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Question

Gene Research for Functional Annotation

⚠️ CRITICAL: Gene/Protein Identification Context

BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.

Target Gene/Protein Identity (from UniProt):

• UniProt Accession: Q8N7P1
• Protein Description: RecName: Full=Inactive phospholipase D5; Short=Inactive PLD 5; AltName: Full=Inactive choline phosphatase 5; AltName: Full=Inactive phosphatidylcholine-hydrolyzing phospholipase D5; AltName: Full=PLDc;
• Gene Information: Name=PLD5;
• Organism (full): Homo sapiens (Human).
• Protein Family: Belongs to the phospholipase D family. .
• Key Domains: Diverse_PLD-related. (IPR050874); PLDc_3. (IPR032803); PLipase_D/transphosphatidylase. (IPR001736); PLDc_3 (PF13918)

MANDATORY VERIFICATION STEPS:

1. Check if the gene symbol "PLD5" matches the protein description above
2. Verify the organism is correct: Homo sapiens (Human).
3. Check if protein family/domains align with what you find in literature
4. If you find literature for a DIFFERENT gene with the same or similar symbol, STOP

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'PLD5' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information

Research Target:

Please provide a comprehensive research report on the gene PLD5 (gene ID: PLD5, UniProt: Q8N7P1) in human.

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this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.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.

Output

PLD5 (Phospholipase D Family Member 5): A Comprehensive Review

Introduction and Summary

Phospholipase D family member 5 (PLD5), encoded by the PLD5 gene located on human chromosome 1q43, represents an enigmatic member of the phospholipase D superfamily. Despite its classification within a family of enzymes that typically catalyze the hydrolysis of phosphatidylcholine to phosphatidic acid and choline, PLD5 is designated as an "inactive" phospholipase due to nonconservative substitutions in its putative catalytic site that render it very unlikely to possess canonical phospholipase D enzymatic activity [stutchfield-2015-pld-roles-abstract]. The protein is alternatively known as Inactive phospholipase D5, Inactive PLD 5, Inactive choline phosphatase 5, and PLDc [ncbi-gene-200150-summary]. Definitive cellular and physiological roles for PLD5 have not yet been established, making it one of the least characterized members of the mammalian PLD family [stutchfield-2015-pld-roles-abstract].

The PLD5 gene spans approximately 450 kilobases on chromosome 1q43 (coordinates 242,082,986–242,530,546 on the complement strand of GRCh38.p14) and contains 21 exons that give rise to at least four validated transcript isoforms [ncbi-gene-200150-summary]. The encoded protein contains two putative catalytic domain repeats characteristic of the phospholipase D superfamily (PLDc_vPLD5_1 and PLDc_vPLD5_2), yet lacks the phosphatidylinositol-binding PX (phox homology) and PH (pleckstrin homology) domains that are essential for the membrane interactions and regulatory functions of the catalytically active classical PLDs, PLD1 and PLD2 [becconcino-2014-pld-signaling-abstract].

The Phospholipase D Family Context

Understanding PLD5 requires placing it within the broader context of the phospholipase D superfamily. In mammals, six PLD isoforms have been identified (PLD1 through PLD6), which can be classified into "classical" and "non-classical" categories based on their domain architecture and enzymatic activities [becconcino-2014-pld-signaling-abstract]. The classical PLDs, PLD1 and PLD2, share approximately 57% amino acid conservation and possess the full complement of regulatory domains including tandem PX and PH domains that govern membrane localization and activity regulation, along with two HKD catalytic motifs that combine to form a functional active site [stutchfield-2015-pld-roles-abstract]. These enzymes catalyze the hydrolysis of phosphatidylcholine to generate phosphatidic acid, a bioactive lipid second messenger with diverse downstream signaling effects, and choline, the precursor for the neurotransmitter acetylcholine.

The non-classical PLDs (PLD3, PLD4, PLD5, and PLD6) all lack the PX and PH domains characteristic of the classical isoforms [becconcino-2014-pld-signaling-abstract]. PLD3, PLD4, and PLD5 retain two HKD motifs, while PLD6 (also known as MitoPLD) possesses only one. Among the mammalian PLD isoforms, only PLD1, PLD2, and PLD6 have been demonstrated to possess lipase activity [becconcino-2014-pld-signaling-abstract]. The lack of lipase activity in PLD3 and PLD4 cannot be attributed solely to the absence of PX and PH domains, since PLD6 also lacks these domains yet remains enzymatically active upon dimerization.

A paradigm-shifting discovery revealed that PLD3 and PLD4, despite their classification as phospholipases, actually function as 5' exonucleases that degrade single-stranded DNA in the acidic environment of endolysosomes [gavin-2018-pld3-pld4-exonuclease-abstract]. These enzymes regulate Toll-like receptor 9 (TLR9) signaling by degrading its nucleic acid ligands, and loss of function leads to autoinflammatory disease in mice [gavin-2018-pld3-pld4-exonuclease-abstract]. This functional repurposing within the PLD superfamily raises important questions about whether PLD5 might similarly possess an unexpected enzymatic activity unrelated to phospholipid hydrolysis.

Structural Features and Catalytic Inactivity

The defining characteristic of PLD5 is its predicted lack of phospholipase D enzymatic activity. The PLD5 protein consists of 506 amino acids and contains two putative PLDc catalytic domains [zhang-2024-pld-neurodegenerative-abstract]. Sequence analysis has revealed that PLD5 contains nonconservative substitutions in its putative catalytic site that make it very unlikely to be enzymatically active as a phospholipase [stutchfield-2015-pld-roles-abstract]. Specifically, PLD5 lacks critical residues including the first catalytic motif's histidine and the second motif's histidine that are essential for the catalytic mechanism [zhang-2024-pld-neurodegenerative-abstract]. The HKD motif (HxKx4D), which forms the catalytic core of active PLDs, is not well conserved in PLD5 compared to its paralogues [becconcino-2014-pld-signaling-abstract].

Structural studies of PLD4, a related family member, have provided insights into the molecular basis of catalytic inactivity in non-classical PLDs [voshol-2010-pld4-transmembrane-abstract]. In PLD4, several alterations disable catalytic function: modified HKD motifs with critical sequence differences, altered hydrophobic patches containing aromatic amino acids (Phe, Trp, Tyr) instead of conserved hydrophobic residues essential for catalysis, substitution of GT for the GS motif found in functional enzymes, and altered active site geometry relative to enzymatically active family members [voshol-2010-pld4-transmembrane-abstract]. Cell lysates transfected with PLD4 did not exhibit significant PLD activity in either choline release or transphosphatidylation assays under various pH conditions [voshol-2010-pld4-transmembrane-abstract]. PLD5 is noted to contain "less conserved sequences in the HKD motifs" than even PLD4, suggesting even more extensive divergence from the catalytically competent ancestral sequence [voshol-2010-pld4-transmembrane-abstract].

While PLD3 and PLD4 have been shown to function as 5' exonucleases, whether PLD5 possesses any enzymatic activity, phospholipase-related or otherwise, remains an open question. The more extensive divergence of PLD5's catalytic motifs compared to PLD3 and PLD4 may indicate that PLD5 has lost all enzymatic function, or alternatively, that it has acquired an as-yet-undiscovered novel activity.

Expression Patterns and Tissue Distribution

PLD5 exhibits a highly restricted expression pattern that distinguishes it from other family members. According to data from the Human Protein Atlas, PLD5 shows remarkably concentrated expression with the highest levels observed in the choroid plexus (26.1 nTPM), followed by blood vessels (10.5 nTPM) and the cerebellum (7.0 nTPM) [human-protein-atlas-pld5-summary]. The protein is classified as "group enriched" across blood vessel, brain, and choroid plexus tissues, with a tau specificity score of 0.84 indicating high tissue specificity [human-protein-atlas-pld5-summary]. This pattern places PLD5 among genes detected in only some tissues rather than showing widespread distribution.

The NCBI Gene database reports that during fetal development, PLD5 expression is highest in adrenal tissue (0.532 RPKM at 10 weeks), with moderate expression in stomach tissue and low expression in heart, lung, kidney, and intestine [ncbi-gene-200150-summary]. The enrichment of PLD5 in choroid plexus, a specialized brain structure responsible for cerebrospinal fluid production and the blood-CSF barrier, is particularly intriguing given the gene's reported association with neuropsychiatric disorders.

PLD5 has been assigned to the "Choroid plexus - Transmembrane transport" expression cluster in the Human Protein Atlas, suggesting potential involvement in transport-related processes [human-protein-atlas-pld5-summary]. A 2024 review additionally reported PLD5 expression in liver, spleen, brain, and lymph nodes [zhang-2024-pld-neurodegenerative-abstract], which partially overlaps with but extends the Human Protein Atlas findings. This functional classification is consistent with the prediction that PLD5 is membrane-localized, although the specific transport functions, if any, remain to be characterized.

Subcellular Localization

The subcellular localization of PLD5 has been investigated through multiple approaches, though some discrepancies exist between studies. Immunocytochemistry studies using confocal microscopy have localized PLD5 to the mitochondria, with this localization receiving an "approved" reliability score based on experiments with the validated antibody HPA028389 [human-protein-atlas-pld5-summary]. This finding was corroborated by a 2024 study examining all six mammalian PLD family members, which demonstrated that when expressed in HMC3 cells, PLD5 and PLD6 both localized to mitochondria, in contrast to PLD1, PLD3, and PLD4 which localized to lysosomes, and PLD2 which localized to the plasma membrane [singh-2024-pld3-pld4-bmp-abstract].

However, some sources report alternative localizations for PLD5. A 2024 review described PLD5 as localizing to the endoplasmic reticulum and Golgi apparatus [zhang-2024-pld-neurodegenerative-abstract], while earlier literature also reported PLD5 as a cytoplasmic protein [becconcino-2014-pld-signaling-abstract]. These discrepancies could reflect cell-type specific differences in PLD5 localization, methodological variations between studies, or the protein's potential trafficking through multiple compartments.

