Structural basis for Ca2+-regulated muscle relaxation at interaction sites of troponin with actin and tropomyosin
Structural basis for Ca2+-regulated muscle relaxation at interaction sites of troponin with actin and tropomyosin
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DOI：
10.1016/j.jmb.2005.06.067
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发表时间：
2005-09-09
影响因子：
5.6
通讯作者：
Wakabayashi, T
中科院分区：
文献类型：
--
作者：
Murakami, K;Yumoto, F;Wakabayashi, T
肌动蛋白丝上的肌钙蛋白和原肌球蛋白构成Ca2+敏感开关，通过肌动蛋白细丝内的一系列构象变化调节脊椎动物横纹肌的收缩。肌钙蛋白由三个亚基组成：抑制亚基（TnI）， Ca2+结合亚基（TnC）和原肌球蛋白结合亚基（TnT）。Ca2+结合TnC被认为削弱了肌钙蛋白和肌动蛋白之间的相互作用，并引发了肌钙蛋白复合物的大构象变化。然而，肌钙蛋白的肌动蛋白结合位点的原子细节尚未确定。用重组鸡骨骼TnI、TnC和TnT(2) （TnT的c端区）构建了三元肌钙蛋白复合物，其中只有TnI被统一标记为N-15和/或C-13。通过核磁共振波谱法，确定了肌钙蛋白三元配合物（52 kDa）中“可移动的”肌动蛋白结合结构域（类似6.1 kDa）的溶液结构。移动结构域似乎独立于肌钙蛋白的核心结构域翻滚。Ca2+诱导的化学位移和线形变化表明，在高Ca2+浓度下，其翻滚更受限制。肌动蛋白和肌钙蛋白移动结构域之间相互作用的原子细节被定义为低[Ca2+]细丝的对接图，从而确定了TnI残基133的3D位置，这是纳入现有信息的重要里程碑。这使得肌钙蛋白的整个球形头部区域在低Ca2+浓度下进入细丝低温电镜图的独特对接。由此产生的原子模型表明，肌钙蛋白与肌动蛋白静电相互作用，引起原肌球蛋白的移位，从而实现肌肉松弛。一个重要的特征是肌钙蛋白的盘绕区推动原肌凝蛋白在低Ca2+浓度。此外，肌凝蛋白和肌动蛋白丝上的移动结构域之间的关系表明，后者作为一个故障安全锁存器。(c) 2005 Elsevier Ltd版权所有。
Troponin and tropomyosin on actin filaments constitute a Ca2+-sensitive switch that regulates the contraction of vertebrate striated muscle through a series of conformational changes within the actin-based thin filament. Troponin consists of three subunits: an inhibitory subunit (TnI), a Ca2+-binding subunit (TnC), and a tropomyosin-binding subunit (TnT). Ca2+-binding to TnC is believed to weaken interactions between troponin and actin, and triggers a large conformational change of the troponin complex. However, the atomic details of the actin-binding sites of troponin have not been determined. Ternary troponin complexes have been reconstituted from recombinant chicken skeletal TnI, TnC, and TnT(2) (the C-terminal region of TnT), among which only TnI was uniformly labelled with N-15 and/or C-13. By applying NMR spectroscopy, the solution structures of a "mobile" actin-binding domain (similar to 6.1 kDa) in the troponin ternary complex (similar to 52 kDa) were determined. The mobile domain appears to tumble independently of the core domain of troponin. Ca2+-induced changes in the chemical shift and line shape suggested that its tumbling was more restricted at high Ca2+ concentrations. The atomic details of interactions between actin and the mobile domain of troponin were defined de docking map of thin filament at low [Ca2+] This allowed the determination of the 3D position of residue 133 of TnI, which has been an important landmark to incorporate the available information. This enabled unique docking of the entire globular head region of troponin into the thin filament cryo-EM map at a low Ca2+ concentration. The resultant atomic model suggests that troponin interacted electrostatically with actin and caused the shift of tropomyosin to achieve muscle relaxation. An important feature is that the coiled-coil region of troponin pushed tropomyosin at a low Ca2+ concentration. Moreover, the relationship between myosin and the mobile domain on actin filaments suggests that the latter works as a fail-safe latch. (c) 2005 Elsevier Ltd. All rights reserved.