Affinity of cefotiam for the alternative penicillin binding protein PBP3SAL used by Salmonella inside host eukaryotic cells.

BACKGROUND: Following the invasion of eukaryotic cells, Salmonella enterica serovar Typhimurium replaces PBP2/PBP3, main targets of ß-lactam antibiotics, with PBP2SAL/PBP3SAL, two homologue peptidoglycan synthases absent in Escherichia coli. PBP3SAL promotes pathogen cell division in acidic environments independently of PBP3 and shows low affinity for ß-lactams that bind to PBP3 such as aztreonam, cefepime, cefotaxime, ceftazidime, ceftriaxone, cefuroxime and cefalotin. OBJECTIVES: To find compounds with high affinity for PBP3SAL to control Salmonella intracellular infections. METHODS: An S. Typhimurium ΔPBP3 mutant that divides using PBP3SAL and its parental wild-type strain, were exposed to a library of 1520 approved drugs in acidified (pH 4.6) nutrient-rich LB medium. Changes in optical density associated with cell filamentation, a read-out of blockage in cell division, were monitored. Compounds causing filamentation in the ΔPBP3 mutant but not in wild-type strain-the latter strain expressing both PBP3 and PBP3SAL in LB pH 4.6-were selected for further study. The bactericidal effect due to PBP3SAL inhibition was evaluated in vitro using a bacterial infection model of cultured fibroblasts. RESULTS: The cephalosporin cefotiam exhibited higher affinity for PBP3SAL than for PBP3 in bacteria growing in acidified LB pH 4.6 medium. Cefotiam also proved to be effective against intracellular Salmonella in a PBP3SAL-dependent manner. Conversely, cefuroxime, which has higher affinity for PBP3, showed decreased effectiveness in killing intracellular Salmonella. CONCLUSIONS: Antibiotics with affinity for PBP3SAL, like the cephalosporin cefotiam, have therapeutic value for treating Salmonella intracellular infections.

The G protein database, GproteinDb.

Two-thirds of signaling substances, several sensory stimuli and over one-third of drugs act via receptors coupling to G proteins. Here, we present an online platform for G protein research with reference data and tools for analysis, visualization and design of scientific studies across disciplines and areas. This platform may help translate new pharmacological, structural and genomic data into insights on G protein signaling vital for human physiology and medicine. The G protein database is accessible at https://gproteindb.org.

Imaging-Guided Delivery of a Hydrophilic Drug to Eukaryotic Cells Based on Its Hydrophobic Ion Pairing with Poly(hexamethylene guanidine) in a Maleated Chitosan Carrier.

Imaging-guided delivery is developed for hydrophobic drugs, and to a much lesser extent, hydrophilic ones. In this work we have designed a novel strategy for real-time monitoring of hydrophilic drug delivery. Traditionally, the drug and the dye are covalently attached to a nanocarrier or are electrostatically adsorbed. Recently, we found an efficient way to bind the drug by ion-paring with an appropriate counter-ion to form the aggregate that embeds a hydrophobic dye with a considerable fluorescence enhancement. We synthesized a series of carbocyanine dyes of hydrophobicity sufficient for solubilization in hydrophobic ion pairs, which restores their emission in the near-infrared (NIR) region upon the formation of the ternary aggregates. To avoid using toxic surfactants, we applied an amphiphilic polymer-oligomer poly(hexamethylene guanidine) (PHMG) as a counter-ion. Сeftriaxone was used as a model hydrophilic drug ensuring the highest fluorescent signal. The so-formed drug-counter-ion-dye aggregates were encapsulated into a cross-linked maleated chitosan carrier. Confocal laser scanning microscopy (CLSM) studies have demonstrated internalization of the encapsulated model drug by breast adenocarcinoma cells at 40 min after treatment. These results suggest the potential application of hydrophobic ion pairs containing an NIR dye in imaging-guided delivery of hydrophilic compounds.

The Emerging Role of Decellularized Plant-Based Scaffolds as a New Biomaterial.