The mitochondrial localization of PLD5 is noteworthy in the context of the PLD family, as PLD6 (MitoPLD) is also anchored to the outer mitochondrial membrane where it plays roles in mitochondrial dynamics and the generation of piwi-interacting RNAs [becconcino-2014-pld-signaling-abstract]. However, while PLD6 has demonstrated phospholipase activity toward cardiolipin on the mitochondrial surface, no such activity has been demonstrated for PLD5. Importantly, the 2024 Cell study investigating BMP synthesis found that PLD5 did not localize to lysosomes and did not participate in the lysosomal BMP synthesis pathway that PLD3 and PLD4 catalyze [singh-2024-pld3-pld4-bmp-abstract], further distinguishing PLD5 functionally from its closest paralogues.

Disease Associations

Despite the lack of established enzymatic function, PLD5 has been implicated in several disease contexts through genetic association studies, suggesting that the protein serves biologically important functions.

Neuropsychiatric Disorders

PLD5 is perhaps most widely known for its potential correlation with neuropsychiatric disorders [stutchfield-2015-pld-roles-abstract]. The Autism Genome Project, which genotyped 1,558 rigorously defined autism spectrum disorder (ASD) families for one million SNPs, identified PLD5 among genes showing strong association signals in exploratory analyses of phenotypic subtypes [stutchfield-2015-pld-roles-abstract]. While these signals did not reach genome-wide significance after correction for multiple testing, a SNP in the PLD5 gene has been reported to correlate with verbal performance in autism patients [becconcino-2014-pld-signaling-abstract]. The enriched expression of PLD5 in choroid plexus and cerebellum provides biological plausibility for a role in neurodevelopment or brain function.

Uterine Fibroids

Association mapping studies have linked PLD5 to uterine fibroid (leiomyoma) risk and growth. A study examining genetic associations across a two-megabase interval on chromosome 1q43 in 1,152 premenopausal women identified several association peaks with fibroid development, with PLD5 emerging among genes acting in signal transduction that appeared to affect tumor growth [aissani-2013-fibroids-1q43-abstract]. PLD5 is located near other candidate genes on 1q43 including FH (fumarate hydratase), EXO1, MAP1LC3C, and RGS7 [aissani-2013-fibroids-1q43-abstract]. The proximity to FH is noteworthy as mutations in this gene cause hereditary leiomyomatosis and renal cell carcinoma syndrome.

Cancer

PLD5 has been implicated in prostate cancer progression. A study found that PLD5 overexpression exerted oncogenic effects, promoting cell proliferation, migration, invasion, and metastasis in prostate cancer cells [liu-2021-mir145-pld5-prostate-abstract]. The microRNA miR-145-5p was identified as a direct regulator of PLD5 that reverses these oncogenic effects; upregulation of miR-145-5p increased apoptosis and repressed the malignant phenotype through PLD5 suppression [liu-2021-mir145-pld5-prostate-abstract]. This finding suggests that despite lacking classical phospholipase activity, PLD5 participates in signaling pathways relevant to cancer biology.

Other GWAS Associations

According to the NCBI Gene database, PLD5 has been associated through GWAS with several additional phenotypes including drug response variation, coronary artery calcification, tuberculosis risk, immunoglobulin glycosylation, and childhood obesity [ncbi-gene-200150-summary]. The breadth of these associations, spanning metabolic, immune, and cardiovascular domains, suggests that PLD5 may influence fundamental cellular processes with pleiotropic effects.

Mouse Knockout Phenotypes

Mice lacking PLD5 have been generated and phenotyped by the International Mouse Phenotyping Consortium (IMPC). Initial reports indicated that no significant abnormalities were observed in high-throughput phenotypic screens [becconcino-2014-pld-signaling-abstract]. However, more detailed IMPC data from standardized phenotyping pipelines testing 20 of 24 physiological systems identified 6 significant phenotypes, with effects observed in homeostasis/metabolism, growth/size/body region, hematopoietic system, and skeletal system [impc-pld5-knockout-summary].

Importantly, no significant phenotypes were detected in 16 other systems including the nervous system, behavior/neurological measures, immune system, cardiovascular system, and reproductive system [impc-pld5-knockout-summary]. The absence of overt neurological phenotypes in PLD5 knockout mice may seem inconsistent with the human genetic associations with autism, but this could reflect species differences, genetic redundancy, or subtle phenotypes not captured by standard behavioral assays. Notably, no associated human diseases are currently documented in the IMPC database for PLD5 [impc-pld5-knockout-summary].

Potential Functions and Mechanisms

Given the lack of phospholipase D activity and the absence of demonstrated alternative enzymatic function, the molecular mechanisms by which PLD5 might influence the disease phenotypes with which it has been associated remain speculative. Several possibilities warrant consideration.

First, PLD5 might function as a scaffolding or regulatory protein independent of any enzymatic activity. The protein retains the overall fold of the PLD catalytic domain, which could serve as a protein-protein interaction interface even if catalysis is abolished. Such non-enzymatic functions have been demonstrated for other "dead" enzyme homologs across various protein families.

Second, the close evolutionary relationship between PLD5 and the nuclease-active PLD3/PLD4 raises the possibility that PLD5 retains some form of nucleic acid-related function, perhaps as a sensor or regulator rather than an enzyme. However, no experimental evidence currently supports this hypothesis.

Third, the mitochondrial localization of PLD5 suggests potential roles in mitochondrial function, dynamics, or signaling that could account for the metabolic and growth-related phenotypes observed in knockout mice. The relationship to the mitochondrial-localized PLD6 warrants investigation.

Fourth, PLD5's expression in the choroid plexus suggests potential roles in cerebrospinal fluid production, blood-CSF barrier function, or brain homeostasis that could be relevant to its association with neuropsychiatric disorders.

Open Questions

Several important questions remain regarding PLD5 biology:

1. Does PLD5 possess any enzymatic activity? While phospholipase D activity is unlikely, the protein has not been systematically tested for alternative activities such as nuclease function (by analogy to PLD3/PLD4), transphosphatidylation with alternative substrates, or entirely novel catalytic activities.

2. What are the structural features of PLD5? No crystal structure or cryo-EM structure of PLD5 has been reported. Structural analysis would reveal whether the protein adopts the canonical PLD fold and identify any unique features that might suggest function.

3. What proteins interact with PLD5? Systematic interactome studies could identify binding partners that would illuminate PLD5's cellular role, whether enzymatic or non-enzymatic.

4. Why is PLD5 enriched in the choroid plexus? The striking expression pattern suggests a specialized function in this tissue that merits investigation.

5. What is the molecular basis for the GWAS associations? The mechanisms by which PLD5 variants influence autism risk, fibroid development, prostate cancer progression, and other phenotypes remain unknown.

6. Does PLD5 have redundant functions with other family members? The relatively mild phenotypes in knockout mice could reflect compensation by PLD3, PLD4, or other proteins.

7. What are the precise catalytic site mutations? A detailed sequence comparison of the HKD motifs across all PLD family members, with structural modeling, would define exactly which residues are altered in PLD5 and predict whether any residual activity is possible.

8. Is PLD5 expression or function altered in disease states? Beyond genetic association, expression changes or post-translational modifications of PLD5 in neuropsychiatric disorders, fibroids, or cancer have not been characterized.

References

1. [stutchfield-2015-pld-roles-abstract] Stutchfield BM, Bhinder T, Horgan PG. Physiological and pathophysiological roles for phospholipase D. Journal of Lipid Research. 2015. PMID: 26637523, PMCID: PMC4655994, DOI: 10.1194/jlr.R056705

2. [liu-2021-mir145-pld5-prostate-abstract] Liu J, Li J, Ma Y, Xu C, Wang Y, He Y. MicroRNA miR-145-5p inhibits Phospholipase D 5 (PLD5) to downregulate cell proliferation and metastasis to mitigate prostate cancer. Bioengineered. 2021;12(1):3240-3251. PMID: 34238129, DOI: 10.1080/21655979.2021.1945361

3. [aissani-2013-fibroids-1q43-abstract] Aissani B, Wiener H, Zhang K. Multiple hits for the association of uterine fibroids on human chromosome 1q43. PLoS One. 2013;8(3):e58399. PMID: 23555580, DOI: 10.1371/journal.pone.0058399

4. [gavin-2018-pld3-pld4-exonuclease-abstract] Gavin AL, Huang D, Huber C, et al. PLD3 and PLD4 are single stranded acid exonucleases that regulate endosomal nucleic acid sensing. Nature Immunology. 2018;19(9):942-953. PMID: 30111894, PMCID: PMC6105523, DOI: 10.1038/s41590-018-0179-y

5. [voshol-2010-pld4-transmembrane-abstract] Voshol H, Strang AM, Bhathena A, et al. Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia. PLoS One. 2010;5(11):e13932. PMID: 21085682, PMCID: PMC2978679, DOI: 10.1371/journal.pone.0013932

6. [becconcino-2014-pld-signaling-abstract] Phospholipase D in Cell Signaling: From a Myriad of Cell Functions to Cancer Growth and Metastasis. Molecular and Cellular Biology. 2014. PMCID: PMC4132763

7. [ncbi-gene-200150-summary] NCBI Gene Entry for PLD5. Gene ID: 200150. URL: https://www.ncbi.nlm.nih.gov/gene/200150

8. [human-protein-atlas-pld5-summary] Human Protein Atlas Entry for PLD5. Gene ID: ENSG00000180287. URLs: https://www.proteinatlas.org/ENSG00000180287-PLD5/tissue and https://www.proteinatlas.org/ENSG00000180287-PLD5/subcellular

9. [impc-pld5-knockout-summary] International Mouse Phenotyping Consortium. Pld5 Knockout Mouse Phenotype Data. MGI ID: MGI:2442056. URL: https://www.mousephenotype.org/data/genes/MGI:2442056

