The Ca²⁺- and phospholipid-binding protein Annexin A2 is able to increase and decrease plasma membrane order.

Area of Science:

• Biochemistry
• Cell Biology
• Biophysics

Background:

• Annexin A2 (AnxA2) is a calcium- and phospholipid-binding protein involved in membrane and cytoskeleton dynamics.
• AnxA2 associates with negatively charged phospholipids, including phosphatidylserine and phosphatidylinositol-(4,5)-phosphate.

Purpose of the Study:

• To investigate membrane lipid rearrangements induced by AnxA2 binding.
• To understand how AnxA2 affects membrane structure and lipid order in model and cellular systems.

Main Methods:

• X-ray diffraction to analyze lipid structures.
• Pyrene-labeled cholesterol and di-4-ANEPPDHQ probes for model membranes.
• Observation of AnxA2 localization and membrane order in epithelial cells.

Main Results:

• AnxA2 stabilizes lamellar lipid structures and inhibits the formation of highly curved phases (H_II).
• AnxA2 modifies cholesterol distribution and lipid compaction in model membranes.
• AnxA2 binding alters membrane lipid order in epithelial cells, causing increases or decreases depending on the region.

Conclusions:

• AnxA2 modulates plasma membrane properties by inducing lipid redistribution.
• AnxA2's effects on lipid order can lead to increased or decreased membrane fluidity.
• AnxA2 plays a significant role in regulating membrane organization and dynamics.