Essential transmembrane GTPase, which mediates mitochondrial fusion (PubMed:9685359, PubMed:9786948, PubMed:10562274, PubMed:11266460, PubMed:15297626, PubMed:15760898, PubMed:16624808, PubMed:19812251, PubMed:21385840, PubMed:21502136, PubMed:23317502, PubMed:27253069). Fusion proceeds through several steps; first mitochondria are tethered together, then brought into close contact, followed by the formation of a docking ring around contact areas, and finally membrane fusion (PubMed:27253069). Fusion of mitochondria occurs in many cell types and constitutes an important step in mitochondrial morphology, which is balanced between fusion and fission, mediated by FZO1 and DNM1, respectively (PubMed:10562274). Functions antagonistically with DNM1 (PubMed:10562274). Probably acts by forming membrane contact sites that mediate mitochondrial membrane fusion (PubMed:27253069). Mitochondrial docking and fusion requires GTP hydrolysis (PubMed:15297626, PubMed:19812251, PubMed:27253069). Mitochondrial fusion promotes also increased lifespan. GTP + H2O = GDP + H(+) + phosphate Homodimer (PubMed:16624808, PubMed:21385840, PubMed:19812251). Dimerization depends on GTP binding (PubMed:16624808, PubMed:21385840, PubMed:19812251). Component of a large multiprotein complex of 800 kDa (PubMed:9685359). Binds the cytoplasmic domain of UGO1 which binds MGM1 through its intermembrane space domain (PubMed:15087460, PubMed:12808034). Interacts with MDM30 (PubMed:21385840, PubMed:21502136, PubMed:16735578). Interacts with UBP2 and UBP12 (PubMed:23317502). Interacts (when ubiquitinated) with DOA1; the interaction recruits FZO1 to CDC48 and promotes FZO1 proteasomal degradation (PubMed:27044889). Detected at the periphery of mitochondrial contact sites that form before mitochondrial fusion. The GTPase domain may regulate the interaction with UGO1 since FZO1 lacking the GTPase domain binds 5-fold higher amount of UGO1 than full-length FZO1. The coiled-coil heptad repeat domains HRN, HR1 and HR2 are required for the oligomerization and function in mitochondrial fusion. Ubiquitinated at Lys-398 and Lys-464 (PubMed:19812251, PubMed:23317502, PubMed:27044889). MDM30 and UGO1 are involved in ubiquitination (PubMed:18353967, PubMed:21385840, PubMed:21502136). Deubiquitinated by UBP2 and UBP12 (PubMed:23317502). UBP2 and UBP12 recognize distinct ubiquitin chains on FZO1 that have opposing effects on mitochondrial fusion (PubMed:23317502). UBP2 removes ubiquitin chains that initiate proteolysis of FZO1 and inhibit fusion (PubMed:23317502). UBP12 recognizes ubiquitin chains that stabilize FZO1 and promote mitochondrial fusion. UBP12 deubiquitylates FZO1 only after oligomerization (PubMed:23317502). Present with 1000 molecules/cell in log phase SD medium. Belongs to the TRAFAC class dynamin-like GTPase superfamily. Dynamin/Fzo/YdjA family. Mitofusin subfamily.