10. UniProt Entry Q8N7P1 - Inactive phospholipase D5 [Homo sapiens]. URL: https://www.uniprot.org/uniprotkb/Q8N7P1/entry

11. [singh-2024-pld3-pld4-bmp-abstract] Singh S, Dransfeld U, Ambaw Y, Lopez-Scarim J, Farese RV Jr, Walther TC. PLD3 and PLD4 synthesize S,S-BMP, a key phospholipid enabling lipid degradation in lysosomes. Cell. 2024;187(22):6261-6277.e22. PMID: 38562702, DOI: 10.1016/j.cell.2024.08.042

12. [zhang-2024-pld-neurodegenerative-abstract] Zhang et al. Phospholipase D, a Novel Therapeutic Target Contributes to the Pathogenesis of Neurodegenerative and Neuroimmune Diseases. Analytical Cellular Pathology. 2024. PMCID: PMC10940030, DOI: 10.1155/2024/6681911

Citations

1. aissani-2013-fibroids-1q43-abstract.md
2. becconcino-2014-pld-signaling-abstract.md
3. gavin-2018-pld3-pld4-exonuclease-abstract.md
4. human-protein-atlas-pld5-summary.md
5. impc-pld5-knockout-summary.md
6. liu-2021-mir145-pld5-prostate-abstract.md
7. ncbi-gene-200150-summary.md
8. singh-2024-pld3-pld4-bmp-abstract.md
9. stutchfield-2015-pld-roles-abstract.md
10. voshol-2010-pld4-transmembrane-abstract.md
11. zhang-2024-pld-neurodegenerative-abstract.md

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Question

Gene Research for Functional Annotation

⚠️ CRITICAL: Gene/Protein Identification Context

BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.

Target Gene/Protein Identity (from UniProt):

• UniProt Accession: Q8N7P1
• Protein Description: RecName: Full=Inactive phospholipase D5; Short=Inactive PLD 5; AltName: Full=Inactive choline phosphatase 5; AltName: Full=Inactive phosphatidylcholine-hydrolyzing phospholipase D5; AltName: Full=PLDc;
• Gene Information: Name=PLD5;
• Organism (full): Homo sapiens (Human).
• Protein Family: Belongs to the phospholipase D family. .
• Key Domains: Diverse_PLD-related. (IPR050874); PLDc_3. (IPR032803); PLipase_D/transphosphatidylase. (IPR001736); PLDc_3 (PF13918)

MANDATORY VERIFICATION STEPS:

1. Check if the gene symbol "PLD5" matches the protein description above
2. Verify the organism is correct: Homo sapiens (Human).
3. Check if protein family/domains align with what you find in literature
4. If you find literature for a DIFFERENT gene with the same or similar symbol, STOP

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'PLD5' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information

Research Target:

Please provide a comprehensive research report on the gene PLD5 (gene ID: PLD5, UniProt: Q8N7P1) in human.

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.

Output

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on:
1. Key concepts and definitions with current understanding
2. Recent developments and latest research (prioritize 2023-2024 sources)
3. Current applications and real-world implementations
4. Expert opinions and analysis from authoritative sources
5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available.
Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Gene Research for Functional Annotation

⚠️ CRITICAL: Gene/Protein Identification Context

BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.

Target Gene/Protein Identity (from UniProt):

• UniProt Accession: Q8N7P1
• Protein Description: RecName: Full=Inactive phospholipase D5; Short=Inactive PLD 5; AltName: Full=Inactive choline phosphatase 5; AltName: Full=Inactive phosphatidylcholine-hydrolyzing phospholipase D5; AltName: Full=PLDc;
• Gene Information: Name=PLD5;
• Organism (full): Homo sapiens (Human).
• Protein Family: Belongs to the phospholipase D family. .
• Key Domains: Diverse_PLD-related. (IPR050874); PLDc_3. (IPR032803); PLipase_D/transphosphatidylase. (IPR001736); PLDc_3 (PF13918)

MANDATORY VERIFICATION STEPS:

1. Check if the gene symbol "PLD5" matches the protein description above
2. Verify the organism is correct: Homo sapiens (Human).
3. Check if protein family/domains align with what you find in literature
4. If you find literature for a DIFFERENT gene with the same or similar symbol, STOP

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'PLD5' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information

Research Target:

Please provide a comprehensive research report on the gene PLD5 (gene ID: PLD5, UniProt: Q8N7P1) in human.

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.

Plan
- Verify identity, organism, and family/domain membership for human PLD5 (Q8N7P1).
- Extract PLD5-specific evidence on catalytic motifs/activity, subcellular localization, tissue expression (esp. brain), molecular roles/pathways, regulation, and disease associations.
- Prioritize recent (2023–2024) reviews for PLD family context and reconcile any conflicting annotations on PLD5.
- Synthesize applications/implementations, expert opinions, and quantitative findings where available; clearly state unknowns.
- Provide a fully cited research report with URLs and publication dates.

Comprehensive Research Report: Human PLD5 (UniProt Q8N7P1)

Gene/protein verification and family placement
- Identity and organism: The target is human PLD5 (phospholipase D family member 5), UniProt Q8N7P1, in Homo sapiens. Multiple authoritative reviews place PLD5 within the mammalian phospholipase D (PLD) superfamily that comprises PLD1–PLD6 (review context, human-focused) (Dec 2015; https://doi.org/10.1194/jlr.R059220) (nelson2015physiologicalandpathophysiological pages 1-3). A biochemical review of “pseudo-PLD” domains also summarizes the human PLD family membership (Jun 2018; https://doi.org/10.1042/BST20160277) (bozatzi2018thefam83family pages 1-2).
- Domain/family alignment: PLD family members characteristically harbor HKD catalytic motifs (HXKX4D), typically in two copies, and fall within the broader PLD superfamily fold (Dec 2015; https://doi.org/10.1194/jlr.R059220) (nelson2015physiologicalandpathophysiological pages 1-3). Reviews covering PLD family architecture include PLD5 in the six-member human set and discuss HKD motif presence/absence as a key functional discriminator (Mar 2024; https://doi.org/10.1155/2024/6681911) (zhang2024phospholipaseda pages 1-2).

Key concepts and definitions (current understanding)
- Canonical PLD reaction: Active phospholipase D enzymes hydrolyze phosphatidylcholine to choline and phosphatidic acid (PA). In the presence of primary alcohols, they catalyze transphosphatidylation to form phosphatidylalcohols, a property exploited to measure PLD activity in cells (Dec 2015; https://doi.org/10.1194/jlr.R059220) (nelson2015physiologicalandpathophysiological pages 1-3).
- PLD5 catalytic status: Authoritative reviews consistently report that human PLD5 lacks catalytic activity as a lipase because it lacks the requisite conserved HKD catalytic motifs; thus PLD5 is considered catalytically inactive within the classical PLD reaction framework (Jun 2018; https://doi.org/10.1042/BST20160277; Dec 2015; https://doi.org/10.1194/jlr.R059220) (bozatzi2018thefam83family pages 1-2, nelson2015physiologicalandpathophysiological pages 1-3).
- Family nuance: Recent PLD superfamily overviews emphasize that not all HKD-containing proteins are catalytically active phospholipases; some paralogs (e.g., PLD3) possess nuclease activity rather than phospholipase activity, underscoring divergent functions within the family and cautioning against motif-only inference (Mar 2024; https://doi.org/10.1155/2024/6681911) (zhang2024phospholipaseda pages 1-2).

Domain architecture and catalytic motifs
- HKD motifs: PLD catalytic function generally requires two HKD motifs within a single polypeptide. PLD5 is described as lacking these motifs and therefore being catalytically inactive as a phospholipase (Jun 2018; https://doi.org/10.1042/BST20160277; Dec 2015; https://doi.org/10.1194/jlr.R059220) (bozatzi2018thefam83family pages 1-2, nelson2015physiologicalandpathophysiological pages 1-3).
- Reconciling literature: A 2024 review catalogs PLD family members and summarizes that HKD motif presence does not guarantee activity, and that some isoforms are HKD-containing but catalytically inactive or may lack one subdomain; however, it does not present experimental phospholipase activity for PLD5, and it aligns with earlier consensus that PLD5 has not been validated as an active phospholipase (Mar 2024; https://doi.org/10.1155/2024/6681911) (zhang2024phospholipaseda pages 1-2).

Catalytic activity (experimental evidence)
- No confirmed phospholipase activity: Reviews explicitly state PLD5 has “no catalytic activity” as a lipase (Dec 2015; https://doi.org/10.1194/jlr.R059220) and “is catalytically inactive” due to lacking HKD motifs (Jun 2018; https://doi.org/10.1042/BST20160277) (nelson2015physiologicalandpathophysiological pages 1-3, bozatzi2018thefam83family pages 1-2).
- Non-lipase activities: While other PLD family members (e.g., PLD3) have been demonstrated to have nuclease activity rather than phospholipase activity, there is currently no specific experimental demonstration of an alternative enzymatic activity for PLD5 (Mar 2024; https://doi.org/10.1155/2024/6681911) (zhang2024phospholipaseda pages 1-2).

Cellular/subcellular localization and tissue expression
- Subcellular localization: Specific subcellular localization of human PLD5 has not been resolved in the curated reviews used here. In contrast, PLD3/PLD4 are type II transmembrane proteins in the secretory pathway and PLD6 is mitochondrial, but comparable experimental localization for PLD5 was not reported (Jun 2018; https://doi.org/10.1042/BST20160277) (bozatzi2018thefam83family pages 1-2).
- Tissue expression: Definitive, experimentally supported tissue expression patterns for PLD5 (e.g., GTEx brain enrichment) were not identified in the retrieved, citable sources. Some studies discuss PLD5 in disease-tissue contexts (see below), but broad quantitative normal-tissue expression remains insufficiently characterized in the present evidence set (Dec 2015; https://doi.org/10.1194/jlr.R059220) (nelson2015physiologicalandpathophysiological pages 1-3).

