SpoIIGA is a membrane-embedded, signal-transducing aspartic protease essential for sporulation in Bacillus subtilis. It is responsible for proteolytic processing of the inactive pro-sigma-E (pro-sigmaE/P31) to generate the active sigma factor sigmaE in the mother cell during endospore formation. SpoIIGA contains an N-terminal multi-pass transmembrane domain that anchors it to the mother cell side of the sporulation septum, and a C-terminal catalytic domain that faces the mother cell cytoplasm. The enzyme is activated by interaction with the forespore-secreted signaling protein SpoIIR, representing a key intercellular signaling mechanism that coordinates gene expression between the forespore and mother cell compartments. SpoIIGA belongs to the peptidase U4 family and functions as a novel type of aspartic protease with a dimeric active site architecture similar to retroviral proteases. The catalytic mechanism requires the conserved aspartate residue D183. Upon activation, SpoIIGA cleaves the N-terminal pro-sequence from pro-sigmaE, releasing mature sigmaE to associate with RNA polymerase and activate the mother cell transcriptional program required for spore development.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0004190
aspartic-type endopeptidase activity
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: This IEA annotation correctly identifies SpoIIGA as an aspartic-type endopeptidase. Experimental studies have demonstrated that SpoIIGA functions as a signal-transducing aspartic protease, with the catalytic aspartate D183 being essential for activity. The annotation is well-supported by biochemical and mutational evidence from PMID:18378688 and PMID:21362630.
Reason: This annotation accurately reflects the core molecular function of SpoIIGA. The protein has been experimentally characterized as an aspartic protease that cleaves pro-sigmaE. Mutation of the catalytic aspartate D183 abolishes protease activity. While SpoIIGA belongs to the peptidase U4 family rather than typical pepsin-like aspartic proteases, it functions via an aspartic protease mechanism with a dimeric active site.
Supporting Evidence:
PMID:18378688
Modeling and mutational analyses provide evidence that SpoIIGA is a novel type of aspartic protease whose C-terminal half forms a dimer similar to the human immunodeficiency virus type 1 protease.
PMID:21362630
SpoIIGA is a novel type of membrane-associated aspartic protease that responds to a signal from the forespore by cleaving Pro-σ(E) in the mother cell during sporulation of Bacillus subtilis.
file:BACSU/spoIIGA/spoIIGA-deep-research-falcon.md
See deep research file for comprehensive analysis
|
|
GO:0005886
plasma membrane
|
IEA
GO_REF:0000044 |
ACCEPT |
Summary: This IEA annotation indicates plasma membrane localization for SpoIIGA. This is correct but lacks specificity. SpoIIGA is specifically localized to the sporulation septum on the mother cell side. The protein is an integral membrane protein with multiple transmembrane segments.
Reason: While 'plasma membrane' is technically correct, SpoIIGA is more specifically localized to the sporulation septum. However, GO does not have a more specific term for bacterial sporulation septum membrane. The annotation correctly captures that SpoIIGA is membrane-associated as demonstrated by experimental evidence.
Supporting Evidence:
PMID:18378688
We found that SpoIIGA expressed in E. coli is membrane-associated and that after detergent treatment SpoIIGA was self-associated.
|
|
GO:0006508
proteolysis
|
IEA
GO_REF:0000120 |
KEEP AS NON CORE |
Summary: This IEA annotation to 'proteolysis' is a general biological process term. SpoIIGA does perform proteolysis, specifically cleaving pro-sigmaE to generate active sigmaE. The term is accurate but lacks specificity about the biological context.
Reason: While accurate, 'proteolysis' is a very general term. The more informative annotation would be to a sporulation-specific process. This annotation should be kept as it correctly identifies the general process, but the core function is better captured by the endospore formation annotation.
