The protein tau associates and stabilizes microtubules (MT) to maintain neuronal health. Post-translational modifications that lead to tau aggregation in brains with neurodegenerative diseases. To understand the mechanism of the early misfolding events in AD, we are using magic-angle-spinning (MAS) solid-state NMR spectroscopy and cryo-electron microscopy to investigate the structure and dynamics of tau bound to microtubules, lipid bilayers, as well as amyloid fibrils formed with anionic cofactors or co-factor-free pseudophosphorylation mutations[4].
When complexed with MTs, tau exhibits well-resolved dipolar 2D correlation spectra that can be assigned to a 45- residue segment spanning the R’ and the C-terminal half of the R4 repeat. This result changes the prevailing model that all 5 MT-binding regions are immobilized.

When complexed to lipid membranes, tau converted from a disordered random coil to an ordered b-sheet. Small unilamellar vesicles (SUVs) and large unilamellar vesicles (LUVs) cause different equilibrium conformations. SUV-bound tau developed amyloid fibrils while LUV-bound tau does not. Removing cholesterol from the SUV abolished fibril formation.

In the presence of heparin, P2R tau assembles into amyloid fibrils. We assigned the rigid b-sheet core to the R2 and R3 repeats. Unexpectedly, the folds differ between 24C and 12C: R2 forms a b-arch at 24C but a continuous b- strand at 12C. This indicates that R2 has enhanced conformational plasticity than R3, similarly to in brain-extracted 4R tau aggregates.

Pseudo-phosphorylated mutants of tau can self-assemble in the absence of any co-factors. Using SSNMR and cryoEM, we found that specific disease-related phosphorylation patterns induce specific amyloid structures.

These results have implications for the functional and pathological state of tau in diseases. They also demonstrate the power of solid-state NMR to reveal both the structure and dynamics of complex biomolecular assemblies in neurodegenerative diseases.

<b><i>Figure 1.</i></b> (<b>a</b>) 2D NCA correlation spectrum (left) and TEM image (bottom right) of microtubule-bound tau. (<b>b</b>) 2D NCA spectrum (left) and TEM image (bottom right) of tau bound to SUVs. (<b>c</b>) 2D NCA spectrum (left) and TEM image (bottom right) of heparin-induced tau at 24C.

Figure 1. (a) 2D NCA correlation spectrum (left) and TEM image (bottom right) of microtubule-bound tau. (b) 2D NCA spectrum (left) and TEM image (bottom right) of tau bound to SUVs. (c) 2D NCA spectrum (left) and TEM image (bottom right) of heparin-induced tau at 24C.

Prof. Mei Hong

Professor of Chemistry, Iowa State Univ

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