Biology subjects

Dutta, D.

Publications and source records attributed to Dutta, D..

At least 37 records · Page 2Linked to original sources

bioRxiv2024

Kinase activity of histone chaperone APLF maintains steady state of centrosomes in mouse embryonic stem cells

Our recent studies revealed the role of mouse Aprataxin PNK-like Factor (APLF) in development. Nevertheless, the comprehensive characterization of mouse APLF remains entirely unexplored. Based on domain deletion studies, here we report that mouse APLFs Acidic Domain and Fork Head Associated (FHA) domain can chaperone histones and repair DNA like the respective human orthologs. Immunofluorescence studies in mouse embryonic stem cells showed APLF co-localized with {gamma}-tubulin within and around the centrosomes and govern the number and integrity of centrosomes via PLK4 phosphorylation. Enzymatic analysis established mouse APLF as a kinase. Docking studies identified three putative ATP binding sites within the FHA domain. Site-directed mutagenesis showed that R37 residue is indispensable for the kinase activity of APLF thereby regulating the centrosome number. These findings might assist us comprehend APLF in different pathological and developmental conditions and reveal non-canonical kinase activity of proteins harbouring FHA domains that might impact multiple cellular processes.

biochemistry↗

bioRxiv2023

Rho and a riboswitch regulate mntP expression evading manganese stress and membrane toxicity

The trace metal ion manganese in excess is toxic. Therefore, a small subset of factors tightly maintains its cellular level, among which an efflux protein MntP is the champion. Multiple transcriptional regulators and a manganese-dependent translational riboswitch regulate the MntP expression. As riboswitches are untranslated RNAs, they are often associated with the Rho-dependent transcription termination in bacteria. Here we demonstrate that Rho efficiently terminates transcription at the mntP riboswitch region. The addition of manganese activates the riboswitch, thereby restoring the coupling between transcription and translation to evade Rho-dependent transcription termination partially. Deletion of the riboswitch abolishes Rho-dependent termination and renders bacteria sensitive to manganese due to overexpression of mntP. The high mntP expression is associated with reactive oxygen species (ROS) production, slow growth, and cell filamentation phenotypes. We posit that manganese-dependent transcriptional activation in the absence of Rho-dependent termination leads to the observed toxicity arising from excessive MntP expression, a membrane protein. Thus, we identified a novel regulatory role of Rho in preventing membrane protein toxicity by terminating at the riboswitch element.

biochemistry↗

bioRxiv2023

Dissection and reconstruction of the colorectal cancer tumor microenvironment

Patient-derived organoids (PDOs) are the reference in vitro human disease models. However, the utility of colorectal cancer (CRC) PDOs is hindered by the lack of a tumor microenvironment (TME). To address this limitation, we built a living biobank of CRC PDOs with autologous stromal and immune TME. We characterized the original tumors and traditional monocultures using single-cell RNA-seq (scRNA-seq) and whole exome sequencing (WES) to obtain insights into cell type selection and phenotypic drift in culture. Subsequently, we developed culture conditions supporting all cell types to recapitulate the CRC-TME around PDOs. From the transcriptomes of >180k cells obtained from 260 such co-cultures, we illuminated the mutual influence of cells within CRC tumors. Based on original tumor data, atlases of predicted interactions and transcriptional networks elucidated why monocultures were altered and suggested that TME reconstruction more accurately reflected original tumor behavior. We found that inflammatory signals were absent in vitro and recovered upon co-culture with tumor-infiltrating lymphocytes (TILs). We also functionally confirmed that stromal, not cancer cells, mediated immune evasion. Additionally, stroma induced an invasive phenotype in cancer cells. From this deep dive into CRC-TME interactions, we built the human CRC-TME atlas (https://crc-tme.com/), an online portal for interactive exploration of gene expression data, prediction of cell-cell interactions at the pathway and receptor/ligand levels, transcriptional networks, and more. We anticipate PDO cultures with reconstructed TMEs will be valuable for discovery efforts, preclinical studies, and personalized medicine, with the atlas as a framework and inspiration for future CRC-TME studies.

