Using Shape Fluctuations to Probe the Mechanics of Stress Granules

Abstract

Surface tension plays a significant role in many functions of biomolecular condensates, from governing the dynamics of droplet coalescence to determining how condensates interact with and deform lipid membranes and biological filaments. To date, however, there is a lack of accurate methods to measure the surface tension of condensates in living cells. Here, we present a high-throughput flicker spectroscopy technique that is able to analyse the thermal fluctuations of the surfaces of tens of thousands of condensates to extract the distribution of surface tensions. Demonstrating this approach on stress granules, we show for the first time that the measured fluctuation spectra cannot be explained by surface tension alone. It is necessary to include an additional energy contribution, which we attribute to an elastic bending rigidity and suggests the presence of structure at the granule-cytoplasm interface. Our data also show that stress granules do not have a spherical base-shape, but fluctuate around a more irregular geometry. Taken together, these results demonstrate quantitatively that the mechanics of stress granules clearly deviate from those expected for simple liquid droplets.

Condensates formed by prion-like low-complexity domains have small-world network structures and interfaces defined by expanded conformations

“…It is known that the interfacial tension decreases as the inverse square of the size of the molecule 50 . Accordingly, the low interfacial tensions that have been measured to date 47,[67][68][69] appear to originate from chains being most expanded as they traverse the interface. Importantly, the interface features a high number of unsatisfied stickers, achieved due to the high number of chains that project perpendicularly to the interface.…”

Phase Transitions of Associative Biomacromolecules

“…Aspherical interfaces have been reported in several contexts. , These can result from dynamical arrest, ,,, especially when RNA is involved, or equilibrium considerations that define the interfaces of complex materials. Comparative analyses of these interfaces on distinct length scales are imperative to understand the complexities that contribute to the characteristics of interfaces and reactions at interfaces …”

“…Comparative analyses of these interfaces on distinct length scales are imperative to understand the complexities that contribute to the characteristics of interfaces and reactions at interfaces. 273 Recent work has highlighted a feature referred to as interfacial resistance. 274 This has emerged from careful analysis of molecular flux across interfaces.…”

Peptide‐Based Coacervate‐Core Vesicles with Semipermeable Membranes

“…CCVs shown in Flicker Spectroscopy Calculations: Time-series microscopy videos of thermally fluctuating coacervate-core vesicles were obtained as described above. Flicker spectroscopy was carried out as described in Law et al [36] Briefly, the boundary of thermally fluctuating coacervatecore vesicles was extracted from confocal microscopy videos and the Fourier transform of this boundary was taken for each vesicle and averaged over time, yielding a fluctuation spectrum. A correction was made to account for the possible non-spherical base-shape.…”