id: P43251
gene_symbol: BTD
product_type: PROTEIN
status: INITIALIZED
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  Biotinidase (EC 3.5.1.12) is the enzyme responsible for recycling the water-soluble
  vitamin biotin. It hydrolyses biocytin (biotinyl-lysine) and short biotinyl-peptides
  that are released when the biotin-dependent holo-carboxylases are degraded, liberating
  free biotin so it can be reused for biotinylation of newly synthesized apo-carboxylases;
  it also cleaves protein-bound (dietary) biotin, making ingested biotin bioavailable.
  It is a secreted, N-glycosylated glycoprotein found in serum/plasma and other body
  fluids (e.g. colostrum), and belongs to the carbon-nitrogen hydrolase superfamily
  (BTD/VNN family) with a nitrilase-like catalytic triad. Loss of biotinidase activity
  causes biotinidase deficiency, an autosomal recessive, treatable, newborn-screened
  disorder (late-onset/juvenile multiple carboxylase deficiency) in which failure
  to recycle biotin depletes free biotin and secondarily impairs the four biotin-dependent
  carboxylases, producing organic aciduria with neurological, cutaneous, ophthalmological
  and auditory manifestations that are largely preventable with oral biotin supplementation.
alternative_products:
- name: '4'
  id: P43251-4
- name: '1'
  id: P43251-1
  sequence_note: VSP_062634
- name: '2'
  id: P43251-2
  sequence_note: VSP_062635
- name: '3'
  id: P43251-3
  sequence_note: VSP_062636
existing_annotations:
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: Biotinidase is a secreted enzyme; the phylogenetically inferred extracellular
      localization is correct and represents the canonical site of the serum/plasma
      form.
    action: ACCEPT
    reason: UniProt records the subcellular location as secreted/extracellular space,
      and biotinidase is a well-characterized serum glycoprotein. The IBA is consistent
      with the direct evidence and represents a core localization for the active enzyme.
    supported_by:
    - reference_id: file:human/BTD/BTD-uniprot.txt
      supporting_text: 'Secreted, extracellular space'
- term:
    id: GO:0006768
    label: biotin metabolic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: Biotinidase recycles biotin from biocytin and biotinyl-peptides, a central
      step in biotin metabolism/salvage. This is a core biological process for the
      gene.
    action: ACCEPT
    reason: The enzyme completes the biotin cycle by releasing free biotin from the
      degradation products of the biotin-dependent carboxylases, making biotin metabolic
      process the correct high-level BP. Supported by the enzymatic function and by
      the disease mechanism (loss of recycling causes secondary biotin deficiency).
    supported_by:
    - reference_id: file:human/BTD/BTD-uniprot.txt
      supporting_text: Catalytic release of biotin from biocytin, the product of
    - reference_id: Reactome:R-HSA-3076905
      supporting_text: As a result, Btn is again available to be used in the biotinylation
        of apo-carboxylases in the mitochondrion.
- term:
    id: GO:0047708
    label: biotinidase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: Biotinidase activity (biotin-amide amidohydrolase, EC 3.5.1.12) is the
      defining, core molecular function of BTD.
    action: ACCEPT
    reason: Direct biochemical characterization establishes hydrolysis of biocytin
      to biotin and lysine; the IBA correctly identifies the core molecular function
      and is at the right level of specificity.
    supported_by:
    - reference_id: file:human/BTD/BTD-uniprot.txt
      supporting_text: Reaction=biocytin + H2O = biotin + L-lysine
    - reference_id: Reactome:R-HSA-3076905
      supporting_text: Human biotinidase (BTD, EC 3.5.1.12) (Cole et al. 1994) catalyzes
        the hydrolysis of biocytin (BCTN, aka biotinyl-lysine), a product of biotin
        dependent carboxylase degradation, to biotin (Btn) and lysine.
