Fig. 5. Schematic picture of the A+ and A− oligomers of Aβ₄₂. Toxic A+ oligomers are characterized by exposure of hydrophobic clusters (blue), as found previously for this and related protein systems,^9–11 as well as of Tyr and Lys residues (red), which is the major finding of the present study. Toxic A+ species are able to penetrate the cell membrane causing an influx of Ca²⁺ ions from the extracellular space to the cytosol.