From fundamental mechanism to biological function – explore biomolecular condensates across scales

Here, researchers from the lab of Dr. Bo Sun at ShanghaiTech assessed how variations in low-complexity domains influence droplet solidification. The investigators used force-induced droplet fusion to evaluate peptide droplet properties. They evaluated the influence of low-complexity domain cores within hnRNPA1 proteins called reversible amyloid core (RAC).

Compared with wild-type hnRNPA1 droplets, the deletion of hnRAC1, a specific segment within the protein, resulted in faster droplet fusion (10 seconds and 8 seconds, respectively). Conversely, hnRAC1 missense mutation of the aspartic acid to valine (D214V; associated with irreversible amyloid formation) resulted in an even slower droplet fusion (16 seconds; Figure 1).

Data courtesy of Dr. Bo Sun at ShanghaiTech

Using the polyethylene glycol PEG8000 as a model structure, researchers from the Banerjee lab measured the concentration-dependent effect of molecular crowders on the properties of FUS protein droplets. They moved one of two trapped FUS droplets towards the other at a constant velocity and timed their fusion (time-to-relaxation) at different PEG8000 concentrations.

While the absence of PEG8000 crowders resulted in a fast droplet fusion (about 200 ms/μm), the presence of 150 mg/ml PEG8000 almost arrested the condensation (Figure 1).

Data courtesy of Dr. Priya Banerjee at the University at Buffalo

Scientists from the Banerjee lab at the University at Buffalo investigated the condensation properties between different RNAs and polypeptides. The researchers assessed the molecule-dependent effect of interactions between poly(A) or poly(U) RNAs and different peptide domains (R/G-rich or K/G-rich) on droplet stability, measured through droplet fusion.

They found that peptide droplets composed of K/G-rich peptides and poly(U) fused twice as fast (mean, 0.0028 s/µm) as droplets with R/G-rich peptides and poly(A) RNA (Figure 3). The results indicate a higher fluidity and lower viscosity in the former structure and suggest that short-range attractions and long-range forces regulate RNA–peptide condensate formation.

Data courtesy of Dr. Priya Banerjee at the University at Buffalo

Using two optical traps, scientists from the Hyman lab at the Max Planck Institute of Molecular Cell Biology and Genetics could study the microrheology of protein droplets consisting of PGL-3 proteins in different salt concentrations (75, 115, 150, and 180 mM KCl).

They brought two independently trapped beads into adhesive contact with the droplet and applied force on one bead, moving it bi-directionally to deform the droplet. Since the forces needed to move the trap changes with altered thickness, they could measure the structure’s viscosity as a result of different salt concentrations.

The team found that both the viscosity and surface tension of the protein droplet decreased with increasing salt concentrations (1 to 0.1 Pa s and 5 to 1 µN/m, respectively: Figure 1).

Data courtesy of Prof. Dr. Anthony Hyman at the Max Planck Institute of Molecular Cell Biology and Genetics