The effect of the lipid A analog E5531 on phospholipid membrane properties

In order to determine the effect of the lipid A analog, E5531, on phospholipid membranes, we used dipalmitoylphosphatidylcholine (DPPC) and investigated the physicochemical interaction between E5531 and DPPC membranes. E5531 and DPPC are miscible in the bulk phase at 25 degrees C. Within the E5531 mole fraction range (X(E5531)) of 0-0.5, E5531 decreased the zeta potentials of DPPC membranes but did not change the size of the DPPC liposomes. E5531/DPPC mixtures formed liposome-like structures. E5531 increased the fluidity of the DPPC membrane and decreased pyrene diffusion in the membrane. E5531 decreased the phase transition temperature and the cooperative interactions between DPPC molecules. These effects of E5531 on phospholipid membranes were different from those of lipid A from Escherichia coli and Salmonella minnesota.