Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing, 100084, China.
College of Life Sciences, Fujian Agriculture and Forestry University, Fuzhou, Fujian, China.
Plant J. 2024 Sep;119(6):2854-2866. doi: 10.1111/tpj.16956. Epub 2024 Aug 2.
Being a bona fide actin bundler, Arabidopsis villin5 (VLN5) plays a crucial role in regulating actin stability and organization within pollen tubes. Despite its significance, the precise mechanism through which VLN5 bundles actin filaments has remained elusive. Through meticulous deletion analysis, we have unveiled that the link between gelsolin repeat 6 (G6) and the headpiece domain (VHP), rather than VHP itself, is indispensable for VLN5-mediated actin bundling. Further refinement of this region has pinpointed a critical sequence spanning from Val763 to Ser823, essential for VLN5's actin-bundling activity. Notably, the absence of Val763-Ser823 in VLN5 results in decreased filamentous decoration within pollen tubes and a diminished ability to rescue actin bundling defects in vln2vln5 mutant pollen tubes compared to intact VLN5. Moreover, our findings highlight that the Val763-Ser823 sequence harbors a binding site for F-actin, suggesting that this linker-based F-actin binding site, in conjunction with the F-actin binding site localized in G1-G6, enables a single VLN5 to concurrently bind to two adjacent actin filaments. Therefore, our study unveils a novel mechanism by which VLN5 bundles actin filaments.
作为一个真正的肌动蛋白结合蛋白，拟南芥 villin5（VLN5）在调节花粉管中肌动蛋白的稳定性和组织中起着至关重要的作用。尽管它很重要，但 VLN5 结合肌动蛋白丝的精确机制仍然难以捉摸。通过细致的删除分析，我们揭示了肌球蛋白重复 6（G6）和头部结构域（VHP）之间的连接，而不是 VHP 本身，对于 VLN5 介导的肌动蛋白结合是必不可少的。对该区域的进一步细化确定了一个关键序列，从 Val763 到 Ser823，对于 VLN5 的肌动蛋白结合活性是必不可少的。值得注意的是，VLN5 中缺失 Val763-Ser823 会导致花粉管中丝状装饰减少，并且与完整的 VLN5 相比，VLN5 突变体花粉管中 actin 结合缺陷的恢复能力降低。此外，我们的研究结果表明，Val763-Ser823 序列含有 F-肌动蛋白的结合位点，这表明该基于接头的 F-肌动蛋白结合位点与位于 G1-G6 中的 F-肌动蛋白结合位点结合，使单个 VLN5 能够同时结合两个相邻的肌动蛋白丝。因此，我们的研究揭示了 VLN5 结合肌动蛋白丝的一种新机制。
