MICOS13

MICOS13 (QIL1/MIC13/C19orf70) is an inner mitochondrial membrane subunit of the MICOS complex that is strictly required for crista junction formation and normal cristae architecture (PMID:25997101, PMID:27479602). It governs the hierarchical assembly of MICOS by coupling the two structural modules: it is dispensable for the MIC60/MIC19/MIC25 subcomplex but is required for incorporation and stability of the MIC10-containing membrane-sculpting subcomplex (MIC10/MIC26/MIC27), such that its loss collapses MICOS into a residual MIC60 subcomplex with loss of MIC10 (PMID:25997101, PMID:27479602). The yeast ortholog Mic12 plays the equivalent bridging role between the two subcomplexes (PMID:26968360). Membrane insertion of MIC13 depends on an N-terminal GxxxG transmembrane motif, while an internal WN motif is required for its own stability and for its interaction with both the MIC10- and MIC60-subcomplexes (PMID:34271005). Its primary action is stabilization of the MIC10-subcomplex: MIC13 interacts with stomatin-like protein 2 (SLP2) to protect MIC26 and the MIC10-subcomplex from YME1L-mediated degradation, and depleting YME1L in MIC13-knockout cells restores the MIC10-subcomplex, MIC60-MIC10 interaction, and crista junctions (PMID:39720525). Through this assembly role MICOS13 is required for mitochondrial respiratory chain function, with re-expression rescuing respiratory deficiencies in patient cells (PMID:32749073). Loss-of-function mutations in human MICOS13 cause a fatal infantile mitochondrial hepato-encephalopathy with MICOS disassembly, cristae defects, and impaired OXPHOS (PMID:27623147, PMID:27485409, PMID:29618761).

1. 2015 High

   Established that an uncharacterized protein is an obligate subunit of the human MICOS complex, answering whether MICOS assembly requires factors beyond the known MIC60/MIC10 cores.

   Evidence Quantitative AP-MS, siRNA knockdown in human cells and Drosophila, and reciprocal Co-IP

   PMID:25997101

   Open questions at the time

   • Did not resolve whether MIC10 loss reflected failed integration versus instability
   • No structural basis for how QIL1 couples subcomplexes
2. 2015 Medium

   Distinguished assembly from stability by showing QIL1 is needed to integrate MIC10 into MICOS rather than merely to maintain MIC10 levels.

   Evidence Co-IP after MIC10 overexpression in QIL1-depleted human cells

   PMID:25997101

   Open questions at the time

   • Overexpression rescue is indirect; molecular contact points untested
   • Did not address SAMM50/MIB integration mechanism
3. 2016 High

   Defined MIC13 as strictly required for crista junction formation and mapped the hierarchical MICOS assembly dependency in human cells.

   Evidence CRISPR/Cas9 knockout with complexome profiling, Co-IP, and electron microscopy

   PMID:27479602

   Open questions at the time

   • Did not identify the residues mediating bridging
   • Crista junction loss without supercomplex disruption left functional consequence partly open
4. 2016 High

   Confirmed the bridging role is evolutionarily conserved by showing the yeast ortholog Mic12 couples the Mic60 and Mic10 modules.

   Evidence Yeast deletion genetics, Co-IP, and BN-PAGE

   PMID:26968360

   Open questions at the time

   • Yeast subunit composition differs from mammals
   • No structural model of the coupling interface
5. 2016 High

   Linked MICOS13 to human disease and confirmed causality by showing patient null alleles disassemble MICOS and that re-expression rescues cristae defects.

   Evidence Patient fibroblast analysis with lentiviral rescue, immunoblotting, and EM across independent families

   PMID:27485409 PMID:27623147

   Open questions at the time

   • Tissue-specific basis of hepato-encephalopathy not explained
   • Mechanism connecting cristae loss to bioenergetic failure not dissected
6. 2018 Medium

   Extended the disease phenotype to liver and muscle tissue, showing a splice-site mutation selectively eliminates the MIC10-MIC26-MIC27-QIL1 subcomplex with severe OXPHOS impairment.

   Evidence Patient tissue immunoblotting, BN-PAGE, EM, and respiratory chain enzyme assays

   PMID:29618761

   Open questions at the time

   • No rescue experiment reported
   • Single patient/lab
7. 2020 Medium

   Confirmed the causal role of MICOS13 in maintaining respiratory chain function through genetic complementation in patient cells.

   Evidence Patient fibroblasts with lentiviral wild-type re-expression, EM, and respiratory chain complex activity assays

   PMID:32749073

   Open questions at the time

   • Single lab
   • Did not separate cristae structural defect from direct respiratory effects
8. 2021 High

   Mapped the functional architecture of MIC13 to specific motifs, defining a GxxxG motif for membrane insertion and a WN motif for stability and dual-subcomplex interaction.

   Evidence Systematic deletion-variant expression in MIC13-KO cells with BN-PAGE, Co-IP, and EM

   PMID:34271005

   Open questions at the time

   • No atomic structure of motif-mediated contacts
   • Single lab
9. 2024 High

   Refined the mechanistic model from direct bridging to subcomplex stabilization by showing MIC13 acts via SLP2 to protect the MIC10-subcomplex from YME1L proteolysis.

   Evidence Multiple genetic KO combinations (MIC13, SLP2, YME1L), Co-IP, BN-PAGE, STED nanoscopy, and EM with functional rescue

   PMID:39720525

   Open questions at the time

   • Precise SLP2-MIC13 interaction interface unresolved
   • How stabilization translates into crista junction geometry not fully defined
10. 2025 Medium

    Defined the nanoscale molecular neighborhood of MIC13, placing it adjacent to OXPHOS, translocase, ribosomal, and solute carrier machinery.

    Evidence APEX2 proximity biotinylation in KO cells with mass spectrometry, STED nanoscopy, and DAB-EM (preprint)

    PMID:bio_10.1101_2025.05.20.655052

    Open questions at the time

    • Proximity does not establish direct interaction
    • Preprint, single lab, awaits peer review

• How MIC13-dependent stabilization of the MIC10-subcomplex is mechanically converted into crista junction formation, and the structural basis of its motif-mediated contacts, remain unresolved.
• No high-resolution structure of MIC13 within MICOS
• Mechanistic link between cristae morphology and tissue-specific disease severity unknown