Structural analysis of Dnm1, a dynamin involved in mitochondrial fission

动力蛋白家族由独特的gtpase组成，参与整个细胞的膜裂变和融合事件。我们的目标是了解这些蛋白质的动态结构特性，并将它们与不同的细胞功能联系起来。动力蛋白对细胞内吞作用和囊泡事件至关重要。其他动力蛋白家族成员参与了多种基本的细胞过程，包括线粒体分裂和融合、抗病毒活性、细胞板形成和叶绿体生物发生。在这些蛋白质中，自组装和寡聚化成有序结构是一个共同的特征，对大多数蛋白质来说，这对它们的功能至关重要。虽然关于动力蛋白的信息非常丰富，但对动力蛋白相关蛋白的结构特性知之甚少。

The dynamin family of proteins consists of unique GTPases involved in membrane fission and fusion events throughout the cell. Our goal is to understand the dynamic structural properties of these proteins and correlate them with their diverse cellular functions. Dynamin is essential for endocytosis and vesiculation events in the cell. Additional dynamin family members have been implicated in a variety of fundamental cellular processes, including mitochondrial fission and fusion, anti-viral activity, cell plate formation and chloroplast biogenesis. Among these proteins, self-assembly and oligomerization into ordered structures is a common characteristic and, for the majority, is essential for their function. Although there is a wealth of information regarding dynamin, little is known about the structural properties of dynamin-related proteins. To determine if a common mechanism of action exists among the dynamin family members, we examined the structure and function of Dnm1, a yeast dynamin family member involved in mitochondria fission. We have shown that Dnm1 assembles into large spirals, 100 nm in diameter compared to the 50 nm for dynamin spirals. Remarkably, the diameter of Dnm1 spirals is the same as that of mitochondrial constriction sites observed in cells. Dnm1 also assembles onto liposomes in the absence or presence of nucleotides, forming well-decorated tubes. In addition, the GTP hydrolysis rate of Dnm1 is highly cooperative with respect to its self-assembly state and concentration, which is consistent with the kinetic properties of dynamin. These results suggest that although dynamin family members share common characteristics, their structural properties are uniquely tailored to fit their function. Though Dnm1 can assemble onto liposomes in vitro, their assembly in cells is tightly regulated. Two additional mitochondrial proteins, Fis1 and Mdv1, are required and function together with Dnm1 in mitochondrial division. We have shown that Mdv1 interacts with Dnm1 only when Dnm1 is assembled into GTP-bound ring or spiral structures. GTPase mutants defective in binding GTP, which failed to self-assemble into spirals, no longer localized with Mdv1. These findings suggest Mdv1 functions in fission by stabilizing or promoting the formation of Dnm1 into spiral-like structures. Mdv1 may accomplish this by stabilizing the GTP bound form of Dnm1 or by acting as a nucleator, promoting Dnm1 to form spirals at sites of membrane constriction.