ABHD2

id: P08910
gene_symbol: ABHD2
product_type: PROTEIN
status: DRAFT
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  ABHD2 (Abhydrolase domain-containing protein 2) is an integral membrane serine hydrolase
  belonging to the alpha/beta hydrolase superfamily. It functions as a monoacylglycerol lipase
  that hydrolyzes 2-arachidonoylglycerol (2-AG) and 1-arachidonoylglycerol (1-AG) to glycerol
  and arachidonic acid, as well as displaying triacylglycerol lipase and ester hydrolase
  activities against short- and long-chain ester substrates. The catalytic triad consists of
  Ser207, Asp345, and His376. ABHD2 is anchored to membranes via an N-terminal transmembrane
  domain (type II orientation). In human sperm, ABHD2 localizes to the flagellum and plasma
  membrane where it plays a key role in sperm capacitation: progesterone activates ABHD2 lipase
  activity, leading to depletion of the endocannabinoid 2-AG from the membrane, which relieves
  2-AG-mediated inhibition of the CatSper calcium channel and permits calcium influx required
  for sperm activation. However, whether progesterone directly binds ABHD2 or acts through an
  indirect mechanism remains debated. In somatic cells, ABHD2 has been localized to the
  endoplasmic reticulum where it may regulate calcium release. Mouse knockout studies also
  implicate ABHD2 in hepatic phospholipid and cardiolipin metabolism.

existing_annotations:
- term:
    id: GO:0043401
    label: steroid hormone receptor signaling pathway
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation for involvement in steroid hormone receptor signaling pathway. ABHD2 is
      proposed to mediate non-genomic progesterone signaling in sperm, where progesterone
      activates ABHD2 lipase activity to regulate CatSper channel opening [PMID:26989199].
      This is a non-genomic steroid signaling pathway rather than a classical nuclear receptor
      pathway.
    action: ACCEPT
    reason: >-
      ABHD2 functions in a progesterone-dependent signaling cascade in sperm. The IBA annotation
      at the level of "steroid hormone receptor signaling pathway" is appropriate as it captures
      the progesterone-responsive role without being overly specific about the mechanism (which
      remains debated).
    supported_by:
    - reference_id: PMID:26989199
      supporting_text: >-
        ABHD2 is highly expressed in spermatozoa, binds progesterone, and acts as a
        progesterone-dependent lipid hydrolase by depleting the endocannabinoid
        2-arachidonoylglycerol (2AG) from plasma membrane
    - reference_id: file:human/ABHD2/ABHD2-deep-research-falcon.md
      supporting_text: >-
        ABHD2 is proposed to function as (or within) this membrane progesterone-sensing
        machinery by hydrolyzing 2-AG

- term:
    id: GO:0008126
    label: acetylesterase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation for acetylesterase activity. Recombinant ABHD2 was shown to hydrolyze
      p-nitrophenyl acetate with Km of 12.40 mM [PMID:27247428], directly demonstrating
      acetylesterase activity.
    action: ACCEPT
    reason: >-
      Acetylesterase activity is experimentally validated for ABHD2 by direct enzymatic assay
      with pNP acetate substrate. The IBA annotation is consistent with the experimental data
      from PMID:27247428.
    supported_by:
    - reference_id: PMID:27247428
      supporting_text: >-
        ABHD2 cleaved, pNPA with a Km of 12.40±1.02 mM, Vmax of 2.69±0.15 μmol/s·mg

- term:
    id: GO:0047372
    label: monoacylglycerol lipase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation for monoacylglycerol lipase activity. This is the best-characterized core
      enzymatic function of ABHD2. Miller et al. (2016) demonstrated that ABHD2 hydrolyzes
      2-arachidonoylglycerol and 1-arachidonoylglycerol, producing glycerol and arachidonic
      acid [PMID:26989199].
    action: ACCEPT
    reason: >-
      Monoacylglycerol lipase activity is the primary physiologically relevant enzymatic
      function of ABHD2. The hydrolysis of 2-AG by ABHD2 is central to its role in sperm
      activation and CatSper channel regulation.
    supported_by:
    - reference_id: PMID:26989199
      supporting_text: >-
        acts as a progesterone-dependent lipid hydrolase by depleting the endocannabinoid
        2-arachidonoylglycerol (2AG) from plasma membrane

