Infrared study of synthetic peptide analogues of the calcium‐binding site III of troponin C: The role of helix F of an EF‐hand motif

The EF‐hand motif (helix–loop–helix) is a Ca 2+ ‐binding domain that is common among many intracellular Ca 2+ ‐binding proteins. We applied Fourier‐transform infrared spectroscopy to study the synthetic peptide analogues of site III of rabbit skeletal muscle troponin C (helix E–loop–helix F). The 17‐residue peptides corresponding to loop–helix F (DRDADGYIDAEELAEIF), where one residue is substituted by the D ‐type amino acid, were investigated to disturb the α‐helical conformation of helix F systematically. These D ‐type‐substituted peptides showed no band at about 1555 cm −1 even in the Ca 2+ ‐loaded state although the native peptide ( L ‐type only) showed a band at about 1555 cm −1 in the Ca 2+ ‐loaded state, which is assigned to the side‐chain COO − group of Glu at the 12th position, serving as the ligand for Ca 2+ in the bidentate coordination mode. Therefore, helix F is vital to the interaction between the Ca 2+ and the side‐chain COO − group of Glu at the 12th position. Implications of the COO − antisymmetric stretch and the amide‐I′ of the synthetic peptide analogues of the Ca 2+ ‐binding sites are discussed. © 2012 Wiley Periodicals, Inc. Biopolymers 99: 342–347, 2013.