TIMM21 encodes a non-enzymatic accessory subunit of the mitochondrial TIM23 presequence translocase. In human cells it is best supported as a TIM23SORT factor that works with ROMO1 to promote lateral insertion/sorting of selected presequence-containing proteins into the inner mitochondrial membrane, with secondary links to respiratory-chain assembly contexts through this import/sorting role.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005744 TIM23 mitochondrial import inner membrane translocase complex | IBA GO_REF:0000033 | ACCEPT | Summary: Correct. TIMM21 is a TIM23-associated accessory subunit and, with ROMO1, defines the TIM23SORT state of the TIM23 presequence translocase. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **TIM23SORT (lateral insertion/sorting mode):** specialized for **lateral insertion** of single- or dual-pass IMM proteins. In this mode, association with **TIMM21** and **ROMO1** defines the “sort-specific” configuration and supports lateral release of substrates into the IMM. |
| GO:0030150 protein import into mitochondrial matrix | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: TIMM21 participates in the TIM23 pathway, but the best-supported human role is TIM23SORT-mediated lateral insertion into the inner membrane rather than matrix-import motor function. Reason: Prefer TIM23 complex membership and protein insertion into mitochondrial inner membrane for TIMM21; matrix import is primarily a TIM23MOTOR/core translocase output rather than TIMM21-specific activity. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **TIM23SORT (lateral insertion/sorting mode):** specialized for **lateral insertion** of single- or dual-pass IMM proteins. In this mode, association with **TIMM21** and **ROMO1** defines the “sort-specific” configuration and supports lateral release of substrates into the IMM. file:human/TIMM21/TIMM21-deep-research-falcon.md 2) **facilitates lateral insertion** of specific IMM proteins (rather than acting as an enzyme or transporter with a small-molecule substrate). |
| GO:0005744 TIM23 mitochondrial import inner membrane translocase complex | IEA GO_REF:0000002 | ACCEPT | Summary: Correct. TIMM21 is a TIM23-associated accessory subunit and, with ROMO1, defines the TIM23SORT state of the TIM23 presequence translocase. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **TIM23SORT (lateral insertion/sorting mode):** specialized for **lateral insertion** of single- or dual-pass IMM proteins. In this mode, association with **TIMM21** and **ROMO1** defines the “sort-specific” configuration and supports lateral release of substrates into the IMM. |
| GO:0030150 protein import into mitochondrial matrix | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: TIMM21 participates in the TIM23 pathway, but the best-supported human role is TIM23SORT-mediated lateral insertion into the inner membrane rather than matrix-import motor function. Reason: Prefer TIM23 complex membership and protein insertion into mitochondrial inner membrane for TIMM21; matrix import is primarily a TIM23MOTOR/core translocase output rather than TIMM21-specific activity. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **TIM23SORT (lateral insertion/sorting mode):** specialized for **lateral insertion** of single- or dual-pass IMM proteins. In this mode, association with **TIMM21** and **ROMO1** defines the “sort-specific” configuration and supports lateral release of substrates into the IMM. file:human/TIMM21/TIMM21-deep-research-falcon.md 2) **facilitates lateral insertion** of specific IMM proteins (rather than acting as an enzyme or transporter with a small-molecule substrate). |
| GO:0031966 mitochondrial membrane | IEA GO_REF:0000044 | MARK AS OVER ANNOTATED | Summary: Correct but too broad. TIMM21 is specifically associated with the mitochondrial inner membrane TIM23 machinery. Reason: Use mitochondrial inner membrane and TIM23 complex annotations instead of generic mitochondrial membrane. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **Cellular location:** mitochondria, associated with the **inner mitochondrial membrane** as part of TIM23-related assemblies. (crameri2024reducedproteinimport pages 1-3) |
