id: P13674
gene_symbol: P4HA1
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: P4HA1 is the catalytic alpha-1 subunit of collagen prolyl 4-hydroxylase (C-P4H; EC 1.14.11.2), an endoplasmic reticulum-lumenal, Fe(II)- and 2-oxoglutarate-dependent dioxygenase. The active enzyme is an alpha2-beta2 heterotetramer in which the beta subunit is P4HB (protein disulfide-isomerase, PDI); the two catalytic alpha subunits provide the peptide-substrate-binding and Fe2OG dioxygenase domains, while P4HB acts as a structural subunit and retains the tetramer in the ER lumen through its C-terminal KDEL sequence (the alpha subunit lacks a retention signal). C-P4H catalyzes the post-translational formation of trans-4-hydroxy-L-proline from proline residues in -Xaa-Pro-Gly- sequences of procollagen and other proteins, consuming O2 and 2-oxoglutarate (which is decarboxylated to succinate and CO2) and requiring ascorbate (vitamin C) to maintain the active-site iron in the reduced state. 4-Hydroxyproline is essential for the thermal stability of the collagen triple helix, making this the key rate-limiting modification in collagen maturation and a central enzyme of collagen biosynthesis. Two enzyme isotypes exist (type I, with P4HA1, and type II, with the paralog P4HA2); the alpha-1 and alpha-2 subunits do not form mixed tetramers. P4HA1 is broadly expressed, with highest levels in collagen-producing tissues.
alternative_products:
- name: '1'
  id: P13674-1
- name: '2'
  id: P13674-2
  sequence_note: VSP_004504
- name: '3'
  id: P13674-3
  sequence_note: VSP_004504, VSP_044578
existing_annotations:
- term:
    id: GO:0004656
    label: procollagen-proline 4-dioxygenase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: Phylogenetic (IBA) assignment of the core catalytic molecular function of P4HA1 as the alpha subunit of collagen prolyl 4-hydroxylase.
    action: ACCEPT
    reason: This is the defining, experimentally demonstrated molecular function of P4HA1; the IBA call is consistent with the direct IDA evidence (PMID:9211872) and EC 1.14.11.2.
    supported_by:
    - reference_id: file:human/P4HA1/P4HA1-uniprot.txt
      supporting_text: Catalyzes the post-translational formation of 4-
- term:
    id: GO:0016222
    label: procollagen-proline 4-dioxygenase complex
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: part_of
  review:
    summary: P4HA1 is part of the alpha2-beta2 collagen prolyl 4-hydroxylase complex (alpha = P4HA1, beta = P4HB/PDI); phylogenetic assignment of complex membership.
    action: ACCEPT
    reason: The active enzyme is the alpha2-beta2 tetramer; P4HA1 is a constitutive catalytic subunit of this complex. Core cellular component.
    supported_by:
    - reference_id: file:human/P4HA1/P4HA1-uniprot.txt
      supporting_text: Heterotetramer of two alpha-1 chains and two beta chains
- term:
    id: GO:0030199
    label: collagen fibril organization
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: P4HA1-catalyzed 4-hydroxyproline formation stabilizes the collagen triple helix and is a prerequisite for proper collagen fibril formation; this is a downstream process role.
    action: KEEP_AS_NON_CORE
    reason: P4HA1 contributes indirectly to fibril organization by modifying procollagen, but fibril assembly itself is carried out by other machinery. The direct function is peptidyl-proline hydroxylation; this BP is a valid non-core involvement.
    supported_by:
    - reference_id: file:human/P4HA1/P4HA1-uniprot.txt
      supporting_text: this tetramer catalyzes the formation of 4-hydroxyproline in collagen
- term:
    id: GO:0004656
    label: procollagen-proline 4-dioxygenase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: Electronic assignment of the core procollagen-proline 4-dioxygenase activity, redundant with the IDA/TAS/IBA evidence.
    action: ACCEPT
    reason: Correct core molecular function; consistent with EC 1.14.11.2 and the experimental IDA annotation.
    supported_by:
    - reference_id: file:human/P4HA1/P4HA1-uniprot.txt
      supporting_text: EC=1.14.11.2
- term:
    id: GO:0005506
    label: iron ion binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: P4HA1 binds one catalytic Fe(2+) per subunit in its Fe2OG dioxygenase domain; this cofactor binding is required for the dioxygenase mechanism.
    action: ACCEPT
    reason: Supported by the UniProt COFACTOR (Fe(2+), one per subunit) and the Fe-binding residues in the Fe2OG domain; a genuine, mechanistically essential molecular function.
    supported_by:
    - reference_id: file:human/P4HA1/P4HA1-uniprot.txt
      supporting_text: Binds 1 Fe(2+) ion per subunit.
