EFA6 activates Arf6 and participates in its targeting to the Flemming body during cytokinesis.

The small GTPase Arf6 is transiently associated with the ingressing cleavage furrow and subsequently targeted to the Flemming body during cytokinesis, suggesting its activation around the cleavage furrow. Here, we show that EFA6 (exchange factor for Arf6) localizes on the cleavage furrow through its PH domain. Time-lapse analysis showed that both EFA6 and Arf6 are transiently localized around the ingressing cleavage furrow, but only Arf6 is subsequently targeted to the Flemming body. Expression of an EFA6 mutant suppresses Arf6 recruitment onto the Flemming body. These results suggest that EFA6 participates in activation of Arf6 around the cleavage furrow during cytokinesis

Structural basis for Arf6-MKLP1 complex formation on the Flemming body responsible for cytokinesis

正常な細胞分裂に不可欠なタンパク質の機能と構造を解明. 京都大学プレスリリース. 2012-05-31.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