| GO:0005515 protein binding | IPI PMID:23260140 MITRAC links mitochondrial protein translocation to respirat... | MARK AS OVER ANNOTATED | Summary: Protein binding is too generic for TIMM21. The informative biology is TIM23SORT/TIM23-complex association with ROMO1/TIM23 machinery rather than undifferentiated binding. Reason: Replace generic protein binding interpretation with specific TIM23 complex and TIM23SORT functional context. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **TIM23SORT (lateral insertion/sorting mode):** specialized for **lateral insertion** of single- or dual-pass IMM proteins. In this mode, association with **TIMM21** and **ROMO1** defines the “sort-specific” configuration and supports lateral release of substrates into the IMM. |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | MARK AS OVER ANNOTATED | Summary: Protein binding is too generic for TIMM21. The informative biology is TIM23SORT/TIM23-complex association with ROMO1/TIM23 machinery rather than undifferentiated binding. Reason: Replace generic protein binding interpretation with specific TIM23 complex and TIM23SORT functional context. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **TIM23SORT (lateral insertion/sorting mode):** specialized for **lateral insertion** of single- or dual-pass IMM proteins. In this mode, association with **TIMM21** and **ROMO1** defines the “sort-specific” configuration and supports lateral release of substrates into the IMM. |
| GO:0005743 mitochondrial inner membrane | NAS PMID:10339406 Genetic and structural characterization of the human mitocho... | ACCEPT | Summary: Correct. TIMM21 is associated with the mitochondrial inner membrane as part of TIM23-related assemblies. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **Cellular location:** mitochondria, associated with the **inner mitochondrial membrane** as part of TIM23-related assemblies. (crameri2024reducedproteinimport pages 1-3) |
| GO:0005744 TIM23 mitochondrial import inner membrane translocase complex | NAS PMID:10339406 Genetic and structural characterization of the human mitocho... | ACCEPT | Summary: Correct. TIMM21 is a TIM23-associated accessory subunit and, with ROMO1, defines the TIM23SORT state of the TIM23 presequence translocase. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **TIM23SORT (lateral insertion/sorting mode):** specialized for **lateral insertion** of single- or dual-pass IMM proteins. In this mode, association with **TIMM21** and **ROMO1** defines the “sort-specific” configuration and supports lateral release of substrates into the IMM. |
| GO:0006886 intracellular protein transport | NAS PMID:10339406 Genetic and structural characterization of the human mitocho... | MARK AS OVER ANNOTATED | Summary: Correct pathway family but too broad. TIMM21 is specifically involved in TIM23SORT-mediated mitochondrial inner-membrane protein insertion/sorting. Reason: Use specific mitochondrial protein import/sorting terms and TIM23 complex annotation rather than generic intracellular protein transport. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **TIM23SORT (lateral insertion/sorting mode):** specialized for **lateral insertion** of single- or dual-pass IMM proteins. In this mode, association with **TIMM21** and **ROMO1** defines the “sort-specific” configuration and supports lateral release of substrates into the IMM. file:human/TIMM21/TIMM21-deep-research-falcon.md 2) **facilitates lateral insertion** of specific IMM proteins (rather than acting as an enzyme or transporter with a small-molecule substrate). |
| GO:0005739 mitochondrion | HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an... | MARK AS OVER ANNOTATED | Summary: Correct but broad. TIMM21 is better captured by mitochondrial inner membrane and TIM23 complex annotations. Reason: Prefer mitochondrial inner membrane/TIM23 complex over generic mitochondrion. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **Cellular location:** mitochondria, associated with the **inner mitochondrial membrane** as part of TIM23-related assemblies. (crameri2024reducedproteinimport pages 1-3) |
| GO:0005758 mitochondrial intermembrane space | TAS Reactome:R-HSA-9865412 | ACCEPT | Summary: Supported as TIMM21 function at the inner-membrane/intermembrane-space interface during TOM-TIM23 handover, not as a soluble IMS protein. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md In this framework, **Tim21** is discussed as participating in TOM–TIM23 contact-site biology and regulating early transfer steps through the intermembrane space (IMS), though much of this detailed mechanistic evidence is rooted in yeast/conserved systems and then extrapolated to mammals. |
| GO:0005758 mitochondrial intermembrane space | TAS Reactome:R-HSA-9865579 | ACCEPT | Summary: Supported as TIMM21 function at the inner-membrane/intermembrane-space interface during TOM-TIM23 handover, not as a soluble IMS protein. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md In this framework, **Tim21** is discussed as participating in TOM–TIM23 contact-site biology and regulating early transfer steps through the intermembrane space (IMS), though much of this detailed mechanistic evidence is rooted in yeast/conserved systems and then extrapolated to mammals. |
