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

Abstract

To investigate the Ca-dependent regulation of [rabbit] muscle contraction, a synthetic analog of the inhibitory region of troponin I, N.alpha.-acetyl[FPhe106]TnI-(104-115) amide, was made by solid-phase peptide synthesis. This region represents the minimum sequence necessary for inhibition of actomyosin ATPase activity in the presence of tropomyosin. Conformational changes induced by the formation of the synthetic peptide-troponin C complex are followed by proton NMR 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 Ca, this region of troponin I (104-115) is bound to actin-tropomyosin, inhibiting actomyosin ATPase activity. Evidently, the binding site for this region of troponin I is induced in troponin C in the presence of Ca and the formation of this complex releases actomyosin ATPase inhibition.