Electrostatics of Salt-Dependent Reentrant Phase Behaviors Highlights Diverse Roles of ATP in Biomolecular Condensates

TL;DR

This study investigates how electrostatic interactions, salt, and ATP influence liquid-liquid phase separation in biomolecular condensates, revealing diverse behaviors and underlying mechanisms through combined experimental and theoretical approaches.

Contribution

It provides a comprehensive analysis of electrostatic effects on phase separation, highlighting ATP's multifaceted roles and introducing new modeling insights into biomolecular condensate behavior.

Findings

Electrostatic effects significantly influence LLPS of IDRs.

ATP's high valency promotes colocalization with condensates.

Reentrant phase behaviors depend on salt and ATP concentrations.

Abstract

Liquid-liquid phase separation (LLPS) involving intrinsically disordered protein regions (IDRs) is a major physical mechanism for biological membraneless compartmentalization. The multifaceted electrostatic effects in these biomolecular condensates are exemplified here by experimental and theoretical investigations of the different salt- and ATP-dependent LLPSs of an IDR of messenger RNA-regulating protein Caprin1 and its phosphorylated variant pY-Caprin1, exhibiting, e.g., reentrant behaviors in some instances but not others. Experimental data are rationalized by physical modeling using analytical theory, molecular dynamics, and polymer field-theoretic simulations, indicating that interchain ion bridges enhance LLPS of polyelectrolytes such as Caprin1 and the high valency of ATP-magnesium is a significant factor for its colocalization with the condensed phases, as similar trends are observed for other IDRs. The electrostatic nature of these features complements ATP's involvement in $\pi$-related interactions and as an amphiphilic hydrotrope, underscoring a general role of biomolecular condensates in modulating ion concentrations and its functional ramifications.