PGRPLD

UniProt ID: A7UTR2
Organism: Anopheles gambiae
Review Status: DRAFT
📝 Provide Detailed Feedback

Gene Description

PGRP-LD is a long-form peptidoglycan recognition protein (PGRP) that functions as a non-catalytic, negative regulator of innate immune responses in the mosquito gut. Despite containing an Amidase_2/PGRP domain, PGRP-LD lacks the conserved residues required for peptidoglycan binding and amidase catalytic activity. Instead, it acts to restrain immune hyper-activation, thereby preserving gut commensal microbiota and maintaining peritrophic matrix integrity. This microbiota-PM barrier axis indirectly limits Plasmodium infection. PGRP-LD is a transmembrane protein localized at the gut epithelial barrier.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0002376 immune system process
IEA
GO_REF:0000043 		ACCEPT
Summary: PGRP-LD is involved in immune system processes. Deep research synthesis indicates that PGRP-LD modulates gut immunity by restraining hyper-activation of immune effectors, thereby maintaining microbiota homeostasis and peritrophic matrix integrity. This is supported by functional studies in the closely related Anopheles stephensi ortholog.
Reason: The annotation is correct but very broad. PGRP-LD plays a regulatory role in innate immunity at the gut barrier. The term is appropriately general for an IEA annotation derived from UniProt keyword mapping.
Supporting Evidence:
file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
PGRP-LD restrains hyper-activation of innate immune effectors (e.g., AMPs, DUOX), thereby protecting commensal bacteria
GO:0008270 zinc ion binding
IEA
GO_REF:0000002 		UNDECIDED
Summary: The PGRP/Amidase_2 domain family typically coordinates a zinc ion at the active site. However, PGRP-LD lacks the conserved residues required for catalytic activity, raising the question of whether the zinc-binding site is functional. Sequence analysis shows that PGRP-LD lacks most conserved residues for PGN binding and catalytic activity.
Reason: While catalytic PGRPs bind zinc at the active site, the absence of key catalytic residues in PGRP-LD raises uncertainty about whether zinc binding is retained. No direct experimental evidence confirms zinc binding in this non-catalytic PGRP. The annotation may be a case of domain-based over-annotation.
Supporting Evidence:
file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
The A. stephensi PGRP-LD lacks most conserved residues required for PGN binding and amidase catalytic activity
GO:0008745 N-acetylmuramoyl-L-alanine amidase activity
IEA
GO_REF:0000002 		REMOVE
Summary: This annotation is INCORRECT. Despite belonging to the Amidase_2/PGRP superfamily, PGRP-LD is a non-catalytic PGRP that lacks the conserved residues required for peptidoglycan binding and amidase catalytic activity. Sequence analysis of the Anopheles stephensi ortholog demonstrated the absence of key catalytic residues. PGRP-LD functions as a regulatory PGRP rather than an enzymatic amidase.
Reason: This is a classic example of domain-based over-annotation. The presence of an Amidase_2 domain (IPR002502) led to automatic annotation of amidase activity, but detailed sequence analysis shows PGRP-LD lacks the conserved residues required for catalysis. Not all PGRP family members are enzymatically active; many function as pattern recognition receptors or immune regulators without catalytic activity. The functional evidence clearly indicates PGRP-LD is non-catalytic.
Supporting Evidence:
file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
The A. stephensi PGRP-LD lacks most conserved residues required for PGN binding and amidase catalytic activity
file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
Current evidence supports a regulatory PGRP model for PGRP-LD, not an enzymatic PGN hydrolase
GO:0009253 peptidoglycan catabolic process
IEA
GO_REF:0000002 		REMOVE
Summary: This annotation is INCORRECT. Peptidoglycan catabolic process implies enzymatic degradation of peptidoglycan, which requires amidase activity. Since PGRP-LD lacks the conserved catalytic residues and does not function as an active amidase, it cannot be involved in peptidoglycan catabolism. The protein may recognize peptidoglycan as a pattern recognition molecule, but does not degrade it.
Reason: This annotation logically follows from the incorrect amidase activity annotation. Since PGRP-LD lacks amidase catalytic activity, it cannot participate in peptidoglycan catabolic processes. The annotation should be removed along with the amidase activity annotation.
Supporting Evidence:
file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
No direct amidase activity or substrate specificity has been demonstrated for PGRP-LD; rather, sequence features argue against catalysis
GO:0045087 innate immune response
IEA
GO_REF:0000043 		MODIFY
Summary: PGRP-LD is clearly involved in the innate immune response. However, it functions as a NEGATIVE regulator rather than a positive effector. RNAi knockdown of PGRP-LD upregulates multiple immune effectors (cecropin, gambicin, defensin, DUOX), indicating its normal function is to restrain immune activation. This immune tolerance function preserves commensal bacteria and maintains peritrophic matrix integrity.
Reason: While PGRP-LD is involved in innate immune response, a more accurate annotation would capture its specific role as a negative regulator. The current annotation is not wrong but could be more informative about the direction of regulation.
Supporting Evidence:
file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
Knockdown of PGRP-LD upregulates multiple immune effectors (e.g., cecropin, gambicin, defensin, DUOX), consistent with a negative regulatory role constraining immune activation in response to microbiota
file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
Functions to restrain hyper-activation of immune effectors (negative regulator-like role), thereby limiting overactive Imd/Toll-like responses that deplete commensals
GO:0045824 negative regulation of innate immune response
ISS
PMID:29489896
PGRP-LD mediates A. stephensi vector competency by regulatin... 		NEW
Summary: Functional studies in Anopheles stephensi demonstrate that PGRP-LD negatively regulates innate immune responses. Knockdown leads to upregulation of antimicrobial peptides and DUOX, indicating PGRP-LD normally restrains immune activation.
Reason: This annotation captures the core function of PGRP-LD as a negative regulator of innate immunity. Evidence is from the closely related A. stephensi ortholog (ISS - inferred from sequence similarity), as direct A. gambiae knockdown data is not available in the literature.
Supporting Evidence:
file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
Knockdown of PGRP-LD upregulates multiple immune effectors (e.g., cecropin, gambicin, defensin, DUOX), consistent with a negative regulatory role constraining immune activation
GO:0061060 negative regulation of peptidoglycan recognition protein signaling pathway
ISS
PMID:29489896
PGRP-LD mediates A. stephensi vector competency by regulatin... 		NEW
Summary: PGRP-LD modulates the PGRP signaling pathway as a negative regulator. The protein restrains immune hyper-activation through the Imd/Toll pathways that are canonically activated by peptidoglycan recognition.
Reason: This term accurately describes the molecular role of PGRP-LD in dampening PGRP-mediated immune signaling. The evidence is from orthologous studies in A. stephensi.
Supporting Evidence:
file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
Functional data are most consistent with PGRP-LD acting upstream as a modulator that limits overactive responses commonly associated with the Imd/Toll axes in the gut
GO:0016021 integral component of membrane
IEA
GO_REF:0000002 		NEW
Summary: UniProt annotation and Phobius prediction indicate PGRP-LD has a transmembrane helix (residues 70-94). The protein is described as a transmembrane PGRP in functional studies.
Reason: The UniProt entry shows transmembrane domain prediction by Phobius. Functional studies describe PGRP-LD as a transmembrane PGRP at the gut barrier.
Supporting Evidence:
file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
Described as a transmembrane PGRP
GO:0140678 molecular function inhibitor activity
ISS
PMID:29489896
PGRP-LD mediates A. stephensi vector competency by regulatin... 		NEW
Summary: PGRP-LD functions as an inhibitor of immune signaling pathways. By restraining the activity of Imd/Toll signaling, it prevents hyper-activation of downstream immune effectors. This inhibitory molecular function underlies its biological role in negative regulation of innate immunity.
Reason: This molecular function term captures PGRP-LD's role as an inhibitor of immune signaling. While the precise molecular mechanism is not fully characterized, the functional evidence clearly demonstrates inhibitory activity on immune pathway components.
Supporting Evidence:
file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
Functions to restrain hyper-activation of immune effectors (negative regulator-like role), thereby limiting overactive Imd/Toll-like responses that deplete commensals

