Concentration-dependent Changes Research Articles

Concentration-dependent changes in the reaction behavior of whey proteins: Diffusion-controlled or transition state-controlled reactions?

The denaturation of whey proteins can be used in a controlled manner to design protein-based products with new specific structures or functionalities e.g., meat and dairy analogues, as well as protein-based emulsifiers and thickeners with specific functionalities. For this, the influence of thermal and/or mechanical treatment, and milieu conditions including the protein concentration, on the denaturation reaction must be determined. Previous results of whey protein denaturation at concentrations above 50% suggested a strong change in the reaction behavior of whey proteins compared to more dilute conditions (concentration < 20%). Therefore, in this study the reaction behavior of whey proteins at a broad range of concentrations 17–70% after thermal and mechanical treatment was investigated. The results of this study suggest that the reaction limiting step depends on the concentration of the system. Calculations of the collision rate as a function of protein concentration indicate that the collision theory can only be applied to explain the denaturation reaction mechanisms for certain conditions. At dilute- and semi-dilute conditions, since the protein molecules are quasi-isolated and unentangled, the diffusion of molecules controls the aggregation step, and consequently the denaturation reaction is a diffusion-limited reaction. In contrast at concentrated conditions, the protein molecules are entangled, which can hinder the unfolding of the globular structure and consequently the formation of a transition-state becomes the limiting step.

Label-Free Electrochemical Sensor for Rapid Bacterial Pathogen Detection Using Vancomycin-Modified Highly Branched Polymers.

Rapid point of care tests for bacterial infection diagnosis are of great importance to reduce the misuse of antibiotics and burden of antimicrobial resistance. Here, we have successfully combined a new class of non-biological binder molecules with electrochemical impedance spectroscopy (EIS)-based sensor detection for direct, label-free detection of Gram-positive bacteria making use of the specific coil-to-globule conformation change of the vancomycin-modified highly branched polymers immobilized on the surface of gold screen-printed electrodes upon binding to Gram-positive bacteria. Staphylococcus carnosus was detected after just 20 min incubation of the sample solution with the polymer-functionalized electrodes. The polymer conformation change was quantified with two simple 1 min EIS tests before and after incubation with the sample. Tests revealed a concentration dependent signal change within an OD600 range of Staphylococcus carnosus from 0.002 to 0.1 and a clear discrimination between Gram-positive Staphylococcus carnosus and Gram-negative Escherichia coli bacteria. This exhibits a clear advancement in terms of simplified test complexity compared to existing bacteria detection tests. In addition, the polymer-functionalized electrodes showed good storage and operational stability.

Thermodynamics and structure of model bio-membrane of liver lipids in presence of imidazolium-based ionic liquids

Ionic liquids (ILs) are the attractions of researchers today due to their vast area of potential applications. For biomedical uses, it becomes essential to understand their interactions with cellular membrane. Here, the membrane is mimicked with lipid bilayer and monolayer composed of liver lipids extract. Three archetypal imidazolium based ILs, 1-decyl-3-methylimidazolium tetrafluoroborate ([DMIM][BF4] or [C10MIM][BF4]), 1-octyl-3-methylimidazolium tetrafluoroborate, ([OMIM][BF4] or [C8MIM][BF4]) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4] or [C2MIM][BF4]) having different alkyl chain lengths are used in the present study. The isothermal titration calorimetry (ITC) measurements showed that [DMIM][BF4] interacts strongest with the liver lipid membrane compared to other two ILs which have relatively shorter alkyl chain length. The low values of stoichiometry ratio of ILs indicates that ILs penetrate within the core of the lipid bilayer. The interaction of ILs with the liver lipid membrane is found to be mainly driven by entropy which could be due to the change in the structure of the lipid membrane at local or global scales. Dynamic light scattering (DLS) measurements indicate that there are no changes in the size of vesicles due to addition of [DMIM][BF4] indicating stability of the vesicles. On the other hand, x-ray reflectivity (XRR) measurements showed a concentration dependent change in the monolayer structure. At low concentration of the IL, the monolayer thickness decreases, exhibiting an increase in the electron density of the layer. However, at higher concentrations, the monolayer thickness increases proving a concentration dependent effects of the IL on the arrangement of the molecules.

