F8: cofactor activities, locations and product boundaries

The displayed human FVIII precursor has 2351 residues. Its signal peptide and processed heavy, B and light chains are proteolytic forms, distinct from the naturally spliced 216-residue F8B product. Historical mature-FVIII residue numbering differs from the displayed precursor by the 19-residue signal peptide. Engineered B-domain deletions and furin-site variants must not be equated with natural F8B. The original articles do not establish equivalent function of both natural products.

VWF association and enzyme activation

FVIII binds its VWF carrier. All three imported binding contexts name VWF (P04275), including PMID:18492805, whose Figure 5/ELISA Methods directly test that association. These rows retain the supported interaction as contextual binding; they do not mean that FVIII transports or stabilizes VWF. The same ADAMTS13 study separately reports enhanced VWF cleavage under shear and a smaller direct enzyme/peptide-substrate effect. Those results are retained with their physiological and construct limits, but do not replace the imported VWF partner by ADAMTS13. The independently tested FVIIIa–FIXa reaction grounds the proposed endopeptidase activator activity annotation; FIXa remains the protease.

The intrinsic-tenase experiments measure activated FVIII as a cofactor for FIXa-mediated FX cleavage. Intrinsic coagulation includes this performed step; the term does not require every physiological initiation route to begin with FXII. The genetic inversion study is supporting disease context, not the operative biochemical experiment.

Human cofactor chemistry and the membrane face

The complete Hultin 1982 original, PMID:6804496 was recovered. Printed pages 950–958 contain the operative purification, reaction, activation-control and platelet/lipid experiments. Actual page images 955–956 were inspected, including Tables II/III and Figures 4/5. The experiments use human FVIII preparations and human FIXa; the bovine-factor-X series and the human-factor-X series are distinct. Human factor X activation was measured through released radiolabeled activation peptide. Activation and contamination controls distinguish the FVIII cofactor from the proteases. The FVIII preparations contain VWF, an explicit author limitation rather than proof of a partner-free molecule. Externally supplied FVIII supports tenase on washed activated human platelets and phospholipid surfaces. This supports peripheral external-face association, not an integral membrane chain or every proposed binding mechanism.

The official supplement was recovered for PMID:27749002(https://doi.org/10.1111/jth.13543). Its Figures S1/S2 assay descriptions were independently read in the database assessment: human B-domain-deleted or Delta3 FVIII is activated by thrombin, thrombin is quenched by hirudin, and FVIIIa is added to human FIXa/FX and PC/PS vesicles. Chromogenic generated FXa reports the cofactor-supported reaction. The engineered constructs, BHK expression host and natural 216-residue F8B product are not interchangeable. No supplementary figure pixels were inspected in this consultation.

GO:0009897 includes proteins attached to or peripherally associated with the external plasma-membrane face. It is more precise than the seven imported broad membrane contexts. All seven are refined consistently. The Reactome disease events are not interchangeable: R-HSA-9668253 and R-HSA-9670874 alter F9 while their FVIII chains are native; R-HSA-9668365 contains FVIII A2 variants. Refining the positive compartment does not assign wild-type activity to each variant.

Copper binding is distinct from oxidoreductase chemistry

The complete accessible PMID:17965321 main was read selectively: Methods, Results, Tables 1/2, relevant Discussion and structural captions. The human CHO-expressed B-domain-deleted heterodimer has A1/A3 copper sites supported by anomalous diffraction. No figure pixels or supplement were read. This directly supports copper binding, while retaining the preparation and occupancy qualifications. Current IPR011706/IPR011707 occur on the human target and map to copper binding; an older non-copper-binding phrase in their family description is not substituted for the human structure.

IPR011706 also currently maps to GO:0016491 oxidoreductase activity. That term requires catalytic oxidation-state change. FVIII's coordinated copper and its enhancement of FIXa-mediated proteolysis do not establish such chemistry. The electronic oxidoreductase propagation is removed while the actual domain and copper-binding observations remain. This is a domain-function overgeneralization, not rejection of an unread experimental oxidoreductase paper.

Actual phylogenetic and automated source provenance

The actual v19 PANTHER tree/MSA places human P00451 at PTN002555836 with an exactly matching 2351-residue sequence. Its path contains extracellular IBD PTN009099846 and intrinsic-coagulation IBD PTN002815617. The positive IBD records and every target-path NOT record were checked; no relevant NOT contradicts these assertions. Current UniProt PTHR46806 and the v19 gene-information family PTHR24543 are separate versioned observations. The current-family tree lacks the target, and is not silently substituted for the recovered historical family. Neither donor count nor valid self-WITH is a reason to reject an inheritance assertion.

