The Tropomyosin Binding Region of Cardiac Troponin T Modulates Crossbridge Recruitment Dynamics in Rat Cardiac Muscle Fibers
The Tropomyosin Binding Region of Cardiac Troponin T Modulates Crossbridge Recruitment Dynamics in Rat Cardiac Muscle Fibers
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DOI：
10.1016/j.jmb.2013.01.028
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发表时间：
2013-05-13
影响因子：
5.6
通讯作者：
Chandra, Murali
中科院分区：
文献类型：
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作者：
Gollapudi, Sampath K.;Gallon, Clare E.;Chandra, Murali
心肌由动态相互作用的成分组成，这些成分使用变构/协作机制来产生独特的心脏特异性特性。这种变构/协作机制中的一个重要蛋白质是心肌肌钙蛋白 T (cTnT)，其中心区 (CR) 和 T2 区与快骨骼肌肌钙蛋白 T (fsTnT) 显着不同。为了了解这种序列异质性的生物学意义，我们将大鼠 cTnT（RcT1 或 RcT2）的 T1 或 T2 结构域替换为大鼠 fsTnT（RfsT1 或 RfsT2）的对应结构域，以生成 RfsT1-RcT2 和 RcT1-RfsT2 重组蛋白。除了收缩功能测量之外，还通过将募集扭曲模型拟合到小幅度（0.5％）肌肉长度变化的力响应来捕获RfsT1-RcT2-和RcT1-RfsT2-重建的大鼠心肌纤维的动态特征。 RfsT1-RcT2 纤维的张力降低了 40%，ATP 酶活性降低了 44%，但 RcT1-RfsT2 纤维不受影响。在 RfsT1-RcT2 纤维中，长度介导的跨桥 (XB) 募集 (E-0) 增加幅度降低了约 33%，XB 募集速度 (b) 增加了约 100%。我们的数据表明：（1）cTnT 的 CR 调节 XB 招募动态； (2) cTnT的N端末端区域对CR调节XB募集动态的能力具有协同作用； (3) T2 区对于调节心脏细丝的 Ca2+ 调节很重要。 CR-原肌球蛋白相互作用和 cTnT N 末端对 CR-原肌球蛋白相互作用的调节作用的综合作用可能导致出现一种独特的特性，可以根据心率调节收缩动力学。 (C) 2013 Elsevier Ltd. 保留所有权利。
The cardiac muscle comprises dynamically interacting components that use allosteric/cooperative mechanisms to yield unique heart-specific properties. An essential protein in this allosteric/cooperative mechanism is cardiac muscle troponin T (cTnT), the central region (CR) and the T2 region of which differ significantly from those of fast skeletal muscle troponin T (fsTnT). To understand the biological significance of such sequence heterogeneity, we replaced the T1 or T2 domain of rat cTnT (RcT1 or RcT2) with its counterpart from rat fsTnT (RfsT1 or RfsT2) to generate RfsT1-RcT2 and RcT1-RfsT2 recombinant proteins. In addition to contractile function measurements, dynamic features of RfsT1-RcT2- and RcT1-RfsT2-reconstituted rat cardiac muscle fibers were captured by fitting the recruitment-distortion model to the force response of small-amplitude (0.5%) muscle length changes. RfsT1-RcT2 fibers showed a 40% decrease in tension and a 44% decrease in ATPase activity, but RcT1-RfsT2 fibers were unaffected. The magnitude of length-mediated increase in crossbridge (XB) recruitment (E-0) decreased by similar to 33% and the speed of XB recruitment (b) increased by similar to 100% in RfsT1-RcT2 fibers. Our data suggest the following: (1) the CR of cTnT modulates XB recruitment dynamics; (2) the N-terminal end region of cTnT has a synergistic effect on the ability of the CR to modulate XB recruitment dynamics; (3) the T2 region is important for tuning the Ca2+ regulation of cardiac thin filaments. The combined effects of CR-tropomyosin interactions and the modulating effect of the N-terminal end of cTnT on CR-tropomyosin interactions may lead to the emergence of a unique property that tunes contractile dynamics to heart rates. (C) 2013 Elsevier Ltd. All rights reserved.