Aβ(1-42) tetramer and octamer structures reveal edge pores as a mechanism for membrane damage

The formation of amyloid-beta (Aβ) oligomer pores in the membrane of neurons has been proposed as the means to explain neurotoxicity in Alzheimer9s disease (AD). It is therefore critical to characterize Aβ oligomer samples in membrane-mimicking environments. Here we present the first three-dimensional structure of an Aβ oligomer formed in dodecyl phosphocholine (DPC) micelles, namely an Aβ(1-42) tetramer. It comprises a β-sheet core made of six β-strands, connected by only two β-turns. The two faces of the β-sheet core are hydrophobic and surrounded by the membrane-mimicking environment. In contrast, the edges of the core are hydrophilic and are solvent-exposed. By increasing the concentration of Aβ(1-42), we prepared a sample enriched in Aβ(1-42) octamers, formed by two Aβ(1-42) tetramers facing each other forming a β-sandwich structure. Notably, samples enriched in Aβ(1-42) tetramers and octamers are both active in lipid bilayers and exhibit the same types of pore-like behaviour, but they show different occurrence rates. Remarkably, molecular dynamics simulations showed a new mechanism of membrane disruption in which water and ion permeation occurred through lipid-stabilized pores mediated by the hydrophilic residues located on the core β-sheets edges of the Aβ(1-42) tetramers and octamers.