Illuminating intracellular signaling and molecules for single cell analysis

Ebselen analogues delay disease onset and its course in fALS by on-target SOD-1 engagement

Amyotrophic lateral sclerosis (ALS) selectively affects motor neurons. SOD1 is the first causative gene to be identified for ALS and accounts for at least 20% of the familial (fALS) and up to 4% of sporadic (sALS) cases globally with some geographical variability. The destabilisation of the SOD1 dimer is a key driving force in fALS and sALS. Protein aggregation resulting from the destabilised SOD1 is arrested by the clinical drug ebselen and its analogues (MR6-8-2 and MR6-26-2) by redeeming the stability of the SOD1 dimer. The in vitro target engagement of these compounds is demonstrated using the bimolecular fluorescence complementation assay with protein-ligand binding directly visualised by co-crystallography in G93A SOD1. MR6-26-2 offers neuroprotection slowing disease onset of SOD1G93A mice by approximately 15 days. It also protected neuromuscular junction from muscle denervation in SOD1G93A mice clearly indicating functional improvement.

A novel turn-on fluorescent sensor for the sensitive detection of glutathione via gold nanocluster preparation based on controllable ligand-induced etching

In this study, we report a facile one-pot chemical etching approach to simply and rapidly prepare gold nanoclusters capped with luminol (Lum-AuNCs) in an alkaline aqueous solution at room temperature. A series of characterization studies have been carried out to explore the morphology, the optical properties and chemical components of Lum-AuNCs. The average diameter of Lum-AuNCs is 1.8 ± 0.3 nm, exhibiting fluorescence near 510 nm upon excitation at 420 nm with a quantum yield of 14.29% and an average fluorescence lifetime of 9.47 ns. On the basis of the ligand-induced etching of glutathione (GSH) to the intermediate (luminol capped gold nanoparticles, abbreviated as Lum-AuNPs), a novel and simple method for the fluorescence determination of GSH has been established. The method displays a good linear response in the range of 0.05-300 μM toward GSH with a limit of detection of 35 nM. This detection strategy with high sensitivity and selectivity facilitates its practical application for the detection of GSH levels in cell extracts. The in vitro cell results illustrate that Lum-AuNCs have good cytocompatibility and can be used to readily differentiate normal cells and tumor cells.

Bioluminescence Measurement of Time-Dependent Dynamic Changes of CYP-Mediated Cytotoxicity in CYP-Expressing Luminescent HepG2 Cells

We sought to develop a cell-based cytotoxicity assay using human hepatocytes, which reflect the effects of drug-metabolizing enzymes on cytotoxicity. In this study, we generated luminescent human hepatoblastoma HepG2 cells using the mouse artificial chromosome vector, in which click beetle luciferase alone or luciferase and major drug-metabolizing enzymes (CYP2C9, CYP2C19, CYP2D6, and CYP3A4) are expressed, and monitored the time-dependent changes of CYP-mediated cytotoxicity expression by bioluminescence measurement. Real-time bioluminescence measurement revealed that compared with CYP-non-expressing cells, the luminescence intensity of CYP-expressing cells rapidly decreased when the cells were treated with low concentrations of aflatoxin B1 or primaquine, which exhibits cytotoxicity in the presence of CYP3A4 or CYP2D6, respectively. Using kinetics data obtained by the real-time bioluminescence measurement, we estimated the time-dependent changes of 50% inhibitory concentration (IC₅₀) values in the aflatoxin B1- and primaquine-treated cell lines. The first IC₅₀ value was detected much earlier and at a lower concentration in primaquine-treated CYP-expressing HepG2 cells than in primaquine-treated CYP-non-expressing cells, and the decrease of IC₅₀ values was much faster in the former than the latter. Thus, we successfully monitored time- and concentration-dependent dynamic changes of CYP-mediated cytotoxicity expression in CYP-expressing luminescent HepG2 cells by means of real-time bioluminescence measurement.

