Ca2+-cardiolipin interaction in a model system. Selectivity and apparent high affinity

Area of Science:

• Biochemistry
• Biophysics
• Cell Biology

Background:

• Cardiolipin is a key phospholipid in mitochondrial membranes.
• Calcium ions (Ca2+) play crucial roles in cellular signaling and mitochondrial function.
• Understanding cardiolipin-calcium interactions is vital for elucidating mitochondrial physiology.

Purpose of the Study:

• To quantify the binding affinity of cardiolipin for Ca2+.
• To investigate the selectivity of cardiolipin-cation interactions.
• To explore the influence of other lipids and ions on Ca2+-cardiolipin binding.

Main Methods:

• Cardiolipin-mediated extraction of 45Ca2+ from aqueous to organic phases.
• Measurement of apparent dissociation constants (Kd).
• Assessment of inhibition by various cations and phosphatidylcholine.

Main Results:

• Cardiolipin exhibits high-affinity binding for Ca2+ (Kd(apparent) = 0.70 ± 0.17 μM).
• Ca2+ binding is insensitive to Na+ but inhibited by Mn2+, Zn2+, and Mg2+.
• Potent inhibition observed with La3+ and Ruthenium red; phosphatidylcholine also inhibits binding.

Conclusions:

• Cardiolipin demonstrates specific and high-affinity binding for Ca2+.
• The binding is modulated by other cations and phospholipids.
• Inhibition by phosphatidylcholine suggests involvement of non-bilayer lipid structures in Ca2+-cardiolipin interactions.