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: Electronic mapping from the UniProt "Secreted, extracellular space" subcellular
      location; correct and consistent with the experimental and IBA evidence.
    action: ACCEPT
    reason: This IEA is derived from the curated UniProt subcellular location (SL-0112)
      and correctly places the secreted enzyme in the extracellular region. Redundant
      with the IBA/TAS/HDA extracellular annotations but not incorrect.
    supported_by:
    - reference_id: file:human/BTD/BTD-uniprot.txt
      supporting_text: 'Secreted, extracellular space'
- term:
    id: GO:0016811
    label: hydrolase activity, acting on carbon-nitrogen (but not peptide) bonds,
      in linear amides
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: A correct but broader parent of biotinidase activity, capturing the chemistry
      (hydrolysis of a non-peptide C-N bond in a linear amide, i.e. the biotin-amide
      bond).
    action: ACCEPT
    reason: Biotinidase hydrolyses the amide bond linking biotin to the epsilon-amino
      group of lysine (biocytin) or to ammonia (biotin amide), a non-peptide carbon-nitrogen
      bond in a linear amide, so this InterPro/ARBA-based mapping is chemically correct.
      It is more general than the specific GO:0047708 biotinidase activity term but
      is not wrong; retained as a broader IEA.
    supported_by:
    - reference_id: file:human/BTD/BTD-uniprot.txt
      supporting_text: Reaction=biotin amide + H2O = biotin + NH4(+)
- term:
    id: GO:0047708
    label: biotinidase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: Biotinidase activity assigned electronically via RHEA:13081 / EC 3.5.1.12;
      this is the correct core molecular function.
    action: ACCEPT
    reason: The EC/RHEA-based electronic mapping matches the experimentally established
      EC 3.5.1.12 activity of the enzyme. Redundant with the IBA and TAS biotinidase-activity
      annotations but correct.
    supported_by:
    - reference_id: file:human/BTD/BTD-uniprot.txt
      supporting_text: EC=3.5.1.12
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:28514442
  qualifier: enables
  review:
    summary: A single high-throughput affinity-purification/mass-spectrometry interaction
      (BioPlex 2.0; reported partner MYO1D, O94832). "Protein binding" is uninformative
      about biotinidase function.
    action: MARK_AS_OVER_ANNOTATED
    reason: This is a bare GO:0005515 "protein binding" term derived from a large-scale
      AP-MS interactome screen (IntAct) rather than a characterized functional interaction.
      Per curation guidelines, bare protein binding conveys no useful functional information;
      the single MYO1D co-purification has no established biological role in biotin
      recycling. Kept (not removed) as a low-value interaction record, but flagged
      as over-annotated.
    supported_by:
    - reference_id: PMID:28514442
      supporting_text: which uses robust affinity purification-mass spectrometry methodology
        to elucidate protein interaction networks and co-complexes nucleated by more
        than 25% of protein-coding genes from the human genome
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33961781
  qualifier: enables
  review:
    summary: A second high-throughput AP-MS interactome dataset (BioPlex 3.0; reported
      partner MYO1D, O94832) supporting the same uninformative "protein binding" term.
    action: MARK_AS_OVER_ANNOTATED
    reason: As with PMID:28514442, this is a bare protein-binding annotation from a
      proteome-scale AP-MS screen with no demonstrated functional relevance to biotinidase
      activity. Retained as a low-value interaction record but flagged as over-annotated
      per the guideline to avoid uninformative "protein binding" terms.
    supported_by:
    - reference_id: PMID:33961781
      supporting_text: Through affinity-purification mass spectrometry, we have created
        two proteome-scale, cell-line-specific interaction networks.
- term:
    id: GO:0006768
    label: biotin metabolic process
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-196780
  qualifier: involved_in
  review:
    summary: Reactome places biotinidase within biotin transport and metabolism (biotin
      salvage/recycling); a correct core biological process annotation.
    action: ACCEPT
    reason: The Reactome pathway "Biotin transport and metabolism" describes biotin
      uptake, conjugation to apoenzymes and salvage, of which biotinidase-mediated
      recycling is a key step. Consistent with the IBA biotin metabolic process annotation.
    supported_by:
    - reference_id: Reactome:R-HSA-196780
      supporting_text: Its uptake, intracellular translocation, covalent conjugation
        to apoenzymes, and salvage are described here.
