Annexin-V stabilizes membrane defects by inducing lipid phase transition

Area of Science:

• Cell Biology
• Biophysics
• Materials Science

Background:

• Annexins are cytoplasmic proteins binding to negatively charged phospholipids on membranes in a calcium-dependent manner.
• Extracellular calcium influx during cell injury activates annexin membrane binding, initiating repair.
• The precise mechanism of annexin action in membrane repair is not fully understood.

Purpose of the Study:

• To elucidate the mechanistic action of annexin-V (A5) in cellular membrane repair.
• To investigate how A5 binding to phosphatidylserine (PS)-rich membranes influences lipid dynamics and membrane phase transitions.
• To explore the role of A5 self-assembly in stabilizing and structuring damaged membranes.

Main Methods:

• High-speed atomic force microscopy (HS-AFM) for visualizing molecular interactions.
• Fluorescence recovery after photobleaching (FRAP) to study lipid dynamics.
• Confocal laser scanning microscopy (CLSM) for cellular imaging.
• Molecular dynamics simulations (MDSs) for computational analysis.

Main Results:

• Annexin-V binding to phosphatidylserine-rich membranes induces high local calcium concentrations.
• A5 binding alters lipid dynamics and organization, leading to a membrane phase transition.
• A5 self-assembles into lattices, stabilizing the membrane and inducing a gel phase.

Conclusions:

• Findings support a patch resealing mechanism via vesicle fusion in membrane repair.
• Annexin-V plays a crucial role in retaining negatively charged lipids in the inner leaflet of injured cells.
• A5 self-assembly into lattices is key to stabilizing and structuring the membrane during repair.