Biology subjects

Pedraza, E.

Publications and source records attributed to Pedraza, E..

6 recordsLinked to original sources

bioRxiv2026

Size Control of hnRNPK-based Nucleolar Condensates by RNA-Regulated Fusion Dynamics

Nucleoli are liquid-like condensates whose size is actively conserved--they remain small, numerous, and resistant to coalescence--yet the molecular mechanisms that constrain their fusion remain poorly understood. Heterogeneous nuclear ribonucleoprotein K (hnRNPK), an RNA-binding protein implicated in nucleolar organization and cancer, interacts directly with the scaffold protein Nucleolin. Combining residue-resolution coarse-grained simulations with biochemical experiments, we find that hnRNPK and Nucleolin condense through distinct interaction networks--a localized cation-{pi}/electrostatic hotspot in hnRNPK versus broadly distributed electrostatic contacts in Nucleolin, reorganized upon co-assembly. To probe how RNAs reshape these condensates, we develop and validate, against re-entrant phase-separation experiments and AlphaLISA binding data, a nucleotide-resolution coarse-grained model for single-stranded RNA. Using this framework, we show that RNA is asymmetrically and preferentially recruited by hnRNPK over Nucleolin, an asymmetry that grows stronger when the two proteins compete for the same RNAs. This selective recruitment sustains a dynamic fission-fusion equilibrium: hnRNPK-containing condensates repeatedly fuse and split rather than coalescing into a single condensate, whereas Nucleolin-containing and ternary condensates fuse into one dominant cluster. These results reveal a molecular mechanism, grounded in sequence-encoded, RNA-controlled fusion dynamics, by which nucleolar condensates conserve a controlled, non-coalescing size despite their liquid-like character.

biophysics↗

bioRxiv2026

Compositional control of FUS condensate ageing through aggregation-prone interaction networks

Stress granules are multicomponent biomolecular condensates whose aberrant ageing has been implicated in numerous neurodegenerative diseases. Although their composition is known to influence condensate properties, the molecular principles linking composition to structural maturation remain poorly understood. Here, we perform equilibrium and non-equilibrium residue-resolution molecular dynamics simulations to determine how RNA and heterotypic protein interactions regulate the pathological hardening of multicomponent FUS-containing condensates inspired by stress-granule composition. We show that diverse compositional changes--including RNA concentration, heterotypic protein partitioning, interfacial enrichment of G3BP1, and charged peptide recruitment--reshape condensate organization through distinct molecular mechanisms. Despite these different modes of action, all converge on a common physical principle: modulation of the local clustering and persistence of contacts between low-complexity aromatic-rich kinked segments (LARKS) governs the nucleation and accumulation of long-lived intermolecular cross-{beta}-sheet structures. Intermediate RNA concentrations enhance condensate density and promote LARKS contacts, whereas high RNA levels, heterotypic interactions, and interfacial coating reduce their availability and delay ageing. Our results establish a unified molecular framework linking condensate composition, internal organization and ageing. This framework provides mechanistic insight into the regulation of multicomponent condensate material properties and suggests general design principles for modulating their pathological aggregation.

biophysics↗

bioRxiv2026

Length Scale-Dependent Dynamics in Electrostatic Protein Coacervates

Biomolecular condensates formed by complex coacervation of highly charged proteins provide a powerful framework to understand how microscopic interactions give rise to macroscopic material properties. Atomistic molecular dynamics simulations provide detailed insights but remain limited in accesing the spatio-temporal scales relevant for condensate behavior. Here, we use the residue-level coarse-grained Mpipi-Recharged model to investigate condensates formed by ProT and positively charged partners, including histone H1, protamine, poly-lysine, and poly-arginine. Material properties, in this context, provide a stringent experimental benchamark for coarse-grained models. Our model reproduces salt-dependent phase behavior, protein binding affinities, and sequence-specific stability trends in agreement with in vitro experiments, despite the fact that material properties were not included in the model parametrization. We then establish a direct link between protein dynamics and macroscopic material properties by quantifying monomeric diffusion, conformational reconfiguration, and translational mobility within the dense phase, and relating these to condensate viscosity. By comparing dynamics across dense and dilute phases, we uncover a pronounced length scale-dependent behavior. While residue-level binding and unbinding events remain equally fast in both phases, protein reconfiguration time and self-diffusion are significantly slowed down within the condensates. This decoupling reveals how fast intermolecular interactions coexist with slow mesoscale condensate dynamics depending on the molecular length scale. Together, our results establish a predictive framework that links encoded sequence intermolecular forces and multiscale dynamics to the emergent material properties of complex biomolecular condensates.

biophysics↗

bioRxiv2025

Determination of nucleotide-nucleotide and nucleotide-amino acid binding interactions from all-atom potential-of-mean-force calculations

