title: Modulation of cardiac troponin C-cardiac troponin I regulatory interactions by the amino-terminus of cardiac troponin I.
abstract: Multidimensional heteronuclear magnetic resonance studies of the cardiac troponin C/troponin I(1-80)/troponin I(129-166) complex demonstrated that cardiac troponin I(129-166), corresponding to the adjacent inhibitory and regulatory regions, interacts with and induces an opening of the cardiac troponin C regulatory domain. Chemical shift perturbation mapping and (15)N transverse relaxation rates for intact cardiac troponin C bound to either cardiac troponin I(1-80)/troponin I(129-166) or troponin I(1-167) suggested that troponin I residues 81-128 do not interact strongly with troponin C but likely serve to modulate the interaction of troponin I(129-166) with the cardiac troponin C regulatory domain. Chemical shift perturbations due to troponin I(129-166) binding the cardiac troponin C/troponin I(1-80) complex correlate with partial opening of the cardiac troponin C regulatory domain previously demonstrated by distance measurements using fluorescence methodologies. Fluorescence emission from cardiac troponin C(F20W/N51C)(AEDANS) complexed to cardiac troponin I(1-80) was used to monitor binding of cardiac troponin I(129-166) to the regulatory domain of cardiac troponin C. The apparent K(d) for cardiac troponin I(129-166) binding to cardiac troponin C/troponin I(1-80) was 43.3 +/- 3.2 microM. After bisphosphorylation of cardiac troponin I(1-80) the apparent K(d) increased to 59.1 +/- 1.3 microM. Thus, phosphorylation of the cardiac-specific N-terminus of troponin I reduces the apparent binding affinity of the regulatory domain of cardiac troponin C for cardiac troponin I(129-166) and provides further evidence for beta-adrenergic modulation of troponin Ca(2+) sensitivity through a direct interaction between the cardiac-specific amino-terminus of troponin I and the cardiac troponin C regulatory domain.
authors.affiliation: Department of Molecular Genetics, Biochemistry, and Microbiology, College of Medicine, University of Cincinnati, Cincinnati, Ohio 45267, USA.
authors.forename: M B
authors.initials: MB
authors.lastname: Abbott
authors.forename: W J
authors.initials: WJ
authors.lastname: Dong
authors.forename: A
authors.initials: A
authors.lastname: Dvoretsky
authors.forename: B
authors.initials: B
authors.lastname: DaGue
authors.forename: R M
authors.initials: RM
authors.lastname: Caprioli
authors.forename: H C
authors.initials: HC
authors.lastname: Cheung
authors.forename: P R
authors.initials: PR
authors.lastname: Rosevear
mesh_terms: D000595:Amino Acid Sequence; D004735:Energy Transfer; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000502:physiology; D009206:Myocardium / Q000378:metabolism*; D009587:Nitrogen Isotopes; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011522:Protons; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D019209:Troponin C / Q000737:chemistry / Q000378:metabolism*; D019210:Troponin I / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D009587:Nitrogen Isotopes; D010446:Peptide Fragments; D011522:Protons; D019209:Troponin C; D019210:Troponin I