Sdhaf2 (also called Sdh5 or Pgl2) encodes succinate dehydrogenase assembly factor 2, a small nuclear-encoded protein of the mitochondrial matrix. Isoform 1 (Q8C6I2-1) has 164 residues with a predicted N-terminal mitochondrial transit peptide (residues 1-27) and a single Sdh5/SdhE domain (Pfam PF03937). It belongs to the SDHAF2/Sdh5/SdhE family (PANTHER PTHR12469:SF2), shared with human SDHAF2, yeast Sdh5 and bacterial SdhE. Members of this family are assembly factors for succinate dehydrogenase (respiratory complex II). They bind the flavoprotein subunit SDHA and, together with a dicarboxylate, position the flavin and capping domains of SDHA so that FAD can be covalently attached (flavinylation), a step needed for a catalytically competent complex II. Sdhaf2 is not a subunit of the mature enzyme and has no catalytic activity of its own. The flavinylation mechanism has been shown for the human, yeast and bacterial orthologs, not for the mouse protein. Mouse evidence places Sdhaf2 in mitochondria, with a cytosolic pre-import pool in myotubes. In mouse skeletal muscle and C2C12 myocytes, the mitochondrial fission GTPase Drp1 interacts with Sdhaf2 and promotes its mitochondrial translocation. Loss of Drp1 lowers mitochondrial Sdhaf2 and selectively reduces complex II assembly, and overexpressing Sdhaf2 restores succinate-dependent respiration in Drp1-deficient myocytes. One study of Sdhaf2-knockout mice and lung cancer cells linked loss of the protein to epithelial-mesenchymal transition through GSK-3beta/beta-catenin signalling. This is a context-dependent role, separate from complex II maturation.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003674 molecular_function | ND GO_REF:0000015 | ACCEPT | Summary: Root molecular function ND annotation: when it was made, no molecular function had been curated for this gene product from literature. Reason: ACCEPT under the ND acceptance rule (projects/NO_DATA.md). The evidence this review cites for the molecular function is inferred (from orthologs, family membership or sequence features) or comes from other species; none of it is literature on this gene product in this species. This was judged from the review's own content during the NO_DATA re-action pass, not from a new literature search. Earlier action: MODIFY. Re-checked 2026-10-31: the chaperone activity rests on human and yeast SDHAF2/SDH5 (PMID:32887801, PMID:19628817); the mouse study cited (PMID:38569044) shows a role in complex II assembly, not the activity. The term the earlier MODIFY proposed, protein folding chaperone, is kept as its own NEW row. The gene's notes, which list the mouse-specific literature found, record that no molecular activity (SDHA binding, flavinylation or chaperone activity) has been established in mouse. Supporting Evidence: file:mouse/Sdhaf2__Q8C6I2/Sdhaf2__Q8C6I2-notes.md Not established in mouse: SDHA binding, covalent flavinylation of SDHA, and chaperone activity. |
| GO:0005730 nucleolus | ISO GO_REF:0000119 | MARK AS OVER ANNOTATED | Summary: Automated mouse-human orthology transfer of a nucleolar localization for human SDHAF2. The current human GOA set no longer carries a nucleolus annotation; the human review records only mitochondrial and matrix locations. Sdhaf2 has a mitochondrial transit peptide and works on SDHA inside the matrix. No mouse or family evidence supports a nucleolar pool. Reason: The only likely source is a single antibody-based human observation, which is not reproduced for mouse. It conflicts with the matrix function of the protein and with the mouse fractionation data, which show cytosolic and mitochondrial pools only. It should not be propagated as a mouse location. Propagation Review Root cause: SOURCE STALE OR MISSING Failure modes: COMPARTMENT OR COMPLEX MISMATCH Supporting Evidence: file:mouse/Sdhaf2__Q8C6I2/Sdhaf2__Q8C6I2-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion matrix |
| GO:0005739 mitochondrion | HDA PMID:18614015 A mitochondrial protein compendium elucidates complex I dise... | MODIFY | Summary: Mouse experimental (HDA) evidence. Sdhaf2 was in the MitoCarta compendium, built from mass spectrometry of purified mitochondria from 14 mouse tissues. This is direct mouse evidence that the protein is mitochondrial. Reason: The term is correct but general. The protein sits in the mitochondrial matrix, a term this gene already carries (GO:0005759, by UniRule/SubCell and by ISO from the human experimental annotation). This MODIFY refines the location; it does not dispute the MitoCarta evidence. Proposed replacements: mitochondrial matrix Supporting Evidence: PMID:18614015 The resulting compendium consists of 1098 genes ( Figure 1 ) and their protein expression across 14 mouse tissues. PMID:38569044 Drp1 interacts with Sdhaf2 and enhances its mitochondrial translocation. |