- term:
    id: GO:0005783
    label: endoplasmic reticulum
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: located_in
  review:
    summary: Electronic assignment of endoplasmic reticulum localization, the parent compartment of the documented ER lumen location.
    action: ACCEPT
    reason: Correct compartment; consistent with the UniProt ER lumen subcellular location and the IDA (HPA) ER annotation.
    supported_by:
    - reference_id: file:human/P4HA1/P4HA1-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum lumen.'
- term:
    id: GO:0005788
    label: endoplasmic reticulum lumen
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: ER lumen localization derived electronically from the UniProt subcellular location vocabulary; this is the precise documented compartment for C-P4H.
    action: ACCEPT
    reason: Matches the curated UniProt subcellular location; the soluble tetramer acts in the ER lumen, retained there via the P4HB KDEL.
    supported_by:
    - reference_id: file:human/P4HA1/P4HA1-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum lumen.'
- term:
    id: GO:0016705
    label: oxidoreductase activity, acting on paired donors, with incorporation or
      reduction of molecular oxygen
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: General oxidoreductase/dioxygenase activity term, a parent of the precise procollagen-proline 4-dioxygenase activity, reflecting incorporation of molecular oxygen.
    action: ACCEPT
    reason: Correct and consistent with the 2-oxoglutarate/O2-dependent dioxygenase mechanism; the more specific GO:0004656 captures the precise core function.
    supported_by:
    - reference_id: file:human/P4HA1/P4HA1-uniprot.txt
      supporting_text: L-prolyl-[collagen] + 2-oxoglutarate + O2 = trans-4-hydroxy-L-
- term:
    id: GO:0031418
    label: L-ascorbic acid binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: C-P4H requires ascorbate (vitamin C) as a cofactor to keep the active-site iron reduced; L-ascorbic acid binding is a genuine cofactor-binding function.
    action: ACCEPT
    reason: Supported by the UniProt COFACTOR (L-ascorbate) and the Vitamin C keyword; mechanistically required and biologically central (collagen hydroxylation depends on vitamin C).
    supported_by:
    - reference_id: file:human/P4HA1/P4HA1-uniprot.txt
      supporting_text: Name=L-ascorbate
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:17500595
  qualifier: enables
  review:
    summary: High-throughput huntingtin-interactome screen reporting a P4HA1-HTT interaction (IntAct P13674-P42858). Bare protein binding is uninformative and unrelated to the catalytic core function.
    action: KEEP_AS_NON_CORE
    reason: Records a real IntAct interaction also listed in UniProt, but the bare protein binding term gives no functional information and the HTT partner does not reflect P4HA1's collagen-hydroxylase role; per guidelines not elevated to core.
    supported_by:
    - reference_id: file:human/P4HA1/P4HA1-uniprot.txt
      supporting_text: 'P13674; P42858: HTT'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:30021884
  qualifier: enables
  review:
    summary: Crosslinking mass spectrometry of intact nuclei capturing a P4HA1 interaction (IntAct partner P4HA2/O15460). Bare protein binding from a high-throughput screen.
    action: KEEP_AS_NON_CORE
    reason: Uninformative bare protein binding term from a high-throughput XL-MS dataset; the partner is the paralog P4HA2 and the interaction does not inform the core catalytic function.
    supported_by:
    - reference_id: PMID:30021884
      supporting_text: we use crosslinking mass spectrometry (XL-MS) to chart the protein-protein interactions in intact human nuclei
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:40205054
  qualifier: enables
  review:
    summary: Multimodal cell map (AP-MS/immunofluorescence in U2OS) reporting a P4HA1 interaction (IntAct partner P4HA2/O15460). High-throughput, uninformative bare term.
    action: KEEP_AS_NON_CORE
    reason: Bare protein binding from a proteome-scale interaction/imaging map; the paralog partner does not establish a specific function beyond the already-captured complex membership.
    supported_by:
    - reference_id: PMID:40205054
      supporting_text: protein biophysical interactions and protein IF images for a matched set of more than 5,100 proteins in U2OS cells
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:24207127
  qualifier: enables
  review:
    summary: P4HA1 alpha subunits homodimerize via an antiparallel coiled-coil four-helix bundle in the N domain, an assembly step of the alpha2-beta2 tetramer; this is the structural basis of the identical protein binding (self-interaction) annotation.
