Soft matter physics division, Institute for Experimental Physics I, University of Leipzig, 04103, Leipzig, Germany.
Eur Biophys J. 2011 Jan;40(1):93-101. doi: 10.1007/s00249-010-0621-z. Epub 2010 Aug 24.
F-actin bundles are prominent cytoskeletal structures in eukaryotes. They provide mechanical stability in stereocilia, microvilli, filopodia, stress fibers and the sperm acrosome. Bundles are typically stabilized by a wide range of specific crosslinking proteins, most of which exhibit off-rates on the order of 1s(-1). Yet F-actin bundles exhibit structural and mechanical integrity on time scales that are orders of magnitude longer. By applying large deformations to reconstituted F-actin bundles using optical tweezers, we provide direct evidence of their differential mechanical response in vitro: bundles exhibit fully reversible, elastic response on short time scales and irreversible, elasto-plastic response on time scales that are long compared to the characteristic crosslink dissociation time. Our measurements show a broad range of characteristic relaxation times for reconstituted F-actin bundles. This can be reconciled by considering that bundle relaxation behavior is also modulated by the number of filaments, crosslinking type and occupation number as well as the consideration of defects due to filament ends.
F-肌动蛋白纤维束是真核生物中突出的细胞骨架结构。它们为纤毛、微绒毛、丝状伪足、应力纤维和精子顶体提供机械稳定性。纤维束通常通过广泛的特定交联蛋白稳定，其中大多数蛋白的解交联速率为 1s(-1)。然而，F-肌动蛋白纤维束在时间尺度上表现出结构和机械完整性，其时间尺度要长几个数量级。通过使用光学镊子对重组成纤维的 F-肌动蛋白纤维束施加大变形，我们提供了其在体外具有差异力学响应的直接证据：纤维束在短时间尺度上表现出完全可逆的弹性响应，而在与特征交联解离时间相比长的时间尺度上表现出不可逆的弹塑性响应。我们的测量结果显示，重组成纤维的 F-肌动蛋白纤维束具有广泛的特征弛豫时间。通过考虑纤维束的弛豫行为也受到纤维数量、交联类型和占据数的调制以及由于纤维末端引起的缺陷的考虑，可以协调这一点。
