title: TDP-43 N terminus encodes a novel ubiquitin-like fold and its unfolded form in equilibrium that can be shifted by binding to ssDNA.
abstract: Transactivation response element (TAR) DNA-binding protein 43 (TDP-43) is the principal component of ubiquitinated inclusions characteristic of most forms of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia-frontotemporal lobar degeneration with TDP-43-positive inclusions (FTLD-TDP), as well as an increasing spectrum of other neurodegenerative diseases. Previous structural and functional studies on TDP-43 have been mostly focused on its recognized domains. Very recently, however, its extreme N terminus was identified to be a double-edged sword indispensable for both physiology and proteinopathy, but thus far its structure remains unknown due to the severe aggregation. Here as facilitated by our previous discovery that protein aggregation can be significantly minimized by reducing salt concentrations, by circular dichroism and NMR spectroscopy we revealed that the TDP-43 N terminus encodes a well-folded structure in concentration-dependent equilibrium with its unfolded form. Despite previous failure in detecting any sequence homology to ubiquitin, the folded state was determined to adopt a novel ubiquitin-like fold by the CS-Rosetta program with NMR chemical shifts and 78 unambiguous long-range nuclear Overhauser effect (NOE) constraints. Remarkably, this ubiquitin-like fold could bind ssDNA, and the binding shifted the conformational equilibrium toward reducing the unfolded population. To the best of our knowledge, the TDP-43 N terminus represents the first ubiquitin-like fold capable of directly binding nucleic acid. Our results provide a molecular mechanism rationalizing the functional dichotomy of TDP-43 and might also shed light on the formation and dynamics of cellular ribonucleoprotein granules, which have been recently linked to ALS pathogenesis. As a consequence, one therapeutic strategy for TDP-43-causing diseases might be to stabilize its ubiquitin-like fold by ssDNA or designed molecules.
authors.affiliation: Department of Biological Sciences, Faculty of Science, and.
authors.forename: Haina
authors.initials: H
authors.lastname: Qin
authors.affiliation: Department of Biological Sciences, Faculty of Science, and.
authors.forename: Liang-Zhong
authors.initials: LZ
authors.lastname: Lim
authors.affiliation: National University of Singapore Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore 119260.
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Wei
authors.affiliation: Department of Biological Sciences, Faculty of Science, and National University of Singapore Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore 119260 dbssjx@nus.edu.sg.
authors.forename: Jianxing
authors.initials: J
authors.lastname: Song
mesh_terms: D000690:Amyotrophic Lateral Sclerosis; D002942:Circular Dichroism; D004277:DNA, Single-Stranded / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D019906:Nuclear Magnetic Resonance, Biomolecular; D066263:Protein Aggregation, Pathological; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D058767:Protein Unfolding
chemical_list: D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins
keywords: FTLD-TDP; NMR spectroscopy; TDP-43; amyotrophic lateral sclerosis; ubiquitin-like fold