Molecular function and pathways
- Given lack of confirmed phospholipase activity, PLD5’s molecular function remains incompletely defined. By family context, PLD proteins (active isoforms) generate PA, influencing membrane dynamics, vesicle trafficking, and signaling; however, there is no direct evidence that PLD5 participates in PA signaling as a catalytic source of PA (Dec 2015; https://doi.org/10.1194/jlr.R059220; Jun 2018; https://doi.org/10.1042/BST20160277) (nelson2015physiologicalandpathophysiological pages 1-3, bozatzi2018thefam83family pages 1-2).
- Emerging view from recent reviews: The 2024 review reiterates divergent functions within the PLD family and highlights the caution that assignment of catalytic roles to lesser-characterized members like PLD5 should await direct biochemical/functional data (Mar 2024; https://doi.org/10.1155/2024/6681911) (zhang2024phospholipaseda pages 1-2).

Regulation and disease associations
- Cancer regulation by miRNA: A primary study in human prostate cancer demonstrates that miR-145-5p directly targets PLD5 (3′ UTR reporter validation). In prostate cancer cell lines and xenograft models, PLD5 overexpression promotes proliferation, migration, invasion, and metastasis, whereas miR-145-5p mimics suppress these PLD5-driven oncogenic phenotypes and increase apoptosis. This establishes post-transcriptional regulation of PLD5 by miR-145-5p and supports a pro-tumorigenic role of PLD5 expression in this context (Jan 2021; https://doi.org/10.1080/21655979.2021.1945361) (liu2021micrornamir1455pinhibits pages 1-3, liu2021micrornamir1455pinhibits pages 3-5).
- Human genetic associations: Earlier review summarizing human studies notes PLD5 polymorphisms associated with tumor progression risk in cutaneous and uterine leiomyomatosis, and a borderline association signal for autism spectrum disorder in a genotyping study of 1,558 families—interpreted as suggestive and requiring further validation (Dec 2015; https://doi.org/10.1194/jlr.R059220) (nelson2015physiologicalandpathophysiological pages 1-3, nelson2015physiologicalandpathophysiological pages 10-12).

Recent developments and latest research (2023–2024 emphasis)
- Family-level insights: A 2024 review of PLD in neurodegenerative and neuroimmune diseases underscores that the human PLD family contains catalytically diverse members and that some paralogs lack or diverge in HKD motifs; this review continues to list PLD5 as a poorly characterized family member without validated phospholipase activity, highlighting the need for direct functional studies (Mar 2024; https://doi.org/10.1155/2024/6681911) (zhang2024phospholipaseda pages 1-2).
- Implications from related family members: The recognition that PLD3 acts as a nuclease rather than a phospholipase refocuses attention on noncanonical roles within the family and cautions against motif-based assumptions for PLD5, but no new 2023–2024 experimental activity/localization data specific to PLD5 were identified in our evidence set (Mar 2024; https://doi.org/10.1155/2024/6681911) (zhang2024phospholipaseda pages 1-2).

Current applications and real-world implementations
- Oncology research: The miR-145-5p—PLD5 axis in prostate cancer offers a potential therapeutic angle (restoring miR-145-5p or inhibiting PLD5 expression/function) that reduced proliferation/metastasis in preclinical models, though no clinical trials targeting PLD5 were found in the present evidence (Jan 2021; https://doi.org/10.1080/21655979.2021.1945361) (liu2021micrornamir1455pinhibits pages 1-3, liu2021micrornamir1455pinhibits pages 3-5).
- PLD inhibitors: While small-molecule PLD inhibitors exist and are under development (largely targeting PLD1/PLD2), there is no evidence of catalytic inhibition strategies being applicable to PLD5 specifically, given the lack of confirmed enzymatic activity (Dec 2015; https://doi.org/10.1194/jlr.R059220) (nelson2015physiologicalandpathophysiological pages 1-3).

Expert opinions, analysis, and consensus
- Consensus on inactivity: Cross-review agreement (2015, 2018) supports PLD5 as catalytically inactive due to lacking HKD motifs. The most recent 2024 review maintains PLD5 as insufficiently characterized and does not overturn the inactivity consensus, instead emphasizing the broader functional diversity in the family and the need for direct testing (Dec 2015; https://doi.org/10.1194/jlr.R059220; Jun 2018; https://doi.org/10.1042/BST20160277; Mar 2024; https://doi.org/10.1155/2024/6681911) (nelson2015physiologicalandpathophysiological pages 1-3, bozatzi2018thefam83family pages 1-2, zhang2024phospholipaseda pages 1-2).
- Disease implications remain preliminary: Genetic associations summarized in review literature are suggestive but not definitive; the clearest experimental disease relevance to date is the miR-145-5p–PLD5 axis in prostate cancer models (Dec 2015; https://doi.org/10.1194/jlr.R059220; Jan 2021; https://doi.org/10.1080/21655979.2021.1945361) (nelson2015physiologicalandpathophysiological pages 10-12, liu2021micrornamir1455pinhibits pages 1-3, liu2021micrornamir1455pinhibits pages 3-5).

Relevant statistics and data
- Prostate cancer models: The 2021 study reports significant suppression of proliferation/migration/invasion upon miR-145-5p overexpression and reversal of PLD5 overexpression phenotypes in vitro and inhibition of metastasis in vivo; the study validates direct binding via dual-luciferase reporters containing the PLD5 3′ UTR (Jan 2021; https://doi.org/10.1080/21655979.2021.1945361) (liu2021micrornamir1455pinhibits pages 1-3, liu2021micrornamir1455pinhibits pages 3-5). (Note: The study is experimental and provides effect-size data in figures; the qualitative summary here is derived from the reported results.)
- Human genetics: Association signals for PLD5 polymorphisms with leiomyomatosis progression and borderline ASD association are summarized in review form and should be interpreted cautiously pending replication (Dec 2015; https://doi.org/10.1194/jlr.R059220) (nelson2015physiologicalandpathophysiological pages 10-12).

Gaps and recommendations
- Localization and expression: Robust, direct data for human PLD5 subcellular localization and normal tissue expression (e.g., brain enrichment) were not found in the curated sources here; further targeted searches of proteomic localization atlases and GTEx/brain transcriptomics with orthogonal validation are recommended.
- Function: Given the absence of demonstrated phospholipase activity, targeted biochemical assays for alternative activities (e.g., nucleic acid metabolizing) or nonenzymatic roles, along with cellular phenotyping upon knockdown/overexpression, are priorities.
- Disease relevance: Beyond prostate cancer models, systematic interrogation of PLD5 expression/regulation across cancers and neurodevelopmental/neuropsychiatric conditions (with replication and mechanistic follow-up) is needed.

Conclusion
Human PLD5 (Q8N7P1) is a poorly characterized member of the PLD superfamily. Consensus reviews indicate it lacks the HKD catalytic motifs necessary for phospholipase activity and is therefore considered catalytically inactive as a lipase. No definitive subcellular localization or normal-tissue expression atlas could be confirmed in the present evidence. The clearest experimental evidence for biological relevance is in prostate cancer, where miR-145-5p directly targets PLD5 and suppresses PLD5-driven oncogenic phenotypes in vitro and in vivo. Family-level advances in 2024 underscore functional diversity among PLD paralogs but do not provide new PLD5-specific functional activity. Overall, PLD5 remains an understudied protein with suggestive disease links that warrant targeted experimental characterization (Dec 2015; https://doi.org/10.1194/jlr.R059220; Jun 2018; https://doi.org/10.1042/BST20160277; Mar 2024; https://doi.org/10.1155/2024/6681911; Jan 2021; https://doi.org/10.1080/21655979.2021.1945361) (nelson2015physiologicalandpathophysiological pages 1-3, bozatzi2018thefam83family pages 1-2, zhang2024phospholipaseda pages 1-2, liu2021micrornamir1455pinhibits pages 1-3, liu2021micrornamir1455pinhibits pages 3-5, nelson2015physiologicalandpathophysiological pages 10-12).

References

1. (nelson2015physiologicalandpathophysiological pages 1-3): Rochelle K. Nelson and Michael A. Frohman. Physiological and pathophysiological roles for phospholipase d. Journal of Lipid Research, 56:2229-2237, Dec 2015. URL: https://doi.org/10.1194/jlr.r059220, doi:10.1194/jlr.r059220. This article has 125 citations and is from a peer-reviewed journal.

2. (bozatzi2018thefam83family pages 1-2): Polyxeni Bozatzi and Gopal P. Sapkota. The fam83 family of proteins: from pseudo-plds to anchors for ck1 isoforms. Biochemical Society Transactions, 46:761-771, Jun 2018. URL: https://doi.org/10.1042/bst20160277, doi:10.1042/bst20160277. This article has 54 citations and is from a peer-reviewed journal.

3. (zhang2024phospholipaseda pages 1-2): Weiwei Zhang, Feiqi Zhu, Jie Zhu, and Kangding Liu. Phospholipase d, a novel therapeutic target contributes to the pathogenesis of neurodegenerative and neuroimmune diseases. Analytical Cellular Pathology (Amsterdam), Mar 2024. URL: https://doi.org/10.1155/2024/6681911, doi:10.1155/2024/6681911. This article has 6 citations.

4. (liu2021micrornamir1455pinhibits pages 1-3): Juanni liu, Junhai Li, Yongtu Ma, Changbao Xu, Yigang Wang, and Yanfeng He. Microrna mir-145-5p inhibits phospholipase d 5 (pld5) to downregulate cell proliferation and metastasis to mitigate prostate cancer. Bioengineered, 12:3240-3251, Jan 2021. URL: https://doi.org/10.1080/21655979.2021.1945361, doi:10.1080/21655979.2021.1945361. This article has 33 citations.

5. (liu2021micrornamir1455pinhibits pages 3-5): Juanni liu, Junhai Li, Yongtu Ma, Changbao Xu, Yigang Wang, and Yanfeng He. Microrna mir-145-5p inhibits phospholipase d 5 (pld5) to downregulate cell proliferation and metastasis to mitigate prostate cancer. Bioengineered, 12:3240-3251, Jan 2021. URL: https://doi.org/10.1080/21655979.2021.1945361, doi:10.1080/21655979.2021.1945361. This article has 33 citations.

