CLIPB4 is a CLIP domain-containing serine protease that functions as a central upstream node in the melanization cascade of Anopheles gambiae. It is secreted into the hemolymph as a zymogen and, upon proteolytic activation, cleaves and activates downstream proteases including CLIPB8. CLIPB4 plays a key role in the innate immune response against protozoan parasites (Plasmodium) and bacterial pathogens by activating the prophenoloxidase (PPO) cascade leading to melanin deposition at pathogen surfaces. The protein is regulated by serpins (particularly SRPN2) that rapidly inhibit the active form to prevent collateral damage from uncontrolled melanization.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0005615
extracellular space
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: CLIPB4 is secreted into hemolymph as a zymogen and functions in the extracellular space where it participates in the melanization cascade. UniProt annotation indicates "Secreted" for subcellular location. The IBA annotation is based on phylogenetic inference from related CLIP-domain proteases in Drosophila and other insects that are established hemolymph proteins.
Reason: The extracellular space localization is well-supported. UniProt states "SUBCELLULAR LOCATION: Secreted" and the deep research confirms "CLIPB4 is secreted into hemolymph as a zymogen" (saab2024insightintothe). The IBA evidence from phylogenetic inference across multiple insect species provides strong support for this conserved localization.
Supporting Evidence:
Q7PEV7
SUBCELLULAR LOCATION: Secreted {ECO:0000305}
saab2024insightintothe
CLIPB4 is secreted into hemolymph as a zymogen
|
|
GO:0045087
innate immune response
|
IBA
GO_REF:0000033 |
MODIFY |
Summary: CLIPB4 plays a well-documented role in innate immunity through its function in the melanization cascade. RNAi knockdown experiments demonstrate reduced melanization after microbial challenge and increased Plasmodium infection, establishing a clear immune function. However, a more specific term such as "melanization defense response" (GO:0035006) or "positive regulation of melanization defense response" (GO:0035008) would better capture the precise function.
Reason: While the innate immune response annotation is correct, it is too general for CLIPB4's specific role. The protein functions specifically in the melanization arm of innate immunity. UniProt states "Serine protease which plays a role in the innate immune response against protozoan and bacterial pathogens... by activating the melanization cascade" (PMID:16922859, PMID:37703846). The more specific term GO:0035006 (melanization defense response) or GO:0035008 (positive regulation of melanization defense response) would be more informative.
Proposed replacements:
melanization defense response
positive regulation of melanization defense response
Supporting Evidence:
Q7PEV7
Serine protease which plays a role in the innate immune response against protozoan and bacterial pathogens, such as Plasmodium bergei, Staphylococcus aureus, Micrococcus luteus and Escherichia coli, by activating the melanization cascade
saab2024insightintothe
CLIPB4 functions upstream of CLIPB8 and independently controls CLIPB10 cleavage; knockdown reduces infection-induced melanin excreta
|
|
GO:0002376
immune system process
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: This is an IEA annotation based on UniProtKB keyword mapping from the "Immunity" and "Innate immunity" keywords. While accurate, this term is extremely broad and adds little information beyond what is captured by more specific immune annotations.
Reason: This is a broad parental term that is technically correct but not very informative. It is acceptable to retain as an IEA annotation since it correctly captures the general functional category, and more specific annotations (like GO:0045087 innate immune response) provide the needed specificity. The IBA annotation for innate immune response is more informative.
Supporting Evidence:
Q7PEV7
KW: Immunity; Innate immunity
|
|
GO:0004252
serine-type endopeptidase activity
|
IEA
GO_REF:0000002 |
ACCEPT |
Summary: CLIPB4 contains a trypsin-like serine protease domain (Peptidase S1) with the canonical His-Asp-Ser catalytic triad. Experimental evidence confirms catalytic activity - CLIPB4 cleaves CLIPB8 and the cSPH cofactor CLIPA8 in vitro (PMID:37703846). The InterPro-based IEA annotation is well-supported by both domain architecture and experimental validation.
Reason: This is the core molecular function of CLIPB4 and is strongly supported. UniProt annotates EC=3.4.21.- based on experimental evidence (PMID:37703846). The protein has the complete catalytic triad (His153, Asp213, Ser311) and experimentally demonstrated protease activity cleaving CLIPB8 and CLIPA8. The term is appropriately specific for the enzymatic activity.
Supporting Evidence:
Q7PEV7
EC=3.4.21.- {ECO:0000255|PROSITE-ProRule:PRU00274, ECO:0000269|PubMed:37703846}
Q7PEV7
Cleaves and activates CLIPB8 (PubMed:37703846)
saab2024insightintothe
In vitro, CLIPB4 cleaves the cSPH cofactor CLIPA8
|
|
GO:0005576
extracellular region
|
IEA
GO_REF:0000044 |
ACCEPT |
Summary: This IEA annotation is based on UniProt subcellular location vocabulary mapping for "Secreted" proteins. It is a broader parent term of GO:0005615 (extracellular space) which is already annotated via IBA. Both terms are valid but this one is less specific.
Reason: The extracellular region annotation is correct and supported by the "Secreted" annotation in UniProt. While GO:0005615 (extracellular space) is more specific and also annotated, retaining this broader IEA annotation is acceptable as it represents the standard mapping from UniProt subcellular location vocabulary.
Supporting Evidence:
Q7PEV7
SUBCELLULAR LOCATION: Secreted {ECO:0000305}
|
|
GO:0006508
proteolysis
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: This broad biological process term indicates involvement in proteolytic processes. CLIPB4 is an active serine protease that cleaves specific protein substrates (CLIPB8, CLIPA8) as part of the melanization cascade. This is a generic annotation derived from the protease domain.