The rat F8 donor RGD:727845 is verified against current identifiers and experimental GOA. The accessible PMID:2513867 abstract reports cultured rat sinusoidal endothelial cells secreting active FVIII with antigen/activity controls; its complete Methods were unavailable. The other extracellular donors were identified from actual database records, without claiming their primary experiments were all reread. Independently read human cofactor and secretion evidence supports the target assignments.

Current ARBA00027486 set 4, ARBA00084788 set 2 and ARBA00092682 set 0 match the actual target FunFam/taxonomy data. Their COPII, granule and ERGIC predictions remain subject to source-specific biological review. Current ARBA00027128 has no complete human match: the target FunFam pair occurs in a reptile-specific condition. This may reflect a version boundary; no historical condition set was reconstructed. Actual SL-0112 maps to extracellular region, but its narrower prose excludes freely circulating blood proteins. Broad extracellular FVIII is accepted on direct target evidence, without claiming that the current human rule or narrower vocabulary wording was validated. The four official GO_REF methods were read from the actual GO source metadata.

Reactome roles, compartments and disease products

All 34 event roots were traversed through input, output, catalystActivity, physicalEntity, hasComponent, hasMember, hasCandidate, activeUnit, regulatedBy and regulator links. The final graph has 817 fetched objects and no unresolved participant links. Target-own compartments, reference sequences and modifications were retained. The initial bulk service returned only 20 objects for a larger request; that incomplete capture and bounded recovery are documented rather than presented as a complete first fetch. A graph read is not a claim that every event-cited original paper was read.

Native circulating and processed extracellular FVIII pools are retained as core locations. The five disease-associated extracellular contexts also contain exact native P00451 companion chains with their own extracellular compartment. Their location claims are therefore accepted consistently; the source-specific variant routes remain explicit and do not establish wild-type activity for every mutant. In particular, R-HSA-9665809 contains native heavy chain 158250; 9666383 includes native light/heavy companions; 9670049 includes native light and released A2 chains; 9670054 includes native A1/light chains; and 9670189 includes native A1/A2 chains. A thrombin/APC/TF-associated cleavage event makes FVIII the substrate; it does not transfer protease activity. TPST1/2 sulfate FVIII in the Golgi. ER, Golgi, COPII and receptor-associated ERGIC pools are retained as contextual biosynthetic locations. FVIII is cargo, not a coat, tether, receptor or vesicle-fusion catalyst. The ERGIC membrane model does not establish a transmembrane F8 protein.

The independently read PMID:18492805 main supports enhancement of ADAMTS13-dependent VWF cleavage, plus a smaller direct effect on ADAMTS13 peptide-substrate turnover. Main Results and operative Methods distinguish human full-length/recombinant constructs, VWF-dependent and peptide-substrate effects, controls and binding assays. ADAMTS13 performs the cleavage. This substantiates the extracellular cofactor context of R-HSA-9934645, without an F8 protease claim or a new figure-pixel read.

F8B and the narrow ER-compartment query

The source products remain P00451-1, displayed 2351 residues, and P00451-2/F8B, 216 residues. The latter is reconstructed from both actual UniProt sequence edits and matches NP_063916.1. Signal peptide 1–19, mature chain and released B-domain segments are processing features of the displayed product, not additional splice products.

R-HSA-9661980 contains heterogeneous nonsecretion variants. Its member 9666368 starts at modeled mature residue 20 and replaces 20–2143 by MRIQDPGK; applying those literal fields gives the natural F8B sequence. That equality does not locate the product. The actual PMID:24037092 main, selected Results, Methods for expression vectors and cells, and captions establish intracellular F8B expression and lack of secretion. They distinguish its alternative eight-residue N terminus without a recognizable leader from the signal-containing long inversion product. The localization work does not resolve F8B to ER lumen with an ER-specific marker. The later synthesis, PMID:25406352, retains that product distinction rather than supplying an independent ER assay.

A PROBABLE/CHECK query therefore asks Reactome about this member's precise ER compartment and any additional localization/engineered-leader evidence. It does not deny the positive intracellular/nonsecretion observations, infer a replacement compartment, reject the other ER-retained variants, or claim that all F8 products lack ER entry. No upstream report has been sent.

Native platelet alpha-granule attribution remains unresolved

R-HSA-481007 explicitly models native P00451 in alpha-granule lumen entity 114591 and extracellular output 54601. The complete author main and supplemental assay Methods/figures of PMID:23640497(https://doi.org/10.1161/ATVBAHA.113.301147) were recovered from the Utrecht repository. The study compares washed platelet preparations from three human donors before/after thrombin plus collagen stimulation using quantitative proteomics. The supplementary protein Tables I/II required to establish an exact P00451 identification were not recovered. No F8 peptide or target row is claimed, and lack of an F8 string in the main article is not a negative experiment.

