MIEF2

MIEF2 (MiD49) is a mitochondrial outer membrane adaptor that drives mitochondrial fission by directly recruiting the cytosolic GTPase Drp1 to the mitochondrial surface, where it forms foci and rings; its loss reduces Drp1 association and produces unopposed, mitofusin-dependent fusion (PMID:21508961, PMID:23921378). MiD49 confers organelle specificity to fission, operating independently of Fis1 and Mff and, unlike those factors, sparing peroxisomes (PMID:23921378, PMID:23283981). Structurally, MiD49 adopts a nucleotidyl transferase fold that has lost the functional nucleotide-binding pocket conserved in its paralog MiD51, but retains a surface loop that physically engages Drp1 and is required for Drp1 recruitment — an interface that is druggable, as a small molecule binding this site locks Drp1 in a closed, inactive dimer (PMID:25581164, PMID:37583827). Beyond passive recruitment, MiD49 is allosterically activated by long-chain acyl-CoA, which induces its oligomerization and thereby stimulates Drp1 GTPase activity in synergy with Mff (PMID:38594588). MiD49 abundance is set by MARCH5-mediated ubiquitination and proteasomal degradation, a process antagonized by Drp1 and Mff and by transcriptional repression through Foxo3a (PMID:26564796, PMID:27932492, PMID:28137654). Functionally, MiD49/MiD51-dependent fission — but not Mff-dependent fission — is specifically required for apoptotic cristae remodeling and cytochrome c release, so that combined loss of the two MiDs confers resistance to intrinsic apoptosis and protects against cardiac and other stress injury (PMID:26903540, PMID:27076521, PMID:41892348). MiD activity is further linked to cell-cycle progression in pulmonary arterial hypertension and to PINK1-Parkin mitophagy and fatty acid oxidation (PMID:29431643, PMID:40846102).

1. 2011 High

   Established MiD49 as a mitochondrial outer-membrane factor that physically recruits Drp1 to mitochondria, answering how cytosolic Drp1 is targeted to the fission machinery.

   Evidence Immunofluorescence, knockdown, and overexpression in cell lines

   PMID:21508961

   Open questions at the time

   • Did not define the structural basis of the Drp1 interaction
   • Relationship to existing receptors Fis1 and Mff unresolved
2. 2013 High

   Showed MiD49 mediates fission independently of Fis1 and Mff and confers mitochondrial specificity by not targeting peroxisomes, distinguishing it mechanistically from prior Drp1 receptors.

   Evidence Organelle-targeting constructs and immunofluorescence in Fis1/Mff-null cells; mitofusin double-knockout epistasis

   PMID:23283981 PMID:23921378

   Open questions at the time

   • Why overexpression sequesters Drp1 in an inactive state rather than activating it not fully explained
3. 2015 High

   Resolved the MiD49 atomic structure, revealing a nucleotidyl transferase fold lacking a functional nucleotide pocket and a defined surface loop required for Drp1 recruitment, explaining how MiD49 engages Drp1 and diverges from MiD51.

   Evidence X-ray crystallography at 2.4 Å with surface-entropy-reduction mutagenesis and binding/rescue assays

   PMID:25581164

   Open questions at the time

   • Functional consequence of the absent nucleotide pocket left open at the time
   • Did not capture the Drp1-bound complex
4. 2015 High

   Identified MARCH5 as the E3 ligase controlling MiD49 turnover, establishing ubiquitin-proteasome regulation of fission-receptor abundance and linking it to apoptosis sensitivity.

   Evidence MARCH5/MiD49 knockout cells, ubiquitination and proteasome-inhibitor assays, co-immunoprecipitation

   PMID:26564796

   Open questions at the time

   • Signals triggering MARCH5-dependent MiD49 degradation not defined
5. 2016 High

   Defined the apoptotic role of MiD-dependent fission, showing MiD49/51 but not Mff is required for cristae remodeling and cytochrome c release, separating fission receptors by downstream function.

   Evidence MiD49/51 and Mff knockout panels, apoptosis and cytochrome c assays, OPA1 depletion epistasis; BioID proximity labeling and Drp1 GTPase assays

   PMID:26903540 PMID:27076521

   Open questions at the time

   • Molecular link between MiD-driven fission and inner-membrane cristae remodeling unresolved
6. 2016 High

   Revealed a feedback loop in which Drp1 and Mff protect MiD49 from MARCH5-mediated degradation, coupling fission-machinery occupancy to receptor stability.

