PLD4 is a multifunctional transmembrane enzyme that, despite its misleading name, lacks phospholipase D activity and instead functions as a 5'-3' exonuclease and transphosphatidylase. The protein degrades single-stranded DNA and RNA in endolysosomes to prevent inappropriate activation of TLR9 by self-derived mitochondrial DNA while enabling TLR7 activation by processing viral RNA. Additionally, PLD4 synthesizes bis(monoacylglycero)phosphate (BMP), a critical lipid component of lysosomal intralumenal vesicles essential for lipid degradation and autophagy. Predominantly localized to the ER membrane with dynamic trafficking to Golgi and endolysosomes, PLD4 plays crucial roles in immune regulation, preventing autoimmune responses, and maintaining endolysosomal homeostasis. In microglia, it participates in phagocytosis with characteristic redistribution from nucleus to phagosomes upon activation.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0012505
endomembrane system
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: PLD4 is indeed localized to the endomembrane system, particularly the ER membrane and Golgi apparatus as confirmed by multiple studies (PMID:21085684, PMID:22102906). The IBA annotation correctly captures this broad cellular localization.
Reason: The endomembrane system annotation is well-supported by experimental evidence showing PLD4 localization to ER membrane, Golgi apparatus, and endolysosomes. This IBA annotation represents an appropriate level of specificity.
Supporting Evidence:
PMID:21085684
EGFP fluorescence formed a meshwork-like structure in the peripheral region of the nucleus in HEK293 cells... PLD4 immunoreactivity was co-localized with calnexin, an endoplasmic reticulum (ER) resident protein... and PLD4 expression also formed a clustered pattern with golgin 97, a trans-Golgi network protein
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0006909
phagocytosis
|
IBA
GO_REF:0000033 |
KEEP AS NON CORE |
Summary: PLD4 participates in microglial phagocytosis and redistributes to phagosomes during activation, but phagocytosis is a cell-context phenotype rather than the main biochemical function of PLD4.
Reason: Falcon synthesis identifies PLD4 core activities as acidic endolysosomal 5-prime-to-3-prime exonuclease activity and S,S-BMP synthase/transphosphatidylase activity. Phagocytosis is retained as a supported non-core immune-cell process.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0002376
immune system process
|
IEA
GO_REF:0000043 |
KEEP AS NON CORE |
Summary: PLD4 contributes to immune system processes through endolysosomal nucleic-acid and lipid metabolism, but this term is very broad.
Reason: More specific annotations capture the core biology: endolysosomal exonuclease activity, regulation of TLR9/TLR7 nucleic-acid sensing, and BMP synthesis. Retain this as a non-core umbrella process.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0003824
catalytic activity
|
IEA
GO_REF:0000002 |
MODIFY |
Summary: PLD4 is catalytic, but the parent term catalytic activity is too general for curation. Direct evidence supports acidic 5-prime-to-3-prime exonuclease activity on ssDNA/ssRNA and S,S-BMP synthase/transphosphatidylase activity.
Reason: Replace the generic parent with the specific activities supported by Falcon synthesis and primary biochemical work.
Proposed replacements:
single-stranded DNA 5'-3' DNA exonuclease activity
bis(monoacylglycero)phosphate synthase activity
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0004518
nuclease activity
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: PLD4 does have nuclease activity, specifically functioning as a 5'-3' exonuclease on single-stranded DNA and RNA. This annotation is correct but could be more specific.
Reason: The nuclease activity annotation is correct. PLD4 functions as a 5'-3' exonuclease that degrades ssDNA and RNA. While more specific terms exist (GO:0004527 for exonuclease activity), this parent term is acceptable for an IEA annotation.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
5'->3' exonuclease that hydrolyzes the phosphodiester bond of single-stranded DNA (ssDNA) and RNA molecules to form nucleoside 3'- monophosphates and 5'-end 5'-hydroxy deoxyribonucleotide/ribonucleotide fragments
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0004527
exonuclease activity
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: PLD4 has 5'-3' exonuclease activity on single-stranded DNA and RNA. This annotation is correct and represents a core molecular function.
Reason: The exonuclease activity annotation is accurate. PLD4 functions as a 5'-3' exonuclease that degrades ssDNA and RNA to produce nucleoside 3'-monophosphates.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
5'->3' exonuclease that hydrolyzes the phosphodiester bond of single-stranded DNA (ssDNA) and RNA molecules to form nucleoside 3'- monophosphates
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0005634
nucleus
|
IEA
GO_REF:0000044 |
KEEP AS NON CORE |
Summary: PLD4 shows some nuclear localization in microglia, particularly in resting state, but this is not its primary localization. It redistributes from nucleus to phagosomes upon activation.
Reason: While PLD4 can be found in the nucleus of resting microglia, this is a transient localization that changes with cell activation state. The primary localizations are ER membrane and endolysosomes.
Supporting Evidence:
PMID:22102906
Primary cultured microglia and the microglial cell line MG6 showed that PLD4 immuno-signals were mainly present in the nucleus, apart from the nucleolus
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0005764
lysosome
|
IEA
GO_REF:0000044 |
ACCEPT |
Summary: PLD4 localizes to lysosomes where it performs critical functions including nucleic acid degradation and BMP synthesis. This is a core localization.
Reason: Lysosomal localization is well-supported. PLD4 synthesizes BMP, the main phospholipid constituent of lysosomal intralumenal vesicle membranes, and degrades nucleic acids in the endolysosomal compartment.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
Can synthesize a variety of (S,S)-BMPs representing the main phospholipid constituent of lysosomal intralumenal vesicle (ILV) membranes that bind acid hydrolases for lipid degradation
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0005768
endosome
|
IEA
GO_REF:0000117 |
ACCEPT |
Summary: PLD4 localizes to endosomes as part of the endolysosomal pathway where it processes nucleic acids for immune sensing. This is a core localization.
Reason: Endosomal localization is well-supported. PLD4 processes nucleic acids that reach the endolysosomal compartment and participates in immune surveillance.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
Processes self and pathogenic ssDNA and RNA molecules that reach the endolysosomal compartment via phagocytosis or autophagy
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0005769
early endosome
|
IEA
GO_REF:0000044 |
MODIFY |
Summary: PLD4 localizes to transferrin-positive BioParticle-containing early phagosomes during microglial phagocytosis, not generic early endosomes.
Reason: PMID:22102906 describes PLD4 in BioParticle-containing early phagosomes. Replace the generic early endosome component with the more precise early phagosome term.
Proposed replacements:
early phagosome
Supporting Evidence:
PMID:22102906
The results suggest that PLD4 is predominantly present in early phagosomes
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0005789
endoplasmic reticulum membrane
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: PLD4 is predominantly localized to the ER membrane as confirmed by multiple studies. This is its primary subcellular localization and represents a core component.
Reason: ER membrane localization is well-established by experimental evidence. PLD4 is a transmembrane glycoprotein that resides primarily in the ER membrane.
Supporting Evidence:
PMID:21085684
PLD4 immunoreactivity was co-localized with calnexin, an endoplasmic reticulum (ER) resident protein
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0005794
Golgi apparatus
|
IEA
GO_REF:0000044 |
ACCEPT |
Summary: PLD4 localizes to the Golgi apparatus, particularly the trans-Golgi network, as shown by colocalization studies.
Reason: Golgi localization is supported by experimental evidence showing PLD4 colocalization with trans-Golgi network markers.
Supporting Evidence:
PMID:21085684
PLD4 expression also formed a clustered pattern with golgin 97, a trans-Golgi network protein
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0006259
DNA metabolic process
|
IEA
GO_REF:0000108 |
ACCEPT |
Summary: DNA metabolism via PLD4 exonuclease activity on ssDNA.
Reason: PLD4 degrades ssDNA in endolysosomes, contributing to nucleic acid metabolism.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
5'->3' exonuclease that hydrolyzes the phosphodiester bond of single-stranded DNA (ssDNA) and RNA molecules to form nucleoside 3'- monophosphates
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0006629
lipid metabolic process
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: PLD4 synthesizes BMP lipids in lysosomes.
Reason: PLD4 catalyzes BMP synthesis, a lipid metabolic process in endolysosomes.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
Can synthesize a variety of (S,S)-BMPs representing the main phospholipid constituent of lysosomal intralumenal vesicle (ILV) membranes
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0006954
inflammatory response
|
IEA
GO_REF:0000043 |
KEEP AS NON CORE |
Summary: PLD4 is linked to microglial activation and inflammatory contexts.
Reason: Inflammatory responses are context-dependent downstream outcomes of microglial activation.
Supporting Evidence:
PMID:22102906
Binding of antibodies to Fc receptors on the microglial surface induces phagocytosis activity in microglia, which is associated with inflammation
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0016787
hydrolase activity
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: Broad hydrolase annotation for PLD4 exonuclease activity.
Reason: PLD4 functions as a hydrolase through its exonuclease activity.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
5'->3' exonuclease that hydrolyzes the phosphodiester bond of single-stranded DNA (ssDNA) and RNA molecules
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0031410
cytoplasmic vesicle
|
IEA
GO_REF:0000043 |
KEEP AS NON CORE |
Summary: PLD4 associates with phagocytic vesicles in microglia.
Reason: Vesicular localization is context-dependent in activated microglia.
Supporting Evidence:
PMID:22102906
PLD4 immunoreactivity accumulated in phagosomes when BioParticles were added to primary microglial cultures
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0045087
innate immune response
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: PLD4 processes nucleic acids that act as innate immune danger signals.
Reason: PLD4 modulates innate immune receptor activation through nucleic acid processing.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
Processes self and pathogenic ssDNA and RNA molecules that reach the endolysosomal compartment via phagocytosis or autophagy and may serve as danger signals for recognition by innate immune receptors such as toll-like receptors (TLRs)
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0045145
single-stranded DNA 5'-3' DNA exonuclease activity
|
IEA
GO_REF:0000117 |
ACCEPT |
Summary: PLD4 has 5'-3' exonuclease activity on single-stranded DNA. This is one of its core molecular functions, degrading ssDNA to produce nucleoside 3'-monophosphates.
Reason: This annotation correctly identifies PLD4's core exonuclease function. The protein degrades single-stranded DNA in a 5' to 3' direction, which is critical for preventing inappropriate TLR9 activation.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
5'->3' exonuclease that hydrolyzes the phosphodiester bond of single-stranded DNA (ssDNA) and RNA molecules to form nucleoside 3'- monophosphates
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0045335
phagocytic vesicle
|
IEA
GO_REF:0000044 |
ACCEPT |
Summary: PLD4 localizes to phagocytic vesicles in microglia.
Reason: PLD4 accumulates in phagosomes during phagocytosis.
Supporting Evidence:
PMID:22102906
PLD4 immunoreactivity accumulated in phagosomes when BioParticles were added to primary microglial cultures
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:1900015
regulation of cytokine production involved in inflammatory response
|
IEA
GO_REF:0000117 |
KEEP AS NON CORE |
Summary: PLD4 loss or combined PLD3/PLD4 loss can alter cytokine and inflammatory outputs by changing endosomal nucleic-acid sensing, but cytokine regulation is downstream of the enzymatic function.
Reason: Falcon synthesis supports cytokine dysregulation as an immune consequence of defective endolysosomal nucleic-acid clearance. Retain as supported non-core biology rather than a core function.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0004630
D-type glycerophospholipase activity
|
TAS
Reactome:R-MMU-1483172 |
REMOVE |
Summary: This is a positive Reactome annotation to phospholipase D activity, but experimental evidence shows PLD4 lacks authentic PLD activity.
Reason: The GOA has a separate explicit NOT annotation for this term. The positive Reactome TAS row should be removed because PMID:21085684 directly refutes authentic phospholipase D activity for PLD4.
Supporting Evidence:
PMID:21085684
these results suggested that PLD4 is a HKD motif-containing protein family member that lacks authentic PLD activity
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0004630
D-type glycerophospholipase activity
|
IDA
NOT
PMID:21085684 Phospholipase D family member 4, a transmembrane glycoprotei... |
ACCEPT |
Summary: This annotation has a NOT qualifier in the GOA file (line 24), indicating PLD4 does NOT have phospholipase D activity. This negative annotation correctly reflects that PLD4 lacks this activity despite its misleading name.
Reason: This is a negative annotation (NOT enables GO:0004630) that correctly documents the experimental finding that PLD4 lacks phospholipase D activity. The study explicitly tested and disproved PLD activity.
Supporting Evidence:
PMID:21085684
However, cell lysates transfected with PLD4 did not exhibit significant PLD activity, such as cells transfected with vector alone
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0005634
nucleus
|
IDA
PMID:22102906 PLD$ is involved in phagocytosis of microglia: expression an... |
KEEP AS NON CORE |
Summary: PLD4 is nuclear in resting microglia.
Reason: Nuclear localization is context-dependent and not the primary localization.
Supporting Evidence:
PMID:22102906
PLD4 immuno-signals were mainly present in the nucleus, apart from the nucleolus
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0005769
early endosome
|
IDA
PMID:22102906 PLD$ is involved in phagocytosis of microglia: expression an... |
MODIFY |
Summary: PLD4 accumulates in early phagosomes during microglial activation.
Reason: The PMID:22102906 microscopy supports early phagosome localization. The existing early endosome term is less accurate because the transferrin-positive structures are BioParticle-containing phagosomes.
Proposed replacements:
early phagosome
Supporting Evidence:
PMID:22102906
In the phagocytotic state eating BioParticles, PLD4 accumulated in the early phagosomes.
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0045145
single-stranded DNA 5'-3' DNA exonuclease activity
|
IMP
PMID:22102906 PLD$ is involved in phagocytosis of microglia: expression an... |
REMOVE |
Summary: The 2011 microglial paper does not itself biochemically demonstrate exonuclease activity, but the annotation is now directly supported by later biochemical and structural work showing PLD4 is a single-stranded DNA 5-prime-to-3-prime exonuclease.
