Myosin motors that cannot bind actin leave their folded OFF state on activation of skeletal muscle.
Myosin motors that cannot bind actin leave their folded OFF state on activation of skeletal muscle.
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DOI：
10.1085/jgp.202112896
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发表时间：
2021-11-01
期刊：
影响因子：
--
通讯作者：
Piazzesi G
中科院分区：
文献类型：
--
作者：
Reconditi M;Brunello E;Fusi L;Linari M;Lombardi V;Irving M;Piazzesi G
骨骼肌的激活包括将肌球蛋白马达从静息肌肉的非构象中解开。从较长肌节长度收缩的肌肉的X射线衍射显示，运动的展开不依赖于局部肌动蛋白结合位点的可用性。静息骨骼肌中的肌球蛋白马达在粗大的细丝中向后折叠，靠在尾巴上，形成一种构象，使它们无法与肌动蛋白结合。当肌肉被激活时，钙与肌钙蛋白的结合导致含有肌动蛋白的细丝结构迅速变化，揭示了肌动蛋白上的肌球蛋白结合部位。几乎以同样的速度，肌球蛋白马达离开折叠状态，离开粗大的细丝表面。为了测试附近肌动蛋白结合位点的可用性是否触发了运动展开，我们测量了当肌肉在较长的肌节长度被激活时，报告运动构象的X射线反射的变化，以便部分粗丝不再与细丝重叠。我们发现，马达沿粗丝的轴向重复产生的M3反射强度几乎随着肌节长度的增加而线性下降，直到2.8微米，如果非重叠区的马达已经离开折叠状态并变得相对无序，就像预期的那样。在最近发表在JGP上的一篇文章中，Squire和Knupp对这种对数据的解释提出了质疑。我们在这里表明，他们的分析是基于一个错误的假设，即M3反射的干涉子峰是如何在我们之前的论文中报告的。我们扩展了以前的肌球蛋白沿肌丝质量分布的模型，表明M3反射的肌节长度依赖于在主动收缩过程中10%的无重叠马达保持在折叠构象中，证实了我们之前的结论，即肌球蛋白马达的展开对肌肉激活不是由于局部肌动蛋白结合位点的可用性。
Activation of skeletal muscle involves unfolding of myosin motors from their OFF conformation in resting muscle. X-ray diffraction from muscles contracting at longer sarcomere length show that motor unfolding does not depend on the availability of local actin-binding sites. The myosin motors in resting skeletal muscle are folded back against their tails in the thick filament in a conformation that makes them unavailable for binding to actin. When muscles are activated, calcium binding to troponin leads to a rapid change in the structure of the actin-containing thin filaments that uncovers the myosin binding sites on actin. Almost as quickly, myosin motors leave the folded state and move away from the surface of the thick filament. To test whether motor unfolding is triggered by the availability of nearby actin binding sites, we measured changes in the x-ray reflections that report motor conformation when muscles are activated at longer sarcomere length, so that part of the thick filaments no longer overlaps with thin filaments. We found that the intensity of the M3 reflection from the axial repeat of the motors along the thick filaments declines almost linearly with increasing sarcomere length up to 2.8 µm, as expected if motors in the nonoverlap zone had left the folded state and become relatively disordered. In a recent article in JGP, Squire and Knupp challenged this interpretation of the data. We show here that their analysis is based on an incorrect assumption about how the interference subpeaks of the M3 reflection were reported in our previous paper. We extend previous models of mass distribution along the filaments to show that the sarcomere length dependence of the M3 reflection is consistent with <10% of no-overlap motors remaining in the folded conformation during active contraction, confirming our previous conclusion that unfolding of myosin motors on muscle activation is not due to the availability of local actin binding sites.
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影响因子：
64.8
作者：
Reconditi, M;Linari, M;Lombardi, V
通讯作者：
Lombardi, V
影响因子：
5.6
作者：
HUXLEY, HE;BROWN, W
通讯作者：
BROWN, W
影响因子：
4.8
作者：
Shaffer, Justin F.;Kensler, Robert W.;Harris, Samantha P.
通讯作者：
Harris, Samantha P.
DOI：
10.1073/pnas.1619484114
发表时间：
2017-03-21
影响因子：
11.1
作者：
Reconditi, Massimo;Caremani, Marco;Piazzesi, Gabriella
通讯作者：
Piazzesi, Gabriella
影响因子：
16.6
作者：
Fusi, L.;Brunello, E.;Yan, Z.;Irving, M.
通讯作者：
Irving, M.