Systematic Identification of MACC1-Driven Metabolic Networks in Colorectal Cancer.

Simple SummaryWe aimed at the systematic identification of MACC1-driven metabolic networks in colorectal cancer. By this systematic analysis, our studies revealed new insights into MACC1-caused metabolomics phenotypes: (i) MACC1 fosters metastasis by rewiring glucose and glutamine metabolism, (ii) MACC1 increases glucose use by enhanced surface GLUT1; (iii) MACC1 increases glutamine and pyruvate use by enhanced uptake, and (iv) MACC1 reduces glutamine flux but has minor effects on pyruvate flux. Therefore, MACC1 is an important regulator of cancer metabolism.MACC1 is a prognostic and predictive metastasis biomarker for more than 20 solid cancer entities. However, its role in cancer metabolism is not sufficiently explored. Here, we report on how MACC1 impacts the use of glucose, glutamine, lactate, pyruvate and fatty acids and show the comprehensive analysis of MACC1-driven metabolic networks. We analyzed concentration-dependent changes in nutrient use, nutrient depletion, metabolic tracing employing 13C-labeled substrates, and in vivo studies. We found that MACC1 permits numerous effects on cancer metabolism. Most of those effects increased nutrient uptake. Furthermore, MACC1 alters metabolic pathways by affecting metabolite production or turnover from metabolic substrates. MACC1 supports use of glucose, glutamine and pyruvate via their increased depletion or altered distribution within metabolic pathways. In summary, we demonstrate that MACC1 is an important regulator of metabolism in cancer cells.

Probing the interaction of glutathione with different shape of silver-nanoparticles by optical spectroscopy

To understand the influence of the shape of the particles on assay sensitivity using surface plasmon resonance phenomenon (SPR), three different types of silver nanoparticles spherical (SAgNPs), triangular (TAgNPs), and octahedral (OAgNPs) of around 20 nm in size and similar aspect ratio were analyzed after interaction with glutathione (GSH). FTIR peak of Ag-S peak at 2312 cm−1and 2305 cm−1, 2312 cm−1 in SAgNPs, TAgNPs, and OAgNPs respectively confirming interactions. DLS and TEM studies agglomeration of SAgNPs and TAgNPs but not in OAgNPs due to the interaction. Detailed SPR analysis showed interaction of GSH with nanoparticles resulted in alteration of three characteristic features namely changes a decrease in peak height at (506 nm and 398 nm) an increase in peak height (987 nm and 987 nm) and bathochromic shift of absorption peak in 600−700 nm range in the case of SAgNPs and TAgNPs, but no such changes were observed for OAgNPs. To understand the physical phenomenon Marquardt-Levenberg algorithm based non-linear curve fitting analysis where done. In the fitting analysis, GSH concentration-dependent changes of the AS characteristics were fitted to polynomials of different orders, and from the weighted residuals and 95 % prediction interval of the fits, the best models are suggested that describe the changes in the AS of the triangular AgNPs (TAgNPs). The probable reason for the phenomenon lies in surface protection and accessibility of the interaction surface. Unlike SAgNPs, in TAgNPs and OAgNPs the edges of each side are loosely protected with Polyvinylpyrrolidone (PVP) allowing enhanced interaction with GSH from the edges and linear joining. Further, the majority of the ridge of the surface of OAgNPs are not accessible to the other particles which reduce the stability of interaction and joining. As a cumulative result TAgNPs are the best choice for GSH titration among these 3 types of particles.

