Biology subjects

Bignon, E.

Publications and source records attributed to Bignon, E..

At least 19 recordsLinked to original sources

bioRxiv2026

Structural basis of the two-photon photoactivation mechanism of orange carotenoid protein

Cyanobacteria have produced Earths oxygen for 2.4 billion years by adapting to fluctuating irradiance. This adaptation relies on orange carotenoid protein (OCP), which mediates light-intensity- dependent photoprotective energy dissipation using a unique two-photon absorption mechanism. Photon absorption by ground-state OCP (OCPO) generates a metastable intermediate (OCP1h{nu}) that either relaxes thermally or, upon absorption of a second photon within [~]1 s, converts to the active photoprotective state (OCPR). By integrating static and time-resolved crystallography, cryo-EM, computation, spectroscopy and biochemistry, we assign the structure of OCP1h{nu}, establish its functional relevance and capture structural snapshots along the OCPO[->]OCP1h{nu} and OCP1h{nu}[->]OCPR photochemical pathways. We elucidate the molecular mechanism of OCP, which serves as a unique biological circuit breaker protecting the photosynthetic machinery from high light flux.

biochemistry↗

bioRxiv2026

Molecular basis of nick ligation in the nucleosome by DNA Ligase IIIα

Eukaryotic genomic DNA is packaged into chromatin through a fundamental repeating unit known as the nucleosome core particle. Within this chromatin context, genomic DNA is constantly exposed to endogenous and exogenous stress that result in the formation of DNA damage, which must be effectively repaired to maintain genome stability. Single-strand breaks (SSBs) are among the most prevalent forms of DNA damage that arise via the oxidation-induced disintegration of the sugar-phosphate backbone or as repair intermediates during base excision repair. DNA ligase III (LigIII) is one of the primary enzymes responsible for repairing SSBs containing an intact 5'-phosphate and 3'-OH (nick) during the terminal step of single-strand break repair (SSBR) and base excision repair (BER) pathways. To date, a complete mechanistic description for how LigIII processes nicks within chromatin remains elusive. Here, we use a combination of biochemical assays, molecular dynamics simulations, and cryogenic electron microscopy (cryo-EM) to define the molecular basis of nick ligation in the nucleosome by LigIII. Quantitative enzyme kinetics reveal that the LigIII ligation rate is highly dependent on the translational position of the nick in the nucleosome, where nicks near the nucleosome entry/exit site are ligated with moderate efficiency and nicks near the nucleosome dyad are refractory to ligation. Cryo-EM structures of LigIII bound to nicks at four unique translational positions in the nucleosome reveal the structural basis for this position-dependent catalytic activity, identifying that local steric constraints imposed by the histone octamer prevent LigIII from readily adopting a ligation-competent conformation. Further biochemical and structural analysis demonstrates that the scaffolding protein XRCC1, which forms a heterodimer with LigIII, does not substantially alter the ability of LigIII to bind or ligate nicks in the nucleosome. Together, this work provides foundational insight into the processing of nicks in the nucleosome during the terminal step of SSBR/BER.

biochemistry↗

bioRxiv2025

InterMap: Accelerated Detection of Interaction Fingerprints on Large-Scale Molecular Ensembles

MotivationMolecular dynamics is a key technique for exploring biomolecular systems at the atomic level. The rapid growth in accessible system sizes and timescales has intensified the need for efficient post-processing methods that extract meaningful insights from the resulting data. Interaction fingerprint (IFP) analyses are a valuable tool for elucidating key atomic interactions within molecular ensembles, yet current specialized software often struggle with extensive trajectories or complex systems. Here, we introduce InterMap, a Python package designed to accelerate IFP detection on large-scale molecular ensembles. ResultsBy actively exploiting k-d trees, InterMap efficiently handles the massive amount of distance calculations necessary to detect IFPs, particularly when dealing with intra-molecular interactions. The seamless integration with MDAnalysis ensures broad format compatibility and allows using SMARTS patterns for flexible interaction definitions. InterMap adopts a deeply compressed binary encoding to manage IFPs, which makes it very memory-friendly. Furthermore, convenient interactive visualizations are provided to enhance data interpretation through a locally hosted web-browser application. Benchmark results indicate that InterMap significantly outperforms existing tools for processing complex biomolecular systems, achieving up to a 99% reduction in both runtime and peak memory usage. AvailabilityInterMaps code and issue tracker are available at https://github.com/Delta-Research-Team/intermap.git, while documentation and tutorials can be found at https://delta-research-team.github.io/intermap/. Contactroy.gonzalez-aleman@inria.fr, yasaman.karami@inria.fr Supplementary informationSupplementary data are available at Nucleic Acid Research online.

