Biology subjects

Mandal, S.

Publications and source records attributed to Mandal, S..

At least 19 recordsLinked to original sources

bioRxiv2026

Non-canonical alternate interactors of SARS CoV-2 Spike protein implicated in placental susceptibilty

Vertical transmission of SARS-CoV-2 is controversial. Owing to the low expression of ACE2 along with TMPRSS2 in placenta, role of secondary receptors becomes significant. In our study we predicted twelve interactors of spike protein expressed in placenta through interactome analysis followed by docking and molecular dynamic simulation. Three interactors of SARS-CoV-2 spike protein were found to be CD147, EGFR and LDLR. Expression at transcriptomic and translational level by real-time PCR and immunohistochemistry respectively was observed in placenta samples obtained from women with COVID exposure risk and compared to control. Elevated protein levels of CD147 (OR=14.667), ACE2 (OR=8.25) and LDLR (OR=1.9) was associated with higher exposure risk. However, the variation in mRNA expression was not statistically significant. Computational study showed that CD147/basigin, EGFR and LDLR stably interact with spike protein outside its primary receptor binding domain. In-vitro binding assay confirmed the physical interaction between spike protein and the placental receptors. In-silico site-directed mutagenesis further identified key potential binding hotspots of spike protein- Tyr28 and Trp64 for CD147, Phe643, Val642, Thr632 for LDLR and Leu8, Phe59, Phe32, Tyr28, Trp64, Trwp152, His245, and Val213 for EGFR. Finally, concluded that CD147, EGFR and LDLR might act as secondary non-canonical cofactors for SARS-CoV-2 spike protein in placenta, thereby increasing its susceptibility and tissue tropism. The study overall gives a better insight into potential placental suscpetibility providing targeted therapeutic opportunities.

microbiology↗

bioRxiv2026

Mechanistic Investigation of Reversible Hibernation-Driven Immune Suppression in Thirteen-Lined Ground Squirrels

Torpor in mammals imposes extreme energetic constraints, yet how it reshapes the immune system remains poorly understood. Here we combined single-cell RNA sequencing with quantitative image analysis of immune cell populations in splenic tissues to define immune remodeling during torpor in a natural hibernator, 13-lined ground squirrels. The torpid spleen showed a significant contraction of white pulp with a preferential reduction of B cell- and T cell-rich adaptive niches and relative preservation of innate myeloid populations. Across immune cell lineages, a conserved transcriptional program of metabolic downscaling emerged, marked by suppression of glycolysis, cell-cycle progression, RNA processing, and translation, together with reduced glucose transporter expression and induction of cold-shock RNA-binding proteins. Despite this pervasive metabolic quiescence, immune cells maintain lineage identity, with B cells undergoing numerical and transcriptional contraction linked to follicular remodeling and T cells adopting a quiescent, stress-resistant state without apoptotic enrichment. Innate cell populations remained numerically enriched but transcriptionally restrained, consistent with low-energy tissue surveillance rather than inflammatory activation. These findings identified torpor as a coordinated, multi-tiered state of reversible immune suppression, in which hierarchical metabolic and lineage-specific programs conserve energy while preserving essential immune infrastructure for rapid restoration. Our identified key molecules and pathways in immune suppression at the cellular and transcriptional levels have important implications for future development of targeted treatment for autoimmune diseases, cancers, and infectious diseases.

immunology↗

bioRxiv2026

Progressive Post-Acute Gut Microbiome Disruption Following SARS-CoV-2 Infection in Mice