Core Functions

PGRP-LD functions as a negative regulator of innate immunity, restraining immune hyper-activation to preserve gut microbiota and peritrophic matrix integrity.

Molecular Function:
molecular function inhibitor activity
Directly Involved In:
negative regulation of innate immune response negative regulation of peptidoglycan recognition protein signaling pathway
Cellular Locations:
integral component of membrane
Supporting Evidence:
  • file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
    Knockdown of PGRP-LD upregulates multiple immune effectors (e.g., cecropin, gambicin, defensin, DUOX), consistent with a negative regulatory role constraining immune activation

References

GO_REF:0000002
Gene Ontology annotation through association of InterPro records with GO terms
  • InterPro domain-based annotations can lead to over-annotation when domain presence does not guarantee the associated function, particularly for domains like Amidase_2 where not all family members are enzymatically active.
GO_REF:0000043
Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
  • Keyword-based annotations correctly identify PGRP-LD as involved in immunity, but lack specificity about its regulatory role.
PMID:29489896
PGRP-LD mediates A. stephensi vector competency by regulating homeostasis of microbiota-induced peritrophic matrix synthesis
  • PGRP-LD is a non-catalytic PGRP that lacks conserved residues for amidase activity
  • Functions as a negative regulator of innate immunity
  • Maintains gut microbiota homeostasis
  • Required for peritrophic matrix integrity
  • Knockdown increases Plasmodium susceptibility
PMID:31907025
Gut microbiota is essential in PGRP-LA regulated immune protection against Plasmodium berghei infection
  • Contextual evidence for PGRP family regulation of immunity and microbiota interactions in Anopheles
file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
Deep research synthesis for PGRPLD
  • PGRP-LD is a non-catalytic PGRP lacking key residues for amidase activity
    "The A. stephensi PGRP-LD lacks most conserved residues required for PGN binding and amidase catalytic activity"
  • Functions as negative regulator of innate immunity
    "Knockdown of PGRP-LD upregulates multiple immune effectors (e.g., cecropin, gambicin, defensin, DUOX), consistent with a negative regulatory role constraining immune activation in response to microbiota"
  • Transmembrane protein at gut barrier
    "Described as a transmembrane PGRP"

Suggested Questions for Experts

Q: Does A. gambiae PGRP-LD retain any zinc-binding capacity despite lacking catalytic residues?

Q: What is the mechanism by which PGRP-LD inhibits immune signaling?

Suggested Experiments

Experiment: Direct biochemical assay for amidase activity in recombinant A. gambiae PGRP-LD. While sequence analysis strongly suggests PGRP-LD is non-catalytic, direct enzymatic assays on the A. gambiae protein would definitively confirm the absence of amidase activity.

Experiment: RNAi knockdown of PGRP-LD in A. gambiae to confirm functional conservation. The functional characterization was performed in A. stephensi. Direct knockdown in A. gambiae would confirm the conserved immune regulatory function.

📚 Additional Documentation

Deep Research Falcon

(PGRPLD-deep-research-falcon.md)

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organism: ANOGA
gene_id: PGRPLD
gene_symbol: PGRPLD
uniprot_accession: A7UTR2
protein_description: 'SubName: Full=AGAP005552-PA {ECO:0000313|EMBL:EDO63684.1};'
gene_info: Name=PGRPLD {ECO:0000313|EMBL:EDO63684.1}; Synonyms=3289995 {ECO:0000313|EnsemblMetazoa:AGAP005552-PB};
ORFNames=AgaP_AGAP005552 {ECO:0000313|EMBL:EDO63684.1};
organism_full: Anopheles gambiae (African malaria mosquito).
protein_family: Belongs to the N-acetylmuramoyl-L-alanine amidase 2 family.
protein_domains: Amidase/PGRP_sf. (IPR036505); Amidase_domain. (IPR002502); PGRP.
(IPR015510); PGRP_domain_met/bac. (IPR006619); Amidase_2 (PF01510)
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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: A7UTR2
  • Protein Description: SubName: Full=AGAP005552-PA {ECO:0000313|EMBL:EDO63684.1};
  • Gene Information: Name=PGRPLD {ECO:0000313|EMBL:EDO63684.1}; Synonyms=3289995 {ECO:0000313|EnsemblMetazoa:AGAP005552-PB}; ORFNames=AgaP_AGAP005552 {ECO:0000313|EMBL:EDO63684.1};
  • Organism (full): Anopheles gambiae (African malaria mosquito).
  • Protein Family: Belongs to the N-acetylmuramoyl-L-alanine amidase 2 family.
  • Key Domains: Amidase/PGRP_sf. (IPR036505); Amidase_domain. (IPR002502); PGRP. (IPR015510); PGRP_domain_met/bac. (IPR006619); Amidase_2 (PF01510)

MANDATORY VERIFICATION STEPS:

  1. Check if the gene symbol "PGRPLD" matches the protein description above
  2. Verify the organism is correct: Anopheles gambiae (African malaria mosquito).
  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 'PGRPLD' 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 PGRPLD (gene ID: PGRPLD, UniProt: A7UTR2) in ANOGA.

