Decoding the physical principles of two-component biomolecular phase separation.

Area of Science:

• Biophysics
• Cell Biology
• Polymer Physics

Background:

• Cells utilize non-membrane-bound compartments formed by liquid-liquid phase separation for essential functions.
• A key class of these compartments involves two polymer species forming specific one-to-one bonds.

Purpose of the Study:

• To investigate the physical principles governing phase separation in systems with specific polymer-protein interactions.
• To understand how polymer properties influence the phase boundaries of these cellular condensates.

Main Methods:

• Coarse-grained molecular dynamics simulations were used to model polymer interactions.
• Phase boundaries were analyzed concerning polymer valence, stoichiometry, and binding strength.
• An analytical dimer-gel theory was developed to complement simulation findings.

Main Results:

• A phenomenon termed the "magic-ratio effect" was discovered, where phase separation is suppressed at specific rational polymer stoichiometries under strong binding conditions.
• The dimer-gel theory confirmed the magic-ratio effect and elucidated the roles of individual polymer characteristics.
• Phase diagrams were shown to be highly sensitive to polymer properties and their specific interactions.

Conclusions:

• The study provides critical insights into the physical factors controlling the phase diagrams of biomolecular condensates.
• The magic-ratio effect offers a new principle for understanding condensate formation and stability.
• Findings have implications for both understanding natural cellular processes and designing synthetic systems.