SRPN2

UniProt ID: Q7QIJ8
Organism: Anopheles gambiae
Review Status: IN PROGRESS
๐Ÿ“ Provide Detailed Feedback

Gene Description

SRPN2 (Serpin-2) is a secreted serine protease inhibitor that functions as a key negative regulator of the melanization defense response in Anopheles gambiae. It acts in the hemolymph to inhibit CLIP-domain serine proteases (CLIPB9, CLIPB10, CLIPB4) that would otherwise activate prophenoloxidase, thereby preventing excessive melanization. SRPN2 knockdown causes spontaneous melanotic pseudotumors, shortened lifespan, and enhanced killing of Plasmodium parasites through ookinete lysis and melanization.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0004867 serine-type endopeptidase inhibitor activity
IBA
GO_REF:0000033 		ACCEPT
Summary: SRPN2 is a well-characterized serpin that directly inhibits CLIP-domain serine proteases including CLIPB9, CLIPB10, and CLIPB4. The IBA annotation based on phylogenetic inference is strongly supported by multiple direct experimental studies demonstrating serine protease inhibitor activity [PMID:20953892, PMID:25525260, PMID:33520733].
Reason: This molecular function annotation is the core enzymatic activity of SRPN2. Biochemical studies have demonstrated that SRPN2 forms covalent, SDS-stable inhibitory complexes with its target proteases (CLIPB9, CLIPB10) with stoichiometry consistent with classic serpin inhibition mechanism [PMID:25525260, PMID:33520733]. The IBA annotation is phylogenetically appropriate given serpin family conservation.
Supporting Evidence:
PMID:20953892
we identified the Anopheles gambiae clip-serine proteinase CLIPB9 as a PPO-activating proteinase, which is inhibited by SRPN2
PMID:25525260
SRPN2 irreversibly inhibits clip domain serine proteinase 9 (CLIPB9), which functions in a serine proteinase cascade culminating in the activation of prophenoloxidase and melanization
PMID:33520733
The stoichiometry of inhibition was 1.89, indicating that, under the used experimental conditions, SRPN2 acts as an inhibitor and not as substrate for CLIPB10
GO:0050776 regulation of immune response
IBA
GO_REF:0000033 		MODIFY
Summary: SRPN2 regulates the melanization arm of the innate immune response by inhibiting proteases that activate prophenoloxidase. However, a more specific term exists (GO:0035009 negative regulation of melanization defense response) that precisely captures SRPN2's function [PMID:16113656, PMID:20953892].
Reason: While technically accurate that SRPN2 is involved in regulation of immune response, this term is too broad. SRPN2 specifically negatively regulates the melanization defense response, not immune responses generally. The more specific term GO:0035009 is already annotated and better represents the biological function.
Supporting Evidence:
PMID:16113656
knockdown of SRPN2 in adult Anopheles gambiae produced a notable phenotype: the appearance of melanotic pseudotumours, which increased in size and number with time, indicating spontaneous melanization
PMID:20953892
serpin-2 (SRPN2), which was previously identified as a key negative regulator of melanization
GO:0005615 extracellular space
IBA
GO_REF:0000033 		ACCEPT
Summary: SRPN2 is a secreted serpin that functions in the hemolymph (the insect equivalent of blood/extracellular fluid). Multiple studies confirm its extracellular localization [PMID:16113656, PMID:20953892]. The IBA annotation aligns with experimental evidence.
Reason: The extracellular space annotation is well-supported. SRPN2 contains a signal peptide and is secreted into the hemolymph where it functions to inhibit circulating proteases. This is consistent with the phylogenetic inference and the serpin family biology.
Supporting Evidence:
PMID:20953892
controlled by an extracellular proteinase cascade and serpin inhibitors
GO:0002376 immune system process
IEA
GO_REF:0000043 		ACCEPT
Summary: This IEA annotation from UniProt keyword mapping is accurate but very broad. SRPN2 is involved in the melanization branch of innate immunity, specifically as a negative regulator. More specific terms are already annotated [PMID:16113656].
Reason: While broad, this IEA annotation is not incorrect - SRPN2 does function in an immune system process (melanization). More specific annotations are already present (GO:0035009, GO:0045087). IEA annotations providing broader context alongside more specific experimental annotations is acceptable practice.
Supporting Evidence:
PMID:20953892
Melanization is an innate immune response in arthropods that encapsulates and kills invading pathogens
GO:0004867 serine-type endopeptidase inhibitor activity
IEA
GO_REF:0000120 		ACCEPT
Summary: Redundant with the IBA and IDA annotations for the same term but from automated InterPro/ARBA mapping. The annotation is correct and consistent with experimental evidence.
Reason: This IEA annotation is accurate. SRPN2 belongs to the serpin family (IPR000215) and exhibits serine-type endopeptidase inhibitor activity as demonstrated experimentally. The IEA provides supporting evidence from sequence/domain analysis consistent with experimental findings.
Supporting Evidence:
PMID:25525260
SRPN2 irreversibly inhibits clip domain serine proteinase 9 (CLIPB9)
GO:0005576 extracellular region
IEA
GO_REF:0000044 		ACCEPT
Summary: IEA annotation from UniProt subcellular location mapping. SRPN2 is secreted into the hemolymph, making this annotation accurate. The more specific child term GO:0005615 (extracellular space) is also annotated.
Reason: This broader cellular component term is accurate - SRPN2 is indeed located in the extracellular region (secreted into hemolymph). Having both this broader term and the more specific extracellular space term is acceptable.
Supporting Evidence:
PMID:20953892
controlled by an extracellular proteinase cascade and serpin inhibitors
GO:0005615 extracellular space
IEA
GO_REF:0000002 		ACCEPT
Summary: IEA annotation from InterPro2GO mapping for serpin family. Redundant with IBA and IDA annotations but consistent with the established extracellular localization of SRPN2.
Reason: Accurate annotation derived from serpin domain presence. Serpins of this type are typically secreted, and SRPN2 has been experimentally confirmed to be secreted into the hemolymph.
Supporting Evidence:
PMID:20953892
extracellular proteinase cascade and serpin inhibitors
GO:0030414 peptidase inhibitor activity
IEA
GO_REF:0000043 		ACCEPT
Summary: IEA annotation from UniProt keyword mapping. This is a parent term of GO:0004867 (serine-type endopeptidase inhibitor activity). While accurate, it is less specific than what is known about SRPN2.
Reason: This parent-level annotation is technically correct but adds limited information beyond the more specific serine-type endopeptidase inhibitor activity annotation. However, it is not wrong to have both parent and child terms annotated when the evidence supports it.
Supporting Evidence:
PMID:25525260
SRPN2 irreversibly inhibits clip domain serine proteinase 9 (CLIPB9)
GO:0045087 innate immune response
IEA
GO_REF:0000043 		ACCEPT
Summary: IEA annotation from UniProt keyword mapping (Innate immunity). SRPN2 functions in the melanization arm of innate immunity. This is an appropriate level of specificity for the immune process aspect of SRPN2 function.
Reason: Melanization is a component of the innate immune response in arthropods. SRPN2's role in regulating melanization means it participates in innate immunity. The annotation is appropriate.
Supporting Evidence:
PMID:20953892
Melanization is an innate immune response in arthropods that encapsulates and kills invading pathogens
GO:0004867 serine-type endopeptidase inhibitor activity
IMP
PMID:33520733
CLIPB10 is a Terminal Protease in the Regulatory Network Tha... 		ACCEPT
Summary: IMP annotation based on mutant phenotype evidence from PMID:33520733. The study demonstrates that SRPN2 knockdown causes spontaneous melanization, which is partially rescued by CLIPB10 co-knockdown, supporting SRPN2's role as a serine protease inhibitor.
Reason: The study shows that SRPN2 knockdown leads to uncontrolled melanization (due to loss of protease inhibition), and this is partially rescued by depleting the target protease CLIPB10. This genetic evidence supports the serine protease inhibitor function.
Supporting Evidence:
PMID:33520733
The kd of SRPN2 caused severe melanotic tumors on the abdomen of mosquitoes, which were partially reversed by CLIPB10 kd in SRPN2-depleted mosquitoes
GO:0005515 protein binding
IPI
PMID:33520733
CLIPB10 is a Terminal Protease in the Regulatory Network Tha... 		MODIFY
Summary: IPI annotation based on physical interaction with CLIPB10 (UniProtKB:Q7QBP4). While the interaction is real and biologically meaningful, "protein binding" is too vague and does not capture the nature of the serpin-protease inhibitory complex formation.
Reason: Per curation guidelines, "protein binding" is too uninformative when more specific MF terms are available. The SRPN2-CLIPB10 interaction is specifically an inhibitory serpin-protease complex. A better annotation would be the specific inhibitor activity term or a more informative binding term that indicates the functional outcome.
Supporting Evidence:
PMID:33520733
formed a SDS-stable protein complex with activated recombinant CLIPB10
GO:0010951 negative regulation of endopeptidase activity
IMP
PMID:33520733
CLIPB10 is a Terminal Protease in the Regulatory Network Tha... 		ACCEPT
