The C-Terminus of Troponin T Is Essential for Maintaining the Inactive State of Regulated Actin
The C-Terminus of Troponin T Is Essential for Maintaining the Inactive State of Regulated Actin
复制标题
DOI：
10.1016/j.bpj.2012.04.037
复制
发表时间：
2012-06-06
影响因子：
3.4
通讯作者：
Chalovich, Joseph M.
中科院分区：
文献类型：
--
作者：
Franklin, Andrew J.;Baxley, Tamatha;Chalovich, Joseph M.
横纹肌收缩由肌动蛋白结合蛋白原肌球蛋白和肌钙蛋白调节。这些蛋白质的缺陷会导致肌病和心肌病。心肌肌钙蛋白 T 14 个 C 端残基的缺失会导致肥厚型心肌病。我们之前表明，含有 Delta 14 TnT 的调节肌动蛋白比野生型调节肌动蛋白更容易被激活。我们建议非活性（阻断）、中间（封闭或钙）和活性（开放或肌球蛋白）状态之间的平衡转移到活性状态。此外，我们现在表明，这种受调节的肌动蛋白丝不能进入非活性或阻断状态。含有 Delta 14 TnT 的调节肌动蛋白在缺乏 Ca2+ 的情况下具有 ATP 酶活性，该活性高于野生型丝，但远低于完全活性率。 S1-ATP 从含有 Delta 14 TnT 和 acrylodan 标记的原肌球蛋白的调节肌动蛋白丝中快速解离，没有显示出进入非活性状态的荧光增加特征。用有利于非活性状态的 S45E TnI 替换野生型 TnI 并不能恢复荧光变化。我们得出的结论是，TnT 在形成受调节肌动蛋白的非活性状态方面具有以前未被认识到的作用。
Striated muscle contraction is regulated by the actin binding proteins tropomyosin and troponin. Defects in these proteins lead to myopathies and cardiomyopathies. Deletion of the 14 C-terminal residues of cardiac troponin T leads to hypertrophic cardiomyopathy. We showed earlier that regulated actin containing Delta 14 TnT was more readily activated than wild-type regulated actin. We suggested that the equilibria among the inactive (blocked), intermediate (closed or calcium), and active (open or myosin) states was shifted to the active state. We now show that, in addition, such regulated actin filaments cannot enter the inactive or blocked state. Regulated actin containing Delta 14 TnT had ATPase activities in the absence of Ca2+ that were higher than wild-type filaments but far below the fully active rate. The rapid dissociation of S1-ATP from regulated actin filaments containing Delta 14 TnT and acrylodan-labeled tropomyosin did not show the fluorescence increase characteristic of moving to the inactive state. Replacing wild-type TnI with S45E TnI, that favors the inactive state, did not restore the fluorescence change. We conclude that TnT has a previously unrecognized role in forming the inactive state of regulated actin.