A Dilated Cardiomyopathy Troponin C Mutation Lowers Contractile Force by Reducing Strong Myosin-Actin Binding
A Dilated Cardiomyopathy Troponin C Mutation Lowers Contractile Force by Reducing Strong Myosin-Actin Binding
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DOI：
10.1074/jbc.m109.064105
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发表时间：
2010-06-04
影响因子：
4.8
通讯作者：
Potter, James D.
中科院分区：
文献类型：
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作者：
Dweck, David;Reynaldo, Daniel P.;Potter, James D.
在这项研究中，我们探讨了与扩张型心肌病相关的心肌肌钙蛋白C（CTnC）双突变（E59 D/D 75 Y）降低心肌钙激活最大张力的机制。研究单个突变体（即E59 D或D 75 Y）表明，D 75 Y，而不是E59 D，导致肌钙蛋白复合物中CTnC的钙亲和力降低，调节细丝（RTF），以及心肌制备物中收缩和ATP酶的Ca 2+敏感性降低。然而，D 75 Y和E59 D都需要降低肌动球蛋白ATP酶活性和肌纤维中的最大力，表明E59 D增强了D 75 Y的作用。力/ATP酶的部分降低可能是由于CTnC和心肌肌钙蛋白T之间的相互作用缺陷，已知这是ATP酶激活所必需的。力/ATP酶降低的另一种机制来自肌球蛋白亚片段-1（S-1）与RTF结合化学计量的测量。使用野生型RTF，每摩尔丝（7个肌动蛋白）结合4.8mol S-1，而使用E59 D/D 75 Y RTF，结合位点的数量减少了23%至3.7。总之，这些结果表明，力和ATP酶激活的减少可能是由于一个薄的细丝构象，促进更少的可访问的S-1结合位点。在没有任何家族分离数据的情况下，这里提出的功能结果支持这可能是一个扩张型心肌病引起的突变的概念。
In this study we explore the mechanisms by which a double mutation (E59D/D75Y) in cardiac troponin C (CTnC) associated with dilated cardiomyopathy reduces the Ca2+-activated maximal tension of cardiac muscle. Studying the single mutants (i.e. E59D or D75Y) indicates that D75Y, but not E59D, causes a reduction in the calcium affinity of CTnC in troponin complex, regulated thin filaments (RTF), and the Ca2+ sensitivity of contraction and ATPase in cardiac muscle preparations. However, both D75Y and E59D are required to reduce the actomyosin ATPase activity and maximal force in muscle fibers, indicating that E59D enhances the effects of D75Y. Part of the reduction in force/ATPase may be due to a defect in the interactions between CTnC and cardiac troponin T, which are known to be necessary for ATPase activation. An additional mechanism for the reduction in force/ATPase comes from measurements of the binding stoichiometry of myosin subfragment-1 (S-1) to the RTF. Using wild type RTFs, 4.8 mol S-1 was bound per mol filament (seven actins), whereas with E59D/D75Y RTFs, the number of binding sites was reduced by similar to 23% to 3.7. Altogether, these results suggest that the reduction in force and ATPase activation is possibly due to a thin filament conformation that promotes fewer accessible S-1-binding sites. In the absence of any family segregation data, the functional results presented here support the concept that this is likely a dilated cardiomyopathy-causing mutation.