cancer biology↗

bioRxiv2023

Bicyclomycin generates ROS and blocks cell division in Escherichia coli

The role of reactive oxygen species (ROS) in the killing exerted by antibiotics on bacteria is debated. Evidences attribute the part of toxicity of many antibiotics to their ability to generate ROS by interfering with cellular metabolism, but some studies dismiss the role of ROS. Bicyclomycin (BCM) is a broad-spectrum antibiotic that is the only known compound to inhibit E. coli transcription terminator factor Rho with no known other cellular targets. In the present study, we addressed this question by checking whether the induction of oxidative stress could explain the increased sensitivity to Bicyclomycin in the hns deleted strain even in {Delta}kil background in E. coli. BCM evoked the generation of ROS in E. coli cells. BCM is known to cause the cell filamentation phenotype in E. coli. Performing fluorescence microscopic analysis, we show that bicyclomycin-dependent cell filamentation is associated with SOS response. RecA- GFP filaments were found to colocalize with the damaged DNA sites in the cell. Further analyzes revealed that the genomic DNA was partitioned but the cell septum formation was severely affected under BCM treatment. Furthermore, we observed biofilm formation by E. coli after BCM treatment. We hypothesize that ROS production after BCM treatment could lead to cell filamentation in bacteria. A better understanding of the mode of toxicity of BCM will help us in designing better antibiotic treatment regimes for clinical practices, including combinatorial drug therapies. The cell filamentation phenotype observed after BCM treatment makes this antibiotic a promising drug for PAS therapy.

microbiology↗

bioRxiv2023

Loss of Mitochondrial Enoyl CoA Reductase causes elevated ceramide levels and impairs iron metabolism

In most eukaryotic cells fatty acid synthesis occurs in the cytoplasm as well as in mitochondria. However, the relative contribution of mitochondrial fatty acid synthesis (mtFAS) to the cellular lipidome of metazoans is ill-defined. Hence, we studied the function of the fly Mitochondria enoyl CoA reductase (Mecr), the enzyme required for the last step of mtFAS. Loss of mecr causes lethality while neuronal loss leads to progressive neurological defects. We observe an elevated level of ceramides, a defect in Fe-S cluster biogenesis and increased iron levels in mecr mutants. Reducing the levels of either iron or ceramide suppresses the neurodegenerative phenotypes indicating that increased ceramides and iron metabolism are interrelated and play an important role in the pathogenesis. Mutations in human MECR cause pediatric-onset neurodegeneration and patient-derived fibroblasts display similar elevated ceramide levels and impaired iron homeostasis. In summary, this study shows an as-yet-unidentified role of mecr/MECR in ceramide and iron metabolism providing a mechanistic link between mtFAS and neurodegeneration.

neuroscience↗

bioRxiv2023

Cryo-EM structure of the human cardiac myosin filament

AbstractPumping of the heart is powered by filaments of the motor protein myosin, which pull on actin filaments to generate cardiac contraction. In addition to myosin, the filaments contain cardiac myosin-binding protein C (cMyBP-C), which modulates contractility in response to physiological stimuli, and titin, which functions as a scaffold for filament assembly1. Myosin, cMyBP-C and titin are all subject to mutation, which can lead to heart failure. Despite the central importance of cardiac myosin filaments to life, their molecular structure has remained a mystery for 60 years2. Here, we have solved the structure of the main (cMyBP-C-containing) region of the human cardiac filament to 6 [A] resolution by cryo-EM. The reconstruction reveals the architecture of titin and cMyBP-C for the first time, and shows how myosins motor domains (heads) form 3 different types of motif (providing functional flexibility), which interact with each other and with specific domains of titin and cMyBP-C to dictate filament architecture and regulate function. A novel packing of myosin tails in the filament backbone is also resolved. The structure suggests how cMyBP-C helps generate the cardiac super-relaxed state3, how titin and cMyBP-C may contribute to length-dependent activation4, and how mutations in myosin and cMyBP-C might disrupt interactions, causing disease5, 6. A similar structure is likely in vertebrate skeletal myosin filaments. The reconstruction resolves past uncertainties, and integrates previous data on cardiac muscle structure and function. It provides a new paradigm for interpreting structural, physiological and clinical observations, and for the design of potential therapeutic drugs.

