FRAP and FRET Investigation of α-Synuclein Fibrillization via Liquid-Liquid Phase Separation In Vitro and in HeLa Cells

Liquid-liquid phase separation (LLPS) acts as an important biological phenomenon in membraneless organelle formation. These phase-separated bodies can also act as nucleation centers for disease-associated amyloid formation. Fluorescence recovery after photobleaching (FRAP) is a crucial technique to analyze the material property (liquid or solid) of protein LLPS. On the other hand, Förster resonance energy transfer (FRET) is used to understand the domain-specific involvement (intermolecular interactions) of protein molecules inside the phase-separated droplets. In this protocol, we delineate mechanisms of liquid-to-solid transition of α-synuclein LLPS by using in vitro and in cell FRAP as well as in vitro FRET techniques.

Host-guest interaction aided Zinc carry and delivery by ESIPT active 2-(2'-hydroxyphenyl)benzoxazole

The effect of solvents and supramolecular hosts on the binding of metal ion with an excited state intramolecular proton transfer (ESIPT) active fluorophore 2-(2'-hydroxyphenyl)benzoxazole (HPBO) are investigated to scrutinize a possible metal ion carry and delivery system. The fluorophore forms strong fluorescent complex with Zn²⁺ ion. In aqueous medium, β-cyclodextrin (β-CD) breaks the HPBO-Zn²⁺ complex and encapsulate the freed fluorophore. Hence, the initially blocked ESIPT process is restored by forming an inclusion complex with the host molecules. However, in dimethyl sulphoxide (DMSO), β-CD does not break the complex. But cucurbit[7]uril (CB-7) breaks the complex in both DMSO and water. The tuned emission characteristics are considered for constructing different molecular logic gates. BUFFER, NOT, PASS, IMPLICATION and INHIBIT logic operations are substantiated based on Zn²⁺, CB-7 and β-CD response.

Vaccine-Induced Subcutaneous Granulomas in Goats Reflect Differences in Host–Mycobacterium Interactions between BCG- and Recombinant BCG-Derivative Vaccines

Tuberculous granulomas are highly dynamic structures reflecting the complex host–mycobacterium interactions. The objective of this study was to compare granuloma development at the site of vaccination with BCG and its recombinant derivatives in goats. To characterize the host response, epithelioid cells, multinucleated giant cells (MNGC), T cell subsets, B cells, plasma cells, dendritic cells and mycobacterial antigen were labelled by immunohistochemistry, and lipids and acid-fast bacteria (AFB) were labelled by specific staining. Granulomas with central caseous necrosis developed at the injection site of most goats though lesion size and extent of necrosis differed between vaccine strains. CD4⁺ T and B cells were more scarce and CD8⁺ cells were more numerous in granulomas induced by recombinant derivatives compared to their parental BCG strain. Further, the numbers of MNGCs and cells with lipid bodies were markedly lower in groups administered with recombinant BCG strains. Microscopic detection of AFB and mycobacterial antigen was rather frequent in the area of central necrosis, however, the isolation of bacteria in culture was rarely successful. In summary, BCG and its recombinant derivatives induced reproducibly subcutaneous caseous granulomas in goats that can be easily monitored and surgically removed for further studies. The granulomas reflected the genetic modifications of the recombinant BCG-derivatives and are therefore suitable models to compare reactions to different mycobacteria or TB vaccines.

Modifying the proton transfer of 3,5-bis(2-hydroxyphenyl)-1H-1,2,4-triazole by water, confinement and confined water

The effect of water, confinement and confined water on the proton transfer of 3,5-bis(2-hydroxyphenyl)-1H-1,2,4-triazole (bis-HPTA) was investigated. Water alters the proton transfer process. At higher pH, an anion is formed in water and it undergoes intermolecular proton transfer and forms a keto tautomer. Confinement of molecule in β-cyclodextrin affects the intramolecular proton transfer. It also prevents the intermolecular proton transfer of the anionic form. In reverse micelle, the molecule resides in the interfacial region and interacts with bound water. The intermolecular hydrogen bond of the surfactants opens the intramolecular hydrogen bond in the weaker β-ring of bis-HPTA. It led to single tautomer emission from bis-HPTA. An increase in water amount enhances the relative amount of trans-enol, but predominantly tautomer emission is observed.

Nanoparticle and surfactant controlled switching between proton transfer and charge transfer reaction coordinates

The reaction coordinates of a molecular photo-switch 2-(4'-diethylamino-2'-hydroxyphenyl)-1H-imidazo-[4,5-b]pyridine (DHP) was tuned with a nanoparticle and surfactant. DHP undergoes excited state intramolecular proton transfer (ESIPT) and emits normal and tautomer emissions in N,N-dimethylformamide. Silver nanoparticles suppress the ESIPT and induce twisted intramolecular charge transfer (TICT). Further addition of surfactants alters the process. Interestingly, different surfactants cause different effects. Accordingly, the luminescence characteristics are altered. The anionic surfactant sodium dodecyl sulfate (SDS) restores the ESIPT process by completely detaching the molecule from the nanoparticle. The nonionic surfactant Triton X-100 (TX-100), at lower concentration, enhances the TICT emission and the ESIPT process is also observed due to the release of some fluorophore from the nanoparticle complex. But at higher concentration the fluorophores are released completely and the ESIPT process is restored. The cationic surfactant cetyltrimethyl ammonium bromide (CTAB), at lower concentration, simply restores the ESIPT process by releasing the fluorophore. But at higher CTAB concentration, DHP enters the metalparticle-CTAB aggregate and shows enhanced ESIPT.