Reason: The term is correct for PLD4, but this specific PMID:22102906 IMP annotation is unsupported because that paper localized PLD4 in activated microglia and did not demonstrate exonuclease activity. The function is retained through the other ssDNA exonuclease annotation supported by PMID:30111894.
Supporting Evidence:
PMID:30111894
PLD4 degraded a 55 nt ssDNA
|
|
GO:0045335
phagocytic vesicle
|
IDA
PMID:22102906 PLD$ is involved in phagocytosis of microglia: expression an... |
ACCEPT |
Summary: PLD4 accumulates in phagosomes during phagocytosis.
Reason: Direct microscopy shows PLD4 in phagosomes during microglial activation.
Supporting Evidence:
PMID:22102906
PLD4 immunoreactivity accumulated in phagosomes when BioParticles were added to primary microglial cultures
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:1900015
regulation of cytokine production involved in inflammatory response
|
IMP
PMID:22102906 PLD$ is involved in phagocytosis of microglia: expression an... |
KEEP AS NON CORE |
Summary: PLD4 loss or combined PLD3/PLD4 loss can alter cytokine and inflammatory outputs by changing endosomal nucleic-acid sensing, but cytokine regulation is downstream of the enzymatic function.
Reason: Falcon synthesis supports cytokine dysregulation as an immune consequence of defective endolysosomal nucleic-acid clearance. Retain as supported non-core biology rather than a core function.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0005789
endoplasmic reticulum membrane
|
IDA
PMID:21085684 Phospholipase D family member 4, a transmembrane glycoprotei... |
ACCEPT |
Summary: PLD4 localizes to the ER membrane.
Reason: Colocalization with ER markers supports ER membrane localization.
Supporting Evidence:
PMID:21085684
PLD4 immunoreactivity was co-localized with calnexin, an endoplasmic reticulum (ER) resident protein
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0032588
trans-Golgi network membrane
|
IDA
PMID:21085684 Phospholipase D family member 4, a transmembrane glycoprotei... |
ACCEPT |
Summary: PLD4 localizes to the trans-Golgi network.
Reason: Colocalization with golgin 97 supports trans-Golgi network localization.
Supporting Evidence:
PMID:21085684
PLD4 expression also formed a clustered pattern with golgin 97, a trans-Golgi network protein
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0002244
hematopoietic progenitor cell differentiation
|
IMP
PMID:24029230 Haploinsufficiency of SAMD9L, an endosome fusion facilitator... |
REMOVE |
Summary: The cited publication is about Samd9l haploinsufficiency and myeloid malignancy, not a direct functional role of Pld4 in hematopoietic progenitor differentiation.
Reason: No reviewed Pld4 literature or Falcon synthesis supports hematopoietic progenitor differentiation as a Pld4 function. This appears to be an erroneous or indirect annotation and should be removed.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0005783
endoplasmic reticulum
|
IDA
PMID:21085684 Phospholipase D family member 4, a transmembrane glycoprotei... |
ACCEPT |
Summary: PLD4 localizes to the ER.
Reason: ER localization is supported by colocalization with ER markers.
Supporting Evidence:
PMID:21085684
PLD4 immunoreactivity was co-localized with calnexin, an endoplasmic reticulum (ER) resident protein
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0006909
phagocytosis
|
IMP
PMID:22102906 PLD$ is involved in phagocytosis of microglia: expression an... |
KEEP AS NON CORE |
Summary: PLD4 participates in microglial phagocytosis and redistributes to phagosomes during activation, but phagocytosis is a cell-context phenotype rather than the main biochemical function of PLD4.
Reason: Falcon synthesis identifies PLD4 core activities as acidic endolysosomal 5-prime-to-3-prime exonuclease activity and S,S-BMP synthase/transphosphatidylase activity. Phagocytosis is retained as a supported non-core immune-cell process.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0005789
endoplasmic reticulum membrane
|
TAS
Reactome:R-MMU-1483172 |
ACCEPT |
Summary: ER membrane localization in agreement with experimental evidence.
Reason: PLD4 localizes to the ER membrane based on colocalization studies.
Supporting Evidence:
PMID:21085684
PLD4 immunoreactivity was co-localized with calnexin, an endoplasmic reticulum (ER) resident protein
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0005515
protein binding
|
IPI
PMID:18706977 Interaction assays in yeast and cultured cells confirm known... |
REMOVE |
Summary: Generic protein binding annotation is uninformative.
Reason: Protein binding is too general to be useful for PLD4 function.
Supporting Evidence:
PMID:18706977
Interaction assays in yeast and cultured cells confirm known and identify novel partners of the synaptic vesicle protein synaptophysin.
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0036019
endolysosome
|
NAS | NEW |
Summary: PLD4 carries out its nuclease and BMP-synthase functions in endolysosomal/lysosomal compartments.
Reason: Endolysosomal localization is directly tied to acidic-pH catalytic activity and nucleic-acid/lipid substrate availability.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0034164
negative regulation of toll-like receptor 9 signaling pathway
|
NAS | NEW |
Summary: PLD4 degrades endolysosomal self ssDNA, including mitochondrial CpG-rich DNA, thereby limiting inappropriate TLR9 activation.
Reason: This is a direct biological consequence of the core exonuclease function and is well supported by Falcon synthesis and primary PLD3/PLD4 studies.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0160121
bis(monoacylglycero)phosphate synthase activity
|
NAS | NEW |
Summary: Falcon synthesis and the 2024 Cell study support PLD4 as an S,S-BMP synthase/transphosphatidylase in lysosomes.
Reason: This specific molecular function is directly supported by purified enzyme and tissue lipidomic evidence and is not represented by the older broad catalytic-activity annotation.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:2001312
lysobisphosphatidic acid biosynthetic process
|
NAS | NEW |
Summary: PLD4-dependent S,S-BMP synthesis supports lysobisphosphatidic acid/BMP biosynthesis in lysosomes.
Reason: The 2024 Falcon report and Cell study support this NEW process term as a direct consequence of PLD4 BMP synthase activity.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0004534
5'-3' RNA exonuclease activity
|
NAS | NEW |
Summary: PLD4 has single-stranded RNA exonuclease activity and can shape endosomal TLR7-dependent antiviral sensing outputs.
Reason: Direct PLD3/PLD4 nuclease studies support RNA cleavage and altered nucleic-acid sensor activation. Retain as conservative NEW support for the RNA/TLR7 arm of PLD4 biology.
Supporting Evidence:
file:mouse/Pld4/Pld4-deep-research-falcon.md
[Falcon deep-research synthesis used for this annotation decision.]
|
|
GO:0034122
negative regulation of toll-like receptor signaling pathway
|
NAS | NEW |
Summary: PLD4/PLD3 ssRNA degradation limits inappropriate endosomal nucleic-acid-sensor activation and resulting autoinflammation.
Reason: The accessible RNA nuclease evidence supports negative regulation of TLR/nucleic-acid sensor activation from accumulated self ssRNA, not direct positive TLR7 signaling or antiviral defense.
Supporting Evidence:
PMID:34620855
Pld3-/-Pld4-/- mice accumulate small ssRNAs and develop spontaneous fatal hemophagocytic lymphohistiocytosis
|
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
The UniProt accession Q8BG07 corresponds to Mus musculus Pld4 (PLD4; phospholipase D family member 4), an endolysosomal/lysosomal, type II transmembrane PLD-family protein with the canonical dual HKD catalytic motifs typical of the phospholipase D superfamily. This matches primary literature that characterizes mouse PLD4 as a glycosylated type II transmembrane endolysosomal protein and assigns it enzymatic activities in the lysosomal lumen at acidic pH. (gavin2018pld3andpld4 pages 1-2, yuan2024structuralandmechanistic pages 1-5)
PLD4 (together with its paralog PLD3) is now best understood as an endolysosomal/lysosomal, acidic 5โฒโ3โฒ exonuclease that degrades single-stranded DNA (ssDNA) and single-stranded RNA (ssRNA) within the endolysosomal system. This enzymatic activity is directly tied to limiting activation of endosomal nucleic-acid sensors, particularly TLR pathways. (gavin2018pld3andpld4 pages 1-2, gavin2021cleavageofdna pages 1-2, yuan2024structuralandmechanistic pages 1-5)
A 2024 structural/mechanistic study further refined substrate rules: PLD4 can process very short single-stranded substrates (down to dinucleotides), but 5โฒ-phosphorylation blocks activity, highlighting an important specificity determinant for which nucleic acids in lysosomes will be efficiently degraded. (yuan2024structuralandmechanistic pages 1-5)
In 2024, PLD4 (with PLD3) was reported to catalyze synthesis of S,S-bis(monoacylglycero)phosphate (S,S-BMP), a major lipid of lysosomal intraluminal vesicles important for lysosomal lipid degradation. The proposed role is to perform a stereo-inversion step that yields the lysosomally stable S,S stereoisomer of BMP, thereby enabling proper lysosomal degradation of lipids such as gangliosides. (singh2024pld3andpld4 pages 1-3, singh2024pld3andpld4 pages 7-8, singh2024pld3andpld4 pages 8-10)
This places PLD4 at the intersection of (i) nucleic-acid catabolism and (ii) lysosomal lipid homeostasis, both occurring in acidic endolysosomal compartments. (singh2024pld3andpld4 pages 1-3, yuan2024structuralandmechanistic pages 1-5)
Reaction (conceptual): processive or distributive removal of nucleotides from the 5โฒ end of single-stranded nucleic acids under acidic conditions typical of endolysosomes/lysosomes. (gavin2018pld3andpld4 pages 1-2, gavin2021cleavageofdna pages 1-2, yuan2024structuralandmechanistic pages 1-5)
Substrates and specificity:
- Substrates: ssDNA and ssRNA; the activity is directly relevant to degradation of nucleic-acid ligands that would otherwise stimulate endosomal receptors (e.g., TLR9 DNA ligands; also RNA ligands relevant to TLR7). (gavin2018pld3andpld4 pages 1-2, gavin2021cleavageofdna pages 1-2)
- Directionality: 5โฒโ3โฒ exonucleolytic digestion. (yuan2024structuralandmechanistic pages 1-5)
- A key negative determinant: 5โฒ phosphorylation inhibits cleavage, indicating PLD4 preferentially acts on nucleic acids with accessible, appropriately configured 5โฒ ends. (yuan2024structuralandmechanistic pages 1-5)
Catalytic motifs/mechanism:
PLD4 contains two conserved HxKxxxxD/E (โHKD/Eโ) motifs that assemble into a basic catalytic center. Structural/mechanistic evidence indicates catalysis can proceed via a covalent 3โฒ-phosphohistidine intermediate, and PLD4 includes an additional hydrophobic clamp implicated in stabilizing substrates and influencing product release. (yuan2024structuralandmechanistic pages 1-5)
Reaction (reported in 2024): PLD4 catalyzes formation of S,S-BMP in lysosomes via a reaction consistent with transphosphatidylation/glycerol-exchange using lyso-phosphatidylglycerol (lyso-PG) and monoacylglycerol (MAG) as substrates, producing lysosomal BMP species enriched in the S,S stereoisomer. (singh2024pld3andpld4 pages 3-5, singh2024pld3andpld4 pages 7-8)
Mechanistic evidence:
- BMP synthesis was observed in vitro at acidic pH (~5.4), consistent with lysosomal lumen conditions. (singh2024pld3andpld4 pages 3-5, singh2024pld3andpld4 pages 13-15)
- Incorporation of a deuterium-labeled MAG headgroup into BMP provided direct evidence for glycerol exchange/transphosphatidylation, supporting an enzyme-catalyzed remodeling step rather than passive isomerization. (singh2024pld3andpld4 pages 3-5)
Physiological readouts: PLD4 loss leads to substantial depletion of BMP in tissues where PLD4 is highly expressed (notably spleen), with downstream lysosomal lipid catabolism defects. (singh2024pld3andpld4 pages 7-8, singh2024pld3andpld4 pages 8-10)
Mouse PLD4 is a type II transmembrane protein localized to endolysosomal/lysosomal compartments. A type II topology implies an N-terminal cytosolic region followed by a transmembrane segment and a luminal catalytic/extracellular domain positioned to act within the acidic lumen. (gavin2018pld3andpld4 pages 1-2, yuan2024structuralandmechanistic pages 1-5)
PLD4 expression is enriched in dendritic cells and other myeloid-lineage immune cells, with lower expression in B cells, consistent with a primary role in regulating nucleic-acid sensing in antigen-presenting compartments. (gavin2018pld3andpld4 pages 1-2)
Recent lipid-focused work also reports highest PLD4 mRNA in murine spleen and myeloid cells, which aligns with the tissue where PLD4 deletion most strongly reduces BMP abundance. (singh2024pld3andpld4 pages 7-8)
In Pld4โ/โ mice, loss of PLD4 produces an inflammatory syndrome marked by splenomegaly and elevated inflammatory/IFN-related features, traced to altered responses of dendritic cells to TLR9 ligands (endosomal ssDNA sensing). These data support PLD4 as a lysosomal โbrakeโ on nucleic-acid-driven innate immune activation by degrading nucleic acids within endolysosomes. (gavin2018pld3andpld4 pages 1-2)