Supporting Evidence:
PMID:18378688
We report that expression of SpoIIR, a putative signaling protein normally made in the forespore, and SpoIIGA, a putative protease, is necessary and sufficient for accurate, rapid, and abundant processing of pro-sigma(E) to sigma(E) in Escherichia coli.
|
|
GO:0008233
peptidase activity
|
IEA
GO_REF:0000043 |
KEEP AS NON CORE |
Summary: This annotation to 'peptidase activity' is correct but redundant with the more specific 'aspartic-type endopeptidase activity' annotation. SpoIIGA is indeed a peptidase, but the more specific term better captures its mechanism.
Reason: This annotation is accurate but less informative than the aspartic-type endopeptidase annotation. It should be kept for compatibility with keyword-based annotations but is not the core function term. The more specific aspartic-type endopeptidase term should be preferred.
Supporting Evidence:
PMID:21362630
SpoIIGA is a novel type of membrane-associated aspartic protease that responds to a signal from the forespore by cleaving Pro-σ(E) in the mother cell during sporulation of Bacillus subtilis.
|
|
GO:0016787
hydrolase activity
|
IEA
GO_REF:0000043 |
MARK AS OVER ANNOTATED |
Summary: This annotation to 'hydrolase activity' is a very high-level molecular function term. While technically correct since peptidases are hydrolases, this term is too general to be informative about SpoIIGA function.
Reason: This is a very general parent term. Since more specific terms (aspartic-type endopeptidase activity, peptidase activity) are already annotated, this high-level term adds no informational value and represents over-annotation. It is implied by the more specific terms.
Supporting Evidence:
PMID:18378688
Modeling and mutational analyses provide evidence that SpoIIGA is a novel type of aspartic protease whose C-terminal half forms a dimer similar to the human immunodeficiency virus type 1 protease.
|
|
GO:0030435
sporulation resulting in formation of a cellular spore
|
IEA
GO_REF:0000043 |
MODIFY |
Summary: This annotation correctly identifies SpoIIGA involvement in sporulation. However, a more specific term exists: 'endospore formation' (GO:0034301) which better describes the bacterial endospore formation process in which SpoIIGA functions.
Reason: While SpoIIGA is involved in sporulation, the term 'endospore formation' (GO:0034301) is more precise for Bacillus subtilis. SpoIIGA specifically functions in the process of bacterial endospore formation by activating sigmaE in the mother cell.
Proposed replacements:
endospore formation
Supporting Evidence:
PMID:18378688
The bacterium Bacillus subtilis undergoes endospore formation in response to starvation.
|
|
GO:0030436
asexual sporulation
|
IEA
GO_REF:0000002 |
MODIFY |
Summary: This annotation from InterPro correctly identifies involvement in asexual sporulation. Bacterial endospore formation is indeed a form of asexual sporulation. However, the more specific term 'endospore formation' better captures the specific process.
Reason: While 'asexual sporulation' is correct, 'endospore formation' (GO:0034301) is more specific and appropriate for the bacterial context. Endospore formation is the relevant biological process in Bacillus subtilis.
Proposed replacements:
endospore formation
Supporting Evidence:
PMID:18378688
The bacterium Bacillus subtilis undergoes endospore formation in response to starvation.
|
|
GO:0004190
aspartic-type endopeptidase activity
|
IMP
PMID:18378688 Evidence that the Bacillus subtilis SpoIIGA protein is a nov... |
ACCEPT |
Summary: This experimental (IMP) annotation provides direct evidence for aspartic-type endopeptidase activity. The study demonstrated that SpoIIGA processes pro-sigmaE via an aspartic protease mechanism, with the catalytic aspartate D183 being essential for activity.
Reason: This is a high-quality experimental annotation based on mutational analysis. The study showed that D183A mutation abolishes protease activity, consistent with an aspartic protease mechanism. The modeling and biochemical data strongly support this annotation.
