Biology subjects

Verma, C. S.

Publications and source records attributed to Verma, C. S..

At least 19 recordsLinked to original sources

bioRxiv2025

A Multiscale Framework for Uncovering Surfactant Mediated Viral Capsid Disruption

Disinfection remains a critical strategy for controlling the transmission of infectious diseases. However, small non-enveloped viruses exhibit exceptional resistance to many disinfectants, often requiring harsh protein-disrupting chemicals for effective inactivation, thereby limiting their applicability in personal care products due to associated side effects. Sodium dodecyl sulphate (SDS) is a widely used anionic surfactant known for its virucidal efficacy; however, the molecular details of its action against robust non-enveloped viruses remain poorly understood, limiting efforts to design safer and more targeted antiviral formulations. In this study, a multiscale simulation approach combining a novel atomic-resolution icosahedral "scaffold framework" and coarse-grained modelling was developed to elucidate the mechanism of SDS-driven disruption of MS2 bacteriophage capsid, a surrogate for non-enveloped viruses. Experimental analyses including dynamic light scattering and transmission electron microscopy revealed that SDS inactivates MS2 in a strongly pH-dependent manner, triggering capsid disassembly at acidic pH while leaving particles largely intact at neutral pH. Molecular dynamics simulations demonstrated that SDS micelles preferentially associate with hexameric pores and inter-dimer clefts under acidic conditions, where protonation of acidic residues weakens the electrostatic network of the capsid surface. Together, these findings provide a detailed molecular framework for SDS virucidal action and highlight the importance of environmental pH in modulating surfactant-virus interactions. These insights offer a foundation for designing next-generation antiviral surfactants with improved efficacy and biocompatibility.

biophysics↗

bioRxiv2024

Peptide-Based Complex Coacervates Stabilized by Cation-π Interactions for Cell Engineering

Complex coacervation is a form of liquid-liquid phase separation (LLPS), whereby two types of macromolecules, usually bearing opposite net charges, self-assemble into dense microdroplets driven by weak molecular interactions. Peptide-based coacervates have recently emerged as promising carriers to deliver large macromolecules (nucleic acids, proteins and complex thereof) inside cells. Thus, it is essential to understand their assembly/disassembly mechanisms at the molecular level in order to tune the thermodynamics of coacervates formation and the kinetics of cargo release upon entering the cell. In this study, we design histidine-rich peptides consisting of modular sequences in which we systematically incorporate cationic, anionic, or aromatic residues at specific positions along the sequence in order to modulate intermolecular interactions and the resulting coacervation stability. We show that cation-{pi} interactions between arginine and aromatic side chains are particularly efficient in stabilizing complex coacervates, and these interactions can be disrupted in the protein-rich intracellular environment, triggering the disassembly of complex coacervates followed by cargo release. With the additional grafting of a disulfide-based self-immolative sidechain, these complex coacervates exhibit enhanced stability and can deliver proteins, mRNA, and CRISPR/Cas9 genome editing tools with tunable release kinetics into cells. This capability extends to challenging cell types, such as macrophages. Our study highlights the critical role of cation-{pi} interactions in the design of peptide-based coacervates, expanding the biomedical and biotechnology potential of this emerging innovative intracellular delivery platform. Table of ContentTandem peptides designed from histidine-rich beak proteins are modified with either negative, positive, or aromatic residues that can undergo complex coacervation through cation-{pi} rather than electrostatic interactions. These complex coacervates can effectively recruit various macromolecular cargos and deliver them intracellularly with controlled release kinetics, including in hard-to-transfect macrophages. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=183 SRC="FIGDIR/small/619264v1_ufig1.gif" ALT="Figure 1"> View larger version (65K): org.highwire.dtl.DTLVardef@1e92628org.highwire.dtl.DTLVardef@1c80e19org.highwire.dtl.DTLVardef@115ac05org.highwire.dtl.DTLVardef@1d0b122_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioengineering↗

bioRxiv2024

Phase-Separating Peptide Coacervates with Programmable Material Properties for Universal Intracellular Delivery of Macromolecules