Preclinical Assessment of Bacteriophage Therapy against Experimental Acinetobacter baumannii Lung Infection

Respiratory infections caused by multidrug-resistant Acinetobacter baumannii are difficult to treat and associated with high mortality among critically ill hospitalized patients. Bacteriophages (phages) eliminate pathogens with high host specificity and efficacy. However, the lack of appropriate preclinical experimental models hampers the progress of clinical development of phages as therapeutic agents. Therefore, we tested the efficacy of a purified lytic phage, vB_AbaM_Acibel004, against multidrug-resistant A. baumannii clinical isolate RUH 2037 infection in immunocompetent mice and a human lung tissue model. Sham- and A. baumannii-infected mice received a single-dose of phage or buffer via intratracheal aerosolization. Group-specific differences in bacterial burden, immune and clinical responses were compared. Phage-treated mice not only recovered faster from infection-associated hypothermia but also had lower pulmonary bacterial burden, lower lung permeability, and cytokine release. Histopathological examination revealed less inflammation with unaffected inflammatory cellular recruitment. No phage-specific adverse events were noted. Additionally, the bactericidal effect of the purified phage on A. baumannii was confirmed after single-dose treatment in an ex vivo human lung infection model. Taken together, our data suggest that the investigated phage has significant potential to treat multidrug-resistant A. baumannii infections and further support the development of appropriate methods for preclinical evaluation of antibacterial efficacy of phages.

A detailed insight on fabricated porous chitosan in eliminating synthetic anionic dyes from single and multi-adsorptive systems with related studies

Chitosan was fabricated via gelation method using CaBr₂.xH₂O/methanol solution and was studied as a potential adsorbent (MCh) in adsorbing anionic synthetic dyes like Bromophenol blue (BB), Direct blue 6 (DB) and Congo red (CR) from single (one dye species at a time) and multi (having two dyes; binary and all three dyes; tertiary) adsorptive systems. Physico-chemical modifications of MCh surface prior and post modification and dye adsorption were evaluated using scanning electron microscopy, Energy-dispersive X-ray spectroscopy, powder X-ray diffraction analysis, surface area analysis and Fourier-transformed infrared spectroscopy. Influential parameters influencing the adsorption process viz. initial pH of dye solution, MCh dosage, adsorption temperature and initial concentration of dye species were optimised. Adsorptive studies involving single adsorptive setups verified formation of sorbate's (dye species) monolayer over the sorbent's (MCh) surface via chemisorption; as established by Langmuir isotherm and pseudo-second order kinetics model analysis. Theoretical maximum adsorption capacities of MCh for BB, DB and CR was found to be 81.301 mg/g, 163.934 mg/g and 75.758 mg/g, respectively. Meanwhile, for all multi-adsorptive systems, competitive Langmuir isotherm model verified antagonistic behaviour of an individual dye over other dye adsorption over MCh surface in their respective adsorptive systems. Thermodynamics of the sorbate-sorbent interaction was exothermic, spontaneous, with elevated degree of disorderedness; concluding the interaction as thermodynamically favourable. Co-existing metal cations and anionic salts had minimal effect on MCh's adsorption efficiency. Phytotoxicity assay via germination of Vigna mungo seeds verified the efficacy of the adsorbent in eliminating the dye species from single and multi-adsorptive systems.

Role of Premycofactocin Synthase in Growth, Microaerophilic Adaptation, and Metabolism of Mycobacterium tuberculosis

Mycofactocin is a new class of peptide-derived redox cofactors present in a selected group of bacteria including Mycobacterium tuberculosis. Mycofactocin biosynthesis requires at least six genes, including mftD, encoding putative lactate dehydrogenase, which catalyzes the penultimate biosynthetic step. Cellular functions remained unknown until recent reports on the significance of mycofactocin in primary alcohol metabolism. Here, we show that mftD transcript levels were increased in hypoxia-adapted M. tuberculosis; however, mftD functionality was found likely dispensable for l-lactate metabolism. Targeted deletion of mftD reduced the survival of M. tuberculosis in in vitro and in vivo hypoxia models but increased the bacterial growth in glucose-containing broth as well as in the lungs and spleens, albeit modestly, of aerosol-infected C57BL/6J mice. The cause of this growth advantage remains unestablished; however, the mftD-deficient M. tuberculosis strain had reduced NAD(H)/NADP(H) levels and glucose-6-phosphate dehydrogenase activity with no impairment in phthiocerol dimycocerosate lipid synthesis. An ultrastructural examination of parental and mycofactocin biosynthesis gene mutants in M. tuberculosis, M. marinum, and M. smegmatis showed no altered cell morphology and size except the presence of outer membrane-bound fibril-like features only in a mutant subpopulation. A cell surface-protein analysis of M. smegmatis mycofactocin biosynthesis mutants with trypsin revealed differential abundances of a subset of proteins that are known to interact with mycofactocin and their homologs that can enhance protein aggregation or amyloid-like fibrils in riboflavin-starved eukaryotic cells. In sum, phenotypic analyses of the mutant strain implicate the significance of MftD/mycofactocin in M. tuberculosis growth and persistence in its host. IMPORTANCE Characterization of proteins with unknown functions is a critical research priority as the intracellular growth and metabolic state of Mycobacterium tuberculosis, the causative agent of tuberculosis, remain poorly understood. Mycofactocin is a peptide-derived redox cofactor present in almost all mycobacterial species; however, its functional relevance in M. tuberculosis pathogenesis and host survival has never been studied experimentally. In this study, we examine the phenotypes of an M. tuberculosis mutant strain lacking a key mycofactocin biosynthesis gene in in vitro and disease-relevant mouse models. Our results pinpoint the multifaceted role of mycofactocin in M. tuberculosis growth, hypoxia adaptation, glucose metabolism, and redox homeostasis. This evidence strongly implies that mycofactocin could fulfill specialized biochemical functions that increase the survival fitness of mycobacteria within their specific niche.

