Ionic Effect on the Microenvironment of Biomolecular Condensates.

Area of Science:

• Biophysics
• Molecular Biology
• Cell Biology

Background:

• Biomolecular condensates form via liquid-liquid phase separation (LLPS), creating unique microenvironments essential for biological functions.
• The cellular microenvironment, including ion concentrations, can influence LLPS and condensate properties.
• The specific effects of ions on the internal microenvironment of these condensates are not well understood.

Purpose of the Study:

• To investigate the ion-specific effects on the microenvironment of protein condensates.
• To quantitatively analyze how different ions impact condensate properties such as micropolarity and microviscosity.

Main Methods:

• Utilized fluorescence lifetime imaging microscopy (FLIM) to assess micropolarity.
• Employed fluorescence recovery after photobleaching (FRAP) and microrheology to measure microviscosity and viscoelasticity.

Main Results:

• Salting-in ions decreased condensate microviscosity and increased micropolarity.
• Salting-out ions exhibited opposite effects, increasing microviscosity and decreasing micropolarity.
• Ion-specific effects were found to modulate condensate miscibility and multilayering behavior.

Conclusions:

• This study provides the first quantitative survey of ion effects on the microenvironment of protein condensates.
• Ions from the Hofmeister series significantly impact condensate micropolarity, microviscosity, and viscoelasticity.
• Findings have implications for understanding how cellular conditions affect membrane-less organelles.