Phase-separating peptides (PSPs) self-assembling into coacervate microdroplets (CMs) are a promising new class of intracellular delivery vehicles that can release macromolecular modalities deployed in a wide range of therapeutic treatments. However, the molecular grammar governing intracellular uptake and release kinetics of CMs remains elusive. Here, we systematically manipulated the sequence of PSPs to unravel the relationships between their molecular structure, the physical properties of the resulting CMs, and their delivery efficacy. We show that a few amino acid alterations are sufficient to modulate the viscoelastic properties of CMs towards either a gel-like or a liquid-like state as well as their binding interaction with cellular membranes, collectively enabling to tune the kinetics of intracellular cargo release. Our findings provide molecular guidelines to precisely program the material properties of PSP CMs and achieve tunable cellular uptake and release kinetics depending on the cargo modality, with broad implications for therapeutic applications.

bioengineering↗

bioRxiv2024

Rarγ-Foxa1 signaling promotes luminal identity in prostate progenitors and is disrupted in prostate cancer

Retinoic acid (RA) signaling is a master regulator of vertebrate development with crucial roles in directing body axis orientation and tissue differentiation, including in the reproductive system. However, a mechanistic understanding of how RA signaling promotes cell lineage identity in different tissues is often missing. Here, leveraging prostate organoid technology, we demonstrated that RA signaling orchestrates the commitment of adult mouse prostate progenitors to glandular identity, epithelial barrier integrity, and ultimately, proper specification of the prostatic lumen. Mechanistically, RA-dependent RAR{gamma} activation promotes the expression of the pioneer factor Foxa1, which synergizes with the androgen pathway for proper luminal expansion, cytoarchitecture and function. FOXA1 nucleotide variants are common in human prostate and breast cancers and considered driver mutations, though their pathogenic mechanism is incompletely understood. Combining functional genetics experiments with structural modeling of FOXA1 folding and chromatin binding analyses, we discovered that FOXA1F254E255 is a loss-of-function mutation leading to compromised transcriptional function and lack of luminal fate commitment of prostate progenitors. Overall, we define RA as a crucial instructive signal for glandular identity in adult prostate progenitors. We propose deregulation of vitamin A metabolism as a risk factor for benign and malignant prostate disease, and identified cancer associated FOXA1 indels affecting residue F254 as loss-of-function mutations promoting dedifferentiation of adult prostate progenitors. Summary: Retinoic acid signaling orchestrates luminal differentiation of adult prostate progenitors

cancer biology↗

bioRxiv2023

A coarse-grained model of glycosaminoglycans for biomolecular simulation

Proteoglycans contain glycosaminoglycans (GAGs), negatively charged linear polymers made of repeating disaccharide units of uronic acid and hexosamine units. They play vital roles in numerous physiological and pathological processes, particularly governing cellular communication and attachment. Depending on their sulphonation state, acetylation, and glycosidic linkages, GAGs belong to different families. The high molecular weight, heterogeneity, and flexibility of GAGs hampers their characterization at atomic resolution, but this may be circumvented via coarse-grained (CG) approaches. In this work, we report a CG model for a library of common GAG types in their isolated or proteoglycan-linked states compatible with the widely popular CG Martini forcefields (versions 2.2 and 3.0). The model reproduces conformational and thermodynamic properties for a wide variety of GAGs, as well as matching structural and binding data for selected proteoglycan test systems. The parameters developed here may thus be employed to study a range of GAG-containing biomolecular systems, benefitting from the efficiency and broad applicability of the Martini framework.

biophysics↗

bioRxiv2023

Development of Constrained Peptide Inhibitors Targeting an Oncogenic E3 Ubiquitin Ligase

SCFSkp2/Cks1 is an E3 ubiquitin ligase, whose substrate specificity is determined by the oncogenic F-box protein Skp2 and the adaptor protein Cks1. A principal target of SCFSkp2/Cks1 is the cyclin-dependent kinase inhibitor p27. Elevated levels of Skp2 and reduced levels of p27 are common in a variety of cancers, and there is consequently a need to develop effective inhibitors of the Skp2-p27 interaction. However, conventional small-molecule approaches are challenging due to the extended bi-molecular interface that spans both Skp2 and Cks1, the lack of suitable binding pockets on this surface, and the intrinsically disordered nature of p27. Here, we develop macrocyclic peptides capable of binding to SCFSkp2/Cks1 with nanomolar affinities, an enhancement of almost two orders of magnitude over the natural p27 peptide. We show that these macrocyclic peptides inhibit p27 ubiquitination in vitro, restore p27 levels in a breast cancer cell line, and reduce cell proliferation.

