Monomeric α-syn preferably coaggregates with pTau oligomers in presence of metal ions. A. Cross-correlation amplitudes (G (0)) show mild coaggregation of α-syn monomers with pre-formed tau oligomers induced by DMSO and Fe3+, while Al3+ promotes intense coaggregation. Combinations of DMSO and metal ions show a synergistic effect especially for mTau. 2D histograms show the formation of smaller mixed oligomers induced by DMSO compared to the metal ions. 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. Measurements were taken from 20 independent samples; each sample was measured four times. Levels of significance are displayed as * = p < 0.05; ** = p < 0.01; ‡ = p < 0.001.