Pld3โ/โPld4โ/โ double-knockout mice accumulate small ssRNAs and develop spontaneous fatal immune pathology described as hemophagocytic lymphohistiocytosis (HLH) with inflammatory liver damage and cytokine dysregulation. Genetic blockade of endosomal TLR signaling by Unc93b1 deficiency rescues disease, while targeting only TLR7 or TLR9 is less effective, implying that both RNA and DNA sensing contribute. Residual perturbations in the rescued background require STING (Tmem173), connecting lysosomal nucleic-acid catabolism to both endosomal TLR and cytosolic nucleic-acid sensing networks. (gavin2021cleavageofdna pages 1-2)
PLD4 knockout mice show marked depletion of BMP in spleen (~80% reduction) and concomitant lysosomal lipid degradation defects reflected by ~2-fold accumulation of multiple gangliosides (e.g., GM3, GD1a, GD2, GT1, GT3) in spleen. These findings support a role for PLD4 in maintaining the lysosomal lipid cofactor BMP required for efficient breakdown of complex glycosphingolipids. (singh2024pld3andpld4 pages 7-8, singh2024pld3andpld4 media b87b0738)
A 2024 Structure paper provided structural/mechanistic insights into PLD4โs endolysosomal nuclease activity, including: (i) dual HKD motif active site architecture, (ii) lower pH optimum for PLD4 compared with PLD3, (iii) inhibitory effect of 5โฒ phosphorylation, and (iv) identification of a 3โฒ-phosphohistidine intermediate and a PLD4-specific clamp feature affecting substrate handling. (Yuan et al., June 2024, https://doi.org/10.1016/j.str.2024.02.019) (yuan2024structuralandmechanistic pages 1-5)
A 2024 Cell study proposed and experimentally supported that PLD4 (and PLD3) catalyze S,S-BMP synthesis in lysosomes via transphosphatidylation/stereo-inversion chemistry. This directly revises the functional landscape of PLD4 from โnuclease onlyโ to a multifunctional lysosomal enzyme linking lipid and nucleic-acid homeostasis. (Singh et al., Nov 2024, https://doi.org/10.1016/j.cell.2024.09.036) (singh2024pld3andpld4 pages 1-3, singh2024pld3andpld4 pages 3-5)
Although this report focuses on mouse Pld4, the mechanistic framework has translational implications: PLD4 activity restrains activation of nucleic-acid sensing pathways (endosomal TLR7/TLR9 and a STING-coupled axis), implying therapeutic leverage points at endosomal TLR trafficking/signaling and/or STING/type I IFN pathways in nucleic-acid-driven inflammatory disease contexts. The double-knockout rescue by Unc93b1 deficiency provides causal pathway positioning and a โproof-of-principleโ that suppressing endosomal TLR signaling can overcome consequences of defective lysosomal nucleic-acid catabolism. (gavin2021cleavageofdna pages 1-2)
The 2024 BMP synthesis work provides a functional rationale for using BMP species and/or downstream ganglioside accumulation patterns as biochemical readouts of PLD4-dependent lysosomal lipid degradation capacity in relevant tissues and cell types. In the mouse spleen, PLD4 knockout produced a large BMP depletion (~80%) and measurable ganglioside increases, illustrating assayable, quantitative endpoints for functional studies. (singh2024pld3andpld4 pages 7-8, singh2024pld3andpld4 media b87b0738)
The literature supports a model in which PLD4 is a luminal endolysosomal enzyme whose catalytic HKD core has been repurposed (relative to canonical PLD1/PLD2 lipid signaling enzymes) for lysosomal catabolism/maintenance functions. Earlier work established PLD4 as an acid exonuclease limiting immunostimulatory nucleic acids in endosomes/lysosomes, thereby preventing inappropriate activation of nucleic-acid sensing receptors and autoinflammation. (gavin2018pld3andpld4 pages 1-2, gavin2021cleavageofdna pages 1-2)
The 2024 findings add a second axis: PLD4 is also implicated as a key enzyme in generating the lysosomally stable S,S stereoisomer of BMP, a lipid thought to be required for efficient lysosomal lipid breakdown, consistent with ganglioside accumulation in Pld4 knockout spleen. This discovery suggests that PLD4 contributes to immune homeostasis through at least two lysosomal โbufferingโ functionsโnucleic-acid clearance and lipid cofactor productionโeach of which can influence innate immune activation (via TLR/STING pathways) when lysosomal physiology is perturbed. (singh2024pld3andpld4 pages 1-3, yuan2024structuralandmechanistic pages 1-5, singh2024pld3andpld4 pages 7-8)
A key open question (not resolved in the cited excerpts) is whether both reactions are catalyzed by the same active-site chemistry under physiological conditions and how cells allocate PLD4โs apparent activities across substrates; nonetheless, both roles are supported by direct biochemical and in vivo evidence and align with PLD4โs endolysosomal localization and acidic pH preference. (yuan2024structuralandmechanistic pages 1-5, singh2024pld3andpld4 pages 3-5)
The following extracted figure panels provide visual evidence for PLD4โs role in BMP homeostasis and downstream lipid phenotypes in vivo:
- Spleen lipidomics volcano plot and BMP decrease in Pld4 KO vs WT (singh2024pld3andpld4 media b87b0738, singh2024pld3andpld4 media ede139a8)
- Quantification of BMP species reduction in Pld4 KO spleen (singh2024pld3andpld4 media 48303b21)
- Ganglioside accumulation in Pld4 KO spleen (singh2024pld3andpld4 media 55bfabcb)
- Proposed biosynthetic pathway/model involving PLD3/4-catalyzed steps to generate S,S-BMP (singh2024pld3andpld4 media 5cf2359e)
| Claim/Function | Evidence type (biochemical/structural/genetic) | Key details (substrate/reaction/localization) | System/Model | Citation (paper + DOI URL + pub month/year) |
|---|---|---|---|---|
| PLD4 is a 5โฒโ3โฒ acid exonuclease on single-stranded nucleic acids | Biochemical | Digests ssDNA and ssRNA in the 5โฒโ3โฒ direction; active in acidic conditions consistent with lysosomes/endolysosomes; activity reported on very short substrates and relevant to degradation of TLR ligands | Recombinant/biochemical assays; mouse-focused functional studies | Yuan et al., Structure (https://doi.org/10.1016/j.str.2024.02.019), Jun 2024; Gavin et al., Nature Immunology (https://doi.org/10.1038/s41590-018-0179-y), Aug 2018; Gavin et al., Nature Communications (https://doi.org/10.1038/s41467-021-26150-w), Oct 2021 (yuan2024structuralandmechanistic pages 1-5, gavin2018pld3andpld4 pages 1-2, gavin2021cleavageofdna pages 1-2) |
| PLD4 exonuclease activity is inhibited by 5โฒ phosphorylation of substrate | Structural/biochemical | Structural-mechanistic work reports that 5โฒ phosphorylation blocks efficient processing, helping define substrate specificity for single-stranded nucleic acids | Structural snapshots and enzyme assays of PLD4/PLD3 | Yuan et al., Structure (https://doi.org/10.1016/j.str.2024.02.019), Jun 2024 (yuan2024structuralandmechanistic pages 1-5) |
| PLD4 catalytic core uses PLD-family HKD motifs and forms a 3โฒ-phosphohistidine intermediate | Structural/mechanistic | Two conserved HxKxxxxD/E motifs form the active site; catalysis proceeds through a covalent 3โฒ-phosphohistidine intermediate; PLD4 also has a hydrophobic clamp proposed to influence substrate handling/product release | Structural analysis of endolysosomal exonucleases PLD3/PLD4 | Yuan et al., Structure (https://doi.org/10.1016/j.str.2024.02.019), Jun 2024 (yuan2024structuralandmechanistic pages 1-5) |
| PLD4 is an endolysosomal, glycosylated type II transmembrane protein | Biochemical/cell biological | Type II transmembrane topology with cytoplasmic N-terminus, transmembrane segment, and luminal catalytic domain; localized to endolysosomal compartments where acidic pH supports activity | Cell biological localization and protein characterization | Gavin et al., Nature Immunology (https://doi.org/10.1038/s41590-018-0179-y), Aug 2018; Yuan et al., Structure (https://doi.org/10.1016/j.str.2024.02.019), Jun 2024 (gavin2018pld3andpld4 pages 1-2, yuan2024structuralandmechanistic pages 1-5) |
| PLD4 is highly expressed in dendritic/myeloid compartments and spleen | Expression/functional | High expression in dendritic cells and other myeloid cells, lower in B cells; 2024 lipid study notes highest murine PLD4 mRNA in spleen and myeloid cells | Mouse immune cells; tissue expression comparisons | Gavin et al., Nature Immunology (https://doi.org/10.1038/s41590-018-0179-y), Aug 2018; Singh et al., Cell (https://doi.org/10.1016/j.cell.2024.09.036), Nov 2024 (gavin2018pld3andpld4 pages 1-2, singh2024pld3andpld4 pages 7-8) |
| PLD4 restrains endosomal nucleic-acid sensing and inflammation | Genetic/functional | PLD4 degrades nucleic acids that would otherwise activate endosomal sensors, especially TLR9, thereby limiting inflammatory cytokine responses | Pld4-deficient mice and immune cells | Gavin et al., Nature Immunology (https://doi.org/10.1038/s41590-018-0179-y), Aug 2018; Gavin et al., Nature Communications (https://doi.org/10.1038/s41467-021-26150-w), Oct 2021 (gavin2018pld3andpld4 pages 1-2, gavin2021cleavageofdna pages 1-2) |
| Pld4โ/โ mice develop inflammatory/immune phenotypes | Genetic/in vivo | Reported phenotypes include splenomegaly, elevated IFN-ฮณ, interferon-inducible gene signature, elevated MHC II on macrophages, altered immune-cell subsets, and exaggerated responsiveness linked to TLR9 signaling | Mouse knockout | Gavin et al., Nature Immunology (https://doi.org/10.1038/s41590-018-0179-y), Aug 2018 (gavin2018pld3andpld4 pages 1-2) |
| Pld3โ/โPld4โ/โ mice develop severe lethal autoinflammation/HLH-like disease | Genetic/in vivo | Double deficiency causes accumulation of small ssRNAs, fatal hemophagocytic lymphohistiocytosis-like disease with inflammatory liver damage, splenomegaly, thrombocytopenia, hemophagocytosis, increased IFN-ฮณ and type I IFN; rescue by loss of endosomal TLR signaling implicates TLR7/TLR9 and STING-linked pathways | Double-knockout mice with pathway-genetic rescue | Gavin et al., Nature Communications (https://doi.org/10.1038/s41467-021-26150-w), Oct 2021; Gavin et al., Nature Immunology (https://doi.org/10.1038/s41590-018-0179-y), Aug 2018 (gavin2021cleavageofdna pages 1-2, gavin2018pld3andpld4 pages 1-2) |
| 2024 work identified PLD4 as an S,S-BMP synthase rather than only a nuclease | Biochemical/lipidomic | Purified PLD4 catalyzes lysosomal S,S-bis(monoacylglycero)phosphate synthesis via transphosphatidylation/stereo-inversion chemistry; reaction uses lyso-PG and monoacylglycerol substrates under acidic lysosomal conditions | Purified enzyme, isolated lysosomes, cell-based lipidomics | Singh et al., Cell (https://doi.org/10.1016/j.cell.2024.09.036), Nov 2024 (singh2024pld3andpld4 pages 1-3, singh2024pld3andpld4 pages 3-5, singh2024pld3andpld4 pages 13-15) |
| PLD4-dependent lipid reaction is supported by direct transphosphatidylation evidence | Biochemical/mechanistic | Deuterium-labeled MAG incorporation into BMP demonstrated glycerol exchange/transphosphatidylation; activity observed at pH ~5.4 and not neutral pH, matching lysosomal environment | Lysosomal extracts and purified PLD4/PLD3 assays | Singh et al., Cell (https://doi.org/10.1016/j.cell.2024.09.036), Nov 2024 (singh2024pld3andpld4 pages 3-5, singh2024pld3andpld4 pages 13-15, singh2024pld3andpld4 media b87b0738) |
| PLD4 is required for normal spleen BMP abundance in vivo | Genetic/lipidomic | In tissues where PLD4 is highly expressed, especially spleen, Pld4 knockout markedly lowers BMP; reported reduction is ~80% in spleen, with little effect on brain BMP | Pld4 knockout mouse tissue lipidomics | Singh et al., Cell (https://doi.org/10.1016/j.cell.2024.09.036), Nov 2024 (singh2024pld3andpld4 pages 7-8, singh2024pld3andpld4 media b87b0738) |
| PLD4 loss causes lysosomal lipid-catabolism defects | Genetic/lipidomic/phenotypic | Pld4 knockout spleen shows roughly ~2-fold accumulation of multiple gangliosides (e.g., GM3, GD1a, GD2, GT1, GT3), consistent with BMP-dependent lysosomal lipid degradation defects; splenomegaly also reported | Pld4 knockout mouse spleen lipidomics and phenotype | Singh et al., Cell (https://doi.org/10.1016/j.cell.2024.09.036), Nov 2024; Gavin et al., Nature Immunology (https://doi.org/10.1038/s41590-018-0179-y), Aug 2018 (singh2024pld3andpld4 pages 7-8, singh2024pld3andpld4 media b87b0738, gavin2018pld3andpld4 pages 1-2) |
| Current interpretation: PLD4 is multifunctional in lysosomes/endolysosomes | Integrative biochemical/structural/genetic | Evidence now supports two experimentally validated activities linked to the same lysosomal compartment: nucleic-acid turnover that restrains innate immune sensing, and S,S-BMP synthesis that supports lysosomal lipid degradation | Integrated interpretation across structural, genetic, and lipidomic studies | Yuan et al., Structure (https://doi.org/10.1016/j.str.2024.02.019), Jun 2024; Gavin et al., Nature Immunology (https://doi.org/10.1038/s41590-018-0179-y), Aug 2018; Gavin et al., Nature Communications (https://doi.org/10.1038/s41467-021-26150-w), Oct 2021; Singh et al., Cell (https://doi.org/10.1016/j.cell.2024.09.036), Nov 2024 (yuan2024structuralandmechanistic pages 1-5, gavin2018pld3andpld4 pages 1-2, gavin2021cleavageofdna pages 1-2, singh2024pld3andpld4 pages 1-3) |
Table: This table summarizes validated functional annotation for mouse PLD4/Pld4 (UniProt Q8BG07), integrating biochemical, structural, genetic, and lipidomic evidence. It is useful for distinguishing the established exonuclease role in nucleic-acid sensing control from the newly reported 2024 lysosomal S,S-BMP synthase activity.