bioinformatics↗

bioRxiv2025

Structure, dynamics, and processing of 8oxoG:A in the nucleosome

Eukaryotic genomic DNA is packaged into chromatin through a repeating unit known as the nucleosome. In this chromatin environment, DNA is constantly exposed to several sources of DNA damage, such as reactive oxygen species (ROS), which can lead to the formation of 8-oxo-7,8-dihydroguanine (8oxoG). 8oxoG can base pair with cytosine (8oxoG:C) or form a mutagenic base pair with adenine (8oxoG:A), which can lead to single base transversions if left unrepaired. To date, the structure and dynamics of these two possible 8oxoG base pairs in the nucleosome remain unclear. Furthermore, whether MutY homologue (MUTYH) excises 8oxoG:A base pairs in the nucleosome remains elusive. Here using a combination of cryogenic-electron microscopy, molecular dynamics simulations, and biochemistry we determined the structure and dynamics of 8oxoG:C and 8oxoG:A base pairs in the nucleosome and characterize MUTYH activity in nucleosomal DNA. We found that nucleosomal 8oxoG:C forms a stable base pair using its anti conformation, while nucleosomal 8oxoG:A forms a more dynamic base pair using its syn conformation that is unable to be processed by MUTYH. This work provides fundamental insight into the accommodation of oxidative damage in the nucleosome and how this damage contributes to increased mutagenic transversions in nucleosomal compared to linker DNA.

biochemistry↗

bioRxiv2025

DynaRepo: The repository of macromolecular conformational dynamics

Proteins, RNA, and DNA are central to virtually all cellular processes, often assembling into macro-molecular complexes to perform their functions. While these molecules are inherently dynamic, most methods for studying their mechanisms focus on static structures. Recent deep learning advances in protein structure prediction highlight the potential of data-driven approaches, yet dynamic behavior that is critical for interactions such as antibody-antigen recognition, intrinsically disordered proteins, and protein-nucleic acid binding, remains underexplored. To address this gap, we present DynaRepo, a repository of macromolecular conformational dynamics comprising ~450 complexes and ~270 single-chain proteins from PDBbind, the Structural Antibody Database (SAbDab), and benchmark sets. Each complex was simulated in triplicate for 500 ns, totaling >1100 {micro}s of molecular dynamics data, with extensive pre-calculated analyses. DynaRepo provides a foundation for dynamics-aware deep learning frameworks and is freely available at: https://dynarepo.inria.fr/.

biophysics↗

bioRxiv2025

Specific binding modes of SIRT6 C-terminal domain to the nucleosome core particle influence DNA unwrapping and H3K27 accessibility

Sirtuins are a class of NAD-dependent histone deacetylases that regulate important biological pathways in prokaryotes and eukaryotes. This enzyme family comprises seven members, named SIRT1 to SIRT7. Among them, Sirtuin 6 (SIRT6) is a human sirtuin that deacetylates histones and plays a key role in DNA repair, telomere maintenance, carbohydrate and lipid metabolism, and lifespan. SIRT6s structure consists of a zinc finger domain, a Rossmann fold domain containing the NAD+ binding site, and disordered N-terminal and C-terminal (CTD) extensions. The specific role of the CTD on SIRT6 interaction with nucleosomes for histone deacetylation remains unclear. Here, we resort to extended molecular dynamics simulations to uncover the dynamical behavior of the full-length SIRT6 bound to a nucleosome core particle. Our simulations reveal that the CTD preferentially interacts with DNA at the entry/exit near the enzymes docking site, exhibiting a variety of different binding modes. In specific cases, the CTD participates to the promotion of DNA unwrapping and promotes H3K27 accessibility to SIRT6s active site, suggesting a pivotal role of this domain for H3K27 deacetylation. This work provides new structural insights into the binding process of the full-length SIRT6 to a nucleosome core particle, shedding light on the conformational behavior and functional role of its CTD. It constitutes an important step towards the understanding of SIRT6 deacetylation mechanisms and specificity.

