For TEM experiments of Tau:suramin condensates (Fig. 1 i), the Tau:suramin samples were prepared in the similar way as applied for DLS experiments in equimolar concentrations for Tau (25 µM) and suramin (25 µM) and 5 µM for heparin. About 3 µl of undiluted sample was loaded onto glow discharged carbon-coated copper grids, (Quantifoil R 1.2/1.3, Science Services), incubated for 30 seconds to allow adherence of condensates, blotted to remove excess solution, stained with 2% (w/v) uranyl acetate (UA) solution for 15 seconds and dried as per the standard negative staining protocol for proteins to reduce background and increase contrast. The morphology and dimensions of Tau:suramin condensates were analyzed by TEM (JEM-2100-Plus, JEOL, Germany) and micrographs were taken at an accelerating voltage of 200 kV. All TEM experiments were conducted in the XBI Biolab of European XFEL65 (link). The experiments were repeated three times. For Tau TEM fibril investigations the Tau:suramin, Tau:heparin and Tau:suramin:heparin condensate samples were prepared and incubated at 37 °C for 36 hours along with suramin control (Fig. 4 c).
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