The older PMID:6457647 abstract uses factor VIII-related antigen nomenclature; it cannot automatically be treated as native F8 rather than VWF. Its complete original and the PMID:8467233 review remain inaccessible. The two granule-lumen assertions are UNDECIDED. The independently supported extracellular FVIII pool remains accepted. Engineered platelet expression or uptake is not silently substituted for native granule evidence.

Additional original-source and access scopes

PMID:18492805

Complete original main text was recovered from PMC. The Results on shear-dependent VWF cleavage and multimer distribution (Figures 1–4), FVIII–VWF binding (Figure 5), direct ADAMTS13 interaction, and Materials and Methods were read. Recombinant human full-length FVIII and human-cDNA B-domain/a3 derivatives were used; BHK is the expression host for the engineered derivatives. FVIII enhances ADAMTS13-mediated VWF proteolysis but is not the protease. The main article reports direct FVIII–ADAMTS13 SPR binding and a smaller peptide-cleavage enhancement; the authors distinguish this from the stronger VWF-dependent effect and do not establish its in vivo importance. Separate supplementary figures were inaccessible, and no figure pixels were inspected. The normal cache remains abstract-only despite external complete-main availability. https://pmc.ncbi.nlm.nih.gov/articles/PMC2396690/

PMID:27749002

The original main Methods, Table 1 and relevant Results, and the genuine official supplementary DOCX captions for Figures S1–S5 were inspected. Human B-domain-deleted FVIII and furin-site variants produced in BHK cells bind plasma-derived human VWF by background-subtracted SPR; Table 1 reports a 0.7 nM BDD comparator. Supplementary Figures S1–S2 specify thrombin activation followed by hirudin quenching, plasma-derived human FIXa and human FX, PC/PS vesicles and chromogenic detection of generated FXa. These support FVIII cofactor activity rather than FVIII proteolysis. Figure S5 specifies immobilized human VWF and the binding fit. Engineered deletion variants, single-chain/processed states and natural F8B remain distinct. Supplementary image files were extracted but not visually inspected; no historical clone-sequence identity or natural-product equivalence is claimed. https://pmc.ncbi.nlm.nih.gov/articles/PMC5280213/ ; https://www.ebi.ac.uk/biostudies/studies/S-EPMC5280213

PMID:7756647

PubMed/Europe PMC identity and the original abstract were verified; the DOI was independently confirmed in Crossref. The abstract describes human FVIII binding to plasma VWF from healthy donors and severe hemophilia A patients, with solid-phase, gel-filtration and VWF–gold fluid-phase comparisons. Complete original Methods and Results were not recovered after bounded publisher/PDF attempts. Specific reagent processing and natural-product identity therefore remain unverified. Independent inspected human FVIII–VWF experiments in PMID18492805 and PMID27749002 support retention of the interaction without pretending the old paper was read in full. https://doi.org/10.1182/blood.V85.11.3150.bloodjournal85113150

PMID:14718574

Selected original author-upload Methods and Table II excerpts were inspected. Table II explicitly lists P00451/coagulation factor VIII with literature and LCMS1 detections, not positive calls in every dataset. The LCMS1 Methods describe a human serum proteomics input. This supports a bounded extracellular protein observation, not microparticle localization, peptide-level reassignment or natural-product specificity. The complete article was not recovered in this review; selected original access is distinguished from the abstract-only immutable normal cache. https://doi.org/10.1074/mcp.M300127-MCP200 ; https://www.researchgate.net/publication/8480883_The_Human_Plasma_Proteome_A_Nonredundant_List_Developed_by_Combination_of_Four_Separate_Sources

PMID:8275087

PubMed/Europe PMC identity and the original publisher abstract were read. This is the human F8 inversion/Southern-blot study associated with severe hemophilia A; complete operative Methods and Results remain unavailable behind the publisher preview. It is not treated as an isolated coagulation assay or as evidence that natural F8B has the same function as full-length FVIII. The specific performed coagulation step is independently supported by the inspected human intrinsic-tenase assay in PMID27749002, Supplementary Figures S1–S2. https://doi.org/10.1038/ng1193-236

Reading and availability boundaries

Complete-original availability, immutable cache metadata and actual reading scope are separate. The two shared reference assessments retain both independently stated scopes, including the unviewed supplementary images and separately read binding versus tenase experiments. The source guides do not convert engineered B-domain deletions, inversion products or processing chains into equivalent natural F8 products. Supported generic associations remain non-core under the campaign instructions; no new publication quotations are introduced. One independent, directly supported FIXa-activator MF annotation is proposed.

Core synthesis and assay separation

The core represents endopeptidase activator activity in intrinsic coagulation: activated FVIIIa supports FIXa-mediated FX cleavage at the external plasma-membrane face. FIXa is the protease. Human biochemical and activated-platelet evidence in PMID:6804496(https://www.jci.org/articles/view/110534), Methods and Tables II/III/Figures 4/5, and the human construct assays in PMID:27749002(https://pmc.ncbi.nlm.nih.gov/articles/PMC5280213/), supplementary Figures S1/S2, support the performed cofactor step. Human and bovine substrate series, VWF-containing preparations, engineered deletions and natural products remain separate. The bounded current ontology search did not establish a specific tenase-complex identifier; the assembly is described without a guessed identifier.

