Surface tension and viscosity of protein condensates quantified by micropipette aspiration

TLDR

Biomolecular condensate material properties are implicated in biological and pathological processes, yet quantitative measurements of these properties remain scarce despite many identified phase‑separating biomolecules. We develop a micropipette‑based method that uniquely quantifies both surface tension and viscosity of condensates without labeling or surface‑wetting artifacts. The method’s accuracy and versatility are demonstrated by measuring LAF‑1 RGG domain condensates and a polymer aqueous two‑phase system, and confirmed with fusion and FRAP assays. This technique is expected to be broadly applicable to biomolecular condensates and to overcome limitations of current approaches.

Abstract

The material properties of biomolecular condensates have been suggested to play important biological and pathological roles. Despite the rapid increase in the number of biomolecules identified that undergo liquid-liquid phase separation, quantitative studies and direct measurements of the material properties of the resulting condensates have been severely lagging behind. Here, we develop a micropipette-based technique that uniquely, to our knowledge, allows quantifications of both the surface tension and viscosity of biomolecular condensates, independent of labeling and surface-wetting effects. We demonstrate the accuracy and versatility of this technique by measuring condensates of LAF-1 RGG domains and a polymer-based aqueous two-phase system. We further confirm our measurements using established condensate fusion and fluorescence recovery after photobleaching assays. We anticipate the micropipette-based technique will be widely applicable to biomolecular condensates and will resolve several limitations regarding current approaches.