Mechanisms of Processivity in Molecular Motors

描述（由申请人提供）：肌凝蛋白和动蛋白组成了多种分子马达，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共享很少的初级结构，但每个组的成员在细胞内通常具有相似的功能。例如，当一些肌凝蛋白和运动蛋白运输囊泡时，其他的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，对马达的生理需求决定了它作为酶的行为。因此，如果知道马达酶学在细胞内的功能，就有可能预测马达酶学的关键方面。肌凝蛋白V和常规运动蛋白运输囊泡的距离相对较远，并且作为单独的马达单独工作。与中心假设一致，这两种马达在酶学上至少有一个共同的特征——都是进行性的。对于孤立工作的囊泡转运体来说，加工性是必要的，因为过早分离可能会产生可怕的生理后果。因此，加工能力作为一个例子，说明了运动的酶学是如何被它的生理学所塑造的。在这个提议中，我将扩展这个主题的过程性作为生理需求的反应。我将使用我用激酶生成的数据来制定一个分子马达中加工性如何工作的模型，并将通过比较激酶和肌凝蛋白v来测试这个模型。特别是，我将检查分子马达酶学的三个组成部分，它们的特征应该是可预测的，对于分离工作的囊泡转运蛋白。这些包括前进步骤的时间，电机机械元件的灵活性，以及变构沟通的机制。综上所述，这些组成部分很可能决定了一个运动的进程性，就像进程性本身一样，它们也应该由生理学的需求来塑造。因此，确定这些成分与基于生理学的预测的吻合程度将为中心假设提供关键的检验。此外，如果成功，这项工作将支持这样一种观点，即了解马达如何在体外作为一种酶工作，可以为它如何在细胞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.