A balance between mitochondrial membrane fusion and fission is required for normal mitochondrial morphology and function. Mitofusins are outer mitochondrial trans-membrane proteins that are required for mitochondrial fusion and are members of the dynamin family of GTPases. Our goal is to reveal the mechanism of mitofusins by cryo-electron microscopy and biophysical assays. To accomplish this we are studying the structure of mitofusin 1 in a lipid bilayer as well as the function of a soluble truncation. Here, we present a purification strategy of mitofusin 1 and cryo-EM images of full-length mitofusin 1 in a lipid bilayer. In addition, we show that mitofusin 1 alone in the presence of GTP is capable of tethering proteolipsosomes and that the soluble G-domain truncation is enzymatically active. These preliminary findings imply that mitofusins are sufficient for initiating membrane fusion.