Processive molecular motors enable cargo transportation by assembling into dimers capable of taking several consecutive steps along a cytoskeletal filament. In the well-accepted hand-over-hand stepping mechanism, the trailing motor detaches from the track and binds the filament again in the leading position. This requires fuel consumption in the form of ATP hydrolysis and coordination of the catalytic cycles between the leading and the trailing heads. Alternate stepping pathways also exist, including inchworm-like movements, backward steps, and foot stomps. Whether all the pathways are coupled to ATP hydrolysis remains to be determined. Here, to establish the principles governing the dynamics of processive movement, we present a theoretical framework that includes all of the alternative stepping mechanisms. Our theory bridges the gap between the elemental rates describing the biochemical and structural transitions in each head and the experimentally measurable quantities such as velocity, processivity, and probability of backward stepping. Our results, obtained under the assumption that the track is periodic and infinite, provide expressions that hold regardless of the topology of the network connecting the intermediate states, and are therefore capable of describing the function of any molecular motor. We apply the theory to myosin VI, a motor that takes frequent backward steps and moves forward with a combination of hand-over-hand and inchworm-like steps. Our model quantitatively reproduces various observables of myosin VI motility reported by four experimental groups. The theory is used to predict the gating mechanism, the pathway for backward stepping, and the energy consumption as a function of ATP concentration.

中文翻译：

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电机在周期性轨道上踩踏的过程性和速度

进行性分子马达通过组装成能够沿着细胞骨架细丝连续进行几个步骤的二聚体来实现货物运输。在广为接受的手拉手步进机构中，拖曳电机从轨道上分离并再次将灯丝捆扎在引导位置。这需要 ATP 水解形式的燃料消耗和前头和尾头之间催化循环的协调。也存在交替的踏步路径，包括蛲虫状运动、后退步和跺脚。是否所有途径都与 ATP 水解有关还有待确定。在这里，为了建立控制进行性运动动力学的原则，我们提出了一个包含所有替代步进机制的理论框架。我们的理论弥合了描述每个头部生化和结构转变的基本速率与实验可测量的量（如速度、持续性和后退概率）之间的差距。我们的结果是在轨道是周期性和无限的假设下获得的，提供的表达式无论连接中间状态的网络拓扑如何都成立，因此能够描述任何分子马达的功能。我们将该理论应用于肌球蛋白 VI，这是一种电机，它经常向后退步，并通过手牵手和蚱蜢式步法的组合向前移动。我们的模型定量地再现了四个实验组报告的肌球蛋白 VI 运动的各种观察结果。该理论用于预测门控机制，