Solution structure of a polypeptide dimer comprising the fourth Ca(2+)-binding site of troponin C by nuclear magnetic resonance spectroscopy.
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.
Kay
L E
LE
Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Forman-Kay
J D
JD
McCubbin
W D
WD
Kay
C M
CM
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
D014336:Troponin; D019209:Troponin C; D002118:Calcium