Structure and elasticity of healthy and Alzheimer's disease cell membranes revealed by molecular dynamics simulations.

Interactions of amyloid-β (Aβ) peptides with neuronal membrane are associated with the development of Alzheimer's disease (AD). Ganglioside monosialotetrahexosylganglioside (GM1) lipids have been shown to form clusters that induce the structural conversion of Aβ and promote the incorporation of Aβ into the membrane via the membrane surface electrical potential. Prior to the onset of AD symptoms, GM1 clusters may not have formed but the concentration of GM1 may have already changed, and our question is whether this early concentration modification affects the structure and mechanical properties of the membrane. Using one model for healthy cell membranes and three models for AD cell membranes, we carry out 2 µs all-atom molecular dynamics simulations for each model to compare the structure and elasticity of the two membrane types. The simulations show that at the physiological concentration, 1%-3%, GM1 does not form clusters. The reduction of the GM1 lipid does not significantly alter the area per lipid, the membrane thickness, and the lipid order parameters of the AD membranes. However, the dipole potential, the bending, and twist moduli are decreased for the AD membranes. We suggest that these changes in the AD membranes are factors that could trigger the interaction and incorporation of Aβ to the membranes. Finally, we show that changes in the sphingomyelin lipid concentrations do not affect the membrane structure and elasticity.