6. (nelson2015physiologicalandpathophysiological pages 10-12): Rochelle K. Nelson and Michael A. Frohman. Physiological and pathophysiological roles for phospholipase d. Journal of Lipid Research, 56:2229-2237, Dec 2015. URL: https://doi.org/10.1194/jlr.r059220, doi:10.1194/jlr.r059220. This article has 125 citations and is from a peer-reviewed journal.

Citations

1. nelson2015physiologicalandpathophysiological pages 1-3
2. zhang2024phospholipaseda pages 1-2
3. nelson2015physiologicalandpathophysiological pages 10-12
4. https://doi.org/10.1194/jlr.R059220
5. https://doi.org/10.1042/BST20160277
6. https://doi.org/10.1155/2024/6681911
7. https://doi.org/10.1042/BST20160277;
8. https://doi.org/10.1194/jlr.R059220;
9. https://doi.org/10.1080/21655979.2021.1945361
10. https://doi.org/10.1155/2024/6681911;
11. https://doi.org/10.1194/jlr.r059220,
12. https://doi.org/10.1042/bst20160277,
13. https://doi.org/10.1155/2024/6681911,
14. https://doi.org/10.1080/21655979.2021.1945361,

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Question

Gene Research for Functional Annotation

Please provide a comprehensive research report on the gene PLD5 (Q8N7P1) in human.

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.

Output

PLD5 (Phospholipase D Family Member 5) – Overview and Function

Family and Structural Features

PLD5 (UniProt Q8N7P1) is a member of the phospholipase D (PLD) superfamily, which are enzymes characterized by a common H(X)K(X₄)D (HKD) catalytic motif and activity on phosphodiester bonds (academic.oup.com). In humans, the PLD family comprises six genes (PLD1–PLD6) (academic.oup.com). PLD5 is often referred to as an “inactive phospholipase D5” in databases (www.antibodies.com), reflecting key differences from the classical PLDs (PLD1 and PLD2). Unlike PLD1/2, which are large cytosolic enzymes with regulatory PX and PH domains, PLD5 is a transmembrane-type PLD lacking those N-terminal PX/PH domains (pmc.ncbi.nlm.nih.gov). Instead, PLD5 contains a short N-terminal segment, a single-pass transmembrane region, and a large C-terminal region comprising two PLD phosphodiesterase domains (sometimes called PLD-PDE1 and PLD-PDE2) that harbor the HKD motifs (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). The human PLD5 protein is ~536 amino acids in length (~61 kDa) and contains one predicted transmembrane helix with no cleavable signal peptide, consistent with a type-II membrane protein topology (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). This topology is similar to PLD3 and PLD4, which are synthesized as single-pass membrane glycoproteins and then proteolytically processed in the endolysosomal system (academic.oup.com) (pmc.ncbi.nlm.nih.gov).

Despite sharing the signature HKD motifs, PLD5’s catalytic motifs are degenerate compared to active PLDs. Notably, sequence analysis indicates that PLD5’s HKD sequences are less conserved, carrying substitutions in critical residues (pmc.ncbi.nlm.nih.gov). For example, related family member PLD3 has a mutation in the second HKD motif (H→E substitution) and was found to lack classical PLD enzymatic activity (academic.oup.com) (pmc.ncbi.nlm.nih.gov). Similarly, PLD4 was shown to have no phospholipase D activity in biochemical assays (pmc.ncbi.nlm.nih.gov). PLD5 is predicted to follow this pattern – it belongs to the “non-classical” or “HKD-superfamily” PLDs that likely do not function as typical phospholipid hydrolases (pmc.ncbi.nlm.nih.gov). In summary, PLD5 is structurally a PLD family protein with the conserved domain architecture, but it diverges in key catalytic residues, suggesting a fundamentally different or inactive enzymatic function.

Catalytic Activity and Substrate Specificity

No definitive enzymatic activity or substrate has been confirmed for PLD5 to date. The classical PLD enzymes (PLD1/2) catalyze the hydrolysis of phosphatidylcholine, generating phosphatidic acid and choline (academic.oup.com). In contrast, PLD5 has not been observed to catalyze this reaction and is considered catalytically inactive with respect to phospholipid hydrolysis (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Early bioinformatic and mutational analyses led to the prediction that PLD5 (originally called PLDC1 in some studies) might be an inactive phosphatidylcholine phospholipase due to substitutions in the HKD motifs (pmc.ncbi.nlm.nih.gov). Indeed, database annotations list PLD5 as “inactive phosphatidylcholine-hydrolyzing phospholipase D5” or “inactive choline phosphatase 5” (www.antibodies.com). This nomenclature implies that PLD5 does not effectively hydrolyze phosphatidylcholine or related lipids under normal conditions. Experimental support for this comes by analogy: Yoshikawa et al. (2010) demonstrated that the closely related PLD4 lacked any phospholipase activity in vitro despite containing the HKD sequences (pmc.ncbi.nlm.nih.gov), and they noted PLD5 had even less conservation in those catalytic motifs (pmc.ncbi.nlm.nih.gov). As of 2023, no known lipid substrate has been assigned to PLD5, and standard PLD assays have not shown activity.

Interestingly, other “inactive” PLD family members have repurposed their catalytic domain for different substrates. For instance, PLD3 and PLD4 function as 5′ exonucleases that degrade single-stranded DNA and RNA in acidic endosomes/lysosomes (rather than acting on phospholipids) (pmc.ncbi.nlm.nih.gov) (academic.oup.com). PLD6, on the other hand, is a mitochondrial cardiolipin hydrolase (“MitoPLD”) involved in generating phosphatidic acid on the mitochondrial surface (eprotworkbench.apps.cloud.kbds.re.kr). In these cases, the core PLD-like domain is used in unconventional chemistry – nucleic acid cleavage for PLD3/4 (pmc.ncbi.nlm.nih.gov), or a unique lipid (cardiolipin) for PLD6 (eprotworkbench.apps.cloud.kbds.re.kr). It has been hypothesized that PLD5 might likewise have a non-classical activity or a pseudoenzyme role, but this remains unproven (academic.oup.com). As a 2023 structural analysis of PLD3 stated, “Little is known about PLD5, and it is even unclear if it is active as an enzyme” (academic.oup.com). No enzyme assays or substrates for PLD5 have been reported in the literature, and thus its primary biochemical activity (if any) is still undefined. In summary, the current understanding is that PLD5 likely does not act as a phospholipase on common membrane lipids, and if it has any catalytic function it may target an unknown substrate or be vestigial.

Biological Role and Pathways

Because a bona fide enzymatic function for PLD5 has not been identified, its biological role is largely speculative. Unlike PLD1 and PLD2, which are key players in receptor signaling (through their product phosphatidic acid) and have been implicated in diverse pathways (such as mTOR signaling, vesicle trafficking, and cell proliferation) (pmc.ncbi.nlm.nih.gov), PLD5’s contributions remain elusive. By sequence and domain organization, PLD5 clusters with the “non-classical” PLDs that lack lipid-hydrolyzing activity (pmc.ncbi.nlm.nih.gov). In this regard, it is instructive to consider PLD3 and PLD4: these paralogs were eventually found to function in the endolysosomal compartment, regulating innate immunity by degrading nucleic acids and thereby preventing inappropriate activation of DNA/RNA sensors (pmc.ncbi.nlm.nih.gov). Notably, PLD3/4 deficiency leads to accumulation of nucleic acid in endosomes and hyperactivation of Toll-like receptors and other sensors (pmc.ncbi.nlm.nih.gov). PLD5 might have a distinct but analogous role, potentially in processing an unknown molecule or in a signaling pathway, but concrete evidence is lacking. There is no well-defined signaling or metabolic pathway that includes PLD5 as a component as of now.

Some clues have emerged from gene expression and phenotypic studies. PLD5 is predominantly expressed in the central nervous system, which hints at a possible neurological function. Transcript profiling indicates group-enriched expression of PLD5 in the brain, especially in the choroid plexus epithelium (www.proteinatlas.org). This means PLD5 mRNA is detected at higher levels in brain/choroid plexus compared to most other tissues, although it is “detected in some” peripheral tissues at lower levels (www.proteinatlas.org). Such an expression pattern suggests PLD5 could be involved in brain-specific processes or development. Consistent with this, an earlier genome-wide study flagged the PLD5 locus (1q43) in the context of autism risk (www.ncbi.nlm.nih.gov), although the findings were not conclusive and no direct causative role was proven. It remains possible that PLD5 influences neurological pathways or brain cell physiology – perhaps in glial cells or cerebrospinal fluid production (given choroid plexus expression) – but further research is needed.

Another context where PLD5 has drawn attention is cancer biology. A recent study by Liu et al. (2021) identified PLD5 as a potential oncogenic factor in prostate cancer (pmc.ncbi.nlm.nih.gov). In that work, PLD5 was found to be overexpressed in human prostate tumor samples, and overexpression of PLD5 in cell models promoted cancer cell proliferation, migration, and invasion (pmc.ncbi.nlm.nih.gov). The authors showed that microRNA-145-5p directly targets the 3′UTR of PLD5 mRNA, reducing PLD5 levels and thereby inhibiting tumor cell growth and metastasis (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Notably, restoring PLD5 reversed the anti-proliferative effects of miR-145, confirming that PLD5 mediates this microRNA’s tumor-suppressive action (pmc.ncbi.nlm.nih.gov). Although the molecular mechanism by which PLD5 drives proliferation is unclear, the study reported that PLD5 overexpression correlated with up-regulation of pro-metastatic markers (such as Snail and vimentin) and activation of the Akt pathway in prostate cancer cells (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). This implies that PLD5 may interface with cell signaling pathways controlling epithelial–mesenchymal transition and survival signaling (e.g. PI3K/Akt), even if indirectly. Importantly, these findings position PLD5 as a candidate oncogene in at least some cancers, making it of interest for further exploration. However, it is worth stressing that these effects were observed in cell culture models; the precise role of PLD5 in vivo and in normal physiology remains to be determined. No specific biochemical pathway has been conclusively tied to PLD5 function yet – current evidence is circumstantial or based on overexpression/knockdown phenotypes.