Summary: IMP annotation based on SRPN2 knockdown leading to increased endopeptidase activity (evidenced by increased melanization due to uncontrolled PPO activation). This is a direct consequence of SRPN2's inhibitor function.
Reason: SRPN2 knockdown results in enhanced protease activity (CLIPB10, CLIPB9) leading to spontaneous melanization. This genetic evidence supports the annotation that SRPN2 negatively regulates endopeptidase activity in vivo.
Supporting Evidence:
PMID:33520733
CLIPB10 activity decreased linearly with increasing concentrations of SRPN2
GO:0010955 negative regulation of protein processing
IMP
PMID:33045027
The CLIP-domain serine protease CLIPC9 regulates melanizatio... 		ACCEPT
Summary: IMP annotation from PMID:33045027. SRPN2 knockdown results in enhanced cleavage/processing of downstream substrates (CLIPA28, CLIPC9) in the melanization cascade, demonstrating that SRPN2 negatively regulates protein processing.
Reason: The study shows that SRPN2 silencing enhances CLIPC9 cleavage, indicating SRPN2 normally restrains proteolytic processing in the cascade. This is consistent with its role as a protease inhibitor that prevents cascade activation.
Supporting Evidence:
PMID:33045027
CLIPC9 processing is negatively regulated by serine protease inhibitor 2 (SRPN2)
GO:0004867 serine-type endopeptidase inhibitor activity
IDA
PMID:20953892
Characterization of a regulatory unit that controls melaniza... 		ACCEPT
Summary: IDA annotation based on direct biochemical demonstration that SRPN2 inhibits CLIPB9. This is the first study to identify a specific SRPN2 target protease.
Reason: Direct biochemical evidence shows SRPN2 forms an inhibitory complex with CLIPB9 and blocks its protease activity. This is core experimental evidence for SRPN2's molecular function.
Supporting Evidence:
PMID:20953892
we identified the Anopheles gambiae clip-serine proteinase CLIPB9 as a PPO-activating proteinase, which is inhibited by SRPN2
GO:0004867 serine-type endopeptidase inhibitor activity
IDA
PMID:25525260
Structural and inhibitory effects of hinge loop mutagenesis ... 		ACCEPT
Summary: IDA annotation based on detailed biochemical and structural characterization of SRPN2-CLIPB9 interaction. The study includes kinetic analysis and structure-function studies of the inhibitory mechanism.
Reason: High-quality biochemical study demonstrating the inhibitory mechanism of SRPN2 against CLIPB9 with kinetic parameters and structural insights into the hinge region function.
Supporting Evidence:
PMID:25525260
Serpin-2 (SRPN2) is a key negative regulator of the melanization response in the malaria vector Anopheles gambiae. SRPN2 irreversibly inhibits clip domain serine proteinase 9 (CLIPB9)
GO:0005515 protein binding
IPI
PMID:20953892
Characterization of a regulatory unit that controls melaniza... 		MODIFY
Summary: IPI annotation for interaction with CLIPB9 (UniProtKB:F5HKX0). As with the CLIPB10 interaction, "protein binding" is too vague for this specific inhibitory interaction.
Reason: The SRPN2-CLIPB9 interaction is an inhibitory serpin-protease complex formation. The more informative serine-type endopeptidase inhibitor activity term better captures this functional interaction.
Supporting Evidence:
PMID:20953892
clip-serine proteinase CLIPB9 as a PPO-activating proteinase, which is inhibited by SRPN2
GO:0005515 protein binding
IPI
PMID:25525260
Structural and inhibitory effects of hinge loop mutagenesis ... 		MODIFY
Summary: IPI annotation for SRPN2-CLIPB9 interaction from structural/biochemical study. This is redundant with the PMID:20953892 annotation and similarly too vague.
Reason: Same rationale as other protein binding annotations - the interaction represents a specific inhibitory complex formation that is better captured by the serine-type endopeptidase inhibitor activity term.
Supporting Evidence:
PMID:25525260
SRPN2 irreversibly inhibits clip domain serine proteinase 9 (CLIPB9)
GO:0005615 extracellular space
IDA
PMID:20953892
Characterization of a regulatory unit that controls melaniza... 		ACCEPT
Summary: IDA annotation for extracellular localization based on detection of SRPN2 in hemolymph samples and its function in the extracellular protease cascade.
Reason: SRPN2 is detected in hemolymph and functions to inhibit extracellular proteases. This experimental evidence supports the extracellular space localization.
Supporting Evidence:
PMID:20953892
The molecular composition of this system is largely unknown in mosquitoes with the exception of serpin-2 (SRPN2)
GO:0035009 negative regulation of melanization defense response
IDA
PMID:20953892
Characterization of a regulatory unit that controls melaniza... 		ACCEPT
Summary: IDA annotation for SRPN2's core biological function - negative regulation of melanization. This is a highly specific and appropriate term for SRPN2's role in the melanization cascade.
Reason: This is the most specific and informative biological process annotation for SRPN2. SRPN2 knockdown causes spontaneous melanization, demonstrating it is a key negative regulator of this immune response. This represents a core function of the gene.
Supporting Evidence:
PMID:20953892
serpin-2 (SRPN2), which was previously identified as a key negative regulator of melanization
PMID:16113656
knockdown of SRPN2 in adult Anopheles gambiae produced a notable phenotype: the appearance of melanotic pseudotumours
GO:0045861 negative regulation of proteolysis
IDA
PMID:20953892
Characterization of a regulatory unit that controls melaniza... 		ACCEPT
Summary: IDA annotation based on SRPN2's inhibition of proteolytic cascade enzymes. This is an accurate but somewhat redundant annotation given the more specific negative regulation of melanization defense response annotation.
Reason: SRPN2 inhibits CLIPB9 and other proteases, thereby negatively regulating proteolysis in the melanization cascade. While this is a parent term of more specific regulatory processes, it accurately describes SRPN2's biochemical effect.
Supporting Evidence:
PMID:20953892
CLIPB9 as a PPO-activating proteinase, which is inhibited by SRPN2
GO:0045861 negative regulation of proteolysis
IDA
PMID:25525260
Structural and inhibitory effects of hinge loop mutagenesis ... 		ACCEPT
Summary: IDA annotation from the structural/biochemical study showing SRPN2 inhibits CLIPB9 proteolytic activity.
Reason: The study provides detailed biochemical evidence for SRPN2's inhibition of CLIPB9 proteolytic activity, including kinetic analysis. Supports negative regulation of proteolysis.
Supporting Evidence:
PMID:25525260
SRPN2 irreversibly inhibits clip domain serine proteinase 9 (CLIPB9)
GO:0005615 extracellular space
IDA
PMID:16113656
Anopheles gambiae SRPN2 facilitates midgut invasion by the m... 		ACCEPT
Summary: IDA annotation from the original study characterizing SRPN2 function. SRPN2 is secreted into the hemolymph.
Reason: This foundational study established SRPN2's function and localization. The extracellular space annotation is appropriate for this secreted serpin.
Supporting Evidence:
PMID:20953892
controlled by an extracellular proteinase cascade and serpin inhibitors
GO:0035009 negative regulation of melanization defense response
IDA
PMID:16113656
Anopheles gambiae SRPN2 facilitates midgut invasion by the m... 		ACCEPT
Summary: IDA annotation from the foundational study demonstrating SRPN2 knockdown causes spontaneous melanization. This is core evidence for SRPN2's function.
Reason: The original Michel et al. 2005 study provides the primary evidence that SRPN2 is a negative regulator of melanization - knockdown results in melanotic pseudotumors. This is the defining biological function of SRPN2.
Supporting Evidence:
PMID:16113656
knockdown of SRPN2 in adult Anopheles gambiae produced a notable phenotype: the appearance of melanotic pseudotumours, which increased in size and number with time, indicating spontaneous melanization
GO:0042832 defense response to protozoan
IDA
PMID:16113656
Anopheles gambiae SRPN2 facilitates midgut invasion by the m... 		MODIFY
Summary: IDA annotation based on SRPN2's effect on Plasmodium berghei infection outcomes. SRPN2 knockdown results in enhanced ookinete killing through melanization, suggesting SRPN2 modulates defense against the parasite.
Reason: This annotation is problematic. SRPN2 actually FACILITATES parasite survival by suppressing the melanization response that would otherwise kill ookinetes. Knockdown of SRPN2 enhances defense, meaning the wild-type protein acts as a negative regulator of defense response to the protozoan, not a positive contributor to defense. The annotation should be to negative regulation of defense response to protozoan or removed.
Supporting Evidence:
PMID:16113656
knockdown of SRPN2 strongly interfered with the invasion of A. gambiae midguts by the rodent malaria parasite Plasmodium berghei. It did not affect ookinete formation, but markedly reduced oocyst numbers, by 97%, as a result of increased ookinete lysis and melanization

Core Functions

SRPN2 is a classic inhibitory serpin that forms covalent, SDS-stable complexes with target serine proteases including CLIPB9, CLIPB10, and CLIPB4. The inhibition involves the reactive center loop trapping the protease in an inactive complex. SRPN2 is the primary negative regulator of the melanization cascade in A. gambiae, preventing uncontrolled melanization that would otherwise cause melanotic pseudotumors and shortened lifespan.

