Programmable viscoelasticity in protein-RNA condensates with disordered sticker-spacer polypeptides

TLDR

Liquid‑liquid phase separation of multivalent proteins and RNAs forms biomolecular condensates that act as membrane‑free compartments, and recent advances show these condensates behave as network fluids with time‑dependent material properties. The study uses microrheology with optical tweezers to identify molecular determinants governing the viscoelastic behavior of condensates formed by multivalent Arg/Gly‑rich sticker‑spacer polypeptides and RNA. Microrheology with optical tweezers was employed to probe the viscoelastic behavior of condensates formed by multivalent Arg/Gly‑rich sticker‑spacer polypeptides and RNA. The condensates behave as Maxwell fluids, exhibiting elastically‑dominant responses at short timescales and liquid‑like behavior at longer timescales, and their viscous and elastic regimes can be tuned by polypeptide and RNA sequences and mixture compositions, establishing a quantitative link between microscopic sequence‑encoded interactions and mesoscale rheological properties for rational engineering of condensate mechanics.

Abstract

Abstract Liquid-liquid phase separation of multivalent proteins and RNAs drives the formation of biomolecular condensates that facilitate membrane-free compartmentalization of subcellular processes. With recent advances, it is becoming increasingly clear that biomolecular condensates are network fluids with time-dependent material properties. Here, employing microrheology with optical tweezers, we reveal molecular determinants that govern the viscoelastic behavior of condensates formed by multivalent Arg/Gly-rich sticker-spacer polypeptides and RNA. These condensates behave as Maxwell fluids with an elastically-dominant rheological response at shorter timescales and a liquid-like behavior at longer timescales. The viscous and elastic regimes of these condensates can be tuned by the polypeptide and RNA sequences as well as their mixture compositions. Our results establish a quantitative link between the sequence- and structure-encoded biomolecular interactions at the microscopic scale and the rheological properties of the resulting condensates at the mesoscale, enabling a route to systematically probe and rationally engineer biomolecular condensates with programmable mechanics.