A light-switching pyrene probe to detect phase-separated biomolecules

Masaharu Hazawa; Shogo Amemori; Yoshio Nishiyama; Yoshihiro Iga; Yuki Iwashima; Akiko Kobayashi; Hirohisa Nagatani; Motohiro Mizuno; Kenji Takahashi; Richard W Wong

doi:10.1016/j.isci.2021.102865

A light-switching pyrene probe to detect phase-separated biomolecules

iScience. 2021 Jul 15;24(8):102865. doi: 10.1016/j.isci.2021.102865. eCollection 2021 Aug 20.

Authors

Masaharu Hazawa^{1

2

3}, Shogo Amemori^{1

2

4}, Yoshio Nishiyama², Yoshihiro Iga², Yuki Iwashima², Akiko Kobayashi¹, Hirohisa Nagatani², Motohiro Mizuno^{1

2

4}, Kenji Takahashi², Richard W Wong^{1

2

3}

Affiliations

¹ Institute for Frontier Science Initiative, Kanazawa University, Kanazawa, Ishikawa, Japan.
² Institute of Science and Engineering, Kanazawa University, Kanazawa, Ishikawa, Japan.
³ WPI Nano Life Science Institute, Kanazawa University, Kanazawa, Ishikawa, Japan.
⁴ NanoMaterials Research Institute, Kanazawa University, Kanazawa, Ishikawa, Japan.

Abstract

Biomolecules may undergo liquid-liquid phase separation (LLPS) to spatiotemporally compartmentalize and regulate diverse biological processes. Because the number of tools to directly probe LLPS is limited (ie. FRAP, FRET, fluorescence microscopy, fluorescence anisotropy, circular dichroism, etc.), the physicochemical traits of phase-separated condensates remain largely elusive. Here, we introduce a light-switching dipyrene probe (Pyr-A) that forms monomers in either hydrophobic or viscous environments, and intramolecular excimers in aqueous solutions. By exploiting their distinct fluorescence emission spectra, we used fluorescent microscopic imaging to study phase-separated condensates formed by in vitro protein droplets and membraneless intracellular organelles (centrosomes). Ratiometric measurement of excimer and monomer fluorescence intensities showed that protein droplets became hydrophobic and viscous as their size increased. Moreover, centrosomes became hydrophobic and viscous during maturation. Our results show that Pyr-A is a valuable tool to characterize LLPS and enhance our understanding of phase separation underlying biological functions.

Keywords: Biochemistry; Biological Sciences; Biological Sciences Research Methodologies; Biophysical Chemistry; Biophysics.