Regulatory Domain Conformational Exchange and Linker Region Flexibility in Cardiac Troponin C Bound to Cardiac Troponin I

• Published in: The Journal of biological chemistry Vol. 275; no. 27; pp. 20610 - 20617
• Main Authors: Abbott, M.Bret, Gaponenko, Vadim, Abusamhadneh, Ekram, Finley, Natosha, Li, Ge, Dvoretsky, Alex, Rance, Mark, Solaro, R.John, Rosevear, Paul R.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 07.07.2000; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Calcium - metabolism; Fluorescence; Macromolecular Substances; Magnetic Resonance Spectroscopy; Myocardium - metabolism; Naphthalenesulfonates; Phosphorylation; Protein Binding; Protein Conformation; Troponin C - chemistry; Troponin I - metabolism; Urea - pharmacology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M909252199

Previously, we utilized 15N transverse relaxation rates to demonstrate significant mobility in the linker region and conformational exchange in the regulatory domain of Ca2+-saturated cardiac troponin C bound to the isolated N-domain of cardiac troponin I (Gaponenko, V., Abusamhadneh, E., Abbott, M. B., Finley, N., Gasmi-Seabrook, G., Solaro, R.J., Rance, M., and Rosevear, P.R. (1999) J. Biol. Chem.274, 16681–16684). Here we show a large decrease in cardiac troponin C linker flexibility, corresponding to residues 85–93, when bound to intact cardiac troponin I. The addition of 2 m urea to the intact cardiac troponin I-troponin C complex significantly increased linker flexibility. Conformational changes in the regulatory domain of cardiac troponin C were monitored in complexes with troponin I-(1–211), troponin I-(33–211), troponin I-(1–80) and bisphosphorylated troponin I-(1–80). The cardiac specific N terminus, residues 1–32, and the C-domain, residues 81–211, of troponin I are both capable of inducing conformational changes in the troponin C regulatory domain. Phosphorylation of the cardiac specific N terminus reversed its effects on the regulatory domain. These studies provide the first evidence that the cardiac specific N terminus can modulate the function of troponin C by altering the conformational equilibrium of the regulatory domain.