Ca2+-induced switching of troponin and tropomyosin on actin filaments as revealed by electron cryo-microscopy
Ca2+-induced switching of troponin and tropomyosin on actin filaments as revealed by electron cryo-microscopy
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DOI：
10.1006/jmbi.2001.4598
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发表时间：
2001-04-27
影响因子：
5.6
通讯作者：
Wakabayashi, T
中科院分区：
文献类型：
--
作者：
Narita, A;Yasunaga, T;Wakabayashi, T
肌肉收缩受细胞内Ca 2+浓度的调节。在脊椎动物横纹肌中，肌动蛋白丝上的肌钙蛋白和原肌球蛋白构成控制收缩的Ca 2+敏感开关。Ca 2+与肌钙蛋白结合，并引发含肌动蛋白的细丝的一系列变化，导致与肌球蛋白的周期性相互作用，从而产生收缩。然而，肌钙蛋白相对于肌动蛋白和原肌球蛋白的精确位置以及其结构如何随Ca 2+变化尚未确定。为了理解调节机制，我们通过从电子冷冻显微镜确定细丝的三维结构来可视化肌钙蛋白的位置，而不施加螺旋对称性到类似于35埃的分辨率。在Ca 2+的情况下，肌钙蛋白的球形结构域是椭圆形的，并且位于肌动蛋白的内部结构域之上。在没有Ca 2+的情况下，肌钙蛋白的主体向外部域移动了大约30埃，并分叉，其中水平分支（肌钙蛋白臂）覆盖肌动蛋白的N和C末端区域。C-末端三分之一的原肌球蛋白向肌动蛋白的外部结构域移动了类似于35埃，支持空间阻断模型，然而令人惊讶的是，N-末端一半的原肌球蛋白的移动小于类似于12埃。因此，原肌球蛋白在没有Ca-2+的情况下发生差异性变化。与Ca 2+，原肌球蛋白完全位于内部域，从而允许更大的访问肌球蛋白的力量产生。通过将概率距离几何应用于荧光共振能量转移测量的数据来确定肌钙蛋白或原肌球蛋白特定位点上标记的荧光团的三维位置，从而促进了三维地图的解释。(C)北京：科学出版社.
Muscle contraction is regulated by the intracellular Ca2+ concentration. Ln vertebrate striated muscle, troponin and tropomyosin on actin filaments comprise a Ca2+-sensitive switch that controls contraction. Ca2+ binds to troponin and triggers a series of changes in actin-containing filaments that lead to cyclic interactions with myosin that generate contraction. However, the precise location of troponin relative to actin and tropomyosin and how its structure changes with Ca2+ have been not determined. To understand the regulatory mechanism, we visualized the location of troponin by determining the three-dimensional structure of thin filaments from electron cryo-micrographs without imposing helical symmetry to similar to 35 Angstrom resolution With Ca2+, the globular domain of troponin was gourd-shaped and was located over the inner domain of actin. Without Ca2+, the main body of troponin was shifted by similar to 30 Angstrom towards the outer domain and bifurcated, with a horizontal branch (troponin arm) covering the N and C-terminal regions of actin. The C-terminal one-third of tropomyosin shifted towards the outer domain of actin by similar to 35 Angstrom supporting the steric blocking model, however it is surprising that the N-terminal half of troyomyosin shifted less than similar to 12 Angstrom. Therefore tropomyosin shifted differentially without Ca-2+. With Ca2+, tropomyosin was located entirely over the inner domain thereby allowing greater access of myosin for force generation. The interpretation of three-dimensional maps was facilitated by determining the three-dimensional positions of fluorophores labelled on specific sites of troponin or tropomyosin by applying probabilistic distance geometry to data from fluorescence resonance energy transfer measurements. (C) 2001 Academic Press.