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The aggregation pattern of Aβ1-40 is altered by the presence of N-truncated Aβ4-40 and/or Cu(II) ions in a similar way via ionic interactions.

Alzheimer's Disease (AD) is one of the most common multifactorial diseases characterized by a range of abnormal molecular processes such as the accumulation of extracellular plaques containing the amyloid-β (Aβ) peptides and dyshomeostasis of copper in the brain. Herein, we investigate the effect of Cu(II) ions on the aggregation of Aβ1-40, and Aβ4-40, representing two most prevalent families of Aβ peptides, full length and N-truncated ones. Both families are similarly abundant in healthy and AD brains. In either of the studied peptides, substoichiometric Cu(II) concentrations accelerated aggregation, while superstoichiometric Cu(II) inhibited the fibril formation, likely by stabilizing oligomers. The addition of either Aβ4-40 or substoichiometric Cu(II) ions affected the aggregation profile of Aβ1-40, by yielding shorter and thicker fibrils. The similarity of these two effects can be attributed to the increase of positive charge at the Aβ N-terminus, which is caused either by Cu(II) complexation or N-truncation at position 4. Our findings provide a better understanding of the biological Aβ aggregation process as these two Aβ species and Cu(II) ions coexist and interact under physiological conditions.