| GO:0005739 mitochondrion | IBA GO_REF:0000033 | MODIFY | Summary: PAINT IBD at the eukaryotic node PTN000279729 (taxon 2759), seeded from Arabidopsis SDHAF2, yeast Sdh5 and human SDHAF2. Mouse Q8C6I2 is in subfamily PTHR12469:SF2, which descends from this node. The localization is sound and is confirmed in mouse by HDA. Reason: Kept consistent with the other mitochondrion rows. The term is correct but less specific than the supported matrix location (GO:0005759), which the gene already carries. Propagation Review Root cause: NO FAILURE CORE Failure modes: GRANULARITY MISMATCH Proposed replacements: mitochondrial matrix Supporting Evidence: file:mouse/Sdhaf2__Q8C6I2/Sdhaf2__Q8C6I2-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion matrix |
| GO:0005739 mitochondrion | IEA GO_REF:0000120 | MODIFY | Summary: Combined electronic annotation from orthology and the SDHAF2 InterPro entry (IPR028882). Correct. Reason: Correct but general. The specific supported location is the mitochondrial matrix (GO:0005759), which the gene already carries. Proposed replacements: mitochondrial matrix Supporting Evidence: file:mouse/Sdhaf2__Q8C6I2/Sdhaf2__Q8C6I2-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion matrix |
| GO:0005739 mitochondrion | ISO GO_REF:0000119 | MODIFY | Summary: Orthology transfer from human SDHAF2 (IDA, HPA and founding-study evidence). Correct for mouse and independently confirmed by mouse proteomics and fractionation. Reason: Correct but general. The specific supported location is the mitochondrial matrix (GO:0005759), which the gene already carries. Propagation Review Root cause: NO FAILURE CORE Failure modes: GRANULARITY MISMATCH Proposed replacements: mitochondrial matrix Supporting Evidence: PMID:38569044 Drp1 interacts with Sdhaf2 and enhances its mitochondrial translocation. |
| GO:0005739 mitochondrion | ISS GO_REF:0000024 | MODIFY | Summary: UniProt curator transfer by sequence similarity from human SDHAF2. Correct. Reason: Correct but general. The specific supported location is the mitochondrial matrix (GO:0005759), which the gene already carries. Proposed replacements: mitochondrial matrix Supporting Evidence: file:mouse/Sdhaf2__Q8C6I2/Sdhaf2__Q8C6I2-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion matrix |
| GO:0005759 mitochondrial matrix | IEA GO_REF:0000120 | ACCEPT | Summary: UniRule/SubCell electronic annotation of a matrix location. This is the specific, correct site of action: SDHA flavinylation happens in the matrix before SDHA joins the inner-membrane anchor subunits. The evidence is family-level (HAMAP MF_03057) and the human EXP annotation; no mouse sub-mitochondrial fractionation exists. Supporting Evidence: file:mouse/Sdhaf2__Q8C6I2/Sdhaf2__Q8C6I2-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion matrix |
| GO:0005759 mitochondrial matrix | ISO GO_REF:0000119 | ACCEPT | Summary: Orthology transfer of the human experimental matrix localization (PMID:19628817, EXP). Correct, core location; the human and mouse proteins are in the same subfamily (SF2). Supporting Evidence: file:mouse/Sdhaf2__Q8C6I2/Sdhaf2__Q8C6I2-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion matrix |
| GO:0005829 cytosol | ISO GO_REF:0000119 | KEEP AS NON CORE | Summary: Orthology transfer of a cytosolic localization. In mouse, Sdhaf2 is found in the cytosolic fraction of C2C12 myotubes, and its mitochondrial import there depends on Drp1. A cytosolic pool therefore exists in mouse cells. It appears to be the pre-import precursor, not the site where Sdhaf2 acts on SDHA. Reason: The location is supported (mouse fractionation), but it is peripheral to the core function, which is carried out in the matrix. Supporting Evidence: PMID:38569044 Immunoblot of Sdhaf2 in cytosolic and mitochondrial fractions of control (Scr) and Drp1KD myotubes |
