Divalent cation binding to phospholipid veiscles. Dependence on temperature and lipid fluidity

Area of Science:

• Biochemistry
• Biophysics
• Materials Science

Background:

• Anionic phospholipids are crucial components of biological membranes.
• Understanding cation binding to lipid bilayers is essential for membrane function.
• Previous models did not fully account for temperature-dependent lipid fluidity effects on cation interactions.

Purpose of the Study:

• To investigate the temperature dependence of Mn2+ binding to various anionic phospholipid vesicles.
• To correlate Mn2+ affinity with membrane fluidity and phase transitions.
• To elucidate the role of lipid physical state in divalent cation interactions.

Main Methods:

• Electron paramagnetic resonance (EPR) spectroscopy was used to measure Mn2+ binding.
• Lipid vesicle preparations from phosphatidylserine, cardiolipin, and phosphatidylglycerol were utilized.
• Hydrocarbon chain fluidity and light scattering were also monitored.

Main Results:

• Mn2+ affinities for phosphatidylserine, cardiolipin, and egg yolk phosphatidylglycerol increased monotonically with temperature.
• Contrary to surface potential expectations, phosphatidylserine affinity did not decrease from gel to crystalline states.
• Increased lipid fluidity correlated with enhanced cation affinity, while phospholipid melting showed complex hysteresis possibly due to vesicle aggregation.

Conclusions:

• Cation affinity for anionic phospholipids is significantly influenced by lipid fluidity.
• Temperature-induced changes in membrane fluidity play a key role in divalent cation binding.
• The observed hysteresis in dipalmitoyl phosphatidylglycerol binding suggests complex interactions involving vesicle aggregation.