title: Troponin structure: its modulation by Ca(2+) and phosphorylation studied by molecular dynamics simulations.
abstract: The only available crystal structure of the human cardiac troponin molecule (cTn) in the Ca(2+) activated state does not include crucial segments, including the N-terminus of the cTn inhibitory subunit (cTnI). We have applied all-atom molecular dynamics (MD) simulations to study the structure and dynamics of cTn, both in the unphosphorylated and bis-phosphorylated states at Ser23/Ser24 of cTnI. We performed multiple microsecond MD simulations of wild type (WT) cTn (6, 5 μs) and bisphosphorylated (SP23/SP24) cTn (9 μs) on a 419 amino acid cTn model containing human sequence cTnC (1-161), cTnI (1-171) and cTnT (212-298), including residues not present in the crystal structure. We have compared our results to previous computational studies, and proven that longer simulations and a water box of at least 25 Å are needed to sample the interesting conformational shifts both in the native and bis-phosphorylated states. As a consequence of the introduction into the model of the C-terminus of cTnT that was missing in previous studies, cTnC-cTnI interactions that are responsible for the cTn dynamics are altered. We have also shown that phosphorylation does not increase cTn fluctuations, and its effects on the protein-protein interaction profiles cannot be assessed in a significant way. Finally, we propose that phosphorylation could provoke a loss of Ca(2+) by stabilizing out-of-coordination distances of the cTnC's EF hand II residues, and in particular Ser 69.
authors.affiliation: Department of Chemistry, Institute of Chemical Biology, Imperial College London, SW7 2AZ, UK. i.gould@imperial.ac.uk.
authors.forename: Juan Eiros
authors.initials: JE
authors.lastname: Zamora
authors.affiliation: National Heart & Lung Institute, Myocardial Function Section, Imperial College London, W12 0NN, UK.
authors.forename: Maria
authors.initials: M
authors.lastname: Papadaki
authors.affiliation: National Heart & Lung Institute, Myocardial Function Section, Imperial College London, W12 0NN, UK.
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Messer
authors.affiliation: National Heart & Lung Institute, Myocardial Function Section, Imperial College London, W12 0NN, UK.
authors.forename: Steven B
authors.initials: SB
authors.lastname: Marston
authors.affiliation: Department of Chemistry, Institute of Chemical Biology, Imperial College London, SW7 2AZ, UK. i.gould@imperial.ac.uk.
authors.forename: Ian R
authors.initials: IR
authors.lastname: Gould
mesh_terms: D002118:Calcium; D006801:Humans; D056004:Molecular Dynamics Simulation; D010766:Phosphorylation; D019210:Troponin I / Q000737:chemistry*
chemical_list: D019210:Troponin I; D002118:Calcium