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Abstract Age-dependent transition of metastable, liquid-like protein condensates to amyloid fibrils is an emergent phenomenon of numerous neurodegeneration-linked protein systems. A key question is whether the thermodynamic forces underlying reversible phase separation and maturation to irreversible amyloids are distinct and separable. Here, we address this question using an engineered version of the microtubule-associated protein Tau, which forms biochemically active condensates. Liquid-like Tau condensates exhibit rapid aging to amyloid fibrils under quiescent, cofactor-free conditions. Tau condensate interface promotes fibril nucleation, impairing their activity to recruit tubulin and catalyze microtubule assembly. Remarkably, a small molecule metabolite, L-arginine, selectively impedes condensate-to-fibril transition without perturbing phase separation in a valence and chemistry-specific manner. By heightening the fibril nucleation barrier, L-arginine counteracts age-dependent decline in the biochemical activity of Tau condensates. These results provide a proof-of-principle demonstration that small molecule metabolites can enhance the metastability of protein condensates against a liquid-to-amyloid transition, thereby preserving condensate function.
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Phe-Gly motifs drive fibrillization of TDP-43’s prion-like domain condensates
Transactive response DNA-binding Protein of 43 kDa (TDP-43) assembles various aggregate forms, including biomolecular condensates or functional and pathological amyloids, with roles in disparate scenarios (e.g., muscle regeneration versus neurodegeneration). The link between condensates and fibrils remains unclear, just as the factors controlling conformational transitions within these aggregate species: Salt- or RNA-induced droplets may evolve into fibrils or remain in the droplet form, suggesting distinct end point species of different aggregation pathways. Using microscopy and NMR methods, we unexpectedly observed in vitro droplet formation in the absence of salts or RNAs and provided visual evidence for fibrillization at the droplet surface/solvent interface but not the droplet interior. Our NMR analyses unambiguously uncovered a distinct amyloid conformation in which Phe-Gly motifs are key elements of the reconstituted fibril form, suggesting a pivotal role for these residues in creating the fibril core. This contrasts the minor participation of Phe-Gly motifs in initiation of the droplet form. Our results point to an intrinsic (i.e., non-induced) aggregation pathway that may exist over a broad range of conditions and illustrate structural features that distinguishes between aggregate forms.
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- Award ID(s):
- 1913885
- PAR ID:
- 10285896
- Editor(s):
- Walters, Kylie J.
- Date Published:
- Journal Name:
- PLOS Biology
- Volume:
- 19
- Issue:
- 4
- ISSN:
- 1545-7885
- Page Range / eLocation ID:
- e3001198
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1371/journal.pbio.3001198