biochemistry↗

bioRxiv2025

Communication pathway analysis within protein-nucleic acid complexes

Inter-residue communication forms a vast and intricate network that underpins essential biological processes such as catalysis, gene expression, and cell signaling. Allostery, a crucial phenomenon where distant regions of a macromolecule are energetically coupled to elicit functional responses, operates through these intricate communication networks within macromolecular complexes. Despite the pivotal role of nucleic acids in these networks, their contributions to allostery remain largely overlooked. To address this gap, we developed ComPASS, a large-scale computational method designed to study communication networks in protein-protein and protein-nucleic acid complexes. Recognizing the significance of dynamics in the communication of macromolecules, our approach leverages molecular dynamics (MD) simulation data to extract inter-residue key properties, including dynamical correlations, interactions, and distances. These properties are integrated to construct a weighted communication network that comprehensively represents dependencies among amino acids and nucleotides. Using ComPASS, we uncovered distinct mechanisms of signal transmission in diverse macromolecular systems. In Cysteinyl-tRNA synthetase, the central domain was found to mediate the coordination between substrate recognition and enzymatic activity, ensuring functional precision. In the LacI repressor, allosteric communication occurs through interface pathways within the dimer, effectively linking ligand sensing to DNA binding. For the Type IIF restriction endonuclease Bse634I, structural communication across dimer and tetramer interfaces was crucial for specific DNA recognition. In the liver X receptor, a key helical region was identified as a bridge connecting ligand-binding events to DNA interactions. Finally, our analysis with ComPASS aligned with previous literature, confirmed the role of H2A L1 loops in mediating communication across histone interfaces and coordinating interactions between structural domains in nucleosome complexes. ComPASS is available as an open-source tool, maintained at https://github.com/yasamankarami/compass. By offering an integrated framework for studying communication networks, ComPASS advances our understanding of conformational dynamics, particularly within protein-nucleic acid complexes.

bioinformatics↗

bioRxiv2024

Histone H3 as a redox switch in the nucleosome core particle: insights from molecular modeling

Histones post-translational modifications are major regulators of the chromatin dynamics. Understanding the structural signature of these marks in the nucleosome context is of major importance to unravel their mechanisms of action and open perspectives for the development of new therapies. In this work, we rely on multi-microseconds molecular dynamics simulations and advanced structural analysis to unravel the effect of two modifications of the histone H3: S-sulfenylation and S-nitrosylation. These oxidative modifications are known to target the cysteine 110 on the histone H3, but there their effect on the nucleosome dynamics. In this study, we show that in a nucleosome core particle, S-sulfenylation and S-nitrosylation exhibit different structural signatures, which suggests that they play a different function. While S-sulfenylation destabilizes DNA-histone communication at the dyad and could be linked to the promotion of nucleosome disassembly events, S-nitrosylation exhibits a mild effect on the nucleosome dynamics and might have a different function. Our results highlight the fine tune link between the chemical nature of histone core post-translational modifications and their impact on the nucleosomes large architecture. We provide new insights into the regulatory mechanisms of histone oxidative modifications, about which very little is known so far.

biophysics↗

bioRxiv2024

Molecular bases and specificity behind the activation of the immune system OAS/RNAse L pathway by viral RNA.

The first line of defense against invading pathogens usually relies on the innate immune systems. In this context the recognition of exogenous RNA structure is primordial to fight, notably, against RNA viruses. One of the most efficient immune response pathways is based on the sensing of RNA double helical motifs by the oligoadenylate synthase (OAS) proteins, which in turns triggers the activity of RNase L and, thus, cleaving cellular and viral RNA. In this contribution by using long range molecular dynamics simulation, complemented with enhanced sampling techniques, we elu-cidate the structural features leading to the activation of OAS by interaction with a model double strand RNA oligomer mimicking a viral RNA. We characterize the allosteric regulation induced by the nucleic acid leading to the population of the active form of the protein. Furthermore, we also identify the free energy profile connected to the active vs. inactive conformational transitions in presence and absence of RNA. Finally, the role of two RNA mutations, identified as able to down-regulate OAS activation, in shaping the protein/nucleic acid interface and the conformational land-scape of OAS are also analyzed.

biophysics↗

bioRxiv2023

Cysteine hyperoxidation rewires communication pathways in the nucleosome and destabilizes the dyad

Gene activity is tightly controlled by reversible chemical modifications called epigenetic marks, which are of various types and modulate gene accessibility without affecting the DNA sequence. Despite an increasing body of evidence demonstrating the role of oxidative-type modifications of histones in gene expression regulation, there remains a complete absence of structural data at the atomistic level to understand the molecular mechanisms behind their regulatory action. Owing to s time-scale MD simulations and protein communication networks analysis, we describe the impact of histone H3 hyperoxidation (i.e., S-sulfonylation) on the nucleosome dynamics. Our results reveal the atomic-scale details of the intrinsic structural networks within the canonical histone core and their perturbation by hyperoxidation of the histone H3 C110. We show that this modification involves local rearrangement of the communication networks and destabilizes the dyad, which could be important for nucleosome disassembly.