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: A7UTR2
  • Protein Description: SubName: Full=AGAP005552-PA {ECO:0000313|EMBL:EDO63684.1};
  • Gene Information: Name=PGRPLD {ECO:0000313|EMBL:EDO63684.1}; Synonyms=3289995 {ECO:0000313|EnsemblMetazoa:AGAP005552-PB}; ORFNames=AgaP_AGAP005552 {ECO:0000313|EMBL:EDO63684.1};
  • Organism (full): Anopheles gambiae (African malaria mosquito).
  • Protein Family: Belongs to the N-acetylmuramoyl-L-alanine amidase 2 family.
  • Key Domains: Amidase/PGRP_sf. (IPR036505); Amidase_domain. (IPR002502); PGRP. (IPR015510); PGRP_domain_met/bac. (IPR006619); Amidase_2 (PF01510)

MANDATORY VERIFICATION STEPS:

  1. Check if the gene symbol "PGRPLD" matches the protein description above
  2. Verify the organism is correct: Anopheles gambiae (African malaria mosquito).
  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 'PGRPLD' 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 PGRPLD (gene ID: PGRPLD, UniProt: A7UTR2) in ANOGA.

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.

Research plan and approach
We verified the target identity and organism, gathered primary and recent literature with emphasis on 2018–2024 sources, extracted mechanistic and phenotypic evidence (function, localization, immune pathways, microbiota–PM interactions), and synthesized findings into a concise report. A compact evidence table is embedded to support traceability.

Executive summary
PGRP-LD (AGAP005552; UniProt A7UTR2) in Anopheles gambiae is a long peptidoglycan-recognition protein within the Amidase_2/PGRP superfamily. Cross-species functional evidence from the Anopheles stephensi ortholog indicates PGRP-LD lacks key residues for peptidoglycan binding and amidase catalytic activity and acts as a non-catalytic, negative regulator of immune activation that preserves gut microbiota and peritrophic matrix (PM) integrity. This indirect barrier function limits Plasmodium infection. Recent 2024 literature further highlights PGRP-LD in contemporary discussions of mosquito immunity and vector competence. (song2018pgrpldmediatesa. pages 12-14, song2018pgrpldmediatesa. pages 11-12, song2018pgrpldmediatesa. pages 1-2, daou2024characterizinganophelesgambiae pages 22-26)

1) Key concepts and definitions
- Identity and domains: PGRP-LD corresponds to AGAP005552 in A. gambiae and belongs to the PGRP/Amidase_2 family of proteins. Domain analyses in functional work include the A. gambiae PGRP-LD sequence in alignments, consistent with a PGRP fold characteristic of N-acetylmuramoyl-L-alanine amidase-like domains. (2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899) (song2018pgrpldmediatesa. pages 12-14)
- Catalytic capability vs recognition: The A. stephensi PGRP-LD ortholog lacks most conserved residues required for PGN binding and catalytic activity, implying a non-catalytic recognition/regulatory role rather than an active amidase. This provides a strong inference for A. gambiae PGRP-LD given close sequence conservation. (2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899) (song2018pgrpldmediatesa. pages 11-12)
- PGRP family context: Anopheles PGRPs diversify into catalytic amidases and non-catalytic receptors/regulators, reflecting immune system adaptation. Foundational analyses documented expanded and diversified immune gene families, including PGRPs, in A. gambiae. (2002, Science, https://doi.org/10.1126/science.1077136) (song2018pgrpldmediatesa. pages 16-17)

2) Biochemical function and substrate specificity
- Primary function: Current evidence supports a regulatory PGRP model for PGRP-LD, not an enzymatic PGN hydrolase. No direct amidase activity or substrate specificity has been demonstrated for PGRP-LD; rather, sequence features argue against catalysis. (2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899) (song2018pgrpldmediatesa. pages 11-12)
- Mechanistic role: PGRP-LD restrains hyper-activation of innate immune effectors (e.g., AMPs, DUOX), thereby protecting commensal bacteria. This immune tolerance maintains microbiota-dependent PM integrity, which in turn restricts Plasmodium ookinete invasion. (2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899) (song2018pgrpldmediatesa. pages 4-6, song2018pgrpldmediatesa. pages 1-2)

3) Expression, localization, and regulation
- Localization: The A. stephensi ortholog is described as a transmembrane PGRP, suggesting a membrane-associated role at the gut barrier; detailed subcellular localization for A. gambiae PGRP-LD has not been specified in the retrieved evidence. (2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899) (song2018pgrpldmediatesa. pages 2-4)
- Regulation and expression context: Knockdown of PGRP-LD upregulates multiple immune effectors (e.g., cecropin, gambicin, defensin, DUOX), consistent with a negative regulatory role constraining immune activation in response to microbiota. (2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899) (song2018pgrpldmediatesa. pages 4-6)

4) Roles in immune pathways and microbiota–PM interactions
- Immune pathway positioning: Functional data are most consistent with PGRP-LD acting upstream as a modulator that limits overactive responses commonly associated with the Imd/Toll axes in the gut, thereby maintaining a eubiotic microbiota. (2018, PLOS Pathogens; 2020 review context) (https://doi.org/10.1371/journal.ppat.1006899; https://doi.org/10.1186/s13071-019-3876-y) (song2018pgrpldmediatesa. pages 4-6, gao2020gutmicrobiotais pages 9-9)
- Microbiota and PM integrity: PGRP-LD is necessary to preserve commensal abundance and spatial segregation from the epithelium. Its knockdown produces approximately a 500-fold reduction of culturable midgut bacteria, disrupts microbiota spatial organization, and fragments the PM, increasing gut permeability. Antibiotic depletion of microbiota reproduces PM loss by 48 h post-blood meal, while recolonization with indigenous Enterobacter restores PM integrity and reduces vector competence. These results place PGRP-LD in a microbiota–immune–PM axis that indirectly limits Plasmodium infection. (2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899) (song2018pgrpldmediatesa. pages 4-6, song2018pgrpldmediatesa. pages 1-2, song2018pgrpldmediatesa. pages 11-12)

