Fig. 6.

At high osmotic pressures, Tau mediates short-range attractions between MTs in the bundled phase. (A–F) The wall to wall distance between MTs in hexagonally packed bundles plotted as a function of increasing osmotic pressure. Increasing concentrations of (A) 3RS, (B) 3RM, (C) 3RL, (D) 4RS, (E) 4RM, and (F) 4RL isoforms decrease the wall to wall distance between MTs, indicative of the onset of Tau-induced short-range attractions (black circles correspond to distances between bare MTs). (G and H) Schematic cartoons show differing MT–MT interactions mediated by Tau. (G) The repulsion of the anionic component of Tau PDs at long distances, where low osmotic pressures do not favor chain interpenetration. (H) The favorable cationic/anionic interaction between overlapping Tau PDs (possibly including sections of the PRR) at short distances, where high osmotic pressures favor chain interpenetration.