxic drugs. Induction of apoptosis, inflammation, and autophagy following dysregulation of the PI3K/Akt signaling pathway contributes to the cardiac damage induced by these drugs. Several natural compounds (NCs), including ferulic acid, gingerol, salvianolic acid B, paeonol, apigenin, calycosin, rutin, neferine, higenamine, vincristine, micheliolide, astragaloside IV, and astragalus polysaccharide, have been reported to suppress cytotoxic drug-induced cardiac injury. This article reviews these NCs that have been reported to have a protective effect against cytotoxic drug-induced cardiotoxicity through regulation of the PI3K/Akt signaling pathway.

Optogenetic control of the lac operon for bacterial chemical and protein production

Control of the lac operon with isopropyl β-D-1-thiogalactopyranoside (IPTG) has been used to regulate gene expression in Escherichia coli for countless applications, including metabolic engineering and recombinant protein production. However, optogenetics offers unique capabilities, such as easy tunability, reversibility, dynamic induction strength and spatial control, that are difficult to obtain with chemical inducers. We have developed a series of circuits for optogenetic regulation of the lac operon, which we call OptoLAC, to control gene expression from various IPTG-inducible promoters using only blue light. Applying them to metabolic engineering improves mevalonate and isobutanol production by 24% and 27% respectively, compared to IPTG induction, in light-controlled fermentations scalable to at least two-litre bioreactors. Furthermore, OptoLAC circuits enable control of recombinant protein production, reaching yields comparable to IPTG induction but with easier tunability of expression. OptoLAC circuits are potentially useful to confer light control over other cell functions originally designed to be IPTG-inducible.

Novel Chiral Quantum Spin Liquids in Kitaev Magnets

Quantum magnets with pure Kitaev spin exchange interactions can host a gapped quantum spin liquid with a single Majorana edge mode propagating in the counterclockwise direction when a small positive magnetic field is applied. Here, we show how under a sufficiently strong positive magnetic field a topological transition into a gapped quantum spin liquid with two Majorana edge modes propagating in the clockwise direction occurs. The Dzyaloshinskii-Moriya interaction is found to turn the nonchiral Kitaev's gapless quantum spin liquid into a chiral one with equal Berry phases at the two Dirac points. Thermal Hall conductance experiments can provide evidence of the novel topologically gapped quantum spin liquid states predicted.

AMPfret: synthetic nanosensor for cellular energy states

Cellular energy is a cornerstone of metabolism and is crucial for human health and disease. Knowledge of the cellular energy states and the underlying regulatory mechanisms is therefore key to understanding cell physiology and to design therapeutic interventions. Cellular energy states are characterised by concentration ratios of adenylates, in particular ATP:ADP and ATP:AMP. We applied synthetic biology approaches to design, engineer and validate a genetically encoded nano-sensor for cellular energy state, AMPfret. It employs the naturally evolved energy sensing of eukaryotic cells provided by the AMP-activated protein kinase (AMPK). Our synthetic nano-sensor relies on fluorescence resonance energy transfer (FRET) to detect changes in ATP:ADP and ATP:AMP ratios both in vitro and in cells in vivo. Construction and iterative optimisation relied on ACEMBL, a parallelised DNA assembly and construct screening technology we developed, facilitated by a method we termed tandem recombineering (TR). Our approach allowed rapid testing of numerous permutations of the AMPfret sensor to identify the most sensitive construct, which we characterised and validated both in the test tube and within cells.

AMPK and TOR: The Yin and Yang of Cellular Nutrient Sensing and Growth Control

The AMPK (AMP-activated protein kinase) and TOR (target-of-rapamycin) pathways are interlinked, opposing signaling pathways involved in sensing availability of nutrients and energy and regulation of cell growth. AMPK (Yin, or the "dark side") is switched on by lack of energy or nutrients and inhibits cell growth, while TOR (Yang, or the "bright side") is switched on by nutrient availability and promotes cell growth. Genes encoding the AMPK and TOR complexes are found in almost all eukaryotes, suggesting that these pathways arose very early during eukaryotic evolution. During the development of multicellularity, an additional tier of cell-extrinsic growth control arose that is mediated by growth factors, but these often act by modulating nutrient uptake so that AMPK and TOR remain the underlying regulators of cellular growth control. In this review, we discuss the evolution, structure, and regulation of the AMPK and TOR pathways and the complex mechanisms by which they interact.

Illuminating the kinome: Visualizing real-time kinase activity in biological systems using genetically encoded fluorescent protein-based biosensors

Genetically encoded fluorescent protein-based kinase biosensors are a central tool for illumination of the kinome. The adaptability and versatility of biosensors have allowed for spatiotemporal observation of real-time kinase activity in living cells and organisms. In this review, we highlight various types of kinase biosensors, along with their burgeoning applications in complex biological systems. Specifically, we focus on kinase activity reporters used in neuronal systems and whole animal settings. Genetically encoded kinase biosensors are key for elucidation of the spatiotemporal regulation of protein kinases, with broader applications beyond the Petri dish.

The spatio-temporal organization of mitochondrial F1FO ATP synthase in cristae depends on its activity mode

F₁F_O ATP synthase, also known as complex V, is a key enzyme of mitochondrial energy metabolism that can synthesize and hydrolyze ATP. It is not known whether the ATP synthase and ATPase function are correlated with a different spatio-temporal organisation of the enzyme. In order to analyze this, we tracked and localized single ATP synthase molecules in situ using live cell microscopy. Under normal conditions, complex V was mainly restricted to cristae indicated by orthogonal trajectories along the cristae membranes. In addition confined trajectories that are quasi immobile exist. By inhibiting glycolysis with 2-DG, the activity and mobility of complex V was altered. The distinct cristae-related orthogonal trajectories of complex V were obliterated. Moreover, a mobile subpopulation of complex V was found in the inner boundary membrane. The observed changes in the ratio of dimeric/monomeric complex V, respectively less mobile/more mobile complex V and its activity changes were reversible. In IF1-KO cells, in which ATP hydrolysis is not inhibited by IF1, complex V was more mobile, while inhibition of ATP hydrolysis by BMS-199264 reduced the mobility of complex V. Taken together, these data support the existence of different subpopulations of complex V, ATP synthase and ATP hydrolase, the latter with higher mobility and probably not prevailing at the cristae edges. Obviously, complex V reacts quickly and reversibly to metabolic conditions, not only by functional, but also by spatial and structural reorganization.

Altered short chain fatty acid profiles induced by dietary fiber intervention regulate AMPK levels and intestinal homeostasis

Butanoate-mediated maintenance of intestinal integrity and homeostasis and the AMPK-dependent co-regulated pathway.