| GO:0005744 TIM23 mitochondrial import inner membrane translocase complex | IDA PMID:30598479 ROMO1 is a constituent of the human presequence translocase ... | ACCEPT | Summary: Correct. TIMM21 is a TIM23-associated accessory subunit and, with ROMO1, defines the TIM23SORT state of the TIM23 presequence translocase. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **TIM23SORT (lateral insertion/sorting mode):** specialized for **lateral insertion** of single- or dual-pass IMM proteins. In this mode, association with **TIMM21** and **ROMO1** defines the “sort-specific” configuration and supports lateral release of substrates into the IMM. |
| GO:0005515 protein binding | IPI PMID:26321642 MITRAC7 Acts as a COX1-Specific Chaperone and Reveals a Chec... | MARK AS OVER ANNOTATED | Summary: Protein binding is too generic for TIMM21. The informative biology is TIM23SORT/TIM23-complex association with ROMO1/TIM23 machinery rather than undifferentiated binding. Reason: Replace generic protein binding interpretation with specific TIM23 complex and TIM23SORT functional context. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **TIM23SORT (lateral insertion/sorting mode):** specialized for **lateral insertion** of single- or dual-pass IMM proteins. In this mode, association with **TIMM21** and **ROMO1** defines the “sort-specific” configuration and supports lateral release of substrates into the IMM. |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-9865412 | ACCEPT | Summary: Correct. TIMM21 is associated with the mitochondrial inner membrane as part of TIM23-related assemblies. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **Cellular location:** mitochondria, associated with the **inner mitochondrial membrane** as part of TIM23-related assemblies. (crameri2024reducedproteinimport pages 1-3) |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-9865449 | ACCEPT | Summary: Correct. TIMM21 is associated with the mitochondrial inner membrane as part of TIM23-related assemblies. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **Cellular location:** mitochondria, associated with the **inner mitochondrial membrane** as part of TIM23-related assemblies. (crameri2024reducedproteinimport pages 1-3) |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-9865579 | ACCEPT | Summary: Correct. TIMM21 is associated with the mitochondrial inner membrane as part of TIM23-related assemblies. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **Cellular location:** mitochondria, associated with the **inner mitochondrial membrane** as part of TIM23-related assemblies. (crameri2024reducedproteinimport pages 1-3) |
| GO:0005744 TIM23 mitochondrial import inner membrane translocase complex | IDA PMID:23260140 MITRAC links mitochondrial protein translocation to respirat... | ACCEPT | Summary: Correct. TIMM21 is a TIM23-associated accessory subunit and, with ROMO1, defines the TIM23SORT state of the TIM23 presequence translocase. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **TIM23SORT (lateral insertion/sorting mode):** specialized for **lateral insertion** of single- or dual-pass IMM proteins. In this mode, association with **TIMM21** and **ROMO1** defines the “sort-specific” configuration and supports lateral release of substrates into the IMM. |
| GO:0030150 protein import into mitochondrial matrix | IMP PMID:23260140 MITRAC links mitochondrial protein translocation to respirat... | MARK AS OVER ANNOTATED | Summary: TIMM21 participates in the TIM23 pathway, but the best-supported human role is TIM23SORT-mediated lateral insertion into the inner membrane rather than matrix-import motor function. Reason: Prefer TIM23 complex membership and protein insertion into mitochondrial inner membrane for TIMM21; matrix import is primarily a TIM23MOTOR/core translocase output rather than TIMM21-specific activity. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **TIM23SORT (lateral insertion/sorting mode):** specialized for **lateral insertion** of single- or dual-pass IMM proteins. In this mode, association with **TIMM21** and **ROMO1** defines the “sort-specific” configuration and supports lateral release of substrates into the IMM. file:human/TIMM21/TIMM21-deep-research-falcon.md 2) **facilitates lateral insertion** of specific IMM proteins (rather than acting as an enzyme or transporter with a small-molecule substrate). |