Supporting Evidence:
PMID:18378688
Modeling and mutational analyses provide evidence that SpoIIGA is a novel type of aspartic protease whose C-terminal half forms a dimer similar to the human immunodeficiency virus type 1 protease.
|
|
GO:0005515
protein binding
|
IPI
PMID:18378688 Evidence that the Bacillus subtilis SpoIIGA protein is a nov... |
MODIFY |
Summary: This annotation indicates protein binding based on physical interaction evidence. SpoIIGA has been shown to interact with SpoIIR (the signaling protein from the forespore) and with SigE (the substrate pro-sigmaE). However, 'protein binding' is uninformative.
Reason: The generic 'protein binding' term does not capture the functional significance of the interactions. SpoIIGA interacts with SpoIIR as part of signal transduction, and with pro-sigmaE as its substrate. A more specific term would be preferable, but since GO lacks a term for 'aspartic protease substrate binding', this annotation should be removed in favor of more informative terms.
Proposed replacements:
aspartic-type endopeptidase activity
Supporting Evidence:
PMID:18378688
Also, SpoIIGA interacts with SpoIIR.
|
|
GO:0005886
plasma membrane
|
IDA
PMID:18378688 Evidence that the Bacillus subtilis SpoIIGA protein is a nov... |
ACCEPT |
Summary: This experimental (IDA) annotation provides direct evidence for plasma membrane localization. The study demonstrated that SpoIIGA is membrane-associated when expressed in E. coli.
Reason: This is a high-quality experimental annotation demonstrating membrane association. While SpoIIGA is more specifically localized to the sporulation septum in B. subtilis, GO lacks a more specific term for this location, so plasma membrane is the appropriate term.
Supporting Evidence:
PMID:18378688
We found that SpoIIGA expressed in E. coli is membrane-associated and that after detergent treatment SpoIIGA was self-associated.
|
|
GO:0006508
proteolysis
|
IMP
PMID:18378688 Evidence that the Bacillus subtilis SpoIIGA protein is a nov... |
KEEP AS NON CORE |
Summary: This experimental (IMP) annotation indicates proteolysis based on mutant phenotype evidence. The study demonstrated pro-sigmaE processing to sigmaE by SpoIIGA.
Reason: This annotation is accurate but general. The more informative biological process annotation would be to endospore formation. However, this annotation correctly captures the general biochemical activity demonstrated in the study.
Supporting Evidence:
PMID:18378688
We report that expression of SpoIIR, a putative signaling protein normally made in the forespore, and SpoIIGA, a putative protease, is necessary and sufficient for accurate, rapid, and abundant processing of pro-sigma(E) to sigma(E) in Escherichia coli.
|
|
GO:0006508
proteolysis
|
IMP
PMID:21362630 Substrate specificity of SpoIIGA, a signal-transducing aspar... |
KEEP AS NON CORE |
Summary: This experimental (IMP) annotation from a second study confirms proteolytic activity through substrate specificity analysis. The study examined cleavage of pro-sigmaE orthologs by SpoIIGA.
Reason: This annotation provides additional experimental support for proteolytic activity. The study extended understanding of substrate specificity but the term remains general. Both proteolysis annotations should be kept as they come from different studies with complementary evidence.
Supporting Evidence:
PMID:21362630
SpoIIGA is a novel type of membrane-associated aspartic protease that responds to a signal from the forespore by cleaving Pro-σ(E) in the mother cell during sporulation of Bacillus subtilis.
|
|
GO:0008233
peptidase activity
|
IMP
PMID:21362630 Substrate specificity of SpoIIGA, a signal-transducing aspar... |
KEEP AS NON CORE |
Summary: This experimental (IMP) annotation indicates peptidase activity based on the substrate specificity study. The annotation is correct but less specific than the aspartic-type endopeptidase term.
Reason: This annotation is accurate and experimentally supported. While the aspartic-type endopeptidase term is more informative, this annotation correctly captures the general peptidase function demonstrated in the study examining substrate recognition and cleavage.
Supporting Evidence:
PMID:21362630
By co-expressing proteins in Escherichia coli, it was shown that charge reversal substitutions for acidic residues 24 and 25 of Pro-σ(E), and for basic residues 245 and 284 of SpoIIGA, impaired cleavage.
|
Q: What is the structural basis for SpoIIR-mediated activation of SpoIIGA protease activity?
