Composition-dependent thermodynamics of intracellular phase separation.

TitleComposition-dependent thermodynamics of intracellular phase separation.
Publication TypeJournal Article
Year of Publication2020
AuthorsRiback, JA, Zhu, L, Ferrolino, MC, Tolbert, M, Mitrea, DM, Sanders, DW, Wei, M-T, Kriwacki, RW, Brangwynne, CP
JournalNature
Volume581
Issue7807
Pagination209-214
Date Published2020 05
ISSN1476-4687
KeywordsAdaptor Proteins, Signal Transducing, Cell Nucleolus, Coiled Bodies, Cytoplasmic Granules, DNA Helicases, HeLa Cells, Humans, Intracellular Space, Nuclear Proteins, Organelles, Phase Transition, Poly-ADP-Ribose Binding Proteins, Ribosomes, RNA Helicases, RNA Recognition Motif Proteins, RNA, Ribosomal, RNA-Binding Proteins, Thermodynamics
Abstract

Intracellular bodies such as nucleoli, Cajal bodies and various signalling assemblies represent membraneless organelles, or condensates, that form via liquid-liquid phase separation (LLPS)1,2. Biomolecular interactions-particularly homotypic interactions mediated by self-associating intrinsically disordered protein regions-are thought to underlie the thermodynamic driving forces for LLPS, forming condensates that can facilitate the assembly and processing of biochemically active complexes, such as ribosomal subunits within the nucleolus. Simplified model systems3-6 have led to the concept that a single fixed saturation concentration is a defining feature of endogenous LLPS7-9, and has been suggested as a mechanism for intracellular concentration buffering2,7,8,10. However, the assumption of a fixed saturation concentration remains largely untested within living cells, in which the richly multicomponent nature of condensates could complicate this simple picture. Here we show that heterotypic multicomponent interactions dominate endogenous LLPS, and give rise to nucleoli and other condensates that do not exhibit a fixed saturation concentration. As the concentration of individual components is varied, their partition coefficients change in a manner that can be used to determine the thermodynamic free energies that underlie LLPS. We find that heterotypic interactions among protein and RNA components stabilize various archetypal intracellular condensates-including the nucleolus, Cajal bodies, stress granules and P-bodies-implying that the composition of condensates is finely tuned by the thermodynamics of the underlying biomolecular interaction network. In the context of RNA-processing condensates such as the nucleolus, this manifests in the selective exclusion of fully assembled ribonucleoprotein complexes, providing a thermodynamic basis for vectorial ribosomal RNA flux out of the nucleolus. This methodology is conceptually straightforward and readily implemented, and can be broadly used to extract thermodynamic parameters from microscopy images. These approaches pave the way for a deeper understanding of the thermodynamics of multicomponent intracellular phase behaviour and its interplay with the nonequilibrium activity that is characteristic of endogenous condensates.

DOI10.1038/s41586-020-2256-2
Alternate JournalNature
PubMed ID32405004
Grant ListR01 GM115634 / GM / NIGMS NIH HHS / United States
/ HHMI / Howard Hughes Medical Institute / United States
F32 GM131524 / GM / NIGMS NIH HHS / United States
P30 CA021765 / CA / NCI NIH HHS / United States
R35 GM131891 / GM / NIGMS NIH HHS / United States
U01 DA040601 / DA / NIDA NIH HHS / United States