Molecular Function:
serine-type endopeptidase inhibitor activity
Directly Involved In:
negative regulation of melanization defense response
Cellular Locations:
extracellular space
Supporting Evidence:
  • PMID:16113656
    knockdown of SRPN2 in adult Anopheles gambiae produced a notable phenotype: the appearance of melanotic pseudotumours
  • PMID:20953892
    we identified the Anopheles gambiae clip-serine proteinase CLIPB9 as a PPO-activating proteinase, which is inhibited by SRPN2
  • PMID:33520733
    CLIPB10 activity decreased linearly with increasing concentrations of SRPN2

References

GO_REF:0000002
Gene Ontology annotation through association of InterPro records with GO terms
GO_REF:0000033
Annotation inferences using phylogenetic trees
GO_REF:0000043
Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
GO_REF:0000044
Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
GO_REF:0000120
Combined Automated Annotation using Multiple IEA Methods
PMID:16113656
Anopheles gambiae SRPN2 facilitates midgut invasion by the malaria parasite Plasmodium berghei.
  • SRPN2 knockdown causes spontaneous melanotic pseudotumors and reduced lifespan
  • SRPN2 knockdown reduces Plasmodium oocyst numbers by 97% through enhanced ookinete melanization
  • SRPN2 is secreted into the hemolymph
PMID:20953892
Characterization of a regulatory unit that controls melanization and affects longevity of mosquitoes.
  • CLIPB9 is a PPO-activating proteinase inhibited by SRPN2
  • SRPN2-CLIPB9 is the first characterized inhibitory serpin-protease pair in mosquitoes
  • Double knockdown of SRPN2 and CLIPB9 reverses the SRPN2-knockdown phenotype
PMID:25525260
Structural and inhibitory effects of hinge loop mutagenesis in serpin-2 from the malaria vector Anopheles gambiae.
  • SRPN2 irreversibly inhibits CLIPB9 via classic serpin mechanism
  • Crystal structures reveal hinge region function in serpin-protease complex formation
  • Kinetic analysis of SRPN2-CLIPB9 inhibition
PMID:33045027
The CLIP-domain serine protease CLIPC9 regulates melanization downstream of SPCLIP1, CLIPA8, and CLIPA28 in the malaria vector Anopheles gambiae.
  • SRPN2 negatively regulates CLIPC9 processing
  • CLIPC9 functions downstream in the melanization cascade
PMID:33520733
CLIPB10 is a Terminal Protease in the Regulatory Network That Controls Melanization in the African Malaria Mosquito Anopheles gambiae.
  • SRPN2 directly inhibits CLIPB10 with stoichiometry of 1.89
  • SRPN2 forms SDS-stable complex with CLIPB10
  • CLIPB10 knockdown partially rescues SRPN2-knockdown melanotic tumor phenotype

Suggested Questions for Experts

Q: Are there additional CLIPB proteases that are SRPN2 targets? The incomplete rescue of SRPN2-knockdown phenotype by single CLIPB knockdowns suggests additional targets.

Q: What is the physiological role of the partial hinge insertion in SRPN2? The structural studies suggest it may represent a trade-off between RCL accessibility and inhibitory efficiency.

Q: How does SRPN2 expression and activity change during Plasmodium infection to permit localized melanization while preventing systemic pathology?

Suggested Experiments

Experiment: Proteomics analysis of SRPN2 complexes in hemolymph to identify the complete set of SRPN2 target proteases under different immune challenge conditions.

Experiment: Time-course analysis of SRPN2 protein levels during Plasmodium infection to understand how melanization is permitted at the ookinete invasion site.

๐Ÿ“š Additional Documentation

Deep Research Falcon

(SRPN2-deep-research-falcon.md)

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gene_id: SRPN2
gene_symbol: SRPN2
uniprot_accession: Q7QIJ8
protein_description: 'RecName: Full=Serine protease inhibitor 2 {ECO:0000303|PubMed:19394412};
Short=Serpin 2 {ECO:0000303|PubMed:19394412}; Flags: Precursor;'
gene_info: Name=SRPN2 {ECO:0000303|PubMed:19394412}; Synonyms=1270169; ORFNames=AgaP_AGAP006911
{ECO:0000312|EMBL:EAA04043.4};
organism_full: Anopheles gambiae (African malaria mosquito).
protein_family: Belongs to the serpin family.
protein_domains: Serpin_CS. (IPR023795); Serpin_dom. (IPR023796); Serpin_fam. (IPR000215);
Serpin_sf. (IPR036186); Serpin_sf_1. (IPR042178)
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Question

Gene Research for Functional Annotation

โš ๏ธ 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: Q7QIJ8
  • Protein Description: RecName: Full=Serine protease inhibitor 2 {ECO:0000303|PubMed:19394412}; Short=Serpin 2 {ECO:0000303|PubMed:19394412}; Flags: Precursor;
  • Gene Information: Name=SRPN2 {ECO:0000303|PubMed:19394412}; Synonyms=1270169; ORFNames=AgaP_AGAP006911 {ECO:0000312|EMBL:EAA04043.4};
  • Organism (full): Anopheles gambiae (African malaria mosquito).
  • Protein Family: Belongs to the serpin family.
  • Key Domains: Serpin_CS. (IPR023795); Serpin_dom. (IPR023796); Serpin_fam. (IPR000215); Serpin_sf. (IPR036186); Serpin_sf_1. (IPR042178)

MANDATORY VERIFICATION STEPS:

  1. Check if the gene symbol "SRPN2" 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 'SRPN2' 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 SRPN2 (gene ID: SRPN2, UniProt: Q7QIJ8) 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

โš ๏ธ 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: Q7QIJ8
  • Protein Description: RecName: Full=Serine protease inhibitor 2 {ECO:0000303|PubMed:19394412}; Short=Serpin 2 {ECO:0000303|PubMed:19394412}; Flags: Precursor;
  • Gene Information: Name=SRPN2 {ECO:0000303|PubMed:19394412}; Synonyms=1270169; ORFNames=AgaP_AGAP006911 {ECO:0000312|EMBL:EAA04043.4};
  • Organism (full): Anopheles gambiae (African malaria mosquito).
  • Protein Family: Belongs to the serpin family.
  • Key Domains: Serpin_CS. (IPR023795); Serpin_dom. (IPR023796); Serpin_fam. (IPR000215); Serpin_sf. (IPR036186); Serpin_sf_1. (IPR042178)

MANDATORY VERIFICATION STEPS:

  1. Check if the gene symbol "SRPN2" 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 'SRPN2' 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 SRPN2 (gene ID: SRPN2, UniProt: Q7QIJ8) 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.

Plan status
- Identity verification: Completed. Target is Anopheles gambiae serpin SRPN2 (UniProt Q7QIJ8; AGAP006911), a secreted serine protease inhibitor in the serpin superfamily that regulates melanization. Domains and serpin fold match UniProt and literature; no conflicting gene symbol usage detected (an2011crystalstructureof pages 1-2, michel2005anophelesgambiaesrpn2 pages 1-2).