Q: How does SpoIIGA achieve specificity for pro-sigmaE over other cellular substrates?
Q: What determines the species-specific differences in SpoIIGA substrate recognition among Bacillus species?
Experiment: Cryo-EM structure determination of SpoIIGA alone and in complex with SpoIIR
Hypothesis: Determining the structure of SpoIIGA will reveal the mechanism of SpoIIR-mediated activation and the architecture of the substrate binding site.
Type: structural biology
Experiment: In vivo crosslinking studies to map the SpoIIR-SpoIIGA interaction interface at the septum
Hypothesis: Crosslinking will identify specific residues involved in the SpoIIR-SpoIIGA interaction and validate the predicted interaction model.
Type: biochemistry
Experiment: Quantitative proteomics to determine if SpoIIGA has additional substrates beyond pro-sigmaE
Hypothesis: SpoIIGA may have additional substrates that contribute to mother cell development beyond the known pro-sigmaE substrate.
Type: proteomics
Exported on March 22, 2026 at 02:22 AM
Organism: Bacillus subtilis
Sequence:
MKIYLDVIWLLNFCFDALLLLLTAFILKRHVKKRRLVGGAFIGSSIVLLMFTPFSPIVEHPAGKLAFSVVIVVVTFGFKRFRFFFQNLFSFYFATFLMGGGIIGAHSLLQSNSIVQNGVMITNQTGFGDPISWLFIVGGFPALWFFSKRRIEDIETKNIQYEERVSVQADLGSQTLHVRGLIDSGNQLYDPLTKTPVMIIYIDKLEPIFGTAETMIIRNTDPLEAIEQLDDSFRFLDKMRLIPYRGVGQQNQFLLCVKPDHVTIMTKEEMISADKCLIGISTTKLSADGEFDAIIHPKMLSGKAVKHVS
I begin with the InterPro architecture. The sequence is covered end-to-end by IPR005081 (Sigma-E processing peptidase SpoIIGA family) from residues 1–301. A single, full-length family signature of this kind defines a dedicated processing peptidase rather than a broad-spectrum endopeptidase. SpoIIGA-family peptidases are characterized by an intramembrane-cleaving chemistry that recognizes a cognate precursor and executes site-specific endoproteolysis within or adjacent to the membrane. This architecture causes a precise maturation step rather than bulk proteolysis, and it typically functions as a membrane-tethered processing endopeptidase.
From this domain identity and its placement in sporulation-specific processing pathways, I infer the molecular function as endopeptidase activity that cleaves protein substrates at defined internal sites (GO:0004175 endopeptidase activity). The biological role follows from the known substrate logic of sporulation regulon activation: the peptidase activates a master transcriptional regulator by processing its sigma factor precursor. This maturation event triggers the transcriptional cascade that executes spore formation. Therefore, the biological process is sporulation (GO:0030435 sporulation), because the proteolytic activation of the sporulation sigma factor commits the developmental program toward spore production and maturation.
The cellular context is clarified by the combination of the SpoIIGA-family membrane-tethered architecture and the experimentally grounded subcellular label of a single-pass membrane protein. Processing of membrane-associated sigma-factor precursors is typically coordinated at the membrane interface, with the catalytic core positioned to access its substrate in the plane of the membrane. Thus, I place the protein in the membrane system (GO:0016020 membrane), consistent with a single-pass topology that anchors the protease for intramembrane proteolysis.
Putting these elements together yields a mechanism: a membrane-anchored processing endopeptidase that recognizes the membrane-associated precursor of the sporulation sigma factor and cleaves it to produce the active transcriptional regulator. By catalyzing this decisive maturation step at the membrane, the enzyme couples spatially restricted proteolysis to the irreversible transition into the sporulation program. The most direct interaction partner is the sigma-factor precursor that it processes; additional transient contacts with membrane assembly or quality-control factors may position the protease within sporulation-specific membrane microdomains, but the high-affinity, functionally critical interaction is with the substrate during its maturation.