biophysics↗

bioRxiv2023

Robust of AMBER force field parameters for glutathionylated cysteines

S-glutathionylation is an oxidative post-translational modification which is involved in the regulation of many cell signaling pathways. Increasing amounts of studies show that it is crucial in cell homeostasis and deregulated in several pathologies. However, the effect of S-glutathionylation on proteins structure and activity is poorly understood, and a drastic lack of structural information at the atomic scale remains. Studies based on the use of molecular dynamics simulations, which can provide important information about modification-induced modulation of proteins structure and function, are also sparse and there is no benchmarked force field parameters for this modified cysteine. In this contribution, we provide robust AMBER parameters for S-glutathionylation, that we tested extensively against experimental data through a total of 33 s molecular dynamics simulations. We show that our parameters set efficiently describe the global and local structural properties of S-glutathionylated proteins. These data provide the community with an important tool to stimulate investigations about the effect of S-glutathionylation on protein dynamics and function, in a common effort to unravel the structural mechanisms underlying its critical role in cellular processes.

biophysics↗

bioRxiv2023

Mechanism of the Covalent Inhibition of Human Transmembrane Protease Serine 2 as an Original Antiviral Strategy

The Transmembrane Protease Serine 2 (TMPRSS2) is a human enzyme which is involved in the maturation and post-translation of different proteins. In addition of being overexpressed in cancer cells, TMPRSS2 plays a further fundamental role in favoring viral infections by allowing the fusion of the virus envelope and the cellular membrane, notably in SARS-CoV-2. In this contribution we resort to multiscale molecular modeling to unravel the structural and dynamical features of TMPRSS2 and its interaction with a model lipid bilayer. Furthermore, we shed light into the mechanism of action of a potential inhibitor (Nafamostat), determining the free-energy profile associated with the inhibition reaction, and showing the facile poisoning of the enzyme. Our study, while providing the first atomistically resolved mechanism of TMPRSS2 inhibition, is also fundamental in furnishing a solid framework for further rational design targeting transmembrane proteases in a host-directed antiviral strategy. TOC GRAPHICS O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=193 SRC="FIGDIR/small/537985v1_ufig1.gif" ALT="Figure 1"> View larger version (108K): org.highwire.dtl.DTLVardef@19dd8c9org.highwire.dtl.DTLVardef@394c0org.highwire.dtl.DTLVardef@11ad383org.highwire.dtl.DTLVardef@347a8c_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2023

Resolving a Guanine-Quadruplex Structure in the SARS-CoV-2 Genome through Circular Dichroism and Multiscale Molecular Modeling.

The genome of SARS-CoV-2 coronavirus is made up of a single-stranded RNA fragment that can assume a specific secondary structure, whose stability can influence the virus ability to reproduce. Recent studies have identified putative guanine quadruplex sequences in SARS-CoV-2 genome fragments that are involved in coding for both structural and non-structural proteins. In this contribution, we focus on a specific G-rich sequence referred as RG-2, which codes for the non-structural protein 10 (Nsp10) and assumes a guanine-quadruplex (G4) arrangement. We provide the secondary structure of the RG-2 G4 at atomistic resolution by molecular modeling and simulation, validated by the superposition of experimental and calculated electronic circular dichroism spectrum. Through both experimental and simulation approaches, we have demonstrated that pyridostatin (PDS), a widely recognized G4 binder, can bind to and stabilize RG-2 G4 more strongly than RG-1, another G4 forming sequence that was previously proposed as a potential target for antiviral drug candidates. Overall, this study highlights RG-2 as a valuable target to inhibit the translation and replication of SARS-CoV-2 paving the way towards original therapeutic approaches against emerging RNA viruses.