- term:
    id: GO:0036126
    label: sperm flagellum
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation for localization to sperm flagellum. Immunostaining in the Miller et al.
      (2016) study showed ABHD2 localized to the human sperm flagellum [PMID:26989199],
      consistent with proximity to the flagellar CatSper channel.
    action: ACCEPT
    reason: >-
      Sperm flagellum localization is directly supported by immunostaining data and is
      consistent with ABHD2's functional role in regulating the flagellar CatSper channel
      during sperm activation.
    supported_by:
    - reference_id: PMID:26989199
      supporting_text: >-
        ABHD2 is highly expressed in spermatozoa, binds progesterone, and acts as a
        progesterone-dependent lipid hydrolase
    - reference_id: file:human/ABHD2/ABHD2-deep-research-falcon.md
      supporting_text: >-
        Immunostaining shows ABHD2 localized to the human sperm flagellum, consistent with
        proximity to the flagellar CatSper channel

- term:
    id: GO:0046464
    label: acylglycerol catabolic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation for involvement in acylglycerol catabolic process. ABHD2 hydrolyzes
      2-arachidonoylglycerol and triacylglycerols [PMID:26989199, PMID:27247428], directly
      contributing to acylglycerol catabolism.
    action: ACCEPT
    reason: >-
      ABHD2 catalyzes the hydrolysis of both monoacylglycerols (2-AG) and triacylglycerols,
      making acylglycerol catabolic process an appropriate biological process annotation
      that accurately reflects the enzyme's function.
    supported_by:
    - reference_id: PMID:26989199
      supporting_text: >-
        acts as a progesterone-dependent lipid hydrolase by depleting the endocannabinoid
        2-arachidonoylglycerol (2AG) from plasma membrane
    - reference_id: PMID:27247428
      supporting_text: >-
        His-tag purified protein showed TAG lipase activity

- term:
    id: GO:0048240
    label: sperm capacitation
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation for involvement in sperm capacitation. The Miller et al. (2016) study
      demonstrated that ABHD2-mediated depletion of 2-AG in response to progesterone leads to
      CatSper activation and calcium influx required for sperm activation [PMID:26989199].
    action: ACCEPT
    reason: >-
      Sperm capacitation is the primary biological context in which ABHD2 function has been
      characterized. The progesterone-ABHD2-2AG-CatSper axis is the dominant functional model
      for ABHD2 in reproductive biology.
    supported_by:
    - reference_id: PMID:26989199
      supporting_text: >-
        its removal leads to calcium influx via CatSper and ensures sperm activation

- term:
    id: GO:0051792
    label: medium-chain fatty acid biosynthetic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation for involvement in medium-chain fatty acid biosynthetic process. This
      annotation appears to be derived from phylogenetic inference based on yeast orthologs
      (SGD references in the WITH/FROM column). While ABHD2 does have ester hydrolase activity
      against medium-chain substrates like pNP butyrate [PMID:27247428], the primary substrates
      of ABHD2 are long-chain arachidonoylglycerols and triacylglycerols, not medium-chain
      fatty acids.
    action: KEEP_AS_NON_CORE
    reason: >-
      The annotation is based on phylogenetic inference from yeast orthologs. While ABHD2 can
      hydrolyze medium-chain ester substrates in vitro, its primary physiological substrates
      are long-chain acylglycerols (2-AG, TAG). Medium-chain fatty acid biosynthesis is not a
      well-established function of ABHD2 in human cells.
    supported_by:
    - reference_id: PMID:27247428
      supporting_text: >-
        ABHD2 cleaved, pNPA with a Km of 12.40±1.02 mM, Vmax of 2.69±0.15 μmol/s·mg and
        kcat/Km of 11.23±1.22 M−1·s−1, pNPB with a Km of 11.76±1.15 mM

- term:
    id: GO:0051793
    label: medium-chain fatty acid catabolic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation for involvement in medium-chain fatty acid catabolic process. Similar to
      the biosynthetic process annotation, this is derived from phylogenetic inference via yeast
      orthologs. ABHD2 can cleave medium-chain ester substrates in vitro but its primary
      physiological role involves long-chain arachidonoylglycerol hydrolysis.
    action: KEEP_AS_NON_CORE
    reason: >-
      Same rationale as for GO:0051792 above. The in vitro activity against medium-chain
      substrates is documented but the primary physiological function of ABHD2 involves
      long-chain substrates. This is not a core function.
    supported_by:
    - reference_id: PMID:27247428
      supporting_text: >-
        the present study highlights the TAG lipase activity of ABHD2 along with both long
        and short chain esterase activities against pNP palmitate, butyrate and acetate
        substrates respectively