Reason: While broad, this term accurately captures CLIPB4's role in proteolytic processing. The protein has demonstrated proteolytic activity against specific substrates in the melanization cascade. More specific biological process terms related to melanization would be more informative, but this annotation is not incorrect.
Supporting Evidence:
Q7PEV7
KW: Protease
saab2024insightintothe
CLIPB4 cleaves the cSPH cofactor CLIPA8
|
|
GO:0008233
peptidase activity
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: This is a broad parent term for peptidase/protease activity. CLIPB4 is annotated more specifically with GO:0004252 (serine-type endopeptidase activity) which is a child term. This annotation adds no additional information beyond what the more specific term provides.
Reason: While this is a broad parent term that is largely redundant with the more specific GO:0004252 (serine-type endopeptidase activity), it is an accurate IEA annotation from keyword mapping. GO annotation guidelines allow parent terms alongside child terms, particularly when derived from different evidence sources.
Supporting Evidence:
Q7PEV7
KW: Protease
|
|
GO:0008236
serine-type peptidase activity
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: This term is a parent of GO:0004252 (serine-type endopeptidase activity) which is also annotated. CLIPB4 is specifically an endopeptidase (cleaves internal peptide bonds), so GO:0004252 is more accurate. This annotation is correct but less specific.
Reason: This is an accurate annotation based on UniProt keyword mapping for "Serine protease". While GO:0004252 (serine-type endopeptidase activity) is more specific and preferred, this parental term is not incorrect. The annotation reflects the protein family classification.
Supporting Evidence:
Q7PEV7
KW: Serine protease
Q7PEV7
Belongs to the peptidase S1 family. CLIP subfamily.
|
|
GO:0016787
hydrolase activity
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: This is a very broad molecular function term for enzymes that catalyze hydrolysis reactions. Serine proteases are hydrolases, so this is technically accurate but provides minimal functional information. More specific terms (GO:0004252) are already annotated.
Reason: This high-level term is accurate - serine proteases catalyze peptide bond hydrolysis. However, it is extremely broad and the more specific GO:0004252 (serine-type endopeptidase activity) provides much more functional information. Retaining the IEA annotation is acceptable as it represents standard keyword mapping.
Supporting Evidence:
Q7PEV7
KW: Hydrolase
|
|
GO:0045087
innate immune response
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: This is a duplicate annotation of the same GO term (GO:0045087) that is also annotated via IBA evidence. The IEA annotation comes from UniProt keyword mapping for "Innate immunity". Both evidence codes support the same biological process involvement.
Reason: While this is the same GO term as the IBA annotation, having both IEA and IBA evidence is valid in GO annotation. The IEA annotation from keyword mapping and the IBA annotation from phylogenetic inference independently support the same functional assignment. As noted above, a more specific term like GO:0035006 (melanization defense response) would be more informative.
Supporting Evidence:
Q7PEV7
KW: Innate immunity
|
|
GO:0035006
melanization defense response
|
IDA
PMID:16922859 A genetic module regulates the melanization response of Anop... |
NEW |
Summary: CLIPB4 is directly involved in the melanization defense response against Plasmodium and bacterial pathogens. RNAi knockdown experiments demonstrate reduced melanization of P. berghei ookinetes in resistant mosquito strains, and reduced melanin excreta after bacterial challenge. This term captures the specific immune function of CLIPB4 better than the generic "innate immune response" term.
Reason: This annotation is strongly supported by experimental evidence. UniProt describes CLIPB4 as playing "a role in the innate immune response... by activating the melanization cascade" (PMID:16922859, PMID:37703846). RNAi knockdown reduces melanization of P. berghei ookinetes in resistant strains. The deep research confirms "knockdown reduces infection-induced melanin excreta" (saab2024insightintothe). This specific term is more appropriate than generic innate immune response.
Supporting Evidence:
Q7PEV7
In the resistant strain L3-5, involved in the melanization of killed parasite P.berghei ookinetes which results in their clearance (PubMed:16922859)
Q7PEV7
RNAi-mediated knockdown results in reduced melanization after microbial challenge (PubMed:37703846)
saab2024insightintothe
CLIPB4 functions upstream of CLIPB8 and independently controls CLIPB10 cleavage; knockdown reduces infection-induced melanin excreta
|
|
GO:0042832
defense response to protozoan
|
IMP
PMID:16922859 A genetic module regulates the melanization response of Anop... |
NEW |
Summary: CLIPB4 contributes to defense against Plasmodium berghei in Anopheles gambiae. In the resistant strain L3-5, RNAi knockdown of CLIPB4 causes a 5-fold reduction in melanized ookinetes. Combined knockdown with CLIPB17 causes a 52-fold reduction. This demonstrates a functional role in anti-Plasmodium defense.
Reason: This annotation is supported by mutant phenotype evidence (IMP). UniProt describes the disruption phenotype: "RNAi-mediated knockdown in the resistant strain L3-5 infected with P.berghei, causes a 5-fold reduction in the number of melanized ookinetes" (PMID:16922859). Additional evidence from An. stephensi shows that CLIPB4 knockdown increases P. falciparum oocyst intensity and prevalence (vandana2024wolbachiainfectionresponsiveimmune).
