Electric Double Layer Phenomena Near Surfaces Irreversibly Trigger Assembly of Tau Protein.

The reversible folding and assembly of the human brain protein tau are regulated by charge neutralization through limited and reversible phosphorylation, enabling tau to bind tubulin and maintain the structural integrity of neuronal microtubules. However, in neurodegenerative diseases like Alzheimer's and related tauopathies, tau becomes hyperphosphorylated, detaches from tubulin, and irreversibly assembles into β-structured amyloid filaments responsible for neuronal death. In previous work, we showed that charge neutralization via Faradaic electroreduction of cationic residues in tau and other intrinsically disordered proteins can mimic phosphorylation to trigger protein condensation, folding, and assembly. Here, we demonstrate that even non-Faradaic effects─including large electric fields and concentration gradients in the electric double layer, together with spatial ordering of ions at the solution-electrode interface─can induce folding and assembly of tau, its microtubule-binding region K18, and a 19-residue tau peptide (jR2R3 P301L) containing a mutation known to induce early aggregation