| GO:0032981 mitochondrial respiratory chain complex I assembly | IMP PMID:23260140 MITRAC links mitochondrial protein translocation to respirat... | KEEP AS NON CORE | Summary: Supported as a secondary respiratory-chain assembly linkage, but mitochondrial respiratory chain complex I assembly is not the primary TIMM21 function. The main mechanistic role is TIM23SORT-associated mitochondrial protein insertion/sorting. Reason: Treat respiratory-chain assembly phenotypes as downstream or context-specific consequences of TIMM21-mediated import/sorting rather than the core molecular role. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md The strongest experimentally grounded respiratory-chain linkage in this evidence set is indirect: TIM23SORT substrates are enriched for OXPHOS/ultrastructure proteins in disease mapping studies, and yeast-centric work links Tim21-containing TIM23 states to respiratory chain interactions (notably complex III) in conserved models. |
| GO:0033617 mitochondrial respiratory chain complex IV assembly | IMP PMID:23260140 MITRAC links mitochondrial protein translocation to respirat... | KEEP AS NON CORE | Summary: Supported as a secondary respiratory-chain assembly linkage, but mitochondrial respiratory chain complex IV assembly is not the primary TIMM21 function. The main mechanistic role is TIM23SORT-associated mitochondrial protein insertion/sorting. Reason: Treat respiratory-chain assembly phenotypes as downstream or context-specific consequences of TIMM21-mediated import/sorting rather than the core molecular role. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md The strongest experimentally grounded respiratory-chain linkage in this evidence set is indirect: TIM23SORT substrates are enriched for OXPHOS/ultrastructure proteins in disease mapping studies, and yeast-centric work links Tim21-containing TIM23 states to respiratory chain interactions (notably complex III) in conserved models. |
| GO:0003674 molecular_function | ND GO_REF:0000015 | REMOVE | Summary: The no-data molecular_function placeholder is superseded by specific evidence for TIMM21 as a TIM23SORT/TIM23 complex accessory factor. Reason: Specific literature-supported functional annotations are available; the ND molecular_function placeholder should not be retained in a completed review. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **TIM23SORT (lateral insertion/sorting mode):** specialized for **lateral insertion** of single- or dual-pass IMM proteins. In this mode, association with **TIMM21** and **ROMO1** defines the “sort-specific” configuration and supports lateral release of substrates into the IMM. |
| GO:0045039 protein insertion into mitochondrial inner membrane | NAS file:human/TIMM21/TIMM21-deep-research-falcon.md | NEW | Summary: New annotation recommended. TIMM21 is best supported as a TIM23SORT accessory factor that promotes lateral insertion/sorting of selected proteins into the mitochondrial inner membrane. Reason: Current GOA captures TIM23 complex membership and broad transport terms, but misses the more specific TIM23SORT-associated inner-membrane insertion role. Supporting Evidence: file:human/TIMM21/TIMM21-deep-research-falcon.md - **TIM23SORT (lateral insertion/sorting mode):** specialized for **lateral insertion** of single- or dual-pass IMM proteins. In this mode, association with **TIMM21** and **ROMO1** defines the “sort-specific” configuration and supports lateral release of substrates into the IMM. file:human/TIMM21/TIMM21-deep-research-falcon.md 2) **facilitates lateral insertion** of specific IMM proteins (rather than acting as an enzyme or transporter with a small-molecule substrate). |
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Download this section (compressed HTML)Q: Which human TIM23SORT client proteins require TIMM21 directly, and which phenotypes attributed to TIMM21 are downstream of altered client insertion?
Q: How much of the reported complex I and complex IV assembly phenotype reflects a direct MITRAC role versus impaired TIM23SORT delivery of OXPHOS assembly substrates?
Experiment: Use TIMM21 knockout/rescue cells with TIMM21 mutants defective for ROMO1/TIM23 association and compare import of matrix-targeted TIM23MOTOR substrates with radiolabeled TIM23SORT inner-membrane substrates by protease protection and BN-PAGE.
Hypothesis: TIMM21 primarily supports TIM23SORT lateral insertion rather than TIM23MOTOR matrix import.
Experiment: Perform quantitative mitochondrial proteomics and pulse import assays after acute TIMM21 depletion, then test whether restoring selected TIM23SORT substrates rescues complex I/IV assembly readouts.
Hypothesis: TIMM21-linked respiratory-chain assembly phenotypes are mediated by defective insertion of a restricted set of OXPHOS assembly clients.
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