Surface tension and viscosity of protein condensates quantified by micropipette aspiration

TLDR: A micropipette-based technique is developed that uniquely, to the knowledge, allows quantifications of both the surface tension and viscosity of biomolecular condensates, independent of labeling and surface-wetting effects.

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.