Synthetic analog of a high affinity calcium binding site in rabbit skeletal troponin C.

A 21-residue peptide analog of the Ca2+ binding Site 3 in rabbit skeletal troponin C has been synthesized by the solid phase method. CD studies as well as uv difference spectroscopy did not show any changes upon addition of Ca2+ to this peptide in aqueous solution. Acetylation of the NH2-terminal residue of the analog resulted in Ca2+-induced CD and uv difference spectral changes and these changes could be accentuated upon increasing the hydrophobicity of the solvent system. It was also found that the nonacetylated peptide showed Ca2+-induced changes in CD and uv difference spectroscopy when the studies were carried out in the hydrophobic solvent system. These results indicate that the complete helix-loop-helix unit is not required for Ca2+ binding to the loop region of the unit and that synthetic analogs can be prepared to determine the molecular requirements of the unit for metal ion affinity and selectivity. We describe the folding of this peptide about a calcium cation based on these preliminary results.