Structural details of helix-mediated multimerization of the conserved region of TDP-43 C-terminal domain.

Pathological inclusions of the C-terminal domain (CTD) of TAR DNA binding protein-43 (TDP-43) are neurodegenerative hallmarks in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia, yet CTD's aggregation propensity complicates structural characterization of native TDP-43. Here we propose structural models for the physiological multimerization of TDP-43 CTD's conserved region (CR) essential for TDP-43 RNA processing. Using NMR spectroscopy, we establish that the native state of TDP-43 CR at physiological conditions is α-helical. Hydrophobic residues drive CR helix-helix assembly, phase separation, and TDP-43 nuclear retention, while polar residues down regulate these processes. An integrative approach combining analytical ultracentrifugation, NMR-derived contacts, AlphaFold2-Multimer modeling, and all-atom molecular dynamics simulations together suggest that TDP-43 CR forms dynamic, multimeric helical assemblies stabilized by a methionine-rich core with specific contributions from a tryptophan/leucine pair. These structures show how ALS-associated mutations disrupt TDP-43 function and provide pharmacologically targetable structures to prevent its conversion into pathogenic β-sheet aggregates.