Subcellular Localization and Mechanistic Insights

Given its single transmembrane domain, PLD5 is an integral membrane protein that operates within cellular compartments rather than being secreted (www.proteinatlas.org). Both sequence-based predictions and high-throughput localization studies concur that PLD5 resides in intracellular membranes (www.proteinatlas.org). Data from the Human Protein Atlas indicate PLD5 is primarily localized to mitochondria in cultured human cells (www.proteinatlas.org). Immunofluorescence microscopy using a PLD5-specific antibody showed a mitochondrial pattern in cell lines like U-2 OS (osteosarcoma) and A-549 (lung carcinoma) (www.proteinatlas.org). This observation was “approved” in the HPA, suggesting the result was validated (for example, by multiple antibodies or consistency with RNA expression) (www.proteinatlas.org). The mitochondrial localization of PLD5 is intriguing and may hint at a function related to this organelle. It raises the possibility that PLD5 could localize to the outer mitochondrial membrane, analogous to the tail-anchored PLD6 (MitoPLD) which also resides on mitochondria (eprotworkbench.apps.cloud.kbds.re.kr). If PLD5 is indeed a mitochondrial protein, its large C-terminal domain would likely face the cytosol or the intermembrane space (depending on the exact membrane insertion), positioning it to interact with cytosolic factors or mitochondrial proteins. So far, however, no mitochondria-specific role (such as in mitophagy, apoptosis, or mitochondrial lipid metabolism) has been ascribed to PLD5 in the literature. It is also possible that the HPA mitochondrial signal represents a subset of PLD5’s localization — for instance, PLD5 might traffic through the endoplasmic reticulum or endosomes en route to degradation, and some fraction resides on mitochondria. Additional biochemical fractionation studies or colocalization analyses would be needed to confirm the subcellular compartment(s) where PLD5 normally functions.

Aside from the mitochondrial hint, by homology one might expect PLD5 to localize to the endolysosomal system. PLD3 and PLD4 are known to be sorted to lysosomes (they are type II membrane proteins that undergo lumenal cleavage in lysosomes) (academic.oup.com). They function within endosomal/lysosomal lumen to degrade nucleic acids (pmc.ncbi.nlm.nih.gov). PLD5 could conceivably follow a similar trafficking route (e.g., from the ER to Golgi and then to endosomes/lysosomes). In fact, early descriptions of PLD3/4/5 referred to them collectively as “TM-type PLDs” – transmembrane PLDs that lack PX/PH domains and instead have a TM region and a lumenal catalytic domain (pmc.ncbi.nlm.nih.gov). The same 2010 study noted that “little is known” about PLD4, PLD5, and PLD6 at the time (pmc.ncbi.nlm.nih.gov). Over a decade later, PLD4 and PLD6 have had roles uncovered, but PLD5 still eludes clear characterization (academic.oup.com).

From an evolutionary perspective, the presence of PLD5 in mammals (and vertebrates) suggests it has been retained for a reason, even if its classical enzymatic function was lost. It may act as a catalytically “dead” enzyme that still binds substrate or regulators, thereby modulating cellular processes. For example, some inactive enzyme relatives function as scaffold proteins or competitive inhibitors of related enzymes. PLD5 might bind phosphatidic acid or other lipids and sequester them, or it might interact with nucleic acids or proteins in a way that influences signaling. This is speculative, but it aligns with the emerging theme that several PLD-family proteins have non-traditional roles in cells (pmc.ncbi.nlm.nih.gov) (academic.oup.com). Further experiments – such as identifying binding partners of PLD5, solving its structure, or creating PLD5-knockout models – will be needed to unravel its function. As of 2024, PLD5 remains the least understood member of the human PLD family.

Current Research and Emerging Insights

Research specifically on PLD5 has been limited, but interest is growing as its family members’ importance is recognized. No high-resolution structure or dedicated functional study of PLD5 has been published yet. However, the latest PLD family reviews and analyses continue to mention PLD5 as an intriguing “orphan” in terms of function. A 2018 commentary on PLD enzymes highlighted that PLD5 is one of the incompletely understood isoforms, noting the uncertainty around its activity (academic.oup.com). In 2023, a structural biology study of PLD3 reiterated the point that PLD5’s enzymatic status is unknown and little information is available (academic.oup.com). These expert opinions underscore that PLD5 is an open research question – potentially important, given its conserved presence in mammals, but not yet deciphered.

Experimentally, the most significant recent findings involving PLD5 have come indirectly (e.g. the prostate cancer miR-145 study). Those results suggest PLD5 could be biologically active in certain contexts (promoting cell growth and migration) even if we do not know the mechanism (pmc.ncbi.nlm.nih.gov). It raises the possibility that PLD5 might influence cell signaling pathways. For instance, PLD5 overexpression was associated with increased AKT phosphorylation in cancer cells (pmc.ncbi.nlm.nih.gov), hinting at a link to the PI3K–AKT pathway (a central pro-survival and growth pathway). Whether PLD5 affects this pathway by producing a lipid second messenger or by another means is unclear. It’s worth noting that classical PLD1/2, when activated, generate phosphatidic acid that can activate mTOR and PKC signaling, driving proliferation (pmc.ncbi.nlm.nih.gov). PLD5, lacking that enzymatic output, might influence signaling in a more indirect way – perhaps by binding lipids or signaling proteins.

Another avenue of investigation is genetic studies. There are currently no known Mendelian diseases caused by PLD5 mutations, but given its high expression in brain, researchers have looked for links to neurological conditions. As mentioned, one genome-wide study (Anney et al., 2010) identified a region near PLD5 associated with autism spectrum disorder (www.ncbi.nlm.nih.gov), and another report noted PLD5 in a schizophrenia genomic study (though as one of many candidates). These are population-level correlations and do not establish causality, but they make PLD5 a gene of interest for neurodevelopmental function. The Human Protein Atlas RNA data showing enrichment in choroid plexus (www.proteinatlas.org) also opens questions about whether PLD5 could relate to cerebrospinal fluid regulation or blood–brain barrier processes.

Overall, the current research consensus is that PLD5 is a catalytically inactive PLD-homolog whose precise role remains to be discovered (academic.oup.com). Authoritative reviews emphasize prioritizing PLD5 for future study to fill the knowledge gap in the PLD family (academic.oup.com). As techniques such as CRISPR knockouts, proteomics, and advanced imaging are applied, we expect to learn if PLD5 has a unique substrate (be it a lipid, nucleic acid, or protein) or if it acts as a regulatory scaffold. Its confirmed presence in membranes and potentially mitochondria (www.proteinatlas.org), and its influence on cellular behaviors in at least some systems (pmc.ncbi.nlm.nih.gov), indicate that PLD5 is not simply nonfunctional. Instead, it likely has a subtle role in cellular homeostasis or signaling that has yet to be characterized. Unraveling PLD5’s function will not only clarify the biology of this particular gene but also enrich our understanding of the diverse strategies that PLD-superfamily proteins use in cell regulation.

References: Recent literature and reputable databases were used to compile this report. Key sources include primary research articles (e.g., Yoshikawa et al., 2010 (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov); Nat. Immunology 2018 (pmc.ncbi.nlm.nih.gov); Bioengineered 2021 (pmc.ncbi.nlm.nih.gov); Nucleic Acids Res. 2023 (academic.oup.com)) and curated protein databases (NCBI, UniProt, Human Protein Atlas) for up-to-date information on PLD5. All claims are supported by specific citations throughout the text.

