Mechanisms of Processivity in Molecular Motors

描述（由申请人提供）：肌球蛋白和驱动蛋白组成了多种分子马达的集合，这些分子马达以核苷酸水解为代价产生力和运动。尽管这两个运动超家族的基本结构几乎没有共同之处，但每组成员在细胞内的功能往往相似。例如，当一些肌球蛋白和驱动蛋白运输囊泡时，其他蛋白产生维持细胞骨架和有丝分裂装置所需的皮质张力。这个项目的中心假设是，对运动的生理需求决定了它如何作为酶发挥作用。因此，如果细胞内马达的功能是已知的，就有可能预测马达酶学的关键方面。肌球蛋白V和传统的驱动蛋白运输囊泡相对较长的距离和工作作为单一的马达隔离。与中心假设一致，这两个马达至少有一个共同的酶学特征--都是进行性的。对于单独工作的囊泡转运蛋白来说，持续合成能力是必要的，因为过早的解离可能会产生可怕的生理后果。因此，持续合成能力是一个例子，说明了运动员的酶学是如何被其生理学塑造的。在这个建议中，我将扩展这个主题的持续性作为一种生理需求的反应。 我将使用我所产生的数据与驱动蛋白，制定一个模型的持续合成能力如何在分子马达中工作，并将测试这个模型，通过比较驱动蛋白肌球蛋白V，特别是，我将检查三个组件的分子马达酶学的功能应该是可预测的囊泡转运蛋白，在隔离工作。这些因素包括向前一步的时机、马达机械元件的灵活性以及变构通讯的机制。综合起来，这些组成部分很可能决定了运动的持续性，就像持续性本身一样，它们也应该由生理需求来塑造。因此，确定这些成分与基于生理学的预测的一致程度，将为中心假设提供一个关键的检验。此外，如果成功的话，这项工作将支持这样一种论点，即理解马达在体外如何作为酶工作，可以为它在细胞中如何在体内工作提供有价值的见解。

DESCRIPTION (provided by applicant): Myosins and kinesins make up a diverse collection of molecular motors that generate force and movement at the expense of nucleotide hydrolysis. Despite the fact that these two motor superfamilies share little primary structure, members of each group often serve similar functions within the cell. For example, while some myosins and kinesins transport vesicles, others generate the cortical tension required to maintain the cytoskeleton and the mitotic apparatus. The central hypothesis of this project is that the physiologic demands placed on a motor determine how it behaves as an enzyme. It should therefore be possible to predict key aspects of a motor's enzymology if its function within the cell is known. Myosin V and conventional kinesin transport vesicles relatively long distances and work as single motors in isolation. Consistent with the central hypothesis, these two motors share at least one feature of their enzymology--both are processive. Processivity would be necessary for vesicle transporters that work in isolation, since premature dissociation could have dire physiologic consequence. Thus, processivity serves as an example of how a motor's enzymology can be shaped by its physiology. In this proposal, I will expand on this theme of processivity as a response to physiologic demands. I will use the data I have generated with kinesin to formulate a model of how processivity works in molecular motors, and will test this model by comparing kinesin to myosin V. In particular, I will examine three components of molecular motor enzymology whose features should be predictable for vesicle transporters that work in isolation. These include the timing of the forward step, the flexibility of the motor's mechanical element, and the mechanism of allosteric communication. Taken together, these components are likely to determine how processive a motor is, and like processivity itself, they too should be shaped by the demands of physiology. Determining how closely these components conform to the predictions based on physiology will therefore provide a critical test of the central hypothesis. Furthermore, if successful, this work will support the argument that understanding how a motor works in vitro as an enzyme can provide valuable insights into how it works in vivo in the cell.