Helical twist controls the thickness of F-actin bundles
Helical twist controls the thickness of F-actin bundles
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DOI：
10.1073/pnas.0711149105
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发表时间：
2008-07-01
影响因子：
11.1
通讯作者：
Bausch, A. R.
中科院分区：
文献类型：
--
作者：
Claessens, M. M. A. E.;Semmrich, C.;Bausch, A. R.
在凝聚剂如非吸附性聚合物、多价反离子和特定集束蛋白的存在下，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。虽然短程排斥相互作用或几何挫折被认为是迫使平衡束的大小是有限的，精确的机制还有待解决。生物聚合物束大小的严格控制的重要性是由无处不在的细胞骨架肌动蛋白丝束，是至关重要的细胞的正常运作。使用体外模型系统，我们表明，大小控制依赖于单个肌动蛋白丝的螺旋结构和束内的几何包装约束之间的不匹配。小的刚性肌动蛋白结合蛋白以浓度依赖性的方式改变丝状肌动蛋白（F-肌动蛋白）的扭曲，导致小的，定义明确的束厚度高达约20丝，与丝状伪足中发现的那些相当。其他F-肌动蛋白交联蛋白随后可以将这些小的，组织良好的束连接成数百根细丝的更大结构，与果蝇刚毛中发现的结构相当。纤维束内的纤维缠绕和交联剂结合之间的能量平衡被认为是细胞可以精确调节纤维束尺寸和强度的基本机制。
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 approximate 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.