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TMEM126A

Transmembrane protein 126A · UniProt Q9H061

Length
195 aa
Mass
21.5 kDa
Annotated
2026-06-10
11 papers in source corpus 9 papers cited in narrative 9 extracted findings
Cross-family judge vs UniProt: tie faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

TMEM126A is an inner mitochondrial membrane protein localized to the cristae compartment that functions in the biogenesis of the oxidative phosphorylation machinery (PMID:23500070, PMID:33879611). It acts as an assembly factor for the ND4 distal membrane module of mitochondrial complex I, associating with the newly synthesized mtDNA-encoded ND4 subunit during assembly and remaining bound to a stable ND4-module intermediate; this role is distinct from its paralog TMEM126B, which serves the ND2 module (PMID:33879611, PMID:33882309). Mechanistically, TMEM126A cooperates with the inner-membrane insertase OXA1L and associates with mitochondrial ribosomes and nascent translation products to support co-translational insertion of mtDNA-encoded proteins; in its absence, translation products are destabilized and cleared by the iAAA protease, and cargo-blocked OXA1L complexes are likewise removed proteolytically (PMID:38199007). Consistent with this biogenesis role, biallelic TMEM126A mutations cause autosomal-recessive nonsyndromic optic atrophy through mitochondrial dysfunction (PMID:19327736). Loss of TMEM126A also produces isolated complex I deficiency (PMID:33879611).

Mechanistic history

Synthesis pass · year-by-year structured walk · 6 steps
  1. 2009 Medium

    Established TMEM126A as a disease gene, linking it to mitochondrial dysfunction before any direct molecular role was known.

    Evidence whole-genome homozygosity mapping and positional cloning in optic atrophy families

    PMID:19327736

    Open questions at the time
    • Mitochondrial localization inferred but not directly demonstrated
    • No molecular function assigned
    • Mechanism linking mutation to optic atrophy unresolved
  2. 2013 High

    Resolved where TMEM126A acts by placing it in the inner mitochondrial membrane cristae and showing a transmembrane domain dictates targeting.

    Evidence fractionation, proteolysis protection, EM, confocal imaging of deletion constructs, and mRNA FISH

    PMID:23500070

    Open questions at the time
    • No molecular activity or interaction partners identified
    • Functional consequence of cristae localization not defined
  3. 2018 Medium

    Connected TMEM126A loss to downstream cellular phenotypes via ROS-driven mitochondrial retrograde signaling in cancer cells.

    Evidence siRNA/overexpression with ROS and membrane-potential assays, metastasis assays, and ROS-scavenger rescue in breast cancer cells

    PMID:30393159

    Open questions at the time
    • No direct biochemical mechanism linking TMEM126A to ROS
    • Single lab without reconstitution
    • Relationship to complex I role not established at the time
  4. 2021 High

    Defined the core molecular function: TMEM126A is an assembly factor for the complex I ND4 distal membrane module that binds newly synthesized ND4.

    Evidence knockout, reciprocal interaction studies, pulse-labeling, and quantitative proteomics, independently corroborated by NDUFS3 ablation with native PAGE and MS

    PMID:33879611 PMID:33882309

    Open questions at the time
    • Structural basis of ND4 recognition not resolved
    • How TMEM126A is released from the intermediate unknown
  5. 2024 High

    Extended the mechanism to co-translational membrane insertion, showing TMEM126A partners with OXA1L and the mitoribosome and links to iAAA protease quality control.

    Evidence interaction proteomics, ribosome association assays, and iAAA protease dependency assays in loss-of-function cells

    PMID:38199007

    Open questions at the time
    • Direct structural arrangement with OXA1L not defined
    • How insertion role and ND4-module assembly role are coordinated unclear
  6. 2024 Medium

    Refined sub-organellar localization to the cristae using integrative structural and imaging approaches.

    Evidence cross-linking MS and coarse-grained MD validated by super-resolution microscopy (preprint)

    PMID:bio_10.1101_2024.09.11.612425

    Open questions at the time
    • Preprint, single lab
    • Does not address functional consequences of cristae positioning

Open questions

Synthesis pass · forward-looking unresolved questions
  • How the disease-causing mutations mechanistically disrupt ND4-module assembly or OXA1L cooperation to produce optic atrophy remains unresolved.
  • Mutation effect on ND4 binding untested
  • Tissue selectivity for optic neurons unexplained

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140096 catalytic activity, acting on a protein 2
Localization
GO:0005739 mitochondrion 2
Pathway
R-HSA-1430728 Metabolism 2 R-HSA-392499 Metabolism of proteins 1
Partners
ND4OXA1L
Complex memberships
mitochondrial complex I ND4 module

