Optical characterization of molecular interaction strength in protein condensates

Area of Science:

• Cell Biology
• Biophysics

Background:

• Biomolecular condensates are crucial for intracellular organization but their material properties and molecular interactions are poorly understood.
• Existing techniques for characterizing condensate properties are limited.

Purpose of the Study:

• To introduce and validate Brillouin microscopy and quantitative phase imaging (QPI) for characterizing biomolecular condensate material properties.
• To investigate the effects of temperature, ion concentration, and sequence variations on condensate properties.

Main Methods:

• Utilized Brillouin microscopy to measure Brillouin shift and linewidth, correlating them with molecular interaction strength and dissipation.
• Employed quantitative phase imaging (QPI) to determine protein concentration within condensates.
• Studied condensates formed by FUS and hnRNPA1 low-complexity domain (A1-LCD) under varying conditions.

Main Results:

• Brillouin shift, linewidth, and protein concentration increased under conditions favoring phase separation.
• Ion-dependent aging of FUS condensates showed minimal impact on internal molecular interaction strength compared to chemical crosslinking.
• Sequence variations in A1-LCD altered condensate physical properties, reflecting changes in phase separation driving forces.

Conclusions:

• Brillouin microscopy and QPI provide robust, quantitative methods for assessing biomolecular condensate material properties.
• These techniques offer new experimental insights into how condensate physical properties relate to their biological function and dysfunction.
• Quantitative characterization is essential for understanding the role of biomolecular condensates in cellular processes.