cancer biology↗

bioRxiv2023

On quantum computing and geometry optimization

Quantum computers have demonstrated advantage in tackling problems considered hard for classical computers and hold promise for tackling complex problems in molecular mechanics such as mapping the conformational landscapes of biomolecules. This work attempts to explore a few ways in which classical data, relating to the Cartesian space representation of biomolecules, can be encoded for interaction with empirical quantum circuits not demonstrating quantum advantage. Using the quantum circuit in a variational arrangement together with a classical optimizer, this work deals with the optimization of spatial geometries with potential application to molecular assemblies. Additionally this work uses quantum machine learning for protein side-chain rotamer classification and uses an empirical quantum circuit for random state generation for Monte Carlo simulation for side-chain conformation sampling. Altogether, this novel work suggests ways of bridging the gap between conventional problems in life sciences and how potential solutions can be obtained using quantum computers. It is hoped that this work will provide the necessary impetus for wide-scale adoption of quantum computing in life sciences.

bioinformatics↗

bioRxiv2023

Design-Rules for Stapled Alpha-Helical Peptides with On-Target In Vivo Activity: Application toMdm2/X dual antagonists

Stapled -helical peptides can bind to and modulate historically intractable targets while addressing the traditional liabilities associated with peptide therapeutics. However, their pipeline advancement has been impeded by the challenges of identifying peptides with sufficient cellular uptake to engage the target protein while lacking off-target toxicities. Here, we advance the field to arrive at a workflow for identifying advanced stapled peptide lead molecules with on-target in vivo activity with no off-target cell proliferation effects. Specifically, we generated a >350-member library based on ATSP-7041, a stapled peptide Mdm2(X) antagonist with validated on-target cellular effects but with significant off-target activity. Key insights from library analysis include 1) a clear correlation between lipophilicity and permeability, 2) removal of positive charge to avoid off-target toxicities, 3) judicious placement of anionic residues to enhance peptide solubility/behavior, 4) optimization of C-terminal length and helicity to enhance cell activity, 5) optimization of staple type/number to avoid polypharmacology. Incorporation of one or more of these attributes led to molecules with improved in vitro and in vivo activities (up to a >292x improved cell proliferation EC50). A subset of peptides were devoid of off-target cell proliferation effects in cell lines lacking wild-type p53 protein (up to a >3800x on-target index). This latter improvement contrasted with clinical Mdm2 antagonistic molecules. Application of these design rules to a distinct Mdm2(X) peptide series resulted in rapid improvement in cellular activity (>150x) and removal of off-target toxicities. Overall, the detailed workflow outlined here should help researchers identify stapled -helical peptides for therapeutic impact.

biochemistry↗

bioRxiv2023

Structome: Exploring the structural neighbourhood of proteins

Protein structures carry signal of common ancestry and can therefore aid in reconstructing their evolutionary histories. To expedite the structure-informed inference process, a web server, Structome, has been developed, that allows users to rapidly identify protein structures similar to a query protein and to assemble datasets useful for structure-based phylogenetics. Structome was created by clustering[~] 94% of the structures in RCSB PDB using 90% sequence identity and representing each cluster by a centroid structure. Structure similarity between centroid proteins was calculated, and annotations from PDB, SCOP and CATH were integrated. To illustrate utility, an H3 histone was used as a query, and results show that the protein structures returned by Structome span both sequence and structural diversity of the histone fold. Additionally, the pre-computed nexus-formated distance matrix, provided by Structome, enables analysis of evolutionary relationships between proteins not identifiable using searches based on sequence similarity alone. Our results demonstrate that, beginning with a single structure, Structome can be used to rapidly generate a dataset of structural neighbours and allows deep evolutionary history of proteins to be studied. Structome is available at: https://structome.bii.a-star.edu.sg