Supporting Evidence:
Q7PEV7
RNAi-mediated knockdown in the resistant strain L3-5 infected with P.berghei, causes a 5-fold reduction in the number of melanized ookinetes (PubMed:16922859)
vandana2024wolbachiainfectionresponsiveimmune
RNAi of CLIPB4 increases P. falciparum oocyst intensity and prevalence
|
Q: What are the complete substrate specificities of CLIPB4 beyond CLIPB8 and CLIPA8?
Q: What is the precise mechanism of CLIPB4 zymogen activation - which upstream proteases cleave it?
Q: How is CLIPB4 activity coordinated with the TEP1 complement-like pathway?
Experiment: In vitro cleavage assays to determine if CLIPB4 directly activates prophenoloxidase
Hypothesis: CLIPB4 may have direct prophenoloxidase-activating protease (PAP) activity
Experiment: Identification of the protease(s) responsible for CLIPB4 zymogen activation
Hypothesis: An upstream initiator protease activates CLIPB4 upon immune challenge
Experiment: Structural characterization of CLIPB4-SRPN2 inhibitory complex
Hypothesis: SRPN2 forms a covalent inhibitory complex with CLIPB4 active site serine
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template_variables:
organism: ANOGA
gene_id: CLIPB4
gene_symbol: CLIPB4
uniprot_accession: Q7PEV7
protein_description: 'RecName: Full=CLIP domain-containing serine protease B4 {ECO:0000305};
EC=3.4.21.- {ECO:0000255|PROSITE-ProRule:PRU00274, ECO:0000269|PubMed:37703846};
AltName: Full=CLIP domain-containing serine protease 14D {ECO:0000305}; Short=AgSp14D1
{ECO:0000303|PubMed:10469250}; Flags: Precursor;'
gene_info: Name=CLIPB4 {ECO:0000312|EMBL:EAA45573.1}; Synonyms=SP14D1 {ECO:0000303|PubMed:10469250};
ORFNames=AGAP003250 {ECO:0000312|EMBL:EAA45573.1};
organism_full: Anopheles gambiae (African malaria mosquito).
protein_family: Belongs to the peptidase S1 family. CLIP subfamily.
protein_domains: CLIP. (IPR022700); CLIP_sf. (IPR038565); Peptidase_S1_PA. (IPR009003);
Peptidase_S1_PA_chymotrypsin. (IPR043504); Peptidase_S1A. (IPR001314)
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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.
DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'CLIPB4' 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
Please provide a comprehensive research report on the gene CLIPB4 (gene ID: CLIPB4, UniProt: Q7PEV7) 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.
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.
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.
DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'CLIPB4' 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
Please provide a comprehensive research report on the gene CLIPB4 (gene ID: CLIPB4, UniProt: Q7PEV7) 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 overview
We verified target identity and gathered recent primary literature and authoritative background to annotate CLIPB4 (AgSp14D1/SP14D1; UniProt Q7PEV7) from Anopheles gambiae, focusing on function, pathways, localization, and 2023–2024 developments. We synthesize applications, expert perspectives, and relevant quantitative findings.
Key concepts and definitions
CLIPB4 (gene symbol: CLIPB4; aliases: AgSp14D1/SP14D1; locus AGAP003250) encodes a clip-domain serine protease of the S1A family secreted as a zymogen into hemolymph. The protein has an N‑terminal CLIP domain and a C‑terminal trypsin/chymotrypsin-like catalytic domain harboring the His-Asp-Ser catalytic triad typical of active catalytic CLIPs (cSPs). Upon proteolytic activation between domains, the two fragments remain disulfide-linked. In Anopheles, catalytic CLIPs (families B, C, D) and noncatalytic serine protease homologs (cSPHs; families A, E) form extracellular cascades that regulate immune processes, notably prophenoloxidase (PPO) activation leading to melanization, and interface with complement-like TEP1 pathways; serpins (e.g., SRPN2) irreversibly inhibit active CLIPs to prevent damage (architecture/background for CLIPs; domain definitions) (awada2018functionalandmolecular pages 26-31, awada2018functionalandmoleculara pages 26-31, nakhleh2018theroleof pages 30-36, moussawi2019functionalandmolecular pages 33-38).
Function, substrates, and pathway position of CLIPB4
Recent network mapping in An. gambiae positions CLIPB4 as an upstream catalytic node in the melanization cascade. Genetic epistasis and western analyses indicate that downstream of CLIPB4 (and CLIPB17) the cascade bifurcates into two branches converging on CLIPB8 and CLIPB10, with CLIPB4 controlling CLIPB10 processing independently of CLIPB8. In vitro, CLIPB4 cleaves the cSPH cofactor CLIPA8, consistent with regulatory interactions between cSPs and cSPHs in signal amplification. Direct PPO activation is strongest for CLIPB10; CLIPB4 has been suggested to have PAP-like activity based on cross-species assays cleaving Manduca sexta PPO, but in vivo PPO activation is better supported for downstream CLIPBs (CLIPB10; earlier work for CLIPB9/CLIPB8). Collectively, CLIPB4 functions upstream within the prophenoloxidase activation network that drives melanization, under control of cSPH cofactors (SPCLIP1, CLIPA8/CLIPA28) and serpins (notably SRPN2) (saab2024insightintothe pages 14-17, saab2024insightintothe pages 1-4, kamareddine2016theroleof pages 40-45).
Localization and activation
CLIPB4 is secreted into hemolymph as a zymogen. In systemic infection models, activation fragments for some downstream CLIPs (e.g., CLIPB10) are detectable in hemolymph; however, CLIPB4 activation products are rarely detected, suggesting that only a small active fraction exists transiently and is rapidly neutralized by serpins or sequestered at pathogen surfaces where localized melanization occurs (saab2024insightintothe pages 14-17).
