title: Interaction of bepridil with the cardiac troponin C/troponin I complex.
abstract: We have investigated the binding of bepridil to calcium-saturated cardiac troponin C in a cardiac troponin C/troponin I complex. Nuclear magnetic resonance spectroscopy and [(15)N,(2)H]cardiac troponin C permitted the mapping of bepridil-induced amide proton chemical shifts. A single bepridil-binding site in the regulatory domain was found with an affinity constant of approximately 140 microM(-1). In the presence of cardiac troponin I, bepridil binding to the C domain of cardiac troponin C was not detected. The pattern of bepridil-induced chemical shifts is consistent with stabilization of more open regulatory domain conformational states. A similar pattern of chemical shift perturbations was observed for interaction of the troponin I cardiac-specific amino-terminus with the cardiac troponin C regulatory domain. These results suggest that both bepridil and the cardiac-specific amino-terminus may mediate an increase in calcium affinity by interacting with and stabilizing open regulatory domain conformations. Chemical shift mapping suggests a possible role for inactive calcium-binding site I in the modulation of calcium affinity.
authors.affiliation: Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, College of Medicine, 231 Albert B. Sabin Way, Cincinnati, OH 45267, USA.
authors.forename: E
authors.initials: E
authors.lastname: Abusamhadneh
authors.forename: M B
authors.initials: MB
authors.lastname: Abbott
authors.forename: A
authors.initials: A
authors.lastname: Dvoretsky
authors.forename: N
authors.initials: N
authors.lastname: Finley
authors.forename: S
authors.initials: S
authors.lastname: Sasi
authors.forename: P R
authors.initials: PR
authors.lastname: Rosevear
mesh_terms: D015764:Bepridil / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding; D011487:Protein Conformation; D019209:Troponin C / Q000737:chemistry / Q000378:metabolism*; D019210:Troponin I / Q000737:chemistry / Q000378:metabolism*
chemical_list: D019209:Troponin C; D019210:Troponin I; D015764:Bepridil; D002118:Calcium