ETFB contributes to the soluble ETFA–ETFB electron carrier in the mitochondrial matrix. The canonical human beta product is 255 residues; the 346-residue product has a different N terminus. Initiator-methionine removal gives the modeled canonical chain 2–255 and is distinct from ETFA's 19-residue transit-peptide cleavage. The experiments below do not establish equivalent import, assembly or activity of the longer ETFB product.
PMID8962055, human ETF structure: Experimental Procedures describes recombinant human alpha/beta ETF expressed in E. coli and its crystallographic analysis. Results, the overall-structure and cofactor-site sections, resolve beta density from Leu4 to Ile255. The FAD-containing cleft spans both subunits, with most FAD contacts in alpha and beta Phe41/Tyr16 near the flavin. AMP is buried within beta domain III; a role in stabilizing the fold is proposed, rather than AMP catalysis. The Introduction identifies fatty-acid, amino-acid and choline-catabolic donor classes, including glutaryl-, isovaleryl-, short/branched-chain, sarcosine and dimethylglycine dehydrogenases. That passage is pathway synthesis, not a new assay of every donor. The actual body and captions were read; figure pixels and raw coordinates were not reanalyzed. The paper's introductory alpha Q21 differs from the current alpha sequence at that particular position; no universal residue offset is inferred, and beta positions retain the paper's numbering.
PMID25416781, human ETF methylation and activity: Experimental Procedures, cloning and protein production, specifies human ORFs, mature untagged Δ19-alpha and full-length N-His6-beta coexpressed in bacteria. The electron-transfer assay and Figure 5 use MCAD/octanoyl-CoA or GCDH/glutaryl-CoA with DCIP as the final acceptor. Beta Lys200/Lys203 methylation and site mutations change electron transfer by assembled ETF. METTL20/ETFBKMT performs methylation; ETFB is its substrate. Isolated beta had stability problems and was not the preparation used to establish independent carrier turnover. The actual Methods, Results and captions were read, without figure-pixel inspection. The assay establishes the donor–ETF redox step, not complete fatty-acid flux or direct ETFDH/ubiquinone reduction. The proposed explanation linking methylation to partner recognition is mechanistic interpretation.
The human ETF–MCAD structure, PMID15159392, reports a recognition-loop anchor coupled to a mobile FAD domain. PMID15975918 reports human beta-E165A structural and kinetic effects with MCAD and dimethylglycine dehydrogenase. Their identifiers and titles were checked against primary registry records and their original abstracts were read. Publisher body and PDF routes returned access failures; detailed Methods, figure pixels and historical construct sequences remain uninspected. These positive reports support a beta contribution to donor recognition and conformational dynamics, without establishing identical docking for every donor or activity of the 346-residue product.
PMID27499296, LYRM5/ETFRF1: Results and Figure 5B–E, together with the clone/transfection and ETF/LYRM5 purification Methods, show endogenous ETF-beta enrichment with tagged LYRM5 in human cells, overlapping native-complex migration and recombinant co-purification/size-exclusion. LYRM5 removes FAD from and inhibits ETF. The main purification Methods do not independently resolve every ETF construct's species/residue provenance, and the association is not an invariant isolated beta–LYRM5 binary interface. No ETFB deflavinase activity follows from being LYRM5's partner. Text and captions were read, not figure pixels.
PMID35362222, S1P/MBTPS1: Results and Figure 3B–D report six ETFA and fifteen ETFB unique peptides in human HaCaT anti-S1P material, reciprocal co-IP and GST-based association. Figures 4/6 and the corresponding Results examine ETF abundance, flavination and metabolic rescue. The proposed S1P–ETFA–ETFB architecture is a computational docking model, described explicitly in the structure-prediction Methods; association and perturbation do not establish an obligatory third ETF subunit. Figure 3D calls S1P in-vitro translated, whereas the GST Methods describe Flag-S1P preparations, so a clean purified-binary reconstitution is not claimed. Figure 4G's caption and Results give differing directions for an association effect; that direction is not used. Actual operative text and captions were read, without figure-pixel inspection. The inherited trimer quotation remains a quotation from the paper, while the finding distinguishes the model from measured association.
BioPlex 3.0, PMID33961781: STAR Methods specifies the human ORFeome/clone, 293T and HCT116 AP-MS, protein inference and CompPASS workflow. Original released network and bait tables contain ETFA–ETFB and LYRM5–ETFB in both networks: 293T network lines 39927/43725 and HCT116 lines 16998/24183. The 293T accession is P38117; HCT116 labels ETFB P38117-2. Gene-level protein inference and those labels do not authenticate the historical clone sequence or prove native-product equivalence. The interactions are associations; structural specificity for the ETFA heterodimer comes from the independent human ETF structure.
Multimodal cell map, PMID40205054: the actual U2OS tagged-bait AP-MS Methods and released experimental network identify ETFB node 569998, ETFA node 617814 and edge 629908. This is an experimental association record, not an interaction inferred from microscopy or structural prediction. Exact clone sequence and natural-product equivalence were not established.
