The earliest molecular response to stretch of insect flight muscle as revealed by fast X-ray diffraction recording.
The earliest molecular response to stretch of insect flight muscle as revealed by fast X-ray diffraction recording.
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DOI：
10.1038/srep42272
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发表时间：
2017-02-08
影响因子：
4.6
通讯作者：
Iwamoto H
中科院分区：
文献类型：
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作者：
Iwamoto H
小昆虫以高达1,000赫兹的频率驱动它们的飞行肌肉。这种非凡的能力归功于牵张激活机制。然而，它仍然是未知的，以什么肌节组件的感觉拉伸，并触发以下的力量产生。在这里，我们表明，最早的结构变化后，一步拉伸是反映在闪烁的111和201反射，观察到的快速X射线衍射记录从孤立的大黄蜂飞行肌纤维。在活的大黄蜂身上也观察到了同样的信号。我们证明：（1）信号几乎伴随着一个快速的步骤拉伸，（2）信号的增长与增加钙水平的拉伸激活力，（3）一个完整的三维模型表明，当物体具有38.7 nm的肌动蛋白周期旅行约20 nm沿着丝轴信号最大化。如果肌球蛋白头与肌动蛋白靶区（肌动蛋白单体有利地定向的地方）松散地结合，并且被1.3%的拉伸拖曳，这有效地引起拉伸诱导的激活，则这是预期的位移。这些结果支持并加强了我们的建议，即肌球蛋白头本身作为拉伸传感器，钙诱导的协会与肌动蛋白在低力的形式。
Small insects drive their flight muscle at frequencies up to 1,000 Hz. This remarkable ability owes to the mechanism of stretch activation. However, it remains unknown as to what sarcomeric component senses the stretch and triggers the following force generation. Here we show that the earliest structural change after a step stretch is reflected in the blinking of the 111 and 201 reflections, as observed in the fast X-ray diffraction recording from isolated bumblebee flight muscle fibers. The same signal has also been observed in live bumblebee. We demonstrate that (1) the signal responds almost concomitantly to a quick step stretch, (2) the signal grows with increasing calcium levels as the stretch-activated force does, and (3) a full 3-dimensional model demonstrates that the signal is maximized when objects having a 38.7-nm actin periodicity travel by ~20 nm along the filament axis. This is the expected displacement if myosin heads are loosely associated with actin target zones (where actin monomers are favorably oriented), and are dragged by a 1.3% stretch, which effectively causes stretch-induced activation. These results support and strengthen our proposal that the myosin head itself acts as the stretch sensor, after calcium-induced association with actin in a low-force form.