Cation-Selectivity of a Self-Assembled Peptide Pore in Planar Phospholipid Bilayers using Electrical Impedance Spectroscopy

GALA is a 30-residue, amphipathic peptide that self-assembles into multimeric, transmembrane pores in a pH-dependent fashion. Based on kinetic data and dye release assays, previous studies have reported that in liposomes GALA forms large multimeric pores composed of 8-12 peptides, but no direct structural information is available. In this study, we characterize the pore size and multimeric structure of GALA pores in planar phospholipid bilayers using electrical impedance spectroscopy (EIS) and molecular dynamics (MD) simulations. Specifically, we used a number of alkaline earth cations and the large organic cations, Choline and TEA, to estimate the pore size by measuring concentration-dependent changes in membrane conduction. This data was combined with MD simulations to estimate the multimeric state of GALA pores. We report that in planar tethered lipid bilayers composed of POPC, GALA pores likely consist of six peptide monomers rather than eight to twelve monomers as previously reported in liposomes. We further demonstrate, for the first time, that GALA exhibits cation selectivity, which is based on the free energy of hydration of the ions. We propose that the difference in predicted pore structure between planar bilayers and lipid vesicles exemplifies the importance of phospholipid bilayer structure, which include lipid packing, area per lipid, hydration or charge distribution caused by asymmetry between the inner and outer bilayer leaflets. These bilayer properties could have significant effects on the aggregation of transmembrane helical structures.

Concentration-dependent oscillation of specific loss power in magnetic nanofluid hyperthermia

Magnetic dipole coupling between the colloidal superparamagnetic nanoparticles (SPNPs) depending on the concentration has been paid significant attention due to its critical role in characterizing the Specific Loss Power (SLP) in magnetic nanofluid hyperthermia (MNFH). However, despite immense efforts, the physical mechanism of concentration-dependent SLP change behavior is still poorly understood and some contradictory results have been recently reported. Here, we first report that the SLP of SPNP MNFH agent shows strong concentration-dependent oscillation behavior. According to the experimentally and theoretically analyzed results, the energy competition among the magnetic dipole interaction energy, magnetic potential energy, and exchange energy, was revealed as the main physical reason for the oscillation behavior. Empirically demonstrated new finding and physically established model on the concentration-dependent SLP oscillation behavior is expected to provide biomedically crucial information in determining the critical dose of an agent for clinically safe and highly efficient MNFH in cancer clinics.

Electrochemistry, ion adsorption and dynamics in the double layer: a study of NaCl(aq) on graphite.

Graphite and related sp2 carbons are ubiquitous electrode materials with particular promise for use in e.g., energy storage and desalination devices, but very little is known about the properties of the carbon–electrolyte double layer at technologically relevant concentrations. Here, the (electrified) graphite–NaCl(aq) interface was examined using constant chemical potential molecular dynamics (CμMD) simulations; this approach avoids ion depletion (due to surface adsorption) and maintains a constant concentration, electroneutral bulk solution beyond the surface. Specific Na+ adsorption at the graphite basal surface causes charging of the interface in the absence of an applied potential. At moderate bulk concentrations, this leads to accumulation of counter-ions in a diffuse layer to balance the effective surface charge, consistent with established models of the electrical double layer. Beyond ∼0.6 M, however, a combination of over-screening and ion crowding in the double layer results in alternating compact layers of charge density perpendicular to the interface. The transition to this regime is marked by an increasing double layer size and anomalous negative shifts to the potential of zero charge with incremental changes to the bulk concentration. Our observations are supported by changes to the position of the differential capacitance minimum measured by electrochemical impedance spectroscopy, and are explained in terms of the screening behaviour and asymmetric ion adsorption. Furthermore, a striking level of agreement between the differential capacitance from solution evaluated in simulations and measured in experiments allows us to critically assess electrochemical capacitance measurements which have previously been considered to report simply on the density of states of the graphite material at the potential of zero charge. Our work shows that the solution side of the double layer provides the more dominant contribution to the overall measured capacitance. Finally, ion crowding at the highest concentrations (beyond ∼5 M) leads to the formation of liquid-like NaCl clusters confined to highly non-ideal regions of the double layer, where ion diffusion is up to five times slower than in the bulk. The implications of changes to the speciation of ions on reactive events in the double layer are discussed.

1-Nitropyrene Induced Reactive Oxygen Species-Mediated Apoptosis in Macrophages through AIF Nuclear Translocation and AMPK/Nrf-2/HO-1 Pathway Activation.

