Cryo-EM structure of amyloid fibrils formed by the entire low complexity domain of TDP-43

Abstract

Amyotrophic lateral sclerosis and several other neurodegenerative diseases are associated with brain deposits of TDP-43 aggregates. Cryo-EM structure of amyloid formed from the entire TDP-43 low complexity domain reveals single protofilament fibrils containing a large (138-residue), tightly packed core with structural features that differ from those previously found for fibrils formed from short protein fragments. The atomic model provides insight into potential structural perturbations caused by phosphorylation and disease-related mutations.

FTLD‐TDP assemblies seed neoaggregates with subtype‐specific features via a prion‐like cascade

“…However, this directionality may be lost upon fibril formation. Indeed, a recent cryoEM structure of amyloid fibrils formed by the TDP-43 low complexity domain suggests that hyperphosphorylation of TDP-43 would impose steric hindrance during fibril formation leading to fibril structure polymorphism (Li et al, 2021). Therefore, the differential phosphorylation we observed for FTLD-TDP-A and FTLD-TDP-C could underlie disease subtype heterogeneity.…”

“…This difference may be due to different structures of the neoaggregates and differential accessibility of the phosphorylation sites in the two subtypes. It is conceivable that as the aggregates mature and grow in size, one phosphorylation is favored over the other, and in turn, phosphorylation might influence aggregate structure, as recently proposed (Li et al, 2021).…”

“…Recent studies support the notion that serine phosphorylation within the low complexity region of TDP-43 may inhibit protein aggregation in vitro and in cells. Indeed, cryo-EM studies showed that the core fibril structure would be significantly disrupted by phosphorylation at key residues in that same domain (Li et al, 2021), whereas an independent study showed that TDP-43 phosphorylation within the C-terminal region increases solubility and counteracts protein accumulation in cells (preprint: Silva et al, 2021). In combination with our results pointing to fibril structure polymorphism between the subtypes, these data suggest that the phosphorylation state of TDP-43 could play a key role in the mechanism underlying the disease-specific subtypes.…”

“…Furthermore, TDP-43 forms liquid-liquid phase separated droplet-like structures in the nucleus (Murray et al, 2017;Guo et al, 2018;Maharana et al, 2018;Gasset-Rosa et al, 2019;Mann et al, 2019;Bhopatkar et al, 2020), as well as physiological oligomers through interaction of its N-terminal domains, which regulate RNA splicing (Afroz et al, 2017;Wang et al, 2018). In disease, TDP-43 forms amyloid fibrils via association of its low complexity domains at the C-terminal site (Babinchak et al, 2019;Cao et al, 2019;Shenoy et al, 2020;Li et al, 2021). Upon oxidative stress or destabilization of physiological oligomerization, nuclear droplets unmix and TDP-43 translocates to the cytoplasm where it incorporates into cytoplasmic droplets leading to cellular toxicity (Afroz et al, 2017;Gasset-Rosa et al, 2019).…”

Phe-Gly motifs drive fibrillization of TDP-43’s prion-like domain condensates

“…Tentatively, it seems reasonable to speculate that these motifs may be part of the structural core. Along this line, a recent cryo-EM structural model of fibrils from the entire PrLD of TDP-43 formed under conditions akin to those of the present work was posted in bioRxiv [31] after the submission of this manuscript. Interestingly enough, this cryo-EM study provides direct visual evidence that all Phe residues from the GAroS segment are present in the structure, as proposed here based on the unambiguous observation of various cross-peaks corresponding to Phe residues in the aromatic region of the 13 C- 13 C Dipolar Assisted Rotational Resonance (DARR) spectra (Fig 4).…”