title: Regulatory domain conformational exchange and linker region flexibility in cardiac troponin C bound to cardiac troponin I.
abstract: Previously, we utilized (15)N transverse relaxation rates to demonstrate significant mobility in the linker region and conformational exchange in the regulatory domain of Ca(2+)-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.
authors.affiliation: Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, College of Medicine, Cincinnati, Ohio 45267, USA.
authors.forename: M B
authors.initials: MB
authors.lastname: Abbott
authors.forename: V
authors.initials: V
authors.lastname: Gaponenko
authors.forename: E
authors.initials: E
authors.lastname: Abusamhadneh
authors.forename: N
authors.initials: N
authors.lastname: Finley
authors.forename: G
authors.initials: G
authors.lastname: Li
authors.forename: A
authors.initials: A
authors.lastname: Dvoretsky
authors.forename: M
authors.initials: M
authors.lastname: Rance
authors.forename: R J
authors.initials: RJ
authors.lastname: Solaro
authors.forename: P R
authors.initials: PR
authors.lastname: Rosevear
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D005453:Fluorescence; D046911:Macromolecular Substances; D009682:Magnetic Resonance Spectroscopy; D009206:Myocardium / Q000378:metabolism*; D009282:Naphthalenesulfonates; D010766:Phosphorylation; D011485:Protein Binding; D011487:Protein Conformation; D019209:Troponin C / Q000737:chemistry*; D019210:Troponin I / Q000378:metabolism*; D014508:Urea / Q000494:pharmacology
chemical_list: D046911:Macromolecular Substances; D009282:Naphthalenesulfonates; D019209:Troponin C; D019210:Troponin I; C011488:IAANS; D014508:Urea; D002118:Calcium