Démoulin Damien, Carlier Marie-France, Bibette Jérôme, Baudry Jean
Laboratoire Colloïdes et Matériaux Divisés, Institute of Chemistry, Biology and Innovation (CBI), ESPCI ParisTech/CNRS UMR 8231/PSL* Research University, 75005 Paris, France; and
Laboratoire d'Enzymologie et Biologie Structurales, CNRS UPR 3082, 91190 Gif-sur-Yvette, France.
Proc Natl Acad Sci U S A. 2014 Dec 16;111(50):17845-50. doi: 10.1073/pnas.1414184111. Epub 2014 Dec 1.
The actin cytoskeleton has the unique capability of producing pushing forces at the leading edge of motile cells without the implication of molecular motors. This phenomenon has been extensively studied theoretically, and molecular models, including the widely known Brownian ratchet, have been proposed. However, supporting experimental work is lacking, due in part to hardly accessible molecular length scales. We designed an experiment to directly probe the mechanism of force generation in a setup where a population of actin filaments grows against a load applied by magnetic microparticles. The filaments, arranged in stiff bundles by fascin, are constrained to point toward the applied load. In this protrusion-like geometry, we are able to directly measure the velocity of filament elongation and its dependence on force. Using numerical simulations, we provide evidence that our experimental data are consistent with a Brownian ratchet-based model. We further demonstrate the existence of a force regime far below stalling where the mechanical power transduced by the ratcheting filaments to the load is maximal. The actin machinery in migrating cells may tune the number of filaments at the leading edge to work in this force regime.
肌动蛋白细胞骨架具有在运动细胞前沿产生推力的独特能力，而无需分子马达的参与。这种现象已在理论上得到广泛研究，并提出了包括广为人知的布朗棘轮在内的分子模型。然而，由于分子长度尺度难以获取，缺乏支持性的实验工作。我们设计了一个实验，在一个装置中直接探究力产生的机制，在该装置中，一群肌动蛋白丝逆着磁性微粒施加的负载生长。由肌动蛋白结合蛋白排列成刚性束的丝被限制指向施加的负载。在这种类似突出的几何结构中，我们能够直接测量丝伸长的速度及其对力的依赖性。通过数值模拟，我们提供证据表明我们的实验数据与基于布朗棘轮的模型一致。我们进一步证明，在远低于失速的力区域存在一种情况，即通过棘轮丝传递到负载的机械功率最大。迁移细胞中的肌动蛋白机制可能会调节前沿丝的数量，以便在这种力区域发挥作用。