ESX-5-targeted export of ESAT-6 in BCG combines enhanced immunogenicity & efficacy against murine tuberculosis with low virulence and reduced persistence

Tuberculosis (TB) is the leading infectious cause of death globally. The only licensed TB vaccine, Bacille Calmette-Guérin (BCG), has low efficacy against TB in adults and is not recommended in people with impaired immunity. The incorporation of the Mycobacterium tuberculosis (Mtb) secretion system ESX-1 into BCG improves immunogenicity and protection against TB in animal models, which is associated with the secretion of the ESX-1-dependent protein ESAT-6. However, the resulting strain, BCG::ESX1^Mtb, has been deemed unsafe as a human vaccine, due to prolonged persistence and increased virulence in immunocompromised mice. In this study, we describe a new recombinant BCG strain that uncouples the beneficial aspects of ESAT-6 secretion from the detrimental ESX-1effects on virulence and persistence. The strain was constructed by fusing the ESAT-6-encoding gene esxA to the general secretion signal for the mycobacterial type VII secretion pathway protein PE25. This new strain, BCG::ESAT6-PE25SS, secretes full-length ESAT-6 via the ESX-5 secretion system, which in contrast to ESX-1 is also present in BCG. In vivo testing revealed that ESX-5-targeted ESAT-6 export, induces cytosolic contact, generates ESAT-6-specific T cells and enhances the protective efficacy against TB disease, but is associated with low virulence and reduced persistence in immunocompetent and immunocompromised mice. Additionally, compared to BCG::ESX1^Mtb and parental BCG, mucosal administration of BCG::ESAT6-PE25SS is associated with more rapid clearance from the lung. These results warrant further studies to evaluate BCG::ESAT6-PE25SS as a potential live attenuated vaccine candidate for TB.

Light-Driven Switching between Intramolecular Proton-Transfer and Charge-Transfer States

A molecular photoswitch, 2-(4'-diethylamino-2'-hydroxyphenyl)-1H-imidazo-[4,5-b]pyridine (DHP), with mutually independent paths of excited-state intramolecular proton transfer (ESIPT) and twisted intramolecular charge transfer (TICT) was developed. Control over these processes was attained by switching the solvents. Depending on the solvent's hydrogen-bond capacity and polarity, either one of the photoprocesses (ESIPT or TICT) or both can be triggered. Accordingly, normal and tautomer emissions, normal and TICT emissions, or triple emission of normal, tautomer, and TICT were obtained from the molecule. The emissions were resolved by fluorescence lifetime. The conclusions were established by synthesizing and studying the methoxy derivative of the molecule.

Racial disparities in COVID-19 hospitalizations do not lead to disparities in outcomes

OBJECTIVES

The objective of the study is the identification of racial differences in characteristics and comorbidities in patients hospitalized for COVID-19 and the impact on outcomes.

STUDY DESIGN

The study design is a retrospective observational study.

METHODS

Data for all patients admitted to seven community hospitals in Michigan, United States, with polymerase chain reaction confirmed diagnosis of COVID-19 from March 10 to April 15, 2020 were analyzed. The primary outcomes of racial disparity in inpatient mortality and intubation were analyzed using descriptive statistics and multivariate regression models.

RESULTS

The study included 336 Black and 408 White patients. Black patients were younger (62.9 ± 15.0 years vs 71.8 ± 16.4, P < .001), had a higher mean body mass index (32.4 ± 8.6 kg/m2 vs 28.8 ± 7.5, P < .001), had higher prevalence of diabetes (136/336 vs 130/408, P = .02), and presented later (6.6 ± 5.3 days after symptom onset vs. 5.4 ± 5.4, P = .006) compared with White patients. Younger Black patients had a higher prevalence of obesity (age <65 years, 69.9%) than older Black patients (age >65 years, 39.2%) and younger White patients (age < 65, 55.1%). Intubation did not reach statistical significance for racial difference (Black patients 61/335 vs. 54/406, P = .08). Mortality was not higher in Black patients (65/335 vs. 142/406 in White patients, odds ratio 0.61, 95% confidence interval: 0.37 to 0.99, 2-sided P = .05) in multivariate analysis, accounting for other risk factors associated with mortality.

CONCLUSIONS

Higher prevalence of obesity and diabetes in young Black populations may be the critical factor driving disproportionate COVID-19 hospitalizations in Black populations. Hospitalized Black patients do not have worse outcomes compared with White patients.

