Parekh Sapun H, Chaudhuri Ovijit, Theriot Julie A, Fletcher Daniel A
UCSF/UC Berkeley Joint Graduate Group in Bioengineering, University of California at Berkeley, CA 94720, USA.
Nat Cell Biol. 2005 Dec;7(12):1219-23. doi: 10.1038/ncb1336. Epub 2005 Nov 20.
Directional polymerization of actin filaments in branched networks is one of the most powerful force-generating systems in eukaryotic cells. Growth of densely cross-linked actin networks drives cell crawling, intracellular transport of vesicles and organelles, and movement of intracellular pathogens such as Listeria monocytogenes. Using a modified atomic force microscope (AFM), we obtained force-velocity (Fv) measurements of growing actin networks in vitro until network elongation ceased at the stall force. We found that the growth velocity of a branched actin network against increasing forces is load-independent over a wide range of forces before a convex decline to stall. Surprisingly, when force was decreased on a growing network, the velocity increased to a value greater than the previous velocity, such that two or more stable growth velocities can exist at a single load. These results demonstrate that a single Fv relationship does not capture the complete behaviour of this system, unlike other molecular motors in cells, because the growth velocity depends on loading history rather than solely on the instantaneous load.
肌动蛋白丝在分支网络中的定向聚合是真核细胞中最强大的力产生系统之一。密集交联的肌动蛋白网络的生长驱动细胞爬行、囊泡和细胞器的细胞内运输，以及细胞内病原体（如单核细胞增生李斯特菌）的移动。我们使用改良的原子力显微镜（AFM），在体外获得了生长中的肌动蛋白网络的力-速度（Fv）测量值，直到网络伸长在失速力处停止。我们发现，在分支肌动蛋白网络对抗不断增加的力时，在凸形下降至失速之前的广泛力范围内，生长速度与负载无关。令人惊讶的是，当在生长的网络上降低力时，速度增加到大于先前速度的值，使得在单个负载下可以存在两个或更多个稳定的生长速度。这些结果表明，与细胞中的其他分子马达不同，单一的Fv关系并不能捕捉该系统的完整行为，因为生长速度取决于加载历史而非仅取决于瞬时负载。