Using Chromatin-Nuclear Receptor Interactions to Quantitate Endocrine, Paracrine, and Autocrine Signaling

Hormone-activated nuclear receptors (NRs) control myriad cellular processes. The classical paradigm for hormone delivery is secretion from endocrine organs and blood-borne distribution to responding cells. However, many hormones can also be synthesized in the same tissues in which responding cells are found (paracrine signaling). In both endocrine and paracrine signaling, numerous factors affect hormone availability to target cell NRs, including hormone access to and sequestration by carrier proteins, transport across cell membranes, metabolism, and receptor availability. These factors can differ dramatically during development, between anatomical locations, and across cell types, and may cause highly variable responses to the same hormone signal. This has been difficult to study because current approaches are unable to quantify cell-intrinsic exposure to NR hormone ligands, precluding assessment of cell-specific hormone access and signaling. We have used the ligand-dependent interaction of the endogenous glucocorticoid (GC) receptor with chromatin as a biosensor that quantifies systemic access of GCs to cells within tissues at the single cell level, showing that tissues are buffered against circulating GCs. This approach also showed highly targeted paracrine GC signaling within the thymus, where GCs promote the positive selection of thymocytes with moderate affinity for self-antigens and the development of a safe and effective T-cell repertoire. We believe that this and complementary biosensor approaches will be useful to identify endocrine and paracrine target cells in situ and quantify their exposure to hormones regardless of the mode of delivery.

True one cell chemical analysis: a review

The constantly growing field of True One Cell (TOC) analysis has provided important information on the direct chemical composition of various cells and cellular components.

Cell-Based Biosensors Based on Intein-Mediated Protein Engineering for Detection of Biologically Active Signaling Molecules

Live-cell-based biosensors have emerged as a useful tool for biotechnology and chemical biology. Genetically encoded sensor cells often use bimolecular fluorescence complementation or fluorescence resonance energy transfer to build a reporter unit that suffers from nonspecific signal activation at high concentrations. Here, we designed genetically encoded sensor cells that can report the presence of biologically active molecules via fluorescence-translocation based on split intein-mediated conditional protein trans-splicing (PTS) and conditional protein trans-cleavage (PTC) reactions. In this work, the target molecules or the external stimuli activated intein-mediated reactions, which resulted in activation of the fluorophore-conjugated signal peptide. This approach fully valued the bond-making and bond-breaking features of intein-mediated reactions in sensor construction and thus eliminated the interference of false-positive signals resulting from the mere binding of fragmented reporters. We could also avoid the necessity of designing split reporters to refold into active structures upon reconstitution. These live-cell-based sensors were able to detect biologically active signaling molecules, such as Ca2+ and cortisol, as well as relevant biological stimuli, such as histamine-induced Ca2+ stimuli and the glucocorticoid receptor agonist, dexamethasone. These live-cell-based sensing systems hold large potential for applications such as drug screening and toxicology studies, which require functional information about targets.

1001 lights: luciferins, luciferases, their mechanisms of action and applications in chemical analysis, biology and medicine

Bioluminescence (BL) is a spectacular phenomenon involving light emission by live organisms. It is caused by the oxidation of a small organic molecule, luciferin, with molecular oxygen, which is catalysed by the enzyme luciferase. In nature, there are approximately 30 different BL systems, of which only 9 have been studied to various degrees in terms of their reaction mechanisms. A vast range of in vitro and in vivo analytical techniques have been developed based on BL, including tests for different analytes, immunoassays, gene expression assays, drug screening, bioimaging of live organisms, cancer studies, the investigation of infectious diseases and environmental monitoring. This review aims to cover the major existing applications for bioluminescence in the context of the diversity of luciferases and their substrates, luciferins. Particularly, the properties and applications of d-luciferin, coelenterazine, bacterial, Cypridina and dinoflagellate luciferins and their analogues along with their corresponding luciferases are described. Finally, four other rarely studied bioluminescent systems (those of limpet Latia, earthworms Diplocardia and Fridericia and higher fungi), which are promising for future use, are also discussed.

Fluorescent and luminescent fusion proteins for analyses of amyloid beta peptide aggregation

The amyloid beta (Aβ) peptide is regarded as a causative agent of Alzheimer's disease. In this study, fluorescent and luminescent fusion proteins were constructed to analyze Aβ aggregation. A system was developed to monitor changes in luminescence that provides information about Aβ aggregation. In the presence of monomeric Aβ, the fusion protein exhibits higher luminescence intensity, and the luminescence intensity is diminished after aggregation of the fusion protein and Aβ. In contrast, the fluorescence is sustained in the presence of Aβ. In the absence of Aβ, the fusion protein self-aggregates, and its luminescence and fluorescence are quenched, thus decreasing the background fluorescence and enhancing the detection of Aβ inside and outside the cells. The ratio of the luminescence intensity to the fluorescence intensity would allow the aggregation degrees of Aβ to be distinguished. This study would be a promising method for analyzing the aggregation state of a particular amyloid protein/peptide (monomer, oligomer, or fibril), as well as the distribution of the amyloid protein/peptide within and at the cell surface, by using a single fusion protein. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