biophysics↗

bioRxiv2023

Differentiation state and culture conditions impact neural stem/progenitor cell-derived extracellular vesicle bioactivity

Extracellular vesicles (EVs) derived from neural progenitor/stem cells (NPSCs) have shown promising efficacy in a variety of preclinical models. However, NPSCs lack critical neuroregenerative functionality such as myelinating capacity. Further, culture conditions used in NPSC EV production lack standardization and identification of optimal conditions for NPSC EV neurogenic bioactivity. Here, we assessed whether further differentiated oligodendrocyte precursor cells (OPCs) and immature oligodendrocytes (iOLs) that give rise to mature myelinating oligodendrocytes could yield EVs with neurotherapeutic properties comparable or superior to those from NPSCs as well as mesenchymal stromal cells (MSCs), as MSC EVs are also commonly reported to have neurotherapeutic activity. We additionally examined the effects of four different extracellular matrix (ECM) coating materials (laminin, fibronectin, Matrigel, and collagen IV) and the presence or absence of growth factors (EGF, bFGF, and NGF) in cell culture on the ultimate properties of EVs. The data show that OPC EVs and iOL EVs performed similarly to NPSC EVs in PC-12 proliferation and RAW264.7 mouse macrophage antiinflammatory assays, but NPSC EVs performed better in a PC-12 neurite outgrowth assay. Additionally, the presence of nerve growth factor (NGF) in culture was found to be maximize NPSC EV bioactivity among the conditions tested. NPSC EVs produced under rationally-selected culture conditions (fibronectin + NGF) enhanced axonal regeneration and muscle reinnervation in a rat nerve crush injury model. These results highlight the impact of culture conditions on NPSC EV neuroregenerative bioactivity, thus providing additional rationale for standardization and optimization of culture conditions for NPSC EV production. Table of Contents O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=35 SRC="FIGDIR/small/528366v1_ufig1.gif" ALT="Figure 1"> View larger version (13K): org.highwire.dtl.DTLVardef@447d23org.highwire.dtl.DTLVardef@73a5cborg.highwire.dtl.DTLVardef@89dbb0org.highwire.dtl.DTLVardef@b62d39_HPS_FORMAT_FIGEXP M_FIG C_FIG Extracellular vesicles (EVs) purified from neural progenitor/stem cells (NPSCs) have been investigated for neurotherapeutic activity, however significant variability in culture conditions limits reproducibility and efficacy of this approach. Here, we examined the impact of extracellular matrix (ECM) components and growth factors in NPSC culture on the bioactivity on the bioactivity of their EVs. The results show that EVs from NPSCs cultured with a rationally-selected ECM type (fibronectin) and growth factor (nerve growth factor (NGF)) enhanced nerve regeneration and muscle recovery in a rat sciatic nerve crush injury model.

bioengineering↗

bioRxiv2022

An intrinsic alkalization circuit turns on mntP-riboswitch under manganese stress in Escherichia coli