    action: KEEP_AS_NON_CORE
    reason: A genuine, structurally demonstrated alpha-alpha homodimerization within the tetramer, but it is subsidiary to the informative catalytic core function and complex membership; retained as a non-core supporting attribute.
    supported_by:
    - reference_id: PMID:24207127
      supporting_text: forming an extended four-helix bundle that includes an antiparallel coiled-coil dimerization motif between the two α subunits
- term:
    id: GO:0016222
    label: procollagen-proline 4-dioxygenase complex
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: part_of
  review:
    summary: Ortholog-based electronic assignment of membership in the procollagen-proline 4-dioxygenase (C-P4H) complex.
    action: ACCEPT
    reason: Correct; redundant with the IBA complex annotation. P4HA1 is a catalytic subunit of the alpha2-beta2 tetramer with P4HB.
    supported_by:
    - reference_id: file:human/P4HA1/P4HA1-uniprot.txt
      supporting_text: Heterotetramer of two alpha-1 chains and two beta chains
- term:
    id: GO:0005783
    label: endoplasmic reticulum
  evidence_type: IDA
  original_reference_id: GO_REF:0000052
  qualifier: located_in
  review:
    summary: Direct immunofluorescence (HPA) evidence for endoplasmic reticulum localization of P4HA1, consistent with its ER-lumenal site of action.
    action: ACCEPT
    reason: IDA-supported ER localization agrees with the curated ER lumen subcellular location.
    supported_by:
    - reference_id: file:human/P4HA1/P4HA1-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum lumen.'
- term:
    id: GO:0004656
    label: procollagen-proline 4-dioxygenase activity
  evidence_type: IDA
  original_reference_id: PMID:9211872
  qualifier: enables
  review:
    summary: Direct experimental characterization of the purified human prolyl 4-hydroxylase tetramer demonstrating procollagen-proline 4-dioxygenase activity (catalytic activity, kinetics, cofactor, inhibition by poly(L-proline)).
    action: ACCEPT
    reason: Core molecular function with direct (IDA) experimental support; this is the rate-limiting collagen-modifying activity of P4HA1.
    supported_by:
    - reference_id: PMID:9211872
      supporting_text: Prolyl 4-hydroxylase (proline hydroxylase, EC 1.14.11.2) catalyzes the formation of 4-hydroxyproline in collagens.
- term:
    id: GO:0016020
    label: membrane
  evidence_type: HDA
  original_reference_id: PMID:19946888
  qualifier: located_in
  review:
    summary: P4HA1 was detected in a membrane-fraction proteomics screen of NK-like cells. P4HA1 is a soluble ER-lumenal protein, so a generic membrane localization most likely reflects co-fractionation of secretory/ER proteins with membrane preparations.
    action: MARK_AS_OVER_ANNOTATED
    reason: The documented, mechanistically meaningful localization is the soluble ER lumen; a bulk membrane-proteome HDA hit does not establish a credible membrane localization for this lumenal enzyme. The study itself notes many identified proteins are only transiently membrane-associated. Not removed (experimental data), but over-annotated and non-core.
    supported_by:
    - reference_id: PMID:19946888
      supporting_text: The remaining species were largely involved in cellular processes and molecular functions that could be predicted to be transiently associated with membranes.
- term:
    id: GO:0005788
    label: endoplasmic reticulum lumen
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-1650808
  qualifier: located_in
  review:
    summary: Reactome curation places P4HA1 in the ER lumen, where prolyl 4-hydroxylase converts collagen prolines to 4-hydroxyprolines.
    action: ACCEPT
    reason: Correct compartment; consistent with the curated UniProt ER lumen location and the enzyme's site of action.
    supported_by:
    - reference_id: file:human/P4HA1/P4HA1-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum lumen.'
- term:
    id: GO:0005788
    label: endoplasmic reticulum lumen
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9918779
  qualifier: located_in
  review:
    summary: Reactome curation of P4HA1 ER lumen localization (proline hydroxylation context).
    action: ACCEPT
    reason: Correct compartment; redundant with the other ER lumen annotations and the UniProt subcellular location.
    supported_by:
    - reference_id: file:human/P4HA1/P4HA1-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum lumen.'