Genetic/functional evidence in vivo
Cross-species functional support: In Anopheles stephensi, Wolbachia infection upregulates CLIPB4 ortholog transcripts; RNAi silencing of CLIPB4 increases Plasmodium falciparum oocyst intensity and prevalence, indicating that CLIPB4 contributes to anti‑Plasmodium defense modulated by symbionts (April 10, 2024; PLOS Pathogens; https://doi.org/10.1371/journal.ppat.1012145) (vandana2024wolbachiainfectionresponsiveimmune pages 11-13, vandana2024wolbachiainfectionresponsiveimmune pages 9-11).
Recent developments (2023–2024)
Symbiont-mediated regulation and transmission blocking: 2024 PLOS Pathogens reports that Wolbachia wAlbB upregulates CLIPB4 orthologs and that CLIPB4 knockdown increases P. falciparum infection, linking CLIPB4 to symbiont-enhanced anti‑Plasmodium immunity (https://doi.org/10.1371/journal.ppat.1012145; April 10, 2024) (vandana2024wolbachiainfectionresponsiveimmune pages 11-13, vandana2024wolbachiainfectionresponsiveimmune pages 9-11).
Current applications and implementations
Biomarker potential: Infection-induced melanization readouts (MelASA) respond to CLIPB4 perturbation, suggesting potential for CLIPB4 expression or processing as a hemolymph biomarker of melanization capacity in experimental settings (saab2024insightintothe pages 14-17).
Expert perspectives and authoritative background
Contemporary analyses emphasize extensive cSP–cSPH interplay in melanization, with cSPHs (e.g., SPCLIP1, CLIPA8, CLIPA28) acting as central nodes and catalytic CLIPs like CLIPB4 providing signal propagation toward terminal PPO-activating proteases (e.g., CLIPB10). Serpins such as SRPN2 serve as master brakes limiting collateral damage; SRPN2 knockdown unveils the cascade’s capacity for spontaneous melanization and highlights nodes like CLIPB4 in the network (kamareddine2016theroleof pages 40-45, awada2018functionalandmolecular pages 26-31, awada2018functionalandmoleculara pages 26-31).
Relevant data and statistics
Melanization output: In An. gambiae, CLIPB4 RNAi reduces MelASA-measured melanotic excreta following E. coli challenge, indicating diminished melanization output; the study also shows limited detectability of CLIPB4 activation fragments in bulk hemolymph (saab2024insightintothe pages 14-17).
Verification of target identity and nomenclature
The target matches UniProt Q7PEV7: Anopheles gambiae CLIPB4, also known as AgSp14D1/SP14D1 (historical cloning name), a preproenzyme belonging to the S1A serine protease family (CLIP subfamily) with an N‑terminal CLIP domain and a C‑terminal trypsin-like protease domain. This architecture aligns with the literature on Anopheles CLIPs (awada2018functionalandmolecular pages 26-31, awada2018functionalandmoleculara pages 26-31, nakhleh2018theroleof pages 30-36, moussawi2019functionalandmolecular pages 33-38).
Limitations and open questions
- While CLIPB4 shows PAP-like activity in cross-species in vitro assays, direct in vivo demonstration of CLIPB4 cleaving Anopheles PPO remains to be conclusively shown; current evidence places CLIPB4 upstream of terminal PAPs (e.g., CLIPB10) in the cascade. The full set of physiological substrates and serpin specificities for CLIPB4 in An. gambiae remains to be mapped at biochemical resolution (saab2024insightintothe pages 14-17, saab2024insightintothe pages 1-4).
Embedded evidence summary
| Study (first author et al.) | Year | Organism / Context | Approach | Key finding about CLIPB4 (or immediate cascade placement) | Notes on Network / Regulators | URL / DOI |
|---|---:|---|---|---|---|---|
| Saab et al. | 2024 | An. gambiae (melanization assays; SRPN2 knockdown model) | RNAi genetic screens, epistasis, Western blots, in vitro PPO cleavage assays | CLIPB4 functions upstream of CLIPB8 and independently controls CLIPB10 cleavage; knockdown reduces infection-induced melanin excreta; cascade bifurcates downstream of CLIPB4/CLIPB17; little detectable activation in hemolymph (rapidly cleared/entrapped) | Biochemically cleaves cSPH CLIPA8 in vitro; positioned centrally with CLIPB17; serpins likely clear active fraction (SRPN2 implicated in models) | https://doi.org/10.1101/2023.07.13.548954 (saab2024insightintothe pages 14-17, saab2024insightintothe pages 1-4) |
| Vandana et al. | 2024 | An. stephensi (Wolbachia-infected midguts & carcasses) | Transcriptomics (Wolbachia vs control) and RNAi functional validation | Wolbachia upregulates a CLIPB4 ortholog; RNAi of CLIPB4 increases P. falciparum oocyst intensity and prevalence, indicating an anti-Plasmodium role | Suggests Wolbachia-induced CLIPB4 contributes to reduced vector competence; functional RNAi evidence linking CLIPB4 to parasite suppression | https://doi.org/10.1371/journal.ppat.1012145 (vandana2024wolbachiainfectionresponsiveimmune pages 11-13, vandana2024wolbachiainfectionresponsiveimmune pages 9-11) |
| Awada | 2018 | An. gambiae (CLIP family functional/background) | Functional characterization / review-style synthesis of CLIP proteins | CLIP proteins are secreted zymogens with N-terminal clip domains and C-terminal S1A (chymotrypsin-like) catalytic domains; CLIPB subfamily predicted catalytic cSPs and potential PAPs | Describes zymogen activation (proteolytic cleavage, disulfide-linked domains), requirement for cSPH cofactors for PPO activation, and serpin inhibition | n/a (awada2018functionalandmolecular pages 26-31, awada2018functionalandmoleculara pages 26-31) |
| Nakhleh et al. | 2018 | An. gambiae (CLIP/SPH cascade architecture) | Functional/phylogenetic analysis and genetic perturbation context | Defines catalytic triad distinguishing cSPs from noncatalytic cSPHs; frames CLIPBs as terminal proteases in PPO activation cascades | Emphasizes roles of CLIPA cofactors (cSPHs) and serpins in regulating PPO activation intensity and cascade hierarchy | n/a (nakhleh2018theroleof pages 30-36) |
Table: A concise table summarizing primary and recent studies (including 2023–2024 network refinements and functional RNAi evidence) that define CLIPB4's role in Anopheles melanization cascades and anti-Plasmodium immunity.