The decellularization of plant-based biomaterials to generate tissue-engineered substitutes or in vitro cellular models has significantly increased in recent years. These vegetal tissues can be sourced from plant leaves and stems or fruits and vegetables, making them a low-cost, accessible, and sustainable resource from which to generate three-dimensional scaffolds. Each construct is distinct, representing a wide range of architectural and mechanical properties as well as innate vasculature networks. Based on the rapid rise in interest, this review aims to detail the current state of the art and presents the future challenges and perspectives of these unique biomaterials. First, we consider the different existing decellularization techniques, including chemical, detergent-free, enzymatic, and supercritical fluid approaches that are used to generate such scaffolds and examine how these protocols can be selected based on plant cellularity. We next examine strategies for cell seeding onto the plant-derived constructs and the importance of the different functionalization methods used to assist in cell adhesion and promote cell viability. Finally, we discuss how their structural features, such as inherent vasculature, porosity, morphology, and mechanical properties (i.e., stiffness, elasticity, etc.) position plant-based scaffolds as a unique biomaterial and drive their use for specific downstream applications. The main challenges in the field are presented throughout the discussion, and future directions are proposed to help improve the development and use of vegetal constructs in biomedical research.

Marine natural products targeting the eukaryotic cell membrane.

The cell membrane, with high fluidity and alternative curvatures, maintains the robust integrity to distinguish inner and outer space of cells or organelles. Lipids are the main components of the cell membrane, but their functions are largely unknown. Even the visualization of lipids is not straightforward since modification of lipids often hampers its correct physical properties. Many natural products target cell membranes, some of which are used as pharmaceuticals and/or research tools. They show specific recognition on lipids, and thus exhibit desired pharmacological effects and unique biological phenotypes. This review is a catalog of marine natural products that target eukaryotic cell membranes. Chemical structures, biological activities, and molecular mechanisms are summarized. I hope that this review will be helpful for readers to notice the potential of marine natural products in the exploration of the function of lipids and the druggability of eukaryotic cell membranes.

DNA Intercalators Inhibit Eukaryotic Ribosomal RNA Synthesis by Impairing the Initiation of Transcription.

In eukaryotes, ribosome biogenesis is driven by the synthesis of the ribosomal RNA (rRNA) by RNA polymerase I (Pol-I) and is tightly linked to cell growth and proliferation. The 3D-structure of the rDNA promoter plays an important, yet not fully understood role in regulating rRNA synthesis. We hypothesized that DNA intercalators/groove binders could affect this structure and disrupt rRNA transcription. To test this hypothesis, we investigated the effect of a number of compounds on Pol-I transcription in vitro and in cells. We find that intercalators/groove binders are potent inhibitors of Pol-I specific transcription both in vitro and in cells, regardless of their specificity and the strength of its interaction with DNA. Importantly, the synthetic ability of Pol-I is unaffected, suggesting that these compounds are not targeting post-initiating events. Notably, the tested compounds have limited effect on transcription by Pol-II and III, demonstrating the hypersensitivity of Pol-I transcription. We propose that stability of pre-initiation complex and initiation are affected as result of altered 3D architecture of the rDNA promoter, which is well in line with the recently reported importance of biophysical rDNA promoter properties on initiation complex formation in the yeast system.

Tellurium: A Rare Element with Influence on Prokaryotic and Eukaryotic Biological Systems.

Metalloid tellurium is characterized as a chemical element belonging to the chalcogen group without known biological function. However, its compounds, especially the oxyanions, exert numerous negative effects on both prokaryotic and eukaryotic organisms. Recent evidence suggests that increasing environmental pollution with tellurium has a causal link to autoimmune, neurodegenerative and oncological diseases. In this review, we provide an overview about the current knowledge on the mechanisms of tellurium compounds' toxicity in bacteria and humans and we summarise the various ways organisms cope and detoxify these compounds. Over the last decades, several gene clusters conferring resistance to tellurium compounds have been identified in a variety of bacterial species and strains. These genetic determinants exhibit great genetic and functional diversity. Besides the existence of specific resistance mechanisms, tellurium and its toxic compounds interact with molecular systems, mediating general detoxification and mitigation of oxidative stress. We also discuss the similarity of tellurium and selenium biochemistry and the impact of their compounds on humans.

