Mammalian twinfilin sequesters ADP-G-actin and caps filament barbed ends: implications in motility
Mammalian twinfilin sequesters ADP-G-actin and caps filament barbed ends: implications in motility
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DOI：
10.1038/sj.emboj.7601019
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发表时间：
2006-03-22
期刊：
影响因子：
11.4
通讯作者：
Carlier, MF
中科院分区：
文献类型：
--
作者：
Helfer, E;Nevalainen, EM;Carlier, MF
双联丝蛋白是保守的肌动蛋白结合蛋白，由两个肌动蛋白解聚因子同源（ADF - H）结构域组成。双联丝蛋白参与多种形态和运动过程，但其作用机制尚未阐明。在此，我们表明哺乳动物双联丝蛋白既能隔离ADP - G - 肌动蛋白，又能封闭丝状体的带刺端，且对ADP结合端具有优先亲和力。在仿生运动测定中，双联丝蛋白取代封端蛋白并促进N - WASP功能化珠子的运动，这表明封端活性支持双联丝蛋白在运动中的功能。一致地，在体内双联丝蛋白定位于推进内体的肌动蛋白尾。ADP - 肌动蛋白隔离活性与双联丝蛋白的丝状体封端活性协同作用，由于成核蛋白功能化珠子催化的连续性丝状体组装，精细地调节运动。分离的ADF - H结构域既不封闭带刺端也不促进运动，但能隔离ADP - 肌动蛋白，其中C末端结构域显示出最高亲和力。基于双联丝蛋白ADF - H结构域和凝溶胶蛋白片段的相似折叠，提出了双联丝蛋白与带刺端结合的结构模型。
Twinfilins are conserved actin-binding proteins composed of two actin depolymerizing factor homology (ADF-H) domains. Twinfilins are involved in diverse morphological and motile processes, but their mechanism of action has not been elucidated. Here, we show that mammalian twinfilin both sequesters ADP-G-actin and caps filament barbed ends with preferential affinity for ADP-bound ends. Twinfilin replaces capping protein and promotes motility of N-WASP functionalized beads in a biomimetic motility assay, indicating that the capping activity supports twinfilin's function in motility. Consistently, in vivo twinfilin localizes to actin tails of propelling endosomes. The ADP-actin-sequestering activity cooperates with the filament capping activity of twinfilin to finely regulate motility due to processive filament assembly catalyzed by formin-functionalized beads. The isolated ADF-H domains do not cap barbed ends nor promote motility, but sequester ADP-actin, the C-terminal domain showing the highest affinity. A structural model for binding of twinfilin to barbed ends is proposed based on the similar foldings of twinfilin ADF-H domains and gelsolin segments.