Affinage

TMEM126A

Transmembrane protein 126A · UniProt Q9H061

Length
195 aa
Mass
21.5 kDa
Annotated
2026-04-28
11 papers in source corpus 9 papers cited in narrative 9 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

TMEM126A is a mitochondrial inner membrane protein that functions as a dedicated assembly factor for the ND4-module of respiratory chain complex I. It localizes to the cristae membrane, where its second transmembrane domain is required for mitochondrial targeting, and it interacts cotranslationally with newly synthesized mtDNA-encoded ND4 subunit via cooperation with the OXA1L insertase and mitochondrial ribosomes (PMID:33879611, PMID:38199007). Loss of TMEM126A causes isolated complex I deficiency by destabilizing nascent mitochondrial translation products, which are then cleared by the iAAA protease together with cargo-blocked OXA1L complexes, revealing a cotranslational quality-control checkpoint at the inner membrane (PMID:38199007, PMID:33882309). Biallelic mutations in TMEM126A cause autosomal-recessive nonsyndromic optic atrophy (PMID:19327736).

Mechanistic history

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

    Identifying TMEM126A as a mitochondrial protein whose loss causes hereditary optic atrophy established that it is essential for mitochondrial function in retinal ganglion cells, but its molecular role was unknown.

    Evidence Homozygosity mapping and positional cloning in consanguineous families with autosomal-recessive optic atrophy, plus mitochondrial localization

    PMID:19327736

    Open questions at the time
    • Single disease cohort at time of publication
    • No molecular function or pathway identified
    • Mechanism of retinal ganglion cell vulnerability unresolved
  2. 2013 High

    Demonstrating that TMEM126A resides specifically at the inner mitochondrial membrane (cristae) and that its second transmembrane domain is required for targeting resolved the sub-organellar compartment of action.

    Evidence Quantitative FISH, proteolysis protection assays, transmission EM, fractionation, and domain-truncation confocal microscopy

    PMID:23500070

    Open questions at the time
    • No interaction partners or respiratory chain connection identified
    • How the second TM domain mediates targeting is structurally unresolved
  3. 2012 Medium

    An extramitochondrial role was proposed in which TMEM126A associates with CD137L and mediates macrophage inflammatory signaling, but this function diverges from the core mitochondrial role and has not been independently replicated.

    Evidence Yeast two-hybrid, co-localization, siRNA knockdown, and cytokine/phosphorylation assays in macrophages

    PMID:22885069

    Open questions at the time
    • No reciprocal Co-IP or endogenous interaction confirmation
    • Not independently replicated
    • Relationship to mitochondrial complex I function unclear
  4. 2018 Medium

    Connecting TMEM126A loss to mitochondrial ROS production and membrane potential depolarization showed that its deficiency causes retrograde mitochondrial-to-nuclear signaling, but the direct molecular target remained unknown.

    Evidence siRNA knockdown and overexpression in breast cancer cells with ROS measurement, membrane potential assays, RNA-seq, and ROS-scavenger epistasis rescue

    PMID:30393159

    Open questions at the time
    • Downstream EMT effects studied in cancer cell lines only
    • Direct respiratory chain target not identified in this study
  5. 2021 High

    Two independent studies converged to establish TMEM126A as a specific assembly factor for the ND4-module of complex I — distinct from its paralogue TMEM126B (ND2-module) — explaining the isolated complex I deficiency seen upon its loss.

    Evidence CRISPR KO, pulse-labeling Co-IP with newly synthesized ND4, quantitative proteomics (Formosa et al.); NDUFS3 ablation, BN-PAGE, native complex profiling (D'Angelo et al.)

    PMID:33879611 PMID:33882309

    Open questions at the time
    • Structural basis of ND4 interaction unknown
    • Cooperative relationship with OXA1L not yet defined
    • How TMEM126A is itself recruited to the assembly intermediate unclear
  6. 2024 High

    Revealing that TMEM126A cooperates with the OXA1L insertase and associates with mitochondrial ribosomes established a cotranslational membrane insertion role, while showing that loss triggers iAAA protease-mediated clearance of stalled translation products and cargo-blocked OXA1L uncovered a quality-control checkpoint.