A membrane-anchored processing endopeptidase in Bacillus subtilis that catalyzes the maturation of a sporulation transcriptional regulator by site-specific proteolysis of its precursor. By executing this activating cleavage at the membrane interface, it commits the developmental program toward spore formation and coordinates with membrane-tethered substrate recognition to drive the sporulation pathway.
Plays an essential role in sporulation.
IPR005081, family) — residues 1-301Molecular Function: molecular_function (GO:0003674), binding (GO:0005488), catalytic activity (GO:0003824), catalytic activity, acting on a protein (GO:0140096), hydrolase activity (GO:0016787), protein binding (GO:0005515), protein self-association (GO:0043621), peptidase activity (GO:0008233), endopeptidase activity (GO:0004175), aspartic-type peptidase activity (GO:0070001), aspartic-type endopeptidase activity (GO:0004190)
Biological Process: biological_process (GO:0008150), metabolic process (GO:0008152), primary metabolic process (GO:0044238), nitrogen compound metabolic process (GO:0006807), organic substance metabolic process (GO:0071704), macromolecule metabolic process (GO:0043170), organonitrogen compound metabolic process (GO:1901564), protein metabolic process (GO:0019538), proteolysis (GO:0006508)
Cellular Component: cellular_component (GO:0005575), cellular anatomical entity (GO:0110165), cell periphery (GO:0071944), membrane (GO:0016020), plasma membrane (GO:0005886)
Generated by BioReason
Exported on March 22, 2026 at 02:22 AM
Organism: Bacillus subtilis
Sequence:
MKIYLDVIWLLNFCFDALLLLLTAFILKRHVKKRRLVGGAFIGSSIVLLMFTPFSPIVEHPAGKLAFSVVIVVVTFGFKRFRFFFQNLFSFYFATFLMGGGIIGAHSLLQSNSIVQNGVMITNQTGFGDPISWLFIVGGFPALWFFSKRRIEDIETKNIQYEERVSVQADLGSQTLHVRGLIDSGNQLYDPLTKTPVMIIYIDKLEPIFGTAETMIIRNTDPLEAIEQLDDSFRFLDKMRLIPYRGVGQQNQFLLCVKPDHVTIMTKEEMISADKCLIGISTTKLSADGEFDAIIHPKMLSGKAVKHVS
I begin with the InterPro architecture. The sequence is covered end-to-end by IPR005081 (Sigma-E processing peptidase SpoIIGA family) from residues 1–301. A single, full-length family signature of this kind defines a dedicated processing peptidase rather than a broad-spectrum endopeptidase. SpoIIGA-family peptidases are characterized by an intramembrane-cleaving chemistry that recognizes a cognate precursor and executes site-specific endoproteolysis within or adjacent to the membrane. This architecture causes a precise maturation step rather than bulk proteolysis, and it typically functions as a membrane-tethered processing endopeptidase.
From this domain identity and its placement in sporulation-specific processing pathways, I infer the molecular function as endopeptidase activity that cleaves protein substrates at defined internal sites (GO:0004175 endopeptidase activity). The biological role follows from the known substrate logic of sporulation regulon activation: the peptidase activates a master transcriptional regulator by processing its sigma factor precursor. This maturation event triggers the transcriptional cascade that executes spore formation. Therefore, the biological process is sporulation (GO:0030435 sporulation), because the proteolytic activation of the sporulation sigma factor commits the developmental program toward spore production and maturation.
The cellular context is clarified by the combination of the SpoIIGA-family membrane-tethered architecture and the experimentally grounded subcellular label of a single-pass membrane protein. Processing of membrane-associated sigma-factor precursors is typically coordinated at the membrane interface, with the catalytic core positioned to access its substrate in the plane of the membrane. Thus, I place the protein in the membrane system (GO:0016020 membrane), consistent with a single-pass topology that anchors the protease for intramembrane proteolysis.
