Bivalent metal ions induce formation of α-synuclein fibril polymorphs with different cytotoxicities

α-Synuclein (α-Syn) aggregates are key components of intracellular inclusion bodies characteristic of Parkinson’s disease (PD) and other synucleinopathies. Metal ions have been considered as the important etiological factors in PD since their interactions with α-Syn alter the kinetics of fibrillation. In the present study, we have systematically explored the effects of Zn(2+), Cu(2+), Ca(2+), and Mg(2+) cations on α-Syn fibril formation. Specifically, we determined fibrillation kinetics, size, morphology, and secondary structure of the fibrils and their cytotoxic activity. While all cations accelerate fibrillation, we observed distinct effects of the different ions. For example, Zn(2+) induced fibrillation by lower t(lag) and higher k(app) and formation of shorter fibrils, while Ca(2+) ions lead to formation of longer fibrils, as evidenced by dynamic light scattering and atomic force microscopy studies. Additionally, the morphology of formed fibrils was different. Circular dichroism and attenuated total reflection-Fourier transform infrared spectroscopies revealed higher contents of β-sheets in fibrils. Interestingly, cell viability studies indicated nontoxicity of α-Syn fibrils formed in the presence of Zn(2+) ions, while the fibrils formed in the presence of Cu(2+), Ca(2+), and Mg(2+) were cytotoxic. Our results revealed that α-Syn fibrils formed in the presence of different divalent cations have distinct structural and cytotoxic features.