SARS-CoV-2 infection is increasingly recognized to produce long-lasting physiological disturbances that extend beyond the acute phase. The gut microbiome has emerged as a potential contributor to post-infection outcomes, yet the longitudinal progression of microbial disruption following infection remains poorly defined. Here, we used a mouse model of SARS-CoV-2 infection to characterize gut microbiome dynamics at 7 (late acute phase), 14 (early recovery), and 21 (post-COVID condition, PCC) days post-infection (dpi). Viral RNA was detected in the lungs through 21 dpi. Longitudinal microbiome profiling revealed a two-phase restructuring marked by early shifts in Bacillota and Bacteroidota abundance, followed by pronounced post-acute dysbiosis characterized by reduced diversity, expansion of Bacillota, and near-complete loss of Bacteroidota. Functional pathway predictions showed progressive metabolic remodeling, including disruptions in nucleotide turnover, fermentation, and vitamin-related pathways. Together, these findings demonstrate that SARS-CoV-2 infection drives progressive and sustained alterations in gut microbial composition and function after the transition from acute infection through recovery into PCC.

microbiology↗

bioRxiv2026

PAR2 signaling shapes microbial and metabolic remodeling along the gut-lung axis

Introduction: Protease activated receptor (PAR2) is a prominent sensor of environmental and microbial proteases and may serve as an important interface between the host epithelium and mucosal microbes. However, whether PAR2 helps shape microbial community structure and function at barrier surfaces remains unclear. To address this, we examined how PAR2 deficiency or activation affects microbial composition and metabolic potential across the gut lumen, airway lumen, and lung tissue in the context of exposure to protease-rich house dust mite allergen (HDM) exposure. Methods: Wild type and PAR2 deficient littermates of both sexes received a single intranasal challenge with phosphate buffered saline, HDM extract, or a selective PAR2 agonist. Microbial communities from feces, bronchoalveolar lavage fluid (BALF), and lung tissue were profiled using 16S rRNA gene sequencing and PICRUSt2 based functional inference to assess compartment specific taxonomic and metabolic responses. Results: Alpha and beta diversity remained stable across all experimental groups, but distinct conditions resulted in compartment specific remodeling of the microbial population. At baseline, PAR2 deficiency altered multiple genera in the gut and lung and shifted predicted pathways linked to amino acid, lipid, and sulfur metabolism. HDM induced broad taxonomic and functional changes in the gut and lung tissue, including shifts in coenzyme A biosynthesis, reductive TCA activity, lysine fermentation, and nucleotide biosynthesis, while producing only limited taxonomic changes in BALF. PAR2 signaling accounted for a substantial portion of HDM driven remodeling, and direct PAR2 activation reproduced many compartment specific effects, including mucin derived sugar degradation in the gut and suppression of nucleotide biosynthesis in the lung. Sex moderately modified microbial and metabolic responses, with males and females exhibiting divergent, condition dependent functional biases across gut and lung. Conclusion: These findings identify PAR2 as a mucosal niche modifying receptor whose activation or loss reshapes microbial composition and metabolic potential along the gut-lung axis.

microbiology↗

bioRxiv2026

A pretrained unified model enables cellular functional profile prediction and multi-objective virtual drug screening

Cells are characterized by molecular states, coordinated molecular interactions, regulatory programs, and responses to perturbations. Systematic mapping of these cellular functional profiles across biological contexts remains experimentally costly and fragmented. Here we present InsilicoCell, a pretrained multi-modal, multi-task model that unifies prediction of cellular functional profiles spanning molecular states, molecular interactions, and perturbation-induced responses. Built on a supervised transformer architecture and pretrained on more than 88 million measurements across seven tasks, including drug sensitivity, drug-induced gene expression, and drug-protein binding, InsilicoCell learns a shared representation that links molecular profiles to cellular phenotypes, improves performance over task-specific models, and generalizes to unseen entities, contexts, and conditions. InsilicoCell extends beyond cell line systems to patient, spatial and single-cell settings, and enables multi-objective virtual drug screening. It identifies novel candidate compounds with experimental validation, including c-Myc activity inhibitors, antifibrotic agents and stemness-inducing compounds. Together, InsilicoCell provides a scalable framework for predictive cellular biology and therapeutic discovery.

bioinformatics↗

bioRxiv2026

Strand Displacement Activity of Mimiviral Polymerase X Enables Rapid Detection of Sequence-Specific DNA Targets

