Mitochondrial outer membrane GTPase that mediates mitochondrial clustering and fusion (PubMed:12527753, PubMed:23921378, PubMed:24513856, PubMed:15297672). Membrane clustering requires GTPase activity (By similarity). It may involve a major rearrangement of the coiled coil domains (PubMed:15297672). Mitochondria are highly dynamic organelles, and their morphology is determined by the equilibrium between mitochondrial fusion and fission events (PubMed:12527753). Overexpression induces the formation of mitochondrial networks (in vitro). Has low GTPase activity (By similarity). GTP + H2O = GDP + H(+) + phosphate Homodimer, also in the absence of bound GTP (By similarity). Forms higher oligomers in the presence of a transition state GTP analog (By similarity). Forms homomultimers and heteromultimers with MFN2 (PubMed:12527753). Oligomerization is essential for mitochondrion fusion (PubMed:15297672). Component of a high molecular weight multiprotein complex (By similarity). Interacts with VAT1 (By similarity). Interacts with THG1L; THG1L probably functions as a guanyl-nucleotide exchange factor/GEF, activating MFN1. Detected in adult heart (PubMed:12759376). Detected in embryos (at protein level) (PubMed:12527753). Widely expressed (PubMed:11950885). Expressed in 8.5 dpc, 9.5 dpc, 10.5 dpc and 11.5 dpc embryos. A helix bundle is formed by helices from the N-terminal and the C-terminal part of the protein. The GTPase domain cannot be expressed by itself, without the helix bundle. Rearrangement of the helix bundle and/or of the coiled coil domains may bring membranes from adjacent mitochondria into close contact, and thereby play a role in mitochondrial fusion. Ubiquitinated by MARCHF5 (By similarity). When mitochondria are depolarized and dysfunctional, it is ubiquitinated by a SCF (SKP1-CUL1-F-box protein) E3 ubiquitin-protein ligase complex that contains FBXO7 and PRKN. Ubiquitinated by non-degradative ubiquitin by PRKN, promoting mitochondrial fusion; deubiquitination by USP30 inhibits mitochondrial fusion (PubMed:24513856). Full embryonic lethality; nearly 90% of the mutant embryos have been resorbed at 11.5 dpc (PubMed:12527753). Contrary to wild-type embryonic fibroblasts that have elongated, tubular mitochondria, mutant embryonic fibroblasts contain only fragmented mitochondria (PubMed:12527753). In cultured cells, mutant mitochondria show a strongly decreased frequency of mitochondrial fusion events (PubMed:12527753). In spite of the aberrant mitochondrial morphology, there seem to be no gross defects in respiration (PubMed:12527753). Heart-specific disruption of Mfn1 does not impair heart function and has no effect on cardiomyocyte mitochondrial morphometry or respiratory function (PubMed:23620051). Belongs to the TRAFAC class dynamin-like GTPase superfamily. Dynamin/Fzo/YdjA family. Mitofusin subfamily. Extended N-terminus. Extended N-terminus.