Fig. 6: Correlation plot of Brillouin shifts versus FRAP immobile fractions reveals a percolation-like behavior and a fractal internal structure of protein condensates in living cells.
The mechanical properties of liquid-gel phase transition of biomolecular condensates such as stress granules have been explained as a combination of LLPS and networking transitions such as percolation and gelation4,13,80,81. Data were fitted with a power-law model characteristic of a percolation transition, allowing us to extract the percolation threshold x0 (defining the gel point; from the fit, x0 = 0.04 ± 0.2) and the exponent β (here, β = 2.0 ± 0.2, consistent with a 3D gelling system undergoing percolation86). See Supplementary Note 1 for further details. Violet plots: mean (dashed line) ± 2*S.E.M. (shaded area) Brillouin shifts of cytoplasm of control SK-N-BE cells not overexpressing proteins (shown in Supplementary Fig. 4). Green plots: power-law fit (solid line), with 95% C.I. (shaded area). Data labels are colored blue (condensates without stress) or orange (condensates under stress, e.g., ARS treatment or A4V mutation). Data points are shown as mean ± 2*S.E.M, obtained from n = 3 biological independent replicates (in every replicate, at least 10 cells for FRAP or 5 cells for Brillouin were acquired). Source data are provided as Source Data file.