biophysics↗

bioRxiv2023

Binding to nucleosome poises SIRT6 for histone H3 de-acetylation

Sirtuin 6 (SIRT6) is an NAD+ dependent histone H3 deacetylase that is prominently found associated with chromatin, attenuates transcriptionally active promoters and regulates DNA repair, metabolic homeostasis and lifespan. Unlike other sirtuins, it has low affinity to free histone tails but demonstrates strong binding to nucleosomes. It is poorly understood how SIRT6 docking on nucleosomes stimulates its histone deacetylation activity. Here we present the structure of human SIRT6 bound to a nucleosome determined by cryogenic electron microscopy. The zinc finger domain of SIRT6 associates tightly with the acidic patch of the nucleosome through multiple arginine anchors. The Rossmann fold domain binds to the terminus of the looser DNA half of the nucleosome, detaching two turns of the DNA from the histone octamer and placing the NAD+ binding pocket close to the DNA exit site. This domain shows flexibility with respect to the fixed zinc finger and moves with, but also relative to, the unwrapped DNA terminus. We apply molecular dynamics simulations of the histone tails in the nucleosome to show that in this mode of interaction, the active site of SIRT6 is perfectly poised to catalyze deacetylation of the H3 histone tail and that the partial unwrapping of the DNA allows even lysines close to the H3 core to reach the enzyme.

molecular biology↗

bioRxiv2023

Predicting the Three-dimensional Structure of the c-KIT Oncogene Promoter and the Dynamics of Strongly Coupled Guanine-Quadruplexes

Guanine-quadruplexes (G4s) are non-canonical DNA structures that play important protective and regulatory roles within cells, influencing, for instance, gene expression. Although the secondary structure of many human G4s is well characterized, in several gene-promoter regions multiple G4s are located in close proximity and may form three-dimensional structures which could ultimately influence their biological roles. In this contribution, we analyze the interplay between the three neighboring G4s present in the c-KIT proto-oncogene promoter, namely WK1, WSP and WK2. In particular, we highlight how these three G4s are structurally linked and how their crosstalk favors the formation of a parallel structure for WSP, differently from what observed for this isolated G4 in solution. Relying on all-atom molecular dynamic simulations exceeding the s time-scale and using enhanced sampling methods, we provide the first computationally-resolved structure of a well-organized G4 cluster in the promoter of a crucial gene involved in cancer development. Our results indicate that neighboring G4s influence their mutual three-dimensional arrangement and provide a powerful tool to predict and interpret complex DNA structures that ultimately can be used as starting point for drug discovery purposes.

biophysics↗

bioRxiv2022

How SARS-CoV-2 alters the regulation of gene expression in infected cells.

Non-structural accessory proteins in viruses play a key role in hijacking the basic cellular mechanisms, which is essential to promote the virus survival and evasion of the immune system. The immonuglobulin-like open reading frame 8 (ORF8) protein expressed by SARS-CoV-2 accumulates in the nucleus and may influence the regulation of the gene expression in infected cells. In this contribution, by using micro-second time-scale all-atom molecular dynamics simulations, we unravel the structural bases behind the epigenetic action of ORF8. In particular, we highlight how the protein is able to form stable aggregates with DNA through a histone tail-like motif, and how this interaction is influenced by post-translational modifications, such as acetylation and methylation, which are known epigenetic markers in histones. Our work not only clarifies the molecular mechanisms behind the perturbation of the epigenetic regulation caused by the viral infection, but also offers an unusual perspective which may foster the development of original antivirals.

biophysics↗

bioRxiv2022

Molecular basis of the pH-controlled maturation of the tick-borne encephalitis flavivirus

Flaviviruses are enveloped viruses causing high public concerns. Their maturation spans several cellular compartments having different pH. Thus, complex control mechanisms are in place to avoid premature maturation. Here we report the dynamical behavior at neutral and acidic pH of the precursor of the membrane fusion protein E of tick-borne encephalitis, showing the different stabilization of the E dimer and the role played by the small fusion-assisting protomer (pr). The comprehension, at atomic resolution, of the fine regulation of viral maturation will be fundamental to the development of efficient strategies against emerging viral threats.

biophysics↗

bioRxiv2022

G-quadruplex recognition by DARPIns through epitope/paratope analogy

We investigated the mechanisms leading to the specific recognition of Guanine Guadruplex (G4) by DARPins peptides, which can lead to the design of G4s specific sensors. To this end we carried out all-atom molecular dynamic simulations to unravel the interactions between specific nucleic acids, including human-telomeric (h-telo), Bcl-2, and c-Myc, with different peptides, forming a DARPin/G4 complex. By comparing the sequences of DARPin with that of a peptide known for its high affinity for c-Myc, we show that the recognition cannot be ascribed to sequence similarity but, instead, depends on the complementarity between the three-dimensional arrangement of the molecular fragments involved: the -helix/loops domain of DARPin and the G4 backbone. Our results reveal that DARPins tertiary structure presents a charged hollow region in which G4 can be hosted, thus the more complementary the structural shapes, the more stable the interaction.

biophysics↗