A point mutation in the regulatory light chain reduces the step size of skeletal muscle myosin
A point mutation in the regulatory light chain reduces the step size of skeletal muscle myosin
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DOI：
10.1073/pnas.0401699101
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发表时间：
2004-07-27
影响因子：
11.1
通讯作者：
Lowey, S
中科院分区：
文献类型：
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作者：
Sherwood, JJ;Waller, GS;Lowey, S
目前的证据支持这样的理论，即当肌球蛋白的球状运动域附着于肌动蛋白时，轻链结合域或“杠杆臂”旋转，从而产生肌动蛋白丝的运动。肌球蛋白是一种独特的结构，它的催化核心C末端有一个长的α-螺旋（约9 nm），由两个钙调素样分子，调节轻链（RLC）和必需轻链（ELC）稳定。在这里，我们引入一个单点突变到骨骼肌球蛋白RLC，这导致了一个大的（约50%）减少肌动蛋白丝速度（V-肌动蛋白）没有任何损失肌动蛋白激活的MgATPase活性。通过光学捕获对肌球蛋白进行的单分子分析显示，在动力冲程后，单位位移或步长（d）减少了2倍，而强附着状态（tau（on））的持续时间没有显著变化。假设V-肌动蛋白近似于d/tau（on），我们可以主要通过改变杠杆臂的步长来解释速度的变化，而不会引起突变肌球蛋白动力学性质的任何变化。这些结果表明，肌球蛋白II类中的许多轻链亚型的主要作用可能是调节轻链结合域的弯曲刚度，以最大限度地提高肌肉收缩过程中的张力发展和运动。
Current evidence favors the theory that, when the globular motor domain of myosin attaches to actin, the light chain binding domain or "lever arm" rotates, and thereby generates movement of actin filaments. Myosin is uniquely designed for such a role in that a long alpha-helix (approximate to9 nm) extending from the C terminus of the catalytic core is stabilized by two calmodulin-like molecules, the regulatory light chain (RLC) and the essential light chain (ELC). Here, we introduce a single-point mutation into the skeletal myosin RLC, which results in a large (approximate to50%) reduction in actin filament velocity (V-actin) without any loss in actin-activated MgATPase activity. Single-molecule analysis of myosin by optical trapping showed a comparable 2-fold reduction in unitary displacement or step size (d), without a significant change in the duration of the strongly attached state (tau(on)) after the power stroke. Assuming that V-actin approximate to d/tau(on), we can account for the change in velocity primarily by a change in the step size of the lever arm without incurring any change in the kinetic properties of the mutant myosin. These results suggest that a principal role for the many light chain isoforms in the myosin II class may be to modulate the flexural rigidity of the light chain binding domain to maximize tension development and movement during muscle contraction.