Mimiviral polymerase X, mvPolX, is a repair polymerase that is involved in base excision repair (BER) and carries out the gap-filling function in double-stranded DNA (dsDNA). We demonstrate a sensitive and sequence-specific DNA detection method using this polymerase. mvPolX begins polymerizing DNA from the 3 end of a gap, displacing the downstream nucleotides without exonuclease activity. Our detection method is built on this activity of mvPolX. We designed a probe molecule consisting of a partial dsDNA with a 3 over-hang region complementary to the target DNA to be detected. The probe has a fluorophore-quencher (FAM-BHQ1) tag to facilitate detection upon strand removal. Binding of the probe to the complementary target forms a dsDNA with a single nucleotide gap in one strand. mvPolX binds this gap region and begins polymerisation eventually displacing the quencher strand leading to an increase in fluorescence. Proof-of-concept has been established using a synthetic 19 bp target DNA sequence. The method is specific and did not show any strand displacement when a single or double mismatched nucleotide at the 3 end of the target DNA was used. To demonstrate this molecular assay, we used M13 phage as our target. Asymmetric PCR (aPCR) was used to obtain single-stranded target DNA (158 bases) from M13 genomic DNA, which was directly used in the assay as target. The combination of aPCR and mvPolX assay can detect as low as 10 copies of genomic DNA. The enzymatic reaction is fast, requiring only 15 min of incubation with mvPolX at 30 {degrees}C. We have further demonstrated the efficiency of the assay in presence of multiple non-target DNA by detecting the target DNA from M13 phage spiked lakewater samples.

molecular biology↗

bioRxiv2026

An optopharmacological tool for on-demand perturbation of branched actin polymerization

Regulated actin cytoskeletal organization and dynamics are essential for life-sustaining processes in eukaryotic cells. The spatiotemporal regulation of filamentous actin can generate a staggering variety of higher-order architectures to meet diverse cellular needs. However, connecting a specific actin substructure to the selective cellular function remains challenging because tools to specifically inhibit F-actin in a spatiotemporally controlled manner are currently limited. To address this crucial technical gap, we have synthesized and characterized a photocrosslinkable small molecule inhibitor of a major and evolutionarily conserved actin nucleation factor, Arp2/3 complex. The new inhibitor "AZ" combines the specificity of a preexisting inhibitor CK666 with photosensitive crosslinking by an Azido group, such that a light-induced, instantaneous, on-demand, irreversible inhibition of Arp2/3 complex-dependent actin nucleation is achieved in a spatiotemporally defined manner at a subcellular, supracellular, and organismal scale. Whole cell treatment with AZ, followed by subcellular photoirradiation, revealed a divergent actin nucleation homeostasis in the cortex of different cells. Thus, AZ could be a powerful tool to infer actin polymerization homeostasis and network properties in live cells-processes which otherwise remain obscure.

cell biology↗

bioRxiv2026

A Novel MicroRNA-Odorant Receptor Axis Governs Neural Progenitor Cell Proliferation in Zebrafish CNS

Spinal cord injury causes irreversible neurological deficits in mammals; yet zebrafish achieve complete functional recovery through molecular mechanisms that remain poorly defined. In this study we emphasized on a critical miRNA-mediated regulation of Ependymo-radial glial (ERG) cell proliferation in zebrafish spinal cord. Using next-generation sequencing we constructed a spatiotemporal miRNA profile across multiple post-injury time points and identified dre-miR-N1 as a novel injury-responsive miRNA involved in ERG proliferation among several differentially expressed novel miRNAs. Fluorescent in situ hybridization confirmed its robust lesion-site expression and gain-of-function analysis demonstrated that dre-miR-N1 significantly impaired functional recovery. Target prediction and validation unexpectedly identified the odorant receptor gene or42a1 as a high-confidence target and a combinatorial approach of miRNA gain-of-function and or42a1 loss-of-function showed that dre-miR-N1 modulates the proliferative behaviour of or42a1-expressing ERG cells under both homeostatic and injury conditions. These findings uncover a previously unrecognized miRNA-odorant receptor axis governing injury-induced ERG cell expansion establishing a novel molecular framework for endogenous neural regeneration in zebrafish.