bioinformatics↗

bioRxiv2022

Enrichment of charge-absent regions in phase separated proteins

Many studies focus on the relationship between protein charge and liquid-liquid phase separation (LLPS), generally finding that a large degree of charge neutralisation is involved for condensate formation. Here, sequences within human proteins that lack the charge-bearing residues Asp, Glu, Lys, and Arg (termed charge-absent) are analysed alongside annotation for involvement in LLPS. Scaffold proteins, central to condensate formation, on average possess longer charge-absent regions than those not key for LLPS. Charge-absent regions tend to have relatively high hydropathy scores. Overall, they are enriched in Ala, Gly, Pro, and Ser with more specific groupings evident when the subset is clustered by amino acid composition. For several proteins, segments with charge-absent regions have been identified as modulators of LLPS. It is hypothesised that for at least some of the charge-absent regions, a lack of charged group desolvation energy, together with a relatively hydrophobic sequence composition, may facilitate condensation through homomeric interactions. If this is the case, it should be relatively easy to modulate through incorporation of charge through engineering, potentially including pH-sensing.

bioinformatics↗

bioRxiv2022

Stitched peptides as potential cell permeable inhibitors of oncogenic DAXX protein

The death domain associated protein 6 (DAXX) is frequently upregulated in a number of common cancers where its suppression has been linked to reduced tumour progression. As a master regulator protein, with >70 reported protein interaction partners, the role of DAXX in its oncogenecity remains unclear. We designed and developed a set of novel stapled/stitched peptides that target a surface on the N-terminal helical bundle domain of DAXX which is the anchor-point for binding to multiple interaction partners (including Rassf1C, P53, Mdm2 and ATRX) and also for the auto regulation of the DAXX N-terminal SUMO interaction motif (SIM). We demonstrate that these peptides bind to and inhibit DAXX with an affinity higher than those reported for the known interaction partners and release the auto-inhibited SIM for interaction with SUMO-1. NanoBret assays show that the peptides enter cells and that their intracellular concentrations remain at nanomolar levels even after 24 hours, without causing membrane perturbation. Together our data suggest that these peptides are both tools for probing the molecular interactions of DAXX and potential precursors to the development of therapeutics.

biochemistry↗

bioRxiv2022

Development of a Novel Peptide Aptamer that Interacts with the eIF4E Capped-mRNA Binding Site using Peptide Epitope Linker Evolution (PELE).

Identifying new binding sites and poses that modify biological function are an important step towards drug discovery. We have identified a novel disulphide constrained peptide that interacts with the cap-binding site of eIF4E, an attractive therapeutic target that is commonly overexpressed in many cancers and plays a significant role in initiating a cancer specific protein synthesis program though binding the 5cap (7methyl-guanoisine) moiety found on mammalian mRNAs. The use of disulphide constrained peptides to explore intracellular biological targets is limited by their lack of cell permeability and the instability of the disulphide bond in the reducing environment of the cell, loss of which results in abrogation of binding. To overcome these challenges, the cap-binding site interaction motif was placed in a hypervariable loop on an VH domain, and then selections performed to select a molecule that could recapitulate the interaction of the peptide with the target of interest in a process termed Peptide Epitope Linker Evolution (PELE). A novel VH domain was identified that interacted with the eIF4E cap binding site with a nanomolar affinity and that could be intracellularly expressed in mammalian cells. Additionally, it was demonstrated to specifically modulate eIF4E function by decreasing cap-dependent translation and cyclin D1 expression, common effects of eIF4F complex disruption.

biochemistry↗

bioRxiv2021

Evaluation of Host Defense Peptide (CaD23)-Antibiotic Interaction and Mechanism of Action: Insights from Experimental and Molecular Dynamics Simulations Studies

