Institute for Genetics, University of Cologne, 50674 Cologne, Germany.
J Cell Sci. 2011 Apr 1;124(Pt 7):1126-35. doi: 10.1242/jcs.073080. Epub 2011 Mar 8.
Dynamin-related GTPase proteins (DRPs) are main players in membrane remodelling. Conserved DRPs called mitofusins (Mfn1/Mfn2/Fzo1) mediate the fusion of mitochondrial outer membranes (OM). OM fusion depends on self-assembly and GTPase activity of mitofusins as well as on two other proteins, Ugo1 and Mdm30. Here, we define distinct steps of the OM fusion cycle using in vitro and in vivo approaches. We demonstrate that yeast Fzo1 assembles into homo-dimers, depending on Ugo1 and on GTP binding to Fzo1. Fzo1 homo-dimers further associate upon formation of mitochondrial contacts, allowing membrane tethering. Subsequent GTP hydrolysis is required for Fzo1 ubiquitylation by the F-box protein Mdm30. Finally, Mdm30-dependent degradation of Fzo1 completes Fzo1 function in OM fusion. Our results thus unravel functions of Ugo1 and Mdm30 at distinct steps during OM fusion and suggest that protein clearance confers a non-cycling mechanism to mitofusins, which is distinct from other cellular membrane fusion events.
动力相关 GTP 酶蛋白（DRPs）是膜重塑的主要参与者。被称为线粒体融合蛋白（Mfn1/Mfn2/Fzo1）的保守 DRPs 介导线粒体外膜（OM）的融合。OM 融合依赖于线粒体融合蛋白的自组装和 GTPase 活性，以及另外两种蛋白质 Ugo1 和 Mdm30。在这里，我们使用体外和体内方法定义了 OM 融合循环的不同步骤。我们证明酵母 Fzo1 依赖于 Ugo1 和 Fzo1 与 GTP 的结合形成同二聚体。Fzo1 同二聚体进一步在形成线粒体接触时缔合，允许膜连接。随后的 GTP 水解是 F-box 蛋白 Mdm30 对 Fzo1 进行泛素化所必需的。最后，Fzo1 功能的完成依赖于 Mdm30 依赖的 Fzo1 降解。因此，我们的结果揭示了 Ugo1 和 Mdm30 在 OM 融合过程中的不同步骤中的功能，并表明蛋白质清除赋予线粒体融合蛋白一种非循环机制，这与其他细胞的膜融合事件不同。
