Quantifying surface tension and viscosity in biomolecular condensates by FRAP-ID

Area of Science:

• Biophysics
• Cell Biology
• Soft Matter Physics

Background:

• Proteins with intrinsically disordered regions form biomolecular condensates via liquid-liquid phase separation.
• These condensates have distinct mechanical properties that influence their biological functions.
• Measuring these properties, like viscosity and surface tension, is challenging and often requires multiple techniques.

Purpose of the Study:

• To develop a single experimental method for measuring both viscosity and surface tension of biomolecular condensates.
• To introduce Fluorescence Recovery After Probe-induced Dewetting (FRAP-ID) as a correlative microscopy technique.

Main Methods:

• Correlative fluorescence microscopy and atomic force microscopy (AFM) were employed.
• AFM force spectroscopy was used to induce dry spots, and subsequent rewetting dynamics were analyzed.
• Contact line velocity during rewetting was measured to determine condensed-phase viscosity.

Main Results:

• FRAP-ID successfully measured both viscosity and surface tension in a single experiment.
• Rewetting dynamics provided a method to quantify viscosity, distinct from molecular diffusion observed in FRAP.
• Morphological relaxation during rewetting validated viscosity measurements.

Conclusions:

• FRAP-ID is a valuable tool for evaluating the mechanical properties of biomolecular condensates.
• This method allows for the assessment of how mechanical properties impact the temporal dynamics and functionality of condensates.
• The technique offers a cross-validated approach to understanding condensate behavior.