Background/aimHost defense peptides (HDPs) have the potential to provide a novel solution to antimicrobial resistance (AMR) in view of their unique and broad-spectrum antimicrobial activities. We had recently developed a novel hybrid HDP based on LL-37 and human beta-defensin-2, named CaD23, which was shown to exhibit good in vivo antimicrobial efficacy against Staphylococcus aureus in a bacterial keratitis murine model. This study aimed to examine the potential CaD23-antibiotic synergism and to evaluate the underlying mechanism of action of CaD23. MethodsAntimicrobial efficacy was determined using minimum inhibitory concentration (MIC) assay with broth microdilution method. Peptide-antibiotic interaction was evaluated against S. aureus, methicillin-resistant S. aureus (MRSA), and Pseudomonas aeruginosa using established checkerboard assay and time-kill kinetics assay. Fractional inhibitory concentration index (FICI) was calculated and interpreted as synergistic (FICI<0.5), additive (FICI between 0.5-1.0), indifferent (FICI between >1.0 and [≤]4), or antagonistic (FICI>4). SYTOX green uptake assay was performed to determine the membrane-permeabilising action of CaD23. Molecular dynamics (MD) simulations were performed to evaluate the interaction of CaD23 with bacterial and mammalian mimetic membranes. ResultsCaD23-amikacin and CaD23-levofloxacin combination treatment exhibited a strong additive effect against S. aureus SH1000 (FICI=0.56) and MRSA43300 (FICI=0.56) but a borderline additive-to-indifferent effect against P. aeruginosa (FIC=1.0-2.0). CaD23 (at 25 g/ml; 2x MIC) was able to achieve complete killing of S. aureus within 30 mins. When used at sub-MIC concentration (3.1 g/ml; 0.25x MIC), it was able to expedite the antimicrobial action of amikacin against S. aureus by 50%. The rapid antimicrobial action of CaD23 was attributed to the underlying membrane-permeabilising mechanism of action, evidenced by the SYTOX green uptake assay and MD simulations studies. MD simulations revealed that cationicity, alpha-helicity, amphiphilicity and hydrophobicity (related to the Trp residue at C-terminal) play important roles in the antimicrobial action of CaD23. ConclusionsCaD23 is a novel membrane-active synthetic HDP that can enhance and expedite the antimicrobial action of antibiotics against Gram-positive bacteria when used in combination. MD simulation serves as a useful tool in dissecting the mechanism of action and guiding the design and optimisation of HDPs.

microbiology↗

bioRxiv2021

PhosIDP: a web tool to visualize the location of phosphorylation sites in disordered regions

Charge is a key determinant of intrinsically disordered protein (IDP) and intrinsically disordered region (IDR) properties. IDPs and IDRs are enriched in sites of phosphorylation, which alters charge. Visualizing the degree to which phosphorylation modulates the charge profile of a sequence would assist in the functional interpretation of IDPs and IDRs. PhosIDP is a web tool that shows variation of charge and fold propensity upon phosphorylation. In combination with the displayed location of protein domains, the information provided by the web tool can lead to functional inferences for the consequences of phosphorylation. IDRs are components of many proteins that form biological condensates. It is shown that IDR charge, and its modulation by phosphorylation, is more tightly controlled for proteins that are essential for condensate formation than for those present in condensates but inessential.

bioinformatics↗

bioRxiv2020

Predicting Cell-Penetrating Peptides: Building and Interpreting Random Forest based prediction Models

Targeting intracellular pathways with peptide drugs is becoming increasingly desirable but often limited in application due to their poor cell permeability. Understanding cellular permeability of peptides remains a major challenge with very little structure-activity relationship known. Fortunately, there exist a class of peptides called Cell-Penetrating Peptides (CPPs), which have the ability to cross cell membranes and are also capable of delivering biologically active cargo into cells. Discovering patterns that make peptides cell-permeable have a variety of applications in drug delivery. In the current study, we build prediction models for CPPs exploring features covering a range of properties based on amino acid sequences, using Random forest classifiers which are often more interpretable than other ensemble machine learning algorithms. While obtaining prediction accuracies of ~96%, we also interpret our prediction models using TreeInterpreter, LIME and SHAP to decipher the contributions of important features and optimal feature space for CPP class. We propose that our work might offer an intuitive guide for incorporating features that impart cell-penetrability into the design of novel CPPs.

bioinformatics↗

bioRxiv2020

TRAF4 inhibits bladder cancer progression by promoting BMP/SMAD signalling pathway

