The ALS/FTD-linked protein CHCHD10 associates with the TDP-43 C-terminal domain through a CHCH-helix interface

Abstract

Aggregation and cytoplasmic mislocalization of TDP-43 are defining features of several neurodegenerative disorders including Amyotrophic Lateral Sclerosis (ALS) and frontotemporal dementia (FTD). Yet the molecular interactions that regulate its transition from reversible assemblies to aggregation-prone states remain poorly understood. CHCHD10 is a mitochondrial protein genetically and pathologically linked to TDP-43 dysfunction, but the molecular basis connecting both proteins has remained unclear. Here, we combine solution Nuclear Magnetic Resonance (NMR) spectroscopy, biophysical assays and cellular imaging to characterize the interaction between human CHCHD10 and the C-terminal region of TDP-43 (TDP-43CTD). CHCHD10 comprises a dynamic N-terminal region and a folded CHCH domain that samples a reversible monomer-dimer equilibrium. Reciprocal NMR titrations show that the CHCH domain binds the conserved hydrophobic helix of TDP-43CTD through a dynamic submicromolar interaction that overlaps with self-association surfaces in both proteins. CHCHD10 alters the formation of ThT-reactive TDP-43CTD assemblies and reduces TDP-43CTD sedimentation under selected stoichiometric conditions, while itself becoming enriched in the sedimentable fraction. Equilibrium calculations, independently reproduced using a complete numerical mass-balance solution, identify the initial non-homodimeric CHCHD10 population as the strongest predictor of its subsequent sedimentation. In cells, full-length CHCHD10 shows stronger CHCH-dependent spatial association with TDP-43 than a construct lacking the CHCH domain. These findings define a CHCH-helix interface that couples homo- and heterotypic assembly equilibria and support an asymmetric interface-buffering model in which CHCHD10 can divert TDP-43CTD from self-association while increasing its own availability for recruitment into sedimentable assemblies.