Structural Biology Research Center, Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Ibaraki, Japan.
EMBO J. 2012 May 30;31(11):2590-603. doi: 10.1038/emboj.2012.89. Epub 2012 Apr 20.
A small GTPase, Arf6, is involved in cytokinesis by localizing to the Flemming body (the midbody). However, it remains unknown how Arf6 contributes to cytokinesis. Here, we demonstrate that Arf6 directly interacts with mitotic kinesin-like protein 1 (MKLP1), a Flemming body-localizing protein essential for cytokinesis. The crystal structure of the Arf6-MKLP1 complex reveals that MKLP1 forms a homodimer flanked by two Arf6 molecules, forming a 2:2 heterotetramer containing an extended β-sheet composed of 22 β-strands that spans the entire heterotetramer, suitable for interaction with a concave membrane surface at the cleavage furrow. We show that, during cytokinesis, Arf6 is first accumulated around the cleavage furrow and, prior to abscission, recruited onto the Flemming body via interaction with MKLP1. We also show by structure-based mutagenesis and siRNA-mediated knockdowns that the complex formation is required for completion of cytokinesis. A model based on these results suggests that the Arf6-MKLP1 complex plays a crucial role in cytokinesis by connecting the microtubule bundle and membranes at the cleavage plane.
一个小的 GTPase，Arf6，通过定位于弗莱明体（中体）参与胞质分裂。然而，Arf6 如何促进胞质分裂仍不清楚。在这里，我们证明 Arf6 直接与有丝分裂驱动蛋白样蛋白 1（MKLP1）相互作用，MKLP1 是胞质分裂所必需的弗莱明体定位蛋白。Arf6-MKLP1 复合物的晶体结构揭示了 MKLP1 形成一个同源二聚体，两侧是两个 Arf6 分子，形成一个 2:2 的异四聚体，包含一个由 22 条β-链组成的伸展β-片层，横跨整个异四聚体，适合与分裂沟处的凹面膜表面相互作用。我们表明，在胞质分裂过程中，Arf6 首先在分裂沟周围积累，并在分离之前通过与 MKLP1 的相互作用招募到弗莱明体上。我们还通过基于结构的诱变和 siRNA 介导的敲低表明，复合物的形成对于胞质分裂的完成是必需的。基于这些结果的模型表明，Arf6-MKLP1 复合物通过连接分裂平面处的微管束和膜在胞质分裂中发挥关键作用。
