ALS mutations disrupt phase separation mediated by -helical structure in the TDP-43 low complexity C-terminal domain

By Alexander E. Conicella, Gül H. Zerze, Jeetain Mittal, Nicolas L. Fawzi. Structure, 2016

751 citations recorded by the source corpus.

Summary RNA-binding protein TDP-43 mediates essential RNA processing but forms cytoplasmic neuronal inclusions via its C-terminal domain (CTD) in amyotrophic lateral sclerosis (ALS). It remains unclear if aggregated TDP-43 is neurotoxic and if ~50 ALS-associated missense mutations in TDP-43 CTD promote aggregation, or if loss-of-normal-function plays a role in disease. Recent work points to the ability of related proteins to assemble into functional phase-separated ribonucleoprotein granules via their structurally-disordered “prion-like” domains. Here, we provide atomic details on the structure and assembly of the low-complexity CTD of TDP-43 into liquid-liquid phase-separated in vitro granules and demonstrate that ALS-associated variants disrupt interactions within granules. Using NMR spectroscopy, simulation, and microscopy, we find that a subregion cooperatively but transiently folds into a helix that mediates TDP-43 phase separation. ALS-associated mutations disrupt phase separation by inhibiting interaction and helical stabilization. Therefore, ALS-associated mutations can disrupt TDP-43 interactions, affecting function beyond encouraging aggregation.

Subfields: Genetics, Molecular Biology, Neurology

View Paper: https://www.semanticscholar.org/paper/084f41b41b46db0328c86f4c01232de7b8c79450

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Citations in the corpus

Liquid phase condensation in cell physiology and disease (2017, background): “5B) (14); fibrous structures are also seen to nucleate within other ALS-associated protein droplets (15, 51, 52, 69).”
Pi-Pi contacts are an overlooked protein feature relevant to phase separation (2018, background): “…the electrostatic effects of charge patterning (Nott et al., 2015; Lin et al., 2016; Das and Pappu, 2013), multivalency of PTM sites and PTM-binding motifs, and transient structural interactions, including strand formation (Murray et al., 2017) and helical interactions (Conicella et al., 2016).”
Liquid-Liquid Phase Separation in Disease. (2019, background): “that promote protein phase separation are often mutated in diseases and promote a rapid conversion of dense protein solutions to protein aggregates (37, 101, 105, 108, 123).”
Molecular Mechanisms of TDP-43 Misfolding and Pathology in Amyotrophic Lateral Sclerosis (2019, background): “Within these droplets, the C-terminal residues show mild transient interactions, that appear crucial for stress granule formation (Conicella et al., 2016).”
Phosphorylation of the FUS low‐complexity domain disrupts phase separation, aggregation, and toxicity (2017, positive): “Several human proteins including FUS, TDP-43, hnRNPA1, and hnRNPA2 contain low-complexity sequences that are compositionally similar to yeast prion domains.”
Tau protein liquid–liquid phase separation can initiate tau aggregation (2018, positive): “For example, FUS, TDP-43, and hnRNPA1 contain “prion-like” LCDs that drive their phase separation.”
Intrinsically disordered regions contribute promiscuous interactions to RNP granule assembly (2017, background): “…including amyloid-like cross-beta interactions, that could be important in biological contexts where RNP granules need to be long-lived or mechanically stable (Boke and Mitchison, 2017; Kato et al., 2012) or α-helices (Conicella et al., 2016), both of which should show some sequence specificity.”