- term:
    id: GO:0097524
    label: sperm plasma membrane
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation for localization to sperm plasma membrane. ABHD2 is a type II membrane
      protein with an N-terminal transmembrane anchor, and has been localized to the sperm
      flagellum membrane by immunostaining [PMID:26989199]. UniProt annotates it as a
      single-pass type II membrane protein in the cell/flagellum membrane.
    action: ACCEPT
    reason: >-
      Sperm plasma membrane localization is consistent with ABHD2's predicted type II membrane
      topology and its functional role in hydrolyzing membrane-associated 2-AG at the sperm
      surface.
    supported_by:
    - reference_id: PMID:26989199
      supporting_text: >-
        ABHD2 is highly expressed in spermatozoa, binds progesterone, and acts as a
        progesterone-dependent lipid hydrolase by depleting the endocannabinoid
        2-arachidonoylglycerol (2AG) from plasma membrane

- term:
    id: GO:0030518
    label: nuclear receptor-mediated steroid hormone signaling pathway
  evidence_type: IEA
  original_reference_id: GO_REF:0000108
  review:
    summary: >-
      IEA annotation inferred from the IDA annotation of GO:0003707 (nuclear steroid receptor
      activity) via logical inter-ontology link. This is problematic because ABHD2 does not
      function as a nuclear steroid receptor. It is a membrane-bound lipase that responds to
      progesterone via a non-genomic mechanism. The nuclear receptor annotation (GO:0003707)
      from which this was derived is itself questionable.
    action: REMOVE
    reason: >-
      ABHD2 mediates non-genomic progesterone signaling at the cell membrane, not nuclear
      receptor-mediated signaling. It is a serine hydrolase/lipase, not a nuclear receptor.
      This IEA annotation was propagated from an incorrect IDA annotation of nuclear steroid
      receptor activity. The parent GO:0043401 (steroid hormone receptor signaling pathway)
      annotation is more appropriate.
    supported_by:
    - reference_id: PMID:26989199
      supporting_text: >-
        acts as a progesterone-dependent lipid hydrolase by depleting the endocannabinoid
        2-arachidonoylglycerol (2AG) from plasma membrane
    - reference_id: file:human/ABHD2/ABHD2-deep-research-falcon.md
      supporting_text: >-
        ABHD2 is proposed to function as (or within) this membrane progesterone-sensing
        machinery by hydrolyzing 2-AG

- term:
    id: GO:0004806
    label: triacylglycerol lipase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000116
  review:
    summary: >-
      IEA annotation based on Rhea mapping from the UniProt catalytic activity annotation
      (EC 3.1.1.79). Kumar et al. (2016) directly demonstrated TAG lipase activity for
      recombinant ABHD2 with activity of 1.14 +/- 0.11 umol/s/mg [PMID:27247428].
    action: ACCEPT
    reason: >-
      Triacylglycerol lipase activity is experimentally validated for ABHD2 by direct enzymatic
      assay. The IEA mapping is correct and supported by primary experimental evidence.
    supported_by:
    - reference_id: PMID:27247428
      supporting_text: >-
        This affinity purified recombinant hABHD2 protein fraction showed TAG lipase activity
        of 1.14±0.11 μmol/s·mg of protein against controls

- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: >-
      IEA annotation based on UniProt subcellular location mapping. ABHD2 is annotated in
      UniProt as a cell membrane protein with a single-pass type II transmembrane domain.
      More specific sperm plasma membrane (GO:0097524) and sperm flagellum (GO:0036126)
      annotations exist.
    action: ACCEPT
    reason: >-
      Plasma membrane localization is correct for ABHD2, which is a type II single-pass
      membrane protein. This broader annotation is acceptable alongside the more specific
      sperm-related CC annotations, as ABHD2 is expressed in multiple tissues (not just
      sperm).
    supported_by:
    - reference_id: file:human/ABHD2/ABHD2-deep-research-falcon.md
      supporting_text: >-
        ABHD2 is an integral membrane serine hydrolase with an N-terminal transmembrane anchor

- term:
    id: GO:0006629
    label: lipid metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: >-
      IEA annotation based on UniProt keyword mapping (KW-0443 Lipid metabolism). ABHD2 is a
      lipase that hydrolyzes acylglycerols and triacylglycerols, so involvement in lipid
      metabolism is correct but very broad.
    action: ACCEPT
    reason: >-
      While this is a broad term, it is not incorrect. More specific annotations exist for
      acylglycerol catabolic process (GO:0046464). The broader annotation is acceptable as
      it captures the general functional category.

