A bending rigidity parameter for stress granule condensates

Interfacial tension plays an important role in governing the dynamics of droplet coalescence and determining how condensates interact with and deform lipid membranes and biological filaments. We demonstrate that an interfacial tension-only model is inadequate for describing stress granules in live cells. Harnessing a high -throughput flicker spectroscopy pipeline to analyze the shape fluctuations of tens of thousands of stress gran-ules, we find that the measured fluctuation spectra require an additional contribution, which we attribute to elastic bending deformation. We also show that stress granules have an irregular, nonspherical base shape. These results suggest that stress granules are viscoelastic droplets with a structured interface, rather than simple Newtonian liquids. Furthermore, we observe that the measured interfacial tensions and bending rigid-ities span a range of several orders of magnitude. Hence, different types of stress granules (and more generally, other biomolecular condensates) can only be differentiated via large-scale surveys.

Automated summary

Interfacial tension is important for droplet coalescence and interaction with lipid membranes. A model based solely on interfacial tension is inadequate for describing stress granules in live cells, which exhibit elastic bending deformation. Stress granules have an irregular, nonspherical shape and are viscoelastic droplets with a structured interface. Different types of stress granules can only be differentiated through large-scale surveys.