1-Nitropyrene (1-NP), one of the most abundant nitropolycyclic aromatic hydrocarbons (nitro-PAHs), is generated from the incomplete combustion of carbonaceous organic compounds. 1-NP is a specific marker of diesel exhaust and is an environmental pollutant and a probable carcinogen. Macrophages participate in immune defense against the invasive pathogens in heart, lung, and kidney infection diseases. However, no evidence has indicated that 1-NP induces apoptosis in macrophages. In the present study, 1-NP was found to induce concentration-dependent changes in various cellular functions of RAW264.7 macrophages including cell viability reduction; apoptosis generation; mitochondrial dysfunction; apoptosis-inducing factor (AIF) nuclear translocation; intracellular ROS generation; activation of the AMPK/Nrf-2/HO-1 pathway; changes in the expression of BCL-2 family proteins; and depletion of antioxidative enzymes (AOE), such as glutathione peroxidase (GPx), catalase (CAT), and superoxide dismutase (SOD) These results indicate that 1-NP induced apoptosis in macrophages through AIF nuclear translocation and ROS generation due to mitochondrial dysfunction and to the depletion of AOE from the activation of the AMPK/Nrf-2/HO-1 pathway.

Thermodynamic and structural study of DMPC-alkanol systems.

The thermodynamic and structural behaviors of lamellar dimyristoylphosphatidylcholine-alkanol (abbreviation DMPC-CnOH, n = 8-18 is the even number of carbons in the alkyl chain) systems were studied by using DSC and SAXD/WAXD methods at a 0-0.8 CnOH : DMPC molar ratio range. Up to n≤ 10 a significant biphasic effect depending on the main transition temperature tm on the CnOH concentration was observed. Two breakpoints were revealed: turning point (TP), corresponding to the minimum, and threshold concentration (cT), corresponding to the end of the biphasic tendency. These breakpoints were also observed in the alkanol concentration dependent change in the enthalpy of the main transition ΔHm. In the case of CnOHs with n > 10 we propose a marked shift of TP and cT to very low concentrations; consequently, only increase of tm is observed. A partial phase diagram was constructed for a pseudo-binary DMPC-C12OH system. We suggest a fluid-fluid immiscibility of the DMPC-C12OH system above cT with a consequent formation of domains with different C12OH contents. At a constant CnOH concentration, the effects of CnOHs on ΔHm and bilayer repeat distance were found to depend predominantly on the mismatch between CnOH and lipid chain lengths. Observed effects are suggested to be underlined by a counterbalancing effect of interchain van der Waals interactions and headgroup repulsion.

Analysis of the Hindriks and van Putten model for propofol anesthesia: Limitations and extensions

We present a detailed analysis of the Hindriks and van Putten thalamocortical mean-field model for propofol anesthesia [NeuroImage 60(23), 2012]. The Hindriks and van Putten (HvP) model predicts increases in delta and alpha power for moderate (up to 130%) prolongation of GABAA inhibitory response, corresponding to light anesthetic sedation. Our analysis reveals that, for deeper anesthetic effect, the model exhibits an unexpected abrupt jump in cortical activity from a low-firing state to an extremely high-firing stable state (∼250 spikes/s), and remains locked there even at GABAA prolongations as high as 300% which would be expected to induce full comatose suppression of all firing activity. We demonstrate that this unphysiological behavior can be completely suppressed with appropriate tuning of the parameters controlling the sigmoidal functions that map soma voltage to firing rate for the excitatory and inhibitory neural populations, coupled with elimination of the putative population-dependent anesthetic efficacies introduced in the HvP model. The modifications reported here constrain the anesthetized brain activity into a biologically plausible range in which the cortex now has access to a moderate-firing state (“awake”) and a low-firing (“anesthetized”) state such that the brain can transition from “awake” to “anesthetized” states at a critical level of drug concentration. The modified HvP model predicts a drug–effect hysteresis in which the drug concentration required for induction is larger than that at emergence. In addition, the revised model shows a decrease in the intensity and frequency of alpha-band fluctuations, transitioning to delta-band dominance, with deepening anesthesia. These predicted drug concentration-dependent changes in EEG dynamics are consistent with clinical reports.

