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MFN1

Official Full Name
mitofusin 1
Background
The protein encoded by this gene is a mediator of mitochondrial fusion. This protein and mitofusin 2 are homologs of the Drosophila protein fuzzy onion (Fzo). They are mitochondrial membrane proteins that interact with each other to facilitate mitochondrial targeting. [provided by RefSeq, Jul 2008]
Synonyms
MFN1; mitofusin 1; hfzo1; hfzo2; mitofusin-1; fzo homolog; transmembrane GTPase MFN1; putative transmembrane GTPase; mitochondrial transmembrane GTPase FZO-2; mitochondrial transmembrane GTPase Fzo-1; FLJ20693; MGC41806; DKFZp762F247

The mitofusin gene (Mfn) encodes two protein molecules, Mfn1 and Mfn2, which play an important role in mitochondrial fusion, division and apoptosis, and regulate the dynamic changes of mitochondrial morphology. In addition, Mfn1/2 is also involved in the energy metabolism of mitochondria and is closely related to the occurrence of related diseases. Mfn1 consists of 742 amino acid residues, localizes to the mitochondrial outer membrane, contains a transmembrane region, and then forms a U-shaped membrane anchor that terminates in the cytoplasm and forms the C-terminus. The C-terminus also has a transmembrane region, and each of the transmembrane regions has a hydrophobic region on each side, similar to a coiled-coil, which plays an important role in triggering mitochondrial fusion.

The Role of Mfn1

Deletion of any of Mfn1 in mice can cause embryonic lethality and mitochondrial fragmentation. Studies have confirmed the crystal structure of Mfn1 in the hydrolysis stage of different GTPases. The structure consists of a GTPase domain and a four-stranded helical bundle (referred to as HD1). Thus, overall Mfn1 has a typical dymamin superfamily member topology.

Mfn1 is involved in embryonic development. Mfn1 knockout mice have embryonic developmental retardation and embryonic death in the second trimester, whereas if the Mfn1 and Mfn2 genes are simultaneously knocked out, mouse embryonic developmental retardation is more pronounced and embryonic death is earlier. Further studies have found that Mfn2 mutant embryonic placenta nourishes giant cell layer cell function is severely impaired, while Mfn1 mutant embryonic placental trophoblast giant cells are normal. In the Mfn1 knockout embryonic fibroblasts, mitochondria are fragmented to varying degrees. An Mfn1 for structural analysis was designed, containing the GTPase (G) domain and the first half of HR1 and the second half of HR2.

Mfn1.pngFigure 1. Mini-MFN1 and a new proposed model of mitochondrial fusion mediated by MFN1.(Formosa, L E. , et al. 2016)

Mfn1 Fusion with Mitochondria

Studies have shown that the Mfn1 complex plays a role in mitochondrial fusion. Mitochondrial fusion protects cells from apoptosis and acts as a maintenance mechanism for extracellular membrane damage. Studies have shown that a mutation in Mfn1 is highly deleterious in mammalian pregnancy. Mfn1 knockout mice develop severe stunting and tortuosity. If Mfn2 is absent in mouse embryos, the killing effect may be slower, but eventually they will die of placental defects. These studies have shown that cell growth requires mitochondrial fusion, while Mfn1 and Mfn2 are not redundant in this process.

Mfn1 and Mfn2 in mice is beneficial for the protection of mutations in CMT2A type disease caused by mitochondrial fusion defects. Before mitochondria, Mfn1 and Mfn2 form an oligomer-bound mitochondrial outer membrane, and a decrease in Mfn1 or Mfn2 leads to mitochondrial fragmentation. The results of this study show that the mutated Mfn2 forms a complex with Mfn1 or wild-type Mfn2, whereas only the complex containing Mfn1 promotes mitochondrial fusion. In addition, studies have found that patients with dying CMT2A disease may have lower Mfn1/Mfn2 ratios in sensory and motor neurons, and they lack sufficient Mfn1 and Mfn2 to form a complex. Another study found that Mfn1 is a key protein that maintains the tubular structure of the mitochondrial membrane network. When the expression of Mfn1 is decreased, the mitochondria undergo membrane cleavage, and the morphology is broken by the normal tubular membrane network into a small vesicular membrane structure, and the energy synthesis is decreased.

References:

  1. Oanh, N. T. K. , Park, Y. Y. , & Cho, H. . (2017). Mitochondria elongation is mediated through sirt1-mediated mfn1 stabilization. Cellular Signalling, 38, 67-75.
  2. Cao, Y. L. , Meng, S. , Chen, Y. , Feng, J. X. , Gu, D. D. , & Yu, B. , et al. (2017). Mfn1 structures reveal nucleotide-triggered dimerization critical for mitochondrial fusion. Nature,542(7641), 372-376.
  3. Formosa, L E. , Ryan, M T.. (2016) Mitochondrial fusion: Reaching the end of mitofusin's tether. The Journal of cell biology, 5(215), 597-598.

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