Steric-model for activation of muscle thin filaments
Steric-model for activation of muscle thin filaments
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DOI：
10.1006/jmbi.1996.0800
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发表时间：
1997-02-14
影响因子：
5.6
通讯作者：
Lehman, W
中科院分区：
文献类型：
--
作者：
Vibert, P;Craig, R;Lehman, W
肌肉收缩的细肌丝相关调节的结构基础尚未被了解。在此我们利用电子显微镜和三维图像重建来观察Ca2 +以及肌球蛋白头部结合对细肌丝结构，尤其是对原肌球蛋白位置的影响。在乙二醇双（2 - 氨基乙醚）四乙酸（EGTA）中分离出的细肌丝分别用Ca2 +或肌球蛋白头部（S - 1）处理并进行负染。在电子显微照片中原肌球蛋白链可直接被观察到，并且在重建图像中明显呈现出依赖于EGTA、Ca2 +和S - 1的不同位置。通过将重建图像与F - 肌动蛋白的原子模型拟合，在每种条件下确定了位于原肌球蛋白下方的肌动蛋白上的氨基酸簇。在有Ca2 +存在的情况下，原肌球蛋白从其低Ca2 +位置移动了25度，暴露出大部分（但不是全部）先前被阻断的肌球蛋白结合位点。细肌丝被肌球蛋白头部饱和后，原肌球蛋白位置又进一步移动了10度，从而暴露出整个肌球蛋白结合位点。因此我们的结果表明，通过空间位阻的逆转来完全激活细肌丝需要Ca2 +以及肌球蛋白头部按顺序的结合。通过使用部分被头部修饰的细肌丝，原肌球蛋白的移动被证明是协同的，并且直接估算出了肌动蛋白 - 原肌球蛋白协同单位的大小。我们的结果为先前基于肌动蛋白 - 肌球蛋白相互作用动力学的细肌丝激活模型提供了直接的结构支持。（C）1997学术出版社有限公司
The structural basis of thin filament-linked regulation of muscle contraction is not yet understood. Here we have used electron microscopy and three-dimensional image reconstruction to observe the effects of Ca2+ and myosin head binding on thin filament structure, especially on the position of tropomyosin. Thin filaments isolated in EGTA were treated with Ca2+ or myosin heads (S-1) and negatively stained. Tropomyosin strands were directly visualized in electron micrographs, and distinct EGTA, Ca2+ and S-1-dependent positions were apparent in reconstructions. By fitting reconstructions to the atomic model of F-actin, clusters of amino acids on actin lying beneath tropomyosin were defined under each set of conditions. In the presence of Ca2+, tropomyosin moved 25 degrees away from its low Ca2+ position, exposing most, but not all, of the previously blocked myosin-binding sites. Saturation of filaments with myosin heads produced a further 10 degrees shift in tropomyosin position thereby exposing the entire myosin-binding site. Our results thus suggest that full switching-on of thin filaments by reversal of steric-blocking requires both Ca2+ and the binding of myosin heads, acting in sequence. By using filaments which were partially decorated with heads, tropomyosin movement was shown to be cooperative, and the size of the actin-tropomyosin cooperative unit was estimated directly. Our results provide direct structural support for previous models of thin filament activation based on kinetics of actin-myosin interaction. (C) 1997 Academic Press Limited.