Synchrosqueezing Transform Based Powerline Interference Reduction in ECG Recording

This paper presents an adaptive ECG enhancement procedure based on Synchrosqueezing Transform (SST) to eliminate Powerline interference (PLI) from ECG signal. This work also incorporates the principles of modified discrete cosine transform (MDCT) and wiener filter. PLI is a major source of artifacts in the ECG signal which can affect its interpretation. Separating PLI from ECG signal poses a great challenge in the ECG analysis. The existing PLI removal techniques suffer from two major drawbacks such as Mode Mixing, inability to deal with non-stationary characteristics of signal. In this paper, we propose SST based wiener filtering approaches which can overcome the limitation of existing PLI suppression techniques. The proposed approaches undergo three stages of operation: mode decomposition, mode determination and peak restoration to filter out PLI from ECG recording. The mode decomposition uses SST to decompose the corrupted ECG signal into a sum of well separated intrinsic mode functions (IMFs). The objective is to filter out PLI from these IMFs. To do so, mode determination step which is based on Kurtosis and Crest factor is applied to categorize decomposition result into groups such as signal mode and noisy mode. Direct subtraction of the noisy mode from the corrupted ECG observation results in ECG signal with reduced peak since noise mode carries part of signal components in addition to interference. Hence, to restore the peak, wiener filter is applied on noisy mode to estimate actual PLI component. Finally, Noise free ECG signal is reconstructed by subtracting estimated PLI from the corrupted ECG signal. This paper discusses four possible PLI suppression methods which are derived by combining SST domain with wiener filter in various ways. Simulations are carried out to test the effectiveness of proposed methods. It is evident from the simulation results that the proposed methods can remove PLI of 50 Hz and its harmonics. The proposed techniques effectively removed PLI in both real and artificial ECG signals and to test its performance they are compared with state of the art methods. The SST based filtering methods outperformed other methods under the condition of PLI frequency variations. The experimental results also suggest that the SST based wiener filtering with modified reference approach offers better PLI suppression than all other methods.

α-Synuclein aggregation nucleates through liquid-liquid phase separation

α-Synuclein (α-Syn) aggregation and amyloid formation is directly linked with Parkinson's disease pathogenesis. However, the early events involved in this process remain unclear. Here, using the in vitro reconstitution and cellular model, we show that liquid-liquid phase separation of α-Syn precedes its aggregation. In particular, in vitro generated α-Syn liquid-like droplets eventually undergo a liquid-to-solid transition and form an amyloid hydrogel that contains oligomers and fibrillar species. Factors known to aggravate α-Syn aggregation, such as low pH, phosphomimetic substitution and familial Parkinson's disease mutations, also promote α-Syn liquid-liquid phase separation and its subsequent maturation. We further demonstrate α-Syn liquid-droplet formation in cells. These cellular α-Syn droplets eventually transform into perinuclear aggresomes, the process regulated by microtubules. This work provides detailed insights into the phase-separation behaviour of natively unstructured α-Syn and its conversion to a disease-associated aggregated state, which is highly relevant in Parkinson's disease pathogenesis.

The origin of the longer wavelength emission in 2-(4-fluorophenylamino)-5-(2,4-dihydroxybenzeno)-1,3,4-thiadiazole and its analogue 2-phenylamino-5-(2-hydroxybenzono)-1,3,4-thiadiazole† ‡

In aqueous solution, 2-(4-fluorophenylamino)-5-(2,4-dihydroxybenzeno)-1,3,4-thiadiazole (FABT) was found to emit dual emission and the longer wavelength emission was assigned to the combination of aggregation and conformational change. In a number of molecules that possess an intramolecular hydrogen bond between the proton donor and the acceptor, the longer wavelength emission is often observed due to the emission from the tautomer formed by excited state intramolecular proton transfer (ESIPT). Therefore, an analogue of FABT, 2-phenylamino-5-(2-hydroxybenzono)-1,3,4-thiadiazole (PHBT), was synthesized to determine the origin of the longer wavelength emission. The luminescence of PHBT and its methoxy derivatives was studied and compared with that of FABT. Theoretical calculations were also performed on both FABT and PHBT. Based on the experimental and theoretical investigations, the nonexistence of the keto tautomer in the ground state and the origin of the longer wavelength emission are divulged.

FX11 limits Mycobacterium tuberculosis growth and potentiates bactericidal activity of isoniazid through host-directed activity

Lactate dehydrogenase A (LDHA) mediates interconversion of pyruvate and lactate, and increased lactate turnover is exhibited by malignant and infected immune cells. Hypoxic lung granuloma in Mycobacterium tuberculosis-infected animals present elevated levels of Ldha and lactate. Such alterations in the metabolic milieu could influence the outcome of host-M. tuberculosis interactions. Given the central role of LDHA for tumorigenicity, targeting lactate metabolism is a promising approach for cancer therapy. Here, we sought to determine the importance of LDHA for tuberculosis (TB) disease progression and its potential as a target for host-directed therapy. To this end, we orally administered FX11, a known small-molecule NADH-competitive LDHA inhibitor, to M. tuberculosis-infected C57BL/6J mice and Nos2-/- mice with hypoxic necrotizing lung TB lesions. FX11 did not inhibit M. tuberculosis growth in aerobic/hypoxic liquid culture, but modestly reduced the pulmonary bacterial burden in C57BL/6J mice. Intriguingly, FX11 administration limited M. tuberculosis replication and onset of necrotic lung lesions in Nos2-/- mice. In this model, isoniazid (INH) monotherapy has been known to exhibit biphasic killing kinetics owing to the probable selection of an INH-tolerant bacterial subpopulation. However, adjunct FX11 treatment corrected this adverse effect and resulted in sustained bactericidal activity of INH against M. tuberculosis As a limitation, LDHA inhibition as an underlying cause of FX11-mediated effect could not be established as the on-target effect of FX11 in vivo was unconfirmed. Nevertheless, this proof-of-concept study encourages further investigation on the underlying mechanisms of LDHA inhibition and its significance in TB pathogenesis.

