PGRPLC (AGAP005203) is a transmembrane peptidoglycan recognition protein (PGRP) that serves as the principal upstream receptor for the IMD (Immune Deficiency) signaling pathway in Anopheles gambiae. It is the ortholog of Drosophila PGRP-LC. Despite containing an amidase_2 superfamily domain, PGRPLC functions as a NON-CATALYTIC pattern recognition receptor that binds DAP-type peptidoglycan from bacterial cell walls to initiate innate immune signaling. Three main isoforms (LC1, LC2, LC3) arise from alternative splicing and show distinct ligand binding properties: LC1 and LC3 bind polymeric DAP-PGN, while LC2 forms complexes with LC3 in the presence of monomeric TCT muropeptides. PGRPLC-mediated activation of the REL2/NF-kB pathway induces antimicrobial peptide expression, controls gut microbiota homeostasis, and indirectly modulates Plasmodium infection intensity in this malaria vector species.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005615 extracellular space | IBA GO_REF:0000033 | MODIFY | Summary: The IBA annotation for extracellular space is propagated from Drosophila PGRP-LC orthologs and human PGRPs. However, Anopheles PGRPLC is a transmembrane receptor with a single transmembrane helix (residues 218-241 per UniProt) and the PGRP domain is located C-terminal to this transmembrane region, indicating the receptor domain faces extracellularly. The protein is membrane-anchored, not secreted into the extracellular space. Reason: PGRPLC is a type I transmembrane protein based on UniProt domain annotation showing a transmembrane helix at positions 218-241 and the PGRP domain at 280-425. The deep research (file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md) confirms it is localized to the "Epithelial plasma membrane of the midgut". The annotation should reflect plasma membrane localization, not extracellular space which implies a secreted/soluble form. Proposed replacements: plasma membrane Supporting Evidence: file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md Functional analyses localize PGRPLC activity to the midgut epithelium with regionalized expression |
| GO:0006955 immune response | IBA GO_REF:0000033 | ACCEPT | Summary: PGRPLC is firmly established as an immune receptor that initiates the innate immune response against bacterial pathogens in Anopheles gambiae. RNAi knockdown experiments demonstrate increased mortality upon bacterial challenge and impaired antimicrobial peptide induction (file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md). Reason: This is a well-supported core function. The deep research establishes that PGRPLC knockdown "decreased survival - E. coli, 50% mortality by day 4; S. aureus, 50% by day 2 and near-complete by day 6" and impairs AMP induction. The term 'immune response' accurately captures the general biological process. Supporting Evidence: file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md Systemic antibacterial challenge survival (RNAi PGRPLC): Whole-gene KD decreased survival - E. coli, 50% mortality by day 4; S. aureus, 50% by day 2 and near-complete by day 6 (both P<0.001) |
| GO:0008745 N-acetylmuramoyl-L-alanine amidase activity | IBA GO_REF:0000033 | REMOVE | Summary: This is an OVER-ANNOTATION. While PGRPLC contains an amidase_2 superfamily domain (IPR002502), the literature explicitly states that PGRP-LC functions as a non-catalytic pattern recognition receptor in insects. The amidase fold is used for peptidoglycan binding and receptor dimerization, NOT for enzymatic hydrolysis. Reason: The deep research (file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md) explicitly states: "Despite the amidase fold, PGRP-LC functions as a non-catalytic pattern-recognition receptor in mosquitoes (structural alignment/modeling; no amidase activity reported)". OpenScientist independently found that PGRPLC lacks two of the three zinc-binding residues required for PGRP amidase catalysis (H310A and C429S relative to catalytic PGRPs). The fetched GOA line shows live IBA propagation through PANTHER:PTN002475783 from a mixed PGRP source set; this should not be retained for the non-catalytic receptor PGRP-LC subfamily. The correct molecular function is peptidoglycan immune receptor activity (GO:0016019). Propagation Review Root cause: PROPAGATION BAD Failure modes: PSEUDO OR SUBACTIVITY LOSS SOURCE EVIDENCE WEAK Sources checked: PANTHER:PTN002475783 · PAINT PGRP amidase source node SUPPORTS SOURCE BUT NOT TARGET The fetched GOA line propagates GO:0008745 through this node, but PGRPLC is a non-catalytic PGRP-LC receptor and lacks the zinc-ligand residue set needed for amidase catalysis. Supporting Evidence: file:ANOGA/PGRPLC/PGRPLC-goa.tsv UniProtKB A7UTA1 PGRPLC enables GO:0008745 N-acetylmuramoyl-L-alanine amidase activity molecular_function ECO:0000318 IBA GO_REF:0000033 FB:FBgn0033327|FB:FBgn0037906|FB:FBgn0043578|PANTHER:PTN002475783|UniProtKB:Q96PD5|ZFIN:ZDB-GENE-050419-71|ZFIN:ZDB-GENE-071227-1|ZFIN:ZDB-GENE-071227-2 7165 Anopheles gambiae GO_Central AGAP005203-PC 20250731 file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md Despite the amidase fold, PGRP-LC functions as a non-catalytic pattern-recognition receptor in mosquitoes (structural alignment/modeling; no amidase activity reported) file:ANOGA/PGRPLC/PGRPLC-hypotheses/function-hypothesis-go-0008745/openscientist.md PGRPLC lacks two of the three zinc-binding residues absolutely required for amidase catalysis file:ANOGA/PGRPLC/PGRPLC-hypotheses/function-hypothesis-go-0008745/openscientist.md The current annotation of GO:0008745 (N-acetylmuramoyl-L-alanine amidase activity) with IBA evidence should be **removed** from A7UTA1. |