- term:
    id: GO:0004656
    label: procollagen-proline 4-dioxygenase activity
  evidence_type: TAS
  original_reference_id: PMID:2543975
  qualifier: enables
  review:
    summary: Traceable assertion (original cloning paper) of P4HA1 as the alpha subunit of the alpha2-beta2 prolyl 4-hydroxylase that catalyzes 4-hydroxyproline formation in collagens.
    action: ACCEPT
    reason: Core molecular function; the foundational cloning/characterization study supports the catalytic activity, consistent with the IDA evidence.
    supported_by:
    - reference_id: PMID:2543975
      supporting_text: an alpha 2 beta 2 tetramer, catalyzes the formation of 4-hydroxyproline in collagens by the hydroxylation of proline residues in peptide linkages
- term:
    id: GO:0005783
    label: endoplasmic reticulum
  evidence_type: TAS
  original_reference_id: PMID:2543975
  qualifier: located_in
  review:
    summary: Traceable assertion of ER localization, inferred from the demonstration that the beta/PDI subunit retains the tetramer within the ER (the alpha subunit lacks a KDEL signal).
    action: ACCEPT
    reason: Correct compartment; the cloning paper established ER retention of the enzyme via P4HB, consistent with the curated ER lumen location.
    supported_by:
    - reference_id: PMID:2543975
      supporting_text: necessary for the retention of a polypeptide within the lumen of the endoplasmic reticulum
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
    vocabulary mapping, accompanied by conservative changes to GO terms applied by
    UniProt
  findings: []
- id: GO_REF:0000052
  title: Gene Ontology annotation based on curation of immunofluorescence data
  findings: []
- id: GO_REF:0000107
  title: Automatic transfer of experimentally verified manual GO annotation data to
    orthologs using Ensembl Compara
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:17500595
  title: Huntingtin interacting proteins are genetic modifiers of neurodegeneration.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput huntingtin-fragment interactome (Y2H + pull-down/MS); source of the IntAct P4HA1-HTT (P13674-P42858) protein binding annotation. Not relevant to the collagen-hydroxylase function.
- id: PMID:19946888
  title: Defining the membrane proteome of NK cells.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Membrane-fraction proteomics of NK-like YTS cells; basis of the membrane HDA annotation. P4HA1 is a soluble ER-lumenal protein, so this is a likely co-fractionation artifact (the paper notes many hits are only transiently membrane-associated).
- id: PMID:24207127
  title: The structural motifs for substrate binding and dimerization of the α subunit
    of collagen prolyl 4-hydroxylase.
  findings:
  - statement: The C-P4H alpha subunit comprises an N domain (1-143), a peptide-substrate-binding (PSB) domain (144-244) and a catalytic domain (245-517); the N domain forms an antiparallel coiled-coil four-helix bundle that drives alpha-alpha dimerization and tetramer assembly, and the PSB domain binds substrate peptides in a poly-(L)-proline-II conformation.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Structural study establishing the alpha-subunit domain organization, the alpha-alpha dimerization motif (basis of the identical protein binding annotation), and the substrate-binding mode.
- id: PMID:2543975
  title: 'Molecular cloning of the alpha-subunit of human prolyl 4-hydroxylase: the
    complete cDNA-derived amino acid sequence and evidence for alternative splicing
    of RNA transcripts.'
  findings:
  - statement: Prolyl 4-hydroxylase is an alpha2-beta2 tetramer that catalyzes 4-hydroxyproline formation in collagens; the alpha subunit lacks a C-terminal KDEL, so ER retention of the tetramer is conferred by the beta (PDI) subunit. The single alpha gene yields two mRNA types by mutually exclusive alternative splicing.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Foundational cloning/characterization of the human P4HA1 alpha subunit; supports the catalytic activity (TAS), ER localization (via beta/PDI retention), and alternative splicing.
- id: PMID:30021884
  title: Histone Interaction Landscapes Visualized by Crosslinking Mass Spectrometry
    in Intact Cell Nuclei.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Nuclear XL-MS interactome screen; source of an IntAct P4HA1 protein binding annotation (partner paralog P4HA2). Uninformative for the core function.
- id: PMID:40205054
  title: Multimodal cell maps as a foundation for structural and functional genomics.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Proteome-scale AP-MS/immunofluorescence cell map in U2OS cells; source of an IntAct P4HA1 protein binding annotation (partner paralog P4HA2). High-throughput, uninformative for the core function.