Cited sources (URLs and dates)
- 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. Posted July 2024. URL: https://doi.org/10.1101/2023.07.13.548954 (saab2024insightintothe pages 14-17, saab2024insightintothe pages 1-4)
- Vandana V, Dong S, Sheth T, et al. Wolbachia infection-responsive immune genes suppress Plasmodium falciparum infection in Anopheles stephensi. PLOS Pathog. 2024 Apr 10;20:e1012145. URL: https://doi.org/10.1371/journal.ppat.1012145 (vandana2024wolbachiainfectionresponsiveimmune pages 11-13, vandana2024wolbachiainfectionresponsiveimmune pages 9-11)
- Awada MK. Functional and molecular characterization of CLIPA7 in Anopheles gambiae immunity. 2018. Background on CLIP domain proteases (awada2018functionalandmolecular pages 26-31, awada2018functionalandmoleculara pages 26-31)
- Nakhleh JN. The role of clip-domain serine protease homologue CLIPA14 and two carboxypeptidases in A. gambiae immunity. 2018. Background on catalytic triad, cascade regulation (nakhleh2018theroleof pages 30-36)
- Kamareddine LY. The role of clip-domain serine protease homologs in A. gambiae immune responses to systemic infections. 2016. Context on cSPH regulators and serpins (kamareddine2016theroleof pages 40-45)
- El Moussawi LH. Functional and molecular characterization of CLIPA28 in the melanization response of Anopheles gambiae mosquitoes. 2019. Background on CLIP family size and PPO activation models (moussawi2019functionalandmolecular pages 33-38)
References
(awada2018functionalandmolecular pages 26-31): MK Awada. Functional and molecular characterization of clipa7 in anopheles gambiae immunity. Unknown journal, 2018.
(awada2018functionalandmoleculara pages 26-31): MK Awada. Functional and molecular characterization of clipa7 in anopheles gambiae immunity. Unknown journal, 2018.
(nakhleh2018theroleof pages 30-36): JN Nakhleh. The role of clip-domain serine protease homologue clipa14 and two carboxypeptidases, cp1 and cp2 in a. gambiae immunity. Unknown journal, 2018.
(moussawi2019functionalandmolecular pages 33-38): LH El Moussawi. Functional and molecular characterization of the serine protease homologue clipa28 in the melanization response of anopheles gambiae mosquitoes. Unknown journal, 2019.
(saab2024insightintothe pages 14-17): 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.
(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.
(kamareddine2016theroleof pages 40-45): LY Kamareddine. The role of clip-domain serine protease homologs in a. gambiae immune responses to systemic infections. Unknown journal, 2016.
(vandana2024wolbachiainfectionresponsiveimmune pages 11-13): Vandana Vandana, Shengzhang Dong, Tanaya Sheth, Qiang Sun, Han Wen, Amanda Maldonado, Zhiyong Xi, and George Dimopoulos. Wolbachia infection-responsive immune genes suppress plasmodium falciparum infection in anopheles stephensi. PLOS Pathogens, 20:e1012145, Apr 2024. URL: https://doi.org/10.1371/journal.ppat.1012145, doi:10.1371/journal.ppat.1012145. This article has 15 citations and is from a highest quality peer-reviewed journal.
(vandana2024wolbachiainfectionresponsiveimmune pages 9-11): Vandana Vandana, Shengzhang Dong, Tanaya Sheth, Qiang Sun, Han Wen, Amanda Maldonado, Zhiyong Xi, and George Dimopoulos. Wolbachia infection-responsive immune genes suppress plasmodium falciparum infection in anopheles stephensi. PLOS Pathogens, 20:e1012145, Apr 2024. URL: https://doi.org/10.1371/journal.ppat.1012145, doi:10.1371/journal.ppat.1012145. This article has 15 citations and is from a highest quality peer-reviewed journal.
id: Q7PEV7
gene_symbol: CLIPB4
product_type: PROTEIN
status: DRAFT
taxon:
id: NCBITaxon:7165
label: Anopheles gambiae
description: >-
CLIPB4 is a CLIP domain-containing serine protease that functions as a central upstream node in the
melanization cascade of Anopheles gambiae. It is secreted into the hemolymph as a zymogen and, upon
proteolytic activation, cleaves and activates downstream proteases including CLIPB8. CLIPB4 plays a
key role in the innate immune response against protozoan parasites (Plasmodium) and bacterial pathogens
by activating the prophenoloxidase (PPO) cascade leading to melanin deposition at pathogen surfaces.