   Evidence Double-knockout cell lines, pulse-chase half-life and ubiquitination assays, co-immunoprecipitation

   PMID:27932492

   Open questions at the time

   • Mechanism by which Drp1/Mff binding shields MiD49 from MARCH5 not structurally defined
7. 2017 Medium

   Placed MIEF2 downstream of Foxo3a transcriptional repression in doxorubicin cardiotoxicity, adding transcriptional control to the regulation of fission.

   Evidence Foxo3a gain/loss-of-function, MIEF2 knockdown, cardiac-specific Foxo3a transgenic mice

   PMID:28137654

   Open questions at the time

   • Direct ChIP/reporter validation of Foxo3a binding not detailed
   • Single lab
8. 2018 Medium

   Connected MiD49/51 upregulation (via reduced miR-34a-3p) to Drp1-mediated mitotic fission and cell-cycle progression in pulmonary arterial hypertension.

   Evidence siRNA knockdown, cell-cycle flow cytometry, miRNA manipulation, monocrotaline-PAH rat siRNA nebulization

   PMID:29431643

   Open questions at the time

   • ERK1/2- and CDK4-dependent link to fission only partially defined
   • Single lab
9. 2024 High

   Identified long-chain acyl-CoA as an allosteric activator that drives MiD49/51 oligomerization to stimulate Drp1 GTPase activity, explaining how the nucleotide-pocket region functions despite lacking catalytic activity.

   Evidence In vitro Drp1 GTPase and oligomerization assays, point mutagenesis, oleic-acid cellular rescue

   PMID:38594588

   Open questions at the time

   • Physiological conditions producing activating LCACA levels not defined
   • Whether endogenous lipid flux regulates MiD49 oligomerization in vivo unestablished
10. 2023 Medium

    Validated the MiD49-Drp1 interface as a druggable allosteric site by capturing a Drp1-inhibitor co-structure that locks Drp1 in a closed dimer.

    Evidence X-ray co-crystallography and in vitro mitochondrial fragmentation assay

    PMID:37583827

    Open questions at the time

    • Limited functional follow-up
    • Cellular efficacy and selectivity not detailed
11. 2025 Medium

    Extended the MARCH5-MIEF2 degradation axis into alcoholic liver disease, where MIEF2 acts downstream of MARCH5 to control lipid accumulation, MAM formation, and cell death.

    Evidence Co-IP, ubiquitination assays, gain/loss-of-function rescue, zebrafish and mouse models

    PMID:41353882

    Open questions at the time

    • Tissue-specific regulators of the MARCH5-MIEF2 axis unresolved
    • Single lab
12. 2025 Medium

    Demonstrated that combined, but not individual, MiD49/51 inhibition is needed for cardioprotection in ischemia-reperfusion, showing functional redundancy between the two receptors in vivo.

    Evidence siRNA dual knockdown in cardiac cells, MPTP and calcium assays, MiD49 whole-body knockout mice in AMI model

    PMID:41892348

    Open questions at the time

    • MiD49 single knockout effect on infarct size minimal — degree of redundancy not fully mapped
    • Single lab
13. 2022 Medium

    Placed MiD49/51 upstream of PINK1-Parkin mitophagy and CPT-1A-mediated fatty acid oxidation in rheumatoid arthritis synoviocytes, linking fission receptors to mitochondrial quality control and metabolism.

    Evidence siRNA knockdown, mitophagy and fatty acid oxidation assays, CIA mouse model with shRNA

    PMID:40846102

    Open questions at the time

    • Direct biochemical link between MiD-driven fission and PINK1-Parkin recruitment not established
    • Single lab

• How the multiple regulatory inputs on MiD49 — lipid-induced oligomerization, MARCH5 degradation, Drp1/Mff feedback, and transcriptional control — are integrated to time fission in vivo remains unresolved.
• No unified model coupling lipid sensing, stability, and transcriptional control
• Structure of the active MiD49-Drp1 oligomer on the membrane undetermined