- term:
    id: GO:0008126
    label: acetylesterase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: >-
      IEA annotation for acetylesterase activity via combined automated methods (Rhea/EC
      mapping). This is a duplicate of the IBA and IDA annotations for the same term and is
      experimentally supported by PMID:27247428.
    action: ACCEPT
    reason: >-
      Consistent with both the IBA annotation and the direct experimental evidence from
      PMID:27247428 showing ABHD2 cleaves pNP acetate.
    supported_by:
    - reference_id: PMID:27247428
      supporting_text: >-
        ABHD2 cleaved, pNPA with a Km of 12.40±1.02 mM, Vmax of 2.69±0.15 μmol/s·mg

- term:
    id: GO:0016042
    label: lipid catabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: >-
      IEA annotation based on UniProt keyword mapping (KW-0442 Lipid degradation). ABHD2
      catalyzes the hydrolytic degradation of acylglycerols and triacylglycerols, which is
      lipid catabolism.
    action: ACCEPT
    reason: >-
      Lipid catabolic process is correct and consistent with ABHD2's enzymatic function as a
      lipase. The more specific term acylglycerol catabolic process (GO:0046464) is also
      annotated. This broader annotation is acceptable.

- term:
    id: GO:0016787
    label: hydrolase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: >-
      IEA annotation based on UniProt keyword mapping (KW-0378 Hydrolase). ABHD2 is an
      alpha/beta hydrolase with demonstrated lipase and esterase activities.
    action: ACCEPT
    reason: >-
      Hydrolase activity is correct but very broad. More specific MF annotations exist
      (monoacylglycerol lipase activity, acetylesterase activity, triacylglycerol lipase
      activity). This broad parent annotation is acceptable as it is not incorrect.

- term:
    id: GO:0047372
    label: monoacylglycerol lipase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000003
  review:
    summary: >-
      IEA annotation based on EC number mapping (EC:3.1.1.23). This is a duplicate of the IBA
      and IDA annotations and is the core enzymatic function of ABHD2.
    action: ACCEPT
    reason: >-
      Consistent with both IBA and IDA annotations and directly supported by experimental
      evidence showing ABHD2 hydrolyzes 2-arachidonoylglycerol.
    supported_by:
    - reference_id: PMID:26989199
      supporting_text: >-
        acts as a progesterone-dependent lipid hydrolase by depleting the endocannabinoid
        2-arachidonoylglycerol (2AG) from plasma membrane

- term:
    id: GO:0052689
    label: carboxylic ester hydrolase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: >-
      IEA annotation based on UniProt keyword mapping (KW-0719 Serine esterase). ABHD2
      hydrolyzes carboxylic esters including pNP acetate, butyrate, and palmitate
      [PMID:27247428].
    action: ACCEPT
    reason: >-
      Carboxylic ester hydrolase activity is correct and consistent with ABHD2's demonstrated
      esterase activities. This is a broader parent of acetylesterase activity and is acceptable.
    supported_by:
    - reference_id: PMID:27247428
      supporting_text: >-
        the present study highlights the TAG lipase activity of ABHD2 along with both long
        and short chain esterase activities against pNP palmitate, butyrate and acetate
        substrates respectively

- term:
    id: GO:0001669
    label: acrosomal vesicle
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation transferred from mouse ortholog (UniProtKB:Q9QXM0) via Ensembl Compara.
      Acrosomal localization has been reported for mouse ABHD2 but direct evidence for human
      ABHD2 acrosomal localization is limited. The primary human localization data shows
      flagellar and plasma membrane localization [PMID:26989199].
    action: KEEP_AS_NON_CORE
    reason: >-
      This annotation is based on ortholog transfer from mouse. While plausible given the
      sperm context, the direct experimental evidence in human shows flagellar/plasma membrane
      localization rather than specific acrosomal localization. Keeping as non-core since
      it may reflect a species difference or additional localization not yet confirmed in human.

- term:
    id: GO:0007340
    label: acrosome reaction
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation transferred from mouse ortholog via Ensembl Compara. While ABHD2 is
      involved in sperm capacitation which precedes the acrosome reaction, direct involvement
      of ABHD2 in the acrosome reaction itself has not been specifically demonstrated in human.
    action: KEEP_AS_NON_CORE
    reason: >-
      The annotation is based on ortholog transfer from mouse. ABHD2 is involved in sperm
      capacitation and calcium signaling through CatSper, which can influence the acrosome
      reaction. However, the direct role in acrosome reaction is not well established for
      human ABHD2 specifically, so this is kept as non-core.