The protein is regulated by serpins (particularly SRPN2) that rapidly inhibit the active form to
prevent collateral damage from uncontrolled melanization.
existing_annotations:
- term:
id: GO:0005615
label: extracellular space
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
CLIPB4 is secreted into hemolymph as a zymogen and functions in the extracellular space where it
participates in the melanization cascade. UniProt annotation indicates "Secreted" for subcellular
location. The IBA annotation is based on phylogenetic inference from related CLIP-domain proteases
in Drosophila and other insects that are established hemolymph proteins.
action: ACCEPT
reason: >-
The extracellular space localization is well-supported. UniProt states "SUBCELLULAR LOCATION:
Secreted" and the deep research confirms "CLIPB4 is secreted into hemolymph as a zymogen"
(saab2024insightintothe). The IBA evidence from phylogenetic inference across multiple insect
species provides strong support for this conserved localization.
supported_by:
- reference_id: Q7PEV7
supporting_text: "SUBCELLULAR LOCATION: Secreted {ECO:0000305}"
- reference_id: saab2024insightintothe
supporting_text: "CLIPB4 is secreted into hemolymph as a zymogen"
- term:
id: GO:0045087
label: innate immune response
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
CLIPB4 plays a well-documented role in innate immunity through its function in the melanization
cascade. RNAi knockdown experiments demonstrate reduced melanization after microbial challenge
and increased Plasmodium infection, establishing a clear immune function. However, a more specific
term such as "melanization defense response" (GO:0035006) or "positive regulation of melanization
defense response" (GO:0035008) would better capture the precise function.
action: MODIFY
reason: >-
While the innate immune response annotation is correct, it is too general for CLIPB4's specific
role. The protein functions specifically in the melanization arm of innate immunity. UniProt
states "Serine protease which plays a role in the innate immune response against protozoan and
bacterial pathogens... by activating the melanization cascade" (PMID:16922859, PMID:37703846).
The more specific term GO:0035006 (melanization defense response) or GO:0035008 (positive
regulation of melanization defense response) would be more informative.
proposed_replacement_terms:
- id: GO:0035006
label: melanization defense response
- id: GO:0035008
label: positive regulation of melanization defense response
supported_by:
- reference_id: Q7PEV7
supporting_text: "Serine protease which plays a role in the innate immune response against protozoan and bacterial pathogens, such as Plasmodium bergei, Staphylococcus aureus, Micrococcus luteus and Escherichia coli, by activating the melanization cascade"
- reference_id: saab2024insightintothe
supporting_text: "CLIPB4 functions upstream of CLIPB8 and independently controls CLIPB10 cleavage; knockdown reduces infection-induced melanin excreta"
- term:
id: GO:0002376
label: immune system process
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >-
This is an IEA annotation based on UniProtKB keyword mapping from the "Immunity" and "Innate
immunity" keywords. While accurate, this term is extremely broad and adds little information
beyond what is captured by more specific immune annotations.
action: ACCEPT
reason: >-
This is a broad parental term that is technically correct but not very informative. It is
acceptable to retain as an IEA annotation since it correctly captures the general functional
category, and more specific annotations (like GO:0045087 innate immune response) provide the
needed specificity. The IBA annotation for innate immune response is more informative.
supported_by:
- reference_id: Q7PEV7
supporting_text: "KW: Immunity; Innate immunity"
- term:
id: GO:0004252
label: serine-type endopeptidase activity
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >-
CLIPB4 contains a trypsin-like serine protease domain (Peptidase S1) with the canonical
His-Asp-Ser catalytic triad. Experimental evidence confirms catalytic activity - CLIPB4 cleaves
CLIPB8 and the cSPH cofactor CLIPA8 in vitro (PMID:37703846). The InterPro-based IEA annotation
is well-supported by both domain architecture and experimental validation.
action: ACCEPT
reason: >-
This is the core molecular function of CLIPB4 and is strongly supported. UniProt annotates
EC=3.4.21.- based on experimental evidence (PMID:37703846). The protein has the complete
catalytic triad (His153, Asp213, Ser311) and experimentally demonstrated protease activity
cleaving CLIPB8 and CLIPA8. The term is appropriately specific for the enzymatic activity.
supported_by:
- reference_id: Q7PEV7
supporting_text: "EC=3.4.21.- {ECO:0000255|PROSITE-ProRule:PRU00274, ECO:0000269|PubMed:37703846}"
- reference_id: Q7PEV7
supporting_text: "Cleaves and activates CLIPB8 (PubMed:37703846)"
- reference_id: saab2024insightintothe
supporting_text: "In vitro, CLIPB4 cleaves the cSPH cofactor CLIPA8"
- term:
id: GO:0005576
label: extracellular region
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: >-
This IEA annotation is based on UniProt subcellular location vocabulary mapping for "Secreted"
proteins. It is a broader parent term of GO:0005615 (extracellular space) which is already
annotated via IBA. Both terms are valid but this one is less specific.
action: ACCEPT
reason: >-
The extracellular region annotation is correct and supported by the "Secreted" annotation in
UniProt. While GO:0005615 (extracellular space) is more specific and also annotated, retaining
this broader IEA annotation is acceptable as it represents the standard mapping from UniProt
subcellular location vocabulary.
supported_by:
- reference_id: Q7PEV7
supporting_text: "SUBCELLULAR LOCATION: Secreted {ECO:0000305}"
- term:
id: GO:0006508
label: proteolysis
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: >-
This broad biological process term indicates involvement in proteolytic processes. CLIPB4 is
an active serine protease that cleaves specific protein substrates (CLIPB8, CLIPA8) as part
of the melanization cascade. This is a generic annotation derived from the protease domain.
action: ACCEPT
reason: >-
While broad, this term accurately captures CLIPB4's role in proteolytic processing. The protein
has demonstrated proteolytic activity against specific substrates in the melanization cascade.