neuroscience↗

bioRxiv2026

Systematic Data-Driven Penalty Calibration for Constrained Quantum Optimization with Application to Molecular Docking

This paper describes MMP, a three-stage framework for systematic quantum optimization of constrained molecular docking problems. The protocol addresses the "formulation bottleneck"--the critical challenge of translating constrained optimization problems into valid QUBO (Quadratic Unconstrained Binary Optimization) formulations for quantum solvers. MMP replaces heuristic penalty tuning with data-driven calibration through: (1) classical solution-space analysis to validate fragment libraries before quantum deployment, (2) systematic penalty sweeps to identify optimal "Goldilocks Zone" coefficients, and (3) MAC-QAOA (MMP Adaptive Constraint QAOA) with layer-dependent penalty decay. Preliminary benchmarks on synthetic constrained optimization problems demonstrate 99.7% solution validity at identified elbow points and 25.5% improvement in solution quality over static-penalty QAOA. MMP is hardware-agnostic but designed for near-term devices including Pasqals Orion Gamma (140+ qubits). The theoretical framework, algorithmic details, and preliminary validation results of the protocol are discussed, establishing a systematic methodology for quantum-augmented optimization workflows for drug discovery. All benchmarks are conducted on synthetic constrained optimization instances that reproduce structural features of docking formulations; application to real molecular docking targets is left for future work.

bioinformatics↗

bioRxiv2026

An Indole Dimer Antifungal Metabolite from a Rice Seed Endophyte Inhibits Ergosterol Biosynthesis in Fungal Pathogens

The increasing prevalence of fungal phytopathogens and the widespread emergence of fungicide resistance necessitate alternative antifungal strategies with reduced environmental impact. Here, we report the isolation and characterization of a novel antifungal metabolite, SM06, produced by the rice seed-associated endophytic bacterium Phytobacter sp. RSE02. SM06 exhibited broad-spectrum antifungal activity against plant and human pathogenic fungi, including Curvularia lunata, Fusarium oxysporum, and Candida albicans. In vitro assays and micromorphological analyses revealed that SM06, an indole dimer, disrupts fungal cell membrane integrity, while in planta experiments demonstrated significant suppression of brown leaf spot disease in tomato and rice. Molecular docking suggested that SM06 binds to lanosterol 14-demethylase (ERG11), a key enzyme in fungal sterol biosynthesis. Consistent with this prediction, LC-MS-based analyses confirmed a significant reduction in ergosterol content in SM06-treated fungal cells. Together, these findings identify SM06 as a biologically active antifungal metabolite produced by a plant-associated bacterium and highlight its potential application in sustainable fungal disease management. IMPORTANCEFungal diseases cause major losses in crop-production and contribute to the growing challenge of antifungal resistance, underscoring the need for sustainable alternatives to chemical fungicides. This study identifies SM06, a novel indole dimer produced by the rice seed endophyte Phytobacter sp. RSE02, with strong antifungal activity against economically important plant pathogens and clinically relevant fungi. Through integrated chemical, cellular, and in planta analyses, we demonstrate that SM06 disrupts fungal membrane integrity by inhibiting ergosterol biosynthesis. The compound is biocompatible, stable, and effective in plant disease suppression, highlighting its translational potential for crop protection. These findings reveal seed endophytes as an important yet underexplored sources of antifungal metabolites and provide a mechanistic foundation for developing eco-friendly biocontrol strategies with implications beyond agriculture. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=179 SRC="FIGDIR/small/697688v1_ufig1.gif" ALT="Figure 1"> View larger version (86K): org.highwire.dtl.DTLVardef@c7da68org.highwire.dtl.DTLVardef@d3f1a1org.highwire.dtl.DTLVardef@9cab82org.highwire.dtl.DTLVardef@1c01141_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2025

Classpose: foundation model-driven whole slide image-scale cell phenotyping in H&E

