Modulation of Cardiac Troponin C-cardiac Troponin I Regulatory Interactions by the Amino-Terminus of Cardiac Troponin I

Biochemistry. 2001 May 22;40(20):5992-6001. doi: 10.1021/bi0100642.


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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Energy Transfer
  • Molecular Sequence Data
  • Muscle Contraction / physiology
  • Myocardium / metabolism*
  • Nitrogen Isotopes
  • Nuclear Magnetic Resonance, Biomolecular / methods
  • Peptide Fragments / chemistry*
  • Peptide Fragments / metabolism
  • Phosphorylation
  • Protein Binding
  • Protein Conformation
  • Protein Structure, Tertiary
  • Protons
  • Spectrometry, Fluorescence
  • Thermodynamics
  • Troponin C / chemistry
  • Troponin C / metabolism*
  • Troponin I / chemistry*
  • Troponin I / metabolism*


  • Nitrogen Isotopes
  • Peptide Fragments
  • Protons
  • Troponin C
  • Troponin I