The trace metal manganese in excess affects iron-sulfur cluster and heme-protein biogenesis eliciting cellular toxicity. The manganese efflux protein MntP is crucial to evading manganese toxicity in bacteria. Recently, two Mn-sensing riboswitches upstream of mntP and alx in Escherichia coli have been reported to mediate the upregulation of their expression under manganese shock. As the alx-riboswitch is also responsive to alkaline shock administered externally, it is intriguing whether mntP-riboswitch is also responsive to alkaline stress. Furthermore, how both manganese and alkaline pH simultaneously regulate these two riboswitches under physiological conditions is a puzzle. Using multiple approaches, we show that manganese shock activated glutamine synthetase (GlnA) and glutaminases (GlsA and GlsB) to spike ammonia production in E. coli. The elevated ammonia intrinsically alkalizes the cytoplasm. We establish that this alkalization under manganese stress is crucial for attaining the highest degree of riboswitch activation. Additional studies showed that alkaline pH promotes a 17 to 22-fold tighter interaction between manganese and the mntP-riboswitch element. Our study uncovers a physiological linkage between manganese efflux and pH homeostasis that mediates enhanced manganese tolerance. Significance statementRiboswitch RNAs are cis-acting elements that can adopt alternative conformations in the presence or absence of a specific ligand(s) to modulate transcription termination or translation initiation processes. In the present work, we show that how manganese and alkaline pH both are necessary for maximal mntP-riboswitch activation to mitigate the manganese toxicity. This study bridges the gap between earlier studies that separately emphasize the importance of alkaline pH and manganese in activating the riboswitches belonging to the yybP-ykoY-family. This study also ascribes a physiological relevance as to how manganese can rewire cellular physiology to render cytoplasmic pH alkaline for its homeostasis.

biochemistry↗

bioRxiv2022

Genome-Wide Large-Scale Multi-Trait Analysis Characterizes Global Patterns of Pleiotropy and Unique Trait-Specific Variants

Genome-wide association studies (GWAS) have found widespread evidence of pleiotropy, but characterization of global patterns of pleiotropy remain highly incomplete due to insufficient power of current approaches. We develop fastASSET, an extension of the method ASSET, to allow computationally efficient detection of variant-level pleiotropic association across a large number of traits. We analyze GWAS summary statistics of 116 complex traits of diverse types collected from the NIH GRASP repository and a number of other large GWAS consortia. We identify a total of 2,293 independent loci at the genome-wide significance level and found that the lead variants in nearly all of these loci ([~]99%) to be associated with to two or more (median = 6) traits. Further, the estimated degree of pleiotropy for the detected variants strongly predicted their degree of pleiotropy across a much larger number of traits (K=4,114) in the UK Biobank Study. Follow-up analyses of 21 unique trait-specific variants suggest that they are often linked to the expression in trait-related tissues for a small number of genes, some of which are well known to be involved in relevant biological processes. Our findings provide deeper insight into the nature of complex trait pleiotropy and leads to, for the first time, identification of highly unique trait-specific susceptibility variants.

genetics↗

bioRxiv2021

An expanded toolkit for Drosophila gene tagging using synthesized homology donor constructs for CRISPR mediated homologous recombination

Previously, we described a large collection of Drosophila strains that each carry an artificial exon containing a T2AGAL4 cassette inserted in an intron of a target gene based on CRISPR-mediated homologous recombination (Lee et al., 2018). These alleles permit numerous applications and have proven to be very useful. Initially, the homologous recombination-based donor constructs had long homology arms (>500 bps) to promote precise integration of large constructs (>5kb). Recently, we showed that in vivo linearization of the donor constructs enables insertion of large artificial exons in introns using short homology arms (100-200 bps) (Kanca et al., 2019a). Shorter homology arms make it feasible to commercially synthesize homology donors and minimize the cloning steps for donor construct generation. Unfortunately, about 50% of Drosophila genes lack suitable coding introns for integration of artificial exons. Here, we report the development of new set of constructs that allow the replacement of the coding region of genes that lack suitable introns with a KozakGAL4 cassette, generating a knock-out/knock-in allele that expresses GAL4 similarly as the targeted gene. We also developed custom vector backbones to further facilitate and improve transgenesis. Synthesis of homology donor constructs in custom plasmid backbones that contain the target gene sgRNA obviates the need to inject a separate sgRNA plasmid and significantly increases the transgenesis efficiency. These upgrades will enable the targeting of nearly every fly gene, regardless of exon-intron structure, with a 70-80% success rate.

