FOXRED1 is a nuclear-encoded mitochondrial complex I assembly factor with a predicted flavoprotein fold. It associates with the mitochondrial inner membrane and complex I assembly intermediates and supports productive middle-to-late assembly. Human cell studies link its loss to reduced mature complex I and abnormal assembly intermediates; myoblasts also show a context-dependent complex II assembly defect. Biallelic pathogenic variants cause mitochondrial complex I deficiency, nuclear type 19 (MC1DN19). Its physiological molecular activity and flavin-dependent mechanism remain unresolved.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | TOO GENERAL | Summary: Cytoplasm is entailed by the more informative mitochondrial inner-membrane localization already retained in this review. Reason: The official typed path is GO:0005743 mitochondrial inner membrane is_a GO:0031966 mitochondrial membrane part_of GO:0005739 mitochondrion part_of GO:0005737 cytoplasm (checked 2026-10-31). The existing inner-membrane annotations therefore supply the more specific localization, while the four root-organelle mitochondrion annotations remain accepted. Preserve the complete PAINT donor grouping, including FOXRED1 itself, rather than treating self evidence as circular. |
| GO:0032981 mitochondrial respiratory chain complex I assembly | IBA GO_REF:0000033 | ACCEPT | Summary: The phylogenetic assembly annotation agrees with direct human FOXRED1 perturbation and assembly-intermediate evidence. Reason: Retain complex I assembly as a core process, with the original ancestral node and target self-donor support unchanged. Biochemical evidence establishes an assembly role without identifying a FOXRED1 catalytic reaction. |
| GO:0005743 mitochondrial inner membrane | IEA GO_REF:0000044 | ACCEPT | Summary: The UniProt subcellular-location mapping supports mitochondrial inner-membrane association. Reason: Original mitochondrial fractionation and independent characterization support this location. The term does not resolve the disagreement between peripheral matrix-face association and predicted transmembrane topology; preserve the original SL-0168 source. Supporting Evidence: file:human/FOXRED1/FOXRED1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion inner membrane |
| GO:0005739 mitochondrion | IDA GO_REF:0000052 | ACCEPT | Summary: Retain the curated immunofluorescence-based mitochondrial localization. Reason: The HPA annotation agrees with independent mitochondrial localization evidence. It does not by itself establish inner-membrane topology, and no antibody-image reanalysis is claimed. |
| GO:0005739 mitochondrion | HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an... | ACCEPT | Summary: Retain mitochondrial localization from the curated high-throughput proteomics annotation. Reason: The positive source assignment agrees with independent localization evidence. The exact dataset row and experimental fraction details remain a source-access follow-up; no inner-membrane resolution is inferred from this broad term. Supporting Evidence: |
| GO:0005743 mitochondrial inner membrane | EXP PMID:20858599 FOXRED1, encoding an FAD-dependent oxidoreductase complex-I-... | ACCEPT | Summary: The original human study supports association with the mitochondrial inner membrane. Reason: Fractionation and immunoblotting detected FOXRED1 in the inner-membrane and soluble mitochondrial fractions. These observations support the annotation without establishing integral membrane topology or proving the proposed precursor-processing explanation. |
| GO:0005739 mitochondrion | IDA PMID:20858599 FOXRED1, encoding an FAD-dependent oxidoreductase complex-I-... | ACCEPT | Summary: The original study supports mitochondrial localization of FOXRED1. Reason: C-terminal fusion localization and mitochondrial fractionation support the broad compartment. N-terminal tagging affected localization, so tag context is retained; the broad term remains useful source-specific evidence. |
| GO:0005743 mitochondrial inner membrane | IDA PMID:25678554 Characterization of mitochondrial FOXRED1 in the assembly of... | ACCEPT | Summary: Retain the experimentally curated mitochondrial inner-membrane localization. Reason: The original full text for this source was not recovered in this consultation. The curator-assigned IDA is consistent with the official record and independently read 2010 fractionation evidence; this is not a claim to have inspected the inaccessible assay. |
| GO:0032981 mitochondrial respiratory chain complex I assembly | IMP PMID:25678554 Characterization of mitochondrial FOXRED1 in the assembly of... | ACCEPT | Summary: Human FOXRED1 loss and complementation support its participation in productive complex I assembly. Reason: The verified 2015 abstract reports a late ~815-kDa intermediate that fails to mature and breaks down to ~475 kDa, reduced complex I in null cells and co-immunoprecipitation with complex I subunits. The independently read 2016 study reports FOXRED1 association with a ~370-kDa subcomplex and impaired formation of a ~550-kDa mid-assembly complex. Its Discussion notes uncertainty over whether the accumulated ~340-kDa material is an assembly intermediate or breakdown product and whether BN-PAGE mass calibration accounts for the difference from 2015. These source-specific observations support productive assembly without fixing one universal intermediate mass or identifying a FOXRED1 redox substrate. Supporting Evidence: PMID:25678554 Cells lacking FOXRED1 had ∼10% complex I levels, PMID:25678554 that FOXRED1 is a crucial component in the productive assembly of complex I and |
| GO:0005739 mitochondrion | IDA GO_REF:0000054 | ACCEPT | Summary: Retain the curated mitochondrial localization from expressed fusion-protein experiments. Reason: This annotation agrees with the original C-terminal fusion result discussed in PMID:20858599. It is not evidence that every tag placement or natural alternative product has identical localization. |
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Download this section (compressed HTML)Q: Does FOXRED1 bind FAD and catalyze a physiologically relevant reaction, and can those biochemical properties be separated from its complex I assembly role?
Q: Which direct molecular contacts and biochemical changes mediated by FOXRED1 enable productive assembly, beyond the reported co-immunoprecipitation with AIFM1, ACAD9 and complex I subunits, and how do pathogenic variants alter these steps rather than simply protein abundance, folding or localization?
Q: Why does FOXRED1 depletion impair complex II assembly in myoblasts while measured fibroblast complex II levels remain comparatively preserved?
Experiment: Purify correctly folded FOXRED1 and measure cofactor occupancy and candidate redox activity with appropriate protein-free, denatured-protein and substrate controls. If activity is detected, test variants that specifically impair it while retaining folding, abundance and localization before attributing altered cellular assembly to loss of catalysis.
Experiment: Compare calibrated complexome profiles and cross-linking mass spectrometry in FOXRED1-null, wild-type-rescued and variant-rescued cells. Test direct contacts with the reported AIFM1, ACAD9 and complex I partners separately from co-immunoprecipitation or co-migration, and distinguish failed assembly from subsequent intermediate breakdown.
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