title: Drug binding to cardiac troponin C.
abstract: Compounds that sensitize cardiac muscle to Ca(2+) by intervening at the level of regulatory thin filament proteins would have potential therapeutic benefit in the treatment of myocardial infarctions. Two putative Ca(2+) sensitizers, EMD 57033 and levosimendan, are reported to bind to cardiac troponin C (cTnC). In this study, we use heteronuclear NMR techniques to study drug binding to [methyl-(13)C]methionine-labeled cTnC when free or when complexed with cardiac troponin I (cTnI). In the absence of Ca(2+), neither drug interacted with cTnC. In the presence of Ca(2+), one molecule of EMD 57033 bound specifically to the C-terminal domain of free cTnC. NMR and equilibrium dialysis failed to demonstrate binding of levosimendan to free cTnC, and the presence of levosimendan had no apparent effect on the Ca(2+) binding affinity of cTnC. Changes in the N-terminal methionine methyl chemical shifts in cTnC upon association with cTnI suggest that cTnI associates with the A-B helical interface and the N terminus of the central helix in cTnC. NMR experiments failed to show evidence of binding of levosimendan to the cTnC.cTnI complex. However, levosimendan covalently bound to a small percentage of free cTnC after prolonged incubation with the protein. These findings suggest that levosimendan exerts its positive inotropic effect by mechanisms that do not involve binding to cTnC.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Texas Medical School, Houston, Texas 77030, USA.
authors.forename: Q
authors.initials: Q
authors.lastname: Kleerekoper
authors.forename: J A
authors.initials: JA
authors.lastname: Putkey
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D006835:Hydrazones / Q000494:pharmacology; D051379:Mice; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000737:chemistry*; D011487:Protein Conformation; D011724:Pyridazines / Q000494:pharmacology; D011804:Quinolines / Q000494:pharmacology; D000077464:Simendan; D013829:Thiadiazines / Q000494:pharmacology; D019209:Troponin C / Q000737:chemistry / Q000378:metabolism*
chemical_list: D006835:Hydrazones; D011724:Pyridazines; D011804:Quinolines; D013829:Thiadiazines; D019209:Troponin C; C070609:EMD 53998; D000077464:Simendan; D002118:Calcium