Mechanisms governing myosin turnover and exchange in vivo.

摘要 横纹肌肌球蛋白高度组织成粗大的细丝，承受由 肌球蛋白头。虽然粗丝结构和稳定性对于收缩是必不可少的，但 目前尚不清楚是否允许充分发育的肌肉取代肌球蛋白分子，同时保持收缩的保真度。 关键问题包括：肌球蛋白合成和降解(即周转)的时间动力学是什么？ 分子又是如何选择进行降解的呢？横纹肌球蛋白分子是否处于动态平衡状态 用粗丝来允许它们交换出粗丝和进入粗丝？如果粗丝结构是 动力学，控制这种平衡的分子机制是什么？最重要的是，这个机制 可以调整以改变横纹肌的结构和/或功能？我们将在一只成年小鼠身上解决这些问题 三个目标的典范。我们的总体假设是肌球蛋白周转是一个随机过程，它涉及 单个肌球蛋白分子在单体胞浆池和粗丝之间的交换，通过一种 由胞浆中单体折叠控制的机制。目标1将定义以下人员的离职率 我们模型中的心肌肌球蛋白，并确定肌球蛋白降解是否通过随机(即随机) 通过使用同位素标记策略和质谱学相结合的方法来研究其作用机理。目标2将测试 假设横纹肌肌球蛋白的组织是高度动态的，以允许快速交换 通过病毒标记肌球蛋白在粗丝和胞浆单体之间的单个分子 体内荧光标记和多光子荧光法检测肌球蛋白在心脏内的流动性 光漂白后的恢复。目标3将检验以下假设：结构构象(即折叠与 胞浆中单个肌球蛋白分子的延伸)调节肌球蛋白分子之间的交换 泳池。AIM 3将利用一种折叠肌球蛋白并减少心脏质量的药物。我们将测试我们的整体 调整肌球蛋白折叠，影响肌球蛋白与胞浆的有效浓度的假说，以及 规定其可降解性。拟议中的研究将是第一次检查肌球蛋白的周转和 在任何完整的动物模型中横纹肌系统中的大分子交换。结果将提供 充分发展肌肉的概念创新以这样一种方式设计，以允许结构性 肌球蛋白在分钟到分钟的时间尺度上的重排。机械论的发现有可能增加 到目前关于粗丝结构的范例，并解释横纹肌是如何从 从单个分子到整个器官水平。所获得的新知识可能使我们能够利用这一点 调节整个动物的横纹肌结构和/或功能的机制。

ABSTRACT Striated muscle myosin is highly organized into thick filaments that bear the molecular forces generated by the myosin heads. While thick filament structure and stability are essential for contractility, the mechanisms that allow fully developed muscles to replace myosin molecules while maintaining contractile fidelity are unclear. Critical questions include; what are the temporal dynamics of myosin synthesis and degradation (i.e. turnover) and how are molecules selected for degradation? Do striated myosin molecules exist in a dynamic equilibrium with thick filaments to allow for their exchange out of and into thick filaments? If thick filament structure is dynamic, what are the molecular mechanisms governing this equilibrium? Most importantly, is this mechanism tunable to modify striated muscle structure and/or function? We will address these questions in an adult mouse model in three aims. Our overall hypothesis is that myosin turnover is a stochastic process which involves the exchange of individual myosin molecules between a cytosolic pool of monomers and thick filaments, by a mechanism governed by the folding of the monomers within the cytosol. Aim 1 will define the turnover rate of cardiac myosin in our model and determine whether myosin degradation occurs via a stochastic (i.e. random) mechanism by using a combination of isotope labeling strategies and mass spectrometry. Aim 2 will test the hypothesis that the organization of striated muscle myosin is highly dynamic to allow for the rapid exchange of individual molecules between thick filaments and a cytosolic pool of monomers by virally labeling myosin with a fluorescent tag in vivo and examining the mobility of the myosin within hearts using multiphoton fluorescence recovery after photobleaching. Aim 3 will test the hypotheses that the structural conformation (i.e. folded vs. extended) of individual myosin molecules in the cytosol regulates the exchange of myosin molecules between pools. Aim 3 will take advantage of a drug that folds myosin and reduces cardiac mass. We will test our overall hypothesis that tuning myosin folding, affects the effective concentration of myosin with the cytosol, and regulates its availability for degradation. The proposed studies will be the first to examine myosin turnover and macromolecular exchange in a striated muscle system in any intact animal model. The results will provide conceptual innovation that fully developed muscle is designed in such a way to allow for structural rearrangement of myosin on a minute-to-minute timescale. The mechanistic findings have the potential to add to the current paradigm regarding thick filament structure and explain how striated muscle is maintained from the single molecule to whole organ level. The new knowledge gained may allow us to take advantage of this mechanism for tuning striated muscle structure and/or function in whole animals.