Biophysical Society Thematic Meeting | Tutzing 2026

Single-Molecule FRET: The Next 30 Years

Poster Abstracts

67-POS

Board 33

CONFORMATIONAL STATES OF WILD-TYPE AND PHOSPHOMIMETIC TAU ARE MODULATED BY IONIC STRENGTH Yarne Vankerkhoven 1 ; Jelle Hendrix 1 ; 1 Hasselt University, Dynamic Bioimaging Lab, Advanced Optical Microscopy Centre and Biomedical Research Institute, Diepenbeek, Belgium The microtubule associated protein Tau is an intrinsically disordered protein whose aggregation is implicated in Tauopathies. Tau can undergo liquid-liquid phase separation (LLPS) to form biomolecular condensates that are associated with both physiological and pathological processes. It is currently unknown which conformations Tau adopts during aggregation. Uncovering differences in conformations could provide a means of identifying therapeutic targets for Tau aggregation. Here, we employed single-molecule Förster resonance energy transfer (smFRET) to investigate changes in Tau conformations under different ionic strength conditions. Low and medium salt concentrations were investigated for wild-type (WT) 2N4R Tau and a phosphomimetic mutant near the AT8 epitope. We found a predominant high-FRET population for WT Tau under both low and medium ionic strength conditions, with a lower peak FRET efficiency observed at medium ionic strength. Lower-FRET populations were also detected under both conditions but were less prominent at medium ionic strength. The phosphomimetic Tau mutant showed a similar trend towards high FRET efficiencies, which remained largely unaffected by ionic strength. A lower-FRET population was also observed, whose presence slightly decreased at medium salt concentration. Comparing WT and phosphomimetic Tau revealed that the latter favored higher FRET efficiencies under both conditions. Our results suggest a compaction of the microtubule binding region at increased salt concentrations and in the phosphomimetic mutant. Such a compaction could predispose Tau to aggregation. Further investigations will assess conformational differences between WT and phosphomimetic Tau across the full protein in both monomer and LLPS conditions. Such differences could provide potential therapeutic targets to combat Tau aggregation.

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