5) Phenotypic evidence from RNAi/CRISPR and infection outcomes
- RNAi knockdown in An. stephensi: Silencing pgrp-ld increases Plasmodium berghei oocyst numbers (greater susceptibility), decreases midgut bacterial load (~500-fold CFU decrease; reduced 16S copies), perturbs bacterial spatial distribution, and fragments the PM; silencing has no additional effect in mosquitoes lacking a PM, indicating the phenotype is mediated via the microbiota–PM pathway. (2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899) (song2018pgrpldmediatesa. pages 4-6, song2018pgrpldmediatesa. pages 1-2, song2018pgrpldmediatesa. pages 11-12)
- Recent summaries (2024): Contemporary analyses reiterate that PGRP-LD protects commensals by preventing overactivation of immunity; PM fragmentation after PGRP-LD silencing correlates with increased vector competence. (2024, synthesis/report; URL not provided in excerpt) (daou2024characterizinganophelesgambiae pages 22-26)

6) Cross-species considerations (An. stephensi → A. gambiae)
- Orthology and inference: The A. stephensi PGRP-LD study includes alignments featuring A. gambiae PGRP-LD (AGAP005552), supporting cross-species inference given conservation of domain architecture and the reported lack of catalytic residues. While direct A. gambiae loss-of-function phenotypes for AGAP005552 were not captured in the gathered texts, the mechanistic framework is likely conserved across anophelines. (2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899) (song2018pgrpldmediatesa. pages 12-14, song2018pgrpldmediatesa. pages 11-12)

7) Recent developments and latest research (emphasis 2023–2024)
- 2024 perspectives and datasets reference PGRP-LD as part of immune modules that modulate vector competence, emphasizing microbiota–immune–barrier interactions. Although detailed new AGAP005552 biochemical assays were not identified in the gathered evidence, the 2024 reporting strengthens the relevance of PGRP-LD to ongoing vector control biology. (2024, contemporary synthesis) (daou2024characterizinganophelesgambiae pages 22-26)
- Contextual updates: Reviews and primary work continue to highlight PGRP family roles in balancing antimicrobial responses with tolerance to commensals, a balance pivotal for PM integrity and pathogen resistance. (2020, Parasites & Vectors, https://doi.org/10.1186/s13071-019-3876-y) (gao2020gutmicrobiotais pages 9-9)

8) Applications and real-world implementations
- Vector control concepts: Findings implicate PGRP-LD as a host factor modulating vector competence via microbiota–PM homeostasis. Potential applications include microbiota engineering or interventions that bolster PM integrity post-blood meal to reduce malaria transmission. The antibiotic–recolonization experiments show that restoring commensals can rescue PM and decrease infection, suggesting feasible microbiota-based strategies in mosquitoes. (2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899) (song2018pgrpldmediatesa. pages 1-2)
- Immune pathway targeting: Because PGRP-LD limits hyper-immunity, approaches that mimic its tolerance function could preserve beneficial microbiota and gut barriers. This principle aligns with broader Anopheles PGRP literature connecting Imd/Toll signaling, microbiota, and PM. (2018, PLOS Pathogens; 2020 Parasites & Vectors) (https://doi.org/10.1371/journal.ppat.1006899; https://doi.org/10.1186/s13071-019-3876-y) (song2018pgrpldmediatesa. pages 4-6, gao2020gutmicrobiotais pages 9-9)

9) Expert opinions and authoritative reviews
- Genome and immunity foundations: The Science 2002 analysis of A. gambiae immunity-related genes highlighted diversification and expansion of recognition and effector gene families, including PGRPs, laying the foundation for understanding specialized roles such as PGRP-LD’s tolerance function. (2002, Science, https://doi.org/10.1126/science.1077136) (song2018pgrpldmediatesa. pages 16-17)
- Integrative perspectives (2020): Reviews emphasize PGRP-mediated modulation of gut immunity, the central role of microbiota in vector competence, and the PM as a microbiota-driven barrier, situating PGRP-LD within established mechanistic frameworks. (2020, Parasites & Vectors, https://doi.org/10.1186/s13071-019-3876-y) (gao2020gutmicrobiotais pages 9-9)

10) Relevant statistics and data
- Microbiota reduction upon PGRP-LD knockdown: Approximately 500-fold decrease in culturable midgut bacteria (CFU) and reduced 16S rRNA gene copy number, despite largely similar taxonomic composition; altered spatial organization with bacteria contacting/penetrating epithelium. (2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899) (song2018pgrpldmediatesa. pages 4-6)
- PM integrity and permeability: Histological fragmentation of the PM and increased permeability to large FITC-dextran in PGRP-LD knockdown mosquitoes; antibiotic treatment causes PM loss by 48 h post-blood meal; recolonization restores PM integrity. (2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899) (song2018pgrpldmediatesa. pages 4-6, song2018pgrpldmediatesa. pages 1-2, song2018pgrpldmediatesa. pages 11-12)
- Vector competence: PGRP-LD knockdown increases P. berghei oocyst numbers (quantified in the original study; directionality reported here). (2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899) (song2018pgrpldmediatesa. pages 1-2)

Verification of target identity and ambiguity check
- Symbol/organism: PGRP-LD matches AGAP005552 in A. gambiae; functional evidence references the A. gambiae ortholog in alignments. No conflicting symbol usage was detected in retrieved texts. (2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899) (song2018pgrpldmediatesa. pages 12-14)
- Domains/family: Evidence is consistent with PGRP/Amidase_2 fold membership, but with lack of key residues for catalytic activity in the studied ortholog, supporting a non-enzymatic regulatory role. (2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899) (song2018pgrpldmediatesa. pages 11-12)

Limitations and open questions
- Direct biochemical assays for A. gambiae PGRP-LD have not been identified in the gathered evidence; amidase activity and precise PGN ligand specificity remain unproven experimentally for AGAP005552.
- Detailed subcellular localization and tissue-specific expression for A. gambiae PGRP-LD were not captured; the transmembrane description comes from the A. stephensi ortholog.
- While multiple 2024 resources discuss PGRP-LD’s role, additional peer-reviewed primary studies in A. gambiae since 2018 would strengthen species-specific conclusions.

