Graduate School of Engineering, Muroran Institute of Technology, Hokkaido, 050-8585, Japan.
Department of Cell Biology, Graduate School of Medical Science, Tokushima University, Tokushima, 770-8503, Japan.
Biochem Biophys Res Commun. 2021 May 7;552:59-65. doi: 10.1016/j.bbrc.2021.02.139. Epub 2021 Mar 17.
Fimbrin forms bundles of parallel actin filaments in filopodia, but it remains unclear how fimbrin forms well-ordered bundles. To address this issue, we focused on the cooperative interaction between the actin-binding domain of fimbrin and actin filaments. First, we loosely immobilized actin filaments on a glass surface via a positively charged lipid layer and observed the binding of GFP-fused actin-binding domain 2 of fimbrin using fluorescence microscopy. The actin-binding domain formed low-density clusters with unidirectional growth along actin filaments. When the actin filaments were tightly immobilized to the surface by increasing the charge density of the lipid layer, cluster formation was suppressed. This result suggests that the propagation of cooperative structural changes of actin filaments evoked by binding of the actin-binding domain was suppressed by a strong physical interaction with the glass surface. Interestingly, binding of the fimbrin actin-binding domain shortened the length of loosely immobilized actin filaments. Based on these results, we propose that fimbrin-actin interactions accompanied by unidirectional long-range allostery help the formation of well-ordered parallel actin filament bundles.
fimbrin 在丝状伪足中形成平行肌动蛋白丝的束，但 fimbrin 如何形成有序的束仍不清楚。为了解决这个问题，我们专注于 fimbrin 的肌动蛋白结合域与肌动蛋白丝之间的合作相互作用。首先，我们通过带正电荷的脂质层将肌动蛋白丝松散地固定在玻璃表面上，并使用荧光显微镜观察 GFP 融合的 fimbrin 肌动蛋白结合域 2 的结合。肌动蛋白结合域形成具有单向生长沿肌动蛋白丝的低密度聚集体。当通过增加脂质层的电荷密度将肌动蛋白丝紧密固定到表面时，聚集体形成受到抑制。这一结果表明，由肌动蛋白结合域结合引发的肌动蛋白丝协同结构变化的传播被与玻璃表面的强物理相互作用所抑制。有趣的是，fimbrin 肌动蛋白结合域的结合缩短了松散固定的肌动蛋白丝的长度。基于这些结果，我们提出 fimbrin-actin 相互作用伴随着单向远程变构有助于形成有序的平行肌动蛋白丝束。