Research report: SRPN2 (Anopheles gambiae serpin-2) โ€” functional annotation and current understanding

1) Key concepts and definitions
- Protein identity and family: SRPN2 is a secreted serine protease inhibitor (serpin) from Anopheles gambiae that adopts the canonical serpin fold (three ฮฒ-sheets, multiple ฮฑ-helices) with an exposed reactive center loop (RCL) used to โ€œsuicideโ€ inhibit target serine proteases via formation of SDS-stable complexes (Proteins: Structure, Jun 2011; https://doi.org/10.1002/prot.23002) (an2011crystalstructureof pages 1-2).
- Primary biological role: SRPN2 is a principal negative regulator of the insect melanization response by suppressing the prophenoloxidase (proPO) activation cascade in mosquito hemolymph. RNAi-mediated depletion induces spontaneous melanotic tumors, elevated melanin deposition, and reduced mosquito lifespan (EMBO Reports, Sep 2005; https://doi.org/10.1038/sj.embor.7400478) (michel2005anophelesgambiaesrpn2 pages 1-2, michel2005anophelesgambiaesrpn2 pages 2-3). A 2013 expert review consolidated SRPN2 as the only mosquito serpin with a defined molecular function at the time: inhibiting proPO-activating proteases to restrain melanization (Journal of Insect Physiology, Feb 2013; https://doi.org/10.1016/j.jinsphys.2012.08.015) (gulley2013therolesof pages 10-11, gulley2013therolesof pages 8-10).
- Biochemical mechanism and substrates: SRPN2 forms covalent, SDS-stable inhibitory complexes with clip-domain serine proteases that act in proPO activation. Direct targets established to date include CLIPB9 and CLIPB10, both proPO-activating proteases (PAPs) in A. gambiae (Frontiers in Cellular and Infection Microbiology, Jan 2021; https://doi.org/10.3389/fcimb.2020.585986; Journal of Insect Physiology, Feb 2013; https://doi.org/10.1016/j.jinsphys.2012.08.015) (zhang2021clipb10isa pages 1-2, gulley2013therolesof pages 8-10).
- Subcellular localization: SRPN2 is an extracellular, hemolymph serpin; hemolymph depletion and systemic RNAi phenotypes indicate its function in the circulating immune milieu rather than intracellular compartments (Proteins: Structure, Jun 2011; EMBO Reports, Sep 2005) (an2011crystalstructureof pages 1-2, michel2005anophelesgambiaesrpn2 pages 1-2).

2) Molecular function, pathway placement, and localization details
- Negative regulator of melanization/PPO activation: Early functional genetics showed SRPN2 knockdown causes widespread melanotic masses beginning 2 days post-dsRNA (100% by day 4), with a threefold decrease in survival by day 10. Mechanistically, SRPN2 restrains PPAE/PAP activities to prevent excessive phenoloxidase activation and toxic quinone intermediates (EMBO Reports, Sep 2005; https://doi.org/10.1038/sj.embor.7400478) (michel2005anophelesgambiaesrpn2 pages 2-3, michel2005anophelesgambiaesrpn2 pages 1-2).
- Direct inhibitory targets and stoichiometry: Recombinant SRPN2 inhibits activated CLIPB10 in vitro with an inhibition stoichiometry of ~1.89:1 and forms an SDS-stable SRPN2โ€“CLIPB10 complex, consistent with classic serpin inhibition. Genetic epistasis shows CLIPB10 knockdown partially reverses SRPN2-knockdown melanotic tumor formation, supporting CLIPB10 as an in vivo target. SRPN2 also forms an inhibitory complex with CLIPB9 and blocks its amidase activity; CLIPB9 is a PAP that activates proPO (Frontiers in Cellular and Infection Microbiology, Jan 2021; https://doi.org/10.3389/fcimb.2020.585986; Journal of Insect Physiology, Feb 2013; https://doi.org/10.1016/j.jinsphys.2012.08.015) (zhang2021clipb10isa pages 1-2, gulley2013therolesof pages 8-10).
- Placement in the complement-like hierarchy: Complement-like factor TEP1 acts upstream to enable activation of a non-catalytic clip-domain serine protease homolog (cSPH) module consisting hierarchically of SPCLIP1 โ†’ CLIPA8 โ†’ CLIPA28. SRPN2 knockdown enhances cleavage/activation of cSPHs (e.g., CLIPA8/CLIPA28/CLIPA14), indicating SRPN2 restricts proteases that activate the cSPH module downstream of TEP1. Recent 2024 work maps branching among catalytic CLIPs, with convergence on terminal PAPs including CLIPB10, and highlights that SRPN2-kd melanotic tumor phenotypes reflect unrestrained hemolymph PO activity within this architecture (bioRxiv, Jul 2024; https://doi.org/10.1101/2023.07.13.548954; 2019 thesis framework) (saab2024insightintothe pages 1-4, moussawi2019functionalandmolecular pages 90-94, moussawi2019functionalandmolecularb pages 90-94).
- Localization and secretion: Structural and biochemical characterization identify SRPN2 as a native, extracellular/hemolymph serpin. The crystal structure (1.75 ร…) shows a canonical serpin fold with the N-terminal hinge of the RCL partially inserted into ฮฒ-sheet Aโ€”a feature proposed to modulate RCL accessibility and possibly regulation; in contrast to mammalian antithrombin, glycosaminoglycan (heparin) enhancement was not supported for SRPN2 (Proteins: Structure, Jun 2011; Journal of Insect Physiology, Feb 2013) (an2011crystalstructureof pages 1-2, gulley2013therolesof pages 8-10).

3) Recent developments and latest research (priority 2023โ€“2024)
- Cascade architecture and branching: A 2024 integrative genetic/biochemical study refined the melanization cascade hierarchy in A. gambiae, indicating branching downstream of upstream cSPs and convergence on terminal PAPs such as CLIPB10; it situates SRPN2-kd tumor phenotypes within this architecture and emphasizes bidirectional cSPโ€“cSPH interactions for amplification. It also integrates three experimental paradigms for assessing melanization: P. berghei ookinete melanization (in CTL4-kd), SRPN2-kd tumors, and bacterial challengeโ€“induced melanotic excreta (bioRxiv, Jul 2024; https://doi.org/10.1101/2023.07.13.548954) (saab2024insightintothe pages 1-4).
- Methodological advances: A 2023 zone-of-inhibition assay enables medium-throughput assessment of hemolymph antimicrobial activity and the contribution of Toll pathway components and AMPs in A. gambiae hemolymph, facilitating standardized immune phenotyping that can be integrated with melanization studies (Frontiers in Cellular and Infection Microbiology, Jan 2023; https://doi.org/10.3389/fcimb.2023.891577) (moussawi2019functionalandmolecular pages 90-94) (moussawi2019functionalandmolecular pages 90-94) (saab2024insightintothe pages 1-4).

4) Current applications and real-world implementations
- Transmission-blocking biology: SRPN2 facilitates parasite survival during midgut traversal by restraining melanization; SRPN2 knockdown markedly reduces oocyst burden via increased ookinete lysis and melanization, highlighting SRPN2 and its targets as candidates for transmission-blocking strategies (EMBO Reports, Sep 2005; https://doi.org/10.1038/sj.embor.7400478) (michel2005anophelesgambiaesrpn2 pages 3-4, michel2005anophelesgambiaesrpn2 pages 2-3, michel2005anophelesgambiaesrpn2 pages 1-2).
- Insecticide or genetic control target: Structural work emphasized SRPN2 as a potential novel insecticide target given its central role in hemolymph homeostasis and lifespan; excess melanization due to SRPN2 loss reduces longevity, suggesting that targeted perturbation may decrease vector fitness (Proteins: Structure, Jun 2011; https://doi.org/10.1002/prot.23002) (an2011crystalstructureof pages 1-2).
- Epistasis-guided targeting within the cascade: The identification of direct targets (CLIPB9, CLIPB10) and their genetic interactions with SRPN2 provides specific nodes where interventions could modulate melanization strength without catastrophic host toxicity (Frontiers in Cellular and Infection Microbiology, Jan 2021; https://doi.org/10.3389/fcimb.2020.585986) (zhang2021clipb10isa pages 1-2).

5) Expert opinions and authoritative analyses
- 2013 review synthesis: Gulley, Zhang, and Michel emphasized SRPN2 as the best-characterized mosquito serpin with a defined molecular target (CLIPB9) and a clear role in restraining melanization; they highlighted that SRPN2 depletion produces systemic melanotic pathology and impacts parasite outcomes (Journal of Insect Physiology, Feb 2013; https://doi.org/10.1016/j.jinsphys.2012.08.015) (gulley2013therolesof pages 10-11, gulley2013therolesof pages 8-10).
- 2024 cascade perspective: The 2024 preprint proposes a refined hierarchy with cSPH modules upstream and multiple catalytic CLIPs providing redundancy and branching; it frames SRPN2โ€™s negative regulation as a key brake on pathway amplification, consistent with the tumor phenotype on SRPN2 loss (bioRxiv, Jul 2024; https://doi.org/10.1101/2023.07.13.548954) (saab2024insightintothe pages 1-4).

