Phase changes of cardiolipin vesicles mediated by divalent cations

Area of Science:

• Biochemistry
• Materials Science
• Physical Chemistry

Background:

• Cardiolipin is a key component of biological membranes.
• Lipid phase transitions are fundamental to membrane structure and function.
• Divalent cations influence lipid bilayer organization.

Purpose of the Study:

• To investigate the phase behavior of cardiolipin-based small unilamellar vesicles.
• To characterize the transition between lamellar and hexagonal II phases.
• To understand the role of divalent cations (Ca2+, Mg2+) in lipid self-assembly.

Main Methods:

• Preparation of small unilamellar vesicles (SUVs) from cardiolipin.
• Dialysis against divalent cation solutions (CaCl2, MgCl2) to induce phase transition.
• Dialysis against EDTA to remove cations and induce reverse phase transition.
• Characterization of vesicle morphology (lamellar vs. hexagonal II phase).

Main Results:

• Cardiolipin SUVs formed the hexagonal II phase upon dialysis against CaCl2 or MgCl2.
• Removal of divalent cations using EDTA resulted in the formation of large unilamellar vesicles (LUVs).
• The study describes the dynamic events during the lamellar to hexagonal II and back to lamellar phase transitions.

Conclusions:

• Divalent cations are crucial for inducing the hexagonal II phase in cardiolipin lipid systems.
• EDTA-mediated cation removal provides a method for transforming hexagonal II phase back to lamellar structures, forming LUVs.
• This work elucidates the cation-dependent lipid phase transitions relevant to membrane biophysics.