Journal of Muscle Research and Cell Motility

, Volume 36, Issue 2, pp 169–181 | Cite as

Dissecting human skeletal muscle troponin proteoforms by top-down mass spectrometry

  • Yi-Chen Chen
  • Marius P. Sumandea
  • Lars Larsson
  • Richard L. Moss
  • Ying Ge
Original Paper


Skeletal muscles are the most abundant tissues in the human body. They are composed of a heterogeneous collection of muscle fibers that perform various functions. Skeletal muscle troponin (sTn) regulates skeletal muscle contraction and relaxation. sTn consists of 3 subunits, troponin I (TnI), troponin T (TnT), and troponin C (TnC). TnI inhibits the actomyosin Mg2+-ATPase, TnC binds Ca2+, and TnT is the tropomyosin (Tm)-binding subunit. The cardiac and skeletal isoforms of Tn share many similarities but the roles of modifications of Tn in the two muscles may differ. The modifications of cardiac Tn are known to alter muscle contractility and have been well-characterized. However, the modification status of sTn remains unclear. Here, we have employed top-down mass spectrometry (MS) to decipher the modifications of human sTnT and sTnI. We have extensively characterized sTnT and sTnI proteoforms, including alternatively spliced isoforms and post-translationally modified forms, found in human skeletal muscle with high mass accuracy and comprehensive sequence coverage. Moreover, we have localized the phosphorylation site of slow sTnT isoform III to Ser1 by tandem MS with electron capture dissociation. This is the first study to comprehensively characterize human sTn and also the first to identify the basal phosphorylation site for human sTnT by top-down MS.


Muscle contraction Myofilament Proteomics Fourier transform mass spectrometry Electron capture dissociation 



Skeletal muscle troponin


Fast skeletal muscle troponin


Slow skeletal muscle troponin


Troponin I


Troponin C


Troponin T




Mass spectrometry


Post-translational modifications


Collisionally activated dissociation


Electron capture dissociation


Fourier transform ion cyclotron resonance


Electrospray ionization


Molecular weights


Protein kinase A



We would like to thank Ying-Hua (Edith) Chang and Ying (Lynn) Peng for helpful discussions, and Zachery Gregorich for critical reading and editing of the manuscript. We would like to acknowledge National Institutes of Health Grants R01HL096971 and R01HL109810 (to YG). We would also like to thank the Wisconsin Partnership Program for the establishment of UW Human Proteomics Program Mass Spectrometry Facility.

Supplementary material

10974_2015_9404_MOESM1_ESM.pdf (1.1 mb)
Supplementary material 1 (PDF 1115 kb)


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Copyright information

© Springer International Publishing Switzerland 2015

Authors and Affiliations

  • Yi-Chen Chen
    • 1
    • 2
    • 3
  • Marius P. Sumandea
    • 4
  • Lars Larsson
    • 5
  • Richard L. Moss
    • 1
    • 3
  • Ying Ge
    • 1
    • 2
    • 3
  1. 1.Department of Cell and Regenerative BiologyUniversity of Wisconsin-MadisonMadisonUSA
  2. 2.Department of ChemistryUniversity of Wisconsin-MadisonMadisonUSA
  3. 3.Human Proteomics ProgramUniversity of Wisconsin-MadisonMadisonUSA
  4. 4.Eli Lily and CompanyLilly Corporate CenterIndianapolisUSA
  5. 5.Department of Physiology and Pharmacology, Department of Clinical NeuroscienceKarolinska InstitutetStockholmSweden

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