References
(gavin2018pld3andpld4 pages 1-2): Amanda L. Gavin, Deli Huang, Christoph Huber, Annica Mรฅrtensson, Virginie Tardif, Patrick D. Skog, Tanya R. Blane, Therese C. Thinnes, Kent Osborn, Hayley S. Chong, Farnaz Kargaran, Phoebe Kimm, Armen Zeitjian, Rachel L. Sielski, Megan Briggs, Sebastian R. Schulz, Alessandro Zarpellon, Benjamin Cravatt, Ee Shan Pang, John Teijaro, Juan Carlos de la Torre, Meredith OโKeeffe, Hubertus Hochrein, Markus Damme, Luc Teyton, Brian R. Lawson, and David Nemazee. Pld3 and pld4 are single-stranded acid exonucleases that regulate endosomal nucleic-acid sensing. Nature Immunology, 19:942-953, Aug 2018. URL: https://doi.org/10.1038/s41590-018-0179-y, doi:10.1038/s41590-018-0179-y. This article has 154 citations and is from a highest quality peer-reviewed journal.
(yuan2024structuralandmechanistic pages 1-5): Meng Yuan, Linghang Peng, Deli Huang, Amanda Gavin, Fangkun Luan, Jenny Tran, Ziqi Feng, Xueyong Zhu, Jeanne Matteson, Ian A. Wilson, and David Nemazee. Structural and mechanistic insights into disease-associated endolysosomal exonucleases pld3 and pld4. Structure, 32:766-779.e7, Jun 2024. URL: https://doi.org/10.1016/j.str.2024.02.019, doi:10.1016/j.str.2024.02.019. This article has 13 citations and is from a domain leading peer-reviewed journal.
(gavin2021cleavageofdna pages 1-2): Amanda L. Gavin, Deli Huang, Tanya R. Blane, Therese C. Thinnes, Yusuke Murakami, Ryutaro Fukui, Kensuke Miyake, and David Nemazee. Cleavage of dna and rna by pld3 and pld4 limits autoinflammatory triggering by multiple sensors. Nature Communications, Oct 2021. URL: https://doi.org/10.1038/s41467-021-26150-w, doi:10.1038/s41467-021-26150-w. This article has 58 citations and is from a highest quality peer-reviewed journal.
(singh2024pld3andpld4 pages 1-3): Shubham Singh, Ulrich E. Dransfeld, Yohannes A. Ambaw, Joshua Lopez-Scarim, Robert V. Farese, and Tobias C. Walther. Pld3 and pld4 synthesize s,s-bmp, a key phospholipid enabling lipid degradation in lysosomes. Cell, 187:6820-6834.e24, Nov 2024. URL: https://doi.org/10.1016/j.cell.2024.09.036, doi:10.1016/j.cell.2024.09.036. This article has 55 citations and is from a highest quality peer-reviewed journal.
(singh2024pld3andpld4 pages 7-8): Shubham Singh, Ulrich E. Dransfeld, Yohannes A. Ambaw, Joshua Lopez-Scarim, Robert V. Farese, and Tobias C. Walther. Pld3 and pld4 synthesize s,s-bmp, a key phospholipid enabling lipid degradation in lysosomes. Cell, 187:6820-6834.e24, Nov 2024. URL: https://doi.org/10.1016/j.cell.2024.09.036, doi:10.1016/j.cell.2024.09.036. This article has 55 citations and is from a highest quality peer-reviewed journal.
(singh2024pld3andpld4 pages 8-10): Shubham Singh, Ulrich E. Dransfeld, Yohannes A. Ambaw, Joshua Lopez-Scarim, Robert V. Farese, and Tobias C. Walther. Pld3 and pld4 synthesize s,s-bmp, a key phospholipid enabling lipid degradation in lysosomes. Cell, 187:6820-6834.e24, Nov 2024. URL: https://doi.org/10.1016/j.cell.2024.09.036, doi:10.1016/j.cell.2024.09.036. This article has 55 citations and is from a highest quality peer-reviewed journal.
(singh2024pld3andpld4 pages 3-5): Shubham Singh, Ulrich E. Dransfeld, Yohannes A. Ambaw, Joshua Lopez-Scarim, Robert V. Farese, and Tobias C. Walther. Pld3 and pld4 synthesize s,s-bmp, a key phospholipid enabling lipid degradation in lysosomes. Cell, 187:6820-6834.e24, Nov 2024. URL: https://doi.org/10.1016/j.cell.2024.09.036, doi:10.1016/j.cell.2024.09.036. This article has 55 citations and is from a highest quality peer-reviewed journal.
(singh2024pld3andpld4 pages 13-15): Shubham Singh, Ulrich E. Dransfeld, Yohannes A. Ambaw, Joshua Lopez-Scarim, Robert V. Farese, and Tobias C. Walther. Pld3 and pld4 synthesize s,s-bmp, a key phospholipid enabling lipid degradation in lysosomes. Cell, 187:6820-6834.e24, Nov 2024. URL: https://doi.org/10.1016/j.cell.2024.09.036, doi:10.1016/j.cell.2024.09.036. This article has 55 citations and is from a highest quality peer-reviewed journal.
(singh2024pld3andpld4 media b87b0738): Shubham Singh, Ulrich E. Dransfeld, Yohannes A. Ambaw, Joshua Lopez-Scarim, Robert V. Farese, and Tobias C. Walther. Pld3 and pld4 synthesize s,s-bmp, a key phospholipid enabling lipid degradation in lysosomes. Cell, 187:6820-6834.e24, Nov 2024. URL: https://doi.org/10.1016/j.cell.2024.09.036, doi:10.1016/j.cell.2024.09.036. This article has 55 citations and is from a highest quality peer-reviewed journal.
(singh2024pld3andpld4 media ede139a8): Shubham Singh, Ulrich E. Dransfeld, Yohannes A. Ambaw, Joshua Lopez-Scarim, Robert V. Farese, and Tobias C. Walther. Pld3 and pld4 synthesize s,s-bmp, a key phospholipid enabling lipid degradation in lysosomes. Cell, 187:6820-6834.e24, Nov 2024. URL: https://doi.org/10.1016/j.cell.2024.09.036, doi:10.1016/j.cell.2024.09.036. This article has 55 citations and is from a highest quality peer-reviewed journal.
(singh2024pld3andpld4 media 48303b21): Shubham Singh, Ulrich E. Dransfeld, Yohannes A. Ambaw, Joshua Lopez-Scarim, Robert V. Farese, and Tobias C. Walther. Pld3 and pld4 synthesize s,s-bmp, a key phospholipid enabling lipid degradation in lysosomes. Cell, 187:6820-6834.e24, Nov 2024. URL: https://doi.org/10.1016/j.cell.2024.09.036, doi:10.1016/j.cell.2024.09.036. This article has 55 citations and is from a highest quality peer-reviewed journal.
(singh2024pld3andpld4 media 55bfabcb): Shubham Singh, Ulrich E. Dransfeld, Yohannes A. Ambaw, Joshua Lopez-Scarim, Robert V. Farese, and Tobias C. Walther. Pld3 and pld4 synthesize s,s-bmp, a key phospholipid enabling lipid degradation in lysosomes. Cell, 187:6820-6834.e24, Nov 2024. URL: https://doi.org/10.1016/j.cell.2024.09.036, doi:10.1016/j.cell.2024.09.036. This article has 55 citations and is from a highest quality peer-reviewed journal.
(singh2024pld3andpld4 media 5cf2359e): Shubham Singh, Ulrich E. Dransfeld, Yohannes A. Ambaw, Joshua Lopez-Scarim, Robert V. Farese, and Tobias C. Walther. Pld3 and pld4 synthesize s,s-bmp, a key phospholipid enabling lipid degradation in lysosomes. Cell, 187:6820-6834.e24, Nov 2024. URL: https://doi.org/10.1016/j.cell.2024.09.036, doi:10.1016/j.cell.2024.09.036. This article has 55 citations and is from a highest quality peer-reviewed journal.
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UniProt ID: Q8BG07
Directory alias: Pld4
Question: You are a molecular biologist and gene annotation expert conducting comprehensive research to support GO annotation curation.
Provide detailed, well-cited information focusing on:
1. Gene function and molecular mechanisms
2. Cellular localization and subcellular components
3. Biological processes involvement
4. Disease associations and phenotypes
5. Protein domains and structural features
6. Expression patterns and regulation
7. Evolutionary conservation
8. Key experimental evidence and literature
Format as a comprehensive research report with citations suitable for Gene Ontology annotation curation.
Research the Mus musculus gene Pld4.
=== UNIPROT METADATA ===
UniProt ID: Q8BG07
Entry Name: PLD4_MOUSE
Gene Name: Pld4
Protein Name: 5'-3' exonuclease PLD4
EC Number: 3.1.4.-
Organism: Mus musculus (Mouse)
NCBI Taxonomy ID: 10090
Function: 5'->3' exonuclease that hydrolyzes the phosphodiester bond of single-stranded DNA (ssDNA) and RNA molecules to form nucleoside 3'- monophosphates and 5'-end 5'-hydroxy deoxyribonucleotide/ribonucleotide fragments. Partially redundant with PLD4, can cleave all four nucleotides displaying higher efficiency for ssDNA and RNA fragments initiated with uridine and guanosine residues and lower efficiency for cytidine-initiated substrates. As a result, it does not always degrade polynucleotides to the single nucleotide level, it can stall at specific sites sparing certain fragments from exonucleolytic degradation (PubMed:30111894, PubMed:34620855, PubMed:38537643). Processes self and pathogenic ssDNA and RNA molecules that reach the endolysosomal compartment via phagocytosis or autophagy and may serve as 'danger' signals for recognition by innate immune receptors such as toll-like receptors (TLRs). Degrades mitochondrial CpG-rich ssDNA fragments to prevent TLR9 activation and autoinflammatory response, but it can cleave viral RNA to generate ligands for TLR7 activation and initiate antiviral immune responses. In plasmacytoid dendritic cells, it cooperates with endonuclease RNASET2 to release 2',3'-cyclic guanosine monophosphate (2',3'-cGMP), a potent stimulatory ligand for TLR7 (PubMed:34620855). Produces 2',3'-cGMPs and cytidine-rich RNA fragments that occupy TLR7 ligand-binding pockets and trigger a signaling-competent state. Can exert polynucleotide phosphatase activity toward 5'-phosphorylated ssDNA substrates although at a slow rate (PubMed:38537643). Transphosphatidylase that catalyzes the exchange with R to S stereo-inversion of the glycerol moiety between (S,R)-lysophosphatidylglycerol (LPG) and monoacylglycerol (MAG) substrates to yield (S,S)-bis(monoacylglycero)phosphate (BMP) (PubMed:39423811). Can synthesize a variety of (S,S)-BMPs representing the main phospholipid constituent of lysosomal intralumenal vesicle (ILV) membranes that bind acid hydrolases for lipid degradation (PubMed:39423811). Regulates the homeostasis and interorganellar communication of the endolysosomal system with an overall impact on cellular removal of dysfunctional organelles via autophagy as well as proper protein and lipid turnover. May play a role in myotube formation in response to ER stress (By similarity).
Subcellular Location: Endoplasmic reticulum membrane
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Provide a comprehensive report covering function, localization, processes, domains, disease associations, expression, conservation, and relevant GO terms.
IMPORTANT: Focus specifically on the gene identified by the metadata above, particularly the UniProt ID, locus tag, and protein description if provided.
Sometimes different genes in the same organism have the same name. In this case, the gene being reviewed is the one identified by the metadata above.
AbstractโThe Mus musculus gene Pld4 (UniProt Q8BG07) encodes the 5โฒโ3โฒ exonuclease PLD4, a multifunctional enzyme involved in both nucleic acid metabolism and lipid remodeling that plays critical roles in the regulation of immune responses, cellular clearance mechanisms, and endolysosomal homeostasis. PLD4 exerts its functions by degrading singleโstranded DNA and RNA substrates to produce nucleoside 3โฒ-monophosphates, modulating innate immune receptor activation, and catalyzing the synthesis of (S,S)-bis(monoacylglycero)phosphate (BMP) from lysophosphatidylglycerol and monoacylglycerol substrates. The protein is a transmembrane glycoprotein predominantly localized to the endoplasmic reticulum (ER) membrane, although its dynamic distribution in various immune cell subtypes including microglia and plasmacytoid dendritic cells suggests a broader subcellular repertoire. Here, we review the gene function and molecular mechanisms, cellular localization, biological process involvement, disease associations, protein domains and structural features, expression patterns and regulation, evolutionary conservation, and key experimental evidence supporting the annotation of Pld4 for Gene Ontology (GO) curation (akizuki2019pld4isa pages 12-16, yoshikawa2010phospholipasedfamily pages 1-2).
I. Introduction
The Pld4 gene in Mus musculus is emerging as a pivotal regulator of both nucleic acid processing and lipid metabolism within the immune system. Through its dual enzymatic activities, Pld4 plays an essential role in maintaining cellular homeostasis, modulating endolysosomal function, and preventing the aberrant activation of innate immune pathways. Recent studies utilizing Pld4 mutant mice have established a clear link between the loss or dysregulation of PLD4 function and the onset of autoimmune phenotypes, including systemic lupus erythematosus (SLE)โlike symptoms, splenomegaly, and lymphadenopathy (akizuki2019pld4isa pages 12-16, akizuki2019pld4isa pages 16-19). This report outlines the current state of knowledge on PLD4, synthesizing evidence from biochemical, cellular, structural, and genetic studies that collectively contribute to our understanding of its biological significance and relevance for GO annotation (gavin2018pld3andpld4 pages 1-2, singh2024pld3andpld4 pages 7-8).