- term:
    id: GO:0047708
    label: biotinidase activity
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-3076905
  qualifier: enables
  review:
    summary: Reactome-asserted biotinidase activity for the extracellular hydrolysis
      of biocytin; the core molecular function.
    action: ACCEPT
    reason: Reactome reaction "Extracellular BTD hydrolyses BCTN" documents the EC
      3.5.1.12 hydrolysis of biocytin to biotin and lysine, matching the core molecular
      function of the gene.
    supported_by:
    - reference_id: Reactome:R-HSA-3076905
      supporting_text: Human biotinidase (BTD, EC 3.5.1.12) (Cole et al. 1994) catalyzes
        the hydrolysis of biocytin (BCTN, aka biotinyl-lysine), a product of biotin
        dependent carboxylase degradation, to biotin (Btn) and lysine.
- term:
    id: GO:0047708
    label: biotinidase activity
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-3325540
  qualifier: enables
  review:
    summary: Biotinidase activity annotation from the Reactome "defective extracellular
      BTD" disease reaction; the term is the correct core molecular function (its
      loss is what defines the disease reaction).
    action: ACCEPT
    reason: This TAS derives from the Reactome disease reaction describing loss of
      extracellular biotinidase activity in BTD deficiency; the underlying molecular
      function it references (EC 3.5.1.12 biotinidase activity) is correct and core.
    supported_by:
    - reference_id: Reactome:R-HSA-3325540
      supporting_text: Human biotinidase (BTD, EC 3.5.1.12) (Cole et al. 1994) catalyzes
        the hydrolysis of biocytin (BCTN, aka biotinyl-lysine), a product of biotin
        dependent carboxylase degradation, to biotin (Btn) and lysine.
- term:
    id: GO:0047708
    label: biotinidase activity
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-4167509
  qualifier: enables
  review:
    summary: Biotinidase activity annotation from the Reactome "mitochondrial BTD hydrolyses
      BCTN" reaction; the molecular function is correct and core.
    action: ACCEPT
    reason: Reactome asserts a mitochondrial pool of biotinidase performing the same
      EC 3.5.1.12 hydrolysis. Whichever compartment, the molecular function (biotinidase
      activity) is correct and represents the core function.
    supported_by:
    - reference_id: Reactome:R-HSA-4167509
      supporting_text: Human biotinidase (BTD, EC 3.5.1.12) (Cole et al. 1994) catalyzes
        the hydrolysis of biocytin (BCTN, aka biotinyl-lysine), a product of biotin
        dependent carboxylase degradation, to biotin (Btn) and lysine.
- term:
    id: GO:0047708
    label: biotinidase activity
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-4225086
  qualifier: enables
  review:
    summary: Biotinidase activity annotation from the Reactome "defective mitochondrial
      BTD" disease reaction; the referenced molecular function is correct and core.
    action: ACCEPT
    reason: As with the other Reactome biotinidase-activity TAS entries, the molecular
      function referenced (EC 3.5.1.12) is correct. Redundant with the other biotinidase-activity
      annotations but not incorrect.
    supported_by:
    - reference_id: Reactome:R-HSA-4225086
      supporting_text: Human biotinidase (BTD, EC 3.5.1.12) (Cole et al. 1994) catalyzes
        the hydrolysis of biocytin (BCTN, aka biotinyl-lysine), a product of biotin
        dependent carboxylase degradation, to biotin (Btn) and lysine.
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-3325540
  qualifier: located_in
  review:
    summary: Reactome localizes the extracellular biotinidase reaction to the extracellular
      region; consistent with the secreted enzyme.
    action: ACCEPT
    reason: The secreted/extracellular localization is well supported by UniProt and
      by the biology of the serum enzyme; this Reactome TAS is correct and represents
      a core localization.
    supported_by:
    - reference_id: Reactome:R-HSA-3325540
      supporting_text: BTD is both secreted from various cells and localised in the
        mitochondria (Wolf & Jensen 2005).
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-4225086
  qualifier: located_in
  review:
    summary: Reactome asserts a mitochondrial pool of biotinidase. This localization
      is secondary and less well established than the dominant secreted/extracellular
      form.
    action: KEEP_AS_NON_CORE
    reason: The canonical and best-supported localization of biotinidase is secreted/extracellular
      (serum). Reactome cites Wolf & Jensen 2005 for a mitochondrial pool, but this
      is a minor, less-characterized localization relative to the serum enzyme; kept
      as a non-core localization rather than treated as a core site of action.
    supported_by:
    - reference_id: Reactome:R-HSA-4225086
      supporting_text: BTD is both secreted from various cells and localised in the
        mitochondria (Wolf & Jensen 2005).