6) Relevant statistics and quantitative data
- SRPN2 RNAi phenotype kinetics and survival: Melanotic masses are evident by day 2 post-dsRNA, reaching 100% by day 4; survival is reduced approximately threefold by day 10 relative to controls (EMBO Reports, Sep 2005) (michel2005anophelesgambiaesrpn2 pages 2-3, michel2005anophelesgambiaesrpn2 pages 1-2).
- Transmission impact: In SRPN2 knockdowns, infection prevalence decreased by ~55% and oocyst intensity dropped by ~97% at 7 days post-infection with P. berghei (GFP-CON strain), driven by increased ookinete lysis and melanization (EMBO Reports, Sep 2005; https://doi.org/10.1038/sj.embor.7400478) (michel2005anophelesgambiaesrpn2 pages 2-3, michel2005anophelesgambiaesrpn2 pages 1-2).
- Biochemical inhibition: SRPN2 inhibits activated CLIPB10 with an approximate stoichiometry of 1.89:1, forming an SDS-stable complex; SRPN2 also forms a covalent complex with CLIPB9 and inhibits its amidase activity (Frontiers in Cellular and Infection Microbiology, Jan 2021; Journal of Insect Physiology, Feb 2013) (zhang2021clipb10isa pages 1-2, gulley2013therolesof pages 8-10).

7) Open questions and current limitations
- Identification of the full set of SRPN2 targets: While CLIPB9 and CLIPB10 are validated targets, SRPN2 knockdown phenotypes are only partially rescued by single CLIPB knockdowns, implying additional targets in the cascade (Frontiers in Cellular and Infection Microbiology, Jan 2021; Journal of Insect Physiology, Feb 2013) (zhang2021clipb10isa pages 1-2, gulley2013therolesof pages 8-10).
- Upstream cleavers of cSPHs: The specific catalytic CLIPs that activate the core cSPH module (SPCLIP1โ€“CLIPA8โ€“CLIPA28) remain to be conclusively identified; redundancy and branching complicate mapping (bioRxiv, Jul 2024) (saab2024insightintothe pages 1-4).

References (URLs and publication dates)
- Michel K, Budd A, Pinto S, Gibson TJ, Kafatos FC. Anopheles gambiae SRPN2 facilitates midgut invasion by the malaria parasite Plasmodium berghei. EMBO Reports. Sep 2005. https://doi.org/10.1038/sj.embor.7400478 (michel2005anophelesgambiaesrpn2 pages 3-4, michel2005anophelesgambiaesrpn2 pages 2-3, michel2005anophelesgambiaesrpn2 pages 1-2).
- An C, Lovell S, Kanost M, Battaile K, Michel K. Crystal structure of native Anopheles gambiae serpin-2, a negative regulator of melanization in mosquitoes. Proteins: Structure. Jun 2011. https://doi.org/10.1002/prot.23002 (an2011crystalstructureof pages 1-2).
- Gulley MM, Zhang X, Michel K. The roles of serpins in mosquito immunology and physiology. Journal of Insect Physiology. Feb 2013. https://doi.org/10.1016/j.jinsphys.2012.08.015 (gulley2013therolesof pages 10-11, gulley2013therolesof pages 8-10).
- Zhang X, Li M, El Moussawi L, Saab SA, Zhang S, Osta MA, Michel K. CLIPB10 is a Terminal Protease in the Regulatory Network That Controls Melanization in the African Malaria Mosquito Anopheles gambiae. Frontiers in Cellular and Infection Microbiology. Jan 2021. https://doi.org/10.3389/fcimb.2020.585986 (zhang2021clipb10isa pages 1-2).
- Saab SA, Zhang X, Zeineddine S, Morejon B, Michel K, Osta MA. Insight into the structural hierarchy of the protease cascade that regulates the mosquito melanization response. bioRxiv. Jul 2024. https://doi.org/10.1101/2023.07.13.548954 (saab2024insightintothe pages 1-4).
- Morejon B, Michel K. A zone-of-inhibition assay to screen for humoral antimicrobial activity in mosquito hemolymph. Frontiers in Cellular and Infection Microbiology. Jan 2023. https://doi.org/10.3389/fcimb.2023.891577 (saab2024insightintothe pages 1-4).

Conclusion
SRPN2 (Q7QIJ8) is a hemolymph serpin that is essential for maintaining homeostatic control of the melanization cascade in A. gambiae. It directly inhibits terminal proPO-activating proteases (CLIPB9 and CLIPB10) and functions within a hierarchy where complement-like TEP1 and a cSPH module (SPCLIP1โ€“CLIPA8โ€“CLIPA28) operate upstream. SRPN2 loss unleashes PO activity, causing melanotic tumors, shortened lifespan, and strong anti-Plasmodium effects via ookinete lysis and melanization. Recent work in 2023โ€“2024 refines the branching architecture and provides methodological tools to better interrogate hemolymph immunity, underscoring SRPN2 as a strategic node for vector control and transmission-blocking interventions (an2011crystalstructureof pages 1-2, michel2005anophelesgambiaesrpn2 pages 1-2, michel2005anophelesgambiaesrpn2 pages 2-3, gulley2013therolesof pages 8-10, zhang2021clipb10isa pages 1-2, saab2024insightintothe pages 1-4).

References

  1. (an2011crystalstructureof pages 1-2): C. An, S. Lovell, M. Kanost, K. Battaile, and K. Michel. Crystal structure of native anopheles gambiae serpinโ€2, a negative regulator of melanization in mosquitoes. Proteins: Structure, Jun 2011. URL: https://doi.org/10.1002/prot.23002, doi:10.1002/prot.23002. This article has 21 citations.

  2. (michel2005anophelesgambiaesrpn2 pages 1-2): Kristin Michel, Aidan Budd, Sofia Pinto, Toby J Gibson, and Fotis C Kafatos. Anopheles gambiae srpn2 facilitates midgut invasion by the malaria parasite plasmodium berghei. EMBO reports, 6:891-897, Sep 2005. URL: https://doi.org/10.1038/sj.embor.7400478, doi:10.1038/sj.embor.7400478. This article has 208 citations and is from a highest quality peer-reviewed journal.

  3. (michel2005anophelesgambiaesrpn2 pages 2-3): Kristin Michel, Aidan Budd, Sofia Pinto, Toby J Gibson, and Fotis C Kafatos. Anopheles gambiae srpn2 facilitates midgut invasion by the malaria parasite plasmodium berghei. EMBO reports, 6:891-897, Sep 2005. URL: https://doi.org/10.1038/sj.embor.7400478, doi:10.1038/sj.embor.7400478. This article has 208 citations and is from a highest quality peer-reviewed journal.

  4. (gulley2013therolesof pages 10-11): Melissa M. Gulley, Xin Zhang, and Kristin Michel. The roles of serpins in mosquito immunology and physiology. Journal of insect physiology, 59 2:138-47, Feb 2013. URL: https://doi.org/10.1016/j.jinsphys.2012.08.015, doi:10.1016/j.jinsphys.2012.08.015. This article has 127 citations and is from a peer-reviewed journal.

  5. (gulley2013therolesof pages 8-10): Melissa M. Gulley, Xin Zhang, and Kristin Michel. The roles of serpins in mosquito immunology and physiology. Journal of insect physiology, 59 2:138-47, Feb 2013. URL: https://doi.org/10.1016/j.jinsphys.2012.08.015, doi:10.1016/j.jinsphys.2012.08.015. This article has 127 citations and is from a peer-reviewed journal.

  6. (zhang2021clipb10isa pages 1-2): Xin Zhang, Miao Li, Layla El Moussawi, Sally Saab, Shasha Zhang, Mike A. Osta, and Kristin Michel. Clipb10 is a terminal protease in the regulatory network that controls melanization in the african malaria mosquito anopheles gambiae. Frontiers in Cellular and Infection Microbiology, Jan 2021. URL: https://doi.org/10.3389/fcimb.2020.585986, doi:10.3389/fcimb.2020.585986. This article has 29 citations and is from a poor quality or predatory journal.

  7. (saab2024insightintothe pages 1-4): Sally A. Saab, Xiufeng Zhang, Suheir Zeineddine, Bianca Morejon, Kristin Michel, and Mike A. Osta. Insight into the structural hierarchy of the protease cascade that regulates the mosquito melanization response. bioRxiv, Jul 2024. URL: https://doi.org/10.1101/2023.07.13.548954, doi:10.1101/2023.07.13.548954. This article has 10 citations and is from a poor quality or predatory journal.

  8. (moussawi2019functionalandmolecular pages 90-94): LH El Moussawi. Functional and molecular characterization of the serine protease homologue clipa28 in the melanization response of anopheles gambiae mosquitoes. Unknown journal, 2019.

  9. (moussawi2019functionalandmolecularb pages 90-94): LH El Moussawi. Functional and molecular characterization of the serine protease homologue clipa28 in the melanization response of anopheles gambiae mosquitoes. Unknown journal, 2019.

