Biology subjects

Cojocaru, V.

Publications and source records attributed to Cojocaru, V..

6 recordsLinked to original sources

bioRxiv2025

Conformational plasticity modulates sequence specificity in non-canonical tandem RRM-RNA binding

The Dead End protein (DND1), a key regulator of germline cell fate, utilizes two RNA Recognition Motifs (RRM) in tandem to bind AU-rich RNA in a non-canonical manner. Only one RRM uses the known RNA binding interface, whereas the second motif has only minimal contacts with the RNA. To characterize the structural features and dynamics that contribute to RNA binding, we performed a series of atomistic molecular dynamics simulations and found that the complex is highly dynamic, deviating significantly from the experimental structure. We found that RNA binding restricts without abolishing the inter-domain motions of the RRMs and that cooperative binding of both RRMs is required to reduce the flexibility of the bound RNA. Through detailed analysis of the protein-RNA interactions, we show that the RNA binding interface in the tandem RRM-RNA complex remains stable despite extensive conformational plasticity. The RRMs cooperate to sustain a layered RNA binding mechanism, with aromatic stacking of the central adenosine with RRM1 residues as foundation, arginine residues anchoring the RNA backbone, and residues in the inter RRM linker forming hydrogen bonds with the RNA. Despite insufficient conformational space sampling to claim convergence, the protein-RNA interactions were consistent across multiple independent simulations with cognate and non-cognate RNA sequences. This substantiates our findings which showcase how structural dynamics impact RNA recognition, enabling structural adaptation for functional versatility in multi-domain proteins. Statement of SignificanceThe RNA recognition motif (RRM) is the most abundant RNA binding domain in proteins. Often, one protein has multiple RRMs to enhance RNA binding specificity. For example, Dead End, an essential protein in germ cells with context dependent roles in cancer has two RRMs connected by a short linker. It is not understood how the inter-domain dynamics between the two RRMs modulate the RNA binding specificity. We found that the tandem RRMs of Dead End display extensive conformational plasticity in molecular dynamics simulations with variable inter-domain orientations. Despite this plasticity, the core RNA binding specificity is kept as a result of the cooperative binding of the two RRMs. Our findings provide evidence for highly dynamic and adaptable RNA recognition by tandem RRMs.

biophysics↗

bioRxiv2024

Integrative modeling in the age of machine learning: a summary of HADDOCK strategies in CAPRI rounds 47-55

The HADDOCK team participated in CAPRI rounds 47-55 as both server, manual predictor, and scorers. Throughout these CAPRI rounds, we used a plethora of computational strategies to predict the structure of protein complexes. Of the 10 targets comprising 24 interfaces, we achieved acceptable or better models for 3 targets in the human category and 1 in the server category. Our performance in the scoring challenge was slightly better, with our simple scoring protocol being the only one capable of identifying an acceptable model for Target 234. This result highlights the robustness of the simple, fully physics-based HADDOCK scoring function, especially when applied to highly flexible antibody-antigen complexes. Inspired by the significant advances in machine learning for structural biology and the dramatic improvement in our success rates after the public release of Alphafold2, we identify the integration of classical approaches like HADDOCK with AI-driven structure prediction methods as a key strategy for improving the accuracy of model generation and scoring.

