Department of Protein Biochemistry, Institute of Life Science, Kurume University, Kurume 839-0864, Japan.
Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases, Cologne 50931, Germany.
Nat Cell Biol. 2017 Jul;19(7):856-863. doi: 10.1038/ncb3560. Epub 2017 Jun 19.
Mitochondria are highly dynamic organelles that undergo frequent fusion and fission. Optic atrophy 1 (OPA1) is an essential GTPase protein for both mitochondrial inner membrane (IM) fusion and cristae morphology. Under mitochondria-stress conditions, membrane-anchored L-OPA1 is proteolytically cleaved to form peripheral S-OPA1, leading to the selection of damaged mitochondria for mitophagy. However, molecular details of the selective mitochondrial fusion are less well understood. Here, we showed that L-OPA1 and cardiolipin (CL) cooperate in heterotypic mitochondrial IM fusion. We reconstituted an in vitro membrane fusion reaction using purified human L-OPA1 protein expressed in silkworm, and found that L-OPA1 on one side of the membrane and CL on the other side are sufficient for fusion. GTP-independent membrane tethering through L-OPA1 and CL primes the subsequent GTP-hydrolysis-dependent fusion, which can be modulated by the presence of S-OPA1. These results unveil the most minimal intracellular membrane fusion machinery. In contrast, independent of CL, a homotypic trans-OPA1 interaction mediates membrane tethering, thereby supporting the cristae structure. Thus, multiple OPA1 functions are modulated by local CL conditions for regulation of mitochondrial morphology and quality control.
线粒体是高度动态的细胞器，经常发生融合和裂变。视神经萎缩 1（OPA1）是线粒体内膜（IM）融合和嵴形态所必需的 GTPase 蛋白。在应激条件下，膜锚定的 L-OPA1 被蛋白水解切割形成外周 S-OPA1，导致受损线粒体被选择性自噬。然而，对于选择性线粒体融合的分子细节了解较少。在这里，我们表明 L-OPA1 和心磷脂（CL）在异质线粒体 IM 融合中合作。我们使用在蚕中表达的纯化人 L-OPA1 蛋白重新构建了体外膜融合反应，并发现膜一侧的 L-OPA1 和另一侧的 CL 足以融合。通过 L-OPA1 和 CL 的非 GTP 依赖性膜连接为随后的 GTP 依赖性融合做准备，而 S-OPA1 的存在可以调节融合。这些结果揭示了最基本的细胞内膜融合机制。相反，不依赖于 CL，同源跨 OPA1 相互作用介导膜连接，从而支持嵴结构。因此，多个 OPA1 功能受局部 CL 条件的调节，以调节线粒体形态和质量控制。
