Pressure-jump kinetics of liquid-liquid phase separation of fused in sarcoma.

Abstract

The RNA-binding protein fused in sarcoma, FUS, is intrinsically disordered protein consisting of 526 amino acids. Interactions between tyrosine residues in the low-complexity region and arginine resides in Arg-Gly-Gly regions drive a formation of liquid condensates via liquid-liquid phase separation (LLPS). The liquid condensates transform to solid aggregates, which causes onset of familial amyotrophic lateral sclerosis (ALS). To understand the mechanism underlying the liquid-to-solid transition in FUS condensates, we conducted UV-Vis measurements and microscope observation at variety of pressure and temperature. We found two types of FUS-LLPS states, LP-LLPS (<2 kbar) and HP-LLPS (2 kbar <) (Li et al., J. Phys. Chem. B 125, 6821-6829, 2021). We also analyzed formation and vanishing rates of the two LLPS states by pressure-jump UV-Vis experiments (Kitahara et al., J. Am. Chem. Soc. 143, 19697-19702, 2021). The formation and vanishing rates of HP-LLPS are 2-fold and 20-fold slower than those of LP-LLPS, respectively. Interestingly, the liquid-to-solid phase transition was accelerated with HP-LLPS. Arginine suppressed aging of droplets and HP-LLPS formation more strongly than LP-LLPS formation (Li et al., Phys. Chem. Chem. Phys 24, 19346-19353, 2022). Our data highlight the potential of HP-LLPS to be used as a therapeutic target and arginine as a plausible drug candidate for ALS-causing FUS.