    Evidence OXA1L Co-IP, ribosome association assays, mass spectrometry interactomics, TMEM126A KO with iAAA protease functional analysis

    PMID:38199007

    Open questions at the time
    • Structural details of the TMEM126A–OXA1L–ribosome complex are unknown
    • Whether TMEM126A assists insertion of subunits beyond ND4 is unresolved
    • In vivo relevance of iAAA quality-control pathway in optic atrophy pathogenesis not tested

Open questions

Synthesis pass · forward-looking unresolved questions
  • A high-resolution structure of TMEM126A in complex with OXA1L and/or the ND4-module assembly intermediate is needed to understand the mechanism of cotranslational insertion and how disease mutations disrupt it.
  • No atomic-resolution structure of TMEM126A or its complexes
  • Tissue-specific vulnerability (retinal ganglion cells) mechanistically unexplained
  • No therapeutic strategy for TMEM126A-linked optic atrophy

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 3
Localization
GO:0005739 mitochondrion 4
Pathway
R-HSA-1852241 Organelle biogenesis and maintenance 3 R-HSA-1430728 Metabolism 2
Partners
ND4OXA1LTMEM126B
Complex memberships
Mitochondrial complex I (ND4-module assembly intermediate)

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 its essential role in mitochondrial function in retinal ganglion cells. Whole-genome homozygosity mapping, positional cloning, subcellular localization (mitochondrial) American journal of human genetics Medium 19327736
2013 TMEM126A mRNA is enriched near mitochondria (mitochondrial located mRNA, MLR), the protein localizes to the inner mitochondrial membrane (cristae), and the second transmembrane domain is required for mitochondrial localization. Quantitative FISH, cellular fractionation, mitochondrial sub-compartmentalization by proteolysis assay and transmission electron microscopy, immunofluorescence confocal microscopy of truncated constructs Biochimica et biophysica acta High 23500070
2012 TMEM126A associates and co-localizes with CD137L (4-1BB ligand) in macrophages; knockdown of TMEM126A abolishes CD137L-induced tyrosine phosphorylation and regulation of pro-inflammatory cytokines (M-CSF, IL-1β, TN-C), and blocks CD137L-induced cell adherence. Yeast two-hybrid, co-localization, siRNA knockdown, stable retroviral shRNA transduction, cytokine expression assay, phosphorylation assay Cellular signalling Medium 22885069
2014 TMEM126A couples with TLR4 signal transduction in macrophages; loss of TMEM126A diminishes LPS/TLR4-induced upregulation of CD54, MHC II, CD86, CD40 and abolishes late-phase JNK/SAPK and IRF-3 phosphorylation. siRNA knockdown in RAW264.7 macrophages, flow cytometry, phosphorylation assays Molecular immunology Low 25549946
2018 Loss of TMEM126A induces mitochondrial dysfunction (ROS production and mitochondrial membrane potential depolarization), which activates extracellular matrix remodeling and EMT in breast cancer cells; ROS scavengers reverse these effects, placing TMEM126A upstream of ROS-mediated retrograde signaling. siRNA knockdown, overexpression, ROS measurement, mitochondrial membrane potential assay, RNA-seq, in vitro and in vivo metastasis assays, ROS scavenger rescue Cancer letters Medium 30393159
2021 TMEM126A is an assembly factor for the ND4-module of mitochondrial complex I; loss of TMEM126A causes isolated complex I deficiency, and TMEM126A interacts with newly synthesized mtDNA-encoded ND4 subunit as revealed by pulse-labeling interaction studies. Its function is distinct from paralogue TMEM126B (ND2-module assembly). Genome editing (CRISPR KO), interaction studies (co-immunoprecipitation), quantitative proteomics, pulse-labeling interaction studies Proceedings of the National Academy of Sciences of the United States of America High 33879611
2021 TMEM126A (OPA7) is bound to the stable ND4 module intermediate during complex I disassembly; hierarchical ablation of NDUFS3 revealed that the ND4 module remains stable and associated with TMEM126A, confirming TMEM126A as a factor necessary for correct assembly and function of complex I. NDUFS3 ablation/gradual depletion in mammalian cell types, native PAGE, co-immunoprecipitation, BN-PAGE complex profiling Cell reports High 33882309
2024 TMEM126A interacts with OXA1L (the mitochondrial inner membrane insertase) and associates with mitochondrial ribosomes and translation products; loss of TMEM126A destabilizes newly synthesized mitochondrial translation products, which are degraded by the iAAA protease, and causes cargo-blocked OXA1L complexes to also undergo iAAA-mediated proteolytic clearance, revealing a cotranslational quality control function. Co-immunoprecipitation (OXA1L pulldown), ribosome association assays, mass spectrometry interactomics, loss-of-function (KO), protease activity assays, iAAA protease functional analysis Molecular cell High 38199007
2024 Integrative XL-MS, 3D electron microscopy, and coarse-grained molecular dynamics simulations localize TMEM126A to the cristae of the inner mitochondrial membrane, validated by super-resolution microscopy. Cross-linking mass spectrometry, 3D electron microscopy, 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 23 33882309
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
2024 Identification of TMEM126A as OXA1L-interacting protein reveals cotranslational quality control in mitochondria. Molecular cell 18 38199007
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