Nishikawa Masatoshi, Nishikawa So, Inoue Akira, Iwane Atsuko Hikikoshi, Yanagida Toshio, Ikebe Mitsuo
Department of Biophysical Engineering, Osaka University 1-3, Machikaneyama, Toyonaka, Osaka 560-8531, Japan.
Biochem Biophys Res Commun. 2006 May 19;343(4):1159-64. doi: 10.1016/j.bbrc.2006.03.057.
It has been puzzled that in spite of its single-headed structure, myosin-IX shows the typical character of processive motor in multi-molecule in vitro motility assay, because this cannot be explained by hand-over-hand mechanism of the two-headed processive myosins. Here, we show direct evidence of the processive movement of myosin-IX using two different single molecule techniques. Using optical trap nanometry, we found that myosin-IX takes several large ( approximately 20nm) steps before detaching from an actin filament. Furthermore, we directly visualized the single myosin-IX molecules moving on actin filaments for several hundred nanometers without dissociating from actin filament. Since myosin-IX processively moves without anchoring the neck domain, the result suggests that the neck tilting is not involved for the processive movement of myosin-IX. We propose that the myosin-IX head moves processively along an actin filament like an inchworm via a unique long and positively charged insertion in the loop 2 region of the head.
令人困惑的是，尽管肌球蛋白IX具有单头结构，但在多分子体外运动分析中却表现出典型的持续性运动特征，因为这无法用双头持续性肌球蛋白的手换手机制来解释。在这里，我们使用两种不同的单分子技术展示了肌球蛋白IX持续性运动的直接证据。利用光镊纳米技术，我们发现肌球蛋白IX在从肌动蛋白丝上脱离之前会迈出几个大的（约20纳米）步。此外，我们直接观察到单个肌球蛋白IX分子在肌动蛋白丝上移动数百纳米而不与肌动蛋白丝解离。由于肌球蛋白IX在不固定颈部结构域的情况下进行持续性运动，结果表明颈部倾斜与肌球蛋白IX的持续性运动无关。我们提出，肌球蛋白IX的头部通过头部环2区域中独特的长且带正电荷的插入序列，像尺蠖一样沿着肌动蛋白丝进行持续性移动。
