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. 2021 Nov 9;120(23):5169–5186. doi: 10.1016/j.bpj.2021.11.003

Figure 5.

Figure 5

RNA critically regulates the dynamical properties of RBP condensates. (A) Shear stress relaxation modulus of FUS condensates in the absence (red) versus presence (purple) of poly-U strands of 125 nucleotides at 0.24 mg poly-U/mg FUS mass fraction, T/Tc = 0.97 (where Tc refers to the critical temperature of FUS pure condensates) and the corresponding equilibrium bulk density of each droplet at such conditions. The vertical dotted line separates the fast-decay relaxation mode regime (white) and the slow-decay relaxation mode one (beige). A snapshot illustrating a shear stress relaxation experiment over a poly-U/FUS condensate simulation box is included. (B) Viscosity of FUS (at T/Tc = 0.97), hnRNPA1 (at T/Tc = 0.985), and hnRNPA1-A-LCD (at T/Tc = 0.98) condensates as a function of the poly-U/protein mass ratio. An estimate of wt-TDP-43 viscosity in absence of poly-U at T/Tc = 0.97 is also included (green circle). Solid circles depict viscosities when poly-U strands of 125 nt were used and open circles when strands 250 nucleotides were added. The cross symbol in the FUS panel indicates the viscosity of FUS-poly-U condensates when strands of 10 nt were included. Continuous and dashed lines are plotted as a guide for the eye for strands of 125 and 250 nt, respectively. The error bars in viscosity have been estimated using the fit of G(t) to Maxwell modes (as described in Section SVII of the Supporting material). Note that Tc refers to the pure component critical temperature of each protein. (C) Protein diffusion coefficient (solid circles) as a function of poly-U (125 nt)/protein (X) mass ratio. Open circles account for the protein diffusion coefficient when poly-U strands of 250 nt were added, and solid ones for 125 nucleotide RNA strands. The same system conditions described in (B) are applied on these calculations. Continuous curves are included as a guide to the eye. (D) Diffusion coefficient of FUS (red) and poly-U strands (cyan) as a function of the poly-U/FUS mass ratio. Open circles show the diffusion coefficient of FUS (red) and poly-U strands (cyan) when RNA strands of 250 nt were added, and solid circles correspond to values with poly-U strands of 125 nt. The red cross symbols indicate the diffusion of FUS proteins in condensates with poly-U chains of 10 nucleotides. The diffusion of poly-U chains of 10 nt is D ∼3 × 10−3 mm2/s, so it has been omitted from the panel. To see this figure in color, go online.