A lipid bound actin meshwork organizes liquid phase separation in model membranes

Area of Science:

• Cell biology
• Biophysics
• Membrane biophysics

Background:

• Eukaryotic cell membranes are associated with a dense, actin-rich cortex.
• The physical properties of the cell membrane are influenced by this associated actin network.

Purpose of the Study:

• To investigate the impact of membrane-bound actin networks on lipid phase separation in supported lipid bilayers.
• To understand how actin binding affects lipid domain formation and diffusion.

Main Methods:

• Utilized Fluorescence Correlation Spectroscopy (FCS) and Stimulated Emission Depletion (STED) microscopy.
• Created supported lipid bilayers with controlled actin cortex attachment via biotin-streptavidin interactions (pinning sites).
• Developed a new simulation model coupling membrane composition, curvature, and actin pinning sites.

Main Results:

• Actin binding generally prevented macroscopic liquid-ordered and liquid-disordered lipid domain formation.
• Observed actin-correlated multi-domain patterns, dependent on the pinning lipid type.
• FCS measurements indicated hindered lipid diffusion in the presence of the actin network.

Conclusions:

• Membrane-bound actin networks play a crucial role in regulating lipid phase behavior.
• Actin binding prevents large-scale membrane demixing while enabling local composition control.
• The findings provide insights into cellular mechanisms for maintaining membrane organization.