Dehydration entropy drives liquid-liquid phase separation by molecular crowding

Sohee Park,Byoung-Jin Jeon,Glenn H Fredrickson,Ryan Barnes,Joan-Emma Shea,Yanxian Lin,Saeed Najafi,Songi Han,Kris T Delaney,Dong Soo Hwang

doi:10.1038/s42004-020-0328-8

Abstract

Complex coacervation driven liquid-liquid phase separation (LLPS) of biopolymers has been attracting attention as a novel phase in living cells. Studies of LLPS in this context are typically of proteins harboring chemical and structural complexity, leaving unclear which properties are fundamental to complex coacervation versus protein-specific. This study focuses on the role of polyethylene glycol (PEG)—a widely used molecular crowder—in LLPS. Significantly, entropy-driven LLPS is recapitulated with charged polymers lacking hydrophobicity and sequence complexity, and its propensity dramatically enhanced by PEG. Experimental and field-theoretic simulation results are consistent with PEG driving LLPS by dehydration of polymers, and show that PEG exerts its effect without partitioning into the dense coacervate phase. It is then up to biology to impose additional variations of functional significance to the LLPS of biological systems.

Highlights

Complex coacervation driven liquid-liquid phase separation (LLPS) of biopolymers has been attracting attention as a novel phase in living cells
Mixing of εPL and hyaluronic acid (HA) initially resulted in the formation of CC microdroplets, and the microdroplets were condensed to a macroscopic coacervate phase by centrifugation (Fig. 1a)
Added polyethylene glycol (PEG) and elevated temperature stabilized the εPL-HA complex coacervates, even at high NaCl concentration of order 200 mM found under physiological condition. εPLHA CC followed lower critical solution temperature (LCST) behavior, the polyelectrolytes had no hydrophobic constituents

Summary

Introduction

Complex coacervation driven liquid-liquid phase separation (LLPS) of biopolymers has been attracting attention as a novel phase in living cells. Some membraneless organelles composed of IDPs have displayed liquid-like physical properties[9,10,11,12], suggesting that intracellular droplet formation by liquid−liquid phase separation (LLPS) may be a relevant mechanism for the formation of membraneless organelles. Complex coacervation (CC), which results in LLPS, has been suggested to share the genesis of the protocell[15,16]. This is because coacervate can be composed of simple components, while they are capable of taking up various substances and segregate from the environment. IDPs is to be a regulatory state of importance to cellular processes, it makes sense that its formation and dissolution conditions be modulated by physiological relevant factors within crowded environments[22]

Methods

Results

Conclusion