How the amyloid-β peptide and membranes affect each other: An extensive simulation study

The etiology of Alzheimer's disease is thought to be linked to interactions between amyloid-β (Aβ) and neural cell membranes, causing membrane disruption and increased ion conductance. The effects of Aβ on lipid behavior have been characterized experimentally, but structural and causal details are lacking. We used atomistic molecular dynamics simulations totaling over 6 μs in simulation time to investigate the behavior of Aβ42 in zwitterionic and anionic lipid bilayers. We simulated transmembrane β-sheets (monomer and tetramer) resulting from a global optimization study and a helical structure obtained from an NMR study. In all simulations Aβ42 remained embedded in the bilayer. It was found that the surface charge and the lipid tail type are determinants for transmembrane stability of Aβ42 with zwitterionic surfaces and unsaturated lipids promoting stability. From the considered structures, the β-sheet tetramer is most stable as a result of interpeptide interactions. We performed an in-depth analysis of the translocation of water in the Aβ42-bilayer systems. We observed that this process is generally fast (within a few nanoseconds) yet generally slower than in the peptide-free bilayers. It is mainly governed by the lipid type, simulation temperature and Aβ42 conformation. The rate limiting step is the permeation through the hydrophobic core, where interactions between Aβ42 and permeating H2O molecules slow the translocation process. The β-sheet tetramer allows more water molecules to pass through the bilayer compared to monomeric Aβ, allowing us to conclude that the experimentally observed permeabilization of membranes must be due to membrane-bound Aβ oligomers, and not monomers.

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► We model various Aβ structures in membranes on the sub-microsecond time scale.
► Aβ always remains embedded in the bilayer and enables water translocation.
► Zwitterionic headgroups, unsaturated lipids, and Aβ oligomerization add to Aβ stability.
► Water permeation depends on the lipid type and the Aβ structure.
► Transmembrane Aβ oligomerization increases water permeability.