Observation of the Liquid–Liquid Phase Separation of FUS‐LC Using Vacuum‐Ultraviolet Circular Dichroism Spectroscopy.

To reveal the structural mechanism by which the low‐complexity domain of the fused in sarcoma protein (FUS‐LC) mediates liquid–liquid phase separation (LLPS), we conducted a vacuum‐ultraviolet circular dichroism (VUV‐CD) spectroscopic study, a technique to analyze the secondary structures of proteins. The VUV‐CD measurements were performed at the BL12 VUV‐CD station at the Hiroshima Synchrotron Radiation Center (HiSOR) in Japan. CD spectra were measured between 180 and 260 nm while controlling the temperature of samples from 37°C to 5°C to obtain the LLPS of FUS‐LC. The CD spectrum obtained at 37°C exhibited a large negative peak at 195 nm and a small negative shoulder near 220 nm. The peak intensity around 195 nm decreased as the sample temperature decreased. The spectral changes originated from the LLPS formation. [ABSTRACT FROM AUTHOR]