- term:
    id: GO:0008126
    label: acetylesterase activity
  evidence_type: IDA
  original_reference_id: PMID:27247428
  review:
    summary: >-
      IDA annotation based on direct enzymatic assay. Kumar et al. (2016) demonstrated that
      purified recombinant ABHD2 cleaves p-nitrophenyl acetate with Km 12.40 mM and Vmax
      2.69 umol/s/mg [PMID:27247428].
    action: ACCEPT
    reason: >-
      Directly supported by enzymatic kinetics data from recombinant ABHD2 protein assayed
      with pNP acetate substrate. The evidence is clear and well-quantified.
    supported_by:
    - reference_id: PMID:27247428
      supporting_text: >-
        ABHD2 cleaved, pNPA with a Km of 12.40±1.02 mM, Vmax of 2.69±0.15 μmol/s·mg and
        kcat/Km of 11.23±1.22 M−1·s−1

- term:
    id: GO:0120516
    label: diacylglycerol lipase activity
  evidence_type: IDA
  original_reference_id: PMID:27247428
  review:
    summary: >-
      IDA annotation for diacylglycerol lipase activity based on PMID:27247428. However,
      the Kumar et al. (2016) study demonstrated TAG lipase and ester hydrolase activities
      but did not specifically test diacylglycerol as a substrate. The TAG lipase assay
      measures hydrolysis of triacylglycerol to diacylglycerol (which would be an intermediate),
      but the primary activity demonstrated was TAG lipase activity.
    action: UNDECIDED
    reason: >-
      The PMID:27247428 study demonstrated TAG lipase activity (hydrolysis of triacylglycerol)
      and ester hydrolase activity against pNP substrates. Diacylglycerol lipase activity was
      not specifically assayed. TAG lipase activity could produce DAG as an intermediate, but
      this does not constitute direct evidence for DAG lipase activity. The annotation may be
      an over-interpretation of the TAG lipase data. Further evidence would be needed to
      confirm this specific activity.
    supported_by:
    - reference_id: PMID:27247428
      supporting_text: >-
        This affinity purified recombinant hABHD2 protein fraction showed TAG lipase activity
        of 1.14±0.11 μmol/s·mg of protein against controls

- term:
    id: GO:0003707
    label: nuclear steroid receptor activity
  evidence_type: IDA
  original_reference_id: PMID:26989199
  review:
    summary: >-
      IDA annotation for nuclear steroid receptor activity based on the Miller et al. (2016)
      study. This is a problematic annotation. ABHD2 is not a nuclear receptor. It is a
      membrane-bound serine hydrolase that responds to progesterone, but it does so via a
      non-genomic mechanism at the plasma membrane, not through nuclear receptor-mediated
      transcription. The term "nuclear steroid receptor activity" implies nuclear localization
      and transcriptional regulation, which does not apply to ABHD2.
    action: REMOVE
    reason: >-
      ABHD2 is a membrane-anchored serine hydrolase that mediates non-genomic progesterone
      signaling. It is not a nuclear receptor and does not function in transcriptional
      regulation. The Miller et al. (2016) paper describes ABHD2 as a non-genomic progesterone
      receptor on sperm, explicitly contrasting it with nuclear receptor mechanisms. Recent
      work also questions whether progesterone directly binds ABHD2. This annotation is
      incorrect and should be removed. The response to progesterone (GO:0032570) and steroid
      hormone receptor signaling pathway (GO:0043401) annotations better capture the
      progesterone-responsive function.
    supported_by:
    - reference_id: PMID:26989199
      supporting_text: >-
        Steroids regulate cell proliferation, tissue development, and cell signaling via
        two pathways: a nuclear receptor mechanism and genome-independent signaling. Sperm
        activation, egg maturation, and steroid-induced anesthesia are executed via the latter
        pathway
    - reference_id: file:human/ABHD2/ABHD2-deep-research-falcon.md
      supporting_text: >-
        more recent biochemical/cell-based work indicates progesterone may not directly bind
        ABHD2

- term:
    id: GO:0032570
    label: response to progesterone
  evidence_type: IDA
  original_reference_id: PMID:26989199
  review:
    summary: >-
      IDA annotation for involvement in response to progesterone. Miller et al. (2016)
      demonstrated that progesterone activates ABHD2 lipase activity, leading to 2-AG
      depletion and CatSper activation in sperm [PMID:26989199]. UniProt describes ABHD2
      as a "progesterone-sensitive lipase."
    action: ACCEPT
    reason: >-
      Response to progesterone is a well-supported annotation. The Miller et al. (2016) study
      demonstrated progesterone-dependent activation of ABHD2 lipase activity and downstream
      effects on CatSper channel regulation in sperm. Whether progesterone acts directly on
      ABHD2 or through an intermediary, the biological response to progesterone is clear.
    supported_by:
    - reference_id: PMID:26989199
      supporting_text: >-
        acts as a progesterone-dependent lipid hydrolase by depleting the endocannabinoid
        2-arachidonoylglycerol (2AG) from plasma membrane