A Tale Of Two Luciferins: Fungal and Earthworm New Bioluminescent Systems

Bioluminescence, the ability of a living organism to produce light through a chemical reaction, is one of Nature's most amazing phenomena widely spread among marine and terrestrial species. There are various different mechanisms underlying the emission of "cold light", but all involve a small molecule, luciferin, that provides energy for light-generation upon oxidation, and a protein, luciferase, that catalyzes the reaction. Different species often use different proteins and substrates in the process, which suggests that the ability to produce light evolved independently several times throughout evolution. Currently, it is estimated that there are more than 30 different mechanisms of bioluminescence. Even though the chemical foundation underlying the bioluminescence phenomenon is by now generally understood, only a handful of luciferins have been isolated and characterized. Today, the known bioluminescence reactions are used as indispensable analytical tools in various fields of science and technology. A pressing need for new bioluminescent analytical techniques with a wider range of practical applications stimulates the search and chemical studies of new bioluminescent systems. In the past few years two such systems were unraveled: those of the earthworms Fridericia heliota and the higher fungi. The luciferins of these two systems do not share structural similarity with the previously known ones. This Account will survey structure elucidation of the novel luciferins and identification of their mechanisms of action. Fridericia luciferin is a key component of a novel ATP-dependent bioluminescence system. Structural studies were performed on 0.005 mg of natural substance and revealed its unusual extensively modified peptidic nature. Elucidation of Fridericia oxyluciferin revealed that oxidative decarboxylation of a lysine fragment of luciferin supplies energy for light generation, while a fluorescent CompX moiety remains intact and serves as a light emitter. Along with luciferin, a number of its natural analogs were found in the extracts of worm biomass. They occurred to be highly unusual modified peptides comprising a set of amino acids, including threonine, aminobutyric acid, homoarginine, unsymmetrical N,N-dimethylarginine and extensively modified tyrosine. These natural compounds represent a unique peptide chemistry found in terrestrial animals and raise novel questions concerning their biosynthetic origin. Also in this Account we discuss identification of the luciferin of higher fungi 3-hydroxyhispidin which is biosynthesized by oxidation of the precursor hispidin, a known fungal and plant secondary metabolite. Furthermore, it was shown that 3-hydroxyhispidin leads to bioluminescence in extracts from four diverse genera of luminous fungi, thus suggesting a common biochemical mechanism for fungal bioluminescence.

The Effect of Surface Charge Saturation on Heat-induced Aggregation of Firefly Luciferase

We present here the effect of firefly luciferase surface charge saturation and the presence of some additives on its thermal-induced aggregation. Three mutants of firefly luciferase prepared by introduction of surface Arg residues named as 2R, 3R and 5R have two, three and five additional arginine residues substituted at their surface compared to native luciferase; respectively. Turbidimetric study of heat-induced aggregation indicates that all three mutants were reproducibly aggregated at higher rates relative to wild type in spite of their higher thermostability. Among them, 2R had most evaluated propensity to heat-induced aggregation. Therefore, the hydrophilization followed by appearing of more substituted arginine residues with positive charge on the firefly luciferase surface was not reduced its thermal aggregation. Nevertheless, at the same condition in the presence of charged amino acids, e.g. Arg, Lys and Glu, as well as a hydrophobic amino acid, e.g. Val, the heat-induced aggregation of wild type and mutants of firefly luciferases was markedly decelerated than those in the absence of additives. On the basis of obtained results it seems, relinquishment of variety in charge of amino acid side chains, they via local interactions with proteins cause to decrease rate and extent of their thermal aggregation.

Detection of glutathione within single erythrocyte of different ages and pathological state using microfluidic chips coupled with laser induced fluorescence

As a major factor participating in the organism antioxidation and detoxification process, GSH is of vital importance to human beings. Detecting GSH content in single cells is significant to diagnosis and prevention of many diseases. In this work, the amount of GSH within single erythrocytes was detected and analyzed via statistical analysis. All erythrocytes tested were collected from people in different ages and people of different pathological states. The correlation between GSH level, age and pathological state were investigated. Results showed that the GSH level in erythrocytes decreased with the ages of patients increased. There was little difference between the GSH level in erythrocytes from people who had chronic diseases (hyperglycemia, hyperlipidemia and hypertension) and from healthy people. However, the GSH level in erythrocytes from people who had inflammation (myocarditis, nephritis and gastritis) was generally higher than that from the healthy people. This study provides basic data for researches of cell senescence and cytopathic effect and is helpful to diagnosis and prevention of diseases. In addition, it also provides a simple and effective method for rapid GSH detection within single cell.

