Fig. 6. Heparin-free tau fibrils strongly bind RNA.

a Electrostatic surface potential of the tau filament extracted from a CBD patient (PDB code: 6TJO). Positively and negatively charged residues are shown in blue and red, respectively. b Schematic representation of the protocol to determine the binding of RNA to tau fibrils. c Quantitative analysis of the binding of polyU, polyA and tRNA to tau fibrils aggregated without (orange) or with heparin (black) in the aggregation assay buffer (10 mM KCl, 25 mM HEPES, 5 mM MgCl₂, 3 mM TCEP, pH 7.2) or at increased ionic strength (100 mM KCl, 25 mM HEPES, 5 mM MgCl₂, 3 mM TCEP, pH 7.2). The amount of RNA in the pellet represents the % of RNA bound to the fibril and the amount of RNA in the supernatant (SN) represents the % of unbound RNA. The statistical analysis between the % of RNA bound to heparin-free and heparin-induced tau fibrils was performed by Welch’s t test. Four stars represent p < 0.0001, three stars represents p < 0.0002, two stars represents p < 0.0021. Data are represented as mean values of n = 3 independent experiments. Error bars represent the standard deviation of three independent experiments.