COX6B1 is a small peripheral subunit on the intermembrane-space face of complex IV. Its structural contribution to the active respiratory enzyme is the central function. The 86-residue human sequence is distinct from the separately encoded COX6B2 paralog; no alternative splice product is listed in the reviewed record. Arg20 numbering refers to the displayed sequence, including the initiator methionine.
The human HEK293F cryo-EM structure resolves COX6B1 within a 14-subunit monomer derived from a respiratory supercomplex. COX6B1 lies near the cardiolipin/NDUFA4 region on the intermembrane-space side. This is direct membership and structural evidence. The study compares that human monomer with older bovine dimer structures; its detergent/activity experiments use porcine enzyme. It questions obligatory dimerization but does not exclude a dimer in every biological setting. Consequently, the earlier universal dimer-bridge explanation is too strong. PMID:30030519(https://www.nature.com/articles/s41422-018-0071-1), Results, Figures 1–4 and 6, and Materials and Methods. The repository's partial text is supplemented by the original publisher article.
The published successor to the early-assembly preprint tests three human HEK293 knockout clones, full-length COX6B1 with a C-terminal FLAG tag, Arg20 variants and an alternative oxidase from Aspergillus. COX6B1 rescue restores respiratory capacity. Alternative oxidase allows incomplete complex-IV assemblies to accumulate but leaves only about 5% of wild-type COX capacity under the artificial-substrate assay. These results distinguish an early redox-sensitive assembly requirement from later structural/function effects. Direct COX6B1 copper transfer, reductase chemistry and the precise MT-CO2 maturation mechanism remain unresolved. Tagged COX6B2 failed rescue in this cellular system, which does not establish universal noncomplementation in other tissues. PMID:41419202(https://pmc.ncbi.nlm.nih.gov/articles/PMC12870770/), Results, Discussion and Experimental procedures, especially the construct, native-complex and respirometry sections.
The complete bovine-heart VIb-removal abstract reports increased oxidase activity and increased cytochrome-c Km, with unchanged proton pumping. Higher Km is not increased affinity. The accessible abstract does not directly report monomerization, and attempts at reconstitution were unsuccessful. That biochemical preparation must not be treated as equivalent to a human cellular knockout. PMID:1332762(https://pubmed.ncbi.nlm.nih.gov/1332762/). The full original remains unavailable. Similarly, PMID:2172092(https://pubmed.ncbi.nlm.nih.gov/2172092/) establishes human VIb cloning and transcript observations at the accessible abstract level; it is not an isolated catalytic assay.
The oxidase and proton-transport annotations are retained at the structural complex-participation scope. A subunit need not contain an autonomous active site or pore to contribute the structure of the enzyme performing the reaction. The core uses contribution to cytochrome-c oxidase activity and the specific electron-transfer process. This does not assign an isolated COX6B1 redox reaction or proton channel. The broad oxidative-phosphorylation and cellular-respiration annotations remain secondary context. The structural mitochondrial-membrane annotation is refined to the demonstrated inner membrane, preserving its source identity. No separate assembly, copper-transfer, reductase or regulatory molecular function is added from the unresolved early mechanism.
The original MitoCoP supplementary Table S1 directly identifies COX6B1 in sheets A row 251 and B row 226. P14854 is the principal identifier within a protein group. Subtractive Class 1, spatial Cluster 1 and importomics Class 1 support mitochondrial localization. The subtractive mean log2 enrichment is 1.0578, and the TOMM40-depletion log2 change is -2.3375. The membrane-association classification is Ambiguous, so these data do not establish integral topology or an exclusive proteoform. The table's inherited UniProt dimer description is a database field, not a new measurement. PMID:34800366(https://pmc.ncbi.nlm.nih.gov/articles/PMC8664129/), Methods and Table S1.
