The role of local chain stiffness in modulating viscoelasticity of biomolecular condensates

Biomolecular condensates, which exhibit sequence-dependent viscoelastic properties, are widely studied using coarse-grained models. In this work, we systematically investigate the viscoelastic effects of local chain stiffness in the hydrophobicity scale (HPS) model for the low-complexity domain (LCD) of the protein hnRNP A1. Recent experiments have demonstrated that the strengths of aromatic interactions significantly influence the elastic (G') and viscous (G") moduli by comparing various aromatic mutations. Our simulations reveal that incorporating harmonic angular potential to control local chain stiffness enables the elastic and viscous moduli, as well as the relaxation time, of wild-type and mutated A1-LCD condensates to qualitatively match experimental observations. Additionally, we show that the frequency-dependent loss factor (G"/G') can be represented by a characteristic value, which universally correlates with the viscosity across all sequences and potential variations in our simulations. We also find that increased chain stiffness, indicated by a higher radius of gyration, expands the elastic regime of the condensates. Finally, we predict that rearranged sequences exhibit distinct viscoelastic properties, with angular potential further amplifying the differences after sequence rearrangements.