More specific biological process terms related to melanization would be more informative, but
this annotation is not incorrect.
supported_by:
- reference_id: Q7PEV7
supporting_text: "KW: Protease"
- reference_id: saab2024insightintothe
supporting_text: "CLIPB4 cleaves the cSPH cofactor CLIPA8"
- term:
id: GO:0008233
label: peptidase activity
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >-
This is a broad parent term for peptidase/protease activity. CLIPB4 is annotated more
specifically with GO:0004252 (serine-type endopeptidase activity) which is a child term.
This annotation adds no additional information beyond what the more specific term provides.
action: ACCEPT
reason: >-
While this is a broad parent term that is largely redundant with the more specific GO:0004252
(serine-type endopeptidase activity), it is an accurate IEA annotation from keyword mapping.
GO annotation guidelines allow parent terms alongside child terms, particularly when derived
from different evidence sources.
supported_by:
- reference_id: Q7PEV7
supporting_text: "KW: Protease"
- term:
id: GO:0008236
label: serine-type peptidase activity
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >-
This term is a parent of GO:0004252 (serine-type endopeptidase activity) which is also
annotated. CLIPB4 is specifically an endopeptidase (cleaves internal peptide bonds), so
GO:0004252 is more accurate. This annotation is correct but less specific.
action: ACCEPT
reason: >-
This is an accurate annotation based on UniProt keyword mapping for "Serine protease". While
GO:0004252 (serine-type endopeptidase activity) is more specific and preferred, this parental
term is not incorrect. The annotation reflects the protein family classification.
supported_by:
- reference_id: Q7PEV7
supporting_text: "KW: Serine protease"
- reference_id: Q7PEV7
supporting_text: "Belongs to the peptidase S1 family. CLIP subfamily."
- term:
id: GO:0016787
label: hydrolase activity
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >-
This is a very broad molecular function term for enzymes that catalyze hydrolysis reactions.
Serine proteases are hydrolases, so this is technically accurate but provides minimal functional
information. More specific terms (GO:0004252) are already annotated.
action: ACCEPT
reason: >-
This high-level term is accurate - serine proteases catalyze peptide bond hydrolysis. However,
it is extremely broad and the more specific GO:0004252 (serine-type endopeptidase activity)
provides much more functional information. Retaining the IEA annotation is acceptable as it
represents standard keyword mapping.
supported_by:
- reference_id: Q7PEV7
supporting_text: "KW: Hydrolase"
- term:
id: GO:0045087
label: innate immune response
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >-
This is a duplicate annotation of the same GO term (GO:0045087) that is also annotated via
IBA evidence. The IEA annotation comes from UniProt keyword mapping for "Innate immunity".
Both evidence codes support the same biological process involvement.
action: ACCEPT
reason: >-
While this is the same GO term as the IBA annotation, having both IEA and IBA evidence is
valid in GO annotation. The IEA annotation from keyword mapping and the IBA annotation from
phylogenetic inference independently support the same functional assignment. As noted above,
a more specific term like GO:0035006 (melanization defense response) would be more informative.
supported_by:
- reference_id: Q7PEV7
supporting_text: "KW: Innate immunity"
# Suggested new annotation based on literature evidence
- term:
id: GO:0035006
label: melanization defense response
evidence_type: IDA
original_reference_id: PMID:16922859
review:
summary: >-
CLIPB4 is directly involved in the melanization defense response against Plasmodium and
bacterial pathogens. RNAi knockdown experiments demonstrate reduced melanization of
P. berghei ookinetes in resistant mosquito strains, and reduced melanin excreta after
bacterial challenge. This term captures the specific immune function of CLIPB4 better
than the generic "innate immune response" term.
action: NEW
reason: >-
This annotation is strongly supported by experimental evidence. UniProt describes CLIPB4 as
playing "a role in the innate immune response... by activating the melanization cascade"
(PMID:16922859, PMID:37703846). RNAi knockdown reduces melanization of P. berghei ookinetes
in resistant strains. The deep research confirms "knockdown reduces infection-induced melanin
excreta" (saab2024insightintothe). This specific term is more appropriate than generic innate
immune response.
supported_by:
- reference_id: Q7PEV7
supporting_text: "In the resistant strain L3-5, involved in the melanization of killed parasite P.berghei ookinetes which results in their clearance (PubMed:16922859)"
- reference_id: Q7PEV7
supporting_text: "RNAi-mediated knockdown results in reduced melanization after microbial challenge (PubMed:37703846)"
- reference_id: saab2024insightintothe
supporting_text: "CLIPB4 functions upstream of CLIPB8 and independently controls CLIPB10 cleavage; knockdown reduces infection-induced melanin excreta"
- term:
id: GO:0042832
label: defense response to protozoan
evidence_type: IMP
original_reference_id: PMID:16922859
review:
summary: >-
CLIPB4 contributes to defense against Plasmodium berghei in Anopheles gambiae. In the
resistant strain L3-5, RNAi knockdown of CLIPB4 causes a 5-fold reduction in melanized
ookinetes. Combined knockdown with CLIPB17 causes a 52-fold reduction. This demonstrates
a functional role in anti-Plasmodium defense.
action: NEW
reason: >-
This annotation is supported by mutant phenotype evidence (IMP). UniProt describes the
disruption phenotype: "RNAi-mediated knockdown in the resistant strain L3-5 infected with
P.berghei, causes a 5-fold reduction in the number of melanized ookinetes" (PMID:16922859).