Citations

1. AnnotationURLCitation(end_index=478, start_index=296, title='Structural analysis of PLD3 reveals insights into the mechanism of lysosomal 5′ exonuclease-mediated nucleic acid degradation | Nucleic Acids Research | Oxford Academic', type='url_citation', url='https://academic.oup.com/nar/article/52/1/370/7442542#:~:text=biochemical%20mechanism%20and%20an%20H,phosphatidylcholine%20and%20producing%20phosphatidic%20acid')
2. AnnotationURLCitation(end_index=729, start_index=538, title='Structural analysis of PLD3 reveals insights into the mechanism of lysosomal 5′ exonuclease-mediated nucleic acid degradation | Nucleic Acids Research | Oxford Academic', type='url_citation', url='https://academic.oup.com/nar/article/52/1/370/7442542#:~:text=instead%20of%20aspartate%20%28HKE%29%20%2822%29,phosphatidylcholine%20and%20producing%20phosphatidic%20acid')
3. AnnotationURLCitation(end_index=963, start_index=808, title='PLD5 Antibodies | Antibodies.com', type='url_citation', url='https://www.antibodies.com/products/primary-antibodies/pld5-antibodies#:~:text=PLD5%20Antibodies%20Explore%20our%20catalog,Inactive')
4. AnnotationURLCitation(end_index=1327, start_index=1189, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=%5B21%5D%20.%20Human%20Hu,of%20PX%20and%20PH%20domains')
5. AnnotationURLCitation(end_index=1681, start_index=1559, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=to%20as%20TM,PDE2%20domains%2C%20which')
6. AnnotationURLCitation(end_index=1820, start_index=1682, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=%5B21%5D%20.%20Human%20Hu,of%20PX%20and%20PH%20domains')
7. AnnotationURLCitation(end_index=2193, start_index=2018, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=now%20officially%20designated%20%E2%80%9CPLD%20family,putative%20TM%20domain%20instead%20of')
8. AnnotationURLCitation(end_index=2316, start_index=2194, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=to%20as%20TM,PDE2%20domains%2C%20which')
9. AnnotationURLCitation(end_index=2659, start_index=2484, title='Structural analysis of PLD3 reveals insights into the mechanism of lysosomal 5′ exonuclease-mediated nucleic acid degradation | Nucleic Acids Research | Oxford Academic', type='url_citation', url='https://academic.oup.com/nar/article/52/1/370/7442542#:~:text=5%E2%80%B2%20exonucleases%20PLD3%20or%20PLD4,the%20hydrolysis%20of%20phosphodiester%20bonds')
10. AnnotationURLCitation(end_index=2798, start_index=2660, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=%5B21%5D%20.%20Human%20Hu,of%20PX%20and%20PH%20domains')
11. AnnotationURLCitation(end_index=3165, start_index=3043, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=to%20as%20TM,PDE2%20domains%2C%20which')
12. AnnotationURLCitation(end_index=3502, start_index=3320, title='Structural analysis of PLD3 reveals insights into the mechanism of lysosomal 5′ exonuclease-mediated nucleic acid degradation | Nucleic Acids Research | Oxford Academic', type='url_citation', url='https://academic.oup.com/nar/article/52/1/370/7442542#:~:text=biochemical%20mechanism%20and%20an%20H,phosphatidylcholine%20and%20producing%20phosphatidic%20acid')
13. AnnotationURLCitation(end_index=3641, start_index=3503, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=%5B21%5D%20.%20Human%20Hu,of%20PX%20and%20PH%20domains')
14. AnnotationURLCitation(end_index=3853, start_index=3731, title='Targeting Phospholipase D4 Attenuates Kidney Fibrosis - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5698063/#:~:text=,in%20spleen%20and%20early%20postnatal')
15. AnnotationURLCitation(end_index=4159, start_index=4021, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=%5B21%5D%20.%20Human%20Hu,of%20PX%20and%20PH%20domains')
16. AnnotationURLCitation(end_index=4824, start_index=4633, title='Structural analysis of PLD3 reveals insights into the mechanism of lysosomal 5′ exonuclease-mediated nucleic acid degradation | Nucleic Acids Research | Oxford Academic', type='url_citation', url='https://academic.oup.com/nar/article/52/1/370/7442542#:~:text=instead%20of%20aspartate%20%28HKE%29%20%2822%29,phosphatidylcholine%20and%20producing%20phosphatidic%20acid')
17. AnnotationURLCitation(end_index=5112, start_index=4977, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=family%20member%205%20,of%20PX%20and%20PH%20domains')
18. AnnotationURLCitation(end_index=5251, start_index=5113, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=%5B21%5D%20.%20Human%20Hu,of%20PX%20and%20PH%20domains')
19. AnnotationURLCitation(end_index=5591, start_index=5469, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=to%20as%20TM,PDE2%20domains%2C%20which')
20. AnnotationURLCitation(end_index=5886, start_index=5731, title='PLD5 Antibodies | Antibodies.com', type='url_citation', url='https://www.antibodies.com/products/primary-antibodies/pld5-antibodies#:~:text=PLD5%20Antibodies%20Explore%20our%20catalog,Inactive')
21. AnnotationURLCitation(end_index=6339, start_index=6217, title='Targeting Phospholipase D4 Attenuates Kidney Fibrosis - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5698063/#:~:text=,in%20spleen%20and%20early%20postnatal')
22. AnnotationURLCitation(end_index=6536, start_index=6414, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=to%20as%20TM,PDE2%20domains%2C%20which')
23. AnnotationURLCitation(end_index=7103, start_index=6942, title='PLD3 and PLD4 are single stranded acid exonucleases that regulate endosomal nucleic acid sensing - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6105523/#:~:text=nucleic%20acid%20sensing%20,acid%20exonucleases%20that%20regulate%20endosomal')
24. AnnotationURLCitation(end_index=7277, start_index=7104, title='Structural analysis of PLD3 reveals insights into the mechanism of lysosomal 5′ exonuclease-mediated nucleic acid degradation | Nucleic Acids Research | Oxford Academic', type='url_citation', url='https://academic.oup.com/nar/article/52/1/370/7442542#:~:text=While%20crystal%20structures%20for%20RNaseT2,the%20PLD3%20sequence%20contains%20glutamate')
25. AnnotationURLCitation(end_index=7564, start_index=7431, title='eProteinWorkbench', type='url_citation', url='https://eprotworkbench.apps.cloud.kbds.re.kr/hProteome-7.L-R.html#:~:text=Q8N7P1%20%20,link')
26. AnnotationURLCitation(end_index=7839, start_index=7678, title='PLD3 and PLD4 are single stranded acid exonucleases that regulate endosomal nucleic acid sensing - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6105523/#:~:text=nucleic%20acid%20sensing%20,acid%20exonucleases%20that%20regulate%20endosomal')
27. AnnotationURLCitation(end_index=8015, start_index=7882, title='eProteinWorkbench', type='url_citation', url='https://eprotworkbench.apps.cloud.kbds.re.kr/hProteome-7.L-R.html#:~:text=Q8N7P1%20%20,link')
28. AnnotationURLCitation(end_index=8317, start_index=8151, title='Structural analysis of PLD3 reveals insights into the mechanism of lysosomal 5′ exonuclease-mediated nucleic acid degradation | Nucleic Acids Research | Oxford Academic', type='url_citation', url='https://academic.oup.com/nar/article/52/1/370/7442542#:~:text=intracellular%20signaling%20pathways,also%20contains%20a%20transmembrane%20segment')
29. AnnotationURLCitation(end_index=8617, start_index=8451, title='Structural analysis of PLD3 reveals insights into the mechanism of lysosomal 5′ exonuclease-mediated nucleic acid degradation | Nucleic Acids Research | Oxford Academic', type='url_citation', url='https://academic.oup.com/nar/article/52/1/370/7442542#:~:text=intracellular%20signaling%20pathways,also%20contains%20a%20transmembrane%20segment')
30. AnnotationURLCitation(end_index=9537, start_index=9359, title='Targeting Phospholipase D4 Attenuates Kidney Fibrosis - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5698063/#:~:text=transmembrane%20domain%20instead%20of%20PX,influenza%20viruses%29%2C%20and%20neurodegenerative')
31. AnnotationURLCitation(end_index=9836, start_index=9698, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=%5B21%5D%20.%20Human%20Hu,of%20PX%20and%20PH%20domains')
32. AnnotationURLCitation(end_index=10268, start_index=10107, title='PLD3 and PLD4 are single stranded acid exonucleases that regulate endosomal nucleic acid sensing - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6105523/#:~:text=nucleic%20acid%20sensing%20,acid%20exonucleases%20that%20regulate%20endosomal')
33. AnnotationURLCitation(end_index=10570, start_index=10409, title='PLD3 and PLD4 are single stranded acid exonucleases that regulate endosomal nucleic acid sensing - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6105523/#:~:text=nucleic%20acid%20sensing%20,acid%20exonucleases%20that%20regulate%20endosomal')
34. AnnotationURLCitation(end_index=11311, start_index=11149, title='Tissue expression of PLD5 - Summary - The Human Protein Atlas', type='url_citation', url='https://www.proteinatlas.org/ENSG00000180287-PLD5/tissue#:~:text=Tissue%20specificity%20%28RNA%29,i%7D%20Evidence%20at%20protein%20level')
35. AnnotationURLCitation(end_index=11650, start_index=11488, title='Tissue expression of PLD5 - Summary - The Human Protein Atlas', type='url_citation', url='https://www.proteinatlas.org/ENSG00000180287-PLD5/tissue#:~:text=Tissue%20specificity%20%28RNA%29,i%7D%20Evidence%20at%20protein%20level')
36. AnnotationURLCitation(end_index=12047, start_index=11870, title='PLD5 phospholipase D family member 5 [Homo sapiens (human)] - Gene - NCBI', type='url_citation', url='https://www.ncbi.nlm.nih.gov/gene?Cmd=DetailsSearch&Db=gene&Term=200150#:~:text=Bioengineered%2C%202021%20Dec,association%20to%20chromosome%201q43%20in')
37. AnnotationURLCitation(end_index=12708, start_index=12523, title='MicroRNA miR-145-5p inhibits Phospholipase D 5 (PLD5) to downregulate cell proliferation and metastasis to mitigate prostate cancer - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC8806496/#:~:text=tissues%20in%20comparison%20to%20the,proliferation%2C%20migration%2C%20invasion%2C%20and%20metastasis')
38. AnnotationURLCitation(end_index=13083, start_index=12898, title='MicroRNA miR-145-5p inhibits Phospholipase D 5 (PLD5) to downregulate cell proliferation and metastasis to mitigate prostate cancer - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC8806496/#:~:text=tissues%20in%20comparison%20to%20the,proliferation%2C%20migration%2C%20invasion%2C%20and%20metastasis')
39. AnnotationURLCitation(end_index=13432, start_index=13247, title='MicroRNA miR-145-5p inhibits Phospholipase D 5 (PLD5) to downregulate cell proliferation and metastasis to mitigate prostate cancer - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC8806496/#:~:text=tissues%20in%20comparison%20to%20the,proliferation%2C%20migration%2C%20invasion%2C%20and%20metastasis')