| GO:0006099 tricarboxylic acid cycle | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: PAINT IBD at PTN000279729, seeded only from yeast Sdh5. The PAINT curators made a deliberate placement, and mouse Sdhaf2 is inside the clade. However, Sdhaf2 performs no step of the TCA cycle. It matures SDHA before the enzyme that carries out the succinate-to-fumarate step is assembled. The yeast donor annotation reflects necessity (sdh5 mutants lack SDH activity), not participation. Reason: Assembly factor versus catalytic enzyme (role conflation). Sdhaf2 acts upstream of the TCA cycle by enabling complex II maturation. The informative process is complex II assembly (GO:0034553). This is consistent with the treatment of the same IBA on the human ortholog. Propagation Review Root cause: PROPAGATION BAD Failure modes: ROLE CONFLATION Supporting Evidence: file:mouse/Sdhaf2__Q8C6I2/Sdhaf2__Q8C6I2-uniprot.txt Required for flavinylation (covalent |
| GO:0006121 mitochondrial electron transport, succinate to ubiquinone | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: PAINT IBD at PTN000279729. Electron transfer from succinate to ubiquinone is carried out by the assembled complex II (SDHA-D). Sdhaf2 is required for complex II to form, but it does not transfer electrons and is not part of the mature complex. Reason: Necessity, not participation. The electron transport step is performed by SDHA/SDHB/SDHC/SDHD. Sdhaf2's contribution is upstream, through complex II assembly and SDHA flavinylation. Propagation Review Root cause: PROPAGATION BAD Failure modes: ROLE CONFLATION Supporting Evidence: file:mouse/Sdhaf2__Q8C6I2/Sdhaf2__Q8C6I2-uniprot.txt Plays an essential role in the assembly of succinate |
| GO:0006121 mitochondrial electron transport, succinate to ubiquinone | IEA GO_REF:0000104 | MARK AS OVER ANNOTATED | Summary: UniRule electronic transfer of the same process term. Same reasoning as the IBA row: an assembly factor does not carry out the electron transport step. Reason: Consistent with the IBA and ISO rows for this term. Supporting Evidence: file:mouse/Sdhaf2__Q8C6I2/Sdhaf2__Q8C6I2-uniprot.txt Plays an essential role in the assembly of succinate |
| GO:0006121 mitochondrial electron transport, succinate to ubiquinone | ISO GO_REF:0000119 | MARK AS OVER ANNOTATED | Summary: Orthology transfer of the same process term. Same reasoning as the IBA row. Reason: Consistent with the IBA and IEA rows for this term. In mouse, Sdhaf2 restoration in Drp1-knockdown myocytes increased succinate-dependent respiratory control. This shows that Sdhaf2 is needed for complex II-linked respiration, not that it transports electrons. Propagation Review Root cause: PROPAGATION BAD Failure modes: ROLE CONFLATION Supporting Evidence: PMID:38569044 Moreover, we observed that Sdhaf2 overexpression significantly increased the RCR in Drp1KD myocytes, but only in the presence of succinate, not pyruvate |
| GO:0006470 protein dephosphorylation | IMP PMID:23983127 Succinate dehydrogenase 5 (SDH5) regulates glycogen synthase... | KEEP AS NON CORE | Summary: MGI IMP (acts_upstream_of_or_within) from the lung-cancer study. In that study, the Sdhaf2-GSK-3beta interaction was associated with loss of the inhibitory phosphate on GSK-3beta Ser-9. Sdhaf2 has no phosphatase domain and the phosphatase involved was not identified. The effect on GSK-3beta phosphorylation is indirect and context-dependent. The cached full text is partial (results and figures are missing), so we cannot see which experiment in mouse tissue the curator used. Reason: Kept, deferring to the MGI curator who read the full paper. The acts_upstream_of_or_within qualifier already records that the role is indirect. This is peripheral to the mitochondrial assembly-factor function, and the mechanism linking a matrix protein to cytosolic GSK-3beta is unresolved. Supporting Evidence: PMID:23983127 The physical interaction between SDH5 and GSK-3Ξ² facilitates GSK-3Ξ² activation through Ser-9 dephosphorylation |
| GO:0006470 protein dephosphorylation | ISO GO_REF:0000008 | KEEP AS NON CORE | Summary: MGI orthology transfer of the human IGI annotation from the same paper (PMID:23983127). Same assessment as the IMP row. Reason: Consistent with the IMP row. This is an indirect, cancer-context regulatory effect. Supporting Evidence: PMID:23983127 The physical interaction between SDH5 and GSK-3Ξ² facilitates GSK-3Ξ² activation through Ser-9 dephosphorylation |
