Molecular mechanism of muscle regulation by troponin

肌肉收缩是由每块肌肉细胞内短暂的钙脉冲触发的。钙与肌肉细丝中的肌钙蛋白结合，使细丝结构发生变化。这使得附近粗纤维中的运动蛋白肌球蛋白结合并拉动细纤维，导致肌肉缩短。同样的过程发生在所有移动骨骼的肌肉和心脏中，在心脏中，钙的脉冲触发每一次心跳。我们的目的是确定钙与肌钙蛋白结合引起的分子结构变化，并发现它们是如何控制肌肉收缩的。之前已经有很多关于钙与肌钙蛋白分离片段结合的研究，但我们将采取一种完全不同的方法，在工作的肌肉细胞内测量肌钙蛋白的结构变化。这是必要的，以保持正常的短暂相互作用之间的肌肉蛋白发生在一次收缩。我们将用荧光探针标记分离的肌钙蛋白，并用标记的肌钙蛋白代替肌肉细胞中的天然肌钙蛋白。然后我们可以利用荧光灯的偏振来跟踪细胞内肌钙蛋白的结构变化。在过去的十年里，我们已经开发和完善了这种方法，并在其他肌肉蛋白质上进行了测试，所以我们相信这种方法可以揭示肌钙蛋白是如何控制肌肉收缩的。了解肌肉控制的正常机制对于了解它在肌肉疾病中如何失效是很重要的，这有助于设计药物和治疗方法。骨骼肌和心脏的机制基本相同。肌肉无力损害了许多老年人的生活质量，心脏病是人类健康的主要威胁。一些遗传性心脏病是由肌钙蛋白结构的特定错误引起的，但我们不知道。我不知道这些是如何引起疾病的，因为我们不知道。我知道肌钙蛋白是如何正常工作的。本项目旨在提供这方面的知识。所有细胞和组织的正常功能依赖于许多蛋白质以复杂但协调的方式相互作用，通常很难理解一种蛋白质的缺陷如何导致一系列复杂的症状。我们正在开发的测量细胞内蛋白质结构变化的方法应该有助于克服当前生物医学研究的这一普遍限制。

Muscle contraction is triggered by a brief pulse of calcium inside each muscle cell. The calcium binds to a protein called troponin in the muscle thin filaments, producing a change in the filament structure. This allows the motor protein myosin in the nearby thick filaments to bind to and pull on the thin filaments, causing the muscle to shorten. The same process occurs in all the muscles that move the skeleton and in the heart, where a pulse of calcium triggers each heart beat.Our aim is to determine the molecular structural changes caused by binding of calcium to troponin, and to discover how they control muscle contraction. There have been many previous studies of calcium binding to isolated fragments of troponin, but we will take a radically different approach, in which the structural changes in troponin will be measured inside a working muscle cell. This is necessary to preserve the normal transient interactions between the muscle proteins that take place during a single contraction. We will label isolated troponin with fluorescent probes, and replace the native troponin in muscle cells by the labelled troponin. We can then use the polarisation of the fluorescent light to follow structural changes in troponin inside the cell. We have developed and refined this approach over the last ten years, and tested it on other muscle proteins, so we are confident that the method can reveal how troponin controls muscle contraction.It is important to understand the normal mechanism of muscle control to understand how it fails in muscle disease, which can help in designing drugs and therapies. The mechanism is essentially the same in skeletal muscles and in the heart. Muscle weakness impairs the quality of life of many elderly people, and heart disease is a major threat to human health. Some inherited heart diseases are caused by specific errors in the structure of troponin, but we don?t know how these cause the disease because we don?t know how troponin works normally. This project aims to provide this knowledge. Normal function of all cells and tissues depends on many proteins interacting in a complicated but coordinated way, and it is often difficult to understand how a defect in one protein leads to a complex set of symptoms. The approach we are developing to measure changes in protein structures inside cells should help to overcome this general limitation of current biomedical research.