II. Gene Function and Molecular Mechanisms
PLD4 functions as a 5โฒโ3โฒ exonuclease that hydrolyzes the phosphodiester bonds within single-stranded DNA (ssDNA) and RNA molecules to yield nucleoside 3โฒ-monophosphates and 5โฒ-hydroxy fragments (gavin2018pld3andpld4 pages 1-2, gavin2021cleavageofdna pages 1-2). The enzymatic activity of PLD4 is finely tuned toward substrates that initiate with uridine and guanosine residues, displaying higher catalytic efficiency for these nucleotides compared to cytidine-initiated fragments (yuan2024structuralandmechanistic pages 17-20, yuan2024structuralandmechanistic pages 20-23). This substrate-specific degradation allows PLD4 to process self-derived mitochondrial CpG-rich ssDNA fragments that might otherwise trigger TLR9-mediated autoinflammatory responses (akizuki2019pld4isa pages 12-16, yuan2024structuralandmechanistic pages 29-31). Concurrently, the enzyme is capable of cleaving viral RNA to generate ligands for TLR7 activation, thereby contributing to the initiation of antiviral immune responses in plasmacytoid dendritic cells (gavin2018pld3andpld4 pages 1-2, gavin2021cleavageofdna pages 1-2). In addition to its exonuclease activity, PLD4 exerts a polynucleotide phosphatase function with slow kinetics on 5โฒ-phosphorylated ssDNA substrates (yuan2024structuralandmechanistic pages 17-20, yuan2024structuralandmechanistic pages 20-23). A further intriguing aspect of PLD4โs functionality is its transphosphatidylase activity, which catalyzes the stereoinversion of the glycerol moiety in lysophosphatidylglycerol (LPG) and monoacylglycerol (MAG) substrates, resulting in the production of (S,S)-bis(monoacylglycero)phosphate (BMP) (singh2024pld3andpld4 pages 7-8, singh2024pld3andpld4 pages 5-7). The synthesis of (S,S)-BMP is crucial for the formation of intralumenal vesicles in lysosomes, thereby impacting lipid degradation and organellar turnover (singh2024pld3andpld4 pages 5-7, singh2024pld3andpld4 pages 34-40). Collectively, these molecular mechanisms underscore the multifaceted role of PLD4 in processing nucleic acids and lipids, which is central to its function in modulating innate immune responses and maintaining endolysosomal integrity (gavin2018pld3andpld4 pages 1-2, yuan2024structuralandmechanistic pages 1-5).
III. Cellular Localization and Subcellular Components
PLD4 is characterized as a transmembrane glycoprotein, and its predominant subcellular localization is within the endoplasmic reticulum membrane as indicated by UniProt metadata and corroborated through immunolocalization studies (yoshikawa2010phospholipasedfamily pages 1-2, yoshikawa2010phospholipasedfamily pages 3-5). Detailed expression analyses have revealed that, in addition to the ER, PLD4 is present in the Golgi apparatus, and its dynamic trafficking is observed in endolysosomal compartments, particularly in immune cells engaged in nucleic acid sensing (yuan2024structuralandmechanistic pages 1-5, yoshikawa2010phospholipasedfamily pages 8-10). In microglial cells, PLD4โs localization shifts from a predominantly nuclear association to a position on phagosomes upon cellular activation, serving as an indicator of microglial activation status (otani2011pld4isinvolved pages 8-10, yoshikawa2010phospholipasedfamily pages 2-3). Moreover, high expression levels in the splenic marginal zone and red pulp align with PLD4โs involvement in immune cell signaling and antigen processing (yoshikawa2010phospholipasedfamily pages 3-5, akizuki2019pld4isa pages 12-16). This broad distribution across multiple organelles within immune cells further emphasizes its importance in coordinating endolysosomal function and nucleic acid degradation, thereby preventing inappropriate activation of inflammatory signaling pathways (yuan2024structuralandmechanistic pages 29-31, yoshikawa2010phospholipasedfamily pages 12-13).
IV. Biological Processes Involvement
The combined enzymatic and lipid remodeling activities of PLD4 integrate the regulation of several key biological processes. First, by functioning as a 5โฒโ3โฒ exonuclease, PLD4 modulates endosomal nucleic acid sensing by degrading self and pathogen-derived nucleic acid species that accumulate within the endolysosomal pathway (gavin2018pld3andpld4 pages 1-2, gavin2021cleavageofdna pages 1-2). This activity is critical to maintaining immune tolerance and preventing excessive toll-like receptor (TLR) activation, which can lead to chronic inflammatory and autoimmune conditions (akizuki2019pld4isa pages 12-16, gavin2018pld3andpld4 pages 11-12). Second, the synthesis of (S,S)-BMP through its transphosphatidylase activity is indispensable for lysosomal lipid degradation, as BMP comprises the major phospholipid component of intralumenal vesicle membranes that bind acid hydrolases (singh2024pld3andpld4 pages 7-8, singh2024pld3andpld4 pages 5-7). The production of BMP not only supports lipid catabolism but also ensures proper interorganellar communication within the endolysosomal system, thereby influencing protein turnover and autophagy (singh2024pld3andpld4 pages 7-8, singh2024pld3andpld4 pages 34-40). Furthermore, by cooperating with endonucleases such as RNASET2, PLD4 facilitates the generation of cyclic nucleotide derivatives like 2โฒ,3โฒ-cGMP, which play a role in activating TLR7 and potentiating antiviral responses (yuan2024structuralandmechanistic pages 17-20, yuan2024structuralandmechanistic pages 20-23). These interconnected processes position PLD4 at a critical nexus between nucleic acid clearance, lipid metabolism, and immune signal modulation, making it integral to cellular homeostasis and host defense mechanisms (gavin2018pld3andpld4 pages 1-2, gavin2018pld3andpld4 pages 11-12).
V. Disease Associations and Phenotypes
A growing body of experimental evidence links PLD4 function to several autoimmune and autoinflammatory conditions. In mutant mouse models, disruptions in Pld4 have been associated with lupus-like phenotypes, including low body weight, splenomegaly, lymphadenopathy, and heightened B cell activity accompanied by increased BAFF secretion and autoantibody production (akizuki2019pld4isa pages 12-16, akizuki2019pld4isa pages 1-5). These phenotypes strongly implicate PLD4 in the prevention of systemic lupus erythematosus (SLE) and underscore its protective role in immune regulation (akizuki2019pld4isa pages 16-19, gavin2018pld3andpld4 pages 11-12). Moreover, genetic studies have linked PLD4 with other autoimmune disorders such as rheumatoid arthritis and systemic sclerosis, suggesting that aberrations in nucleic acid processing and TLR signaling may serve as common pathological mechanisms underlying these conditions (gavin2018pld3andpld4 pages 1-2). Mixed inflammatory dysregulation has also been observed in PLD4-deficient mice, where the loss of enzyme activity exacerbates liver inflammation and disrupts cytokine balance, further emphasizing its role in mitigating autoinflammatory responses (yuan2024structuralandmechanistic pages 29-31, gavin2018pld3andpld4 pages 11-12). In addition to autoimmune phenotypes, alterations in PLD4 function may influence myotube formation in response to ER stress, thus hinting at broader implications in tissue remodeling and repair (singh2024pld3andpld4 pages 7-8, yuan2024structuralandmechanistic pages 5-8). Collectively, these findings support a multifactorial contribution of PLD4 to disease pathology, where its loss or mutation triggers a cascade of immune dysregulation and metabolic defects (akizuki2019pld4isa pages 12-16, yuan2024structuralandmechanistic pages 29-31).
VI. Protein Domains and Structural Features
The structural architecture of PLD4 is defined by several unique features that distinguish it from classical phospholipase D family members. Although PLD4 contains two highly conserved HKD motifsโtypically found in phospholipase enzymesโit conspicuously lacks the canonical PX (Phox homology) and PH (Pleckstrin homology) domains present in PLD1 and PLD2, accounting for its absence of traditional phospholipase D activity (yoshikawa2010phospholipasedfamily pages 1-2, yoshikawa2010phospholipasedfamily pages 8-10). Structural analyses have revealed that PLD4 functions as a type II transmembrane protein with multiple N-linked glycosylation sites; studies indicate the presence of as many as eight consensus glycosylation motifs that likely contribute to protein folding, stability, and subcellular trafficking (yoshikawa2010phospholipasedfamily pages 3-5, yuan2024structuralandmechanistic pages 5-8). Recent crystallographic investigations have provided insights into its active site topology, indicating that the catalytic center is formed via an intrachain dimer interface that may incorporate a hydrophobic clamp to enhance substrate binding and confer specificity, particularly toward nucleotides with specific 5โฒ-end modifications (yuan2024structuralandmechanistic pages 14-17, yuan2024structuralandmechanistic pages 20-23). These structural characteristics not only elucidate the basis for its exonuclease and transphosphatidylase activities but also suggest evolutionary adaptations that allow PLD4 to participate in diverse biochemical pathways, setting it apart from other members of the phospholipase D superfamily (yuan2024structuralandmechanistic pages 1-5, yoshikawa2010phospholipasedfamily pages 11-12).
VII. Expression Patterns and Regulation
Gene expression studies have consistently demonstrated that Pld4 is expressed in a tissue-specific and developmentally regulated manner. Quantitative analyses reveal that PLD4 mRNA exhibits its highest expression in immune-related tissues, most notably in the spleen, where it localizes to the red pulp and marginal zone macrophages (yoshikawa2010phospholipasedfamily pages 3-5, akizuki2019pld4isa pages 12-16). Additionally, expression in myeloid cells and dendritic cells indicates a specialized role in the immune systemโs nucleic acid processing machinery (gavin2018pld3andpld4 pages 1-2, gavin2018pld3andpld4 pages 11-12). In the central nervous system, PLD4 is notably present in early postnatal microglia, with studies showing a marked increase in mRNA expression during the early developmental stages followed by a reduction in later life stages (yoshikawa2010phospholipasedfamily pages 1-2, yoshikawa2010phospholipasedfamily pages 2-3). Moreover, the dynamic regulation of PLD4 expression in microglia is correlated with cellular activation states; activated microglia undergo a spatial redistribution of PLD4 from the nucleus to phagosomal membranes, a process that potentially aids in the clearance of nucleic acid debris during immune responses (otani2011pld4isinvolved pages 8-10, yoshikawa2010phospholipasedfamily pages 3-5). In addition to developmental cues, inflammatory stimuli and ER stress conditions appear to modulate PLD4 transcription, suggesting that its expression is responsive to cellular stress and immune activation (yuan2024structuralandmechanistic pages 5-8, OpenTargets Search: -Pld4). These spatiotemporal expression patterns underpin the enzymeโs role in orchestrating a rapid and localized response to pathogenic challenges, while also maintaining basal endolysosomal function in healthy tissues (akizuki2019pld4isa pages 1-5, yuan2024structuralandmechanistic pages 29-31).
VIII. Evolutionary Conservation
Comparative genomics and phylogenetic analyses underscore that PLD4 is evolutionarily conserved across multiple species, particularly among mammals, which suggests that its specialized functions in nucleic acid degradation and lipid metabolism are critical for survival (gavin2018pld3andpld4 pages 1-2, singh2024pld3andpld4 pages 7-8). The conservation of HKD motifsโin spite of the atypical domain architectureโfurther supports that the underlying catalytic mechanism of PLD4 has been maintained throughout evolution (yoshikawa2010phospholipasedfamily pages 8-10, yoshikawa2010phospholipasedfamily pages 11-12). In parallel, the functional redundancy observed between PLD4 and its paralog PLD3 reinforces the concept of evolutionary pressure to preserve exonuclease activity in the context of immune regulation, as both proteins share overlapping roles in processing nucleic acid ligands for TLRs (yuan2024structuralandmechanistic pages 14-17, gavin2018pld3andpld4 pages 1-2). Moreover, evolutionary conservation extends to its role in lysosomal BMP synthesis, as the production of (S,S)-BMP is a conserved pathway for lipid degradation and is critical for maintaining endolysosomal dynamics across various species (singh2024pld3andpld4 pages 7-8, singh2024pld3andpld4 pages 5-7). This evolutionary perspective not only highlights the fundamental nature of PLD4โs functions but also provides a rationale for its inclusion in GO annotations related to nucleic acid metabolic processes, immune signaling, and lipid homeostasis (singh2024pld3andpld4 pages 34-40, akizuki2019pld4isa pages 16-19).
IX. Key Experimental Evidence and Literature
A wide spectrum of experimental approaches has been employed to elucidate the function, localization, and regulation of PLD4. Gene knockout studies in mice have been particularly illuminating; Pld4 mutant mice exhibit autoimmune phenotypes that feature clinical signs analogous to SLE, such as reduced birth weight, splenomegaly, lymphadenopathy, and an overactive B cell compartment producing high levels of BAFF and autoantibodies (akizuki2019pld4isa pages 12-16, akizuki2019pld4isa pages 1-5). These in vivo observations provide direct evidence linking PLD4 dysfunction to systemic inflammation and autoimmune disease susceptibility (akizuki2019pld4isa pages 16-19, gavin2018pld3andpld4 pages 11-12). In vitro biochemical assays using purified recombinant PLD4 have delineated its substrate specificity, revealing robust 5โฒโ3โฒ exonuclease activity preferentially against ssDNA and RNA substrates with distinct 5โฒ modifications (gavin2018pld3andpld4 pages 1-2, gavin2021cleavageofdna pages 1-2). Complementary studies employing deglycosylation assays in cell lines such as HEK293T have confirmed the presence of extensive N-linked glycosylationโa modification that is critical for proper folding and subcellular targeting of the protein (yoshikawa2010phospholipasedfamily pages 1-2, yoshikawa2010phospholipasedfamily pages 12-13). Furthermore, crystallographic analyses have provided high-resolution insights into PLD4โs active site architecture, including the identification of a hydrophobic clamp that may be responsible for substrate binding and specificity (yuan2024structuralandmechanistic pages 20-23, yuan2024structuralandmechanistic pages 5-8). These structural studies, in conjunction with mutagenesis experiments that target key catalytic residues within the HKD motifs, have offered a detailed picture of the biochemical mechanism underlying PLD4โs dual roles in nucleic acid cleavage and BMP synthesis (yuan2024structuralandmechanistic pages 1-5, yuan2024structuralandmechanistic pages 14-17). Additionally, transcriptomic and RT-qPCR analyses across different tissues and developmental stages have validated the tissue-specific and activation-dependent expression patterns of Pld4, further underscoring its physiological relevance in the immune system and CNS (yoshikawa2010phospholipasedfamily pages 3-5, yoshikawa2010phospholipasedfamily pages 2-3). Collectively, these diverse experimental strategies, ranging from genetic animal models to structural biology and molecular biochemistry, have substantially advanced our understanding of PLD4โs functional repertoire and have provided critical empirical support for GO annotation (akizuki2019pld4isa pages 12-16, yuan2024structuralandmechanistic pages 29-31).
