Al3+promotes stronger formation of SDS stable tau and α-syn coaggregates than Fe3+, preferably after tau phosphorylation. A. Cross-correlation amplitudes (G (0)) show mild proaggregatory activity of DMSO and Fe3+, while Al3+ promotes intense protein oligomerization. Combinations of DMSO and metal ions show a synergistic effect especially for mTau. 2D histograms show the formation of smaller oligomers induced by DMSO compared to Al3+. B. Cross-correlation amplitude before (T0) and 100 min after (T100) addition of SDS to the aggregation assay. Significant reductions of aggregation levels at T100 are indicated by the symbols over the error bars, while significant differences between pTau and mTau are indicated by the symbols over the wide bars. C. Cross correlation amplitude at T100 normalized against T0 shows increased SDS-resistance of metal ion induced oligomers compared to DMSO. D. Scheme illustrating the appearance of tau and α-syn aggregates and coaggregates of the two proteins. Higher fluorescence intensities of detected oligomers indicate increased oligomer size. Measurements were taken from 16 independent samples; each sample was measured four times. Levels of significance are displayed as * = p < 0.05; ** = p < 0.01; ‡ = p < 0.001.