Diesel exhaust particle role on gut microbiome and onset of Alzheimer disease neuroinflammation

AbstractBackgroundRecent evidence has emerged to show that diesel exhaust particulate (DEP) pollution can double the risk of getting dementia. Evidence suggest that exposure to high levels of air pollution are significantly more likely to develop dementia‐related diseases including Alzheimer’s disease. DEP is primarily composed of polycyclic aromatic hydrocarbons (PAHs) and nitro‐substituted polycyclic aromatic hydrocarbons (n‐PAHs). PAHs have previously been shown to undergo biotransformation through interactions with human colonic microbiota. The goal of the present study is to determine if DEP may influence selective gut microbiota. We will eventually identify gut‐brain‐axis mechanisms associated with DEP mediated neuroinflammatory mechanisms through microbiota dysbiosis.MethodUsing an in vitro model of the human gastrointestinal tract, EBIOME, we are exploring the human gut bacteria exposed to various concentrations of diesel exhaust particulate matter. Bacterial species were quantified over an extended time‐course to monitor log‐scale changes in colony survival and growth. In order to obtain higher resolution of gut microbiome species meta‐genomic analysis will be also conducted.ResultThe current studies have identified concentration dependent changes in microbiome biodiversity. Through ongoing analysis, it is anticipated that altered biodiversity will lead to decreases in the production of brain penetrant metabolites, such as short‐chain fatty acids including butyrate, acetate, and propionate.ConclusionOur studies provide novel information regarding the role of the gut‐brain‐axis in neuroinflammation in Alzheimer’s disease and other forms of dementia.

Measurement of Alcohol-Dependent Physiological Changes in Red Blood Cells Using Resistive Pulse Sensing

Alcohol exposure has been postulated to adversely affect the physiology and function of the red blood cells (RBCs). The global pervasiveness of alcohol abuse, causing health issues and social problems, makes it imperative to resolve the physiological effects of alcohol on RBC physiology. Alcohol consumed recreationally or otherwise almost immediately alters cell physiology in ways that is subtle and still unresolved. In this paper, we introduce a high-resolution device for quantitative electrofluidic measurement of changes in RBC volume upon alcohol exposure. We present an exhaustive calibration of our device using model cells to measure and resolve volume changes down to 0.6 fL. We find an RBC shrinkage of 5.3% at 0.125% ethanol (the legal limit in the United States) and a shrinkage of 18.5% at 0.5% ethanol (the lethal limit) exposure. Further, we also measure the time dependence of cell volume shrinkage (upon alcohol exposure) and then recovery (upon alcohol removal) to quantify shrinkage and recovery of RBC volumes. This work presents the first direct quantification of temporal and concentration-dependent changes in red blood cell volume upon ethanol exposure. Our device presents a universally applicable high-resolution and high-throughput platform to measure changes in cell physiology under native and diseased conditions.

A photo-induced electron transfer based reversible fluorescent chemosensor for specific detection of mercury (II) ions and its applications in logic gate, keypad lock and real samples

A quantitative mercuric detection is very important in the environmental and biological systems. In this paper, we report a novel bis-rhodanine derived fluorescent chemosensor for recognition of Hg2+ ion in DMSO-H2O (1:1) medium. The ‘turn-on’ fluorescence response was exhibited specifically toward Hg2+ over other metal ions by receptor R2 at 410 nm, which could be ascribed to the restriction of photo-induced electron transfer (PET) process and chelation-enhanced fluorescence (CHEF) effect upon the complexation with mercury ions. The complexing stoichiometry of receptor R2 to Hg2+ was estimated to be 1:1 according to Job’s plot experiments. The limit of detection was calculated to be 7.33 × 10−7 M based on the concentration dependent emission changes with good association constant of 8.97 × 104 M−1. As a result, we express that receptor R2 is a promising candidate for Hg2+ recognition without any significant interference of other co-existing cations. The receptor R2 was successfully applied to molecular logic and keypad lock applications and real water samples to determine its potential applications.