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2009 TMEM126A encodes a transmembrane mitochondrial protein; mutations in TMEM126A cause autosomal-recessive nonsyndromic optic atrophy, establishing mitochondrial dysfunction as a pathogenic mechanism. Whole-genome homozygosity mapping, positional cloning, sequence analysis American journal of human genetics Medium 19327736
2013 TMEM126A protein localizes to the inner mitochondrial membrane (cristae compartment), its mRNA is enriched near mitochondria (mitochondria-localized mRNA), and the second transmembrane domain is required for mitochondrial localization. Cellular fractionation, mitochondrial sub-compartmentalization proteolysis assays, transmission electron microscopy, immunofluorescence confocal microscopy of truncated constructs, quantitative fluorescent in situ hybridization Biochimica et biophysica acta High 23500070
2021 TMEM126A is an assembly factor for the ND4-module of mitochondrial complex I; loss of TMEM126A causes isolated complex I deficiency, and TMEM126A associates with the newly synthesized mtDNA-encoded ND4 subunit during pulse-labeling, indicating a role in ND4 distal membrane module assembly. This function is distinct from its paralog TMEM126B, which acts in ND2-module assembly. Genome editing (knockout), co-immunoprecipitation/interaction studies, quantitative proteomics, pulse-labeling interaction studies Proceedings of the National Academy of Sciences of the United States of America High 33879611
2021 In the absence of NDUFS3, a small amount of functional complex I persists and the ND4 module remains stable and bound to TMEM126A, revealing TMEM126A as an assembly factor for the ND4-module intermediate of mitochondrial complex I. NDUFS3 ablation/depletion in mammalian cells, native PAGE, mass spectrometry, co-immunoprecipitation Cell reports High 33882309
2024 TMEM126A physically interacts with the mitochondrial inner membrane insertase OXA1L, associates with mitochondrial ribosomes and translation products, and cooperates with OXA1L in co-translational insertion of mitochondria-encoded proteins into the inner membrane. Loss of TMEM126A destabilizes mitochondrial translation products, triggering their degradation by the iAAA protease; cargo-blocked OXA1L complexes are also cleared proteolytically by iAAA in the absence of TMEM126A. Co-immunoprecipitation/interaction proteomics, ribosome association assays, loss-of-function analysis, iAAA protease functional assays Molecular cell High 38199007
2018 Loss of TMEM126A in breast cancer cells induces mitochondrial dysfunction, ROS production, and mitochondrial membrane potential depolarization, which in turn activates ECM remodeling and EMT via mitochondrial retrograde signaling; ROS scavengers reverse these effects, placing ROS downstream of TMEM126A loss. siRNA knockdown, overexpression, in vitro and in vivo metastasis assays, ROS measurement, mitochondrial membrane potential assay, RNA-sequencing, ROS scavenger rescue experiments Cancer letters Medium 30393159
2012 TMEM126A physically associates and co-localizes with CD137L (4-1BBL) in macrophages (identified by yeast two-hybrid); knockdown of TMEM126A abolishes CD137L-induced tyrosine phosphorylation, upregulation of M-CSF, IL-1β, and TN-C, and CD137L-induced cell adherence, indicating TMEM126A couples CD137L reverse signaling in myeloid cells. Yeast two-hybrid, co-localization, siRNA knockdown, stable shRNA knockdown, tyrosine phosphorylation assay, cytokine expression analysis Cellular signalling Medium 22885069
2014 TMEM126A couples TLR4 signaling in macrophages; TMEM126A-deficient macrophages show diminished upregulation of CD54, MHC II, CD86, and CD40 in response to TLR4 activation, and abolished LPS/TLR4-induced late-phase JNK/SAPK and IRF-3 phosphorylation. TMEM126A-deficient RAW264.7 cells, LPS stimulation, flow cytometry, phosphorylation assays Molecular immunology Low 25549946
2024 Integrative cross-linking mass spectrometry and coarse-grained molecular dynamics simulations, validated by super-resolution microscopy, localizes TMEM126A specifically to the cristae sub-compartment of the inner mitochondrial membrane. Cross-linking mass spectrometry (XL-MS), coarse-grained molecular dynamics simulation, super-resolution microscopy bioRxivpreprint Medium bio_10.1101_2024.09.11.612425

Source papers

Stage 0 corpus · 11 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2009 TMEM126A, encoding a mitochondrial protein, is mutated in autosomal-recessive nonsyndromic optic atrophy. American journal of human genetics 76 19327736
2010 Nonsense mutation in TMEM126A causing autosomal recessive optic atrophy and auditory neuropathy. Molecular vision 39 20405026
2018 Loss of TMEM126A promotes extracellular matrix remodeling, epithelial-to-mesenchymal transition, and breast cancer metastasis by regulating mitochondrial retrograde signaling. Cancer letters 29 30393159
2021 NDUFS3 depletion permits complex I maturation and reveals TMEM126A/OPA7 as an assembly factor binding the ND4-module intermediate. Cell reports 24 33882309
2024 Identification of TMEM126A as OXA1L-interacting protein reveals cotranslational quality control in mitochondria. Molecular cell 21 38199007
2021 Optic atrophy-associated TMEM126A is an assembly factor for the ND4-module of mitochondrial complex I. Proceedings of the National Academy of Sciences of the United States of America 21 33879611
2013 TMEM126A is a mitochondrial located mRNA (MLR) protein of the mitochondrial inner membrane. Biochimica et biophysica acta 21 23500070
2012 TMEM126A mutation in a Moroccan family with autosomal recessive optic atrophy. Molecular vision 18 22815638
2012 Novel transmembrane protein 126A (TMEM126A) couples with CD137L reverse signals in myeloid cells. Cellular signalling 11 22885069
2019 Novel likely pathogenic variants in TMEM126A identified in non-syndromic autosomal recessive optic atrophy: two case reports. BMC medical genetics 10 30961538
2014 TMEM126A, a CD137 ligand binding protein, couples with the TLR4 signal transduction pathway in macrophages. Molecular immunology 10 25549946

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