Differential interactions of the antimicrobial peptide, RQ18, with phospholipids and cholesterol modulate its selectivity for microorganism membranes.

BACKGROUND: Antimicrobial peptides (AMPs) are molecules with potential application for the treatment of microorganism infections. We, herein, describe the structure, activity, and mechanism of action of RQ18, an α-helical AMP that displays antimicrobial activity against Gram-positive and Gram-negative bacteria, and yeasts from the Candida genus. METHODS: A physicochemical-guided design assisted by computer tools was used to obtain our lead peptide candidate, named RQ18. This peptide was assayed against Gram-positive and Gram-negative bacteria, yeasts, and mammalian cells to determine its selectivity index. The secondary structure and the mechanism of action of RQ18 were investigated using circular dichroism, large unilamellar vesicles, and molecular dynamic simulations. RESULTS: RQ18 was not cytotoxic to human lung fibroblasts, peripheral blood mononuclear cells, red blood cells, or Vero cells at MIC values, exhibiting a high selectivity index. Circular dichroism analysis and molecular dynamic simulations revealed that RQ18 presents varying structural profiles in aqueous solution, TFE/water mixtures, SDS micelles, and lipid bilayers. The peptide was virtually unable to release carboxyfluorescein from large unilamellar vesicles composed of POPC/cholesterol, model that mimics the eukaryotic membrane, indicating that vesicles' net charges and the presence of cholesterol may be related with RQ18 selectivity for bacterial and fungal cell surfaces. CONCLUSIONS: RQ18 was characterized as a membrane-active peptide with dual antibacterial and antifungal activities, without compromising mammalian cells viability, thus reinforcing its therapeutic application. GENERAL SIGNIFICANCE: These results provide further insight into the complex process of AMPs interaction with biological membranes, in special with systems that mimic prokaryotic and eukaryotic cell surfaces.

Context-specific action of macrolide antibiotics on the eukaryotic ribosome.

Macrolide antibiotics bind in the nascent peptide exit tunnel of the bacterial ribosome and prevent polymerization of specific amino acid sequences, selectively inhibiting translation of a subset of proteins. Because preventing translation of individual proteins could be beneficial for the treatment of human diseases, we asked whether macrolides, if bound to the eukaryotic ribosome, would retain their context- and protein-specific action. By introducing a single mutation in rRNA, we rendered yeast Saccharomyces cerevisiae cells sensitive to macrolides. Cryo-EM structural analysis showed that the macrolide telithromycin binds in the tunnel of the engineered eukaryotic ribosome. Genome-wide analysis of cellular translation and biochemical studies demonstrated that the drug inhibits eukaryotic translation by preferentially stalling ribosomes at distinct sequence motifs. Context-specific action markedly depends on the macrolide structure. Eliminating macrolide-arrest motifs from a protein renders its translation macrolide-tolerant. Our data illuminate the prospects of adapting macrolides for protein-selective translation inhibition in eukaryotic cells.

Small-Molecule Degraders beyond PROTACs-Challenges and Opportunities.