Putting these elements together yields a mechanism: a membrane-anchored processing endopeptidase that recognizes the membrane-associated precursor of the sporulation sigma factor and cleaves it to produce the active transcriptional regulator. By catalyzing this decisive maturation step at the membrane, the enzyme couples spatially restricted proteolysis to the irreversible transition into the sporulation program. The most direct interaction partner is the sigma-factor precursor that it processes; additional transient contacts with membrane assembly or quality-control factors may position the protease within sporulation-specific membrane microdomains, but the high-affinity, functionally critical interaction is with the substrate during its maturation.
A membrane-anchored processing endopeptidase in Bacillus subtilis that catalyzes the maturation of a sporulation transcriptional regulator by site-specific proteolysis of its precursor. By executing this activating cleavage at the membrane interface, it commits the developmental program toward spore formation and coordinates with membrane-tethered substrate recognition to drive the sporulation pathway.
Plays an essential role in sporulation.
IPR005081, family) — residues 1-301Molecular Function: molecular_function (GO:0003674), binding (GO:0005488), catalytic activity (GO:0003824), catalytic activity, acting on a protein (GO:0140096), hydrolase activity (GO:0016787), protein binding (GO:0005515), protein self-association (GO:0043621), peptidase activity (GO:0008233), endopeptidase activity (GO:0004175), aspartic-type peptidase activity (GO:0070001), aspartic-type endopeptidase activity (GO:0004190)
Biological Process: biological_process (GO:0008150), metabolic process (GO:0008152), primary metabolic process (GO:0044238), nitrogen compound metabolic process (GO:0006807), organic substance metabolic process (GO:0071704), macromolecule metabolic process (GO:0043170), organonitrogen compound metabolic process (GO:1901564), protein metabolic process (GO:0019538), proteolysis (GO:0006508)
Cellular Component: cellular_component (GO:0005575), cellular anatomical entity (GO:0110165), cell periphery (GO:0071944), membrane (GO:0016020), plasma membrane (GO:0005886)
Generated by BioReason
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model: Edison Scientific Literature
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start_time: '2025-12-18T08:26:46.366035'
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template_file: templates/gene_research_go_focused.md
template_variables:
organism: BACSU
gene_id: spoIIGA
gene_symbol: spoIIGA
uniprot_accession: P13801
protein_description: 'RecName: Full=Sporulation sigma-E factor-processing peptidase;
EC=3.4.23.-; AltName: Full=Membrane-associated aspartic protease; AltName: Full=Stage
II sporulation protein GA;'
gene_info: Name=spoIIGA; OrderedLocusNames=BSU15310;
organism_full: Bacillus subtilis (strain 168).
protein_family: Belongs to the peptidase U4 family. .
protein_domains: SpoIIGA. (IPR005081); Peptidase_U4 (PF03419)
provider_config:
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citation_count: 15
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 'spoIIGA' 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 spoIIGA (gene ID: spoIIGA, UniProt: P13801) in BACSU.
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 'spoIIGA' 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 spoIIGA (gene ID: spoIIGA, UniProt: P13801) in BACSU.
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
- Verify identity: Confirm spoIIGA (UniProt P13801) from Bacillus subtilis 168, protein family/domains, and avoid symbol ambiguity (completed). (imamura2011substratespecificityof pages 1-2, imamura2011substratespecificityof pages 2-3)
- Collect and analyze authoritative literature prioritizing 2011–2016 mechanistic papers and check for 2023–2024 updates; acknowledge any recency gaps (completed). (imamura2011substratespecificityof pages 1-2, meeske2016highthroughputgeneticscreens pages 30-31)
- Extract detailed evidence on enzymatic function, substrate specificity, partners, localization, pathway, and phenotypes (completed). (imamura2011substratespecificityof pages 1-2, imamura2011substratespecificityof pages 2-3, imamura2011substratespecificityof pages 3-4, imamura2011substratespecificityof pages 4-5, imamura2011substratespecificityof pages 5-7, meeske2016highthroughputgeneticscreens pages 18-20)
- Synthesize applications/context, expert perspectives, and relevant quantitative data (completed; quantitative Tn-seq figures from pathway-scale study). (meeske2016highthroughputgeneticscreens pages 30-31)
- Present structured artifact of key facts (completed; see embedded table). (imamura2011substratespecificityof pages 1-2, meeske2016highthroughputgeneticscreens pages 30-31)
- Write comprehensive research report with citations and URLs (current step).
