title: Solution structure of a polypeptide dimer comprising the fourth Ca(2+)-binding site of troponin C by nuclear magnetic resonance spectroscopy.
abstract: The structure of a 39 amino acid proteolytic fragment of rabbit skeletal troponin C containing the fourth Ca(2+)-binding site has been determined by an approach involving nuclear magnetic resonance (NMR) spectroscopy combined with hybrid distance geometry-dynamical simulated annealing calculations. Hydrodynamic and NMR evidence establishes unambiguously that the fragment forms a stable dimer in solution in the presence of excess Ca2+. The calculation of the dimeric structure is based on a total of 1056 experimental restraints comprising 422 interproton distances, 35 phi, 28 psi, and 28 chi 1 torsion angle restraints within each subunit, 30 intermonomer distance restraints, and 6 Ca2+ restraints per subunit. A total of 48 final structures were calculated having an rms deviation about the mean atomic backbone coordinate positions of 1.0 A for residues Asp128-Glu156. The solution structure consists of a dimer of helix-loop-helix motifs related by a 2-fold axis of symmetry. The overall architecture of the dimer is very similar to the C-terminal domain in the crystal structure of chicken skeletal troponin C.
authors.affiliation: Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: L E
authors.initials: LE
authors.lastname: Kay
authors.forename: J D
authors.initials: JD
authors.lastname: Forman-Kay
authors.forename: W D
authors.initials: WD
authors.lastname: McCubbin
authors.forename: C M
authors.initials: CM
authors.lastname: Kay
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002850:Chromatography, Gel; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011487:Protein Conformation; D011817:Rabbits; D014336:Troponin / Q000378:metabolism*; D019209:Troponin C
chemical_list: D014336:Troponin; D019209:Troponin C; D002118:Calcium