title: The TDP-43 N-terminal domain structure at high resolution.
abstract: Transactive response DNA-binding protein 43 kDa (TDP-43) is an RNA transporting and processing protein whose aberrant aggregates are implicated in neurodegenerative diseases. The C-terminal domain of this protein plays a key role in mediating this process. However, the N-terminal domain (residues 1-77) is needed to effectively recruit TDP-43 monomers into this aggregate. In the present study, we report, for the first time, the essentially complete (1) H, (15) N and (13) C NMR assignments and the structure of the N-terminal domain determined on the basis of 26 hydrogen-bond, 60 torsion angle and 1058 unambiguous NOE structural restraints. The structure consists of an α-helix and six β-strands. Two β-strands form a β-hairpin not seen in the ubiquitin fold. All Pro residues are in the trans conformer and the two Cys are reduced and distantly separated on the surface of the protein. The domain has a well defined hydrophobic core composed of F35, Y43, W68, Y73 and 17 aliphatic side chains. The fold is topologically similar to the reported structure of axin 1. The protein is stable and no denatured species are observed at pH 4 and 25 °C. At 4 kcal·mol(-1) , the conformational stability of the domain, as measured by hydrogen/deuterium exchange, is comparable to ubiquitin (6 kcal·mol(-1) ). The β-strands, α-helix, and three of four turns are generally rigid, although the loop formed by residues 47-53 is mobile, as determined by model-free analysis of the (15) N{(1) H}NOE, as well as the translational and transversal relaxation rates.
  
  
  METHODS
  Structural data have been deposited in the Protein Data Bank under accession code: 2n4p. The NMR assignments have been deposited in the BMRB database under access code: 25675.
authors.affiliation: Instituto de Química Física Rocasolano, Madrid, Spain.
authors.forename: Miguel
authors.initials: M
authors.lastname: Mompeán
authors.affiliation: International Centre for Genetic Engineering and Biotechnology, Trieste, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Romano
authors.affiliation: Instituto de Química Física Rocasolano, Madrid, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Pantoja-Uceda
authors.affiliation: International Centre for Genetic Engineering and Biotechnology, Trieste, Italy.
authors.forename: Cristiana
authors.initials: C
authors.lastname: Stuani
authors.affiliation: International Centre for Genetic Engineering and Biotechnology, Trieste, Italy.
authors.forename: Francisco E
authors.initials: FE
authors.lastname: Baralle
authors.affiliation: International Centre for Genetic Engineering and Biotechnology, Trieste, Italy.
authors.forename: Emanuele
authors.initials: E
authors.lastname: Buratti
authors.affiliation: Instituto de Química Física Rocasolano, Madrid, Spain.
authors.forename: Douglas V
authors.initials: DV
authors.lastname: Laurents
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D041961:Deuterium Exchange Measurement; D006801:Humans; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013050:Spectrometry, Fluorescence; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D010446:Peptide Fragments
keywords: ALS/FTLD; TAR DNA-binding protein 43 (TDP-43); hydrogen/deuterium exchange; protein dynamics; protein structure