- term:
    id: GO:0036126
    label: sperm flagellum
  evidence_type: IDA
  original_reference_id: PMID:26989199
  review:
    summary: >-
      IDA annotation for localization to sperm flagellum based on immunostaining data from
      Miller et al. (2016) [PMID:26989199]. This is directly supported by microscopy evidence.
    action: ACCEPT
    reason: >-
      Sperm flagellum localization is directly demonstrated by immunostaining in the Miller
      et al. (2016) study. This is consistent with ABHD2's functional role in regulating the
      flagellar CatSper calcium channel.
    supported_by:
    - reference_id: PMID:26989199
      supporting_text: >-
        ABHD2 is highly expressed in spermatozoa
    - reference_id: file:human/ABHD2/ABHD2-deep-research-falcon.md
      supporting_text: >-
        Immunostaining shows ABHD2 localized to the human sperm flagellum, consistent with
        proximity to the flagellar CatSper channel

- term:
    id: GO:0042562
    label: hormone binding
  evidence_type: IDA
  original_reference_id: PMID:26989199
  review:
    summary: >-
      IDA annotation for hormone binding based on Miller et al. (2016), which used a
      photoaffinity progesterone probe to identify ABHD2 as a progesterone-binding protein
      in sperm [PMID:26989199]. However, more recent work from Arnolds et al. (2025) did
      not find progesterone effect on purified ABHD2 activity and questions direct binding.
    action: UNDECIDED
    reason: >-
      The original Miller et al. (2016) study identified ABHD2 via a progesterone photoaffinity
      probe, suggesting direct binding. However, more recent work questions whether progesterone
      directly binds ABHD2 or acts through an indirect mechanism. The evidence is conflicting
      and the annotation may need to be revisited once the mechanism is clarified.
    supported_by:
    - reference_id: PMID:26989199
      supporting_text: >-
        ABHD2 is highly expressed in spermatozoa, binds progesterone
    - reference_id: file:human/ABHD2/ABHD2-deep-research-falcon.md
      supporting_text: >-
        more recent biochemical/cell-based work indicates progesterone may not directly bind
        ABHD2 and that ABHD2 inhibition may not block progesterone-induced Ca2+ influx

- term:
    id: GO:0043401
    label: steroid hormone receptor signaling pathway
  evidence_type: IDA
  original_reference_id: PMID:26989199
  review:
    summary: >-
      IDA annotation for involvement in steroid hormone receptor signaling pathway from
      Miller et al. (2016). ABHD2 mediates progesterone-dependent signaling in sperm by
      hydrolyzing 2-AG to relieve CatSper inhibition [PMID:26989199].
    action: ACCEPT
    reason: >-
      ABHD2 functions in a progesterone-responsive signaling pathway in sperm. The term
      "steroid hormone receptor signaling pathway" is appropriate at this level of specificity,
      as it captures the non-genomic progesterone response without incorrectly implying a
      nuclear receptor mechanism.
    supported_by:
    - reference_id: PMID:26989199
      supporting_text: >-
        Unconventional endocannabinoid signaling governs sperm activation via the sex hormone
        progesterone

- term:
    id: GO:0046464
    label: acylglycerol catabolic process
  evidence_type: IDA
  original_reference_id: PMID:26989199
  review:
    summary: >-
      IDA annotation for involvement in acylglycerol catabolic process based on Miller et al.
      (2016). The study demonstrated that ABHD2 hydrolyzes 2-arachidonoylglycerol to glycerol
      and arachidonic acid [PMID:26989199].
    action: ACCEPT
    reason: >-
      Directly supported by experimental evidence showing ABHD2 catalyzes the hydrolysis
      (catabolism) of the acylglycerol 2-AG. This is a core biological process for ABHD2.
    supported_by:
    - reference_id: PMID:26989199
      supporting_text: >-
        acts as a progesterone-dependent lipid hydrolase by depleting the endocannabinoid
        2-arachidonoylglycerol (2AG) from plasma membrane

- term:
    id: GO:0047372
    label: monoacylglycerol lipase activity
  evidence_type: IDA
  original_reference_id: PMID:26989199
  review:
    summary: >-
      IDA annotation for monoacylglycerol lipase activity from Miller et al. (2016). The study
      demonstrated that recombinant ABHD2 hydrolyzes 2-arachidonoylglycerol (a monoacylglycerol)
      in a progesterone-enhanced manner [PMID:26989199].
    action: ACCEPT
    reason: >-
      This is the core enzymatic function of ABHD2, directly demonstrated by the Miller et al.
      (2016) study showing hydrolysis of 2-AG to glycerol and arachidonic acid.
    supported_by:
    - reference_id: PMID:26989199
      supporting_text: >-
        acts as a progesterone-dependent lipid hydrolase by depleting the endocannabinoid
        2-arachidonoylglycerol (2AG) from plasma membrane