  10. (michel2005anophelesgambiaesrpn2 pages 3-4): Kristin Michel, Aidan Budd, Sofia Pinto, Toby J Gibson, and Fotis C Kafatos. Anopheles gambiae srpn2 facilitates midgut invasion by the malaria parasite plasmodium berghei. EMBO reports, 6:891-897, Sep 2005. URL: https://doi.org/10.1038/sj.embor.7400478, doi:10.1038/sj.embor.7400478. This article has 208 citations and is from a highest quality peer-reviewed journal.

Citations

  1. an2011crystalstructureof pages 1-2
  2. saab2024insightintothe pages 1-4
  3. moussawi2019functionalandmolecular pages 90-94
  4. gulley2013therolesof pages 10-11
  5. gulley2013therolesof pages 8-10
  6. moussawi2019functionalandmolecularb pages 90-94
  7. https://doi.org/10.1002/prot.23002
  8. https://doi.org/10.1038/sj.embor.7400478
  9. https://doi.org/10.1016/j.jinsphys.2012.08.015
  10. https://doi.org/10.3389/fcimb.2020.585986;
  11. https://doi.org/10.1101/2023.07.13.548954;
  12. https://doi.org/10.1101/2023.07.13.548954
  13. https://doi.org/10.3389/fcimb.2023.891577
  14. https://doi.org/10.3389/fcimb.2020.585986
  15. https://doi.org/10.1002/prot.23002,
  16. https://doi.org/10.1038/sj.embor.7400478,
  17. https://doi.org/10.1016/j.jinsphys.2012.08.015,
  18. https://doi.org/10.3389/fcimb.2020.585986,
  19. https://doi.org/10.1101/2023.07.13.548954,

๐Ÿ“„ View Raw YAML

 
id: Q7QIJ8
gene_symbol: SRPN2
product_type: PROTEIN
status: IN_PROGRESS
taxon:
  id: NCBITaxon:7165
  label: Anopheles gambiae
description: >-
  SRPN2 (Serpin-2) is a secreted serine protease inhibitor that functions as a key negative regulator
  of the melanization defense response in Anopheles gambiae. It acts in the hemolymph to inhibit
  CLIP-domain serine proteases (CLIPB9, CLIPB10, CLIPB4) that would otherwise activate prophenoloxidase,
  thereby preventing excessive melanization. SRPN2 knockdown causes spontaneous melanotic pseudotumors,
  shortened lifespan, and enhanced killing of Plasmodium parasites through ookinete lysis and melanization.
existing_annotations:
- term:
    id: GO:0004867
    label: serine-type endopeptidase inhibitor activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      SRPN2 is a well-characterized serpin that directly inhibits CLIP-domain serine proteases including
      CLIPB9, CLIPB10, and CLIPB4. The IBA annotation based on phylogenetic inference is strongly supported
      by multiple direct experimental studies demonstrating serine protease inhibitor activity [PMID:20953892,
      PMID:25525260, PMID:33520733].
    action: ACCEPT
    reason: >-
      This molecular function annotation is the core enzymatic activity of SRPN2. Biochemical studies
      have demonstrated that SRPN2 forms covalent, SDS-stable inhibitory complexes with its target proteases
      (CLIPB9, CLIPB10) with stoichiometry consistent with classic serpin inhibition mechanism
      [PMID:25525260, PMID:33520733]. The IBA annotation is phylogenetically appropriate given serpin
      family conservation.
    supported_by:
      - reference_id: PMID:20953892
        supporting_text: "we identified the Anopheles gambiae clip-serine proteinase CLIPB9 as a PPO-activating proteinase, which is inhibited by SRPN2"
      - reference_id: PMID:25525260
        supporting_text: "SRPN2 irreversibly inhibits clip domain serine proteinase 9 (CLIPB9), which functions in a serine proteinase cascade culminating in the activation of prophenoloxidase and melanization"
      - reference_id: PMID:33520733
        supporting_text: "The stoichiometry of inhibition was 1.89, indicating that, under the used experimental conditions, SRPN2 acts as an inhibitor and not as substrate for CLIPB10"

- term:
    id: GO:0050776
    label: regulation of immune response
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      SRPN2 regulates the melanization arm of the innate immune response by inhibiting proteases that
      activate prophenoloxidase. However, a more specific term exists (GO:0035009 negative regulation
      of melanization defense response) that precisely captures SRPN2's function [PMID:16113656, PMID:20953892].
    action: MODIFY
    reason: >-
      While technically accurate that SRPN2 is involved in regulation of immune response, this term is
      too broad. SRPN2 specifically negatively regulates the melanization defense response, not immune
      responses generally. The more specific term GO:0035009 is already annotated and better represents
      the biological function.
    proposed_replacement_terms:
      - id: GO:0035009
        label: negative regulation of melanization defense response
    supported_by:
      - reference_id: PMID:16113656
        supporting_text: "knockdown of SRPN2 in adult Anopheles gambiae produced a notable phenotype: the appearance of melanotic pseudotumours, which increased in size and number with time, indicating spontaneous melanization"
      - reference_id: PMID:20953892
        supporting_text: "serpin-2 (SRPN2), which was previously identified as a key negative regulator of melanization"

- term:
    id: GO:0005615
    label: extracellular space
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      SRPN2 is a secreted serpin that functions in the hemolymph (the insect equivalent of blood/extracellular
      fluid). Multiple studies confirm its extracellular localization [PMID:16113656, PMID:20953892].
      The IBA annotation aligns with experimental evidence.
    action: ACCEPT
    reason: >-
      The extracellular space annotation is well-supported. SRPN2 contains a signal peptide and is
      secreted into the hemolymph where it functions to inhibit circulating proteases. This is consistent
      with the phylogenetic inference and the serpin family biology.
    supported_by:
      - reference_id: PMID:20953892
        supporting_text: "controlled by an extracellular proteinase cascade and serpin inhibitors"

- term:
    id: GO:0002376
    label: immune system process
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: >-
      This IEA annotation from UniProt keyword mapping is accurate but very broad. SRPN2 is involved
      in the melanization branch of innate immunity, specifically as a negative regulator. More specific
      terms are already annotated [PMID:16113656].
    action: ACCEPT
    reason: >-
      While broad, this IEA annotation is not incorrect - SRPN2 does function in an immune system
      process (melanization). More specific annotations are already present (GO:0035009, GO:0045087).
      IEA annotations providing broader context alongside more specific experimental annotations is
      acceptable practice.
    supported_by:
      - reference_id: PMID:20953892
        supporting_text: "Melanization is an innate immune response in arthropods that encapsulates and kills invading pathogens"

- term:
    id: GO:0004867
    label: serine-type endopeptidase inhibitor activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: >-
      Redundant with the IBA and IDA annotations for the same term but from automated InterPro/ARBA mapping.
      The annotation is correct and consistent with experimental evidence.
    action: ACCEPT
    reason: >-
      This IEA annotation is accurate. SRPN2 belongs to the serpin family (IPR000215) and exhibits
      serine-type endopeptidase inhibitor activity as demonstrated experimentally. The IEA provides
      supporting evidence from sequence/domain analysis consistent with experimental findings.
    supported_by:
      - reference_id: PMID:25525260
        supporting_text: "SRPN2 irreversibly inhibits clip domain serine proteinase 9 (CLIPB9)"

- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: >-
      IEA annotation from UniProt subcellular location mapping. SRPN2 is secreted into the hemolymph,
      making this annotation accurate. The more specific child term GO:0005615 (extracellular space)
      is also annotated.
    action: ACCEPT
    reason: >-
      This broader cellular component term is accurate - SRPN2 is indeed located in the extracellular
      region (secreted into hemolymph). Having both this broader term and the more specific
      extracellular space term is acceptable.
    supported_by:
      - reference_id: PMID:20953892
        supporting_text: "controlled by an extracellular proteinase cascade and serpin inhibitors"

- term:
    id: GO:0005615
    label: extracellular space
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: >-
      IEA annotation from InterPro2GO mapping for serpin family. Redundant with IBA and IDA
      annotations but consistent with the established extracellular localization of SRPN2.
    action: ACCEPT
    reason: >-
      Accurate annotation derived from serpin domain presence. Serpins of this type are typically
      secreted, and SRPN2 has been experimentally confirmed to be secreted into the hemolymph.
    supported_by:
      - reference_id: PMID:20953892
        supporting_text: "extracellular proteinase cascade and serpin inhibitors"

- term:
    id: GO:0030414
    label: peptidase inhibitor activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: >-
      IEA annotation from UniProt keyword mapping. This is a parent term of GO:0004867 (serine-type
      endopeptidase inhibitor activity). While accurate, it is less specific than what is known
      about SRPN2.
    action: ACCEPT
    reason: >-
      This parent-level annotation is technically correct but adds limited information beyond the
      more specific serine-type endopeptidase inhibitor activity annotation. However, it is not
      wrong to have both parent and child terms annotated when the evidence supports it.
    supported_by:
      - reference_id: PMID:25525260
        supporting_text: "SRPN2 irreversibly inhibits clip domain serine proteinase 9 (CLIPB9)"

