Cytoskeletal pinning controls phase separation in multicomponent lipid membranes

Area of Science:

• Biophysics
• Cell Biology
• Membrane Biophysics

Background:

• The cell membrane's physical properties are influenced by its underlying cytoskeleton.
• Giant unilamellar vesicles (GUVs) are model systems for studying membrane behavior.
• Prokaryotic tubulin homolog FtsZ can form cytoskeletal networks.

Purpose of the Study:

• To investigate the impact of an FtsZ-based cytoskeleton on lipid membrane phase separation.
• To model the effect of membrane-associated cytoskeletons on lipid domain formation.
• To explore the role of cytoskeletons in membrane stability and domain preservation.

Main Methods:

• Constructing artificial giant unilamellar vesicles (GUVs) with a quaternary lipid mixture.
• Recruiting a modified FtsZ protein (with MinD targeting sequence) to form a surface cytoskeleton on GUVs.
• Observing and analyzing lipid phase separation and domain formation using microscopy.
• Comparing membrane behavior with and without the artificial cytoskeleton.

Main Results:

• FtsZ efficiently formed an interconnected network on GUVs, mimicking eukaryotic cytoskeletons.
• The artificial cytoskeleton suppressed large-scale lipid phase separation below the transition temperature.
• Lipid phase separation was preserved above the transition temperature in the presence of the cytoskeleton.
• The 'picket fence' effect of the cytoskeleton was proposed to explain domain stability.

Conclusions:

• Membrane-associated cytoskeletons significantly alter lipid phase separation behavior.
• The cytoskeleton plays a crucial role in preventing large-scale phase separation at lower temperatures.
• This study supports the cytoskeleton's cryoprotective role and explains domain organization in cell membranes.