Cell phenotyping in histopathology samples is essential for diagnostic and research workflows. However, human expert annotation requires significant time and expertise while being affected by inter-observer variability. Here, we present Classpose, an easily trainable framework for cell segmenting and phenotyping built on top of Cellpose-SAM with state-of-the-art performance across 6 distinct datasets, outperforming competing methods. We show that this requires fine-tuning the entire network, highlighting how instance segmentation is a poor objective for downstream cellular classification. We apply it to a large whole slide image (WSI) colorectal cancer (CRC) cohort (SurGen) and show that Classpose-derived cellular organisation and morphology features can be used to determine novel spatial morphological phenotypes for clinically relevant molecular conditions (MMR deficiency, BRAF mutations, KRAS mutations) and to predict these same molecular conditions. We make Classpose models available and provide a user-friendly QuPath extension for widespread use by the digital pathology community.

bioinformatics↗

bioRxiv2025

A Site-Specific Organometallic Approach for Installing Tyrosine Phosphorylation Mimics to Decipher the Role of Phosphorylation in Alpha-Synuclein (aSyn) Aggregation and Seeding

Several studies have identified phosphorylation of alpha-synuclein (aSyn) at multiple tyrosine residues (Y39, Y125, Y133, and Y136) within Lewy bodies, which are the pathological hallmarks of Parkinsons disease (PD). However, understanding the specific role of phosphorylation at each site, or how multiple phosphorylation sites interact, has been challenging. Herein, we present an efficient method that leverages an organometallic Pd-complex to site-specifically attach phosphomimetic groups via Cys-arylation, closely mimicking natural phosphorylation. Using this approach, we successfully incorporated native-like tyrosine phosphorylation mimics into cysteine-containing proteins like synthetic transcription factor Max and recombinant aSyn, in good yields. To demonstrate the methods versatility, we created a focused library of mono-, di-, and tri-phosphorylated aSyn analogues. This development enabled, for the first time, the investigation of the effect of site-specific phosphorylation at multiple C-terminal tyrosine residues on aSyn fibrillization and aggregation. Our results show that mono-phosphorylation at any of the C-terminal sites has little effect on aggregation, while di- and tri-phosphorylation slows down the process, extending the lag phase compared to wild-type aSyn. Additionally, phosphorylation at Y39 reduces the seeding activity of aSyn fibrils by almost threefold in both mammalian and neuronal models of synuclein pathology. Overall, our strategy provides a rapid, selective, and scalable way to introduce aromatic PTMs, producing homogeneous protein libraries essential for mechanistic studies, biomarker development, and exploring the therapeutic potential of targeting aSyn-phosphorylation for PD and related disorders.

biochemistry↗

bioRxiv2025

Potential probiotic application of a novel commensal E. coli with antagonistic activity against different enteric pathogens

Diarrheal diseases remain a leading cause of global morbidity and mortality, and treatment options are increasingly compromised by the global rise in multidrug-resistant (MDR) pathogens. Furthermore, the absence of effective vaccines against many causative agents renders large populations vulnerable. This critical gap necessitates the development of novel alternatives that can function both prophylactically to prevent infection and therapeutically to treat established diseases. Here, we investigated the commensal Escherichia coli strain HK220822 (HK5), which was isolated from a healthy human, as a potential live biotherapeutic. Comprehensive genomic and phenotypic characterization established a robust safety profile, confirming the absence of key virulence genes while demonstrating essential probiotic traits, including high tolerance to gastrointestinal stressors, such as acid and bile. The functional efficacy of Escherichia coli HK5 has been validated in murine models of infection. Prophylactic administration before pathogen exposure significantly inhibited intestinal colonization by Salmonella Typhimurium, Shigella flexneri 2a, and Vibrio cholerae (El Tor O1 strain). Moreover, HK5 demonstrated therapeutic potential by significantly reducing pathogen shedding when administered to previously infected animals. These findings establish commensal E. coli (HK5) as a potent candidate with dual preventative and therapeutic efficacy, offering a promising non-antibiotic strategy to combat diarrheal diseases.

