Cell-Like Containers with Inner Organelles Formed by Coacervation of Proteins and Biopolymers

Eukaryotic cells contain multiple inner compartments (organelles) that enable cells to carry out a variety of biochemical processes. Some of these organelles (such as the nucleolus) lack any external membrane. Recent studies have shown that these membraneless organelles are formed by liquid-liquid phase separation, which is also called coacervation. This coacervation is a dynamic process, and it can be turned ‘on’ and ‘off’ as desired; in turn, the nucleolus forms when needed by the cell, and at other times it disappears.<br/><br/>In this study, we mimic cellular architecture by creating biopolymer capsules with a membraneless compartment inside. The inner compartment is created by complex coacervation, which is a liquid-liquid phase separation of a solution containing two oppositely charged polymers. Much like the nucleolus, this compartment can reversibly form and disintegrate by changes in environmental stimuli such as pH, ionic strength, and polymer composition. Different biomolecules and colloidal species can be sequestered by this compartment and in turn, can be released when the compartment disintegrates. Owing to the ‘smart’ inner compartment, the overall capsules exhibit interesting behaviors and can be used for a variety of applications like drug delivery, biosensing, and reaction engineering. The ability to reversibly assemble such membraneless organelles can also provide insight into important biochemical processes.