title: Interaction of levosimendan with cardiac troponin C in the presence of cardiac troponin I peptides.
abstract: The interaction between troponin C (TnC) and troponin I (TnI) is essential for the regulation of muscle contraction. There are several binding sites for TnI on TnC that are differentially occupied depending on the phase of the contraction/relaxation cycle. TnI and TnC interact in an antiparallel fashion with each other. The C-domain of cTnC and the N-domain region of cTnI(residues 33-70) always interact under physiological conditions, whereas the interaction between regulatory regions of TnC and TnI (residues 128-166) is calcium dependent. Previously, it has been shown that levosimendan, a calcium sensitizer used as a treatment for acute heart failure, can interact with both domains of isolated cTnC. To understand which interaction is relevant for the mechanism of calcium sensitization, we used a more complete troponin model obtained by complexing cTnI(32-79) and cTnI(128-180) with calcium-saturated cTnC(CS). The cTnI peptides bound to cTnC(CS) to form a 1:1:1 complex. The interaction of levosimendan with this complex was followed by 1H-(15)N heteronuclear correlation spectroscopy. It was clear that based on chemical shift changes, cTnI(32-79) blocked the levosimendan interaction sites on the C-domain, whereas cTnI(128-180) did not compete with levosimendan for the binding site on the N-domain. Hence, the effective binding site of levosimendan on cTnC resulting in the calcium-sensitizing effect is located in the regulatory domain (N-domain).
authors.affiliation: Structural Biology, Drug Discovery Technologies, Orion Pharma, P.O. Box 65, 02101 Espoo, Finland.
authors.forename: T
authors.initials: T
authors.lastname: Sorsa
authors.forename: P
authors.initials: P
authors.lastname: Pollesello
authors.forename: P
authors.initials: P
authors.lastname: Permi
authors.forename: T
authors.initials: T
authors.lastname: Drakenberg
authors.forename: I
authors.initials: I
authors.lastname: Kilpeläinen
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002316:Cardiotonic Agents / Q000378:metabolism*; D003545:Cysteine / Q000378:metabolism; D004347:Drug Interactions; D006801:Humans; D006835:Hydrazones / Q000378:metabolism*; D008958:Models, Molecular; D009200:Myocardial Contraction; D009587:Nitrogen Isotopes; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism*; D017354:Point Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011724:Pyridazines / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D000077464:Simendan; D014316:Tritium; D019209:Troponin C / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019210:Troponin I / Q000737:chemistry* / Q000378:metabolism
chemical_list: D002316:Cardiotonic Agents; D006835:Hydrazones; D009587:Nitrogen Isotopes; D010446:Peptide Fragments; D011724:Pyridazines; D011994:Recombinant Proteins; D019209:Troponin C; D019210:Troponin I; D014316:Tritium; D000077464:Simendan; D003545:Cysteine; D002118:Calcium