microbiology↗

bioRxiv2025

B-cell follicles of lymphatic tissues act as a critical microanatomical niche for sustained viral replication, virus-host interaction and damage during chronic SIV infection

Most people living with HIV-1 (HIV) are diagnosed during the chronic stage of infection, at which point viral setpoint has been established and a substantial immunopathologic damage in the secondary lymphatic tissues (LTs) has been induced. To better characterize virus-host interaction and immunopathologic damage in LTs, we investigated viral spatial distribution patterns and the corresponding LT structural alterations in SIV chronically infected rhesus macaques. Using RNAscope in-situ hybridization (RNAscope) and a combination of CODEX with RNAscope (Comb-CODEX-RNAscope), we demonstrated that in chronic infection, SIV viral RNA (vRNA) is predominantly resides within B-cell follicles with minimal presence in T-cell zones, and there is significant B-cell follicular damage, encompassing follicular hyperplasia, fibrosis, and disintegration of the germinal center. Our results reveal that the B-cell follicles act as a critical microanatomical niche for sustained viral replication, virus-host interaction and tissue damage during SIV chronic infection.

immunology↗

bioRxiv2025

Analysis of SIV Spatiotemporal Dissemination Patterns in Rhesus Macaques During Early Rectal Transmission Demonstrates Systemic Infection Does Not Require Viral Local Amplification at the Entry Portal

Receptive anal sex is a dominant mode of HIV-1 (HIV) transmission, especially among men who have sex with men (MSM). However, the early events during HIV rectal transmission are not well understood and many questions remain, such as, does virus local amplification at the entry portal require for viral distal seeding? What is the spatiotemporal dissemination pattern across whole body? How do three viral forms, i.e., cell-free virus (VCF), cell-associated virus (VCA), and follicular dendritic cell-trapped virus (VFDC), evolve during early infections? To close this knowledge gap, we comprehensively examined rectum, draining lymph nodes (dLN) and distal lymph nodes (disLN), as well as non-lymphoid organs of brain, lungs, and liver of Indian rhesus macaques (RMs) at the early time points following intrarectal SIVmac251 inoculation (1, 2, 3, 4, 6, 10 14, 28 day post inoculation, dpi). Our findings demonstrated SIV rapidly disseminates to distant tissues and organs (<=1 dpi) and virus local amplification in rectum and dLN is not required for viral distal seeding for the establishment of systemic infection, viral forms shift from VCF and VCA to VFDC accompanying from T cell zones into B cell follicles. Collectively, these findings indicate that an effective HIV vaccine needs to induce immune protection both locally at sites of viral entry and systemically.

immunology↗

bioRxiv2025

Exposure to third generation cephalosporin induces L-form transition in Shigella sonnei, potentially acting as a bacterial reservoir for persistent infection

Shigellosis remains a major global health burden, and the increasing prevalence of multidrug-resistant (MDR) Shigella strains is complicating effective antibiotic therapy. Bacteria may survive antibiotics by transitioning into cell wall-deficient L-forms, which are intrinsically resistant to {beta}-lactams and can revert to a virulent state, potentially causing relapsing infections. Here we characterized a clinical MDR isolate Shigella sonnei HK8, a.k.a. PD552A, whose genome contains key resistance (gyrA, PBP3) and virulence (icsA) genes. Exposure to ceftriaxone induced a transition into a viable L-form state that was hyper-adhesive to macrophages in vitro. However, this survival adaptation was linked to a profound loss of pathogenicity. Using murine and guinea pig models, the L-form variant was shown to be profoundly attenuated, failing to cause the keratoconjunctivitis, diarrheal disease, or significant histopathology characteristic of the wild-type strain. These findings reveal a critical virulence-survival trade-off, positioning the L-form as a "stealth" phenotype that enables bacterial persistence at the expense of acute virulence. This offers a potential mechanism for asymptomatic carriage and recurrent infections, highlighting a previously underappreciated mechanism by which antibiotic treatment may resolve acute symptoms while permitting the persistence of a cryptic bacterial reservoir capable of driving recurrent infection. ImportanceOur research provides critical insight into the challenge of antibiotic treatment failure in shigellosis. By integrating experimental validation of reversible L-form transitions with mathematical modelling, we uncover a crucial virulence-survival trade-off. We show that MDR S. sonnei survives ceftriaxone by adopting a "stealth" phenotype, quantified by a high Stealth Index - maintaining bacterial burden while evading host inflammatory detection. These findings imply that standard antibiotics may resolve acute symptoms while inadvertently selecting for a cryptic, persistent reservoir poised for relapse. This work challenges the conventional view of therapeutic success and highlights an urgent need to develop novel diagnostic and therapeutic strategies capable of identifying and eliminating these resilient, "stealth" L-form persisters to achieve true bacterial clearance and prevent chronic infections.

