Interhead distance measurements in myosin VI via SHRImP support a simplified hand-over-hand model
Interhead distance measurements in myosin VI via SHRImP support a simplified hand-over-hand model
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DOI：
10.1529/biophysj.105.060608
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发表时间：
2005-07-01
影响因子：
3.4
通讯作者：
Selvin, PR
中科院分区：
文献类型：
--
作者：
Balci, H;Ha, T;Selvin, PR
肌球蛋白VI以双手交替的方式行走，平均步长为30 nm，这比其10 nm的杠杆臂大得多。最近的实验表明，肌球蛋白VI结构在近端尾部具有展开的柔性区域，这使得如此大的步长成为可能。此外，肌动球蛋白VI的冷冻电子显微镜图像显示，两个头部与肌动蛋白单体结合，具有广泛的距离分布，包括一些接近几纳米。这一观察结果，当与结构中存在的一个灵活的区域相结合时，它参与了步进，挑战了双手交替模型。在手对手模型中，杠杆臂被认为是刚性的，并且头间间隔不应与30 nm有很大差异。我们考虑了另一种模型，其中肌球蛋白VI头部顺序地采取60 nm的步骤，而头部间的间隔在大值和小值之间交替（x和60 - x，其中x < 30）。为了澄清这些问题，我们使用了一种新的技术，SHRImP，测量近僵硬肌球蛋白VI分子的头间距离。我们的数据显示在29.3 +/- 0.7 nm处有一个单峰，与直接的手-手模型一致。
Myosin VI walks in a hand-over-hand fashion with an average step size of 30 nm, which is much larger than its 10 nm lever arm. Recent experiments suggest that the myosin VI structure has an unfolded and flexible region in the proximal tail which makes such a large step possible. In addition, cryoelectron microscopy images of actomyosin VI show the two heads bound to the actin monomers with a broad distribution of distances, including some as close as a few nanometers. This observation, when combined with the existence of a flexible region in the structure, which takes part in stepping, challenged the hand-over-hand model. In the hand-over-hand model, the lever arm is considered to be rigid and the interhead separation should not be very different from 30 nm. We considered an alternative model in which myosin VI heads sequentially take 60 nm steps whereas the interhead separation alternates between a large and small value (x and 60 - x, where x < 30). To clarify these issues, we used a new technique, SHRImP, to measure the interhead distance of nearly rigor myosin VI molecules. Our data show a single peak at 29.3 +/- 0.7 nm, in agreement with the straightforward hand-over-hand model.