Backbone rigidity encodes universal viscoelastic signatures in biomolecular condensates

Biomolecular condensates exhibit a wide range of viscoelastic properties, shaped by their molecular grammar and composition. Coarse-grained molecular models of biomolecules are widely used to complement experiments for revealing the molecular drivers of thermodynamic stability and dynamics. However, fully flexible chain representations of proteins used in widely popular models often fail to capture their complex viscoelastic dynamics, instead predicting purely viscous responses. In this work, we demonstrate that introducing sequence-dependent chain rigidity enables us to quantitatively reproduce the experimentally observed viscelasticity trends for the low complexity domain of hnRNPA1 protein (A1-LCD) condensates and their variants. Furthermore, we show that the frequency-dependent loss factor can be characterized by a single descriptor that correlates with viscosity across A1-LCD variants and diverse parameter settings within a single-bead, semiflexible coarse-grained model. We further find that increasing backbone rigidity expands the elastic-dominated frequency range and is accompanied by more extended condensate-phase conformations. Finally, we elucidate the microscopic origins of sequence-encoded viscoelasticity by demonstrating how it can be tuned through sequence rearrangements that promote the formation of sticker clusters.