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:23533145
  qualifier: located_in
  review:
    summary: Biotinidase was detected by shotgun proteomics in exosomes from expressed
      prostatic secretions in urine; consistent with a secreted protein but not a
      core localization.
    action: KEEP_AS_NON_CORE
    reason: This high-throughput proteomic detection in prostatic-secretion exosomes
      is consistent with biotinidase being a secreted protein that partitions into
      extracellular vesicles, but the exosome compartment is not a core functional
      site for the enzyme. Retained as a non-core localization.
    supported_by:
    - reference_id: PMID:23533145
      supporting_text: Using expressed prostatic secretions in urine (EPS-urine),
        exosome preparations were characterized by a shotgun proteomics procedure.
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: HDA
  original_reference_id: PMID:16502470
  qualifier: located_in
  review:
    summary: Biotinidase was identified among minor proteins of the aqueous phase of
      human colostrum by proteomics, consistent with its secreted extracellular localization.
    action: ACCEPT
    reason: Detection in the aqueous phase of colostrum (a secreted body fluid) by
      mass spectrometry supports the extracellular localization of the secreted enzyme.
      Consistent with the UniProt-curated secreted location.
    supported_by:
    - reference_id: PMID:16502470
      supporting_text: We have investigated the low abundance proteins in the aqueous
        phase of human colostrum
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-4167509
  qualifier: located_in
  review:
    summary: Reactome asserts a mitochondrial pool of biotinidase (mitochondrial matrix);
      secondary and less well established than the secreted form.
    action: KEEP_AS_NON_CORE
    reason: As with the other mitochondrial-matrix Reactome TAS, the dominant, best-supported
      localization is secreted/extracellular. The mitochondrial pool is a minor, less-characterized
      localization; kept as non-core.
    supported_by:
    - reference_id: Reactome:R-HSA-4167509
      supporting_text: BTD is both secreted from various cells and localised in the
        mitochondria (Wolf & Jensen 2005).
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-3076905
  qualifier: located_in
  review:
    summary: Reactome localizes the extracellular biotinidase reaction to the extracellular
      region; consistent with the secreted enzyme and a core localization.
    action: ACCEPT
    reason: Correct localization of the secreted serum enzyme, consistent with UniProt
      and the experimental proteomic detections in body fluids.
    supported_by:
    - reference_id: Reactome:R-HSA-3076905
      supporting_text: BTD is both secreted from various cells and localised in the
        mitochondria (Wolf & Jensen 2005).
- term:
    id: GO:0007417
    label: central nervous system development
  evidence_type: TAS
  original_reference_id: PMID:7550325
  qualifier: involved_in
  review:
    summary: A legacy ProtInc TAS linking BTD to central nervous system development.
      The cited paper describes a deficiency-causing mutation and the neurological
      symptoms of the disorder, not a direct developmental role of the enzyme.
    action: MARK_AS_OVER_ANNOTATED
    reason: Biotinidase is a metabolic (biotin-recycling) enzyme; it has no direct
      role in CNS development. The cited reference reports a mutational hotspot causing
      profound biotinidase deficiency and notes the disorder's neurological symptoms
      and the need for early treatment to prevent neurological damage. This is a downstream
      disease phenotype of biotin/carboxylase deficiency, not a developmental function
      of the gene product. Flagged as over-annotated (phenotype-to-process over-interpretation);
      not a core function.
    supported_by:
    - reference_id: PMID:7550325
      supporting_text: it is important that biotinidase deficiency is diagnosed early
        so that permanent neurological damage can be prevented.
core_functions:
- description: Recycling of the vitamin biotin by hydrolysis of biocytin and biotinyl-peptides,
    releasing free biotin for reuse in biotinylation of apo-carboxylases; occurs in
    the extracellular/serum compartment.
