Single sarcomere and Structural Protein Mechanics Measurement System

1957年诺贝尔奖获得者赢家AF赫胥黎提出的一个理论描述了横纹肌收缩和产生力量的方式，从而允许人类运动。赫胥黎提出，肌肉收缩是通过两种丝状蛋白质肌动蛋白和肌球蛋白的滑动发生的，这种滑动是由称为横桥的小分子马达产生的。这种所谓的肌肉收缩的跨桥理论在肌肉生理学教科书中有描述，并且在地球仪中教授。这个理论在描述肌肉的收缩机制方面非常出色，肌肉要么保持恒定长度（等长收缩），要么缩短（同心收缩）。然而，跨桥理论从来没有能够预测肌肉拉伸时的收缩机制（所谓的离心收缩）。离心收缩发生在每一个运动，例如当我们走路或跑步。 在2002年，我们发现必须有一个“被动”的结构元素，也有助于积极的力量生产。通过在不同结构水平上进行仔细的实验，我们确定了肌动蛋白和肌球蛋白引起的力之外的力来自一种称为肌联蛋白的结构蛋白。然而，尽管这一发现在15年前，肌联蛋白有助于主动力的分子机制仍然未知，尽管已经提出了大量的理论。这种缺乏进展的主要原因是因为即使肌动蛋白，肌球蛋白和横桥可以使用复杂的成像和衍射技术看到，肌联蛋白不提供衍射图案，因此即使使用当今最复杂的成像技术也无法看到。十年前，我们提出了肌联蛋白在肌肉被激活时改变其固有刚度的理论，并通过与肌动蛋白丝结合来实现这一点。目前，这是最被接受的理论，但没有直接的实验证据支持该理论。在当前的NSERC RTI应用中，我们要求设备系统的组件，这将允许我们直接探索我们的理论。与其他设备系统相比，该系统具有独特的功能，可以对肌动蛋白，肌球蛋白和肌联蛋白的分子相互作用获得前所未有的见解：- 允许对单个肌节进行机械测试（肌肉的最小收缩单位）-它允许肌原纤维内任何数量的肌节的受控激活-它允许以前所未有的准确度测量肌节力学-如果我们的理论被证明是正确的与这个新的设备系统，它将从根本上改变科学家如何看待肌肉收缩，它将产生改变我们的教科书和我们的肌肉生理学教学：这将是自1957年赫胥黎提出跨桥范式以来，肌肉收缩和功能领域最大的范式转变。

The way striated muscles contract and produce force, and so allow for human movement, is described by a theory developed in 1957 by Nobel Prize Winner AF Huxley. Huxley proposed that muscle contraction occurs through the sliding of two filamentous proteins called actin and myosin, and that this sliding is produced by small molecular motors called cross-bridges. This so-called cross-bridge theory of muscle contraction is described in textbooks of muscle physiology and is taught across the globe. This theory is excellent in describing the mechanics of contraction for muscles that either remain at a constant length (isometric contraction) or shorten (concentric contraction). However, the cross-bridge theory was never able to predict the mechanics of contraction when a muscle is stretched (a so-called eccentric contraction). Eccentric contractions occur during every movement, for example when we walk or run. In 2002, we discovered that there must be a "passive" structural element that also contributes to active force production. Using careful experiments at different structural levels, we identified that the force beyond that caused by actin and myosin comes from a structural protein called titin. However, despite this discovery 15 years ago, the molecular mechanism by which titin contributes to active force remains unknown, although ample theories have been proposed. The primary reason for this lack in progress has been because even though actin, myosin and cross-bridges can be seen using sophisticated imaging and diffraction techniques, titin does not provide a diffraction pattern, and thus cannot be seen using even the most sophisticated imaging techniques available today. Ten years ago, we proposed the theory that titin changes its inherent stiffness when a muscle is activated and does so by binding to the actin filament. Currently, this is the most accepted theory, but there is no direct experimental proof supporting the theory. In the current NSERC RTI application, we request the components for an equipment system that will allow us to probe our theory directly. In contrast to other equipment systems, the proposed system has unique features that allow for gaining unprecedented insights into the molecular interaction of actin, myosin, and titin: -It allows for mechanical testing of single sarcomeres (the smallest contractile unit of muscle) -It allows for controlled activation of any number of sarcomeres within a myofibril -It allows for measuring sarcomere mechanics with unprecedented accuracy -And it allows for visualizing titin-actin interactions in activated sarcomeres If our theory was proven correct with this new equipment system, it would fundamentally change how scientists view muscle contraction, it would produce a change in our textbooks and our teachings of muscle physiology: It would be the greatest paradigm shift in the field of muscle contraction and function since Huxley's 1957 proposal of the cross-bridge paradigm.