Aryl Hydrocarbon Receptor Modulation by Tuberculosis Drugs Impairs Host Defense and Treatment Outcomes

Antimicrobial resistance in tuberculosis (TB) is a public health threat of global dimension, worsened by increasing drug resistance. Host-directed therapy (HDT) is an emerging concept currently explored as an adjunct therapeutic strategy for TB. One potential host target is the ligand-activated transcription factor aryl hydrocarbon receptor (AhR), which binds TB virulence factors and controls antibacterial responses. Here, we demonstrate that in the context of therapy, the AhR binds several TB drugs, including front line drugs rifampicin (RIF) and rifabutin (RFB), resulting in altered host defense and drug metabolism. AhR sensing of TB drugs modulates host defense mechanisms, notably impairs phagocytosis, and increases TB drug metabolism. Targeting AhR in vivo with a small-molecule inhibitor increases RFB-treatment efficacy. Thus, the AhR markedly impacts TB outcome by affecting both host defense and drug metabolism. As a corollary, we propose the AhR as a potential target for HDT in TB in adjunct to canonical chemotherapy.

α-Synuclein Spontaneously Adopts Stable and Reversible α-Helical Structure in Water-Less Environment

A highly stable, spontaneous, and reversible α-helical-structure formation in recombinant and chemically modified α-synuclein protein is demonstrated for the first time in a water-less (1.5 % w/w H₂ O) polymer surfactant environment. Using a combination of circular dichroism and ATR-FTIR spectroscopy, we show that whilst native α-synuclein in aqueous solution shows a predominant unordered conformation (≈64 %), mixing with polyethylene glycol based anionic polymer surfactant (PS) and removing water reveals a 25 % unordered, 25 % α-helical, and 27 % β-sheet structure. Interestingly, bioconjugation of native α-synuclein with a diamine molecule, to increase the positive charge on the protein chain, and subsequent electrostatic coupling with the PS forms a conjugate with a retained unordered structure. Removal of water from this system provides a highly stable α-helical (≈74 %) water-less liquid system. Surprisingly, the α-helical-to-unordered state transition is completely reversible and is achieved at ≈25-30 w/w% of water in the system. Moreover, the α-helix shows an extraordinary temporal stability (>6 months) in a waterless environment.

Humanized Mouse Model Mimicking Pathology of Human Tuberculosis for in vivo Evaluation of Drug Regimens

Human immune system mice are highly valuable for in vivo dissection of human immune responses. Although they were employed for analyzing tuberculosis (TB) disease, there is little data on the spatial organization and cellular composition of human immune cells in TB granuloma pathology in this model. We demonstrate that human immune system mice, generated by transplanted human fetal liver derived hematopoietic stem cells develop a continuum of pulmonary lesions upon Mycobacterium tuberculosis aerosol infection. In particular, caseous necrotic granulomas, which contribute to prolonged TB treatment time, developed, and had cellular phenotypic spatial-organization similar to TB patients. By comparing two recommended drug regimens, we confirmed observations made in clinical settings: Adding Moxifloxacin to a classical chemotherapy regimen had no beneficial effects on bacterial eradication. We consider this model instrumental for deeper understanding of human specific features of TB pathogenesis and of particular value for the pre-clinical drug development pipeline.

Tweaking the proton transfer triggered proton transfer of 3,5-bis(2-hydroxyphenyl)-1H-1,2,4-triazole

Proton transfer triggered proton transfer (PTTPT) of the molecule is completely altered by dimethylformamide and the proton transfer paths are changed. The process can be reversed by silver particle.

Phagosomal Copper-Promoted Oxidative Attack on Intracellular Mycobacterium tuberculosis

Copper (Cu) ions are critical in controlling bacterial infections, and successful pathogens like Mycobacterium tuberculosis (Mtb) possess multiple Cu resistance mechanisms. We report, as proof of concept, that a novel Cu hypersensitivity phenotype can be generated in mycobacteria, including Mtb, through a peptide, DAB-10, that is able to form reactive oxygen species (ROS) following Cu-binding. DAB-10 induces intramycobacterial oxidative stress in a Cu-dependent manner in vitro and during infection. DAB-10 penetrates murine macrophages and encounters intracellular mycobacteria. Significant intracellular Cu-dependent protection was observed when Mtb-infected macrophages were treated with DAB-10 alongside a cell-permeable Cu chelator. Treatment with the Cu chelator reversed the intramycobacterial oxidative shift induced by DAB-10. We conclude that DAB-10 utilizes the pool of phagosomal Cu ions in the host-Mtb interface to augment the mycobactericidal activity of macrophages while simultaneously exploiting the susceptibility of Mtb to ROS. DAB-10 serves as a model with which to develop next-generation, multifunctional antimicrobials.

Bioactive compound from Aspergillus terreusDMTMGK004 synergistically contributes towards potential anti-pathogenicity

This study focused on the evaluation of fungal compound for their anti-pathogenic potential against respiratory pathogens. Soil samples were collected from various geographical regions in Madurai, fungal strain was isolated and identified as Aspergillus terreusDMTMGK004 (MGK004). Secondary metabolites were extracted and evaluated for antioxidant potential. It exhibited significantly high anti-proliferative property against gastric adenocarcinoma (AGS) cell lines. Antimicrobial activity against Gram positive (Streptococcus pneumoniae) and Gram negative (Klebsiella pneumoniae and Haemophilus influenzae) respiratory pathogens were analysed and the minimum inhibitory concentration (MIC) values were determined. Furthermore, the time-killing assay illustrated that the metabolite eliminates 50% of the vegetative cells within few hours of the treatment. From the spectral data, the major functional groups present in the compound were determined as carbonyl group and phenolic hydroxyl group which contribute towards its bioactivity. The compound significantly depreciates the production of extracellular polysaccharides which results in the weakening of biofilm architecture and resistance towards serum killing and phagocytosis. It also induced cell membrane damage which leads to protein and nucleic acid leakage. Hence, the results of the present study could provide a better insinuation towards the formulation of new drug targeting respiratory pathogens. SIGNIFICANCE AND IMPACT OF THE STUDY: The ubiquitous fungi Aspergillus terreus is well known for its secondary metabolite production. The fungus was evaluated for production of antagonistic molecule to reduce the growth of infectious agents causing respiratory infections. It exhibited the biological means of antioxidant, anti-proliferative and anti-pathogenic compound production. The compound exhibits killing effect against respiratory pathogens within two hours. It induced cell membrane damage leading to protein and nucleic acid leakage. It significantly reduced the production of extracellular polysaccharides. The results provide needed information to design innovative strategies for targeting pathogenic factors of the respiratory pathogens instead of killing it precisely.