genetics↗

bioRxiv2021

Sustained Released of Bioactive Mesenchymal Stromal Cell-Derived Extracellular Vesicles from 3D-Printed Gelatin Methacrylate Hydrogels

Extracellular vesicles (EVs) represent an emerging class of therapeutics with significant potential and broad applicability. However, a general limitation is their rapid clearance after administration. Thus, methods to enable sustained EV release are of great potential value. Here, we demonstrate that EVs from mesenchymal stem/stromal cells (MSCs) can be incorporated into 3D-printed gelatin methacrylate (GelMA) hydrogel bioink, and that the initial burst release of EVs can be reduced by increasing the concentration of crosslinker during gelation. Further, the data show that MSC EV bioactivity in an endothelial gap closure assay is retained after the 3D printing and photocrosslinking processes. Our group previously showed that MSC EV bioactivity in this assay correlates with pro-angiogenic bioactivity in vivo, thus these results indicate therapeutic potential of MSC EV-laden GelMA bioinks.

bioengineering↗

bioRxiv2021

Free spermidine evokes superoxide radicals that manifest toxicity

Spermidine and other polyamines alleviate oxidative stress, yet excess spermidine seems toxic to Escherichia coli unless it is neutralized by SpeG, an enzyme for the spermidine N-acetyl transferase function. Besides, a specific mechanism of SpeG function conferring pathogenic fitness to Staphylococcus aureus USA300 strain is unknown. Here, we provide evidence that although spermidine mitigates oxidative stress by lowering hydroxyl radical and hydrogen peroxide levels, excess of it simultaneously triggers the production of superoxide radicals, thereby causing toxicity in the E. coli {Delta}speG strain as well as naturally SpeG-deficient S. aureus RN4220 strain. However, wild-type E. coli and S. aureus USA300 with a horizontally-acquired speG gene tolerate applied exogenous spermidine stress. Furthermore, we demonstrate that while RNA-bound spermidine inhibits iron oxidation, free spermidine interacts and oxidizes the iron to evoke superoxide radicals directly. Superoxide radicals thus generated, further affects redox balance and iron homeostasis. Since iron acquisition and metabolism in the host tissues is a challenging task for S. aureus, the current findings helped us explain that the evolutionary gain of SpeG function by S. aureus USA300 strain allows it to neutralize exogenous spermidine- and spermine-mediated toxicity towards iron metabolism inside the host tissues.

biochemistry↗

bioRxiv2021

Probing the killing potency of tumor-infiltrating lymphocytes on microarrayed autologous tumoroids

Immunotherapy has shown promise as an approach to fight cancer by harnessing the immune system. However, due to the lack of biomarkers to guide treatment regimens and predict response rates, there is an unmet need for more robust ex vivo and in vitro systems that recapitulate patient-specific tumor biology and enable response prediction for immune therapies in an autologous setting. To address this issue, we developed a high-content screening-compatible assay based on microcavity arrays to study tumor-infiltrating lymphocyte (TIL) functionality on 3D tumoroid models. We validated our system using the pmel-1 activated T cell mouse model to assess both cancer immunogenicity and T cell functionality. To demonstrate the translational potential of the platform, we used it to evaluate the response of patient-derived TILs to autologous human colorectal cancer (CRC) tumoroids. Using a combination of imaging and flow cytometry, we determined several features of the antitumor activity of TILs, including the extent of tumoroid killing and secretion of cytokines. We then used the approach to identify responders to immunotherapy, such as the immune checkpoint blockade (ICB) agent Nivolumab (PD-1 inhibitor) and Ipilimumab (CTLA-4 inhibitor). Our system allows not only the identification of immunogenic tumors, but also the testing of patients for response to immunomodulators, enabling personalized immuno-oncology.

cancer biology↗

bioRxiv2021

Large Bi-Ethnic Study of Plasma Proteome Leads to Comprehensive Mapping of cis-pQTL and Models for Proteome-wide Association Studies

