Differential effects of Cu(2+) and Fe(3+) ions on in vitro amyloid formation of biologically-relevant α-synuclein variants

Alterations in metal ion homeostasis appear coupled to neurodegenerative disorders but mechanisms are unknown. Amyloid formation of the protein α-synuclein in brain cells is a hallmark of Parkinson’s disease. α-Synuclein can bind several metal ions in vitro and such interactions may affect the assembly process. Here we used biophysical methods to study the effects of micromolar concentrations of Cu(2+) and Fe(3+) ions on amyloid formation of selected α-synuclein variants (wild-type and A53T α-synuclein, in normal and N-terminally acetylated forms). As shown previously, Cu(2+) speeds up aggregation of normal wild-type α-synuclein, but not the acetylated form. However, Cu(2+) has a minimal effect on (the faster) aggregation of normal A53T α-synuclein, despite that Cu(2+) binds to this variant. Like Cu(2+), Fe(3+) speeds up aggregation of non-acetylated wild-type α-synuclein, but with acetylation, Fe(3+) instead slows down aggregation. In contrast, for A53T α-synuclein, regardless of acetylation, Fe(3+) slows down aggregation with the effect being most dramatic for acetylated A53T α-synuclein. The results presented here suggest a correlation between metal-ion modulation effect and intrinsic aggregation speed of the various α-synuclein variants. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s10534-020-00234-4) contains supplementary material, which is available to authorized users.