Fluorescence spectroscopy for revealing mechanisms in biology: Strengths and pitfalls

This article describes the basic principles of steady-state and time-resolved fluorescence. The formal equivalence of the two methodologies is described first, followed by the extra advantages of time-resolved methods in revealing population heterogeneity in complex systems encountered in biology. Several examples from the author's work are described in support of the above contention. Finally, several misinterpretations and pitfalls in the interpretation of fluorescence data and their remedy are described.

Proton transfer triggered proton transfer: a self-assisted twin excited state intramolecular proton transfer

The double excited state intramolecular proton transfer (ESIPT) of 3,5-bis(2-hydroxyphenyl)-1H-1,2,4-triazole (bis-HPTA) has been investigated and found to undergo a new type of proton transfer.

Site-specific time-resolved FRET reveals local variations in the unfolding mechanism in an apparently two-state protein unfolding transition

Using multi-site time-resolved FRET, it is shown that equilibrium unfolding of monellin is not only heterogeneous, but that the degree of non-cooperativity differs between the sole α-helix and different parts of the β-sheet.

A sensitive and selective sensor for picric acid detection with a fluorescence switching response

Low molecular weight organogelator for the detection of picric acid.

Site-Specific Fluorescence Dynamics To Probe Polar Arrest by Fob1 in Replication Fork Barrier Sequences

Fob1 protein plays an important role in aging and maintains genomic stability by avoiding clashes between the replication and transcription machinery. It facilitates polar arrest by binding to replication fork barrier (RFB) sites, present within the nontranscribed spacer region of the ribosomal DNA. Here, we investigate the mechanism of unidirectional arrest by creating multiple prosthetic forks within the RFB, with fluorescent adenine analogue 2-aminopurine incorporated site-specifically in both the "permissible" and "nonpermissible" directions. The motional dynamics of the RFB-Fob1 complexes analyzed by fluorescence lifetime and fluorescence anisotropy decay kinetics shows that Fob1 adopts a clamp-lock model of arrest and causes stronger perturbation with the bases in the double-stranded region of the nonpermissible-directed forks over those of the permissible directed ones, thereby creating a polar barrier. Corroborative thermal melting studies reveal a skewed distribution of GC content within the RFB sequence that potentially assists in Fob1-mediated arrest.

Perturbation of cationic equilibrium by cucurbit-7-uril

The effect of cucurbit-7-uril (CB-7) on a cationic mixture with same charge has been investigated by studying monocationic mixtures of 2-(4'-N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine (DMAPIP-b) and 2-(4'-N,N-dimethylaminophenyl)imidazo[4,5-c]pyridine (DMAPIP-c). The pK_a of both the guests increases in CB-7. DMAPIP-b forms all three monocations in the ground and the excited states in aqueous as well as in CB-7 solution. However, CB-7 shifts the equilibrium more towards the less polar MC2 and MC3. On the other hand, DMAPIP-c exists only as MC1 and MC3 in aqueous solution, however, in CB-7 it exists not only as MC1 and MC3 but also as MC2 in CB-7 in the ground state. In the excited state, as in aqueous solution MC1 forms MC2 by biprotonic phototautomerism in CB-7. The association constants of monocations suggest a pyridyl nitrogen position dependence. All the MC-CB-7 complexes are optimized by density functional theory (DFT).

Aggregation induced enhanced and exclusively highly Stokes shifted emission from an excited state intramolecular proton transfer exhibiting molecule

The inner filter effect due to self-quenching dominates the normal emission of dyes at higher concentrations, which would limit their applications. Since normal emission was also observed with aggregation induced emission enhancement (AIEE) active excited state intramolecular proton transfer (ESIPT) exhibiting molecules, two new molecules are synthesized and studied to obtain normal emission free AIEE. The molecules are 4-(3-(benzo[d]thiazol-2-yl)-5-tert-butyl-4-hydroxybenzyl)-2-(benzo[d]thiazol-2-yl)-6-tert-butyl phenol (bis-HPBT) and its oxazole analogue (bis-HPBO). Of these molecules, bis-HPBT, which is weakly fluorescent in tetrahydrofuran solution, shows a sudden high enhancement in fluorescence upon addition of 70% water due to the formation of aggregates. Though the normal emission is also observed in tetrahydrofuran, it is completely eliminated in the aggregates, and the aggregates display exclusive tautomer emission. However, bis-HPBO does not emit such an exclusive tautomer emission in the water/tetrahydrofuran mixture. The enhancement in the fluorescence quantum yield of bis-HPBT in 70% water is ∼300 times higher than that in tetrahydrofuran. The modulated molecular structure of bis-HPBT is the cause of this outstanding AIEE. The observation of almost exclusive tautomer emission is a new additional advantage of AIEE from bis-HPBT over other ESIPT molecules. Since the tautomer emission is highly Stokes shifted, no overlap with the absorption spectrum occurs and therefore, the inner filter effect is averted. The aggregated structure acts as a good fluorescence chemosensor for metal ions as well as anions. The aggregated structure is cell permeable and can be used for cell imaging.