- term:
    id: GO:0048240
    label: sperm capacitation
  evidence_type: IDA
  original_reference_id: PMID:26989199
  review:
    summary: >-
      IDA annotation for involvement in sperm capacitation based on Miller et al. (2016). The
      study demonstrated that ABHD2-mediated 2-AG depletion leads to CatSper activation,
      calcium influx, and sperm activation [PMID:26989199].
    action: ACCEPT
    reason: >-
      Sperm capacitation is a core biological process for ABHD2. The progesterone-ABHD2-2AG-
      CatSper axis is a well-characterized pathway leading to sperm activation. The IDA
      evidence is based on electrophysiology, lipidomics, and antibody/inhibitor perturbation
      experiments.
    supported_by:
    - reference_id: PMID:26989199
      supporting_text: >-
        its removal leads to calcium influx via CatSper and ensures sperm activation

- term:
    id: GO:0097524
    label: sperm plasma membrane
  evidence_type: IDA
  original_reference_id: PMID:26989199
  review:
    summary: >-
      IDA annotation for localization to sperm plasma membrane based on Miller et al. (2016).
      ABHD2 is a type II membrane protein localized to the sperm flagellum membrane where it
      hydrolyzes 2-AG at the membrane surface [PMID:26989199].
    action: ACCEPT
    reason: >-
      Sperm plasma membrane localization is directly supported by immunostaining data and
      is consistent with ABHD2's function as a membrane-bound lipase acting on plasma
      membrane-associated 2-AG.
    supported_by:
    - reference_id: PMID:26989199
      supporting_text: >-
        ABHD2 is highly expressed in spermatozoa, binds progesterone, and acts as a
        progesterone-dependent lipid hydrolase by depleting the endocannabinoid
        2-arachidonoylglycerol (2AG) from plasma membrane

- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: IDA
  original_reference_id: PMID:28684316
  review:
    summary: >-
      ABHD2 has been experimentally localized to the endoplasmic reticulum membrane in
      somatic cells (fibroblast-like cells), where ABHD2 knockdown attenuated ER calcium
      release and downstream mitochondrial calcium uptake. This represents a distinct
      localization from the sperm flagellum/plasma membrane context.
    action: NEW
    reason: >-
      Yun et al. (2017) [PMID:28684316] demonstrated ER membrane localization of ABHD2 in
      somatic cells using localization experiments. This represents an additional subcellular
      compartment where ABHD2 functions, beyond the sperm flagellum. This annotation is not
      currently in the GOA set but is supported by experimental evidence.
    supported_by:
    - reference_id: file:human/ABHD2/ABHD2-deep-research-falcon.md
      supporting_text: >-
        ABHD2 has been experimentally localized to the endoplasmic reticulum (ER) membrane
        (in fibroblast-like cells), where ABHD2 knockdown attenuated ER Ca2+ release and
        downstream mitochondrial Ca2+ uptake/cell death

references:
- id: PMID:26989199
  title: Unconventional endocannabinoid signaling governs sperm activation via the sex
    hormone progesterone.
  findings:
  - statement: >-
      ABHD2 acts as a progesterone-dependent monoacylglycerol lipase that depletes 2-AG
      from sperm plasma membrane, relieving CatSper inhibition and enabling calcium influx
      for sperm activation.
    supporting_text: >-
      ABHD2 is highly expressed in spermatozoa, binds progesterone, and acts as a
      progesterone-dependent lipid hydrolase by depleting the endocannabinoid
      2-arachidonoylglycerol (2AG) from plasma membrane
  - statement: >-
      ABHD2 localizes to the human sperm flagellum and plasma membrane.
    supporting_text: >-
      ABHD2 is highly expressed in spermatozoa
  - statement: >-
      2-AG inhibits CatSper with IC50 of approximately 350 nM; removal of 2-AG by ABHD2
      enables calcium influx.
    supporting_text: >-
      The 2AG inhibits the sperm calcium channel (CatSper), and its removal leads to calcium
      influx via CatSper and ensures sperm activation
- id: PMID:27247428
  title: Molecular characterization of human ABHD2 as TAG lipase and ester hydrolase.
  findings:
  - statement: >-
      Recombinant ABHD2 has TAG lipase activity (1.14 +/- 0.11 umol/s/mg) and ester
      hydrolase activity against pNP acetate, butyrate, and palmitate substrates.
    supporting_text: >-
      This affinity purified recombinant hABHD2 protein fraction showed TAG lipase activity
      of 1.14±0.11 μmol/s·mg of protein against controls
  - statement: >-
      The catalytic triad of ABHD2 consists of Ser207, Asp345, His376 with Ser207 in the
      conserved GXSXG motif as the catalytic nucleophile.
    supporting_text: >-
      Sequence analysis of ABHD2 revealed the presence of conserved motifs G(205)XS(207)XG(209)
- id: PMID:28684316
  title: Regulation of calcium release from the endoplasmic reticulum by the serine
    hydrolase ABHD2.
  findings:
  - statement: >-
      ABHD2 localizes to the ER membrane in somatic cells and regulates calcium release.
    supporting_text: >-
      pyrrophenone and KT195 inhibit cell death induced by A23187 and H2O2 by blocking
      the release of calcium from the endoplasmic reticulum and mitochondrial calcium uptake
- id: GO_REF:0000003
  title: Gene Ontology annotation based on Enzyme Commission mapping
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000043
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
  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:0000107
  title: Automatic transfer of experimentally verified manual GO annotation data to
    orthologs using Ensembl Compara
  findings: []
- id: GO_REF:0000108
  title: Automatic assignment of GO terms using logical inference, based on on inter-ontology
    links
  findings: []
- id: GO_REF:0000116
  title: Automatic Gene Ontology annotation based on Rhea mapping
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []

