TIMMDC1 (TIM17 domain-containing protein 1; also known as C3orf1/M5-14) is a multi-pass integral protein of the mitochondrial inner membrane and a member of the Tim17/Tim22/Tim23 preprotein-translocase / membrane-insertase-like superfamily. It functions as a chaperone/assembly factor for mitochondrial Complex I (NADH:ubiquinone oxidoreductase), where it acts during the mid-stage, MCIA-associated construction of the membrane arm of the enzyme. It transiently associates with incompletely assembled Complex I intermediates (including the ~315 kDa iron-sulfur/membrane-arm subcomplex) together with other assembly factors such as NDUFAF3, NDUFAF4, TMEM126B and the MCIA complex (ACAD9, NDUFAF1, ECSIT), and dissociates once the mature holoenzyme is formed; it is therefore not a stable structural subunit of the Complex I holoenzyme. TIMMDC1 is broadly expressed with enhanced levels in heart and skeletal muscle. Biallelic loss-of-function variants cause an autosomal-recessive mitochondrial Complex I deficiency (nuclear type 31, MC1DN31).
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005739 mitochondrion | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (IBA) annotation to mitochondrion. Correct but non-specific; TIMMDC1 is a multi-pass inner mitochondrial membrane protein. A more precise inner-membrane term is available and captured by the Reactome TAS annotations. Reason: The PAINT node placing mitochondrial activity on this family is confirmed for the human protein by four independent localization lines (HPA immunofluorescence, LIFEdb GFP-fusion, MitoCoP proteomics and the Reactome inner-membrane reactions) and by the UniProt SUBCELLULAR LOCATION. `is_active_in` is the right qualifier for an assembly factor that does its work there. Accepted; the term is coarser than the available inner-membrane term but is not wrong. Supporting Evidence: file:human/TIMMDC1/TIMMDC1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion membrane |
| GO:0031966 mitochondrial membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Electronic Swiss-Prot subcellular-location mapping to mitochondrial membrane. Consistent with the UniProt SUBCELLULAR LOCATION (mitochondrion membrane, multi-pass). The more specific inner-membrane term (GO:0005743) is the better representation. Reason: Reproduces the UniProt SUBCELLULAR LOCATION faithfully, and UniProt's own statement is at the mitochondrial-membrane level with a multi-pass topology rather than resolving inner versus outer. Accepted as an accurate restatement, with the more specific GO:0005743 carried by the Reactome rows. Supporting Evidence: file:human/TIMMDC1/TIMMDC1-uniprot.txt Multi-pass membrane protein |
| GO:0032981 mitochondrial respiratory chain complex I assembly | IEA GO_REF:0000002 | ACCEPT | Summary: Core biological process. Although sourced electronically (InterPro2GO, IPR055299 = the TIMMDC1 family), this is the well-established function of TIMMDC1: it is a chaperone that participates in constructing the membrane arm of Complex I. Strongly corroborated by the UniProt experimental FUNCTION statement (PMID:24191001), by Reactome Complex I biogenesis, and by the Complex I deficiency disease phenotype. Reason: IPR055299 is the TIMMDC1-specific family signature rather than a broad domain, so the InterPro2GO mapping is narrowly targeted rather than a generic transfer, and it yields the function UniProt states experimentally from PMID:24191001. Unlike a substrate, TIMMDC1 does part of the work of assembly - it is the chaperone that holds the membrane-arm intermediates together - which is what licenses `involved_in`. Supporting Evidence: file:human/TIMMDC1/TIMMDC1-uniprot.txt Chaperone protein involved in the assembly of the mitochondrial NADH:ubiquinone oxidoreductase complex (complex I). Participates in constructing the membrane arm of complex I. PMID:24191001 C3orf1, of another assembly factor, TMEM126B, and of NDUFA11 suggest that they |
| GO:0005515 protein binding | IPI PMID:25416956 A proteome-scale map of the human interactome network. | MARK AS OVER ANNOTATED | Summary: Bare "protein binding" from a large-scale binary interactome screen (CCSB HuRI-related map; WITH/FROM FATE1, a non-mitochondrial protein). Not informative about TIMMDC1's molecular function and the partner is not a known biological interactor. Retained (experimental IPI) but flagged as over-annotation. Reason: Uninformative GO:0005515 from a high-throughput binary interactome; the WITH/FROM partner (FATE1) is not a plausible physiological interactor. Supporting Evidence: PMID:25416956 systematic map of ?14,000 high-quality human binary protein-protein interactions |