An unusual deprotonation trend in 2-(2'-hydroxyphenyl)pyridoimidazoles

The anion sensitivity and the deprotonation nature of the nitrogenous analogues of 2-(2'-hydroxyphenyl)benzimidazole (HPBI) are investigated in a polar aprotic medium. It is observed that the substitution of pyridyl nitrogen enhances the anion sensitivity. However, despite the enhanced sensitivity of the nitrogenous analogues the deprotonation of these molecules in the presence of strong anions is less favored as compared to HPBI. This anomalous trend observed for the nitrogenous analogs is discussed and explained using theoretical calculations and experimental findings. It is also found that the sensitivity towards anions and the formation of anions also depend on the position of the pyridyl nitrogen.

Aggregation induced enhanced emission of 2-(2'-hydroxyphenyl)benzimidazole

In this study, the aggregation induced emission enhancement (AIEE) of 2-(2'-hydroxyphenyl)benzimidazole (HPBI) is reported. To investigate the AIEE process of HPBI, absorption/fluorescence spectroscopy, fluorescence imaging and field emission scanning electron microscopy were employed. A comparative study with 2-phenylbenzimidazole (PBI) divulges the significance of the hydroxyl group in the AIEE process. Further, molecular dynamics simulations have been carried out with explicit solvent molecules to follow the aggregation process of HPBI with time. The obtained molecular dynamics simulation results not only predicted the formation of aggregates but also provided detailed insight and information on the molecular interactions. The cellular studies showed aggregates yield higher fluorescence in the visible region inside HeLa cells in comparison to monomeric compounds which failed to exhibit any visible fluorescence inside the cell. The obtained aggregates were further found to be biocompatible and therefore can be used for bio-imaging applications.

Switching between cis and trans anions of 2-(2'-hydroxyphenyl)benzimidazole: a molecular rotation perturbed by chemical stabilization

Despite the fact that 2-(2'-hydroxyphenyl)benzimidazole (HPBI) exists as the cis and trans enol in neutral form, it was reported to exist only in the trans form upon deprotonation in an aqueous medium. It was also shown that the dianion formed in the ground state can be re-protonated to form the trans-anion in the excited state. In the present study, the cis-anion and dianion could be obtained upon proper stabilization in suitable environments. Switching between the cis and trans-anion was demonstrated to be possible by changing the environment. Theoretical calculations were performed to substantiate the existence of the cis-anion and dianion. In contrast to a literature report, it was shown that the 'OH' group deprotonates before the 'NH' group to form a monoanion not only in protic solvents but also in aprotic solvents.

Exclusive excited state intramolecular proton transfer from a 2-(2′-hydroxyphenyl)benzimidazole derivative

The existence of trans-enol was made unviable by crafting a steric hindrance that stops the normal emission of bis-HPBI.

Depth-Dependent Organization and Dynamics of Archaeal and Eukaryotic Membranes: Development of Membrane Anisotropy Gradient with Natural Evolution

The lipid composition of archaea is unique and has been correlated with increased stability under extreme environmental conditions. In this article, we have focused on the evolution of membrane organization and dynamics with natural evolution. Dynamic anisotropy along the membrane normal (i.e., gradients of mobility, polarity, and heterogeneity) is a hallmark of fluid phase diester or diether phospholipid membranes. We monitored gradients of mobility, polarity, and heterogeneity along the membrane normal in membranes made of a representative archaeal lipid using a series of membrane depth-dependent fluorescent probes, and compared them to membranes prepared from a typical diether lipid from higher organisms (eukaryotes). Our results show that the representative dynamic anisotropy gradient along the membrane normal is absent in membranes made from archaeal lipids. We hypothesize that the dynamic gradient observed in membranes of diester and diether phospholipids is a consequence of natural evolution of membrane lipids in response to the requirement of carrying out complex cellular functions by membrane proteins.

Mode of DNA binding with γ-butyrolactone receptor protein CprB from Streptomyces coelicolor revealed by site-specific fluorescence dynamics

BACKGROUND

The γ-butyrolactone (GBL) binding transcription factors in Streptomyces species are known for their involvement in quorum sensing where they control the expression of various genes initiating secondary metabolic pathways. The structurally characterized member of this family CprB from Streptomyces coelicolor had earlier been demonstrated to bind a multitude of sequences containing a specific binding signature. Though structural breakthrough has been obtained for its complex with a consensus DNA sequence there is, however a dearth of information regarding the overall and site specific dynamics of protein-DNA interaction.

METHODS

To delineate the effect of CprB on the bound DNA, changes in motional dynamics of the fluorescent probe 2-aminopurine were monitored at three conserved base positions (5th, 12th and 23rd) for two DNA sequences: the consensus and the biologically relevant cognate element, on complex formation.

RESULTS

The changes in lifetime and generalized order parameter revealed a similarity in the binding pattern of the protein to both sequences with greater dynamic restriction at the end positions, 5th and 23rd, as compared to the middle 12th position. Also differences within this pattern demonstrated the influence of even small changes in sequence on protein interactions.

CONCLUSIONS

Here the study of motional dynamics was instrumental in establishing a structural footprint for the cognate DNA sequence and explaining the dynamics for the consensus DNA from structural correspondence.