Embedded evidence table
| Aspect | Key finding | Species/Context | Methods | Source (year, journal, URL) | Citation ID |
|---|---|---:|---|---|---:|
| Identity / domains | PGRP-LD corresponds to AgPGRP-LD (AGAP005552); contains a PGRP/amidase-type domain (Amidase_2 / PGRP domain) consistent with PGRP family membership | Anopheles gambiae (AGAP005552) / An. stephensi ortholog studied | Sequence alignment / conserved-domain analysis referenced in functional study | 2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899 | (song2018pgrpldmediatesa. pages 12-14) |
| Catalytic residues (non-catalytic inference) | The A. stephensi PGRP-LD lacks most conserved residues required for PGN binding and amidase catalytic activity → inferred non-catalytic/ regulatory PGRP rather than active amidase | An. stephensi (inferred to apply to AgPGRP-LD by alignment) | Conserved-residue inspection / domain alignment reported in functional paper | 2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899 | (song2018pgrpldmediatesa. pages 11-12) |
| Tissue / cellular localization | Described as a transmembrane PGRP in the An. stephensi study; detailed subcellular localization in An. gambiae not reported in gathered evidence | An. stephensi (functional characterization); inference for An. gambiae | Protein annotation / experimental description (no exhaustive immunolocalization reported) | 2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899 | (song2018pgrpldmediatesa. pages 2-4) |
| Immune-pathway role (Imd/Toll; regulation) | Functions to restrain hyper-activation of immune effectors (negative regulator-like role), thereby limiting overactive Imd/Toll-like responses that deplete commensals | An. stephensi; contextualized for Anopheles PGRPs | RNAi knockdown and immune gene expression profiling (qPCR of AMPs, DUOX, etc.) | 2018, PLOS Pathogens; review/context from PGRP literature (2020 Parasites & Vectors) | (song2018pgrpldmediatesa. pages 4-6, gao2020gutmicrobiotais pages 9-9) |
| Microbiota ↔ Peritrophic matrix (PM) relationship | PGRP-LD maintains gut microbiota homeostasis; microbiota promote PM gene expression and structural integrity; loss of PGRP-LD → hyper-immunity → microbiota depletion → PM fragmentation | An. stephensi (mechanistic demonstration); relevant to An. gambiae by sequence alignment | RNAi, CFU and 16S quantification, FISH, PM histology (H&E, PAS), FITC-dextran permeability assays | 2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899 | (song2018pgrpldmediatesa. pages 1-2) |
| RNAi / phenotypes on Plasmodium infection | Knockdown of PGRP-LD increases susceptibility to Plasmodium berghei (higher oocyst numbers) while reducing culturable midgut bacteria and altering spatial distribution | An. stephensi experimental infections (P. berghei) | dsRNA-mediated knockdown, parasite oocyst counts, microbiota assays | 2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899 | (song2018pgrpldmediatesa. pages 1-2) |
| Antibiotic depletion and recolonization rescue | Antibiotic removal of microbiota causes PM loss and increased vector competence; recolonization with indigenous Enterobacter restores PM integrity and reduces Plasmodium susceptibility (supports microbiota-mediated effect downstream of PGRP-LD) | An. stephensi recolonization experiments | Antibiotic treatment, oral recolonization, PM assays, infection assays | 2018, PLOS Pathogens, https://doi.org/10.1371/journal.ppat.1006899 | (song2018pgrpldmediatesa. pages 1-2) |
| 2023–2024 updates & broader context | Recent 2023–2024 work highlights PGRP family members (including PGRP-LD) in vector immune modulation and microbiota interactions; 2024 summaries note PGRP-LD’s role in protecting commensals and impacting vector competence (recent syntheses/reports) | Anopheles spp.; synthesis of recent literature (2024 summaries/reviews) | Transcriptomics / literature syntheses referencing PGRP-LD roles in immunity and microbiota/PM interplay | 2024 (characterizations/reviews; one 2024 report listed as unknown journal), plus earlier PGRP family reviews | (daou2024characterizinganophelesgambiae pages 22-26, song2018pgrpldmediatesa. pages 16-17) |
| Broader PGRP family context in Anopheles | PGRP gene family in Anopheles includes multiple members with both catalytic (amidase) and non-catalytic regulatory roles; family expansion/diversification underlies varied roles in antibacterial defense and tolerance of commensals | Anopheles gambiae family-level analyses and comparative studies | Genomic surveys, reviews, functional studies of multiple PGRPs | Foundational reviews (2002 Science; 2006 analyses) cited within the collected literature; contextualized in 2018 study | (song2018pgrpldmediatesa. pages 16-17) |

Table: Compact table summarizing experimental and annotation evidence for Anopheles gambiae PGRP-LD (AGAP005552 / A7UTR2) and the An. stephensi ortholog, with methods and sources mapped to gathered context IDs for traceability.

