Cation-Induced Hydration Effects Cause Lower Critical Solution Temperature Behavior in Protein Solutions.

Area of Science:

• Biophysics
• Soft Matter Physics
• Solution Chemistry

Background:

• Protein solution phase behavior is crucial in biological and soft matter systems.
• Understanding protein-ion interactions is key to controlling solution properties.

Purpose of the Study:

• To investigate the lower critical solution temperature (LCST) phase behavior of globular protein solutions induced by multivalent metal ions.
• To elucidate the mechanism behind this thermally induced phase separation.

Main Methods:

• Isothermal titration calorimetry (ITC) to study binding thermodynamics.
• Zeta-potential measurements to assess protein surface charge changes.
• Observation of liquid-liquid phase separation upon heating.

Main Results:

• Aqueous protein solutions exhibited LCST behavior with multivalent metal ions around physiological temperatures.
• Cation-protein binding was identified as an endothermic, entropy-driven process.
• Heating induced liquid-liquid phase separation due to cation-mediated protein bridging.

Conclusions:

• The LCST mechanism involves cation binding driven by hydration water entropy, followed by cation-induced protein bridging.
• Findings have broad implications for understanding (bio)polymer condensation, LCST phenomena, and metal ion biological effects.