Human recombinant TPPP/p25 forms and fragments possessing His-tags were expressed in E. coli BL21 (DE3) cells and isolated on HIS-Select™ Cartridge (Sigma-Aldrich) as described previously515. The purity of proteins was analysed by SDS-PAGE. Protein concentrations of the TPPP/p25 variants were determined on the basis of the absorbance at 280 nm using the extinction coefficients evaluated by ProtParam (http://web.expasy.org/protparam/), 10095 M−1 *cm−1 for FL TPPP/p25 and N-terminal truncated TPPP/p25; 5625 M−1 *cm−1 for C-terminal truncated TPPP/p25 and CORE, respectively.