Current HPA summaries report supported mitochondrial immunofluorescence in A-431, U-251 MG and U2OS cells; image pixels were not independently scored. Three Reactome events reach the human COX6B1 entity through the COX6B1/2 subunit set. Their electron-transfer, carbon-monoxide inhibition and assembly contexts support location within the membrane complex. They do not establish isolated COX6B1 carbon-monoxide binding or copper chemistry.
Current PTHR11387 places the exact human sequence beneath PTN000147427 and PTN000147454. Literal same-term experimental records are present among the target and ortholog evidence. The human target appearing in its own descendant evidence is legitimate. FlyBase resolves to two UniProt products with different evidence records, and COX6B2 supports shared localization without implying equal rescue competence. This is a current tree and source inspection, not a reconstruction of the historical PAINT session.
Current InterPro mappings and mouse/Ensembl evidence agree with complex-IV membership. ARBA00035746 is more limited: none of its eight current condition sets completely matches human COX6B1. The matching FunFam occurs in a branch restricted to Ascomycota. The discrepancy is recorded without overturning direct human membership or claiming to know the rule version used historically. The eight historical annotations with omitted WITH/FROM values remain unchanged; complete current source records and explicit identity mappings are in the evidence index.
The original human postmortem study compared five adults per group, ages 47–94. Its Table 2 detects P14854 and reports an HD/control abundance ratio of 0.58 ± 0.05 with a PLGS downregulation metric of 0.01. That metric is not presented here as a conventional two-sided p value. The study validates other proteins, not COX6B1, by its follow-up immunoblots. The positive detection and disease association are preserved, but adult disease comparison does not establish formation or maturation of the substantia nigra as required by GO:0021762. The developmental annotation is therefore over-annotated at this citation's scope; no developmental incapacity is asserted. PMID:22926577(https://link.springer.com/content/pdf/10.1007/s11064-012-0874-2.pdf), Methods, Table 1 and Table 2, printed page 2808. The complete original is externally available despite the unchanged abstract cache.
The earlier provider findings remain visible as historical statements, with local assessments distinguishing direct observations from unverified dimer/cooperativity and patient-intermediate details. The early-assembly evidence is now a published original rather than only a preprint. Questions and proposed experiments retain their experimental categories while testing unresolved mechanisms without presuming obligatory dimerization or demonstrated copper delivery. Public source locators, current definitions, typed paths, target table cells and source identity reconciliation are collected in the evidence index.
The proton-transport annotation is now retained as non-core. The human structural and complementation evidence establishes contribution to the functional oxidase but does not separately resolve COX6B1's work in proton translocation. The unchanged proton pumping after selective bovine VIb removal is preserved as a preparation-specific result, alongside increased oxidase activity. The authors' proposed active-center interaction is an interpretation to investigate, not a demonstrated contact or an established human regulatory function. This narrows the earlier paragraph's treatment of proton transport while keeping the complex-level association.
The cytochrome-c oxidase annotation remains accepted at structural-contribution scope, with the core explicitly represented by contributes_to_molecular_function. A noncatalytic subunit can provide structure required by a defined complex activity; a generic structural-molecule term would lose that supported specificity. The repository's annotation-reviewer instructions require judging this biology without reasoning from ordinary source qualifiers, so the source qualifier is preserved unchanged. Neither the original cloning abstract nor the curated core asserts isolated COX6B1 metal-centered catalysis.
The core now cites the already corroborated accessory-subunit synthesis in the unchanged Falcon artifact, alongside the primary human structure and complementation sources. Its disputed dimerization and unverified patient-intermediate claims remain separately assessed. The status is recalculated by the ordinary repository updater after this evidence change.
The MitoCoP values above were recovered from the original public Table S1 workbook, and the substantia-nigra values from the original external Table 2; they do not originate in the abstract-only caches. The public locators, exact cells and source hashes remain in the evidence index. Its family-cache differences are now embedded in full, removing dependence on unpublished temporary paths. This index is a manually compiled provenance record, not an independent reference or a claim that an automated analysis generated scientific judgments.