X. Conclusion
In summary, the Mus musculus gene Pld4 encodes a multifunctional transmembrane enzyme that exerts significant regulatory control over both nucleic acid metabolism and lysosomal lipid homeostasis. Its 5โฒโ3โฒ exonuclease activity is essential for the degradation of self and pathogenic single-stranded nucleic acids, a process that prevents aberrant TLR activation and subsequent autoimmune responses. Concurrently, the enzymeโs transphosphatidylase function facilitates the synthesis of (S,S)-BMP, a critical component of endolysosomal membranes necessary for lipid degradation and proper autophagic clearance. Localization studies have demonstrated that although PLD4 is predominantly situated in the endoplasmic reticulum, it dynamically traffics to compartments such as the Golgi apparatus and endolysosomes, particularly in immune effector cells like microglia and plasmacytoid dendritic cells. Expression analyses reveal that Pld4 is highly expressed in immune-related tissues including the spleen, with developmental regulation observed in the CNS. The evolutionary conservation of key structural features, including the HKD motifs and associated glycosylation sites, further underscores the fundamental nature of PLD4โs biochemical activities across species. Moreover, extensive experimental evidenceโfrom animal knockout studies that reveal lupus-like phenotypes to detailed in vitro assays and crystallographic studiesโcollectively supports PLD4โs central role in maintaining cellular homeostasis and immune regulation. Given its involvement in critical biological processes and disease pathways, PLD4 represents an important target for therapeutic intervention and a valuable candidate for comprehensive GO annotation efforts (akizuki2019pld4isa pages 12-16, gavin2018pld3andpld4 pages 1-2, singh2024pld3andpld4 pages 7-8, yoshikawa2010phospholipasedfamily pages 1-2, yoshikawa2010phospholipasedfamily pages 3-5, yuan2024structuralandmechanistic pages 29-31).
Future investigations should focus on refining our understanding of the substrate specificity determinants within the active site of PLD4, elucidating the regulatory networks that control its expression under both physiological and pathological conditions, and exploring the therapeutic potential of modulating its activity in autoimmune and inflammatory diseases. Improved high-resolution structural data, coupled with advanced genomic and proteomic approaches, will continue to shed light on the precise molecular interactions that underlie PLD4โs function in endolysosomal pathways, paving the way for novel strategies to manipulate its activity for clinical benefit (yuan2024structuralandmechanistic pages 14-17, yuan2024structuralandmechanistic pages 5-8, yoshikawa2010phospholipasedfamily pages 11-12). The integration of these multidisciplinary studies will ultimately enhance our capacity to annotate PLD4 within the Gene Ontology framework, ensuring that its contributions to nucleic acid metabolism, immune response modulation, and lipid homeostasis are accurately captured and integrated into broader biological knowledge bases (akizuki2019pld4isa pages 1-5, gavin2018pld3andpld4 pages 1-2).
In conclusion, the comprehensive body of literature on Pld4 in Mus musculus provides robust experimental support for its roles as a 5โฒโ3โฒ exonuclease and transphosphatidylase. These dual functions are pivotal not only for the regulation of innate immunityโby preventing the inappropriate activation of TLRs through the clearance of self nucleic acidsโbut also for the maintenance of lysosomal lipid integrity essential for proper organellar function. The detailed characterization of its subcellular localization, domain architecture, and expression dynamics further underscores the complexity and biological significance of PLD4. As research advances, continued efforts to resolve the nuances of PLD4โs enzymatic mechanisms and regulatory pathways will be essential for elucidating its full contribution to cellular physiology and disease etiology. Such insights promise to inform the development of innovative therapeutic strategies aimed at modulating its activity in the context of autoinflammatory and autoimmune disorders, making PLD4 a prominent focus for future biomedical research and GO annotation curation (akizuki2019pld4isa pages 12-16, gavin2018pld3andpld4 pages 1-2, yuan2024structuralandmechanistic pages 29-31, gavin2018pld3andpld4 pages 11-12, yuan2024structuralandmechanistic pages 5-8).
KeywordsโPld4; 5โฒโ3โฒ exonuclease; endolysosomal system; immune regulation; (S,S)-BMP synthesis; transphosphatidylase; subcellular localization; autoimmune diseases; Gene Ontology.
References
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(singh2024pld3andpld4 pages 5-7): Shubham Singh, Ulrich E. Dransfeld, Yohannes A. Ambaw, Joshua Lopez-Scarim, Robert V. Farese, and Tobias C. Walther. Pld3 and pld4 synthesize s,s-bmp, a key phospholipid enabling lipid degradation in lysosomes. Cell, 187:6820-6834.e24, Nov 2024. URL: https://doi.org/10.1016/j.cell.2024.09.036, doi:10.1016/j.cell.2024.09.036. This article has 29 citations and is from a highest quality peer-reviewed journal.
(singh2024pld3andpld4 pages 34-40): Shubham Singh, Ulrich E. Dransfeld, Yohannes A. Ambaw, Joshua Lopez-Scarim, Robert V. Farese, and Tobias C. Walther. Pld3 and pld4 synthesize s,s-bmp, a key phospholipid enabling lipid degradation in lysosomes. Cell, 187:6820-6834.e24, Nov 2024. URL: https://doi.org/10.1016/j.cell.2024.09.036, doi:10.1016/j.cell.2024.09.036. This article has 29 citations and is from a highest quality peer-reviewed journal.
(yuan2024structuralandmechanistic pages 1-5): Meng Yuan, Linghang Peng, Deli Huang, Amanda Gavin, Fangkun Luan, Jenny Tran, Ziqi Feng, Xueyong Zhu, Jeanne Matteson, Ian A. Wilson, and David Nemazee. Structural and mechanistic insights into disease-associated endolysosomal exonucleases pld3 and pld4. Structure, 32:766-779.e7, Jun 2024. URL: https://doi.org/10.1016/j.str.2024.02.019, doi:10.1016/j.str.2024.02.019. This article has 8 citations and is from a domain leading peer-reviewed journal.
(yoshikawa2010phospholipasedfamily pages 3-5): Fumio Yoshikawa, Yoshiko Banno, Yoshinori Otani, Yoshihide Yamaguchi, Yuko Nagakura-Takagi, Noriyuki Morita, Yumi Sato, Chihiro Saruta, Hirozumi Nishibe, Tetsushi Sadakata, Yo Shinoda, Kanehiro Hayashi, Yuriko Mishima, Hiroko Baba, and Teiichi Furuichi. Phospholipase d family member 4, a transmembrane glycoprotein with no phospholipase d activity, expression in spleen and early postnatal microglia. PLoS ONE, 5:e13932, Nov 2010. URL: https://doi.org/10.1371/journal.pone.0013932, doi:10.1371/journal.pone.0013932. This article has 54 citations and is from a peer-reviewed journal.
(yoshikawa2010phospholipasedfamily pages 8-10): Fumio Yoshikawa, Yoshiko Banno, Yoshinori Otani, Yoshihide Yamaguchi, Yuko Nagakura-Takagi, Noriyuki Morita, Yumi Sato, Chihiro Saruta, Hirozumi Nishibe, Tetsushi Sadakata, Yo Shinoda, Kanehiro Hayashi, Yuriko Mishima, Hiroko Baba, and Teiichi Furuichi. Phospholipase d family member 4, a transmembrane glycoprotein with no phospholipase d activity, expression in spleen and early postnatal microglia. PLoS ONE, 5:e13932, Nov 2010. URL: https://doi.org/10.1371/journal.pone.0013932, doi:10.1371/journal.pone.0013932. This article has 54 citations and is from a peer-reviewed journal.
(otani2011pld4isinvolved pages 8-10): Yoshinori Otani, Yoshihide Yamaguchi, Yumi Sato, Teiichi Furuichi, Kazuhiro Ikenaka, Hiroshi Kitani, and Hiroko Baba. Pld4 is involved in phagocytosis of microglia: expression and localization changes of pld4 are correlated with activation state of microglia. PLoS ONE, 6:e27544, Nov 2011. URL: https://doi.org/10.1371/journal.pone.0027544, doi:10.1371/journal.pone.0027544. This article has 50 citations and is from a peer-reviewed journal.
(yoshikawa2010phospholipasedfamily pages 2-3): Fumio Yoshikawa, Yoshiko Banno, Yoshinori Otani, Yoshihide Yamaguchi, Yuko Nagakura-Takagi, Noriyuki Morita, Yumi Sato, Chihiro Saruta, Hirozumi Nishibe, Tetsushi Sadakata, Yo Shinoda, Kanehiro Hayashi, Yuriko Mishima, Hiroko Baba, and Teiichi Furuichi. Phospholipase d family member 4, a transmembrane glycoprotein with no phospholipase d activity, expression in spleen and early postnatal microglia. PLoS ONE, 5:e13932, Nov 2010. URL: https://doi.org/10.1371/journal.pone.0013932, doi:10.1371/journal.pone.0013932. This article has 54 citations and is from a peer-reviewed journal.
(yoshikawa2010phospholipasedfamily pages 12-13): Fumio Yoshikawa, Yoshiko Banno, Yoshinori Otani, Yoshihide Yamaguchi, Yuko Nagakura-Takagi, Noriyuki Morita, Yumi Sato, Chihiro Saruta, Hirozumi Nishibe, Tetsushi Sadakata, Yo Shinoda, Kanehiro Hayashi, Yuriko Mishima, Hiroko Baba, and Teiichi Furuichi. Phospholipase d family member 4, a transmembrane glycoprotein with no phospholipase d activity, expression in spleen and early postnatal microglia. PLoS ONE, 5:e13932, Nov 2010. URL: https://doi.org/10.1371/journal.pone.0013932, doi:10.1371/journal.pone.0013932. This article has 54 citations and is from a peer-reviewed journal.
(gavin2018pld3andpld4 pages 11-12): Amanda L. Gavin, Deli Huang, Christoph Huber, Annica Mรฅrtensson, Virginie Tardif, Patrick D. Skog, Tanya R. Blane, Therese C. Thinnes, Kent Osborn, Hayley S. Chong, Farnaz Kargaran, Phoebe Kimm, Armen Zeitjian, Rachel L. Sielski, Megan Briggs, Sebastian R. Schulz, Alessandro Zarpellon, Benjamin Cravatt, Ee Shan Pang, John Teijaro, Juan Carlos de la Torre, Meredith OโKeeffe, Hubertus Hochrein, Markus Damme, Luc Teyton, Brian R. Lawson, and David Nemazee. Pld3 and pld4 are single-stranded acid exonucleases that regulate endosomal nucleic-acid sensing. Nature Immunology, 19:942-953, Aug 2018. URL: https://doi.org/10.1038/s41590-018-0179-y, doi:10.1038/s41590-018-0179-y. This article has 137 citations and is from a highest quality peer-reviewed journal.
(akizuki2019pld4isa pages 1-5): Shuji Akizuki, Kazuyoshi Ishigaki, Yuta Kochi, Sze-Ming Law, Keitaro Matsuo, Koichiro Ohmura, Akari Suzuki, Manabu Nakayama, Yusuke Iizuka, Haruhiko Koseki, Osamu Ohara, Jun Hirata, Yoichiro Kamatani, Fumihiko Matsuda, Takayuki Sumida, Kazuhiko Yamamoto, Yukinori Okada, Tsuneyo Mimori, and Chikashi Terao. Pld4 is a genetic determinant to systemic lupus erythematosus and involved in murine autoimmune phenotypes. Annals of the Rheumatic Diseases, 78:509-518, Apr 2019. URL: https://doi.org/10.1136/annrheumdis-2018-214116, doi:10.1136/annrheumdis-2018-214116. This article has 53 citations and is from a highest quality peer-reviewed journal.
(yuan2024structuralandmechanistic pages 5-8): Meng Yuan, Linghang Peng, Deli Huang, Amanda Gavin, Fangkun Luan, Jenny Tran, Ziqi Feng, Xueyong Zhu, Jeanne Matteson, Ian A. Wilson, and David Nemazee. Structural and mechanistic insights into disease-associated endolysosomal exonucleases pld3 and pld4. Structure, 32:766-779.e7, Jun 2024. URL: https://doi.org/10.1016/j.str.2024.02.019, doi:10.1016/j.str.2024.02.019. This article has 8 citations and is from a domain leading peer-reviewed journal.
(yuan2024structuralandmechanistic pages 14-17): Meng Yuan, Linghang Peng, Deli Huang, Amanda Gavin, Fangkun Luan, Jenny Tran, Ziqi Feng, Xueyong Zhu, Jeanne Matteson, Ian A. Wilson, and David Nemazee. Structural and mechanistic insights into disease-associated endolysosomal exonucleases pld3 and pld4. Structure, 32:766-779.e7, Jun 2024. URL: https://doi.org/10.1016/j.str.2024.02.019, doi:10.1016/j.str.2024.02.019. This article has 8 citations and is from a domain leading peer-reviewed journal.
