Peptides were chemically synthesized by Pepscan (Lelystad, Netherlands). Peptides were dissolved in milli-Q water and stored at −80°C. Peptides were fluorescently labeled using Alexa Fluor Labeling Kits (Thermo Scientific).
FUS LC domain was expressed in E. coli and purified as described previously (Burke et al., 2015 (link)). hnRNPA2 LC domain (residues 190-341) was expressed with a TEV-cleavable N-terminal hexahistidine tag, purified from the inclusion body via HisTrap (GE Healthcare) in urea containing buffers, concentrated, diluted into native buffer for TEV cleavage of hexahistidine tag, resolublized by addition of solid urea, separated from his-tagged TEV protease and cleaved his-tag by HisTrap, and concentrated to 1-2 mM in 8M urea 20mM MES pH 5.5. hnRNPA2 was aliquoted and flash frozen. Experiments were conducted by dilution into native buffer conditions.