Additional evidence from An. stephensi shows that CLIPB4 knockdown increases P. falciparum
oocyst intensity and prevalence (vandana2024wolbachiainfectionresponsiveimmune).
supported_by:
- reference_id: Q7PEV7
supporting_text: "RNAi-mediated knockdown in the resistant strain L3-5 infected with P.berghei, causes a 5-fold reduction in the number of melanized ookinetes (PubMed:16922859)"
- reference_id: vandana2024wolbachiainfectionresponsiveimmune
supporting_text: "RNAi of CLIPB4 increases P. falciparum oocyst intensity and prevalence"
references:
- id: GO_REF:0000002
title: Gene Ontology annotation through association of InterPro records with GO terms
findings:
- statement: InterPro domain IPR001254 (Trypsin domain) maps to serine-type endopeptidase activity
- id: GO_REF:0000033
title: Annotation inferences using phylogenetic trees
findings:
- statement: IBA annotations for extracellular space and innate immune response based on PANTHER family PTN000667087
- statement: Orthology to characterized CLIP-domain proteases in Drosophila supports immune and secretion annotations
- id: GO_REF:0000043
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
findings:
- statement: UniProt keywords Immunity, Innate immunity, Protease, Serine protease, Hydrolase mapped to corresponding GO terms
- id: GO_REF:0000044
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping
findings:
- statement: Secreted subcellular location maps to extracellular region (GO:0005576)
- id: GO_REF:0000120
title: Combined Automated Annotation using Multiple IEA Methods
findings:
- statement: Proteolysis annotation derived from InterPro and UniProt keyword evidence
- id: PMID:16922859
title: A genetic module regulates the melanization response of Anopheles to Plasmodium
findings:
- statement: CLIPB4 RNAi knockdown reduces melanization of P. berghei ookinetes in resistant L3-5 strain
- statement: Combined CLIPB4/CLIPB17 knockdown causes 52-fold reduction in melanized ookinetes
- statement: CLIPB4 is dispensable for ookinete elimination in susceptible G3 strain (lysis mechanism)
- id: PMID:37703846
title: CLIPB4 Is a Central Node in the Protease Network that Regulates Humoral Immunity in Anopheles gambiae Mosquitoes
findings:
- statement: CLIPB4 cleaves and activates CLIPB8
- statement: CLIPB4 interacts with SRPN2 which inhibits its activity
- statement: CLIPB4 knockdown reduces melanization after microbial challenge
- statement: CLIPB4 knockdown rescues CLIPB8 depletion after microbial challenge
- id: PMID:10469250
title: An easter-like serine protease from Anopheles gambiae exhibits changes in transcript abundance following immune challenge
findings:
- statement: CLIPB4 (AgSp14D1) is expressed in fat body, cuticle, thorax and ovaries
- statement: Expression is induced by blood meal and bacterial infection
- id: saab2024insightintothe
title: Insight into the structural hierarchy of the protease cascade that regulates the mosquito melanization response
findings:
- statement: CLIPB4 functions upstream in melanization cascade, controlling CLIPB10 cleavage
- statement: CLIPB4 biochemically cleaves cSPH CLIPA8 in vitro
- statement: CLIPB4 knockdown reduces MelASA-measured melanization after E. coli challenge
- id: vandana2024wolbachiainfectionresponsiveimmune
title: Wolbachia infection-responsive immune genes suppress Plasmodium falciparum infection in Anopheles stephensi
findings:
- statement: Wolbachia upregulates CLIPB4 ortholog in An. stephensi
- statement: CLIPB4 RNAi increases P. falciparum oocyst intensity and prevalence
core_functions:
- molecular_function:
id: GO:0004252
label: serine-type endopeptidase activity
description: >-
CLIPB4 is a catalytically active CLIP-domain serine protease with demonstrated proteolytic
activity. It cleaves and activates downstream proteases in the melanization cascade,
including CLIPB8 and the cSPH cofactor CLIPA8.
directly_involved_in:
- id: GO:0035006
label: melanization defense response
locations:
- id: GO:0005615
label: extracellular space
proposed_new_terms: []
suggested_questions:
- question: What are the complete substrate specificities of CLIPB4 beyond CLIPB8 and CLIPA8?
- question: What is the precise mechanism of CLIPB4 zymogen activation - which upstream proteases cleave it?
- question: How is CLIPB4 activity coordinated with the TEP1 complement-like pathway?
suggested_experiments:
- description: In vitro cleavage assays to determine if CLIPB4 directly activates prophenoloxidase
hypothesis: CLIPB4 may have direct prophenoloxidase-activating protease (PAP) activity
- description: Identification of the protease(s) responsible for CLIPB4 zymogen activation
hypothesis: An upstream initiator protease activates CLIPB4 upon immune challenge
- description: Structural characterization of CLIPB4-SRPN2 inhibitory complex
hypothesis: SRPN2 forms a covalent inhibitory complex with CLIPB4 active site serine