| GO:0005515 protein binding | IPI PMID:31515488 Extensive disruption of protein interactions by genetic vari... | MARK AS OVER ANNOTATED | Summary: Bare "protein binding" from a high-throughput variant-interaction perturbation study (WITH/FROM FATE1). Uninformative about molecular function. Retained (experimental IPI) but flagged as over-annotation. Reason: Uninformative GO:0005515 from a high-throughput screen; partner not a known physiological interactor. Supporting Evidence: PMID:31515488 missense single nucleotide variants (SNVs) across 2185 protein-protein |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | MARK AS OVER ANNOTATED | Summary: Bare "protein binding" from the HuRI reference binary (Y2H) interactome. Many WITH/FROM partners (SCD, STX6, YIF1A, FAM20B, SERF1B, ...), mostly non-mitochondrial membrane proteins characteristic of Y2H sticky-membrane noise. Uninformative about molecular function. Retained (experimental IPI) but flagged as over-annotation. Reason: Uninformative GO:0005515 from a large-scale binary interactome; partners are not established physiological interactors. Supporting Evidence: PMID:32296183 the cellular function of most individual PPIs remains to be elucidated |
| GO:0005515 protein binding | IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... | MARK AS OVER ANNOTATED | Summary: Bare "protein binding" from BioPlex 3.0 (AP-MS). The WITH/FROM partner here is NDUFB11 (Q9NX14), a Complex I membrane-arm (ND) subunit, which is biologically consistent with TIMMDC1's role in membrane-arm assembly. The MF term itself remains uninformative, so it is flagged as over-annotation, but the interaction supports the membrane-arm assembly role. Reason: GO:0005515 is uninformative as a molecular function; the biologically meaningful NDUFB11 interaction is better captured by the CI assembly BP. Supporting Evidence: PMID:33961781 of 10,128 human proteins-half the proteome-in 293T cells and includes 118,162 |
| GO:0005654 nucleoplasm | IDA GO_REF:0000052 | MARK AS OVER ANNOTATED | Summary: HPA immunofluorescence (IDA) nucleoplasm annotation. This contradicts all other evidence: TIMMDC1 is a multi-pass integral inner mitochondrial membrane protein with a mitochondrial targeting signal, and every other localization line (IBA/IDA/HTP mitochondrion, TAS inner membrane) places it in mitochondria. The nuclear signal is almost certainly non-specific antibody staining rather than a genuine second compartment, so this is an over-annotation rather than a peripheral truth. Retained per policy (experimental IDA not removed) but flagged as over-annotated. Reason: Contradicted by the multi-pass mitochondrial inner-membrane localization; likely HPA antibody cross-reactivity rather than a genuine nuclear pool. An artefactual signal is not a true-but-peripheral localization, so MARK_AS_OVER_ANNOTATED fits better than KEEP_AS_NON_CORE, while still honouring the policy of not REMOVE-ing an experimental IDA. Supporting Evidence: file:human/TIMMDC1/TIMMDC1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion membrane |
| GO:0005739 mitochondrion | IDA GO_REF:0000052 | ACCEPT | Summary: HPA immunofluorescence (IDA) mitochondrion annotation, consistent with the established mitochondrial localization. Correct but non-specific relative to the inner-membrane term. Reason: Immunofluorescence resolves organelle but not submitochondrial compartment, so this assay can only support the parent term; it agrees with every other localization line and with UniProt. Accepted as correct, with the Reactome inner-membrane rows carrying the more precise claim. Note that the same HPA experiment also produced the nucleoplasm call above, which is why that one is treated as antibody cross-reactivity rather than as a second compartment. No primary publication is attached to this GO_REF, so no literature quote is offered. Supporting Evidence: file:human/TIMMDC1/TIMMDC1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion membrane |
| GO:0005739 mitochondrion | HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an... | ACCEPT | Summary: High-throughput mitochondrial proteome (MitoCoP) localization to mitochondrion. Consistent with all other evidence. Correct but non-specific. Reason: MitoCoP is a quantitatively filtered high-confidence mitochondrial proteome, so inclusion is trustworthy evidence of mitochondrial residence - and an orthogonal method to the antibody-based HPA call, which matters here given that the same HPA experiment also reported nucleoplasm. Correct but coarser than the inner-membrane term. Supporting Evidence: file:human/TIMMDC1/TIMMDC1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion membrane PMID:34800366 mitochondrial high-confidence proteome of >1,100 proteins (MitoCoP) |
