Cu²⁺ Binds to Phosphatidylethanolamine and Increases Oxidation in Lipid Membranes

Herein, we demonstrate that Cu²⁺ binds bivalently to phosphatidylethanolamine (PE), the second most abundant lipid in mammalian cells. The apparent equilibrium dissociation constant, K_DApp, for the Cu²⁺-PE complex at physiological pH is approximately 2 μM and is insensitive to the concentration of PE in the membrane. By contrast, at pH 10.0, where PE lipids bear a negative charge, K_DApp decreases with increasing PE content and has a value of 150 nM for bilayers containing 70 mol % PE. The oxidation of double bonds in PE-containing bilayers can be monitored in the presence of Cu²⁺. Strikingly, it was found that the oxidation rate is 8.2 times faster at pH 7.4 for bilayers containing 70 mol % PE than for pure phosphatidylcholine (PC) bilayers upon exposure of both to 70 μM Cu²⁺ and 10 mM hydrogen peroxide. The rate of oxidation increases linearly with the PE content in the membrane. These results may help explain the high level of lipid oxidation in PE-containing membranes for neurodegenerative diseases and autism where the Cu²⁺ concentration in the body is abnormally high.