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Li MX, Gelozia S, Danmaliki GI, Wen Y, Liu PB, Lemieux MJ, West FG, Sykes BD, Hwang PM. The calcium sensitizer drug MCI-154 binds the structural C-terminal domain of cardiac troponin C. Biochem Biophys Rep 2018; 16:145-151. [PMID: 30417133 PMCID: PMC6218639 DOI: 10.1016/j.bbrep.2018.10.012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2018] [Revised: 10/12/2018] [Accepted: 10/19/2018] [Indexed: 11/27/2022] Open
Abstract
The compound MCI-154 was previously shown to increase the calcium sensitivity of cardiac muscle contraction. Using solution NMR spectroscopy, we demonstrate that MCI-154 interacts with the calcium-sensing subunit of the cardiac troponin complex, cardiac troponin C (cTnC). Surprisingly, however, it binds only to the structural C-terminal domain of cTnC (cCTnC), and not to the regulatory N-terminal domain (cNTnC) that determines the calcium sensitivity of cardiac muscle. Physiologically, cTnC is always bound to cardiac troponin I (cTnI), so we examined its interaction with MCI-154 in the presence of two soluble constructs, cTnI1–77 and cTnI135–209, which contain all of the segments of cTnI known to interact with cTnC. Neither the cTnC-cTnI1–77 complex nor the cTnC-cTnI135–209 complex binds to MCI-154. Since residues 39–60 of cTnI are known to bind tightly to the cCTnC domain to form a structured core that is invariant throughout the cardiac cycle, we conclude that MCI-154 does not bind to cTnC when it is part of the intact cardiac troponin complex. Thus, MCI-154 likely exerts its calcium sensitizing effect by interacting with a target other than cardiac troponin. MCI-154 is a small molecule calcium sensitizer in cardiac muscle. The N-domain of cardiac troponin C controls calcium sensitivity in cardiac muscle. MCI-154 binds weakly to the promiscuous C-terminal domain of troponin C. Cardiac troponin C does not bind MCI-154 in the presence of troponin I. MCI-154 does not exert its calcium sensitizing effect directly through troponin C.
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Affiliation(s)
- Monica X Li
- Department of Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2R3
| | - Shorena Gelozia
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
| | - Gaddafi I Danmaliki
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | - Yurong Wen
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.,School of Life Science and Technology, Xi'an Jiaotong University, Xi'an, China
| | - Philip B Liu
- Department of Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2R3
| | - M Joanne Lemieux
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | - Frederick G West
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
| | - Brian D Sykes
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | - Peter M Hwang
- Department of Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2R3.,Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
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Papadaki M, Marston SB. The Importance of Intrinsically Disordered Segments of Cardiac Troponin in Modulating Function by Phosphorylation and Disease-Causing Mutations. Front Physiol 2016; 7:508. [PMID: 27853436 PMCID: PMC5089987 DOI: 10.3389/fphys.2016.00508] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Accepted: 10/17/2016] [Indexed: 11/18/2022] Open
Abstract
Troponin plays a central role in regulation of muscle contraction. It is the Ca2+ switch of striated muscles including the heart and in the cardiac muscle it is physiologically modulated by PKA-dependent phosphorylation at Ser22 and 23. Many cardiomyopathy-related mutations affect Ca2+ regulation and/or disrupt the relationship between Ca2+ binding and phosphorylation. Unlike the mechanism of heart activation, the modulation of Ca2+-sensitivity by phosphorylation of the cardiac specific N-terminal segment of TnI (1–30) is structurally subtle and has proven hard to investigate. The crystal structure of cardiac troponin describes only the relatively stable core of the molecule and the crucial mobile parts of the molecule are missing including TnI C-terminal region, TnI (1–30), TnI (134–149) (“inhibitory” peptide) and the C-terminal 28 amino acids of TnT that are intrinsically disordered. Recent studies have been performed to answer this matter by building structural models of cardiac troponin in phosphorylated and dephosphorylated states based on peptide NMR studies. Now these have been updated by more recent concepts derived from molecular dynamic simulations treating troponin as a dynamic structure. The emerging model confirms the stable core structure of troponin and the mobile structure of the intrinsically disordered segments. We will discuss how we can describe these segments in terms of dynamic transitions between a small number of states, with the probability distributions being altered by phosphorylation and by HCM or DCM-related mutations that can explain how Ca2+-sensitivity is modulated by phosphorylation and the effects of mutations.
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Affiliation(s)
- Maria Papadaki
- Department of Cell and Molecular Physiology, Loyola University of Chicago Maywood, IL, USA
| | - Steven B Marston
- Myocardial Function, National Heart and Lung Institute, Imperial College London London, UK
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