| GO:0005515 protein binding | IPI PMID:33753518 TMEM70 and TMEM242 help to assemble the rotor ring of human ... | MARK AS OVER ANNOTATED | Summary: Bare "protein binding" (WITH/FROM TMEM70, Q9BUB7). This interaction is experimentally supported and biologically meaningful: TMEM70 co-purifies with TIMMDC1 and other MCIA components (ACAD9, NDUFAF1), linking TIMMDC1 to the MCIA machinery that builds the Complex I membrane arm. The GO:0005515 term itself is uninformative about molecular function, so it is flagged as over-annotation, but the underlying interaction is real. Corroborated by the UniProt SUBUNIT statement. Reason: GO:0005515 is uninformative as a molecular function; the real TMEM70/MCIA interaction is captured by the Complex I assembly BP. Supporting Evidence: PMID:33753518 and also with an additional assembly factor for complex I, the translocase of IMM domain-containing protein 1, or TIMMDC1 file:human/TIMMDC1/TIMMDC1-uniprot.txt Interacts with TMEM70 (PubMed:33753518). |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-6799178 | ACCEPT | Summary: Reactome (TAS) inner mitochondrial membrane localization, from a step of the Complex I biogenesis pathway. This is the most precise, correct location for TIMMDC1 and is consistent with its multi-pass topology. Core location. Reason: This step names TIMMDC1 (C3orf1) explicitly as one of the Intermediate 1 assembly factors anchoring the hydrophobic protein fraction to the inner membrane, so the compartment is intrinsic to the role Reactome assigns it. The inner-membrane compartment matches the multi-pass topology UniProt records and is the most precise location available for TIMMDC1. Reactome entries carry no primary-literature snippet, so the cached reaction record is cited alongside UniProt. Supporting Evidence: file:human/TIMMDC1/TIMMDC1-uniprot.txt Multi-pass membrane protein Reactome:R-HSA-6799178 anchored to the inner mitochondrial membrane by Intermediate |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-6799179 | ACCEPT | Summary: Reactome (TAS) inner mitochondrial membrane localization from the Complex I biogenesis pathway. Correct, precise location. Redundant with the other Reactome TAS inner-membrane annotations. Reason: A peripheral-arm step of the same inner-membrane pathway; correct compartment, but a pathway restatement rather than a TIMMDC1-specific observation. The inner-membrane compartment matches the multi-pass topology UniProt records and is the most precise location available for TIMMDC1. Reactome entries carry no primary-literature snippet, so the cached reaction record is cited alongside UniProt. Supporting Evidence: file:human/TIMMDC1/TIMMDC1-uniprot.txt Multi-pass membrane protein Reactome:R-HSA-6799179 Subunits NDUFA12, NDUFS1, 4, 6, NDUFV1, 2 and 3 with the assembly factor |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-6799191 | ACCEPT | Summary: Reactome (TAS) inner mitochondrial membrane localization from the Complex I biogenesis pathway. Correct, precise location. Reason: The step forming the 315 kDa subcomplex that UniProt records TIMMDC1 as associating with, anchored to the inner membrane by MT-ND1. The inner-membrane compartment matches the multi-pass topology UniProt records and is the most precise location available for TIMMDC1. Reactome entries carry no primary-literature snippet, so the cached reaction record is cited alongside UniProt. Supporting Evidence: file:human/TIMMDC1/TIMMDC1-uniprot.txt Multi-pass membrane protein Reactome:R-HSA-6799191 to the inner mitochondrial membrane by NADH-ubiquinone oxidoreductase chain 1 |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-6799196 | ACCEPT | Summary: Reactome (TAS) inner mitochondrial membrane localization from the Complex I biogenesis pathway (the step in which TIMMDC1/MCIA dissociate from the 980 kDa complex to yield mature Complex I). Correct, precise location. Reason: The maturation step at which TIMMDC1 and the MCIA complex leave the 980 kDa intermediate - the structural reason TIMMDC1 is an assembly factor and not a holoenzyme subunit. The inner-membrane compartment matches the multi-pass topology UniProt records and is the most precise location available for TIMMDC1. Reactome entries carry no primary-literature snippet, so the cached reaction record is cited alongside UniProt. Supporting Evidence: file:human/TIMMDC1/TIMMDC1-uniprot.txt Multi-pass membrane protein Reactome:R-HSA-6799196 The MCIA complex, NDUFAF2-7 all dissociate from the 980kDa complex |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-6799197 | ACCEPT | Summary: Reactome (TAS) inner mitochondrial membrane localization from the Complex I biogenesis pathway. Correct, precise location. Reason: A membrane-arm step of the same inner-membrane pathway, the arm TIMMDC1 helps construct. The inner-membrane compartment matches the multi-pass topology UniProt records and is the most precise location available for TIMMDC1. Reactome entries carry no primary-literature snippet, so the cached reaction record is cited alongside UniProt. Supporting