交联蛋白质对平行肌动蛋白束的结构重组：无公度扭曲状态
Structural Reorganization of Parallel Actin Bundles by Crosslinking Proteins: Incommensurate States of Twist
摘要：
我们构建了一个粗粒度模型的平行肌动蛋白束交联的紧凑，球状捆绑蛋白，如fascin和espin，必要的组件filapodial和mechanosensory束。与束的结构观察一致，我们发现交联的最佳几何形状是过度扭曲，需要一个连贯的结构变化的螺旋几何形状的长丝。我们研究了成束肌动蛋白丝从天然状态到过度扭曲状态的依赖于接头的热力学转变，并根据交联蛋白的可用性和柔性绘制了“扭曲状态”相图。我们预测，从未交联到完全交联状态的过渡是高度敏感的连接器的灵活性：灵活的交联顺利扭曲的扭曲状态的成束长丝，而刚性交联束进行相变，迅速过捻长丝在一个狭窄的范围内的自由交联剂浓度。此外，我们预测一个丰富的频谱的中间结构，稀疏约束（无捻）和强约束（过捻）长丝交替域组成。该模型揭示了交联剂本身的细微差异不仅改变了平行肌动蛋白束的详细结构，而且改变了它们形成的热力学途径。
英文摘要：
We construct a coarse-grained model of parallel actin bundles crosslinked by compact, globular bundling proteins, such as fascin and espin, necessary components of filapodial and mechanosensory bundles. Consistent with structural observations of bundles, we find that the optimal geometry for crosslinking is overtwisted, requiring a coherent structural change of the helical geometry of the filaments. We study the linker-dependent thermodynamic transition of bundled actin filaments from their native state to the overtwisted state and map out the "twist-state'' phase diagram in terms of the availability as well as the flexibility of crosslinker proteins. We predict that the transition from the uncrosslinked to fully-crosslinked state is highly sensitive to linker flexibility: flexible crosslinking smoothly distorts the twist-state of bundled filaments, while rigidly crosslinked bundles undergo a phase transition, rapidly overtwisting filaments over a narrow range of free crosslinker concentrations. Additionally, we predict a rich spectrum of intermediate structures, composed of alternating domains of sparsely-bound (untwisted) and strongly-bound (overtwisted) filaments. This model reveals that subtle differences in crosslinking agents themselves modify not only the detailed structure of parallel actin bundles, but also the thermodynamic pathway by which they form.
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