| GO:0016019 peptidoglycan immune receptor activity | IBA GO_REF:0000033 | ACCEPT | Summary: This is the CORRECT and PRIMARY molecular function annotation for PGRPLC. It accurately describes the protein as a peptidoglycan recognition receptor that initiates immune signaling upon ligand binding. Reason: The deep research (file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md) confirms PGRPLC as the "Transmembrane pattern-recognition receptor of the IMD/REL2 pathway" that "Recognizes DAP-type PGN ligands in both polymeric (bacterial sacculus) and monomeric (TCT-like) forms via isoform assemblies." Pull-down assays demonstrate direct peptidoglycan binding by PGRPLC isoforms. This is the core molecular function term for this protein. Supporting Evidence: file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md Ligand specificity: PGRPLC discriminates between polymeric DAP-type PGN and monomeric muropeptides (TCT). In pull-down assays, LC1 and LC3 bind insoluble polymeric DAP-PGN, while LC2 forms complexes with LC3 in the presence of TCT monomer |
| GO:0050830 defense response to Gram-positive bacterium | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: PGRPLC is primarily known as a receptor for DAP-type peptidoglycan, which is characteristic of Gram-negative bacteria and Bacillus species. However, experimental evidence shows PGRPLC-dependent survival and AMP induction against S. aureus (Gram-positive). Reason: The deep research (file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md) shows PGRPLC knockdown causes mortality after S. aureus challenge: "S. aureus, 50% by day 2 and near-complete by day 6." However, the primary recognized ligand is DAP-type PGN from Gram-negative bacteria. Gram-positive bacteria like S. aureus contain Lys-type PGN, not DAP-type. The defense response may be indirect or involve cross-reactivity. PGRPLC's canonical role is in sensing Gram-negative bacteria through the IMD pathway. A more appropriate annotation would be defense response to Gram-negative bacterium (GO:0050829), but the existing annotation is not wrong as PGRPLC does contribute to Gram-positive defense. Supporting Evidence: file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md Systemic antibacterial challenge survival: S. aureus, 50% by day 2 and near-complete by day 6 (both P<0.001) |
| GO:0002376 immune system process | IEA GO_REF:0000043 | ACCEPT | Summary: This IEA annotation from UniProtKB keyword mapping is a broad parent term of the more specific immune response annotation. It is not wrong but is less informative than the existing IBA annotation for immune response. Reason: The annotation is correct as PGRPLC participates in immune system processes. However, the more specific 'immune response' (GO:0006955) annotation is preferred for capturing the gene's function. This broader term can be retained as it does not conflict and provides a valid hierarchical annotation. Supporting Evidence: file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md PGRP-LC-driven sensing in the gut is particularly important for antibacterial defense |
| GO:0008270 zinc ion binding | IEA GO_REF:0000002 | UNDECIDED | Summary: This IEA annotation is based on InterPro domain IPR006619 (PGRP domain). The PGRP domain structure in catalytic family members coordinates a zinc ion essential for amidase activity. However, since PGRPLC is non-catalytic, the zinc binding function may not be relevant. Reason: The InterPro PGRP domain annotation (IPR006619) suggests potential zinc binding based on structural homology to catalytic PGRPs. However, the deep research (file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md) explicitly states PGRPLC is non-catalytic and "no amidase activity reported." Catalytic PGRPs require zinc for amidase activity, but non-catalytic PGRPs may have lost critical zinc-coordinating residues. Without specific structural data for Anopheles PGRPLC showing zinc coordination, this annotation remains uncertain. Supporting Evidence: file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md Despite the amidase fold, PGRP-LC functions as a non-catalytic pattern-recognition receptor |
| GO:0008745 N-acetylmuramoyl-L-alanine amidase activity | IEA GO_REF:0000002 | REMOVE | Summary: This is the same over-annotation as the IBA version, but derived from InterPro domain mapping instead of phylogenetic inference. PGRPLC does NOT have amidase activity. Reason: Same rationale as for the IBA annotation above. The InterPro domains (IPR002502, IPR006619, IPR036505) are structural domains that can be present in both catalytic and non-catalytic PGRPs. PGRPLC uses this fold for peptidoglycan binding and receptor function, NOT for enzymatic hydrolysis. The literature explicitly confirms this is a non-catalytic receptor PGRP (file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md). Supporting Evidence: file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md It is not an active amidase enzyme; rather, it uses a PGRP/amidase_2 structural fold for ligand binding and receptor dimerization to initiate signaling |