Quantitative analysis of receptor tyrosine kinase-effector coupling at functionally relevant stimulus levels

A major goal of current signaling research is to develop a quantitative understanding of how receptor activation is coupled to downstream signaling events and to functional cellular responses. Here, we measure how activation of the RET receptor tyrosine kinase on mouse neuroblastoma cells by the neurotrophin artemin (ART) is quantitatively coupled to key downstream effectors. We show that the efficiency of RET coupling to ERK and Akt depends strongly on ART concentration, and it is highest at the low (∼100 pM) ART levels required for neurite outgrowth. Quantitative discrimination between ERK and Akt pathway signaling similarly is highest at this low ART concentration. Stimulation of the cells with 100 pM ART activated RET at the rate of ∼10 molecules/cell/min, leading at 5-10 min to a transient peak of ∼150 phospho-ERK (pERK) molecules and ∼50 pAkt molecules per pRET, after which time the levels of these two signaling effectors fell by 25-50% while the pRET levels continued to slowly rise. Kinetic experiments showed that signaling effectors in different pathways respond to RET activation with different lag times, such that the balance of signal flux among the different pathways evolves over time. Our results illustrate that measurements using high, super-physiological growth factor levels can be misleading about quantitative features of receptor signaling. We propose a quantitative model describing how receptor-effector coupling efficiency links signal amplification to signal sensitization between receptor and effector, thereby providing insight into design principles underlying how receptors and their associated signaling machinery decode an extracellular signal to trigger a functional cellular outcome.

Novel split-luciferase-based genetically encoded biosensors for noninvasive visualization of Rho GTPases

Rho family GTPases are critical regulators of many important cellular processes and the dysregulation of their activities is implicated in a variety of human diseases including oncogenesis and propagation of malignancy. The traditional methods, such as “pull-down” or two-hybrid procedures, are poorly suited to dynamically evaluate the activity of Rho GTPases, especially in living mammalian cells. To provide a novel alternative approach to analyzing Rho GTPase-associated signaling pathways in vivo, we developed a series of bioluminescent biosensors based on the genetically engineered firefly luciferase. These split-luciferase-based biosensors enable non-invasive visualization and quantification of the activity of Rho GTPases in living subjects. The strategy is to reasonably split the gene of firefly luciferase protein into two inactive fragments and then respectively fuse the two fragments to Rho GTPase and the GTPase-binding domain (GBD) of the specific effector. Upon Rho GTPase interacting with the binding domain in a GTP-dependent manner, these two luciferase fragments are brought into close proximity, leading to luciferase reconstitution and photon production in the presence of the substrate. Using these bimolecular luminescence complementation (BiLC) biosensors, we successfully visualized and quantified the activities of the three best characterized Rho GTPases by measuring the luminescence in living cells. We also experimentally investigated the sensitivity of these Rho GTPase biosensors to upstream regulatory proteins and extracellular ligands without lysing cells and doing labor-intensive works. By virtue of the unique functional characteristics of bioluminescence imaging, the BiLC-based biosensors provide an enormous potential for in vivo imaging of Rho GTPase signaling pathways and high-throughput screening of therapeutic drugs targeted to Rho GTPases and (or) upstream molecules in the near future.

Approaches to engineer stability of beetle luciferases

Luciferase enzymes from fireflies and other beetles have many important applications in molecular biology, biotechnology, analytical chemistry and several other areas. Many novel beetle luciferases with promising properties have been reported in the recent years. However, actual and potential applications of wild-type beetle luciferases are often limited by insufficient stability or decrease in activity of the enzyme at the conditions of a particular assay. Various examples of genetic engineering of the enhanced beetle luciferases have been reported that successfully solve or alleviate many of these limitations. This mini-review summarizes the recent advances in development of mutant luciferases with improved stability and activity characteristics. It discusses the common limitations of wild-type luciferases in different applications and presents the efficient approaches that can be used to address these problems.