Mechanisms of Processivity in Molecular Motors

描述(由申请人提供)：肌球蛋白和肌动蛋白组成了一种不同的分子马达集合，以核苷酸水解为代价产生力量和运动。尽管这两个运动超家族几乎没有共同的初级结构，但每个家族的成员经常在细胞内发挥相似的功能。例如，当一些肌球蛋白和运动蛋白运输小泡时，另一些则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一种酶的行为方式。因此，如果马达在细胞内的功能是已知的，就应该有可能预测其酶学的关键方面。肌球蛋白V和传统的肌动蛋白在相对较长的距离内运输小泡，并作为单独的马达独立工作。与中心假设一致，这两个马达至少有一个共同的酶学特征--都是过程性的。对于单独工作的囊泡转运体来说，过程性是必要的，因为过早的解离可能会产生可怕的生理后果。因此，过程性可以作为一个例子，说明如何通过生理学来塑造马达的酶学。在这项提议中，我将进一步阐述作为对生理需求的反应的过程性这一主题。我将使用我用Kinesin生成的数据来建立一个分子马达中过程如何工作的模型，并通过比较Kinesin和myosin V来测试这个模型。特别是，我将研究分子马达酶学的三个组成部分，它们的特征对于单独工作的囊泡转运体应该是可以预测的。这些包括前进步骤的时间，电机机械元件的灵活性，以及变构通讯的机制。综上所述，这些因素很可能决定了马达的进程，就像进程本身一样，它们也应该受到生理需求的影响。因此，确定这些成分与基于生理学的预测有多接近，将提供对中心假设的关键检验。此外，如果成功，这项工作将支持这样的论点，即了解马达在体外是如何作为一种酶工作的，可以为它在体内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.