title: Bepridil opens the regulatory N-terminal lobe of cardiac troponin C.
abstract: Cardiac troponin C (cTnC) is the calcium-dependent switch for contraction in heart muscle and a potential target for drugs in the therapy of congestive heart failure. This calmodulin-like protein consists of two lobes connected by a central linker; each lobe contains two EF-hand domains. The regulatory N-terminal lobe of cTnC, unlike that of skeletal troponin C (sTnC), contains only one functional EF-hand and does not open fully upon the binding of Ca(2+). We have determined the crystal structure of cTnC, with three bound Ca(2+) ions, complexed with the calcium-sensitizer bepridil, to 2.15-A resolution. In contrast to apo- and 3Ca(2+)-cTnC, the drug-bound complex displays a fully open N-terminal lobe similar to the N-terminal lobes of 4Ca(2+)-sTnC and cTnC bound to a C-terminal fragment of cardiac troponin I (residues 147-163). The closing of the lobe is sterically hindered by one of the three bound bepridils. Our results provide a structural basis for the Ca(2+)-sensitizing effect of bepridil and reveal the details of a distinctive two-stage mechanism for Ca(2+) regulation by troponin C in cardiac muscle.
authors.affiliation: Biophysics and Structural Biology Program, Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, MA 02454-9110, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Li
authors.forename: M L
authors.initials: ML
authors.lastname: Love
authors.forename: J A
authors.initials: JA
authors.lastname: Putkey
authors.forename: C
authors.initials: C
authors.lastname: Cohen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015764:Bepridil / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002645:Chickens; D003460:Crystallization; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D019209:Troponin C / Q000737:chemistry* / Q000187:drug effects*; D019210:Troponin I / Q000737:chemistry / Q000378:metabolism
chemical_list: D019209:Troponin C; D019210:Troponin I; D015764:Bepridil; D002118:Calcium