The fusion of mammalian inner mitochondrial membranes (IMMs) is mediated by dynamin-like GTPase OPA1. Mutations in human OPA1 cause optic atrophy, but the molecular basis for membrane fusion and pathogenesis is not clear. Here, we determined the crystal structure of the minimal GTPase domain (MGD) of human OPA1. A three-helix bundle (HB) domain including two helices extending from the GTPase (G) domain and the last helix of OPA1 tightly associates with the G domain. In the presence of GDP and BeF3−, OPA1-MGD forms a dimer, the interface of which is critical for the maintenance of mitochondrial morphology. The catalytic core of OPA1 possesses unique features that are not present in other dynamin-like proteins. Biochemical experiments revealed that OPA1-MGD forms nucleotide-dependent dimers, which is important for membrane-stimulated GTP hydrolysis, and an N-terminal extension mediates nucleotide-independent dimerization that facilitates efficient membrane association. Our results suggest a multifaceted assembly of OPA1 and explain the effect of most OPA1 mutations on optic atrophy.

中文翻译：

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G 结构域二聚化和 OPA1 致病突变的结构见解

哺乳动物线粒体内膜 (IMM) 的融合由动力蛋白样 GTPase OPA1 介导。人类OPA1突变导致视神经萎缩，但膜融合和发病机制的分子基础尚不清楚。在这里，我们确定了人类 OPA1 最小 GTP 酶结构域 (MGD) 的晶体结构。三螺旋束 (HB) 结构域包括从 GTPase (G) 结构域延伸的两个螺旋，OPA1 的最后一个螺旋与 G 结构域紧密结合。在 GDP 和 BeF3− 存在的情况下，OPA1-MGD 形成二聚体，其界面对于维持线粒体形态至关重要。OPA1 的催化核心具有其他动力蛋白所不具备的独特功能。生化实验表明，OPA1-MGD 形成核苷酸依赖性二聚体，这对于膜刺激的 GTP 水解非常重要，并且 N 末端延伸介导不依赖于核苷酸的二聚化，从而促进有效的膜缔合。我们的结果表明 OPA1 具有多方面的组装，并解释了大多数 OPA1 突变对视神经萎缩的影响。