Copper binding is retained as a supporting structural facet of this same cofactor unit. The A1/A3 copper sites in the active engineered heterodimer support domain architecture; this is not an inferred redox mechanism or a claim that the structure performed a copper-depletion/reconstitution assay. Expression-dependent occupancy and natural F8B limits remain explicit. The separately measured unactivated-FVIII/ADAMTS13 enhancement in PMID:18492805(https://pmc.ncbi.nlm.nih.gov/articles/PMC2396690/), Figures 1–6, direct-interaction Results and corresponding Methods, is retained explicitly. Its VWF-dependent shear effect, smaller peptide-substrate effect and loss after activation are not interchangeable with the FVIIIa/FIXa reaction. No additional coagulation-regulation process is inferred from those assays. Questions retain the physiological ADAMTS13 contribution, natural F8B molecular role and native platelet-granule attribution as separate issues.

This synthesis reread selected saved original text and captions; it adds no new figure-pixel inspection. Earlier pixel-read scopes remain attributed to their original assessment. Complete-article availability and immutable abstract-only cache metadata remain distinct. No additional normal publication acquisition is required; the selected dependency set is unchanged.

Independent cofactor annotation and source-trace follow-up

The proposed IDA activator annotation takes PMID:6804496 as its primary reference and retains PMID:27749002(https://pmc.ncbi.nlm.nih.gov/articles/PMC5280213/), supplementary Figures S1/S2, as corroboration independently of its imported VWF-binding IPI row. These assays activate human engineered FVIII with thrombin, quench thrombin with hirudin, and measure the ensuing human FIXa/FX reaction on PC/PS. The chromogenic signal is produced by generated FXa. PMID:6804496(https://www.jci.org/articles/view/110534), Methods (printed 951–953) and Figure 5/Results (956), independently compare human FIXa-mediated human FX activation with and without activated human FVIII using radiolabeled activation-peptide release. The separate bovine FX series is not reassigned to human. The VWF-containing preparation and activation controls remain relevant limits.

Current GO:0061133 requires binding to and increasing endopeptidase activity. Its current is_a child, GO:0140608, specifies a cysteine-type enzyme and does not fit FIXa. The bounded search did not establish a serine-specific child; no speculative new term or redundant parent is proposed. Fresh QuickGO molecular-function records for human F5/P12259 and F8/P00451 and mouse F5/O88783 and F8/Q06194 lack activator annotations. That absence is a caution about existing curation, not evidence of an overlooked gap. Human PCOLCE/Q15113, a nonhomologous extracellular protease-enhancer comparator, carries the broader peptidase-activator term; it is not treated as evidence for F8. The F8 proposal rests on the executed human molecular experiments and the current definition.

The granule query is now structured as SUSPECTED/CHECK for R-HSA-481007, physical entity 114591. It requests the F8-specific target experiment/protein record without declaring wrong-gene attribution from historical antigen wording or unavailable originals. Both granule annotations remain UNDECIDED. No upstream report has been sent.

Primary assay and separate supplementary evidence

The NEW endopeptidase-activator annotation uses Hultin 1982, PMID:6804496 as its primary source. Its human FIXa/human FX initial-rate experiment directly compares activation with and without activated human FVIII; the human and bovine substrate series and the VWF-containing preparation remain distinguished. The cached abstract supports the central cofactor result, while the already inspected original Methods and Figure 5 provide the precise assay locator.

The reagent details for PMID:27749002 are in the separate official JTH-15-110-s001.docx supplement, Figure S1 and S2 legends, rather than the abbreviated supplement titles in the immutable cached main text. The main Methods delegate the assay protocol to earlier references. The actual supplementary legends independently state the human B-domain-deleted/Delta3 preparations, thrombin activation followed by hirudin quenching, plasma-derived human FIXa/FX and PC/PS vesicles. The generated-FXa readout supports the FVIIIa cofactor role; it does not make FVIII a protease. The exact supplementary text was inspected, but its figure pixels were not. The main-cache omission therefore limits what that cache alone demonstrates, without invalidating the separately recovered original supplement. No publication cache was rewritten and no new quotation was added.

Cache metadata and external originals

The full_text_unavailable flags for PMID:18492805, PMID:6804496, PMID:23640497 are true because their immutable normal caches are abstract-only. Complete external original availability and the precise previously documented reading scopes remain unchanged in reference_review.review_notes. Cache contents, external availability and actual reading are separate records; this metadata correction changes no annotation decision, citation identity or biological conclusion.