  supported_by:
  - reference_id: file:human/BTD/BTD-uniprot.txt
    supporting_text: Catalytic release of biotin from biocytin, the product of
  - reference_id: Reactome:R-HSA-3076905
    supporting_text: Human biotinidase (BTD, EC 3.5.1.12) (Cole et al. 1994) catalyzes
      the hydrolysis of biocytin (BCTN, aka biotinyl-lysine), a product of biotin dependent
      carboxylase degradation, to biotin (Btn) and lysine.
  molecular_function:
    id: GO:0047708
    label: biotinidase activity
  directly_involved_in:
  - id: GO:0006768
    label: biotin metabolic process
  locations:
  - id: GO:0005576
    label: extracellular region
references:
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: PAN-GO/GO_Central phylogenetic inference; correctly propagates biotinidase
      activity, biotin metabolic process and extracellular localization to BTD.
- 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: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Maps the curated UniProt "Secreted, extracellular space" location
      to GO:0005576; correct.
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: InterPro/ARBA/EC/RHEA-based automated mapping to biotinidase activity
      and the broader C-N hydrolase parent term; consistent with the experimentally
      established EC 3.5.1.12 function.
- id: PMID:16502470
  title: 'Human colostrum: identification of minor proteins in the aqueous phase by
    proteomics.'
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Proteomic survey of human colostrum; supports detection of the secreted
      enzyme in an extracellular body fluid (extracellular-region HDA). Not a functional
      study.
- id: PMID:23533145
  title: In-depth proteomic analyses of exosomes isolated from expressed prostatic
    secretions in urine.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: Shotgun proteomics of prostatic-secretion exosomes; supports the
      extracellular-exosome HDA localization for a secreted protein. Non-core.
- id: PMID:28514442
  title: Architecture of the human interactome defines protein communities and disease
    networks.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: BioPlex 2.0 proteome-scale AP-MS interactome; source of a bare "protein
      binding" IPI (MYO1D). Methodologically sound but functionally uninformative
      for BTD; flagged over-annotated.
- id: PMID:33961781
  title: Dual proteome-scale networks reveal cell-specific remodeling of the human
    interactome.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: BioPlex 3.0 AP-MS interactome; second source of the bare "protein
      binding" IPI (MYO1D). Same assessment as PMID:28514442.
- id: PMID:7550325
  title: Mutational hotspot in the human biotinidase gene causes profound biotinidase
    deficiency.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: MISCITED
    review_notes: Correctly identifies a common BTD mutation causing profound biotinidase
      deficiency and the biotin-recycling function, but does NOT support a "central
      nervous system development" (GO:0007417) role; that annotation over-interprets
      the disorder's neurological phenotype. Relevant to BTD function/disease overall.
- id: Reactome:R-HSA-196780
  title: Biotin transport and metabolism
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Reactome pathway covering biotin uptake, conjugation and salvage;
      supports biotin metabolic process.
- id: Reactome:R-HSA-3076905
  title: Extracellular BTD hydrolyses BCTN
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Reactome reaction documenting extracellular biotinidase-catalysed
      hydrolysis of biocytin; supports core MF (biotinidase activity), BP (biotin
      metabolic process) and extracellular localization.
- id: Reactome:R-HSA-3325540
  title: Defective extracellular BTD does not hydrolyse BCTN
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Reactome disease reaction (loss of extracellular biotinidase activity
      in BTD deficiency); the referenced molecular function and localization are correct.
- id: Reactome:R-HSA-4167509
  title: Mitochondrial BTD hydrolyses BCTN
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Reactome reaction asserting a mitochondrial pool of biotinidase performing
      the same hydrolysis; molecular function correct, mitochondrial localization
      secondary/less established.
- id: Reactome:R-HSA-4225086
  title: Defective mitochondrial BTD does not hydrolyse BCTN
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Reactome disease reaction for the mitochondrial pool; molecular function
      correct, mitochondrial localization secondary.
- id: file:human/BTD/BTD-uniprot.txt
  title: UniProtKB entry P43251 (BTD_HUMAN)
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Curated UniProt record; source for catalytic activity (EC 3.5.1.12;
      biocytin and biotin-amide hydrolysis), secreted localization, glycosylation,
      domain/active-site architecture and disease association.