bioinformatics↗

bioRxiv2022

Enhancing Sox/Oct cooperativity induces higher-grade developmental reset

The discovery of induced pluripotent stem cell (iPSC) technology by Shinya Yamanaka has truly enabled the stem cell field. After 16 years of intense research, the delivery methods and culture media have improved but the original factors--Oct4, Sox2, Klf4, and Myc (OSKM)--remain central for driving reprogramming. Here we define structural elements in chimeric Sox2/Sox17 transcription factors that rescued the ability of nonfunctional Oct factors to induce pluripotency. Most importantly, we discovered a single amino acid swap in the DNA-binding domain of Sox2, A61V, that stabilizes the Sox/Oct heterodimer on DNA through hydrophobic interaction with Oct. The highly cooperative Sox2AV mutant enables iPSC generation with Oct4 orthologs, such as Oct2 and Oct6, as well as rescues otherwise detrimental Oct4 mutants and domain deletions. Sox2AV has a dramatic effect on the cell fate reset, significantly improving the developmental potential of OSKM iPSCs. Moreover, by swapping multiple beneficial elements of Sox17 into Sox2 we have built a chimeric super-SOX factor--Sox2-17--that delivers unprecedented reprogramming efficiency and kinetics in five tested species. Sox2-17 enhances five-, four-, and three-factor reprogramming up to hundreds of times, enables two-factor generation of human iPSCs, and allows integration-free reprogramming of otherwise non-permissive aged human, non-human primate, and cattle fibroblasts. Our study demonstrates that a complete developmental reset requires both robust activation of regulatory elements controlled by the canonical SoxOct motif and limiting cellular proliferation driven by Oct4 and Myc. A high level of Sox2 expression and Sox2/Oct4 heterodimerization emerge as the key determinants of high-grade pluripotency that fades along the naive-to-primed continuum. Transient expression of SK cocktail can restore the naivety, providing a powerful technology to induce more complete developmental reset in pluripotent cells across species.

developmental biology↗

bioRxiv2021

OCT4 interprets and enhances nucleosome flexibility

Pioneer transcription factors are proteins that induce cellular identity transitions by binding to inaccessible regions of DNA in nuclear chromatin. They contribute to chromatin opening and recruit other factors to regulatory DNA elements. The structural features and dynamics modulating their interaction with nucleosomes are still unresolved. From a combination of experiments and molecular simulations, we reveal here how the pioneer factor and master regulator of pluripotency, Oct4, interprets and enhances nucleosome structural flexibility. The magnitude of Oct4s impact on nucleosome dynamics depends on the binding site position and the mobility of the unstructured tails of nucleosomal histone proteins. Oct4 propagates and stabilizes open nucleosome conformations by specific sequence recognition and nonspecific DNA exploration. Our findings provide a structural basis for the versatility of transcription factors in engaging with nucleosomes and have implications for understanding how pioneer factors induce chromatin dynamics.

biophysics↗

bioRxiv2020

Histone tails cooperate to control the breathing of genomic nucleosomes

Genomic DNA is packaged in chromatin, a dynamic fiber variable in size and compaction. In chromatin, repeating nucleosome units wrap 146 DNA basepairs around histone proteins. Genetic and epigenetic regulation of genes relies on structural transitions in chromatin which are driven by intra- and internucleosome dynamics and modulated by chemical modifications of the unstructured terminal tails of histones. Here we demonstrate how the interplay between histone H3 and H2A tails control ample nucleosome breathing motions. We monitored large openings of two genomic nucleosomes, and only moderate breathing of an engineered nucleosome in atomistic molecular simulations amounting to 18s. Transitions between open and closed nucleosome conformations were driven by the displacement and changes in compaction of the two histone tails. These motions involved changes in the DNA interaction profiles of clusters of epigenetic regulatory aminoacids in the tails. Histone tail modulated nucleosome breathing is a key mechanism of chromatin dynamics.

biophysics↗

bioRxiv2019

Nucleosomal DNA dynamics mediate Oct4 pioneer factor binding

Transcription factor (TF) proteins bind to DNA to regulate gene expression. Normally, accessibility to DNA is required for their function. However, in the nucleus the DNA is often inaccessible, wrapped around histone proteins in nucleosomes forming the chromatin. Pioneer TFs are thought to induce chromatin opening by recognizing their DNA binding sites on nucleosomes. For example, Oct4, a master regulator and inducer of stem cell pluripotency, binds to DNA in nucleosomes in a sequence specific manner. Here we reveal the structural dynamics of nucleosomes that mediate Oct4 binding. Nucleosome mobility and the amplitude of nucleosome motions such as breathing and twisting correlate with the number of Oct4 binding sites available. Moreover, the regions around the binding sites display higher local mobility. Probing different structures of Oct4-nucleosome complexes, we show that alternative configurations display stable protein-DNA interactions and are compatible with the DNA curvature and DNA-histone interactions.

biophysics↗