Improved understanding of genetic regulation of proteome can facilitate the identification of causal mechanisms for complex traits. We analyzed data on 4,657 plasma proteins from 7,213 European American (EA) and 1,871 African American (AA) individuals from the ARIC study, and further replicated findings on 467 AA individuals from the AASK study. Here we identified 2,004 proteins in EA and 1,618 in AA, with majority overlapping, which showed associations with common variants in cis-regions. Availability of AA samples led to smaller credible sets and significant number of population-specific cis-pQTLs. Elastic-net produced powerful models for protein prediction in both populations. An application of proteome-wide association studies (PWAS) to serum urate and gout, implicated several proteins, including IL1RN, revealing the promise of the drug anakinra to treat acute gout flares. Our study demonstrates the value of large and diverse ancestry study for genetic mechanisms of molecular phenotypes and their relationship with complex traits.

genetics↗

bioRxiv2020

Swi6/HP1 binding to RNA-DNA hybrids initiates heterochromatin assembly at the centromeric dg-dh repeats in Fission Yeast

Canonically, heterochromatin formation in fission yeast and metazoans is initiated by di/trimethylation of histone H3 at lysine 9 position by the histone methyltransferase Suv39H1/Clr4, followed by binding of Swi6/HP1 to H3-K9-me2/me3 via its chromodomain. Subsequent self-association of Swi6/HP1 on adjacent nucleosomes or a cooperative interaction between Clr4 and Swi6/HP1 leads to folded heterochromatin structure. HP1 binding to RNA is shown to facilitate its localization at and assembly of heterochromatin in metazoans. Likewise, recruitment of Swi6/HP1 to centromere depends on the RNAi pathway in fission yeast; paradoxically, Swi6/HP1 is also thought to play a role in RNA turnover. Here we provide evidence in support of RNAi-independent recruitment of Swi6. We show that, apart from the low affinity binding to RNAs through its hinge domain, as already reported, Swi6/HP1 displays a hierarchy of increasing binding affinity through its chromodomain to the siRNAs corresponding to specific dg-dh repeats and even stronger binding to the cognate siRNA-DNA hybrids than to the siRNA precursors or general RNAs. Our results support a mechanism of recruitment of Swi6, which is dependent on its specific and high affinity binding to siRNA-DNA hybrid at the dg-dh repeats. This binding, which is independent of, albeit augmented by binding to H3-K9-Me2, leads to heterochromatin formation and silencing. We suggest that the net role of Swi6 in RNA physiology may be regulated by a balance between abundance and affinity of Swi6 towards heterochromatic and euchromatic RNAs and siRNAs.

genetics↗

bioRxiv2020

Cell growth model with stochastic gene expression helps understand the growth advantage of metabolic exchange and auxotrophy

During cooperative growth, microbes often experience higher fitness, due to sharing of resources by metabolic exchange and herd protection through biofilm structures. However, the trajectory of evolution of competitive species towards cooperation is not known. Moreover, existing models (based on optimisation of steady-state resources or fluxes) are often unable to explain the growth advantage for the cooperating species, even for simple reciprocally cross-feeding auxotrophic pairs. We present an abstracted model of cell growth that considers the stochastic burst-like gene expression of biosynthetic pathways of limiting biomass precursor metabolites, and directly connects their cellular levels to growth and division using a "metabolic sizer/adder" rule. Our model recapitulates Monods law and yields the experimentally observed right-skewed long-tailed distribution of cell doubling times. The model further predicts the growth effect of secretion and uptake of metabolites, by linking it to changes in the internal metabolite levels. The model also explains why auxotrophs may grow faster when provided the metabolite they cannot produce, and why a pair of reciprocally cross-feeding auxotrophs can grow faster than prototrophs. Overall, our framework allows us to predict the growth effect of metabolic interactions in microbial communities and also sets the stage to study the evolution of these interactions. ImportanceCooperative behaviours are highly prevalent in the wild, but we do not understand how it evolves. Metabolic flux models can demonstrate the viability of metabolic exchange as cooperative interactions, but steady-state growth models cannot explain why cooperators grow faster. We present a stochastic model that connects growth to the cells internal metabolite levels and quantifies the growth effect of metabolite exchange and auxotrophy. We show that a reduction in gene expression noise explains why cells that import metabolites or become auxotrophs can grow faster, and also why reciprocal cross-feeding of metabolites between complementary auxotrophs allow them to grow faster. Our framework can simulate the growth of interacting cells, which will enable us to understand the possible trajectories of the evolution of cooperation in silico.

