Phase-Separation Kinetics in Protein-Salt Mixtures with Compositionally Tuned Interactions

Area of Science:

• Biophysics
• Soft Matter Physics
• Protein Science

Background:

• Liquid-liquid phase separation (LLPS) is crucial for cellular organization and implicated in diseases.
• Controlling protein LLPS is vital for biological soft matter research.
• Bovine serum albumin (BSA) exhibits lower critical solution temperature-LLPS (LCST-LLPS) induced by multivalent salts.

Purpose of the Study:

• Investigate the kinetics of BSA LCST-LLPS using different multivalent cation mixtures.
• Determine how varying interprotein attraction strengths affect LLPS dynamics.
• Establish a method to tune LLPS phase transitions in protein and colloidal systems.

Main Methods:

• Systematic ultrasmall-angle X-ray scattering (USAXS) experiments.
• Inducing LLPS via temperature jumps into coexistence regions.
• Monitoring characteristic length scales (ξ) over time (t) and final temperature (T_fin).

Main Results:

• BSA LLPS kinetics were studied with HoCl₃/LaCl₃ mixtures, altering attraction.
• Increasing interprotein attraction and T_fin led to deviations from the ξ ∼ t^1/3 growth law.
• An increased trend toward LLPS arrest was observed with stronger attraction and higher T_fin.

Conclusions:

• The study demonstrates a multidimensional approach to tune protein LLPS kinetics.
• Findings provide insights into the general principles governing LLPS in proteins and colloids.
• Controlling LLPS through cation mixtures offers a pathway to manipulate protein condensation and crystallization.