1H-NMR resonance assignments, secondary structure, and global fold of the TR1C fragment of turkey skeletal troponin C in the calcium-free state.

The TR 1 C fragment of turkey skeletal muscle TnC (residues 12-87) comprises the two regulatory calcium binding sites of the protein. Complete assignments of the 1 H-NMR resonances of the backbone and amino acid side chains of this domain in the absence of metal ions have been obtained using 2D 1 H-NMR techniques. Sequential (i,i+1) and short-range (i,i+3) NOE connectivities define two helix-loop-helix calcium binding motifs, and long-range NOE connectivities indicate a short two-stranded β-sheet formed between the two calcium binding loops. The two calcium binding sites are different in secondary structure