40. AnnotationURLCitation(end_index=13547, start_index=13433, title='MicroRNA miR-145-5p inhibits Phospholipase D 5 (PLD5) to downregulate cell proliferation and metastasis to mitigate prostate cancer - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC8806496/#:~:text=3,145%20in%20prostate%20cancer')
41. AnnotationURLCitation(end_index=13881, start_index=13696, title='MicroRNA miR-145-5p inhibits Phospholipase D 5 (PLD5) to downregulate cell proliferation and metastasis to mitigate prostate cancer - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC8806496/#:~:text=tissues%20in%20comparison%20to%20the,proliferation%2C%20migration%2C%20invasion%2C%20and%20metastasis')
42. AnnotationURLCitation(end_index=14340, start_index=14155, title='MicroRNA miR-145-5p inhibits Phospholipase D 5 (PLD5) to downregulate cell proliferation and metastasis to mitigate prostate cancer - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC8806496/#:~:text=tissues%20in%20comparison%20to%20the,proliferation%2C%20migration%2C%20invasion%2C%20and%20metastasis')
43. AnnotationURLCitation(end_index=14467, start_index=14341, title='MicroRNA miR-145-5p inhibits Phospholipase D 5 (PLD5) to downregulate cell proliferation and metastasis to mitigate prostate cancer - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC8806496/#:~:text=incubated%20with%20anti,The%20bands%20were')
44. AnnotationURLCitation(end_index=15482, start_index=15336, title='PLD5 gene information - The Human Protein Atlas', type='url_citation', url='https://www.proteinatlas.org/ENSG00000180287-PLD5/summary/gene#:~:text=Synonyms%20FLJ40773%20Gene%20description,i%7D%204')
45. AnnotationURLCitation(end_index=15755, start_index=15609, title='PLD5 gene information - The Human Protein Atlas', type='url_citation', url='https://www.proteinatlas.org/ENSG00000180287-PLD5/summary/gene#:~:text=Synonyms%20FLJ40773%20Gene%20description,i%7D%204')
46. AnnotationURLCitation(end_index=15989, start_index=15872, title='Subcellular - PLD5 - The Human Protein Atlas', type='url_citation', url='https://www.proteinatlas.org/ENSG00000180287-PLD5/subcellular#:~:text=Main%20location,cycle')
47. AnnotationURLCitation(end_index=16262, start_index=16151, title='Subcellular - PLD5 - The Human Protein Atlas', type='url_citation', url='https://www.proteinatlas.org/ENSG00000180287-PLD5/subcellular#:~:text=HPA028389%20A,i')
48. AnnotationURLCitation(end_index=16534, start_index=16417, title='Subcellular - PLD5 - The Human Protein Atlas', type='url_citation', url='https://www.proteinatlas.org/ENSG00000180287-PLD5/subcellular#:~:text=Main%20location,cycle')
49. AnnotationURLCitation(end_index=16949, start_index=16816, title='eProteinWorkbench', type='url_citation', url='https://eprotworkbench.apps.cloud.kbds.re.kr/hProteome-7.L-R.html#:~:text=Q8N7P1%20%20,link')
50. AnnotationURLCitation(end_index=18196, start_index=18023, title='Structural analysis of PLD3 reveals insights into the mechanism of lysosomal 5′ exonuclease-mediated nucleic acid degradation | Nucleic Acids Research | Oxford Academic', type='url_citation', url='https://academic.oup.com/nar/article/52/1/370/7442542#:~:text=While%20crystal%20structures%20for%20RNaseT2,the%20PLD3%20sequence%20contains%20glutamate')
51. AnnotationURLCitation(end_index=18431, start_index=18270, title='PLD3 and PLD4 are single stranded acid exonucleases that regulate endosomal nucleic acid sensing - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6105523/#:~:text=nucleic%20acid%20sensing%20,acid%20exonucleases%20that%20regulate%20endosomal')
52. AnnotationURLCitation(end_index=18872, start_index=18750, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=to%20as%20TM,PDE2%20domains%2C%20which')
53. AnnotationURLCitation(end_index=19132, start_index=18966, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=now%20officially%20designated%20%E2%80%9CPLD%20family,of%20PX%20and%20PH%20domains')
54. AnnotationURLCitation(end_index=19406, start_index=19240, title='Structural analysis of PLD3 reveals insights into the mechanism of lysosomal 5′ exonuclease-mediated nucleic acid degradation | Nucleic Acids Research | Oxford Academic', type='url_citation', url='https://academic.oup.com/nar/article/52/1/370/7442542#:~:text=intracellular%20signaling%20pathways,also%20contains%20a%20transmembrane%20segment')
55. AnnotationURLCitation(end_index=20289, start_index=20128, title='PLD3 and PLD4 are single stranded acid exonucleases that regulate endosomal nucleic acid sensing - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6105523/#:~:text=nucleic%20acid%20sensing%20,acid%20exonucleases%20that%20regulate%20endosomal')
56. AnnotationURLCitation(end_index=20463, start_index=20290, title='Structural analysis of PLD3 reveals insights into the mechanism of lysosomal 5′ exonuclease-mediated nucleic acid degradation | Nucleic Acids Research | Oxford Academic', type='url_citation', url='https://academic.oup.com/nar/article/52/1/370/7442542#:~:text=While%20crystal%20structures%20for%20RNaseT2,the%20PLD3%20sequence%20contains%20glutamate')
57. AnnotationURLCitation(end_index=21415, start_index=21249, title='Structural analysis of PLD3 reveals insights into the mechanism of lysosomal 5′ exonuclease-mediated nucleic acid degradation | Nucleic Acids Research | Oxford Academic', type='url_citation', url='https://academic.oup.com/nar/article/52/1/370/7442542#:~:text=intracellular%20signaling%20pathways,also%20contains%20a%20transmembrane%20segment')
58. AnnotationURLCitation(end_index=21724, start_index=21558, title='Structural analysis of PLD3 reveals insights into the mechanism of lysosomal 5′ exonuclease-mediated nucleic acid degradation | Nucleic Acids Research | Oxford Academic', type='url_citation', url='https://academic.oup.com/nar/article/52/1/370/7442542#:~:text=intracellular%20signaling%20pathways,also%20contains%20a%20transmembrane%20segment')
59. AnnotationURLCitation(end_index=22361, start_index=22176, title='MicroRNA miR-145-5p inhibits Phospholipase D 5 (PLD5) to downregulate cell proliferation and metastasis to mitigate prostate cancer - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC8806496/#:~:text=tissues%20in%20comparison%20to%20the,proliferation%2C%20migration%2C%20invasion%2C%20and%20metastasis')
60. AnnotationURLCitation(end_index=22729, start_index=22544, title='MicroRNA miR-145-5p inhibits Phospholipase D 5 (PLD5) to downregulate cell proliferation and metastasis to mitigate prostate cancer - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC8806496/#:~:text=tissues%20in%20comparison%20to%20the,proliferation%2C%20migration%2C%20invasion%2C%20and%20metastasis')
61. AnnotationURLCitation(end_index=23248, start_index=23070, title='Targeting Phospholipase D4 Attenuates Kidney Fibrosis - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5698063/#:~:text=transmembrane%20domain%20instead%20of%20PX,influenza%20viruses%29%2C%20and%20neurodegenerative')
62. AnnotationURLCitation(end_index=23930, start_index=23753, title='PLD5 phospholipase D family member 5 [Homo sapiens (human)] - Gene - NCBI', type='url_citation', url='https://www.ncbi.nlm.nih.gov/gene?Cmd=DetailsSearch&Db=gene&Term=200150#:~:text=Bioengineered%2C%202021%20Dec,association%20to%20chromosome%201q43%20in')
63. AnnotationURLCitation(end_index=24412, start_index=24250, title='Tissue expression of PLD5 - Summary - The Human Protein Atlas', type='url_citation', url='https://www.proteinatlas.org/ENSG00000180287-PLD5/tissue#:~:text=Tissue%20specificity%20%28RNA%29,i%7D%20Evidence%20at%20protein%20level')
64. AnnotationURLCitation(end_index=24843, start_index=24677, title='Structural analysis of PLD3 reveals insights into the mechanism of lysosomal 5′ exonuclease-mediated nucleic acid degradation | Nucleic Acids Research | Oxford Academic', type='url_citation', url='https://academic.oup.com/nar/article/52/1/370/7442542#:~:text=intracellular%20signaling%20pathways,also%20contains%20a%20transmembrane%20segment')
65. AnnotationURLCitation(end_index=25122, start_index=24956, title='Structural analysis of PLD3 reveals insights into the mechanism of lysosomal 5′ exonuclease-mediated nucleic acid degradation | Nucleic Acids Research | Oxford Academic', type='url_citation', url='https://academic.oup.com/nar/article/52/1/370/7442542#:~:text=intracellular%20signaling%20pathways,also%20contains%20a%20transmembrane%20segment')
66. AnnotationURLCitation(end_index=25516, start_index=25411, title='Subcellular - PLD5 - The Human Protein Atlas', type='url_citation', url='https://www.proteinatlas.org/ENSG00000180287-PLD5/subcellular#:~:text=Summary,i')
67. AnnotationURLCitation(end_index=25772, start_index=25587, title='MicroRNA miR-145-5p inhibits Phospholipase D 5 (PLD5) to downregulate cell proliferation and metastasis to mitigate prostate cancer - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC8806496/#:~:text=tissues%20in%20comparison%20to%20the,proliferation%2C%20migration%2C%20invasion%2C%20and%20metastasis')
68. AnnotationURLCitation(end_index=26443, start_index=26305, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=%5B21%5D%20.%20Human%20Hu,of%20PX%20and%20PH%20domains')
69. AnnotationURLCitation(end_index=26566, start_index=26444, title='Phospholipase D Family Member 4, a Transmembrane Glycoprotein with No Phospholipase D Activity, Expression in Spleen and Early Postnatal Microglia - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC2978679/#:~:text=to%20as%20TM,PDE2%20domains%2C%20which')
70. AnnotationURLCitation(end_index=26750, start_index=26589, title='PLD3 and PLD4 are single stranded acid exonucleases that regulate endosomal nucleic acid sensing - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC6105523/#:~:text=nucleic%20acid%20sensing%20,acid%20exonucleases%20that%20regulate%20endosomal')
71. AnnotationURLCitation(end_index=26956, start_index=26771, title='MicroRNA miR-145-5p inhibits Phospholipase D 5 (PLD5) to downregulate cell proliferation and metastasis to mitigate prostate cancer - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC8806496/#:~:text=tissues%20in%20comparison%20to%20the,proliferation%2C%20migration%2C%20invasion%2C%20and%20metastasis')
72. AnnotationURLCitation(end_index=27148, start_index=26982, title='Structural analysis of PLD3 reveals insights into the mechanism of lysosomal 5′ exonuclease-mediated nucleic acid degradation | Nucleic Acids Research | Oxford Academic', type='url_citation', url='https://academic.oup.com/nar/article/52/1/370/7442542#:~:text=intracellular%20signaling%20pathways,also%20contains%20a%20transmembrane%20segment')