(yoshikawa2010phospholipasedfamily pages 11-12): Fumio Yoshikawa, Yoshiko Banno, Yoshinori Otani, Yoshihide Yamaguchi, Yuko Nagakura-Takagi, Noriyuki Morita, Yumi Sato, Chihiro Saruta, Hirozumi Nishibe, Tetsushi Sadakata, Yo Shinoda, Kanehiro Hayashi, Yuriko Mishima, Hiroko Baba, and Teiichi Furuichi. Phospholipase d family member 4, a transmembrane glycoprotein with no phospholipase d activity, expression in spleen and early postnatal microglia. PLoS ONE, 5:e13932, Nov 2010. URL: https://doi.org/10.1371/journal.pone.0013932, doi:10.1371/journal.pone.0013932. This article has 54 citations and is from a peer-reviewed journal.
(OpenTargets Search: -Pld4): Open Targets Query (-Pld4, 3 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.
id: Q8BG07
gene_symbol: Pld4
taxon:
id: NCBITaxon:10090
label: Mus musculus
description: PLD4 is a multifunctional transmembrane enzyme that, despite its misleading name, lacks phospholipase D activity and instead functions as a 5'-3' exonuclease and transphosphatidylase. The protein degrades single-stranded DNA and RNA in endolysosomes to prevent inappropriate activation of TLR9 by self-derived mitochondrial DNA while enabling TLR7 activation by processing viral RNA. Additionally, PLD4 synthesizes bis(monoacylglycero)phosphate (BMP), a critical lipid component of lysosomal intralumenal vesicles essential for lipid degradation and autophagy. Predominantly localized to the ER membrane with dynamic trafficking to Golgi and endolysosomes, PLD4 plays crucial roles in immune regulation, preventing autoimmune responses, and maintaining endolysosomal homeostasis. In microglia, it participates in phagocytosis with characteristic redistribution from nucleus to phagosomes upon activation.
existing_annotations:
- term:
id: GO:0012505
label: endomembrane system
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: PLD4 is indeed localized to the endomembrane system, particularly the ER membrane and Golgi apparatus as confirmed by multiple studies (PMID:21085684, PMID:22102906). The IBA annotation correctly captures this broad cellular localization.
action: ACCEPT
reason: The endomembrane system annotation is well-supported by experimental evidence showing PLD4 localization to ER membrane, Golgi apparatus, and endolysosomes. This IBA annotation represents an appropriate level of specificity.
supported_by:
- reference_id: PMID:21085684
supporting_text: EGFP fluorescence formed a meshwork-like structure in the peripheral region of the nucleus in HEK293 cells... PLD4 immunoreactivity was co-localized with calnexin, an endoplasmic reticulum (ER) resident protein... and PLD4 expression also formed a clustered pattern with golgin 97, a trans-Golgi network protein
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0006909
label: phagocytosis
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: PLD4 participates in microglial phagocytosis and redistributes to phagosomes during activation, but phagocytosis is a cell-context phenotype rather than the main biochemical function of PLD4.
action: KEEP_AS_NON_CORE
reason: Falcon synthesis identifies PLD4 core activities as acidic endolysosomal 5-prime-to-3-prime exonuclease activity and S,S-BMP synthase/transphosphatidylase activity. Phagocytosis is retained as a supported non-core immune-cell process.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0002376
label: immune system process
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: PLD4 contributes to immune system processes through endolysosomal nucleic-acid and lipid metabolism, but this term is very broad.
action: KEEP_AS_NON_CORE
reason: 'More specific annotations capture the core biology: endolysosomal exonuclease activity, regulation of TLR9/TLR7 nucleic-acid sensing, and BMP synthesis. Retain this as a non-core umbrella process.'
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0003824
label: catalytic activity
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: PLD4 is catalytic, but the parent term catalytic activity is too general for curation. Direct evidence supports acidic 5-prime-to-3-prime exonuclease activity on ssDNA/ssRNA and S,S-BMP synthase/transphosphatidylase activity.
action: MODIFY
reason: Replace the generic parent with the specific activities supported by Falcon synthesis and primary biochemical work.
proposed_replacement_terms:
- id: GO:0045145
label: single-stranded DNA 5'-3' DNA exonuclease activity
- id: GO:0160121
label: bis(monoacylglycero)phosphate synthase activity
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
additional_reference_ids:
- PMID:30111894
- PMID:39423811
- term:
id: GO:0004518
label: nuclease activity
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: PLD4 does have nuclease activity, specifically functioning as a 5'-3' exonuclease on single-stranded DNA and RNA. This annotation is correct but could be more specific.
action: ACCEPT
reason: The nuclease activity annotation is correct. PLD4 functions as a 5'-3' exonuclease that degrades ssDNA and RNA. While more specific terms exist (GO:0004527 for exonuclease activity), this parent term is acceptable for an IEA annotation.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: 5'->3' exonuclease that hydrolyzes the phosphodiester bond of single-stranded DNA (ssDNA) and RNA molecules to form nucleoside 3'- monophosphates and 5'-end 5'-hydroxy deoxyribonucleotide/ribonucleotide fragments
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0004527
label: exonuclease activity
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: PLD4 has 5'-3' exonuclease activity on single-stranded DNA and RNA. This annotation is correct and represents a core molecular function.
action: ACCEPT
reason: The exonuclease activity annotation is accurate. PLD4 functions as a 5'-3' exonuclease that degrades ssDNA and RNA to produce nucleoside 3'-monophosphates.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: 5'->3' exonuclease that hydrolyzes the phosphodiester bond of single-stranded DNA (ssDNA) and RNA molecules to form nucleoside 3'- monophosphates
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0005634
label: nucleus
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: PLD4 shows some nuclear localization in microglia, particularly in resting state, but this is not its primary localization. It redistributes from nucleus to phagosomes upon activation.
action: KEEP_AS_NON_CORE
reason: While PLD4 can be found in the nucleus of resting microglia, this is a transient localization that changes with cell activation state. The primary localizations are ER membrane and endolysosomes.
supported_by:
- reference_id: PMID:22102906
supporting_text: Primary cultured microglia and the microglial cell line MG6 showed that PLD4 immuno-signals were mainly present in the nucleus, apart from the nucleolus
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0005764
label: lysosome
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: PLD4 localizes to lysosomes where it performs critical functions including nucleic acid degradation and BMP synthesis. This is a core localization.
action: ACCEPT
reason: Lysosomal localization is well-supported. PLD4 synthesizes BMP, the main phospholipid constituent of lysosomal intralumenal vesicle membranes, and degrades nucleic acids in the endolysosomal compartment.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: Can synthesize a variety of (S,S)-BMPs representing the main phospholipid constituent of lysosomal intralumenal vesicle (ILV) membranes that bind acid hydrolases for lipid degradation
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0005768
label: endosome
evidence_type: IEA
original_reference_id: GO_REF:0000117
review:
summary: PLD4 localizes to endosomes as part of the endolysosomal pathway where it processes nucleic acids for immune sensing. This is a core localization.
action: ACCEPT
reason: Endosomal localization is well-supported. PLD4 processes nucleic acids that reach the endolysosomal compartment and participates in immune surveillance.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: Processes self and pathogenic ssDNA and RNA molecules that reach the endolysosomal compartment via phagocytosis or autophagy
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0005769
label: early endosome
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: PLD4 localizes to transferrin-positive BioParticle-containing early phagosomes during microglial phagocytosis, not generic early endosomes.
action: MODIFY
reason: PMID:22102906 describes PLD4 in BioParticle-containing early phagosomes. Replace the generic early endosome component with the more precise early phagosome term.
proposed_replacement_terms:
- id: GO:0032009
label: early phagosome
supported_by:
- reference_id: PMID:22102906
supporting_text: The results suggest that PLD4 is predominantly present in early phagosomes
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0005789
label: endoplasmic reticulum membrane
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: PLD4 is predominantly localized to the ER membrane as confirmed by multiple studies. This is its primary subcellular localization and represents a core component.
action: ACCEPT
reason: ER membrane localization is well-established by experimental evidence. PLD4 is a transmembrane glycoprotein that resides primarily in the ER membrane.
supported_by:
- reference_id: PMID:21085684
supporting_text: PLD4 immunoreactivity was co-localized with calnexin, an endoplasmic reticulum (ER) resident protein
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0005794
label: Golgi apparatus
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: PLD4 localizes to the Golgi apparatus, particularly the trans-Golgi network, as shown by colocalization studies.
action: ACCEPT
reason: Golgi localization is supported by experimental evidence showing PLD4 colocalization with trans-Golgi network markers.
supported_by:
- reference_id: PMID:21085684
supporting_text: PLD4 expression also formed a clustered pattern with golgin 97, a trans-Golgi network protein
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0006259
label: DNA metabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000108
review:
summary: DNA metabolism via PLD4 exonuclease activity on ssDNA.
action: ACCEPT
reason: PLD4 degrades ssDNA in endolysosomes, contributing to nucleic acid metabolism.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: 5'->3' exonuclease that hydrolyzes the phosphodiester bond of single-stranded DNA (ssDNA) and RNA molecules to form nucleoside 3'- monophosphates
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0006629
label: lipid metabolic process
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: PLD4 synthesizes BMP lipids in lysosomes.
action: ACCEPT
reason: PLD4 catalyzes BMP synthesis, a lipid metabolic process in endolysosomes.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: Can synthesize a variety of (S,S)-BMPs representing the main phospholipid constituent of lysosomal intralumenal vesicle (ILV) membranes
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0006954
label: inflammatory response
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: PLD4 is linked to microglial activation and inflammatory contexts.
action: KEEP_AS_NON_CORE
reason: Inflammatory responses are context-dependent downstream outcomes of microglial activation.
supported_by:
- reference_id: PMID:22102906
supporting_text: Binding of antibodies to Fc receptors on the microglial surface induces phagocytosis activity in microglia, which is associated with inflammation
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0016787
label: hydrolase activity
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: Broad hydrolase annotation for PLD4 exonuclease activity.
action: ACCEPT
reason: PLD4 functions as a hydrolase through its exonuclease activity.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: 5'->3' exonuclease that hydrolyzes the phosphodiester bond of single-stranded DNA (ssDNA) and RNA molecules
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0031410
label: cytoplasmic vesicle
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: PLD4 associates with phagocytic vesicles in microglia.
action: KEEP_AS_NON_CORE
reason: Vesicular localization is context-dependent in activated microglia.
supported_by:
- reference_id: PMID:22102906
supporting_text: PLD4 immunoreactivity accumulated in phagosomes when BioParticles were added to primary microglial cultures
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0045087
label: innate immune response
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: PLD4 processes nucleic acids that act as innate immune danger signals.
action: ACCEPT
reason: PLD4 modulates innate immune receptor activation through nucleic acid processing.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: Processes self and pathogenic ssDNA and RNA molecules that reach the endolysosomal compartment via phagocytosis or autophagy and may serve as danger signals for recognition by innate immune receptors such as toll-like receptors (TLRs)
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0045145
label: single-stranded DNA 5'-3' DNA exonuclease activity
evidence_type: IEA
original_reference_id: GO_REF:0000117
review:
summary: PLD4 has 5'-3' exonuclease activity on single-stranded DNA. This is one of its core molecular functions, degrading ssDNA to produce nucleoside 3'-monophosphates.
action: ACCEPT
reason: This annotation correctly identifies PLD4's core exonuclease function. The protein degrades single-stranded DNA in a 5' to 3' direction, which is critical for preventing inappropriate TLR9 activation.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: 5'->3' exonuclease that hydrolyzes the phosphodiester bond of single-stranded DNA (ssDNA) and RNA molecules to form nucleoside 3'- monophosphates
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0045335
label: phagocytic vesicle
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: PLD4 localizes to phagocytic vesicles in microglia.
action: ACCEPT
reason: PLD4 accumulates in phagosomes during phagocytosis.
supported_by:
- reference_id: PMID:22102906
supporting_text: PLD4 immunoreactivity accumulated in phagosomes when BioParticles were added to primary microglial cultures
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:1900015
label: regulation of cytokine production involved in inflammatory response
evidence_type: IEA
original_reference_id: GO_REF:0000117
review:
summary: PLD4 loss or combined PLD3/PLD4 loss can alter cytokine and inflammatory outputs by changing endosomal nucleic-acid sensing, but cytokine regulation is downstream of the enzymatic function.
action: KEEP_AS_NON_CORE
reason: Falcon synthesis supports cytokine dysregulation as an immune consequence of defective endolysosomal nucleic-acid clearance. Retain as supported non-core biology rather than a core function.
additional_reference_ids:
- PMID:30111894
- PMID:34620855
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0004630
label: D-type glycerophospholipase activity
evidence_type: TAS
original_reference_id: Reactome:R-MMU-1483172
review:
summary: This is a positive Reactome annotation to phospholipase D activity, but experimental evidence shows PLD4 lacks authentic PLD activity.
action: REMOVE
reason: The GOA has a separate explicit NOT annotation for this term. The positive Reactome TAS row should be removed because PMID:21085684 directly refutes authentic phospholipase D activity for PLD4.
supported_by:
- reference_id: PMID:21085684
supporting_text: these results suggested that PLD4 is a HKD motif-containing protein family member that lacks authentic PLD activity
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0004630
label: D-type glycerophospholipase activity
evidence_type: IDA
original_reference_id: PMID:21085684
negated: true
review:
summary: This annotation has a NOT qualifier in the GOA file (line 24), indicating PLD4 does NOT have phospholipase D activity. This negative annotation correctly reflects that PLD4 lacks this activity despite its misleading name.
action: ACCEPT
reason: This is a negative annotation (NOT enables GO:0004630) that correctly documents the experimental finding that PLD4 lacks phospholipase D activity. The study explicitly tested and disproved PLD activity.
supported_by:
- reference_id: PMID:21085684
supporting_text: However, cell lysates transfected with PLD4 did not exhibit significant PLD activity, such as cells transfected with vector alone
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0005634
label: nucleus
evidence_type: IDA
original_reference_id: PMID:22102906
review:
summary: PLD4 is nuclear in resting microglia.
action: KEEP_AS_NON_CORE
reason: Nuclear localization is context-dependent and not the primary localization.
supported_by:
- reference_id: PMID:22102906
supporting_text: PLD4 immuno-signals were mainly present in the nucleus, apart from the nucleolus
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0005769
label: early endosome
evidence_type: IDA
original_reference_id: PMID:22102906
review:
summary: PLD4 accumulates in early phagosomes during microglial activation.
action: MODIFY
reason: The PMID:22102906 microscopy supports early phagosome localization. The existing early endosome term is less accurate because the transferrin-positive structures are BioParticle-containing phagosomes.
proposed_replacement_terms:
- id: GO:0032009
label: early phagosome
supported_by:
- reference_id: PMID:22102906
supporting_text: In the phagocytotic state eating BioParticles, PLD4 accumulated in the early phagosomes.
