Molecular Origin of Aging in Biomolecular Condensate

Biomolecular condensates represent intriguing, dynamic assemblies within cells whose rheological properties evolve over time. We investigate the aging of biomolecular condensate and modeled condensates as solvent evaporation systems that impact viscosity using Coarse-grained (CG) molecular dynamics simulations. By varying solvent concentrations in bulk condensed systems, we unveil distinct frequency regimes in which the storage ($G^prime$) and loss ($G^{primeprime}$) moduli intersect and their crossover regions. Solvent expulsion brings sticky regions closer, shifting from a fluidic to elastic nature in the intermediate deformation frequencies ($omega$). Comparing elastic and viscous moduli and viscosity, we observe distinct rheological variations in the case of dry entangled polymer melt, in a solvent and while it forms crosslinked gel structures. We also show decreasing polymer chain length correlates with a reduction of viscosity, whereas long chains with excessive frictions and large entanglements make the system more viscous. We found fully flexible chains exhibit viscous dominance throughout the frequency range. However, introducing rigidity renders the interesting elasticity-dominated viscoelastic nature of the system. We reveal the Maxwell fluidic nature of the biomolecular condensates, which was not captured in the previous simulations studies. This comprehensive study sheds light on the aging of the biomolecular condensates and how the rheological nature changes over time.