Holding two heads together: Stability of the myosin II rod measured by resonance energy transfer between the heads
Holding two heads together: Stability of the myosin II rod measured by resonance energy transfer between the heads
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DOI：
10.1073/pnas.082024299
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发表时间：
2002-04-30
影响因子：
11.1
通讯作者：
Selvin, PR
中科院分区：
文献类型：
--
作者：
Chakrabarty, T;Xiao, M;Selvin, PR
肌球蛋白与许多分子马达类似，是一种由盘绕杆连接在一起的双头二聚体。盘绕线圈的稳定性对头与头之间的相互作用、力的产生以及可能的调节具有影响。在这里，我们使用两种不同的共振能量转移技术来测量放置在骨骼重肌球蛋白每个头部的调节轻链中、靠近头杆连接处（位置 2、73 和 94）的探针之间的距离。我们的结果表明，当肌球蛋白在溶液中游离时，杆基本上不会展开，并且至少在第一个七联体之外，即使在与肌动蛋白结合的双头肌球蛋白（严格）相对较大的应变下，亚片段2杆仍保持相对完整。我们推断杆的展开可能对肌球蛋白 11 的运动不起作用。为了保持头杆连接完好，肌球蛋白头部内必须发生变形。当两个头都附着在肌动蛋白上时，这种扭曲可能会导致肌球蛋白二聚体内轻链结构域的不同方向，这可以解释之前令人费解的观察结果，并需要重新解释其他观察结果。此外，通过比较对不同动态时间尺度敏感的共振能量转移技术，我们发现调节轻链的IN末端高度灵活，可能对调节产生影响。完整的杆可能是分子马达的一般特性，因为最近对于驱动蛋白也得出了类似的结论，尽管杆是否保持完整将取决于不同马达中盘绕线圈和头部的相对刚度。
Myosin, similar to many molecular motors, is a two-headed dimer held together by a coiled-coiled rod. The stability of the coiled coil has implications for head-head interactions, force generation, and possibly regulation. Here we used two different resonance energy transfer techniques to measure the distances between probes placed in the regulatory light chain of each head of a skeletal heavy meromyosin, near the head-rod junction (positions 2, 73, and 94). Our results indicate that the rod largely does not uncoil when myosin is free in solution, and at least beyond the first heptad, the subfragment 2 rod remains relatively intact even under the relatively large strain of two-headed myosin (rigor) binding to actin. We infer that uncoiling of the rod likely does not play a role in myosin 11 motility. To keep the head-rod junction intact, a distortion must occur within the myosin heads. This distortion may lead to different orientations of the light-chain domains within the myosin dimer when both heads are attached to actin, which would explain previously puzzling observations and require reinterpretation of others. In addition, by comparing resonance energy transfer techniques sensitive to different dynamical time scales, we find that the IN terminus of the regulatory light chain is highly flexible, with possible implications for regulation. An intact rod may be a general property of molecular motors, because a similar conclusion has been reached recently for kinesin, although whether the rod remains intact will depend on the relative stiffness of the coiled coil and the head in different motors.