MitoCoP, PMID34800366: actual STAR Methods and target workbook cells support mitochondrial localization. Relevant records are mmc2 sheet B row 315; mmc3 subtractive row 2366, spatial row 2637 and multi-cell-line row 3591; mmc4 TOMM40 row 1977, TOMM70 row 1479 and carbonate/sonication row 215. Protein groups combine P38117/P38117-2 and another accession. The soluble classification and a table's existing matrix GO annotation are not a new matrix-resolved or product-specific experiment. Workbook cells, headers and operative Methods were inspected; no microscopy pixels were read here.
The Human Protein Atlas assigns enhanced mitochondrial staining with HPA018910 and HPA018923. Two A-431 images were inspected in the database review; they support organelle-level localization, not matrix resolution. HPA018910's antigen is shared between products. The full HPA018923 antigen maps to the longer product but includes 53 residues shared with canonical ETFB, so staining is not demonstrated to be product-specific.
PMID8504797 reports a human 255-residue cDNA product and energy-dependent matrix import without a cleavable leader. The abstract and partial indexed construct/translation Methods were read, but complete import Methods/Results were unavailable. Rabbit reticulocyte translation lysate does not identify the mitochondrial species used. No 346-residue-product targeting is inferred.
PMID8617498 is a mouse Etfa/Etfb/Etfdh chromosomal-mapping study whose abstract supplies matrix context; human import experiments were not verified. PMID7912128 reports human ETFB variants and patient-fibroblast complementation restoring beta-oxidation flux. Its original assay Methods/figures remain inaccessible. Complementation is necessity/rescue evidence; the independently inspected human carrier assay supplies direct biochemical participation.
The human ETFB Reactome entity 169265 maps to P38117, residues 2–255, with its own mitochondrial-matrix compartment. In R-HSA-169260, catalyst 169261 is ETF:FAD complex 169267 containing this beta participant. In R-HSA-169270, ETF is a redox input/output; the separate catalyst 169271→448210 is ETFDH/Q16134. In R-HSA-8931858, ETFB is a methylation substrate and ETFBKMT is the catalyst. These explicit participant roles distinguish ETFB's carrier contribution from ETFDH reduction and ETFBKMT methylation. UniProt SL-0170 independently maps the recorded location to mitochondrial matrix.
The actual PANTHER PTHR21294 tree, alignment and current IBD records place the exact 255-residue human sequence at PTN002501736. Electron-transfer node PTN007689635 and mitochondrial/beta-oxidation node PTN000480319 lie on its ancestry; no target-path NOT was found. Current electron-transfer IBD lists human P38117, while the captured annotation also lists fly FBgn0039697. This source-version difference is preserved. Target self-WITH is valid experimental grounding; individual donor originals were not reread.
IPR000049 and IPR012255 match the beta conserved site/family and map to electron transfer. ARBA00085069 has a matching FunFam/Metazoa condition set for beta-oxidation. Historical ARBA00026962 is explicitly named in the older mitochondrial source row; its current matching FunFam/Eukaryota conditions are not a reconstruction of the old execution. The current ARBA00092488 request returned 404; ETF-complex membership is independently supported by the human structure, biochemistry and participant records rather than invented rule conditions.
The two ordered core units remain contexts of the same ETF carrier activity. Within the first, GO:0016208 (AMP binding) describes the beta subunit’s own ligand binding, while GO:0009055 is expressed as its contribution to the assembled alpha/beta carrier. GO:0009063 records the amino-acid-catabolic context already accepted in the annotation review. No additional annotation row or third core was created.
| Claim | Evidence and exact locator | Scope |
|---|---|---|
| Beta-subunit AMP binding | Human ETF structure, PMID:8962055, Results “AMP Binding” and Figure 1 caption; preserved UniProt record, FT:BINDING at 9, 11, 39, 42, 66, 123, 125, 126, 132, 133 and 134 | AMP is within beta domain III. Fold stabilization is proposed; AMP catalysis and alternative-product equivalence are not established. |
| Amino-acid-catabolic carrier step | PMID:25416781(https://pmc.ncbi.nlm.nih.gov/articles/PMC4281744/), recombinant-protein and ETF-activity Methods, Results and Figure 5 | Human untagged Δ19 alpha plus full-length His6 beta transfers electrons from GCDH/glutaryl-CoA to DCIP. This is assembled ETF function with an artificial acceptor, not ETFDH/ubiquinone reduction or a complete flux assay. |
| Recognition loop and ETFA association | Preserved UniProt FT:REGION 183–205, CC:DOMAIN and CC:SUBUNIT; official P38117 record | Curated corroboration of the interface and heterodimer. PMID:15159392 and PMID:15975918 remain abstract-only in the accepted access ledger; this revision does not claim newly read full articles. |
The added file reference uses a title derived from the record’s ID, primary accession and recommended-name fields. Supports are reference-only. The record-section backfill tool is run on the private candidate; because no new database quotations are supplied, section locators belong in this guide and the reference assessment rather than being guessed as structured quotation metadata.
The description’s MCAD, GCDH and SARDH examples and the parallel entry routes from complexes I and II are supported by the cited articles’ pathway background and UniProt CC:FUNCTION. The directly reread functional experiment tests MCAD and GCDH; it is not a new SARDH assay. This revision rereads selected original text and captions, not new figure pixels or coordinate files. Retained title quotations and the retired mitochondrial row preserve historical provenance and are not substituted for operative experimental evidence.