Physics of Life Processes, Leiden Institute of Physics, Leiden University, Leiden, The Netherlands.
Biophys J. 2010 Jan 6;98(1):93-100. doi: 10.1016/j.bpj.2009.09.058.
Key cellular processes such as cell division, membrane compartmentalization, and intracellular transport rely on motor proteins. Motors have been studied in detail on the single motor level such that information on their step size, stall force, average run length, and processivity are well known. However, in vivo, motors often work together, so that the question of their collective coordination has raised great interest. Here, we specifically attach motors to giant vesicles and examine collective motor dynamics during membrane tube formation. Image correlation spectroscopy reveals directed motion as processive motors walk at typical speeds (< or = 500 nm/s) along an underlying microtubule and accumulate at the tip of the growing membrane tube. In contrast, nonprocessive motors exhibit purely diffusive behavior, decorating the entire length of a microtubule lattice with diffusion constants at least 1000 times smaller than a freely-diffusing lipid-motor complex in a lipid bilayer (1 microm(2)/s); fluorescence recovery after photobleaching experiments confirm the presence of the slower-moving motor population at the microtubule-membrane tube interface. We suggest that nonprocessive motors dynamically bind and unbind to maintain a continuous interaction with the microtubule. This dynamic and continuous interaction is likely necessary for nonprocessive motors to mediate bidirectional membrane tube dynamics reported previously.
关键的细胞过程，如细胞分裂、膜区室化和细胞内运输，都依赖于马达蛋白。马达蛋白在单个马达水平上已经被详细研究过，因此它们的步长、失速力、平均运行长度和进程性等信息都已经很清楚了。然而，在体内，马达蛋白通常会协同工作，因此它们的集体协调问题引起了极大的兴趣。在这里，我们专门将马达蛋白附着在巨大的囊泡上，并在膜管形成过程中研究集体马达动力学。图像相关光谱学揭示了定向运动，即有进程性的马达蛋白以典型的速度（<或=500nm/s）沿着下面的微管行走，并在生长中的膜管的尖端积累。相比之下，无进程性的马达蛋白表现出纯粹的扩散行为，用扩散常数在微管晶格上扩散，其扩散常数至少比在脂质双层中的自由扩散脂质-马达复合物小 1000 倍（1μm^2/s）；光漂白后荧光恢复实验证实了较慢的马达蛋白群体存在于微管-膜管界面。我们认为，无进程性的马达蛋白通过动态结合和解离来维持与微管的持续相互作用。这种动态和持续的相互作用可能是无进程性的马达蛋白介导以前报道的双向膜管动力学所必需的。