Targeted protein degradation (TPD) is a recent strategy, utilizing the cell's proteostasis machinery to deplete specific proteins. This represents a paradigm shift in early drug discovery, away from occupancy-driven to event-driven mechanisms.Recent efforts have focused on the development of proteolysis-targeting chimeras (PROTACs). These heterobifunctional molecules combine a target-specific binding moiety linked to an E3 ligase ligand and trigger selective ubiquitination of the target protein, marking it for proteasomal degradation. While these molecules can be highly efficacious, they generally have unfavorable physicochemical properties due to their large size.In contrast, smaller molecules that induce degradation could represent an attractive, simple option to overcoming the limitations of both traditional modulators and PROTACs. These molecules may have a range of mechanisms: recruitment of an E3 ligase (molecular glues), introduction of hydrophobic areas, or inducing local unfolding, each of which triggers degradation.We recently completed a high-throughput screen of 111,000 compounds in a cellular HiBiT assay in an effort to identify such molecules. Preliminary analysis indicates that we have been able to identify alternative small-molecule degraders. We highlight methods for triage, characterization, selectivity, and mode of action. In summary, we believe that these types of small-molecule degraders, which may possibly have more acceptable physicochemical properties than the inherently larger heterobifunctional molecules, are an exciting approach for inducing TPD, and we illustrate that a general screening approach can be successful in identifying useful start points for developing such molecules.

The Vital Role of Proteomics in Characterizing Novel Protein Degraders.

Mass spectrometry-based proteomics profiling is a discovery tool that enables researchers to understand the mechanisms of action of drug candidates. When applied to proteolysis targeting chimeras (PROTACs) such approaches provide unbiased perspectives of the binding, degradation selectivity, and mechanism related to efficacy and safety. Specifically, global profiling experiments can identify direct degradation events and assess downstream pathway modulation that may result from degradation or off-target inhibition. Targeted proteomics approaches can be used to quantify the levels of relevant E3 ligases and the protein of interest in cell lines and tissues of interest, which can inform the line of sight and provide insights on possible safety liabilities early in the project. Furthermore, proteomics approaches can be applied to understand protein turnover and resynthesis rates and inform on target tractability, as well as pharmacokinetics/pharmacodynamics understanding. In this perspective, we survey the literature around the impact of mass spectrometry-based proteomics in the development of PROTACs and present our envisioned proteomics cascade for supporting targeted protein degradation projects.

A Tale of Two Tails: Efficient Profiling of Protein Degraders by Specific Functional and Target Engagement Readouts.

Targeted protein degradation represents an area of great interest, potentially offering improvements with respect to dosing, side effects, drug resistance, and reaching "undruggable" proteins compared with traditional small-molecule therapeutics. A major challenge in the design and characterization of degraders acting as molecular glues is that binding of the molecule to the protein of interest (PoI) is not needed for efficient and selective protein degradation; instead, one needs to understand the interaction with the responsible ligase. Similarly, for proteasome targeting chimeras (PROTACs), understanding the binding characteristics of the PoI alone is not sufficient. Therefore, simultaneously assessing the binding to both PoI and the E3 ligase as well as the resulting degradation profile is of great value. The cellular thermal shift assay (CETSA) is an unbiased cell-based method, designed to investigate the interaction of compounds with their cellular protein targets by measuring compound-induced changes in protein thermal stability. In combination with mass spectrometry (MS), CETSA can simultaneously evaluate compound-induced changes in the stability of thousands of proteins. We have used CETSA MS to profile a number of protein degraders, including molecular glues (e.g., immunomodulatory drugs) and PROTACs, to understand mode of action and to deconvolute off-target effects in intact cells. Within the same experiment, we were able to monitor both target engagement by observing changes in protein thermal stability as well as efficacy by simultaneous assessment of protein abundances. This allowed us to correlate target engagement (i.e., binding to the PoI and ligases) and functional readout (i.e., degrader induced protein degradation).

High-Throughput Quantitative Assay Technologies for Accelerating the Discovery and Optimization of Targeted Protein Degradation Therapeutics.