- term:
    id: GO:0045087
    label: innate immune response
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: >-
      IEA annotation from UniProt keyword mapping (Innate immunity). SRPN2 functions in the
      melanization arm of innate immunity. This is an appropriate level of specificity for the
      immune process aspect of SRPN2 function.
    action: ACCEPT
    reason: >-
      Melanization is a component of the innate immune response in arthropods. SRPN2's role in
      regulating melanization means it participates in innate immunity. The annotation is appropriate.
    supported_by:
      - reference_id: PMID:20953892
        supporting_text: "Melanization is an innate immune response in arthropods that encapsulates and kills invading pathogens"

- term:
    id: GO:0004867
    label: serine-type endopeptidase inhibitor activity
  evidence_type: IMP
  original_reference_id: PMID:33520733
  review:
    summary: >-
      IMP annotation based on mutant phenotype evidence from PMID:33520733. The study demonstrates
      that SRPN2 knockdown causes spontaneous melanization, which is partially rescued by CLIPB10
      co-knockdown, supporting SRPN2's role as a serine protease inhibitor.
    action: ACCEPT
    reason: >-
      The study shows that SRPN2 knockdown leads to uncontrolled melanization (due to loss of
      protease inhibition), and this is partially rescued by depleting the target protease CLIPB10.
      This genetic evidence supports the serine protease inhibitor function.
    supported_by:
      - reference_id: PMID:33520733
        supporting_text: "The kd of SRPN2 caused severe melanotic tumors on the abdomen of mosquitoes, which were partially reversed by CLIPB10 kd in SRPN2-depleted mosquitoes"

- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33520733
  review:
    summary: >-
      IPI annotation based on physical interaction with CLIPB10 (UniProtKB:Q7QBP4). While the
      interaction is real and biologically meaningful, "protein binding" is too vague and does not
      capture the nature of the serpin-protease inhibitory complex formation.
    action: MODIFY
    reason: >-
      Per curation guidelines, "protein binding" is too uninformative when more specific MF terms
      are available. The SRPN2-CLIPB10 interaction is specifically an inhibitory serpin-protease
      complex. A better annotation would be the specific inhibitor activity term or a more
      informative binding term that indicates the functional outcome.
    proposed_replacement_terms:
      - id: GO:0004867
        label: serine-type endopeptidase inhibitor activity
    additional_reference_ids:
      - PMID:33520733
    supported_by:
      - reference_id: PMID:33520733
        supporting_text: "formed a SDS-stable protein complex with activated recombinant CLIPB10"

- term:
    id: GO:0010951
    label: negative regulation of endopeptidase activity
  evidence_type: IMP
  original_reference_id: PMID:33520733
  review:
    summary: >-
      IMP annotation based on SRPN2 knockdown leading to increased endopeptidase activity (evidenced
      by increased melanization due to uncontrolled PPO activation). This is a direct consequence
      of SRPN2's inhibitor function.
    action: ACCEPT
    reason: >-
      SRPN2 knockdown results in enhanced protease activity (CLIPB10, CLIPB9) leading to
      spontaneous melanization. This genetic evidence supports the annotation that SRPN2
      negatively regulates endopeptidase activity in vivo.
    supported_by:
      - reference_id: PMID:33520733
        supporting_text: "CLIPB10 activity decreased linearly with increasing concentrations of SRPN2"

- term:
    id: GO:0010955
    label: negative regulation of protein processing
  evidence_type: IMP
  original_reference_id: PMID:33045027
  review:
    summary: >-
      IMP annotation from PMID:33045027. SRPN2 knockdown results in enhanced cleavage/processing
      of downstream substrates (CLIPA28, CLIPC9) in the melanization cascade, demonstrating that
      SRPN2 negatively regulates protein processing.
    action: ACCEPT
    reason: >-
      The study shows that SRPN2 silencing enhances CLIPC9 cleavage, indicating SRPN2 normally
      restrains proteolytic processing in the cascade. This is consistent with its role as a
      protease inhibitor that prevents cascade activation.
    supported_by:
      - reference_id: PMID:33045027
        supporting_text: "CLIPC9 processing is negatively regulated by serine protease inhibitor 2 (SRPN2)"

- term:
    id: GO:0004867
    label: serine-type endopeptidase inhibitor activity
  evidence_type: IDA
  original_reference_id: PMID:20953892
  review:
    summary: >-
      IDA annotation based on direct biochemical demonstration that SRPN2 inhibits CLIPB9.
      This is the first study to identify a specific SRPN2 target protease.
    action: ACCEPT
    reason: >-
      Direct biochemical evidence shows SRPN2 forms an inhibitory complex with CLIPB9 and
      blocks its protease activity. This is core experimental evidence for SRPN2's molecular
      function.
    supported_by:
      - reference_id: PMID:20953892
        supporting_text: "we identified the Anopheles gambiae clip-serine proteinase CLIPB9 as a PPO-activating proteinase, which is inhibited by SRPN2"

- term:
    id: GO:0004867
    label: serine-type endopeptidase inhibitor activity
  evidence_type: IDA
  original_reference_id: PMID:25525260
  review:
    summary: >-
      IDA annotation based on detailed biochemical and structural characterization of SRPN2-CLIPB9
      interaction. The study includes kinetic analysis and structure-function studies of the
      inhibitory mechanism.
    action: ACCEPT
    reason: >-
      High-quality biochemical study demonstrating the inhibitory mechanism of SRPN2 against
      CLIPB9 with kinetic parameters and structural insights into the hinge region function.
    supported_by:
      - reference_id: PMID:25525260
        supporting_text: "Serpin-2 (SRPN2) is a key negative regulator of the melanization response in the malaria vector Anopheles gambiae. SRPN2 irreversibly inhibits clip domain serine proteinase 9 (CLIPB9)"

- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:20953892
  review:
    summary: >-
      IPI annotation for interaction with CLIPB9 (UniProtKB:F5HKX0). As with the CLIPB10 interaction,
      "protein binding" is too vague for this specific inhibitory interaction.
    action: MODIFY
    reason: >-
      The SRPN2-CLIPB9 interaction is an inhibitory serpin-protease complex formation. The more
      informative serine-type endopeptidase inhibitor activity term better captures this
      functional interaction.
    proposed_replacement_terms:
      - id: GO:0004867
        label: serine-type endopeptidase inhibitor activity
    supported_by:
      - reference_id: PMID:20953892
        supporting_text: "clip-serine proteinase CLIPB9 as a PPO-activating proteinase, which is inhibited by SRPN2"

- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25525260
  review:
    summary: >-
      IPI annotation for SRPN2-CLIPB9 interaction from structural/biochemical study. This is
      redundant with the PMID:20953892 annotation and similarly too vague.
    action: MODIFY
    reason: >-
      Same rationale as other protein binding annotations - the interaction represents a specific
      inhibitory complex formation that is better captured by the serine-type endopeptidase
      inhibitor activity term.
    proposed_replacement_terms:
      - id: GO:0004867
        label: serine-type endopeptidase inhibitor activity
    supported_by:
      - reference_id: PMID:25525260
        supporting_text: "SRPN2 irreversibly inhibits clip domain serine proteinase 9 (CLIPB9)"

- term:
    id: GO:0005615
    label: extracellular space
  evidence_type: IDA
  original_reference_id: PMID:20953892
  review:
    summary: >-
      IDA annotation for extracellular localization based on detection of SRPN2 in hemolymph
      samples and its function in the extracellular protease cascade.
    action: ACCEPT
    reason: >-
      SRPN2 is detected in hemolymph and functions to inhibit extracellular proteases. This
      experimental evidence supports the extracellular space localization.
    supported_by:
      - reference_id: PMID:20953892
        supporting_text: "The molecular composition of this system is largely unknown in mosquitoes with the exception of serpin-2 (SRPN2)"

- term:
    id: GO:0035009
    label: negative regulation of melanization defense response
  evidence_type: IDA
  original_reference_id: PMID:20953892
  review:
    summary: >-
      IDA annotation for SRPN2's core biological function - negative regulation of melanization.
      This is a highly specific and appropriate term for SRPN2's role in the melanization cascade.
    action: ACCEPT
    reason: >-
      This is the most specific and informative biological process annotation for SRPN2.
      SRPN2 knockdown causes spontaneous melanization, demonstrating it is a key negative
      regulator of this immune response. This represents a core function of the gene.
    supported_by:
      - reference_id: PMID:20953892
        supporting_text: "serpin-2 (SRPN2), which was previously identified as a key negative regulator of melanization"
      - reference_id: PMID:16113656
        supporting_text: "knockdown of SRPN2 in adult Anopheles gambiae produced a notable phenotype: the appearance of melanotic pseudotumours"

