A Phosphorylation-Induced Micellization Switch in the Low-Complexity Domain of TDP-43

Area of Science:

• Biochemistry
• Molecular Biology
• Neuroscience

Background:

• TDP-43's low-complexity domain (LCD) phase separation is implicated in ALS and FTLD-TDP.
• Understanding TDP-43 aggregation mechanisms is crucial for neurodegenerative disease research.

Purpose of the Study:

• To investigate the effect of C-terminal phosphorylation on TDP-43 LCD self-assembly.
• To determine if phosphorylation can prevent pathogenic phase separation and fibril formation.

Main Methods:

• Coarse-grained Monte Carlo simulations.
• In vitro phosphorylation using casein kinase 1 delta (CK1δ).
• Native mass spectrometry, turbidity assays, confocal imaging, negative-stain and cryo-electron microscopy.

Main Results:

• Extensive phosphorylation (≈12 sites) or phosphomimetic mutations redirected TDP-43 LCD self-assembly.
• Phosphorylated LCD formed spherical nanoparticles (micelles) instead of macroscopic phase separation.
• Increasing ionic strength induced anisotropic morphologies in phosphorylated mutants.

Conclusions:

• Phosphorylation acts as a molecular switch, preventing TDP-43 LCD macrophase separation and fibril formation.
• Microphase separation into micelles may offer a protective mechanism against TDP-43 aggregation.
• The stability of these micellar assemblies in pathological contexts requires further investigation.