Bladder cancer is one of the most prevalent cancer types in the world, frequently exhibiting invasion and metastasis and therefore associated with poor prognosis. It is a progressive disease with high recurrence rates even after surgery, which calls for the urgent need for early intervention and diagnosis. The E3 ubiquitin ligase TNF Receptor Associated Factor 4 (TRAF4) has been largely implicated as a tumour-promoting element in a wide range of cancers. Over-expression and amplification of this gene product has been a common observation in breast and other metastatic tumours. In contrast, we observed that expression of TRAF4 negatively correlated with overall patient survival. Moreover, its expression was repressed at epigenetic levels in aggressive bladder cancer cells. We also describe an ERK kinase phosphorylation site on TRAF4 that inhibits its stability and localization to plasma membrane in such cells. Furthermore, knockdown of TRAF4 in epithelial bladder cancer cell lines leads to gain of mesenchymal genes and a loss of epithelial integrity. Reciprocally, stable over-expression of TRAF4 in mesenchymal cells leads to decreased migratory and invasive properties. Transcriptomic analysis upon TRAF4 mis-expression in bladder cancer cell lines revealed that higher TRAF4 expression enhanced BMP/SMAD and dampened NF-{kappa}B signalling pathways. Importantly, this notion was confirmed in bladder cancer patient material. Mechanistically, we showed that TRAF4 targets the E3 ubiquitin ligase SMURF1, a negative regulator of BMP/SMAD signalling, for proteasomal degradation in bladder cancer cells. We show that genetic and pharmacological inhibition of SMURF1 or its function inhibited migration of aggressive (mesenchymal) bladder cancer cells.

cancer biology↗

bioRxiv2020

Conformational ordering of intrinsically disordered peptides for targeting translation initiation

Intrinsically disordered regions (IDRs) in proteins can regulate their activity by facilitating protein-protein interactions (PPIs) as exemplified in the recruitment of the eukaryotic translation initiation factor 4E (eIF4E) protein by the protein eIF4G. Deregulation of this PPI module is central to a broad spectrum of cancer related malignancies and its targeted inhibition through bioactive peptides is a promising strategy for therapeutic intervention. We have employed a structure-guided approach to rationally develop peptide derivatives from the intrinsically disordered eIF4G scaffold by incorporating non-natural amino acids that facilitates disorder-to-order transition. The conformational heterogeneity of these peptides and the degree of structural reorganization required to adopt the optimum mode of interaction with eIF4E underscores their differential binding affinities. The presence of a pre-structured local helical element in the ensemble of structures was instrumental in the efficient docking of the peptides on to the protein surface. These insights were exploited to further design features into the peptide to propagate bound-state conformations in solution which resulted in the generation of a potent eIF4E binder. The study illustrates the molecular basis of eIF4E recognition by a disordered epitope from eIF4G and its modulation to generate peptides that can potentially attenuate translation initiation in oncology.

biophysics↗

bioRxiv2020

Extending the Martini coarse-grained forcefield to N-glycans

Glycans play a vital role in a large number of cellular processes. Their complex and flexible nature hampers structure-function studies using experimental techniques. Molecular dynamics (MD) simulations can help in understanding dynamic aspects of glycans if the forcefield (FF) parameters used can reproduce key experimentally observed properties. Here, we present optimized coarse-grained (CG) Martini FF parameters for N-glycans, calibrated against experimentally derived binding affinities for lectins. The CG bonded parameters were obtained from atomistic (ATM) simulations for different glycan topologies including high mannose and complex glycans with various branching patterns. In the CG model, additional elastic networks are shown to improve maintenance of the overall conformational distribution. Solvation free energies and octanol-water partition coefficients were also calculated for various n-glycan disaccharide combinations. When using standard Martini non-bonded parameters, we observed that glycans spontaneously aggregated in the solution and required down-scaling of their interactions for reproduction of ATM model radial distribution functions. We also optimised the non-bonded interactions for glycans interacting with seven lectin candidates and show that scaling down the glycan-protein interactions can reproduce free energies obtained from experimental studies. These parameters should be of use in studying the role of glycans in various glycoproteins, carbohydrate binding proteins (CBPs) as well as their complexes, while benefiting from the efficiency of CG sampling.

biophysics↗