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首页> 外文期刊>Journal of Molecular Biology >The tropomyosin binding region of cardiac troponin T modulates crossbridge recruitment dynamics in rat cardiac muscle fibers
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The tropomyosin binding region of cardiac troponin T modulates crossbridge recruitment dynamics in rat cardiac muscle fibers

机译：心肌肌钙蛋白T的原肌球蛋白结合区调节大鼠心肌纤维中的跨桥募集动力学

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摘要

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 (RfsT1or 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 (E0) decreased by ～33% and the speed of XB recruitment (b) increased by ～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.
机译：心肌包括动态相互作用的成分，这些成分使用变构/合作机制产生独特的心脏特异性属性。在这种变构/合作机制中，必不可少的蛋白是心肌肌钙蛋白T（cTnT），其中央区域（CR）和T2区与快速骨骼肌肌钙蛋白T（fsTnT）明显不同。为了了解此类序列异质性的生物学意义，我们用大鼠fsTnT的对应物（RfsT1或RfsT2）替换了大鼠cTnT的T1或T2域（RcT1或RcT2），以生成RfsT1-RcT2和RcT1-RfsT2重组蛋白。除了收缩功能测量外，通过将募集失真模型拟合到小幅度（0.5％）肌肉长度变化的力响应，还可以捕获RfsT1-RcT2-和RcT1-RfsT2重构的大鼠心肌纤维的动态特征。 RfsT1-RcT2纤维的张力降低40％，ATPase活性降低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（E0）的增加幅度降低了〜33％，XB募集（b）的速度提高了〜100％。我们的数据表明：（1）cTnT的CR调节XB募集动力学; （2）cTnT的N末端区域对CR调节XB募集动力学的能力具有协同作用; （3）T2区域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的共同作用以及cTnT N末端对CR-原肌球蛋白相互作用的调节作用可能导致出现一种独特的特性，该特性可以将收缩动态调节至心率。

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