Relationship Between Filament-Polymerizing Muscle Myosin and Droplets Generated by Liquid-Liquid Phase Separation

Area of Science:

• Biophysics
• Cell Biology
• Polymer Science

Background:

• Biological systems utilize macromolecules like nucleic acids and proteins within internal fluids.
• Liquid-liquid phase separation (LLPS) explains complex macromolecular phenomena within cells.
• LLPS principles extend from cellular scales to larger biological organizations.

Purpose of the Study:

• Investigate the interplay between myosin motor protein behavior and LLPS.
• Examine how myosin interacts with and influences LLPS in a binary polymer solution.
• Understand the impact of myosin's presence on droplet formation and morphology.

Main Methods:

• Utilized a binary polymer solution composed of polyethylene glycol and dextran.
• Introduced myosin, a muscle-derived molecular motor, into the polymer solution.
• Varied salt concentrations to observe effects on myosin polymerization and LLPS.

Main Results:

• Myosin localized within dextran-rich phase droplets.
• Myosin polymerized into filaments and formed mesh-like assemblies within droplets, irrespective of salt-induced polymerization conditions.
• The presence of myosin induced deformation of the LLPS droplets, leading to non-spherical shapes.
• At specific salt strengths, myosin-containing droplets exhibited sharp protrusions.

Conclusions:

• LLPS significantly alters myosin's behavior and assembly dynamics within droplets.
• Myosin's presence and polymerization impact the morphology and stability of LLPS droplets.
• This study reveals a reciprocal relationship between molecular motors and phase-separated biomolecular condensates.