Post-Translational\nModifications Control Phase Transitions\nof Tau

The self-assembly of Tau into filaments, which mirror\nthe structures\nobserved in Alzheimer’s disease (AD) brains, raises questions\nabout the role of AD-specific post-translational modifications (PTMs)\nin the formation of paired helical filaments (PHFs). To investigate\nthis, we developed a synthetic approach to produce Tau(291–391)\nfeaturing <i>N</i>-acetyllysine, phosphoserine, phosphotyrosine,\nand <i>N</i>-glycosylation at positions commonly modified\nin post-mortem AD brains. Using various electron and optical microscopy\ntechniques, we discovered that these modifications generally hinder\nthe <i>in vitro</i> assembly of Tau into PHFs. Interestingly,\nwhile acetylation’s effect on Tau assembly displayed variability,\neither promoting or inhibiting phase transitions in cofactor-free\naggregation, heparin-induced aggregation, and RNA-mediated liquid–liquid\nphase separation (LLPS), phosphorylation uniformly mitigated these\nprocesses. Our observations suggest that PTMs, particularly those\nsituated outside the rigid core, are pivotal in the nucleation of\nPHFs. Moreover, with heparin-induced aggregation leading to the formation\nof heterogeneous aggregates, most AD-specific PTMs appeared to decelerate\naggregation. The impact of acetylation on RNA-induced LLPS was notably\nsite-dependent, whereas phosphorylation consistently reduced LLPS\nacross all proteoforms examined. These insights underscore the complex\ninterplay between site-specific PTMs and environmental factors in\nmodulating Tau aggregation kinetics, highlighting the role of PTMs\nlocated outside the ordered filament core in driving the self-assembly.