Calcium-dependent inhibitory region of troponin: a proton nuclear magnetic resonance study on the interaction between troponin C and the synthetic peptide N alpha-acetyl[FPhe106]TnI-(104-115) amide.

To investigate the calcium-dependent regulation of muscle contraction, a synthetic analogue of the inhibitory region of troponin I, N alpha-acetyl[FPhe106]TnI-(104-115) amide, has been made by solid-phase peptide synthesis. This region represents the minimum sequence necessary for inhibition of actomyosin ATPase activity in the presence of tropomyosin [Talbot, J.A., & Hodges, R.S. (1981) J. Biol. Chem. 256, 2798-2802]. Conformational changes induced by the formation of the synthetic peptide-troponin C complex are followed by proton nuclear magnetic resonance spectroscopy. Aliphatic (Leu and Val), aromatic (p-fluorophenylalanine), and charged (Arg) residues are perturbed by interaction with troponin C. In troponin C, peptide-protein interaction results in the redistribution of the Phe envelope of troponin C and perturbations in the aliphatic region. The observed effects on the protein resonances are in agreement with proposed interaction of the peptide with the N-terminal region of site III of troponin C. In the absence of calcium, this region of troponin I (104-115) is bound to actin-tropomyosin, inhibiting actomyosin ATPase activity [Talbot, J.A., & Hodges, R.S. (1981) J. Biol. Chem. 256, 2798-2802]. Our results suggest that the binding site for this region of troponin I is induced in troponin C in the presence of calcium and the formation of this complex releases actomyosin ATPase inhibition.