Biomolecular condensates emerge from multivalent interactions between proteins and nucleic acids and are frequently modeled using coarse-grained molecular dynamics simulations. The parametrization of these models critically depends on atomistic data describing the underlying molecular interactions. In this work, we employ all-atom molecular dynamics simulations and potential-of-mean-force (PMF) calculations to investigate the interaction landscape between RNA nucleotides and protein amino acids. We begin by characterizing nucleotide-nucleotide binding modes through canonical base-pairing analysis, observing notable agreement in the predictions from both AMBER03ws and CHARMM36 force fields. Further rationalization of different nucleotide-nucleotide interaction modes involves the calculation of PMFs for ribose-ribose, phosphate-phosphate, and RNA tertiary interactions such as G-quadruplex formation. We also examine the effect of salt concentration on these interactions, finding a reduction on electrostatic self-repulsion for phosphate-phosphate binding upon increasing the ionic strength. Extending our analysis to amino acids, we first benchmark the performance of both AMBER03ws and a99SB-disp force fields for describing pairwise amino acid interactions, and then we evaluate different nucleotide-amino acid binding profiles. Our findings reveal a subset of amino acids--Lys and Arg (positively charged), Asp and Glu (negatively charged), and Gln, Ser, and Asn (polar residues)--that consistently engage with the nitrogenous bases of different nucleotides. Such binding is primarily mediated by hydrogen bonding and, in some cases, cation-{pi} interactions. Furthermore, we identify strong{pi} -{pi} stacking interactions with aromatic residues and phosphate-Arg contacts as key contributors to condensate cohesion in RNA-protein condensates. Our comprehensive analysis provides a detailed library of nucleotide-amino acid interactions, offering quantitative insights to inform coarse-grained model parametrization and deepening our understanding of condensate self-assembly, nucleic acid recognition, and phase-separation regulation at submolecular scale.

biophysics↗

bioRxiv2025

Predicting Saturation Concentrations of Phase-Separating Proteins via Thermodynamic Integration

Phase separation of proteins and nucleic acids into biomolecular condensates contributes to the regulation of cellular compartmentalisation in membrane-less environments. A key parameter controlling the onset of biomolecular condensate formation via liquid--liquid phase separation is the saturation concentration (Csat)-- the threshold concentration above which condensation takes place. While measuring Csat for protein solutions in vitro is experimentally accessible, determining this quantity in simulations remains challenging due to the extremely low equilibrium concentrations at which many proteins phase separate. This occurs because the gold standard in simulations consists on combining a residue-resolution coarse-grained model with the Direct Coexistence simulation method, which yields poor estimates of the equilibrium concentrations of the dilute phase due to lack of statistics. In this work, we present two independent thermodynamic integration (TI) schemes which, when combined with Direct Coexistence simulations, enable accurate calculation of saturation concentrations and phase diagrams--facilitating direct comparison with experimental measurements across a wide range of conditions. Our methods, combined with the Mpipi-Recharged residue-resolution coarse-grained model, accurately estimate Csat for a wide range of intrinsically disordered and multi-domain proteins, including disease-associated RNA- and DNA-binding proteins involved in the formation of stress granules and P granules, as well as engineered mutants of hnRNPA1. Furthermore, we compare our TI methods against a computationally efficient machine-learning predictor trained to estimate saturation concentrations at sub-physiological temperatures. While both approaches yield realistic predictions, explicit molecular dynamics simulations enable the calculation of complete phase diagrams and provide insight into the molecular mechanisms and interactions driving phase-separation. Overall, our approach offers a robust, physically grounded framework for improving and validating coarse-grained models of biomolecular phase behaviour, effectively bridging the gap between simulation and experiment.

biophysics↗

bioRxiv2025

Charged mutations in the FUS low-complexity domain modulate condensate ageing kinetics

The assembly of biomolecular condensates is tightly regulated by the intracellular environment. Disruptions in the balance between condensate formation and dissolution--such as irreversible aggregation of low-complexity aromatic-rich kinked segments (LARKS)--have been implicated in multiple neuropathologies. Here, we employ non-equilibrium, residue-resolution coarse-grained simulations to investigate how specific mutations in FUS, an RNA-binding protein associated with amyotrophic lateral sclerosis and frontotemporal dementia, modulate its phase separation propensity and transition into insoluble aggregates. Our simulations reveal that mutations increasing the content of negatively charged amino acids in the low-complexity domain slow down inter-protein {beta}-sheet accumulation, while preserving the phase diagram and viscoelastic properties of the wild-type sequence. Conversely, mutations increasing the arginine content accelerate disorder-to-order LARKS transitions, driving rapid formation of amorphous kinetically trapped aggregates. Our computational approach thus provides molecular-level insights into how specific amino acid mutations and associated intermolecular interactions control the ageing kinetics of protein condensates, promoting aberrant solid-like phases.

biophysics↗