Evidence: file:human/TIMMDC1/TIMMDC1-uniprot.txt Multi-pass membrane protein Reactome:R-HSA-6799197 Distal components of the membrane arm MT-ND4 and 5 associate with the 550kDa |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-6799202 | ACCEPT | Summary: Reactome (TAS) inner mitochondrial membrane localization from the Complex I biogenesis pathway. Correct, precise location. Reason: An intermediate assembly step of the same inner-membrane pathway. The inner-membrane compartment matches the multi-pass topology UniProt records and is the most precise location available for TIMMDC1. Reactome entries carry no primary-literature snippet, so the cached reaction record is cited alongside UniProt. Supporting Evidence: file:human/TIMMDC1/TIMMDC1-uniprot.txt Multi-pass membrane protein Reactome:R-HSA-6799202 The 315kDa and 370kDa subcomplexes associate to form a 550kDa complex |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-6799203 | ACCEPT | Summary: Reactome (TAS) inner mitochondrial membrane localization from the step "IP subcomplex binds NDUFAF3, NDUFAF4, TIMMDC1 to form Intermediate 1", which directly documents TIMMDC1's incorporation into the Complex I assembly intermediate. Correct, precise location. Reason: The step in which the IP subcomplex binds NDUFAF3, NDUFAF4 and TIMMDC1 to form Intermediate 1 - the most directly TIMMDC1-relevant of the Reactome rows. The inner-membrane compartment matches the multi-pass topology UniProt records and is the most precise location available for TIMMDC1. Reactome entries carry no primary-literature snippet, so the cached reaction record is cited alongside UniProt. Supporting Evidence: file:human/TIMMDC1/TIMMDC1-uniprot.txt Multi-pass membrane protein Reactome:R-HSA-6799203 around the core subunits NADH dehydrogenase [ubiquinone] iron-sulfur proteins 2 |
| GO:0005739 mitochondrion | IDA GO_REF:0000054 | ACCEPT | Summary: LIFEdb (IDA) localization of a fluorescent fusion protein to mitochondrion. Consistent with all other evidence. Correct but non-specific relative to the inner-membrane term. Reason: LIFEdb expresses GFP-tagged constructs from cDNA, which for a multi-pass inner-membrane protein can mislocalize; here, however, the result agrees with the antibody-based HPA call, the MitoCoP proteome and UniProt, so the three independent methods converge and the annotation is accepted. It remains coarser than the inner-membrane term. No primary publication is attached to this GO_REF, so no literature quote is offered. Supporting Evidence: file:human/TIMMDC1/TIMMDC1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion membrane |
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Download this section (compressed HTML)Q: Does TIMMDC1 have genuine membrane-insertase catalytic activity for the mitochondrially encoded ND subunits, or does it act solely as a scaffold?
Q: Which Complex I membrane-arm (ND) subunits does TIMMDC1 directly contact during assembly, and in what order?
Experiment: Reconstitute purified TIMMDC1 into proteoliposomes or nanodiscs with defined ND-subunit substrates (or model hydrophobic substrates) and assay insertion and topology by protease-protection and site-specific labelling, against a TIMMDC1-free control. A positive result would establish a catalytic activity; a negative result under conditions where a known insertase works would support the passive-scaffold model.
Hypothesis: TIMMDC1 retains genuine membrane-insertase activity inherited from the Tim17/Tim22/Tim23 superfamily, and can catalyse insertion of ND-subunit substrates into a lipid bilayer independently of the rest of the assembly machinery.
Type: In vitro reconstitution insertase assay
Experiment: Determine cryo-EM structures of TIMMDC1-containing Complex I assembly intermediates - for example the 550 and 815 kDa subcomplexes that accumulate on NDUFA11 suppression - and map the TIMMDC1 interface, complementing the structures with in-cell crosslinking mass spectrometry to order the contacts over time.
Hypothesis: TIMMDC1 contacts specific ND (membrane-arm) subunits in a defined order during assembly, and its interface with the membrane arm is resolvable in a stalled intermediate.
Type: Single-particle cryo-electron microscopy with crosslinking MS
Experiment: Validate the interaction by reciprocal co-immunoprecipitation from mitochondria under native conditions, then test its necessity by expressing interface mutants in TIMMDC1-null cells and measuring Complex I assembly by blue-native PAGE and complexome profiling.
Hypothesis: The TIMMDC1-NDUFB11 interaction reported by BioPlex is a genuine assembly contact rather than an affinity-purification artefact, and is required for membrane-arm construction.
Type: Targeted interaction validation with mutant complementation
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