Phosphorylation Mimicking Mutations Cause TDP-43 to Adopt Different Fibril Conformations.

Area of Science:

• Neuroscience
• Biochemistry
• Structural Biology

Background:

• The Tar-DNA Binding Protein-43 C-terminal region (TDP43LC) forms amyloid-like fibrils implicated in Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD).
• Protein inclusions in these diseases contain TDP43 C-terminal fragments and phosphorylated TDP43.

Purpose of the Study:

• To investigate the structural and aggregation properties of phosphomimetic TDP43LC (P-TDP43LC) compared to wild-type TDP43LC.
• To elucidate the role of phosphorylation in TDP43LC fibril formation and structure in the context of neurodegenerative diseases.

Main Methods:

• Solution Nuclear Magnetic Resonance (NMR) spectroscopy to determine the structure of soluble P-TDP43LC.
• Turbidity measurements, imaging, and kinetic assays to assess aggregation behavior.
• Solid-state NMR to analyze the fibril conformation of P-TDP43LC.

Main Results:

• Soluble P-TDP43LC shares structural similarity with wild-type TDP43LC, featuring a helical core and disordered regions.
• P-TDP43LC exhibits distinct aggregation kinetics and behavior compared to wild-type TDP43LC.
• Phosphomimetic mutations alter the wild-type fibril conformation, with electrostatic repulsion influencing fibril formation and selecting for a different in vitro conformation.

Conclusions:

• Phosphorylation significantly perturbs the amyloid-like fibril structure of TDP43LC.
• The findings highlight the structural role of TDP43LC phosphorylation in modulating fibril formation relevant to ALS and FTD pathogenesis.