Structural insights into TDP-43 in nucleic-acid binding and domain interactions

Area of Science:

• Molecular Biology
• Structural Biology
• Neuroscience

Background:

• TDP-43 protein is implicated in cystic fibrosis, frontotemporal lobar degeneration (FTLD), and amyotrophic lateral sclerosis (ALS).
• Pathological aggregation of TDP-43 C-terminal fragments in brain cells is a hallmark of these neurodegenerative diseases.

Purpose of the Study:

• To determine the crystal structure of the TDP-43 C-terminal RRM2 domain.
• To elucidate the molecular mechanisms of TDP-43's nucleic acid binding and self-association.

Main Methods:

• X-ray crystallography (1.65 A resolution) of TDP-43 RRM2 domain with single-stranded DNA.
• Circular dichroism to monitor thermal stability of TDP-43 RRM2 assemblies.

Main Results:

• The crystal structure reveals TDP-43 as a dimer with two RRM domains involved in DNA/RNA binding, explaining its TG/UG preference.
• The RRM2 domain exhibits an atypical fold with an additional beta-strand facilitating protein-protein interactions.
• Self-associated RRM2 domains form thermally stable assemblies (melting point > 85°C).

Conclusions:

• Characterization of TDP-43-nucleic acid recognition and RRM2 self-association modes.
• Provides molecular models for understanding TDP-43's role in cystic fibrosis and TDP-43 proteinopathies (FTLD, ALS).