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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Helical Twist Controls The Thickness Of F-actin Bundles
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Helical Twist Controls The Thickness Of F-actin Bundles

机译：螺旋扭曲控制F-肌动蛋白束的厚度

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摘要

In the presence of condensing agents such as nonadsorbing polymer, multivalent counter ions, and specific bundling proteins, chiral biopolymers typically form bundles with a finite thickness, rather than phase-separating into a polymer-rich phase. Although short-range repulsive interactions or geometrical frustrations are thought to force the equilibrium bundle size to be limited, the precise mechanism is yet to be resolved. The importance of the tight control of biopolymer bundle size is illustrated by the ubiquitous cytoskeletal actin filament bundles that are crucial for the proper functioning of cells. Using an in vitro model system, we show that size control relies on a mismatch between the helical structure of individual actin filaments and the geometric packing constraints within bundles. Small rigid actin-binding proteins change the twist of filamentous actin (F-actin) in a concentration-dependent manner, resulting in small, well defined bundle thickness up to ≈20 filaments, comparable to those found in filopodia. Other F-actin cross-linking proteins can subsequently link these small, well organized bundles into larger structures of several hundred filaments, comparable to those found in, for example, Drosophila bristles. The energetic tradeoff between filament twisting and cross-linker binding within a bundle is suggested as a fundamental mechanism by which cells can precisely adjust bundle size and strength.
机译：在存在诸如非吸附性聚合物，多价抗衡离子和特定的捆绑蛋白之类的缩合剂的情况下，手性生物聚合物通常形成具有有限厚度的束，而不是相分离成富含聚合物的相。尽管人们认为短程排斥性相互作用或几何受挫会迫使平衡束的大小受到限制，但精确的机理尚待解决。严格控制生物聚合物束大小的重要性通过无处不在的细胞骨架肌动蛋白丝束来说明，这对于细胞的正常功能至关重要。使用体外模型系统，我们显示大小控制依赖于单个肌动蛋白丝的螺旋结构与束中的几何堆积约束之间的不匹配。较小的刚性肌动蛋白结合蛋白以浓度依赖的方式改变丝状肌动蛋白（F-actin）的扭曲，从而导致纤细，轮廓分明的束厚度高达≈20个细丝，与丝状伪足中发现的细丝束厚度相当。随后，其他F-肌动蛋白交联蛋白可以将这些小的，组织良好的束连接成几百个细丝的较大结构，这与例如在果蝇刷毛中发现的结构相当。建议在细丝扭曲和束中的交联剂结合之间进行有力的权衡，这是细胞可以精确调节束大小和强度的基本机制。

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