Condensate Size Control by Net Charge

TL;DR

This paper demonstrates how electrostatic interactions, particularly net charge asymmetry, can regulate the size of biomolecular condensates, leading to stable, coexisting droplets of equal size, with implications for biological and synthetic systems.

Contribution

The study introduces a combined molecular dynamics and field theory approach to show electrostatics' role in controlling condensate size, highlighting the impact of charge asymmetry over attraction strength.

Findings

Electrostatic repulsion suppresses droplet coarsening.

Droplet size depends strongly on charge asymmetry.

Droplets tend to acquire a net charge, preventing indefinite growth.

Abstract

Biomolecular condensates are complex droplets comprising diverse molecules that interact using various mechanisms. Condensation is often driven by short-ranged attraction, but net charges can also mediate long-ranged repulsion. Using molecular dynamics simulations and an equilibrium field theory, we show that such opposing interactions can suppress coarsening so that many droplets of equal size coexist at equilibrium. This size control depends strongly on the charge asymmetry between constituents, while the strength of the short-ranged attractions has a weak influence. Essentially, droplets expel ions, so they cannot screen electrostatics effectively, implying droplets acquire a net charge and cannot grow indefinitely. Our work reveals how electrostatic effects control droplet size, which is relevant for understanding biomolecular condensates and creating synthetic patterns in chemical engineering.