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

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          Abstract

          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 Mg(2+)-ATPase, TnC binds Ca(2+), 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.

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          Author and article information

          Journal
          J. Muscle Res. Cell. Motil.
          Journal of muscle research and cell motility
          Springer Nature America, Inc
          1573-2657
          0142-4319
          Apr 2015
          : 36
          : 2
          Affiliations
          [1 ] Department of Cell and Regenerative Biology, University of Wisconsin-Madison, 1300 University Ave., SMI 130, Madison, WI, 53706, USA.
          Article
          NIHMS657914
          10.1007/s10974-015-9404-6
          4427557
          25613324
          9005a068-935d-48cd-8d40-06b0c95063cb
          History

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