microbiology↗

bioRxiv2025

In silico self-assembly and complexation dynamics of cationic lipids with DNA nanocages to enhance lipofection

DNA nanostructures are promising materials for drug delivery due to their unique topology, shape, size control, biocompatibility, structural stability and blood-brain-barrier (BBB) penetration capability. However, their cellular permeability is hindered by strong electrostatic repulsion from negatively charged cellular membranes, posing a significant obstacle to the use of DNA nanostructures as a drug delivery vehicle. Recent experimental studies have shown enhanced cellular uptake for the conjugate binary mixtures of DNA Tetrahedron (TDN) with cationic lipid N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA) compared to TDN alone. However, the cationic DOTMA lipids binding mechanism with the TDN nucleotides is still elusive. Using fully atomistic MD simulations, we aim to understand the molecular interactions that drive the formation and stability of the TDN-DOTMA binary complexes in a physiological environment. Our results uncovered that lipid concentration plays a crucial role in the energetics of the TDN-DOTMA association. We also report that distinct timescales are associated with the self-assembly of cationic DOTMA lipids first, followed by the complexation of self-assembled DOTMA lipid clusters with the TDN nucleotides, where electrostatics, hydrophobicity, and hydrogen bonding are the key interactions that drive the formation and stability of these complexes. These results provide molecular insights into TDN-DOTMA interactions, highlighting the lipid self-assembly dynamics, complex stability, and morphology, paving the way for the better rational design of cationic lipid functionalized DNA nanostructures for efficient drug delivery and transfection.

biophysics↗

bioRxiv2025

Mechanistic Insights into Crossover-Dependent Stability and Exceptional Resistance of PX/JX Nanostructures to DNase I using Enhanced Sampling

Designing biostable DNA nanocarriers for precise therapeutic delivery remains a key challenge in DNA nanotechnology due to susceptibility to nuclease degradation. Multi-stranded DNA nanostructures, such as Paranemic crossover (PX) DNA, show enhanced biostability compared to native duplex DNA due to their unique topology. However, the molecular origin of their exceptional nuclease resistance is still unknown. Using atomistic MD simulation and enhanced sampling, we uncover the molecular origins of PX-DNAs superior resistance over JX-DNA and dsDNA. Our findings reveal that PX-DNAs six crossover points induce an overtwisted helix and narrower minor groove, leading to reduced DNase I binding affinity ([~] +5 kcal/mol for PX-DNA vs. [~] -17 kcal/mol for dsDNA). Mechanical properties, such as the stretch modulus ({gamma}G), confirm enhanced structural rigidity of PX-DNA (4805 pN), while residence time calculations using{tau} -RAMD further highlight shorter residence time of DNase I nuclease on PX-DNA. This is the first theoretical study to explore crossover-dependent biostability, mechanical properties, and residence time of PX/JX nanostructures in the presence of a nuclease using enhanced sampling. Our findings highlight that strategically positioned crossover points can regulate DNA stability against nuclease degradation at the nanoscale and lead to better design of biostable DNA nanostructures for medicinal applications.

biophysics↗