Direct Single Molecule Observations of the Unique Mechanical State of Human Myosin-6
Direct Single Molecule Observations of the Unique Mechanical State of Human Myosin-6
复制标题
人肌球蛋白 6 独特机械状态的直接单分子观察
DOI：
10.1016/j.bpj.2016.11.1438
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发表时间：
2017
影响因子：
3.4
通讯作者：
Sellers JR
中科院分区：
文献类型：
--
作者：
Takagi Y;Hundt N;Billington N;Andrecka J;Cole D;Fineberg AJ;Katagiri N;Bird JE;Friedman TB;Kukura P;Sellers JR
1299-POS Board B367在Myosin VI Mauro L.Mugnai，Dave Thirumalai中杠杆手臂摆动的运动学。化学，德克萨斯大学奥斯汀分校，德克萨斯州奥斯汀，美国。与其他肌球蛋白类似，肌球蛋白VI(MVI)利用储存在ATP中的能量在肌动蛋白细丝上运动。在动力冲程中，在电机领域启动的结构转变导致变流器的运动，而摆动的杠杆臂夸大了这一运动。MVI和肌球蛋白V一样，可以形成在肌动蛋白上连续行走的二聚体。MVI的独特性体现在它的运动细节上：MVI走向肌动蛋白细丝的尖端，并经历了一个不稳定的步进模式，在这个模式中，后退的步伐与手中的手和尺寸虫一样的前进步伐相结合。实验证据表明，MVI二聚体的前导头的杠杆臂与运动域是分离的。我们建立了MVI的功率冲程模型，我们表明它发生在两个步骤：首先，电机领域，包括转换器，达到冲程后的构象，而不指示杠杆臂向前。其次，杠杆臂向其卒中后方向扩散，这只受到运动域的微弱偏向。即使在没有反向载荷的情况下，杠杆臂在动力冲程过程中也会发生解耦，这表明它是一种以MVI结构编码的机构。此外，与MVI二聚体中估计的最大磁头间张力相兼容的向后负载防止了动力行程的第二步，这表明MVI二聚体的前导磁头杠杆臂与电机领域分离。我们的模型在没有任何可调参数的情况下，提供了与监测钙调蛋白结合探针取向的polTIRF实验定量一致的结果，并且他们表明，具有非耦合杠杆臂的两步机制可能有助于解释实验观察到的手把手和尺寸虫样步骤的组合。
1299-Pos Board B367 Kinematics of the Lever Arm Swing in Myosin VI Mauro L. Mugnai, Dave Thirumalai. Chemistry, The University of Texas at Austin, Austin, TX, USA. Similarly to other myosins, Myosin VI (MVI) uses the energy stored in ATP to move on the actin filament. During the power stroke, a structural transition initiated in the motor domain leads to the movement of the converter, which is exaggerated by the swinging lever arm. MVI, like Myosin V, can form dimers that walk processively on actin. The uniqueness of MVI emerges from the details of its motion: MVI walks towards the pointed end of the actin filament, and it does so undergoing an erratic stepping pattern, in which backward steps are combined with hand-over-hand and inchworm-like forward steps. Experimental evidence suggested that the lever arm of the leading head of a MVI dimer is uncoupled from the motor domain. We developed a model of the power stroke of MVI and we show that it occurs in two steps: first the motor domain, including the converter, reaches the post-stroke conformation without directing the lever arm forward. Secondly, the lever arm undergoes a diffusion towards its poststroke orientation, which is only weakly biased by the motor domain. The uncoupling of the lever arm during the power stroke occurs even without backward load, suggesting that it is a mechanism encoded in MVI strucutre. Also, a backward load compatible with the largest estimated interhead tension in a MVI dimer prevents the second step of the power stroke, suggesting that a MVI dimer leading head lever arm is uncoupled from the motor domain. Our model, without any adjustable parameters, provides results that are in quantitative agreement with polTIRF experiments monitoring the orientation of a calmodulin-bound probe, and they suggest that the two-step mechanism with an uncoupled lever arm might contribute to explaining the experimentally-observed combination of hand-over-hand and inchworm-like steps.