PGRPS2 is a short, secreted peptidoglycan recognition protein (PGRP) in Anopheles gambiae. It is one of three short PGRPs (S1, S2, S3) in this mosquito species, with PGRPS2 and PGRPS3 being highly similar tandem genes. Unlike PGRPS1, which lacks catalytic residues, PGRPS2 retains the conserved zinc-binding residues (His-His-Tyr-Cys motif) characteristic of catalytic PGRPs, suggesting it functions as a Zn2+-dependent N-acetylmuramoyl-L-alanine amidase. As a secreted protein with a signal peptide, PGRPS2 likely functions in the hemolymph and extracellular space to modulate peptidoglycan levels, potentially tuning IMD pathway activation and antibacterial defense. Population genetic analysis shows PGRPS2 is under purifying selection, consistent with functional constraint.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0002376 immune system process | IEA GO_REF:0000043 | MODIFY | Summary: This annotation is based on UniProtKB keyword mapping (KW-0391 "Immunity"). PGRPS2 belongs to the PGRP family, which are established pattern recognition receptors in innate immunity. Short PGRPs in Anopheles gambiae are expressed in immune-relevant tissues and participate in antibacterial defense [PMID:20067637]. While the annotation is accurate, it is overly broad - a more specific term like "innate immune response" (GO:0045087) or "defense response to bacterium" (GO:0042742) would be more informative. Reason: The term "immune system process" is too general. PGRPS2 functions specifically in innate immunity through peptidoglycan recognition and processing, modulating antibacterial defense. A more specific child term should be used. Proposed replacements: defense response to bacterium Supporting Evidence: PMID:20067637 Seven PGRP genes are known in the Anopheles gambiae genome file:ANOGA/PGRPS2/PGRPS2-deep-research-falcon.md Anopheles gambiae encodes seven PGRP genes, including three short secreted PGRPs: PGRP-S1, PGRP-S2, and PGRP-S3 |
| GO:0008270 zinc ion binding | IEA GO_REF:0000002 | ACCEPT | Summary: This annotation is based on InterPro domain IPR006619 (PGRP domain). Catalytic PGRPs are Zn2+-dependent enzymes that coordinate zinc through conserved His-His-Tyr-Cys residues. Structural analysis shows that PGRPS2 retains these conserved residues. The main difference between amidase and non-catalytic PGRPs is the presence of Zn2+ in only amidase PGRPs, which is coordinated by two histidines and one cysteine [PMID:34066955]. Reason: PGRPS2 contains the conserved zinc-binding residues (His-His-Tyr-Cys motif) found in all catalytically active PGRPs. This is supported by domain architecture and sequence conservation patterns. Zinc binding is integral to the amidase catalytic mechanism. Supporting Evidence: PMID:34066955 The main difference between amidase and non-catalytic PGRPs is the presence of Zn2+ in only amidase PGRPs, which is coordinated by two histidines and one cysteine PMID:20067637 PGRP-S2 and S3 have predicted amidase activity while PGRP-S1 does not |
| GO:0008745 N-acetylmuramoyl-L-alanine amidase activity | IEA GO_REF:0000002 | ACCEPT | Summary: This annotation is based on InterPro domains IPR002502 (Amidase_domain), IPR006619 (PGRP domain), and IPR036505 (Amidase/PGRP_sf). PGRPS2 belongs to the N-acetylmuramoyl-L-alanine amidase 2 family per UniProt. Critically, unlike PGRPS1 which lacks catalytic residues, PGRPS2 retains the conserved zinc-binding residues (His-His-Tyr-Cys) required for amidase activity [PMID:20067637]. However, direct enzymatic assays for PGRPS2 specifically have not been published. Reason: Strong evidence from domain conservation, sequence analysis showing intact zinc-binding residues, and evolutionary constraint (purifying selection) supports amidase activity. Unlike PGRPS1, PGRPS2 retains all critical catalytic residues. Supporting Evidence: PMID:20067637 Short-PGRP genes from An. gambiae differ in their structure, as PGRP-S2 and S3 have predicted amidase activity while PGRP-S1 does not PMID:34066955 Other PGRPs, including Drosophila PGRP-LB [13] and PGRP-SB1 [14], belong to the N-acetylmuramoyl-L-alanine amidase and cleave PGN into non-immunogenic compounds |
| GO:0009253 peptidoglycan catabolic process | IEA GO_REF:0000002 | ACCEPT | Summary: This annotation follows logically from the N-acetylmuramoyl-L-alanine amidase activity annotation. If PGRPS2 functions as an amidase, it would cleave peptidoglycan between MurNAc and L-Ala, constituting peptidoglycan catabolism. Catalytic short PGRPs like Drosophila PGRP-SC1/2 degrade peptidoglycan to modulate immune signaling [PMID:20067637]. Reason: This biological process annotation is the appropriate consequence of the molecular function (amidase activity). If PGRPS2 has amidase activity as supported by domain conservation and sequence analysis, it would participate in peptidoglycan catabolism. Supporting Evidence: PMID:20067637 PGRP-SC1/2 have catalytic activity and can specifically control the level of activation of the IMD signalling pathway PMID:34066955 Amidase PGRPs are capable of cleaving the PGN into non-immunogenic compounds |