References (URLs and dates)
- Song X, Wang M, Dong L, Zhu H, Wang J. PGRP-LD mediates A. stephensi vector competency by regulating homeostasis of microbiota-induced peritrophic matrix synthesis. PLOS Pathogens. 2018 Feb;14:e1006899. URL: https://doi.org/10.1371/journal.ppat.1006899 (accessed via publisher) (song2018pgrpldmediatesa. pages 1-2, song2018pgrpldmediatesa. pages 4-6, song2018pgrpldmediatesa. pages 11-12, song2018pgrpldmediatesa. pages 12-14, song2018pgrpldmediatesa. pages 2-4)
- Daou H. Characterizing Anopheles gambiae susceptibility to oral infections with a panel of human bacterial pathogens. 2024; summary excerpt. URL: N/A in excerpt. (daou2024characterizinganophelesgambiae pages 22-26)
- Gao L, Song X, Wang J. Gut microbiota is essential in PGRP-LA regulated immune protection against Plasmodium berghei infection. Parasites & Vectors. 2020 Jan;13: Article number not specified in excerpt. URL: https://doi.org/10.1186/s13071-019-3876-y (gao2020gutmicrobiotais pages 9-9)
- Christophides GK, et al. Immunity-Related Genes and Gene Families in Anopheles gambiae. Science. 2002 Oct;298(5591):159–165. URL: https://doi.org/10.1126/science.1077136 (song2018pgrpldmediatesa. pages 16-17)

Conclusions
The available evidence supports that A. gambiae PGRP-LD (AGAP005552; A7UTR2) is a membrane-associated, non-catalytic PGRP that limits gut immune overactivation, preserves commensal microbiota, and thereby sustains a functional PM barrier that constrains Plasmodium infection. While direct biochemical activity and A. gambiae-specific knockdown/knockout data remain to be fully defined, orthologous functional data in A. stephensi and family-level context in Anopheles provide a coherent mechanistic model with clear implications for vector competence and potential microbiota-based interventions. (song2018pgrpldmediatesa. pages 11-12, song2018pgrpldmediatesa. pages 4-6, song2018pgrpldmediatesa. pages 1-2, gao2020gutmicrobiotais pages 9-9, song2018pgrpldmediatesa. pages 16-17, daou2024characterizinganophelesgambiae pages 22-26)

References

  1. (song2018pgrpldmediatesa. pages 12-14): Xiumei Song, Mengfei Wang, Li Dong, Huaimin Zhu, and Jingwen Wang. Pgrp-ld mediates a. stephensi vector competency by regulating homeostasis of microbiota-induced peritrophic matrix synthesis. PLOS Pathogens, 14:e1006899, Feb 2018. URL: https://doi.org/10.1371/journal.ppat.1006899, doi:10.1371/journal.ppat.1006899. This article has 93 citations and is from a highest quality peer-reviewed journal.

  2. (song2018pgrpldmediatesa. pages 11-12): Xiumei Song, Mengfei Wang, Li Dong, Huaimin Zhu, and Jingwen Wang. Pgrp-ld mediates a. stephensi vector competency by regulating homeostasis of microbiota-induced peritrophic matrix synthesis. PLOS Pathogens, 14:e1006899, Feb 2018. URL: https://doi.org/10.1371/journal.ppat.1006899, doi:10.1371/journal.ppat.1006899. This article has 93 citations and is from a highest quality peer-reviewed journal.

  3. (song2018pgrpldmediatesa. pages 1-2): Xiumei Song, Mengfei Wang, Li Dong, Huaimin Zhu, and Jingwen Wang. Pgrp-ld mediates a. stephensi vector competency by regulating homeostasis of microbiota-induced peritrophic matrix synthesis. PLOS Pathogens, 14:e1006899, Feb 2018. URL: https://doi.org/10.1371/journal.ppat.1006899, doi:10.1371/journal.ppat.1006899. This article has 93 citations and is from a highest quality peer-reviewed journal.

  4. (daou2024characterizinganophelesgambiae pages 22-26): H Daou. Characterizing anopheles gambiae susceptibility to oral infections with a panel of human bacterial pathogens. Unknown journal, 2024.

  5. (song2018pgrpldmediatesa. pages 16-17): Xiumei Song, Mengfei Wang, Li Dong, Huaimin Zhu, and Jingwen Wang. Pgrp-ld mediates a. stephensi vector competency by regulating homeostasis of microbiota-induced peritrophic matrix synthesis. PLOS Pathogens, 14:e1006899, Feb 2018. URL: https://doi.org/10.1371/journal.ppat.1006899, doi:10.1371/journal.ppat.1006899. This article has 93 citations and is from a highest quality peer-reviewed journal.

  6. (song2018pgrpldmediatesa. pages 4-6): Xiumei Song, Mengfei Wang, Li Dong, Huaimin Zhu, and Jingwen Wang. Pgrp-ld mediates a. stephensi vector competency by regulating homeostasis of microbiota-induced peritrophic matrix synthesis. PLOS Pathogens, 14:e1006899, Feb 2018. URL: https://doi.org/10.1371/journal.ppat.1006899, doi:10.1371/journal.ppat.1006899. This article has 93 citations and is from a highest quality peer-reviewed journal.

  7. (song2018pgrpldmediatesa. pages 2-4): Xiumei Song, Mengfei Wang, Li Dong, Huaimin Zhu, and Jingwen Wang. Pgrp-ld mediates a. stephensi vector competency by regulating homeostasis of microbiota-induced peritrophic matrix synthesis. PLOS Pathogens, 14:e1006899, Feb 2018. URL: https://doi.org/10.1371/journal.ppat.1006899, doi:10.1371/journal.ppat.1006899. This article has 93 citations and is from a highest quality peer-reviewed journal.

  8. (gao2020gutmicrobiotais pages 9-9): Li Gao, Xiumei Song, and Jingwen Wang. Gut microbiota is essential in pgrp-la regulated immune protection against plasmodium berghei infection. Parasites & Vectors, Jan 2020. URL: https://doi.org/10.1186/s13071-019-3876-y, doi:10.1186/s13071-019-3876-y. This article has 32 citations and is from a peer-reviewed journal.

Citations

  1. daou2024characterizinganophelesgambiae pages 22-26
  2. gao2020gutmicrobiotais pages 9-9
  3. https://doi.org/10.1371/journal.ppat.1006899
  4. https://doi.org/10.1126/science.1077136
  5. https://doi.org/10.1371/journal.ppat.1006899;
  6. https://doi.org/10.1186/s13071-019-3876-y
  7. https://doi.org/10.1371/journal.ppat.1006899,
  8. https://doi.org/10.1186/s13071-019-3876-y,

