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

Area of Science:

• Neuroscience
• Structural Biology
• Biochemistry

Background:

• TAR DNA binding protein-43 (TDP-43) C-terminal domain (CTD) is intrinsically disordered and forms inclusions in neurodegenerative diseases.
• A conserved region (CR) within TDP-43 CTD mediates helix-helix contacts vital for oligomerization and function, but is affected by ALS mutations.
• Structural insights into CR assembly and the impact of ALS variants on TDP-43 phase separation and function are limited.

Purpose of the Study:

• To elucidate the structural basis of TDP-43 CR helical oligomerization.
• To understand the role of specific residues in CR assembly, phase separation, and TDP-43 function.
• To provide a structural model for the initial stages of TDP-43 aggregation.

Main Methods:

• Integrative structural biology approach combining biophysical experiments (NMR) and biochemical assays (alanine scanning mutagenesis).
• Computational modeling using AlphaFold2-Multimer (AF2-Multimer).
• Atomistic Molecular Dynamics (AAMD) simulations.

Main Results:

• TDP-43 CR exists in an alpha-helical state under physiological conditions.
• Hydrophobic residues in CR are critical for assembly, phase separation, and nuclear retention, while polar residues dampen these processes.
• AF2-Multimer and AAMD simulations revealed dynamic, oligomeric TDP-43 assemblies stabilized by a methionine-rich core and a Trp/Leu pair.

Conclusions:

• The study provides novel structural models of TDP-43 CR helical oligomerization.
• Findings advance the understanding of TDP-43's physiological function and its transition to pathogenic aggregates.
• The identified structural features offer insights into mechanisms underlying TDP-43 related neurodegeneration.