Cations Stiffen Actin Filaments by Adhering a Key Structural Element to Adjacent Subunits.
Cations Stiffen Actin Filaments by Adhering a Key Structural Element to Adjacent Subunits.
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DOI：
10.1021/acs.jpcb.6b02741
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发表时间：
2016-05-26
期刊：
影响因子：
--
通讯作者：
Voth GA
中科院分区：
文献类型：
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作者：
Hocky GM;Baker JL;Bradley MJ;Sinitskiy AV;De La Cruz EM;Voth GA
离子调节肌动蛋白丝的组装和机械性能。最近的工作使用结构生物信息学和定点诱变有利于存在两个离散的和特定的二价阳离子结合位点的肌动蛋白丝，定位在肌动蛋白亚基之间的长轴。在一个位点的阳离子结合驱动聚合，而另一个位点调节细丝刚度，并在调节蛋白cofilin的细丝切断中发挥作用。现有的结构方法还没有能够解决的顺磁性相关的阳离子，因此在这项工作中，我们转向分子动力学模拟，建议候选人的结合口袋的几何形状为每个网站，并阐明的机制，通过该机制占用的“刚度网站”影响长丝的机械性能。在“聚合位点”中加入镁离子似乎不需要肌动蛋白亚基构象发生任何大规模的变化。镁离子在“刚性位点”中的结合将肌动蛋白DNA酶结合环（D-环）粘附到其长轴邻居，这增加了细丝的扭转刚度和弯曲持久长度。我们的分析表明，绑定的D-环占据一个较小的区域可访问的构象空间。阳离子占据掩埋了D环的关键保守残基，限制了靶向这些氨基酸的调节蛋白和酶的可及性。
Ions regulate the assembly and mechanical properties of actin filaments. Recent work using structural bioinformatics and site-specific mutagenesis favors the existence of two discrete and specific divalent cation binding sites on actin filaments, positioned in the long axis between actin subunits. Cation binding at one site drives polymerization, while the other modulates filament stiffness and plays a role in filament severing by the regulatory protein, cofilin. Existing structural methods have not been able to resolve filament-associated cations, and so in this work we turn to molecular dynamics simulations to suggest a candidate binding pocket geometry for each site and to elucidate the mechanism by which occupancy of the “stiffness site” affects filament mechanical properties. Incorporating a magnesium ion in the “polymerization site” does not seem to require any large-scale change to an actin subunit’s conformation. Binding of a magnesium ion in the “stiffness site” adheres the actin DNase-binding loop (D-loop) to its long-axis neighbor, which increases the filament torsional stiffness and bending persistence length. Our analysis shows that bound D-loops occupy a smaller region of accessible conformational space. Cation occupancy buries key conserved residues of the D-loop, restricting accessibility to regulatory proteins and enzymes that target these amino acids.