Faculty of Physics and Earth Sciences, Peter Debye Institute, Leipzig University, Linnéstr. 5, 04103 Leipzig, Germany.
Fraunhofer Institute for Cell Therapy and Immunology (IZI), DNA Nanodevices Group, Perlickstraße 1, 04103 Leipzig, Germany.
Molecules. 2017 Oct 24;22(10):1804. doi: 10.3390/molecules22101804.
Bundled actin structures play an essential role in the mechanical response of the actin cytoskeleton in eukaryotic cells. Although responsible for crucial cellular processes, they are rarely investigated in comparison to single filaments and isotropic networks. Presenting a highly anisotropic structure, the determination of the mechanical properties of individual bundles was previously achieved through passive approaches observing bending deformations induced by thermal fluctuations. We present a new method to determine the bending stiffness of individual bundles, by measuring the decay of an actively induced oscillation. This approach allows us to systematically test anisotropic, bundled structures. Our experiments revealed that thin, depletion force-induced bundles behave as semiflexible polymers and obey the theoretical predictions determined by the wormlike chain model. Thickening an individual bundle by merging it with other bundles enabled us to study effects that are solely based on the number of involved filaments. These thicker bundles showed a frequency-dependent bending stiffness, a behavior that is inconsistent with the predictions of the wormlike chain model. We attribute this effect to internal processes and give a possible explanation with regard to the wormlike bundle theory.
成束肌动蛋白结构在真核细胞肌动蛋白细胞骨架的力学响应中起着至关重要的作用。尽管它们负责关键的细胞过程，但与单根纤维和各向同性网络相比，它们很少被研究。作为一种具有高度各向异性结构的物质，单个束的力学性能的确定以前是通过被动方法观察由热波动引起的弯曲变形来实现的。我们提出了一种新的方法来确定单个束的弯曲刚度，通过测量主动诱导的振荡的衰减。这种方法使我们能够系统地测试各向异性的、成束的结构。我们的实验表明，薄的、由耗竭力诱导的束表现为半柔性聚合物，并遵循由蠕虫链模型确定的理论预测。通过将一个束与其他束合并来增加束的厚度，使我们能够研究仅基于参与的纤维数量的效果。这些较厚的束表现出频率相关的弯曲刚度，这一行为与蠕虫链模型的预测不一致。我们将这种效应归因于内部过程，并根据蠕虫束理论给出了一种可能的解释。