📄 View Raw YAML

 
id: A7UTR2
gene_symbol: PGRPLD
product_type: PROTEIN
status: DRAFT
taxon:
  id: NCBITaxon:7165
  label: Anopheles gambiae
description: >-
  PGRP-LD is a long-form peptidoglycan recognition protein (PGRP) that functions as a
  non-catalytic, negative regulator of innate immune responses in the mosquito gut.
  Despite containing an Amidase_2/PGRP domain, PGRP-LD lacks the conserved residues
  required for peptidoglycan binding and amidase catalytic activity. Instead, it acts
  to restrain immune hyper-activation, thereby preserving gut commensal microbiota
  and maintaining peritrophic matrix integrity. This microbiota-PM barrier axis
  indirectly limits Plasmodium infection. PGRP-LD is a transmembrane protein localized
  at the gut epithelial barrier.
existing_annotations:
- term:
    id: GO:0002376
    label: immune system process
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: >-
      PGRP-LD is involved in immune system processes. Deep research synthesis indicates
      that PGRP-LD modulates gut immunity by restraining hyper-activation of immune
      effectors, thereby maintaining microbiota homeostasis and peritrophic matrix
      integrity. This is supported by functional studies in the closely related
      Anopheles stephensi ortholog.
    action: ACCEPT
    reason: >-
      The annotation is correct but very broad. PGRP-LD plays a regulatory role in innate
      immunity at the gut barrier. The term is appropriately general for an IEA annotation
      derived from UniProt keyword mapping.
    additional_reference_ids:
      - file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
    supported_by:
      - reference_id: file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
        supporting_text: "PGRP-LD restrains hyper-activation of innate immune effectors (e.g., AMPs, DUOX), thereby protecting commensal bacteria"

- term:
    id: GO:0008270
    label: zinc ion binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: >-
      The PGRP/Amidase_2 domain family typically coordinates a zinc ion at the active site.
      However, PGRP-LD lacks the conserved residues required for catalytic activity, raising
      the question of whether the zinc-binding site is functional. Sequence analysis shows
      that PGRP-LD lacks most conserved residues for PGN binding and catalytic activity.
    action: UNDECIDED
    reason: >-
      While catalytic PGRPs bind zinc at the active site, the absence of key catalytic
      residues in PGRP-LD raises uncertainty about whether zinc binding is retained.
      No direct experimental evidence confirms zinc binding in this non-catalytic PGRP.
      The annotation may be a case of domain-based over-annotation.
    additional_reference_ids:
      - file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
    supported_by:
      - reference_id: file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
        supporting_text: "The A. stephensi PGRP-LD lacks most conserved residues required for PGN binding and amidase catalytic activity"

- term:
    id: GO:0008745
    label: N-acetylmuramoyl-L-alanine amidase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: >-
      This annotation is INCORRECT. Despite belonging to the Amidase_2/PGRP superfamily,
      PGRP-LD is a non-catalytic PGRP that lacks the conserved residues required for
      peptidoglycan binding and amidase catalytic activity. Sequence analysis of the
      Anopheles stephensi ortholog demonstrated the absence of key catalytic residues.
      PGRP-LD functions as a regulatory PGRP rather than an enzymatic amidase.
    action: REMOVE
    reason: >-
      This is a classic example of domain-based over-annotation. The presence of an
      Amidase_2 domain (IPR002502) led to automatic annotation of amidase activity,
      but detailed sequence analysis shows PGRP-LD lacks the conserved residues required
      for catalysis. Not all PGRP family members are enzymatically active; many function
      as pattern recognition receptors or immune regulators without catalytic activity.
      The functional evidence clearly indicates PGRP-LD is non-catalytic.
    additional_reference_ids:
      - file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
    supported_by:
      - reference_id: file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
        supporting_text: "The A. stephensi PGRP-LD lacks most conserved residues required for PGN binding and amidase catalytic activity"
      - reference_id: file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
        supporting_text: "Current evidence supports a regulatory PGRP model for PGRP-LD, not an enzymatic PGN hydrolase"

- term:
    id: GO:0009253
    label: peptidoglycan catabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: >-
      This annotation is INCORRECT. Peptidoglycan catabolic process implies enzymatic
      degradation of peptidoglycan, which requires amidase activity. Since PGRP-LD
      lacks the conserved catalytic residues and does not function as an active amidase,
      it cannot be involved in peptidoglycan catabolism. The protein may recognize
      peptidoglycan as a pattern recognition molecule, but does not degrade it.
    action: REMOVE
    reason: >-
      This annotation logically follows from the incorrect amidase activity annotation.
      Since PGRP-LD lacks amidase catalytic activity, it cannot participate in
      peptidoglycan catabolic processes. The annotation should be removed along with
      the amidase activity annotation.
    additional_reference_ids:
      - file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
    supported_by:
      - reference_id: file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
        supporting_text: "No direct amidase activity or substrate specificity has been demonstrated for PGRP-LD; rather, sequence features argue against catalysis"

- term:
    id: GO:0045087
    label: innate immune response
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: >-
      PGRP-LD is clearly involved in the innate immune response. However, it functions
      as a NEGATIVE regulator rather than a positive effector. RNAi knockdown of PGRP-LD
      upregulates multiple immune effectors (cecropin, gambicin, defensin, DUOX),
      indicating its normal function is to restrain immune activation. This immune
      tolerance function preserves commensal bacteria and maintains peritrophic matrix
      integrity.
    action: MODIFY
    reason: >-
      While PGRP-LD is involved in innate immune response, a more accurate annotation
      would capture its specific role as a negative regulator. The current annotation
      is not wrong but could be more informative about the direction of regulation.
    proposed_replacement_terms:
      - id: GO:0045824
        label: negative regulation of innate immune response
    additional_reference_ids:
      - file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
    supported_by:
      - reference_id: file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
        supporting_text: "Knockdown of PGRP-LD upregulates multiple immune effectors (e.g., cecropin, gambicin, defensin, DUOX), consistent with a negative regulatory role constraining immune activation in response to microbiota"
      - reference_id: file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
        supporting_text: "Functions to restrain hyper-activation of immune effectors (negative regulator-like role), thereby limiting overactive Imd/Toll-like responses that deplete commensals"

