Ca2+ causes release of myosin heads from the thick filament surface on the milliseconds time scale.
Ca2+ causes release of myosin heads from the thick filament surface on the milliseconds time scale.
复制标题
Ca2 导致肌球蛋白头在毫秒时间尺度上从粗肌丝表面释放。
DOI：
10.1016/s0022-2836(03)00098-6
复制
发表时间：
2003
影响因子：
5.6
通讯作者：
Craig,Roger
中科院分区：
文献类型：
--
作者：
Zhao,Fa-Qing;Craig,Roger
我们已经使用电子显微镜来研究肌球蛋白丝被激活时，由Ca 2+引起的结构变化。负染色显示，当钙离子结合到放松的钙离子调节肌球蛋白丝的头部，螺旋有序的肌球蛋白头变得无序，并进一步从丝表面的项目。未染色，冷冻水合标本的冷冻电子显微镜支持这一发现，并表明，无序是可逆的去除Ca 2+。因此，结构变化是Ca 2+单独结合的结果，而不是染色的伪影。两种技术的比较表明，负染色保留了由Ca 2+结合诱导的结构。因此，我们使用时间分辨负染色技术来确定结构变化的时间尺度。在加入Ca ~（2+）的30 ms内观察到完全无序，并在10 ms内开始发生，表明这种变化发生在生理时间尺度上。与单个重酶解肌球蛋白分子的研究比较表明，Ca 2+结合诱导的肌球蛋白头部流动性增加是我们观察到的肌丝结构变化的基础。我们的结论是，松动的阵列的肌球蛋白头上发生的激活是真实的和生理的，它可能起到使激活的肌球蛋白头更自由地接触肌动蛋白丝在肌肉收缩。
We have used electron microscopy to study the structural changes induced when myosin filaments are activated by Ca2+. Negative staining reveals that when Ca2+binds to the heads of relaxed Ca2+-regulated myosin filaments, the helically ordered myosin heads become disordered and project further from the filament surface. Cryo-electron microscopy of unstained, frozen-hydrated specimens supports this finding, and shows that disordering is reversible on removal of Ca2+. The structural change is thus a result of Ca2+binding alone and not an artifact of staining. Comparison of the two techniques suggests that negative staining preserves the structure induced by Ca2+-binding. We therefore used a time-resolved negative staining technique to determine the time scale of the structural change. Full disordering was observed within 30ms of Ca2+addition, and had started to occur within 10ms, showing that the change occurs on the physiological time scale. Comparison with studies of single heavy meromyosin molecules suggests that an increased mobility of myosin heads induced by Ca2+binding underlies the changes in filament structure that we observe. We conclude that the loosening of the array of myosin heads that occurs on activation is real and physiological; it may function to make activated myosin heads freer to contact actin filaments during muscle contraction.