HAZRA, M. K. | bioRxiv Science

bioRxiv2026

Dual Effect of RNA-like Polyelectrolytes on Stability and Dynamics of Biomolecular Condensates: A Tale of Competitive Short and Long-range Interactions

Heterotypic biomolecular condensates underpin the spatiotemporal organization of cellular components and enable precise biological regulation. These condensates frequently comprise proteins and RNA at variable stoichiometries, with RNA acting as a key modulator through its ability to engage in both long-range electrostatic and short-range specific interactions. How such RNA-like components regulate condensate stability and dynamics across distinct interaction regimes, however, remains unclear. Here, we examine the role of RNA-like polyelectrolytes in tuning the stability and material properties of heterotypic condensates formed by designed short peptide sequences spanning a continuum from long-range electrostatics-to short-range hydrophobic interactions. By systematically strengthening short-range hydrophobic interactions while varying polyelectrolyte composition, we uncover a dual, regime-dependent role of RNA-like species. In electrostatics-dominated condensates, excessive polyelectrolyte concentration rapidly destabilizes droplets due to enhanced long-range repulsive interactions while the droplets retain stability until intermediate polyelectrolyte concentration fairly well. In contrast, in strongly hydrophobic condensates, polyelectrolytes function as multivalent sticker hubs, stabilizing condensates through favourable peptide- polyelectrolyte interactions. Polyelectrolyte enrichment within condensates is nonlinear with respect to mixing fraction and saturates at largest cluster mole fractions of [~]0.2-0.25. Condensate dynamics reflect this interplay: polyelectrolyte diffusivity is 20-40% higher in electrostatics dominated systems than in hydrophobic ones, while in extremely hydrophobic condensates, polyelectrolytes diffuse [~]50% more slowly than peptides, indicative of scaffold-like behaviour. Together, these results reveal tuneable and opposing roles of RNA-like polyelectrolytes in shaping condensate stability, dynamics, and morphology across diverse interaction regimes.

biophysics↗

bioRxiv2025

Differential Sequence Charge-clustering and Mixing-ratio Affect Stability and Dynamics of Heterotypic Peptide Condensates

Phase separation has emerged as a central mechanism cell utilizes to organize its material components and are extremely important in tuning various biological regulations. However, such condensates in cellular media is often very much heterogeneous in nature in terms of proteins and even polynucleotides presence in different concentrations. Present study explores stability and dynamics of heterotypic coacervates formed by polyampholyte binary peptides having differential charge-clustering limits. Systematic increase in differential charge-clustering in peptide pairs tunes the origin of heterogeneity and shows an enhanced stability of droplet than homogeneous ones with same average charge clustering of the two peptide pairs. In addition, stability of the condensate phase enhances linearly with the increase of high charge-clustering polymers in the system. Peptides with higher charge-clustering are 3-4 times slower diffusive within condensate phase than the lower charge-clustering ones due to heterogeneity in structural morphology of droplets, that too diminish as one lowers the difference of charge-clustering among sequence pairs forming the condensate. Coupled to the differential diffusivity of the polymers in condensates, droplet diffusion is nearly 7-35 times lower than bulk depending upon the mixing ratios of the polymers and variable sequence charge-clustering. Condensates with mild heterogeneity have shown an enhanced arrestation than the most heterogeneous ones originating from complementarity and better packing probed by energetics in the condensate. This study quantifies fundamental microscopic properties of heterotypic condensates formed through long-range electrostatic forces and particularly how they can be modulated by the differential charge-pattern in sequences and mixing fraction systematically.

biophysics↗