The aberrant regulation of protein expression and function can drastically alter cellular physiology and lead to numerous pathophysiological conditions such as cancer, inflammatory diseases, and neurodegeneration. The steady-state expression levels of endogenous proteins are controlled by a balance of de novo synthesis rates and degradation rates. Moreover, the levels of activated proteins in signaling cascades can be further modulated by a variety of posttranslational modifications and protein-protein interactions. The field of targeted protein degradation is an emerging area for drug discovery in which small molecules are used to recruit E3 ubiquitin ligases to catalyze the ubiquitination and subsequent degradation of disease-causing target proteins by the proteasome in both a dose- and time-dependent manner. Traditional approaches for quantifying protein level changes in cells, such as Western blots, are typically low throughput with limited quantification, making it hard to drive the rapid development of therapeutics that induce selective, rapid, and sustained protein degradation. In the last decade, a number of techniques and technologies have emerged that have helped to accelerate targeted protein degradation drug discovery efforts, including the use of fluorescent protein fusions and reporter tags, flow cytometry, time-resolved fluorescence energy transfer (TR-FRET), and split luciferase systems. Here we discuss the advantages and disadvantages associated with these technologies and their application to the development and optimization of degraders as therapeutics.

Comparative Determination of Cytotoxicity of Sub-10 nm Copper Nanoparticles to Prokaryotic and Eukaryotic Systems.

Copper nanoparticles demonstrate antibacterial activity, but their toxicity to eukaryotic systems is less understood. Here, we carried out a comparative study to determine the biocompatibility and cytotoxicity of sub-10 nm copper nanoparticles to a variety of biological systems, including prokaryotic cells (Escherichia coli), yeast, mammalian cell lines (HEK293T, PC12), and zebrafish embryos. We determined the bearing threshold for the cell-death-inducing concentration of copper nanoparticles by probing cell growth, viability, as well as embryological features. To exclude the partial toxicity effect from the remnant reactants, we developed a purification approach using agarose gel electrophoresis. Purified CuONP solution inhibits bacterial growth and causes eukaryotic cell death at 170 and 122.5 ppm (w/w) during the 18 h of treatment, respectively. CuONP significantly reduces the pigmentation of retina pigmented epithelium of zebrafish embryos at 85 ppm. The cytotoxicity of CuONP in eukaryotic cells could arise from the oxidative stress induced by CuONP. This result suggests that small copper nanoparticles exert cytotoxicity in both prokaryotic and eukaryotic systems, and therefore, caution should be used to avoid direct contact of copper nanoparticles to human tissues considering the potential use of copper nanoparticles in the clinical setting.

QSAR modeling of algal low level toxicity values of different phenol and aniline derivatives using 2D descriptors.

The deposition of different types of phenol and aniline derivatives in the aquatic environment leads to toxicity to living organisms. Under such condition, evaluation of these toxicants is very much important. Due to non-availability of sufficient experimental data as well as sufficient number of Quantitative Structure-Activity Relationship (QSAR) models for the low level toxicity values for such pollutants, we have employed here the partial least squares (PLS) regression for the development of robust and predictive QSAR models using low level toxicity values against algal species. Here, we have used both Extended Topochemical Atom (ETA) and non-ETA indices as 2D descriptors for model development. The statistical validation parameters ensure the robustness and the predictivity of the developed models. From the insights of the final PLS models, it can be concluded that presence of nitro groups (in the ortho position to phenolic hydroxyl group increasing intramolecular hydrogen bonding capacity), presence of chlorine substituents (influencing lipophilicity) especially at the para position, oxygen and nitrogen at the topological distance three, aliphatic side chain (contributing to hydrophobicity), molecules with large size atoms and higher molecular bulk will increase the toxicity towards the algal species. On the other hand, the phenol ring without any substituent or with a polar substituent (like amino group), presence of chlorine at ortho-ortho or ortho-para position, absence of nitro group, presence of chlorine and oxygen at the topological distance three, presence of lower number of aliphatic groups will decrease the toxic effect towards the algal species.

Saccharomyces cerevisiae and Caffeine Implications on the Eukaryotic Cell.