# NEW annotations based on literature evidence
- term:
    id: GO:0045824
    label: negative regulation of innate immune response
  evidence_type: ISS
  original_reference_id: PMID:29489896
  review:
    summary: >-
      Functional studies in Anopheles stephensi demonstrate that PGRP-LD negatively
      regulates innate immune responses. Knockdown leads to upregulation of antimicrobial
      peptides and DUOX, indicating PGRP-LD normally restrains immune activation.
    action: NEW
    reason: >-
      This annotation captures the core function of PGRP-LD as a negative regulator
      of innate immunity. Evidence is from the closely related A. stephensi ortholog
      (ISS - inferred from sequence similarity), as direct A. gambiae knockdown data
      is not available in the literature.
    supported_by:
      - reference_id: file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
        supporting_text: "Knockdown of PGRP-LD upregulates multiple immune effectors (e.g., cecropin, gambicin, defensin, DUOX), consistent with a negative regulatory role constraining immune activation"

- term:
    id: GO:0061060
    label: negative regulation of peptidoglycan recognition protein signaling pathway
  evidence_type: ISS
  original_reference_id: PMID:29489896
  review:
    summary: >-
      PGRP-LD modulates the PGRP signaling pathway as a negative regulator. The protein
      restrains immune hyper-activation through the Imd/Toll pathways that are canonically
      activated by peptidoglycan recognition.
    action: NEW
    reason: >-
      This term accurately describes the molecular role of PGRP-LD in dampening
      PGRP-mediated immune signaling. The evidence is from orthologous studies in
      A. stephensi.
    additional_reference_ids:
      - file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
    supported_by:
      - reference_id: file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
        supporting_text: "Functional data are most consistent with PGRP-LD acting upstream as a modulator that limits overactive responses commonly associated with the Imd/Toll axes in the gut"

- term:
    id: GO:0016021
    label: integral component of membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: >-
      UniProt annotation and Phobius prediction indicate PGRP-LD has a transmembrane
      helix (residues 70-94). The protein is described as a transmembrane PGRP in
      functional studies.
    action: NEW
    reason: >-
      The UniProt entry shows transmembrane domain prediction by Phobius. Functional
      studies describe PGRP-LD as a transmembrane PGRP at the gut barrier.
    supported_by:
      - reference_id: file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
        supporting_text: "Described as a transmembrane PGRP"

- term:
    id: GO:0140678
    label: molecular function inhibitor activity
  evidence_type: ISS
  original_reference_id: PMID:29489896
  review:
    summary: >-
      PGRP-LD functions as an inhibitor of immune signaling pathways. By restraining
      the activity of Imd/Toll signaling, it prevents hyper-activation of downstream
      immune effectors. This inhibitory molecular function underlies its biological
      role in negative regulation of innate immunity.
    action: NEW
    reason: >-
      This molecular function term captures PGRP-LD's role as an inhibitor of immune
      signaling. While the precise molecular mechanism is not fully characterized,
      the functional evidence clearly demonstrates inhibitory activity on immune
      pathway components.
    supported_by:
      - reference_id: file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
        supporting_text: "Functions to restrain hyper-activation of immune effectors (negative regulator-like role), thereby limiting overactive Imd/Toll-like responses that deplete commensals"

references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO terms
  findings:
    - statement: >-
        InterPro domain-based annotations can lead to over-annotation when domain presence
        does not guarantee the associated function, particularly for domains like Amidase_2
        where not all family members are enzymatically active.

- id: GO_REF:0000043
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
  findings:
    - statement: >-
        Keyword-based annotations correctly identify PGRP-LD as involved in immunity,
        but lack specificity about its regulatory role.

- id: PMID:29489896
  title: PGRP-LD mediates A. stephensi vector competency by regulating homeostasis of microbiota-induced peritrophic matrix synthesis
  full_text_unavailable: true
  findings:
    - statement: PGRP-LD is a non-catalytic PGRP that lacks conserved residues for amidase activity
    - statement: Functions as a negative regulator of innate immunity
    - statement: Maintains gut microbiota homeostasis
    - statement: Required for peritrophic matrix integrity
    - statement: Knockdown increases Plasmodium susceptibility

- id: PMID:31907025
  title: Gut microbiota is essential in PGRP-LA regulated immune protection against Plasmodium berghei infection
  full_text_unavailable: true
  findings:
    - statement: Contextual evidence for PGRP family regulation of immunity and microbiota interactions in Anopheles

- id: file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
  title: Deep research synthesis for PGRPLD
  findings:
    - statement: PGRP-LD is a non-catalytic PGRP lacking key residues for amidase activity
      supporting_text: "The A. stephensi PGRP-LD lacks most conserved residues required for PGN binding and amidase catalytic activity"
    - statement: Functions as negative regulator of innate immunity
      supporting_text: "Knockdown of PGRP-LD upregulates multiple immune effectors (e.g., cecropin, gambicin, defensin, DUOX), consistent with a negative regulatory role constraining immune activation in response to microbiota"
    - statement: Transmembrane protein at gut barrier
      supporting_text: "Described as a transmembrane PGRP"

core_functions:
- description: >-
    PGRP-LD functions as a negative regulator of innate immunity, restraining
    immune hyper-activation to preserve gut microbiota and peritrophic matrix integrity.
  molecular_function:
    id: GO:0140678
    label: molecular function inhibitor activity
  directly_involved_in:
    - id: GO:0045824
      label: negative regulation of innate immune response
    - id: GO:0061060
      label: negative regulation of peptidoglycan recognition protein signaling pathway
  locations:
    - id: GO:0016021
      label: integral component of membrane
  supported_by:
    - reference_id: file:ANOGA/PGRPLD/PGRPLD-deep-research-falcon.md
      supporting_text: "Knockdown of PGRP-LD upregulates multiple immune effectors (e.g., cecropin, gambicin, defensin, DUOX), consistent with a negative regulatory role constraining immune activation"

proposed_new_terms: []

suggested_questions:
- question: Does A. gambiae PGRP-LD retain any zinc-binding capacity despite lacking catalytic residues?

- question: What is the mechanism by which PGRP-LD inhibits immune signaling?

suggested_experiments:
- description: >-
    Direct biochemical assay for amidase activity in recombinant A. gambiae PGRP-LD.
    While sequence analysis strongly suggests PGRP-LD is non-catalytic, direct
    enzymatic assays on the A. gambiae protein would definitively confirm the
    absence of amidase activity.

- description: >-
    RNAi knockdown of PGRP-LD in A. gambiae to confirm functional conservation.
    The functional characterization was performed in A. stephensi. Direct knockdown
    in A. gambiae would confirm the conserved immune regulatory function.