| GO:0010719 negative regulation of epithelial to mesenchymal transition | IEA GO_REF:0000117 | KEEP AS NON CORE | Summary: ARBA machine-learning annotation that repeats the experimental annotation from PMID:23983127. The underlying finding is real but context-dependent, and is kept as non-core with the experimental rows. Reason: Consistent with the IMP and ISO rows for this term. The ARBA rule adds no independent support. Supporting Evidence: PMID:23983127 In SDH5 knock-out mice, lung epithelial cells exhibited elevated mesenchymal markers, which is characteristic of EMT. |
| GO:0010719 negative regulation of epithelial to mesenchymal transition | IMP PMID:23983127 Succinate dehydrogenase 5 (SDH5) regulates glycogen synthase... | KEEP AS NON CORE | Summary: Mouse experimental evidence: lung epithelial cells of SDH5 (Sdhaf2) knockout mice had higher levels of mesenchymal markers. Loss of SDH5 also caused EMT in human lung cancer cells and xenografts. This is a genuine mouse phenotype. Whether it follows from loss of complex II and succinate accumulation, or from a separate GSK-3beta interaction, is not resolved. Reason: A cancer and tissue-context regulatory phenotype, recorded with the acts_upstream_of_or_within qualifier. It is peripheral to the core mitochondrial function and probably indirect. Supporting Evidence: PMID:23983127 In SDH5 knock-out mice, lung epithelial cells exhibited elevated mesenchymal markers, which is characteristic of EMT. |
| GO:0010719 negative regulation of epithelial to mesenchymal transition | ISO GO_REF:0000008 | KEEP AS NON CORE | Summary: Orthology transfer of the human IMP annotation from the same paper. Same assessment. Reason: Consistent with the IMP row for this term. Supporting Evidence: PMID:23983127 loss of succinate dehydrogenase 5 (SDH5) expression initiates epithelial-mesenchymal transition (EMT) |
| GO:0018293 protein-FAD linkage | ISO GO_REF:0000119 | ACCEPT | Summary: Orthology transfer of the human IMP: SDH5 is required for flavination of the SDH flavoprotein. The mouse protein is in the same subfamily (SF2) as human SDHAF2, and this role is conserved from bacterial SdhE to yeast Sdh5 and human SDHAF2. Sdhaf2 contributes structurally to this step by positioning the SDHA flavin and capping domains. Covalent flavinylation of SDHA has not been measured directly in mouse. Reason: Core process, inferred for mouse through the subfamily. GO:0018293 is the precise term for the covalent FAD attachment step that Sdhaf2 enables. Supporting Evidence: PMID:19628817 Sdh5 is required for SDH-dependent respiration and for Sdh1 flavination (incorporation of the flavin adenine dinucleotide cofactor) PMID:32887801 works in synergy with SDHAF2 to properly orient the flavin and capping domains of SDHA |
| GO:0018293 protein-FAD linkage | ISS GO_REF:0000024 | ACCEPT | Summary: UniProt curator similarity transfer of the same core process from human SDHAF2. Same assessment as the ISO row. Reason: Core process, inferred through the subfamily. Consistent with the ISO row. Supporting Evidence: file:mouse/Sdhaf2__Q8C6I2/Sdhaf2__Q8C6I2-uniprot.txt Required for flavinylation (covalent |
| GO:0034553 mitochondrial respiratory chain complex II assembly | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBD at the eukaryotic node PTN000279729, seeded from yeast Sdh5 and human SDHAF2. Mouse Sdhaf2 (SF2) descends from this node. Mouse data agree: Drp1 deficiency lowers mitochondrial Sdhaf2 and selectively reduces complex II assembly on BN-PAGE, and Sdhaf2 restoration normalizes complex II activity in Drp1-knockdown myocytes. Reason: Core process. It is placed phylogenetically and supported by mouse functional data in muscle and myocytes (PMID:38569044). The in vivo perturbation in that study was Drp1, not Sdhaf2 itself. Supporting Evidence: PMID:38569044 Muscle Drp1-KD reduced complex II assembly and activity as a consequence of diminished mitochondrial translocation of succinate dehydrogenase assembly factor 2 (Sdhaf2). file:mouse/Sdhaf2__Q8C6I2/Sdhaf2__Q8C6I2-uniprot.txt Plays an essential role in the assembly of succinate |
| GO:0034553 mitochondrial respiratory chain complex II assembly | IEA GO_REF:0000107 | ACCEPT | Summary: Ensembl Compara orthology transfer of the same core process from human SDHAF2. Correct. Reason: Core process. Consistent with the IBA and ISO rows. Supporting Evidence: file:mouse/Sdhaf2__Q8C6I2/Sdhaf2__Q8C6I2-uniprot.txt Plays an essential role in the assembly of succinate |