- id: PMID:35368589
  title: Mannose Binding Lectin Is Hydroxylated by Collagen Prolyl-4-hydroxylase and
    Inhibited by Some PHD Inhibitors.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: 'PubMed-verified (Bhute et al., Kidney360 2020). Identifies a non-collagen
      C-P4H substrate beyond fibrillar procollagen: mannose-binding lectin (MBL),
      whose collagen-like domain is prolyl-hydroxylated by collagen prolyl-4-hydroxylase
      (P4HA1-dependent; secretion of high-MW MBL oligomers requires hydroxylation).
      Also shows that clinical HIF-PHD inhibitors roxadustat and vadadustat (but not
      molidustat) suppress MBL hydroxylation as an off-target effect on C-P4H. Expands
      the documented substrate scope and gives clinical/pharmacological context not
      in the prior review.'
- id: PMID:38907027
  title: Lactate supports cell-autonomous ECM production to sustain metastatic behavior
    in prostate cancer.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: 'PubMed-verified (Ippolito et al., EMBO Rep 2024). Provides direct
      mechanistic evidence that metabolic supply of alpha-ketoglutarate (from CAF-derived
      lactate) increases P4HA1-dependent collagen 4-hydroxylation (hydroxyproline content),
      driving a collagen-DDR1 signaling loop that supports prostate cancer metastasis.
      Illustrates metabolite (2-oxoglutarate) availability as a functional lever on
      P4HA1 enzymatic output; contextual/non-core for the catalytic annotation but
      informative for the hypoxia/metabolism-ECM axis.'
- id: PMID:38134053
  title: P4HA1 expression and function in esophageal squamous cell carcinoma.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: 'PubMed-verified (Gou et al., Medicine 2023; DOI 10.1097/MD.0000000000036800).
      Clinical IHC/TCGA study reporting P4HA1 overexpression in ESCC (high in 68.7%
      of cases, negative in adjacent tissue) and P4HA1 as an independent prognostic
      factor (OS/PFS). Cancer-biomarker/prognostic context; not core to the catalytic
      collagen-hydroxylase function.'
- id: PMID:39394821
  title: 'Collagen prolyl 4-hydroxylase subunit alpha member-induced head and neck
    squamous cell carcinoma aggressiveness is antagonized by LLGL2 via reduced expression
    of occludin.'
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: 'PubMed-verified (Xu et al., Acta Biochim Biophys Sin 2024; DOI
      10.3724/abbs.2024140). TCGA-based analysis of all three C-P4HA alpha subunits
      (P4HA1/2/3) in HNSCC; higher combined expression of the three is a prognostic
      indicator, antagonized by LLGL2 via occludin. Family-level cancer context; not
      core to P4HA1 catalytic function.'
- id: PMID:39563376
  title: IL-10 mediates pleural remodeling in systemic lupus erythematosus.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: 'PubMed-verified (Niu et al., Cell Commun Signal 2024; DOI 10.1186/s12964-024-01911-4).
      Places P4HA1 as a downstream effector in an IL-10/JAK2/STAT3/HIF1alpha/TMEM45A/P4HA1
      axis driving fibro-inflammatory pleural remodeling/collagen deposition; P4HA1
      knockdown blocks IL-10-induced ECM markers. Fibro-inflammatory ECM-remodeling
      context (non-core); illustrates HIF/hypoxia-linked transcriptional induction
      of P4HA1.'
- id: PMID:39568592
  title: 'P4HA1: an important target for treating fibrosis related diseases and cancer.'
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: 'PubMed-verified (Yang et al., Front Pharmacol 2024; DOI 10.3389/fphar.2024.1493420).
      P4HA1-focused review compiling its role across fibrosis-related diseases and
      cancers, hypoxia/HIF-linked induction, ECM remodeling, and therapeutic-targeting
      strategies (siRNA, small-molecule P4H inhibitors). Useful map of reported (non-core)
      disease mechanisms rather than primary evidence.'
- id: PMID:9211872
  title: Cloning of the human prolyl 4-hydroxylase alpha subunit isoform alpha(II)
    and characterization of the type II enzyme tetramer. The alpha(I) and alpha(II)
    subunits do not form a mixed alpha(I)alpha(II)beta2 tetramer.
  findings:
  - statement: The vertebrate prolyl 4-hydroxylase is an alpha2-beta2 tetramer whose beta subunit is identical to protein disulfide-isomerase (PDI); the type I (alpha-I/P4HA1) and type II (alpha-II/P4HA2) subunits do not form mixed tetramers. The purified enzyme has KM 22 uM for 2-oxoglutarate and is inhibited by poly(L-proline).
    reference_section_type: ABSTRACT
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Direct biochemical characterization of the human prolyl 4-hydroxylase tetramer; primary IDA support for procollagen-proline 4-dioxygenase activity (EC 1.14.11.2) and the alpha2-beta2 subunit composition with P4HB.
