Stewart R J, Semerjian J, Schmidt C F
Department of Bioengineering, University of Utah, Salt Lake City 84112, USA.
Eur Biophys J. 1998;27(4):353-60. doi: 10.1007/s002490050142.
Evidence is presented that the kinesin-related ncd protein is not as processive as kinesin. In low surface density motility experiments, a dimeric ncd fusion protein behaved mechanistically more similar to non-processive myosins than to the highly processive kinesin. First, there was a critical microtubule length for motility; only microtubules longer than this critical length moved in low density ncd surfaces, which suggested that multiple ncd proteins must cooperate to move microtubules in the surface assay. Under similar conditions, native kinesin demonstrated no critical microtubule length, consistent with the behavior of a highly processive motor. Second, addition of methylcellulose to decrease microtubule diffusion decreased the critical microtubule length for motility. Also, the rates of microtubule motility were microtubule length dependent in methylcellulose; short microtubules, that interacted with fewer ncd proteins, moved more slowly than long microtubules that interacted with more ncd proteins. In contrast, short microtubules, that interacted with one or a few kinesin proteins, moved on average slightly faster than long microtubules that interacted with multiple kinesins. We conclude that a degree of processivity as high as that of kinesin, where a single dimer can move over distances on the order of one micrometer, may not be a general mechanistic feature of the kinesin superfamily.
有证据表明，与驱动蛋白相关的ncd蛋白不像驱动蛋白那样具有持续性。在低表面密度运动实验中，二聚体ncd融合蛋白的机械行为与非持续性肌球蛋白更为相似，而与高度持续性的驱动蛋白不同。首先，存在一个运动所需的关键微管长度；只有长度超过这个关键长度的微管才能在低密度ncd表面移动，这表明多个ncd蛋白必须协同作用才能在表面实验中移动微管。在类似条件下，天然驱动蛋白没有显示出关键微管长度，这与高度持续性马达的行为一致。其次，添加甲基纤维素以减少微管扩散会降低运动所需的关键微管长度。此外，在甲基纤维素中微管运动速率取决于微管长度；与较少ncd蛋白相互作用的短微管移动速度比与较多ncd蛋白相互作用的长微管慢。相比之下，与一个或几个驱动蛋白蛋白相互作用的短微管平均移动速度略快于与多个驱动蛋白相互作用的长微管。我们得出结论，像驱动蛋白那样具有高度持续性，即单个二聚体能够在大约一微米的距离上移动，可能不是驱动蛋白超家族的普遍机械特征。