Caffeine-a methylxanthine analogue of the purine bases adenine and guanine-is by far the most consumed neuro-stimulant, being the active principle of widely consumed beverages such as coffee, tea, hot chocolate, and cola. While the best-known action of caffeine is to prevent sleepiness by blocking the adenosine receptors, caffeine exerts a pleiotropic effect on cells, which lead to the activation or inhibition of various cell integrity pathways. The aim of this review is to present the main studies set to investigate the effects of caffeine on cells using the model eukaryotic microorganism Saccharomyces cerevisiae, highlighting the caffeine synergy with external cell stressors, such as irradiation or exposure to various chemical hazards, including cigarette smoke or chemical carcinogens. The review also focuses on the importance of caffeine-related yeast phenotypes used to resolve molecular mechanisms involved in cell signaling through conserved pathways, such as target of rapamycin (TOR) signaling, Pkc1-Mpk1 mitogen activated protein kinase (MAPK) cascade, or Ras/cAMP protein kinase A (PKA) pathway.

Novel insights into the roles of RNA N6-methyladenosine modification in regulating gene expression during environmental exposures.

N6-methyladenosine (m6A) is one of the most common RNA modifications in eukaryotes involved in the regulation of post-transcriptional gene expression, as well as the occurrence and development of diseases related to environmental exposures. Adverse factors produced by environmental exposures, such as reactive oxygen species, inflammation, and cyclobutane pyrimidine dimers, mediate m6A modification, thereby regulating downstream gene and protein expression, and signaling pathways, such as FTO/m6A RNA/p53 axis, PI3K/AKT/mTOR pathway, and PARP/METTL3/m6A RNA/Pol κ pathway. Moreover, an imbalance in m6A methylation levels directly mediates disease pathogenesis. To date, some studies have detailed the mechanisms underlying environmental exposure-mediated global changes in RNA m6A methylation. Based on our current understanding, we aimed to elaborate on the molecular mechanisms through which RNA m6A methylation regulates gene expression under environmental exposures. In this review, we outline the biogenesis and functions of RNA m6A modification. Furthermore, we focus on the effects of environmental exposures on m6A levels and highlight the relationships between environmental exposures (doses and time) and m6A levels. Although the molecular mechanisms regulating gene expression remains to be elucidated, m6A has potential applications as a disease biomarker.

Epigenetic and epitranscriptomic regulation of viral replication.

Eukaryotic gene expression is regulated not only by genomic enhancers and promoters, but also by covalent modifications added to both chromatin and RNAs. Whereas cellular gene expression may be either enhanced or inhibited by specific epigenetic modifications deposited on histones (in particular, histone H3), these epigenetic modifications can also repress viral gene expression, potentially functioning as a potent antiviral innate immune response in DNA virus-infected cells. However, viruses have evolved countermeasures that prevent the epigenetic silencing of their genes during lytic replication, and they can also take advantage of epigenetic silencing to establish latent infections. By contrast, the various covalent modifications added to RNAs, termed epitranscriptomic modifications, can positively regulate mRNA translation and/or stability, and both DNA and RNA viruses have evolved to utilize epitranscriptomic modifications as a means to maximize viral gene expression. As a consequence, both chromatin and RNA modifications could serve as novel targets for the development of antivirals. In this Review, we discuss how host epigenetic and epitranscriptomic processes regulate viral gene expression at the levels of chromatin and RNA function, respectively, and explore how viruses modify, avoid or utilize these processes in order to regulate viral gene expression.

Chemical diversity and mode of action of natural products targeting lipids in the eukaryotic cell membrane.

Covering: up to 2019Nature furnishes bioactive compounds (natural products) with complex chemical structures, yet with simple, sophisticated molecular mechanisms. When natural products exhibit their activities in cells or bodies, they first have to bind or react with a target molecule in/on the cell. The cell membrane is a major target for bioactive compounds. Recently, our understanding of the molecular mechanism of interactions between natural products and membrane lipids progressed with the aid of newly-developed analytical methods. New technology reconnects old compounds with membrane lipids, while new membrane-targeting molecules are being discovered through the screening for antimicrobial potential of natural products. This review article focuses on natural products that bind to eukaryotic membrane lipids, and includes clinically important molecules and key research tools. The chemical diversity of membrane-targeting natural products and the molecular basis of lipid recognition are described. The history of how their mechanism was unveiled, and how these natural products are used in research are also mentioned.