- id: Reactome:R-HSA-1650808
  title: Prolyl 4-hydroxylase converts collagen prolines to 4-hydroxyprolines
  findings: []
- id: Reactome:R-HSA-9918779
  title: Proline hydroxylases hydroxylate Polyprotein
  findings: []
- id: file:human/P4HA1/P4HA1-uniprot.txt
  title: UniProt entry P13674 (P4HA1_HUMAN), Prolyl 4-hydroxylase subunit alpha-1
  findings:
  - statement: Catalytic alpha-1 subunit of collagen prolyl 4-hydroxylase (EC 1.14.11.2); alpha2-beta2 heterotetramer with P4HB (PDI) as structural subunit; ER-lumenal; Fe(2+)- and 2-oxoglutarate-dependent dioxygenase requiring L-ascorbate; catalyzes 4-hydroxyproline formation in collagens.
    reference_section_type: OTHER
core_functions:
- description: Catalytic alpha subunit of collagen prolyl 4-hydroxylase, a Fe(II)/2-oxoglutarate/ascorbate-dependent dioxygenase that forms trans-4-hydroxy-L-proline in -Xaa-Pro-Gly- sequences of procollagen, the rate-limiting modification required for collagen triple-helix stability.
  molecular_function:
    id: GO:0004656
    label: procollagen-proline 4-dioxygenase activity
  locations:
  - id: GO:0005788
    label: endoplasmic reticulum lumen
  supported_by:
  - reference_id: PMID:9211872
    supporting_text: Prolyl 4-hydroxylase (proline hydroxylase, EC 1.14.11.2) catalyzes the formation of 4-hydroxyproline in collagens.
  - reference_id: file:human/P4HA1/P4HA1-uniprot.txt
    supporting_text: Catalyzes the post-translational formation of 4-
- description: Acts within the alpha2-beta2 collagen prolyl 4-hydroxylase (C-P4H) complex, in which two P4HA1 catalytic subunits associate with two P4HB (PDI) structural subunits that retain the soluble tetramer in the endoplasmic reticulum lumen.
  molecular_function:
    id: GO:0004656
    label: procollagen-proline 4-dioxygenase activity
  in_complex:
    id: GO:0016222
    label: procollagen-proline 4-dioxygenase complex
  supported_by:
  - reference_id: file:human/P4HA1/P4HA1-uniprot.txt
    supporting_text: Heterotetramer of two alpha-1 chains and two beta chains
  - reference_id: PMID:9211872
    supporting_text: The vertebrate enzyme is an alpha2beta2 tetramer, the beta subunit of which is identical to protein disulfide-isomerase
proposed_new_terms:
- proposed_name: peptidyl-proline hydroxylation to 4-hydroxy-L-proline
  proposed_definition: The hydroxylation of peptidyl-proline to peptidyl-4-hydroxy-L-proline, the direct biological process catalyzed by P4HA1 (corresponds to the existing term GO:0018401).
  justification: The existing BP annotations (collagen fibril organization) are downstream/indirect. The direct biological process performed by P4HA1 is peptidyl-proline hydroxylation to 4-hydroxy-L-proline (GO:0018401), which would more precisely capture its core process role; consider adding an involved_in annotation to GO:0018401 or a collagen biosynthetic process term.
suggested_questions:
- question: To what extent are the three P4HA1 splice isoforms functionally distinct in substrate preference or tissue-specific collagen hydroxylation, given that the alternatively spliced exon lies within the catalytic region?
- question: Do the high-throughput protein binding interactions (HTT; paralog P4HA2 cross-links) reflect any genuine biology, or are they incidental captures unrelated to the C-P4H catalytic function?
suggested_experiments:
- description: Reconstitute the alpha2-beta2 C-P4H tetramer from purified recombinant P4HA1 and P4HB and measure 4-hydroxyproline formation on defined procollagen peptides as a function of Fe(2+), 2-oxoglutarate, O2 and ascorbate concentrations to quantify cofactor dependence.
- description: Isoform-resolved hydroxyproline mapping (mass spectrometry) of collagen produced by cells expressing individual P4HA1 splice isoforms to test for isoform-specific differences in hydroxylation site usage or efficiency.