Covalent organic frameworks (COF-300-AR) with unique catalytic performance in luminol chemiluminescence for sensitive detection of serotonin

The covalent organic frameworks (COFs), as excellently desirable nanomaterials for catalytic applications, used in the chemiluminescence (CL) system is far from fully developed. Herein, in this work, the COF-300-AR as a catalyst notably increasing the CL intensity of luminol system in alkaline solution with no extra oxidants were first put forward. The presence of serotonin can dramatically decrease the CL of luminol-COF-300-AR system, thus causing the concentration-dependent change of the quenching efficiency (I0/IS). By utilizing these phenomena, the excellent CL sensing method was established for the detection of serotonin by coupling with flow injection analysis (FIA). Under the optimum conditions, the CL quenching efficiency had a linear increase with the concentration of serotonin ranging from 10 nM to 800 nM, and the limit of detection was 2.3 nM (S/N = 3). The method was utilized for the detection of serotonin in rat serum sample with satisfactory results.

Novel and potent antimicrobial effects of caspofungin on drug-resistant Candida and bacteria

Echinocandins, including caspofungin, micafungin, and anidulafungin, are first-line antifungal agents for the treatment of invasive candidiasis. They exhibit fungicidal activity by inhibiting the synthesis of β-1,3-d-glucan, an essential component of the fungal cell wall. However, they are active only against proliferating fungal cells and unable to completely eradicate fungal cells even after a 24 h drug exposure in standard time-kill assays. Surprisingly, we found that caspofungin, when dissolved in low ionic solutions, had rapid and potent antimicrobial activities against multidrug-resistant (MDR) Candida and bacteria cells even in non-growth conditions. This effect was not observed in 0.9% NaCl or other ion-containing solutions and was not exerted by other echinocandins. Furthermore, caspofungin dissolved in low ionic solutions drastically reduced mature biofilm cells of MDR Candida auris in only 5 min, as well as Candida-bacterial polymicrobial biofilms in a catheter-lock therapy model. Caspofungin displayed ion concentration-dependent conformational changes and intracellular accumulation with increased reactive oxygen species production, indicating a novel mechanism of action in low ionic conditions. Importantly, caspofungin dissolved in 5% glucose water did not exhibit increased toxicity to human cells. This study facilitates the development of new therapeutic strategies in the management of catheter-related biofilm infections.

Bayesian approach for automated quantitative analysis of benchtop NMR data

Low-cost, user-friendly benchtop NMR instruments are often touted as a “one-click” solution for data acquisition, however insufficient peak dispersion in their spectra often reduces the accuracy of quantification and requires user expertise with sophisticated processing tools. Our work aims to facilitate the wide acceptance of benchtop NMR instruments as a viable and effective substitute for cryogenic magnets. We propose an algorithmic approach that completely automates the routine analysis of sets of samples with similar compositions – the problem that often underlies many industrial applications concerned with reaction and process monitoring and quality control. Our solution is rooted in the idea of parametric modelling formulated in terms of Bayesian statistics, which effectively incorporates prior knowledge about the studied system (such as concentration-dependent chemical shift changes) that is usually available in industrial applications. Furthermore, the use of quantum mechanical models for chemical species makes our approach invariant to the spectrometer field strength – a necessary prerequisite for the successful analysis of benchtop data. We demonstrate the performance of our method with two representative sets of samples: mixtures of alcohols and acetates, and aqueous mixtures of biologically relevant species. In these examples, our fully automated analysis of benchtop spectra achieves average errors in concentrations of 0.01 mol/mol and 0.02 mol/mol respectively. Our method is competitive with the traditional processing approaches of well resolved high-field data and has the potential to bring the benefits of NMR even to a small chemistry laboratory.

Thiol-suppressed I2-etching of AuNRs: acetylcholinesterase-mediated colorimetric detection of organophosphorus pesticides.

