Regulatory domain conformational exchange and linker region flexibility in cardiac troponin C bound to cardiac troponin I.
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.
Abbott
M B
MB
Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, College of Medicine, Cincinnati, Ohio 45267, USA.
Gaponenko
V
V
Abusamhadneh
E
E
Finley
N
N
Li
G
G
Dvoretsky
A
A
Rance
M
M
Solaro
R J
RJ
Rosevear
P R
PR
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
D046911:Macromolecular Substances; D009282:Naphthalenesulfonates; D019209:Troponin C; D019210:Troponin I; C011488:IAANS; D014508:Urea; D002118:Calcium