| GO:0034553 mitochondrial respiratory chain complex II assembly | ISO GO_REF:0000119 | ACCEPT | Summary: Orthology transfer of the human IDA (SDHA-SDHAF2 structure, PMID:32887801) for complex II assembly. Correct, and agrees with the mouse muscle data. Reason: Core process. Supporting Evidence: PMID:38569044 Restoration of Sdhaf2 normalized complex II |
| GO:0090090 negative regulation of canonical Wnt signaling pathway | IEA GO_REF:0000117 | KEEP AS NON CORE | Summary: ARBA machine-learning annotation that repeats the experimental annotation from PMID:23983127, which reported effects on GSK-3beta/beta-catenin signalling. Kept as non-core with the experimental rows. Reason: Consistent with the IMP and ISO rows for this term. The ARBA rule adds no independent support. Supporting Evidence: PMID:23983127 SDH5 functions as a negative regulator of Wnt-Ξ²-catenin signaling |
| GO:0090090 negative regulation of canonical Wnt signaling pathway | IMP PMID:23983127 Succinate dehydrogenase 5 (SDH5) regulates glycogen synthase... | KEEP AS NON CORE | Summary: MGI IMP from the lung cancer/knockout mouse study. Loss of SDH5 increased nuclear beta-catenin accumulation and beta-catenin transcriptional activity. The effect is reported as mediated through GSK-3beta. It is indirect and context-dependent, and the cached full text does not include the figures that show which data are from mouse. Reason: Kept, deferring to the curator who read the full text. The qualifier records an upstream, indirect role. This is not the core function. Supporting Evidence: PMID:23983127 SDH5 functions as a negative regulator of Wnt-Ξ²-catenin signaling |
| GO:0090090 negative regulation of canonical Wnt signaling pathway | ISO GO_REF:0000008 | KEEP AS NON CORE | Summary: Orthology transfer of the human IGI annotation from the same paper. Same assessment. Reason: Consistent with the IMP row for this term. Supporting Evidence: PMID:23983127 SDH5 functions as a negative regulator of Wnt-Ξ²-catenin signaling |
| GO:0044183 protein folding chaperone | ISO PMID:32887801 The roles of SDHAF2 and dicarboxylate in covalent flavinylat... | NEW | Summary: Inferred protein folding chaperone for this gene product, proposed during the NO_DATA re-action pass. Reason: Protein folding chaperone is inferred for this gene product (ISO), not shown for it experimentally; the ND row for the aspect therefore stays (projects/NO_DATA.md). The root MF term says nothing. An orthology-grounded MF is available: protein folding chaperone (GO:0044183), as used for the human SF2 subfamily member Q9NX18 on structural (IDA) evidence. For mouse this is an inference from the subfamily, not a mouse experiment. The UniRule/HAMAP statement on the mouse record (ECO:0000255|HAMAP-Rule:MF_03057) also describes Sdhaf2 as required for SDHA flavinylation. Supporting Evidence: PMID:32887801 works in synergy with SDHAF2 to properly orient the flavin and capping domains of SDHA file:mouse/Sdhaf2__Q8C6I2/Sdhaf2__Q8C6I2-uniprot.txt Required for flavinylation (covalent |
Loading supporting contentβ¦
Download this section (compressed HTML)Q: Does the cytosolic pool of Sdhaf2 seen in mouse myotubes have a function, or is it only precursor waiting for import? Is the reported Drp1-Sdhaf2 interaction direct on the outer membrane, given that Sdhaf2 has a canonical matrix-targeting presequence?
Q: Does the EMT/Wnt phenotype of Sdhaf2-knockout mouse lung follow from loss of complex II and succinate accumulation (as in other SDHx-deficient tissues), or from a separate Sdhaf2-GSK-3beta interaction?
Q: Is the SDH-independent complex IV assembly role reported for human SDHAF2 conserved in mouse tissues?
Experiment: Measure covalent SDHA flavinylation (FAD fluorescence of SDHA on SDS-PAGE) and complex II assembly by BN-PAGE in tissues from a conditional Sdhaf2-knockout mouse. This would test directly, in mouse, the flavinylation role currently inferred from orthologs.
Type: genetic perturbation with biochemical readout
Experiment: Compare wild-type and SDHA-binding-deficient Sdhaf2 (the residue equivalent to human G78R) for their ability to rescue lung EMT markers in Sdhaf2-null cells. This would separate complex II-dependent effects from the reported GSK-3beta signalling role.
Type: separation-of-function rescue
Loading supporting contentβ¦
Download this section (compressed HTML)Loading supporting contentβ¦
Download this section (compressed HTML)