systems biology↗

bioRxiv2019

A powerful subset-based gene-set analysis method identifies novel associations and improves interpretation in UK Biobank

Tests of association between a phenotype and a set of genes in a biological pathway can provide insights into the genetic architecture of complex phenotypes beyond those obtained from single variant or single gene association analysis. However, most existing gene set tests have limited power to detect gene set-phenotype association when a small fraction of the genes are associated with the phenotype, and no method exists which identifies the potentially "active" genes that might drive a gene-set-based association. To address these issues, we have developed Gene-set analysis Association Using Sparse Signals (GAUSS), a method for gene-set association analysis that requires only GWAS summary statistics. For each significantly associated gene set, GAUSS identifies the subset of genes that have the maximal evidence of association and can best account for the gene set association. Using pre-computed correlation structure among test statistics from a reference panel, our p-value calculation is substantially faster than other permutation or simulation-based approaches. In simulations with varying proportions of causal genes, we find that GAUSS effectively controls type 1 error rate and has greater power than several existing methods, particularly when a small proportion of genes account for the gene set signal. Using GAUSS, we analyzed UK Biobank GWAS summary statistics for 10,679 gene-sets and 1,403 binary phenotypes. We found that GAUSS is scalable and identified 13,466 phenotype and gene-set association pairs. Within these genes sets, we identify an average of 17.2 (max=405) genes that underlie these gene set associations.

genetics↗

bioRxiv2019

Mode of action of the antimicrobial peptide Mel4 is independent of Staphylococcus aureus cell membrane permeability

Mel4 is a novel cationic peptide with potent activity against Gram-positive bacteria. The current study examined the anti-staphylococcal mechanism of action of Mel4 and its precursor peptide melimine. The interaction of peptides with lipoteichoic acid (LTA) and with the cytoplasmic membrane using DiSC(3)-5, Sytox green, Syto-9 and PI dyes were studied. Release of ATP and DNA/RNA from cells exposed to the peptides were determined. Bacteriolysis and autolysin-activated cell death were determined by measuring decreases in OD620nm and killing of Micrococcus luteus cells by cell-free media. Both peptides bound to LTA and rapidly dissipated the membrane potential (within 30 seconds) without affecting bacterial viability. Disturbance of the membrane potential was followed by the release of ATP (50% of total cellular ATP) by melimine and by Mel4 (20%) after 2 minutes exposure (p<0.001). Mel4 resulted in staphylococcal cells taking up PI with 3.9% cells predominantly stained after 150 min exposure, whereas melimine showed 34% staining. Unlike melimine, Mel4 did not release DNA/RNA. Cell-free media from Mel4 treated cells hydrolysed peptidoglycan and produced greater zones of inhibition against M. luteus lawn than melimine treated samples. These findings suggest that pore formation is unlikely to be involved in Mel4-mediated membrane destabilization for Staphylococcci, since there was no significant Mel4-induced PI staining and DNA/RNA leakage. It is likely that the S. aureus killing mechanism of Mel4 involves the release of autolysins followed by cell death. Whereas, membrane interaction is the primary bactericidal activity of melimine, which includes membrane depolarisation, pore formation, release of cellular contents leading to cell death.\n\nThis work is original, has not been published and is not being considered for publication elsewhere. Part of this manuscript has been presented as a poster presentation in Gordon Research Conference Italy in 2019. There are no conflicts of interest for any of the authors that could have influenced the results of this work. Prof. Mark Willcox holds the patent the for the melimine peptide.

microbiology↗