- term:
    id: GO:0045861
    label: negative regulation of proteolysis
  evidence_type: IDA
  original_reference_id: PMID:20953892
  review:
    summary: >-
      IDA annotation based on SRPN2's inhibition of proteolytic cascade enzymes. This is an
      accurate but somewhat redundant annotation given the more specific negative regulation
      of melanization defense response annotation.
    action: ACCEPT
    reason: >-
      SRPN2 inhibits CLIPB9 and other proteases, thereby negatively regulating proteolysis
      in the melanization cascade. While this is a parent term of more specific regulatory
      processes, it accurately describes SRPN2's biochemical effect.
    supported_by:
      - reference_id: PMID:20953892
        supporting_text: "CLIPB9 as a PPO-activating proteinase, which is inhibited by SRPN2"

- term:
    id: GO:0045861
    label: negative regulation of proteolysis
  evidence_type: IDA
  original_reference_id: PMID:25525260
  review:
    summary: >-
      IDA annotation from the structural/biochemical study showing SRPN2 inhibits CLIPB9
      proteolytic activity.
    action: ACCEPT
    reason: >-
      The study provides detailed biochemical evidence for SRPN2's inhibition of CLIPB9
      proteolytic activity, including kinetic analysis. Supports negative regulation of
      proteolysis.
    supported_by:
      - reference_id: PMID:25525260
        supporting_text: "SRPN2 irreversibly inhibits clip domain serine proteinase 9 (CLIPB9)"

- term:
    id: GO:0005615
    label: extracellular space
  evidence_type: IDA
  original_reference_id: PMID:16113656
  review:
    summary: >-
      IDA annotation from the original study characterizing SRPN2 function. SRPN2 is
      secreted into the hemolymph.
    action: ACCEPT
    reason: >-
      This foundational study established SRPN2's function and localization. The
      extracellular space annotation is appropriate for this secreted serpin.
    supported_by:
      - reference_id: PMID:20953892
        supporting_text: "controlled by an extracellular proteinase cascade and serpin inhibitors"

- term:
    id: GO:0035009
    label: negative regulation of melanization defense response
  evidence_type: IDA
  original_reference_id: PMID:16113656
  review:
    summary: >-
      IDA annotation from the foundational study demonstrating SRPN2 knockdown causes
      spontaneous melanization. This is core evidence for SRPN2's function.
    action: ACCEPT
    reason: >-
      The original Michel et al. 2005 study provides the primary evidence that SRPN2
      is a negative regulator of melanization - knockdown results in melanotic pseudotumors.
      This is the defining biological function of SRPN2.
    supported_by:
      - reference_id: PMID:16113656
        supporting_text: "knockdown of SRPN2 in adult Anopheles gambiae produced a notable phenotype: the appearance of melanotic pseudotumours, which increased in size and number with time, indicating spontaneous melanization"

- term:
    id: GO:0042832
    label: defense response to protozoan
  evidence_type: IDA
  original_reference_id: PMID:16113656
  review:
    summary: >-
      IDA annotation based on SRPN2's effect on Plasmodium berghei infection outcomes.
      SRPN2 knockdown results in enhanced ookinete killing through melanization, suggesting
      SRPN2 modulates defense against the parasite.
    action: MODIFY
    reason: >-
      This annotation is problematic. SRPN2 actually FACILITATES parasite survival by
      suppressing the melanization response that would otherwise kill ookinetes. Knockdown
      of SRPN2 enhances defense, meaning the wild-type protein acts as a negative regulator
      of defense response to the protozoan, not a positive contributor to defense.
      The annotation should be to negative regulation of defense response to protozoan
      or removed.
    proposed_replacement_terms:
      - id: GO:0031348
        label: negative regulation of defense response
    additional_reference_ids:
      - PMID:16113656
    supported_by:
      - reference_id: PMID:16113656
        supporting_text: "knockdown of SRPN2 strongly interfered with the invasion of A. gambiae midguts by the rodent malaria parasite Plasmodium berghei. It did not affect ookinete formation, but markedly reduced oocyst numbers, by 97%, as a result of increased ookinete lysis and melanization"

references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO terms
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000043
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
    vocabulary mapping, accompanied by conservative changes to GO terms applied by
    UniProt
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:16113656
  title: Anopheles gambiae SRPN2 facilitates midgut invasion by the malaria parasite
    Plasmodium berghei.
  findings:
    - statement: SRPN2 knockdown causes spontaneous melanotic pseudotumors and reduced lifespan
    - statement: SRPN2 knockdown reduces Plasmodium oocyst numbers by 97% through enhanced ookinete melanization
    - statement: SRPN2 is secreted into the hemolymph
- id: PMID:20953892
  title: Characterization of a regulatory unit that controls melanization and affects
    longevity of mosquitoes.
  findings:
    - statement: CLIPB9 is a PPO-activating proteinase inhibited by SRPN2
    - statement: SRPN2-CLIPB9 is the first characterized inhibitory serpin-protease pair in mosquitoes
    - statement: Double knockdown of SRPN2 and CLIPB9 reverses the SRPN2-knockdown phenotype
- id: PMID:25525260
  title: Structural and inhibitory effects of hinge loop mutagenesis in serpin-2 from
    the malaria vector Anopheles gambiae.
  findings:
    - statement: SRPN2 irreversibly inhibits CLIPB9 via classic serpin mechanism
    - statement: Crystal structures reveal hinge region function in serpin-protease complex formation
    - statement: Kinetic analysis of SRPN2-CLIPB9 inhibition
- id: PMID:33045027
  title: The CLIP-domain serine protease CLIPC9 regulates melanization downstream
    of SPCLIP1, CLIPA8, and CLIPA28 in the malaria vector Anopheles gambiae.
  findings:
    - statement: SRPN2 negatively regulates CLIPC9 processing
    - statement: CLIPC9 functions downstream in the melanization cascade
- id: PMID:33520733
  title: CLIPB10 is a Terminal Protease in the Regulatory Network That Controls Melanization
    in the African Malaria Mosquito Anopheles gambiae.
  findings:
    - statement: SRPN2 directly inhibits CLIPB10 with stoichiometry of 1.89
    - statement: SRPN2 forms SDS-stable complex with CLIPB10
    - statement: CLIPB10 knockdown partially rescues SRPN2-knockdown melanotic tumor phenotype

core_functions:
  - molecular_function:
      id: GO:0004867
      label: serine-type endopeptidase inhibitor activity
    description: >-
      SRPN2 is a classic inhibitory serpin that forms covalent, SDS-stable complexes with target
      serine proteases including CLIPB9, CLIPB10, and CLIPB4. The inhibition involves the reactive
      center loop trapping the protease in an inactive complex. SRPN2 is the primary negative regulator
      of the melanization cascade in A. gambiae, preventing uncontrolled melanization that would
      otherwise cause melanotic pseudotumors and shortened lifespan.
    directly_involved_in:
      - id: GO:0035009
        label: negative regulation of melanization defense response
    locations:
      - id: GO:0005615
        label: extracellular space
    supported_by:
      - reference_id: PMID:16113656
        supporting_text: "knockdown of SRPN2 in adult Anopheles gambiae produced a notable phenotype: the appearance of melanotic pseudotumours"
      - reference_id: PMID:20953892
        supporting_text: "we identified the Anopheles gambiae clip-serine proteinase CLIPB9 as a PPO-activating proteinase, which is inhibited by SRPN2"
      - reference_id: PMID:33520733
        supporting_text: "CLIPB10 activity decreased linearly with increasing concentrations of SRPN2"

suggested_questions:
  - question: >-
      Are there additional CLIPB proteases that are SRPN2 targets? The incomplete rescue of
      SRPN2-knockdown phenotype by single CLIPB knockdowns suggests additional targets.
  - question: >-
      What is the physiological role of the partial hinge insertion in SRPN2? The structural
      studies suggest it may represent a trade-off between RCL accessibility and inhibitory
      efficiency.
  - question: >-
      How does SRPN2 expression and activity change during Plasmodium infection to permit
      localized melanization while preventing systemic pathology?

suggested_experiments:
  - description: >-
      Proteomics analysis of SRPN2 complexes in hemolymph to identify the complete set of
      SRPN2 target proteases under different immune challenge conditions.
  - description: >-
      Time-course analysis of SRPN2 protein levels during Plasmodium infection to understand
      how melanization is permitted at the ookinete invasion site.