DNA-Induced Lateral Segregation of Cationic Amphiphiles in Lipid Bilayer Membranes as Detected via 2H NMR

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Abstract
2H NMR spectroscopy was used to investigate the response of specifically choline-deuterated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) to changes in surface electrostatic charge in membranes consisting of mixtures of POPC plus various cationic amphiphiles plus polyadenylic acid (polyA). Three different cationic amphiphiles were investigated: cetyltrimethylammonium bromide (CTAB), dioleoyldimethylaminopropane (DODAP), and 3 beta [N-(N',N'-dimethylaminoethane)carbamoyl]-cholesterol (DC-CHOL). Each of the cationic amphiphiles elicited a concentration-dependent decrease (increase) in the quadrupolar splitting from POPC-alpha-d2 (POPC-beta-d2), as expected for the accumulation of cationic charges at the surface of a lipid bilayer. However, the strength of the response varied with the cationic amphiphile in the order CTAB > DODAP > DC-CHOL. When polyA was added to the cationic amphiphile-containing lipid bilayers, the 2H NMR spectrum consisted of two overlapping Pake patterns, indicating the presence of two lipid domains with different effective surface charges and only slow exchange of lipids between the two domains. There was no evidence of any non-bilayer lipid arrangements. Analysis of the quadrupolar splittings of the two 2H NMR spectral components demonstrated that the polyA-containing domain was enriched with respect to cationic amphiphiles while the polyA-free domain was depleted with respect to cationic amphiphiles. We conclude that polyA is able to laterally segregate cationic amphiphiles into long-lived lipid domains of distinct composition.