For the first time it isdemonstrated that sulfhydryl compounds can suppress longitudinal etching of gold nanorods via consuming oxidizers, which provides a new signaling mechanism for colorimetric sensing. As a proof of concept, a colorimetric assay is developed for detecting organophosphorus pesticides, which are most widely used in modern agriculture to improve food production but with high toxicity to animals and the ecological environment. Triazophos was selected as a model organophosphorus pesticide. In the absence of triazophos, the active acetylcholinesterase can catalyze the conversion of acetylthiocholine iodide to thiocholine whose thiol group can suppress the I2-induced etching of gold nanorods. When triazophos is present, the activity of AchE is inhibited, and I2-induced etching of gold nanorods results in triazophos concentration-dependent color change from brown to blue, pink, and red. The aspect ratio of gold nanorods reduced with gradually blue-shifted longitudinal absorption. There was a linear detection range from 0 to 117nM (R2 = 0.9908), the detection limit was 4.69nM, and a good application potential was demonstrated by theassay of real water samples. This method will not only contribute to public monitoring of organophosphorus pesticides but also has verified a new signaling mechanism which will open up a new path to develop colorimetric detection methods. It has been first found that sulfhydryl compounds can suppress longitudinal etching of gold nanorods (AuNRs) via consuming oxidizers, which provides a new signaling mechanism for colorimetric sensing. As a proof of concept, a colorimetric assay is developed for sensitively detecting organophosphorus pesticides (OPs). It will not only contribute to public monitoring of OPs but also has verified a new signaling mechanism which will open up a new path to develop multicolor colorimetric methods.

Biased allosteric modulation of formyl peptide receptor 2 leads to distinct receptor conformational states for pro- and anti-inflammatory signaling

Background and purposeFormyl peptide receptor 2 (FPR2) is a Class A G protein-coupled receptor (GPCR) that interacts with multiple ligands and transduces both proinflammatory and anti-inflammatory signals. These ligands include weak agonists and modulators that are produced during inflammation. The present study investigates how prolonged exposure to FPR2 modulators influence receptor signaling. Experimental approachFluorescent biosensors of FPR2 were constructed based on single-molecule fluorescent resonance energy transfer (FRET) and used for measurement of ligand-induced receptor conformational changes. These changes were combined with FPR2-mediated signaling events and used as parameters for the conformational states of FPR2. Ternary complex models were developed to interpret ligand concentration-dependent changes in FPR2 conformational states. Key resultsIncubation with Ac2−26, an anti-inflammatory ligand of FPR2, decreased FRET intensity at picomolar concentrations. In comparison, WKYMVm (W-pep) and Aβ42, both proinflammatory agonists of FPR2, increased FRET intensity. Preincubation with Ac2−26 at 10 pM diminished W-pep-induced Ca2+ flux but potentiated W-pep-stimulated β-arrestin2 membrane translocation and p38 MAPK phosphorylation. The opposite effects were observed with 10 pM of Aβ42. Neither Ac2−26 nor Aβ42 competed for W-pep binding at the picomolar concentrations. Conclusions and implicationsThe results support the presence of two allosteric binding sites on FPR2, each for Ac2−26 and Aβ42, with high and low affinities. Sequential binding of the two allosteric ligands at increasing concentrations induce different conformational changes in FPR2, providing a novel mechanism by which biased allosteric modulators alter receptor conformations and generate pro- and anti-inflammatory signals.

Surfactant flow and transport in the vadose zone: a numerical experiment

The presence of surfactants in the unsaturated zone is one of the scenarios where the flow depends on the solute concentration. The simulation of flow and transport of surfactants requires the coupling of flow and transport, where the surfactant concentration-dependent changes to water retention (i.e. changes in surface tension and/or contact angle) and hydraulic conductivity need to be considered. This research presents a numerical experiment that compares surfactant flow and transport under intermittent boundary conditions to that of a conservative tracer. A modified version of Hydrus 2D, with the concentration-dependent surface tension and viscosity effects, is used. The numerical experiment examines the effect of surfactant infiltration, redistribution and flushing in a low-water content unsaturated porous medium with a deep water table. The numerical experiment encompasses not only the hysteresis as a result of transient localised drainage and rewetting associated with the surfactant-induced pressure gradients, and the intermittent boundary conditions. The comparison of surfactant flow to that of a conservative tracer indicates significant differences for the same boundary conditions. The results from this experiment will be beneficial for the design and optimisation of infiltration galleries employing surfactants for soil and ground water remediation, as well as for the understanding the flow and transport of grey water in the unsaturated zone.