Institute for Genetics, Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), Center for Molecular Medicine Cologne, University of Cologne, Cologne, Germany.
CECAD, University of Cologne, Cologne, Germany.
Life Sci Alliance. 2019 Nov 18;2(6). doi: 10.26508/lsa.201900491. Print 2019 Dec.
Mitofusins are dynamin-related GTPases that drive mitochondrial fusion by sequential events of oligomerization and GTP hydrolysis, followed by their ubiquitylation. Here, we show that fusion requires a trilateral salt bridge at a hinge point of the yeast mitofusin Fzo1, alternatingly forming before and after GTP hydrolysis. Mutations causative of Charcot-Marie-Tooth disease massively map to this hinge point site, underlining the disease relevance of the trilateral salt bridge. A triple charge swap rescues the activity of Fzo1, emphasizing the close coordination of the hinge residues with GTP hydrolysis. Subsequently, ubiquitylation of Fzo1 allows the AAA-ATPase ubiquitin-chaperone Cdc48 to resolve Fzo1 clusters, releasing the dynamin for the next fusion round. Furthermore, cross-complementation within the oligomer unexpectedly revealed ubiquitylated but fusion-incompetent Fzo1 intermediates. However, Cdc48 did not affect the ubiquitylated but fusion-incompetent variants, indicating that Fzo1 ubiquitylation is only controlled after membrane merging. Together, we present an integrated model on how mitochondrial outer membranes fuse, a critical process for their respiratory function but also putatively relevant for therapeutic interventions.
线粒体融合蛋白是动力相关 GTP 酶，通过寡聚化和 GTP 水解的连续事件，以及随后的泛素化，驱动线粒体融合。在这里，我们表明融合需要酵母线粒体融合蛋白 Fzo1 铰链点处的三边盐桥，在 GTP 水解前后交替形成。导致 Charcot-Marie-Tooth 病的突变大量映射到这个铰链点，突出了三边盐桥与疾病的相关性。三重电荷交换挽救了 Fzo1 的活性，强调了铰链残基与 GTP 水解的紧密协调。随后，Fzo1 的泛素化允许 AAA-ATPase 泛素连接酶 Cdc48 解析 Fzo1 簇，为下一轮融合释放动力。此外，出乎意料的是，在寡聚体之间的交叉互补揭示了泛素化但融合失活的 Fzo1 中间体。然而，Cdc48 不会影响泛素化但融合失活的变体，表明 Fzo1 泛素化仅在膜融合后受到控制。总之，我们提出了一个关于线粒体外膜如何融合的综合模型，这是它们呼吸功能的关键过程，但也可能与治疗干预有关。