| GO:0009253 peptidoglycan catabolic process | IEA GO_REF:0000002 | REMOVE | Summary: This annotation implies PGRPLC degrades peptidoglycan, which is incorrect. PGRPLC binds peptidoglycan as a receptor ligand but does not catabolize it. Reason: This annotation is a logical consequence of the incorrect amidase activity annotation. Since PGRPLC is a non-catalytic receptor, it does not participate in peptidoglycan catabolism. It binds peptidoglycan to initiate signaling, but binding is not catabolism. The correct process annotation is the peptidoglycan recognition protein signaling pathway (GO:0061057) or immune response (file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md). Supporting Evidence: file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md It uses a PGRP/amidase_2 structural fold for ligand binding and receptor dimerization to initiate signaling |
| GO:0045087 innate immune response | IEA GO_REF:0000043 | ACCEPT | Summary: This annotation accurately captures that PGRPLC functions in innate immunity. It is more specific than 'immune system process' and appropriately describes the non-adaptive immune function of this receptor. Reason: The deep research (file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md) and multiple publications confirm PGRPLC as the canonical innate immune receptor for the IMD pathway in mosquitoes. The term is appropriate and well-supported by experimental evidence showing PGRPLC initiates innate immune responses including AMP production and defense against bacteria. Supporting Evidence: file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md PGRPLC is the principal transmembrane receptor that activates the mosquito IMD/REL2 NF-kB pathway, leading to induction of antimicrobial peptide (AMP) genes |
| GO:0061057 peptidoglycan recognition protein signaling pathway | TAS file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md | NEW | Summary: PGRPLC is the initiating receptor for the peptidoglycan recognition protein (IMD) signaling pathway. This is a missing core process annotation. Reason: The deep research (file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md) explicitly states PGRPLC is "Upstream PRR of the mosquito IMD pathway, activating REL2/NF-kB to induce AMPs." The GO term GO:0061057 explicitly describes this pathway with definition: "The series of molecular signals initiated by binding of peptidoglycan to a receptor and ending with regulation of a downstream cellular process. The main outcome of the Imd signaling is the production of antimicrobial peptides." This is the most specific and appropriate process term for PGRPLC. Supporting Evidence: file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md PGRPLC is the principal transmembrane receptor that activates the mosquito IMD/REL2 NF-kB pathway |
| GO:0050829 defense response to Gram-negative bacterium | TAS file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md | NEW | Summary: PGRPLC specifically recognizes DAP-type peptidoglycan, which is characteristic of Gram-negative bacteria. This is the primary defense response mediated by PGRPLC. Reason: The deep research (file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md) confirms "Substrate specificity: Discriminates DAP-type PGN." DAP-type peptidoglycan is the signature cell wall component of Gram-negative bacteria. PGRPLC knockdown increases susceptibility to E. coli (Gram-negative) and also affects Plasmodium infection through gut microbiota control (primarily Gram-negative in mosquito gut). This term complements the existing Gram-positive annotation and is arguably more central to PGRPLC function. Supporting Evidence: file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md Substrate specificity: Discriminates DAP-type PGN. LC1/LC3 bind polymeric DAP-PGN |
| GO:0042834 peptidoglycan binding | IDA file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md | NEW | Summary: Biochemical pull-down assays demonstrate direct binding of PGRPLC isoforms to peptidoglycan ligands, supporting a peptidoglycan binding annotation. Reason: The deep research (file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md) reports: "Biochemical ligand interactions: Co-precipitation shows LC1 and LC3 bind insoluble polymeric DAP-type PGN; LC2 forms complexes with LC3 in the presence of the monomeric muropeptide TCT." This is direct experimental evidence for peptidoglycan binding activity. While peptidoglycan immune receptor activity (GO:0016019) encompasses this function, peptidoglycan binding (GO:0042834) is an appropriate supporting annotation for the binding activity itself. Supporting Evidence: file:ANOGA/PGRPLC/PGRPLC-deep-research-falcon.md Co-precipitation shows LC1 and LC3 bind insoluble polymeric DAP-type PGN; LC2 forms complexes with LC3 in the presence of the monomeric muropeptide TCT |
Loading supporting content…
Download this section (compressed HTML)Q: Has the catalytic site residue status been experimentally verified for An. gambiae PGRPLC, confirming it lacks amidase activity?
Q: What is the three-dimensional structure of PGRPLC PGRP domain and how does it compare to catalytic vs non-catalytic PGRP structures?
Q: Does PGRPLC coordinate zinc, and if so, what is its functional role in ligand binding?
Experiment: Recombinant expression and biochemical assay to definitively confirm absence of amidase activity
Hypothesis: PGRPLC lacks amidase activity due to non-catalytic residues in the active site
Experiment: Crystal or cryo-EM structure determination of PGRPLC PGRP domain with and without PGN ligand
Hypothesis: PGRPLC PGRP domain adopts receptor conformation distinct from catalytic PGRPs
Experiment: Metal binding analysis (ITC, ICP-MS) to determine zinc coordination status
Hypothesis: PGRPLC may or may not coordinate zinc depending on retention of zinc-binding residues
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)