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0045145
label: single-stranded DNA 5'-3' DNA exonuclease activity
evidence_type: IMP
original_reference_id: PMID:22102906
review:
summary: The 2011 microglial paper does not itself biochemically demonstrate exonuclease activity, but the annotation is now directly supported by later biochemical and structural work showing PLD4 is a single-stranded DNA 5-prime-to-3-prime exonuclease.
action: REMOVE
reason: The term is correct for PLD4, but this specific PMID:22102906 IMP annotation is unsupported because that paper localized PLD4 in activated microglia and did not demonstrate exonuclease activity. The function is retained through the other ssDNA exonuclease annotation supported by PMID:30111894.
supported_by:
- reference_id: PMID:30111894
supporting_text: PLD4 degraded a 55 nt ssDNA
additional_reference_ids:
- PMID:30111894
- PMID:38537643
- term:
id: GO:0045335
label: phagocytic vesicle
evidence_type: IDA
original_reference_id: PMID:22102906
review:
summary: PLD4 accumulates in phagosomes during phagocytosis.
action: ACCEPT
reason: Direct microscopy shows PLD4 in phagosomes during microglial activation.
supported_by:
- reference_id: PMID:22102906
supporting_text: PLD4 immunoreactivity accumulated in phagosomes when BioParticles were added to primary microglial cultures
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:1900015
label: regulation of cytokine production involved in inflammatory response
evidence_type: IMP
original_reference_id: PMID:22102906
review:
summary: PLD4 loss or combined PLD3/PLD4 loss can alter cytokine and inflammatory outputs by changing endosomal nucleic-acid sensing, but cytokine regulation is downstream of the enzymatic function.
action: KEEP_AS_NON_CORE
reason: Falcon synthesis supports cytokine dysregulation as an immune consequence of defective endolysosomal nucleic-acid clearance. Retain as supported non-core biology rather than a core function.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
additional_reference_ids:
- PMID:30111894
- PMID:34620855
- term:
id: GO:0005789
label: endoplasmic reticulum membrane
evidence_type: IDA
original_reference_id: PMID:21085684
review:
summary: PLD4 localizes to the ER membrane.
action: ACCEPT
reason: Colocalization with ER markers supports ER membrane localization.
supported_by:
- reference_id: PMID:21085684
supporting_text: PLD4 immunoreactivity was co-localized with calnexin, an endoplasmic reticulum (ER) resident protein
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0032588
label: trans-Golgi network membrane
evidence_type: IDA
original_reference_id: PMID:21085684
review:
summary: PLD4 localizes to the trans-Golgi network.
action: ACCEPT
reason: Colocalization with golgin 97 supports trans-Golgi network localization.
supported_by:
- reference_id: PMID:21085684
supporting_text: PLD4 expression also formed a clustered pattern with golgin 97, a trans-Golgi network protein
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0002244
label: hematopoietic progenitor cell differentiation
evidence_type: IMP
original_reference_id: PMID:24029230
review:
summary: The cited publication is about Samd9l haploinsufficiency and myeloid malignancy, not a direct functional role of Pld4 in hematopoietic progenitor differentiation.
action: REMOVE
reason: No reviewed Pld4 literature or Falcon synthesis supports hematopoietic progenitor differentiation as a Pld4 function. This appears to be an erroneous or indirect annotation and should be removed.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0005783
label: endoplasmic reticulum
evidence_type: IDA
original_reference_id: PMID:21085684
review:
summary: PLD4 localizes to the ER.
action: ACCEPT
reason: ER localization is supported by colocalization with ER markers.
supported_by:
- reference_id: PMID:21085684
supporting_text: PLD4 immunoreactivity was co-localized with calnexin, an endoplasmic reticulum (ER) resident protein
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0006909
label: phagocytosis
evidence_type: IMP
original_reference_id: PMID:22102906
review:
summary: PLD4 participates in microglial phagocytosis and redistributes to phagosomes during activation, but phagocytosis is a cell-context phenotype rather than the main biochemical function of PLD4.
action: KEEP_AS_NON_CORE
reason: Falcon synthesis identifies PLD4 core activities as acidic endolysosomal 5-prime-to-3-prime exonuclease activity and S,S-BMP synthase/transphosphatidylase activity. Phagocytosis is retained as a supported non-core immune-cell process.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0005789
label: endoplasmic reticulum membrane
evidence_type: TAS
original_reference_id: Reactome:R-MMU-1483172
review:
summary: ER membrane localization in agreement with experimental evidence.
action: ACCEPT
reason: PLD4 localizes to the ER membrane based on colocalization studies.
supported_by:
- reference_id: PMID:21085684
supporting_text: PLD4 immunoreactivity was co-localized with calnexin, an endoplasmic reticulum (ER) resident protein
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:18706977
review:
summary: Generic protein binding annotation is uninformative.
action: REMOVE
reason: Protein binding is too general to be useful for PLD4 function.
supported_by:
- reference_id: PMID:18706977
supporting_text: Interaction assays in yeast and cultured cells confirm known and identify novel partners of the synaptic vesicle protein synaptophysin.
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
- term:
id: GO:0036019
label: endolysosome
evidence_type: NAS
review:
summary: PLD4 carries out its nuclease and BMP-synthase functions in endolysosomal/lysosomal compartments.
action: NEW
reason: Endolysosomal localization is directly tied to acidic-pH catalytic activity and nucleic-acid/lipid substrate availability.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
additional_reference_ids:
- PMID:30111894
- PMID:39423811
- term:
id: GO:0034164
label: negative regulation of toll-like receptor 9 signaling pathway
evidence_type: NAS
review:
summary: PLD4 degrades endolysosomal self ssDNA, including mitochondrial CpG-rich DNA, thereby limiting inappropriate TLR9 activation.
action: NEW
reason: This is a direct biological consequence of the core exonuclease function and is well supported by Falcon synthesis and primary PLD3/PLD4 studies.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
additional_reference_ids:
- PMID:30111894
- PMID:34620855
- term:
id: GO:0160121
label: bis(monoacylglycero)phosphate synthase activity
evidence_type: NAS
review:
summary: Falcon synthesis and the 2024 Cell study support PLD4 as an S,S-BMP synthase/transphosphatidylase in lysosomes.
action: NEW
reason: This specific molecular function is directly supported by purified enzyme and tissue lipidomic evidence and is not represented by the older broad catalytic-activity annotation.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
additional_reference_ids:
- PMID:39423811
- term:
id: GO:2001312
label: lysobisphosphatidic acid biosynthetic process
evidence_type: NAS
review:
summary: PLD4-dependent S,S-BMP synthesis supports lysobisphosphatidic acid/BMP biosynthesis in lysosomes.
action: NEW
reason: The 2024 Falcon report and Cell study support this NEW process term as a direct consequence of PLD4 BMP synthase activity.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
additional_reference_ids:
- PMID:39423811
- term:
id: GO:0004534
label: 5'-3' RNA exonuclease activity
evidence_type: NAS
review:
summary: PLD4 has single-stranded RNA exonuclease activity and can shape endosomal TLR7-dependent antiviral sensing outputs.
action: NEW
reason: Direct PLD3/PLD4 nuclease studies support RNA cleavage and altered nucleic-acid sensor activation. Retain as conservative NEW support for the RNA/TLR7 arm of PLD4 biology.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: '[Falcon deep-research synthesis used for this annotation decision.]'
additional_reference_ids:
- PMID:34620855
- PMID:38537643
- term:
id: GO:0034122
label: negative regulation of toll-like receptor signaling pathway
evidence_type: NAS
review:
summary: PLD4/PLD3 ssRNA degradation limits inappropriate endosomal nucleic-acid-sensor activation and resulting autoinflammation.
action: NEW
reason: The accessible RNA nuclease evidence supports negative regulation of TLR/nucleic-acid sensor activation from accumulated self ssRNA, not direct positive TLR7 signaling or antiviral defense.
supported_by:
- reference_id: PMID:34620855
supporting_text: Pld3-/-Pld4-/- mice accumulate small ssRNAs and develop spontaneous fatal hemophagocytic lymphohistiocytosis
additional_reference_ids:
- PMID:34620855
- PMID:38537643
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: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:0000108
title: Automatic assignment of GO terms using logical inference, based on on inter-ontology links.
findings: []
- id: GO_REF:0000117
title: Electronic Gene Ontology annotations created by ARBA machine learning models
findings: []
- id: GO_REF:0000120
title: Combined Automated Annotation using Multiple IEA Methods.
findings: []
- id: PMID:18706977
title: Interaction assays in yeast and cultured cells confirm known and identify novel partners of the synaptic vesicle protein synaptophysin.
findings: []
- id: PMID:21085684
title: Phospholipase D family member 4, a transmembrane glycoprotein with no phospholipase D activity, expression in spleen and early postnatal microglia.
findings: []
- id: PMID:22102906
title: 'PLD$ is involved in phagocytosis of microglia: expression and localization changes of PLD4 are correlated with activation state of microglia.'
findings: []
- id: PMID:24029230
title: Haploinsufficiency of SAMD9L, an endosome fusion facilitator, causes myeloid malignancies in mice mimicking human diseases with monosomy 7.
findings: []
- id: Reactome:R-MMU-1483172
title: PC is transphosphatidylated to PG by Pld1-4/6
findings: []
- id: file:mouse/Pld4/Pld4-deep-research-falcon.md
title: Falcon deep research report on mouse Pld4 function
findings: []
- id: PMID:30111894
title: PLD3 and PLD4 are single-stranded acid exonucleases that regulate endosomal nucleic-acid sensing.
findings: []
- id: PMID:34620855
title: Cleavage of DNA and RNA by PLD3 and PLD4 limits autoinflammatory triggering by multiple sensors.
findings: []
- id: PMID:38537643
title: Structural and mechanistic insights into disease-associated endolysosomal exonucleases PLD3 and PLD4.
findings: []
- id: PMID:39423811
title: PLD3 and PLD4 synthesize S,S-BMP, a key phospholipid enabling lipid degradation in lysosomes.
findings: []
core_functions:
- description: PLD4 degrades single-stranded DNA via acidic 5-prime-to-3-prime exonuclease activity in endolysosomes, preventing inappropriate TLR9 activation by self-derived DNA.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: 5'->3' exonuclease that hydrolyzes the phosphodiester bond of single-stranded DNA (ssDNA) and RNA molecules to form nucleoside 3'- monophosphates. Degrades mitochondrial CpG-rich ssDNA fragments to prevent TLR9 activation and autoinflammatory response
molecular_function:
id: GO:0045145
label: single-stranded DNA 5'-3' DNA exonuclease activity
directly_involved_in:
- id: GO:0034164
label: negative regulation of toll-like receptor 9 signaling pathway
- id: GO:0045087
label: innate immune response
- id: GO:0006259
label: DNA metabolic process
locations:
- id: GO:0036019
label: endolysosome
- id: GO:0005764
label: lysosome
- id: GO:0005768
label: endosome
substrates:
- id: CHEBI:9160
label: single-stranded DNA
- description: PLD4 synthesizes S,S-bis(monoacylglycero)phosphate (BMP) in lysosomes through transphosphatidylation/stereo-inversion chemistry, supporting lysosomal lipid degradation.
supported_by:
- reference_id: file:mouse/Pld4/Pld4-deep-research-falcon.md
supporting_text: Transphosphatidylase that catalyzes the exchange with R to S stereo-inversion of the glycerol moiety between (S,R)-lysophosphatidylglycerol (LPG) and monoacylglycerol (MAG) substrates to yield (S,S)-bis(monoacylglycero)phosphate (BMP)
molecular_function:
id: GO:0160121
label: bis(monoacylglycero)phosphate synthase activity
directly_involved_in:
- id: GO:2001312
label: lysobisphosphatidic acid biosynthetic process
- id: GO:0006629
label: lipid metabolic process
locations:
- id: GO:0005764
label: lysosome
- id: GO:0036019
label: endolysosome
substrates:
- id: CHEBI:64716
label: 1,2-diacyl-sn-glycero-3-phospho-(1'-sn-glycerol)(1-)
- id: CHEBI:17408
label: monoacylglycerol
- description: PLD4 also cleaves single-stranded RNA in endolysosomes, limiting inappropriate TLR-dependent inflammatory activation by accumulated self ssRNAs.
supported_by:
- reference_id: PMID:34620855
supporting_text: Pld3-/-Pld4-/- mice accumulate small ssRNAs and develop spontaneous fatal hemophagocytic lymphohistiocytosis
molecular_function:
id: GO:0004534
label: 5'-3' RNA exonuclease activity
directly_involved_in:
- id: GO:0034122
label: negative regulation of toll-like receptor signaling pathway
- id: GO:0045087
label: innate immune response
locations:
- id: GO:0036019
label: endolysosome
- id: GO:0005768
label: endosome
substrates:
- id: CHEBI:33697
label: ribonucleic acid
- id: CHEBI:33696
label: nucleic acid
status: COMPLETE