| GO:0042834 peptidoglycan binding | IEA GO_REF:0000002 | ACCEPT | Summary: This annotation is based on InterPro domain IPR017331 (Peptidoglycan_recognition). All PGRPs, whether catalytic or non-catalytic, bind peptidoglycan through their conserved PGRP domain. The PGRP domain structure comprises three alpha-helices and a central beta-sheet and contains the peptidoglycan-binding groove [PMID:34066955]. PGRPS2 contains this domain and would bind peptidoglycan as a prerequisite to any catalytic function. Reason: Peptidoglycan binding is a defining characteristic of all PGRP family members. PGRPS2 has a well-defined PGRP domain that is structurally homologous to the peptidoglycan-binding domains of characterized family members. Supporting Evidence: PMID:34066955 Structural studies determined that amidase and non-catalytic PGRPs share the same structural domain involved in PGN recognition PMID:20067637 Peptidoglycan recognition proteins (PGRPs) are one family of PRR, which contain a domain very similar to bacterial amidase |
| GO:0045087 innate immune response | IEA GO_REF:0000120 | ACCEPT | Summary: This annotation is derived from combined automated annotation using InterPro domain IPR017331 and UniProtKB keyword KW-0399 (Innate immunity). PGRPS2 functions as a pattern recognition molecule in innate immunity by detecting and processing bacterial peptidoglycan. Short secreted PGRPs contribute to extracellular PGN processing that shapes IMD pathway activation and antibacterial defense [PMID:20067637]. This is more specific and appropriate than GO:0002376. Reason: This is an appropriate and well-supported annotation. PGRPS2 functions specifically in innate immunity as a secreted peptidoglycan recognition/processing protein. The term is at the right level of specificity for the PGRP family function. Supporting Evidence: PMID:20067637 Mosquito immune responses to Plasmodium play an important role in the natural control of the infection and are initiated when pathogen-associated molecular patterns (PAMPs) are recognized by pattern recognition receptor (PRR) molecules PMID:34066955 Some of these PRRs are peptidoglycan recognition proteins (PGRPs) that are ubiquitous in most animals and play a pivotal role in the innate immune system |
| GO:0005576 extracellular region | ISS PMID:20067637 Molecular evolution of the three short PGRPs of the malaria ... | NEW | Summary: PGRPS2 is a short PGRP with a signal peptide (aa 1-20 per UniProt) indicating secretion. Short PGRPs are secreted proteins typically found in hemolymph and extracellular spaces in insects. In Drosophila, short PGRPs are small extracellular proteins about 200 amino acids long present in the hemolymph and cuticle [PMID:20067637]. Reason: The current annotations lack a cellular component term. PGRPS2 has a clear signal peptide and belongs to the short (secreted) PGRP class. Its function as an extracellular modulator of peptidoglycan levels in hemolymph warrants this annotation. Supporting Evidence: PMID:20067637 In Drosophila short PGRPs are small extracellular proteins about 200 amino acids long and 18-20 kDa that are present in the hemolymph and cuticle file:ANOGA/PGRPS2/PGRPS2-deep-research-falcon.md Short (S-class) PGRPs in insects are small secreted proteins |
| GO:0061060 negative regulation of peptidoglycan recognition protein signaling pathway | ISS PMID:20067637 Molecular evolution of the three short PGRPs of the malaria ... | NEW | Summary: Catalytic PGRPs that degrade peptidoglycan serve to dampen immune signaling by reducing the pool of activating ligands. By cleaving PGN, amidase PGRPs prevent hyperactivation of the IMD pathway. In Drosophila, PGRP-SC1/2 have catalytic activity and can specifically control the level of activation of the IMD signalling pathway [PMID:20067637]. Given that PGRPS2 is predicted to have amidase activity, it would similarly function to negatively regulate PGN-induced immune signaling. Reason: Based on the conserved amidase activity and the established role of catalytic PGRPs as negative regulators of IMD signaling in other insects, this annotation captures the likely regulatory function of PGRPS2. Supporting Evidence: PMID:20067637 PGRP-SC1/2 have catalytic activity and can specifically control the level of activation of the IMD signalling pathway PMID:34066955 Drosophila PGRP-LB belongs to the amidase PGRPs and downregulates the immune deficiency (IMD) pathway by cleaving meso-2,6-diaminopimelic (meso-DAP or DAP)-type PGN |
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Download this section (compressed HTML)Q: Does PGRPS2 preferentially cleave DAP-type or Lys-type peptidoglycan, and does this correspond to defense against Gram-negative versus Gram-positive bacteria?
Q: What is the functional redundancy between PGRPS2 and PGRPS3, given their high sequence similarity?
Q: Does PGRPS2 regulate IMD pathway activation through peptidoglycan degradation, and how does this affect Plasmodium development in the mosquito?
Experiment: Express recombinant PGRPS2 and assay N-acetylmuramoyl-L-alanine amidase activity using purified peptidoglycan substrates. Compare activity with and without zinc chelators (EDTA) to confirm Zn2+ dependence. Direct biochemical characterization would definitively establish amidase activity and zinc dependence.
Experiment: Test substrate specificity of PGRPS2 amidase activity against DAP-type versus Lys-type peptidoglycan to determine preference for Gram-negative vs Gram-positive bacterial cell wall components.
Experiment: Generate CRISPR knockout of PGRPS2 in An. gambiae and assess effects on gut microbiota composition, antimicrobial peptide expression, and Plasmodium infection.
Experiment: Mutagenesis of predicted zinc-coordinating residues (His and Cys) to confirm their requirement for amidase activity.
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