Nuclear magnetic resonance determination of metal-proton distances in a synthetic calcium binding site of rabbit skeletal troponin C

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Abstract
The binding of Gd to a synthetic peptide of 13 amino acid residues representing the Ca binding loop of site 3 of rabbit skeletal troponin C [AcSTnC(103-115)amide] was studied by using 1H NMR spectroscopy. The proton line broadening and enhanced spin-lattice relaxation were used to determine proton-metal ion distances for several assigned nuclei in the peptide-metal ion complex. These distances were used in conjunction with other constraints and a distance algorithm procedure to demonstrate that the structure of the peptide-metal complex as shown by 1H NMR is consistent with the structure of the EF Ca binding loop in the X-ray structure of parvalbumin but that the available 1H NMR distances do not uniquely define the solution structure.