GENERAL SIGNIFICANCE

Motional dynamics can be a powerful tool to efficiently study the mode of DNA binding to proteins that interact differentially with a plethora of DNA sequences, even in the absence of structural breakthrough.

Effect of Melatonin on Glutamate: BDNF Signaling in the Cerebral Cortex of Polychlorinated Biphenyls (PCBs)-Exposed Adult Male Rats

Various epidemiological survey suggests that the central nervous system is the target for many environmental contaminants. One among them is Aroclor 1254, a mixture of polychlorinated biphenyls (PCBs) which explore a spectrum of biochemical and neurotoxic responses in humans and laboratory animals. Learning and motor coordination deficits are the profound effects of PCBs which may be related to cerebral dysfunction. The aim of the study is to elicit the protective effect of melatonin (Mel), a potent, blood brain permeable antioxidant against the effect of Aroclor 1254 on the signaling of glutamate-principal excitatory neurotransmitter and brain derived neurotrophic factor (BDNF) in the cerebral cortex of adult rats which plays a key role in brain functions. Adult male Wistar rats were grouped into four and treated intraperitonealy (i.p) Group I with corn oil (Control), Group II with PCBs (2 mg/kg/bwt), Group III with PCBs + Mel (2 mg/kg/bwt + 5 mg/kg/bwt) and Group IV with Mel (5 mg/kg/bwt). The protein expression of glutamate signaling molecules and mRNA expressions of GLAST, BDNF signaling molecules were analyzed. The results suggest that simultaneous melatonin treatment significantly attenuated the NMDA receptor mediated glutamate excitotoxicity and protects the inhibition of BDNF signaling caused by PCBs exposure in cerebral cortex of adult male rats. Schematic pathway illustrating the proposed mechanism by which melatonin protects against A1254 mediated glutamate induced neurodegeneration in the cerebral cortex of adult male rats. PCBs induced neurodegeneration is caused by the overactivation of NMDAR, followed by the activation of voltage dependent calcium channels leading to the increase in intracellular Ca(2+) that stimulates calpain. Calpain inturn inhibits the PKA α and neurtrophin BDNF, its receptor and downstream signaling MAPK pathway leading to neurodegeneration. Melatonin had scavenged the ROS produced by PCBS and decreased the NMDAR expression which inturn protected the cells from neurodegeneration.

Photoinduced intramolecular charge transfer in trans-2-[4'-(N,N-dimethylamino)styryl]imidazo[4,5-b]pyridine: effect of introducing a C[double bond, length as m-dash]C double bond

The spectral characteristics of trans-2-[4'-(N,N-dimethylamino)styryl]imidazo[4,5-b]pyridine (t-DMASIP-b) have been investigated using absorption and fluorescence techniques, and compared with 2-(4'-N,N-dimethylamino)imidazo[4,5-b]pyridine (DMAPIP-b). The study reveals that introduction of a C[double bond, length as m-dash]C double bond strongly perturbs the photophysics of the system. Unlike DMAPIP-b, t-DMASIP-b emits a single emission in aprotic and protic solvents. The emission occurs from the locally excited state in nonpolar solvents and from a planar intramolecular charge transfer (PICT) state in polar solvents. Multiple linear regression analysis suggests that among the different solvent parameters, the dipolar interaction contributes more to the stabilization of the system in both the ground and excited states. Theoretical calculations suggest that, unlike in DMAPIP-b, proton coupled twisted intramolecular charge transfer (TICT) emission does not occur in t-DMASIP-b. The higher quantum yield obtained in the viscous solvent glycerol is attributed to the restriction of the twisting of the olefinic bond. The photoirradiation of t-DMASIP-b shows that isomerization takes place in all solvents, including viscous glycerol. The theoretically simulated potential energy surface shows that isomerization occurs via a phantom state, which is a nonradiative process. The rise in temperature favors the photoisomerization, thus, the fluorescence quantum yield decreases. The prototropic study indicates that, unlike in DMAPIP-b, the protonation takes place at different places to form the monocations.

Dual emission from 2-(4'-N,N-dimethylaminophenyl)pyridoimidazole-nanoparticle composite: effect of β-cyclodextrin

The interactions of the silver nanoparticles with 2-(4'-N,N-dimethylaminophenyl)benzimidazole and its nitrogen substituted analogues, 2-(4'-N,N-dimethylaminophenyl)pyridoimidazoles are investigated by absorption, steady-state and time resolved fluorescence, field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) techniques. The surface plasmon resonance band, the FESEM and the TEM images of the particles suggest that the fluorophores can stabilize the nanoparticles even in the absence of any other stabilizing agent. On the other hand, in the absence of fluorophores the nanoparticles are unstable and coagulate. In contrary to the earlier literature reports that interactions of nanoparticles with intramolecular charge transfer (ICT) or twisted intramolecular charge transfer (TICT) species quenches their fluorescence, to the best of our knowledge, the first ever formation of TICT state by interactions of nanoparticles with the fluorophores is observed. The formation of TICT state in 2-(4'-N,N-dimethylaminophenyl)pyridoimidazoles results in dual emission. The TICT emissions from the nanoparticle-fluorophore complexes are weak. But the emissions become prominent upon complexation with β-cyclodextrin.

A single fluorophore to address multiple logic gates

Logic gates with different radixes have been constructed using a biologically active molecule, 2-(4′-N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine (DMAPIP-b).

Relay proton transfer triggered twisted intramolecular charge transfer

The mechanism for the dual emission of 2-(4′-N,N-dimethylaminophenyl)imidazo[4,5-c]pyridine (DMAPIP-c) in protic solvents was investigated by synthesizing and studying its analogues.