core_functions:
- description: >-
    Monoacylglycerol lipase that hydrolyzes 2-arachidonoylglycerol (2-AG) at the sperm
    plasma membrane in response to progesterone, relieving 2-AG-mediated inhibition of the
    CatSper calcium channel and enabling calcium influx required for sperm capacitation and
    activation. This is the primary characterized function of ABHD2.
  molecular_function:
    id: GO:0047372
    label: monoacylglycerol lipase activity
  directly_involved_in:
  - id: GO:0048240
    label: sperm capacitation
  - id: GO:0046464
    label: acylglycerol catabolic process
  - id: GO:0032570
    label: response to progesterone
  locations:
  - id: GO:0036126
    label: sperm flagellum
  - id: GO:0097524
    label: sperm plasma membrane
  supported_by:
  - reference_id: PMID:26989199
    supporting_text: >-
      ABHD2 is highly expressed in spermatozoa, binds progesterone, and acts as a
      progesterone-dependent lipid hydrolase by depleting the endocannabinoid
      2-arachidonoylglycerol (2AG) from plasma membrane

- description: >-
    Broad ester hydrolase and triacylglycerol lipase activity. ABHD2 hydrolyzes
    triacylglycerols (TAG lipase activity) and p-nitrophenyl esters of varying chain
    lengths (acetate, butyrate, palmitate), reflecting the broad substrate tolerance
    typical of alpha/beta hydrolase family members.
  molecular_function:
    id: GO:0004806
    label: triacylglycerol lipase activity
  directly_involved_in:
  - id: GO:0046464
    label: acylglycerol catabolic process
  locations:
  - id: GO:0005886
    label: plasma membrane
  supported_by:
  - reference_id: PMID:27247428
    supporting_text: >-
      the present study highlights the TAG lipase activity of ABHD2 along with both long
      and short chain esterase activities against pNP palmitate, butyrate and acetate
      substrates respectively

suggested_questions:
- question: >-
    Does progesterone directly bind ABHD2, or does it act through an intermediary mechanism
    to activate ABHD2 lipase activity? Recent work (Arnolds et al. 2025) questions the
    direct binding model proposed by Miller et al. (2016).
  experts:
  - Polina V. Lishko
  - Opher Gileadi
- question: >-
    What are the physiological substrates of ABHD2 in non-sperm tissues, particularly in
    the liver where Abhd2 knockout mice show altered phospholipid and cardiolipin composition?
  experts:
  - Alan D. Attie
  - Christina C. Leslie

suggested_experiments:
- hypothesis: >-
    ABHD2 directly binds progesterone via a specific binding site on its extracellular domain.
  description: >-
    Use purified recombinant ABHD2 with biophysical binding assays (SPR, ITC, or thermal
    shift assays) to determine whether progesterone directly binds ABHD2 with physiologically
    relevant affinity. Include catalytically dead S207A mutant to distinguish binding from
    catalysis.
- hypothesis: >-
    ABHD2 has phospholipase activity against phosphatidylcholine and/or cardiolipin substrates.
  description: >-
    Test purified ABHD2 against phosphatidylcholine and cardiolipin substrates in vitro to
    determine whether ABHD2 has direct phospholipase activity, as suggested by the mouse
    knockout lipidomic data from Price et al. (2023).