Tropomyosin and actin isoforms modulate the localization of tropomyosin strands on actin filaments
Tropomyosin and actin isoforms modulate the localization of tropomyosin strands on actin filaments
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DOI：
10.1006/jmbi.2000.4080
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发表时间：
2000-09-22
影响因子：
5.6
通讯作者：
Craig, R
中科院分区：
文献类型：
--
作者：
Lehman, W;Hatch, V;Craig, R
原肌凝蛋白几乎存在于所有真核细胞中，其功能是调节肌动蛋白-肌凝蛋白相互作用，稳定肌动蛋白丝结构。在横纹肌中，原肌凝蛋白通过在松弛状态下阻断肌动蛋白上的肌凝蛋白结合位点来调节收缩力。激活后，原肌凝蛋白分两步离开这些位点。一种是由Ca2+与肌钙蛋白结合引起的，另一种是由肌球蛋白与肌动蛋白结合引起的。在肌钙蛋白缺失的平滑肌和非肌细胞中，原肌球蛋白对肌动蛋白的确切作用和结构动力学尚不清楚。本研究确定了原肌球蛋白在无肌钙蛋白和其他肌动蛋白结合蛋白的f -肌动蛋白丝上的位置，以更好地了解其在肌肉和非肌肉细胞中功能的结构基础。利用电子显微镜和三维图像重建，研究了来自肌肉和非肌肉来源的多种野生型和突变型肌动蛋白和原肌球蛋白亚型的关联。原肌凝蛋白在肌动蛋白上的位置似乎是由两组结合相互作用确定的，原肌凝蛋白定位于肌动蛋白的内部或外部结构域，这取决于所检查的特定肌动蛋白或原肌凝蛋白异构体。由于这些平衡位置取决于同工异构体之间氨基酸序列的微小差异，我们得出结论，细丝态之间的能量势垒很小。我们的研究结果表明，在横纹肌中，肌钙蛋白和肌球蛋白分别起到稳定原肌球蛋白抑制和激活状态的作用。此外，它们与原肌凝蛋白依赖的协同开关和关闭肌动球蛋白为基础的运动性是一致的。最后，我们确定的原肌凝蛋白的位置表明，原肌凝蛋白和其他细胞肌动蛋白结合蛋白之间可能存在显著的竞争。基于这些结果，我们提出了原肌球蛋白调节运动和细胞骨架模型的一般框架。(C) 2000年学术出版社。
Tropomyosin is present in virtually all eucaryotic cells, where it functions to modulate actin-myosin interaction and to stabilize actin filament structure. In striated muscle, tropomyosin regulates contractility by sterically blocking myosin-binding sites on actin in the relaxed state. On activation, tropomyosin moves away from these sites in two steps. one induced by Ca2+ binding to troponin and a second by the binding of myosin to actin. In smooth muscle and non-muscle cells, where troponin is absent, the precise role and structural dynamics of tropomyosin on actin are poorly understood. Here, the location of tropomyosin on F-actin filaments free of troponin and other actin-binding proteins was determined to better understand the structural basis of its functioning in muscle and non-muscle cells. Using electron microscopy and three-dimensional image reconstruction, the association of a diverse set of wild-type and mutant actin and tropomyosin isoforms, from both muscle and nonmuscle sources, was investigated. Tropomyosin position on actin appeared to be defined by two sets of binding interactions and tropomyosin localized on either the inner or the outer domain of actin, depending on the specific actin or tropomyosin isoform examined. Since these equilibrium positions depended on minor amino acid sequence differences among isoforms, we conclude that the energy barrier between thin filament states is small. Our results imply that, in striated muscles, troponin and myosin serve to stabilize tropomyosin in inhibitory and activating states, respectively. In addition, they are consistent with tropomyosin-dependent cooperative switching on and off of actomyosin-based motility. Finally, the locations of tropomyosin that we have determined suggest the possibility of significant competition between tropomyosin and other cellular actin-binding proteins. Based on these results, we present a general framework for tropomyosin modulation of motility and cytoskeletal modelling. (C) 2000 Academic Press.