Verification of gene/protein identity and context
- Target: spoIIGA (BSU15310) encodes the Sporulation sigma-E factor-processing peptidase (SpoIIGA) in Bacillus subtilis (strain 168). It is a membrane-associated signal-transducing aspartic protease belonging to peptidase family U4, responsible for proteolytic activation of pro-σE during sporulation. These assignments, including membrane topology and protease class, align with the UniProt description for P13801 and with primary literature. URL (Imamura 2011): https://doi.org/10.1093/jb/mvr027 (published Jun 2011). URL (Meeske 2016): https://doi.org/10.1371/journal.pbio.1002341 (published Jan 2016). (imamura2011substratespecificityof pages 1-2, meeske2016highthroughputgeneticscreens pages 30-31, imamura2011substratespecificityof pages 2-3)
Key concepts and definitions with current understanding
- Primary role: SpoIIGA is the dedicated processing protease that converts pro-σE (Pro-σE) to active σE in the mother cell, initiating the σE transcriptional program required for early mother-cell development during sporulation. Mechanistically, it removes the N-terminal pro-sequence of pro-σE to release mature σE into the cytoplasm. URL: https://doi.org/10.1093/jb/mvr027; https://doi.org/10.1371/journal.pbio.1002341. (imamura2011substratespecificityof pages 1-2, meeske2016highthroughputgeneticscreens pages 18-20)
- Enzyme class and mechanism: SpoIIGA functions as a signal-transducing aspartic protease. A conserved aspartate (D183) is essential for catalysis; D183A mutation abrogates processing activity. Modeling suggests a dimeric active site with retroviral-like aspartic protease features (flap and loop regions forming a substrate-binding cleft). URL: https://doi.org/10.1093/jb/mvr027. (imamura2011substratespecificityof pages 2-3, imamura2011substratespecificityof pages 5-7)
- Cellular localization: SpoIIGA is an integral membrane protein with an N-terminal multi-pass transmembrane anchor positioned at the sporulation septum on the mother-cell side; its C-terminal catalytic domain faces the mother-cell cytoplasm. URL: https://doi.org/10.1371/journal.pbio.1002341; https://doi.org/10.1093/jb/mvr027. (meeske2016highthroughputgeneticscreens pages 30-31, imamura2011substratespecificityof pages 2-3)
- Pathway context (cell–cell signaling): Activation of σE is controlled by an intercompartmental signal. The forespore, under σF control, produces SpoIIR, a secreted signaling protein that stimulates SpoIIGA in the mother-cell membrane to process pro-σE. The σE regulon is then activated in the mother cell. URL: https://doi.org/10.1093/jb/mvr027; https://doi.org/10.1371/journal.pbio.1002341. (imamura2011substratespecificityof pages 2-3, meeske2016highthroughputgeneticscreens pages 18-20)
Recent developments and latest research (emphasis on 2023–2024)
- Direct, SpoIIGA-focused primary reports since 2023 are limited. However, the σE activation pathway context remains supported by high-throughput genetic screening and pathway mapping work that identifies SpoIIR as the key forespore signal and places SpoIIGA at the septum as the cognate mother-cell protease; the study also uncovered SpoIIT as an accessory forespore factor enhancing σE activation. URL: https://doi.org/10.1371/journal.pbio.1002341 (2016). We found no SpoIIGA-specific mechanistic papers in 2023–2024 in our search; thus, conclusions rely on established mechanistic studies (Imamura 2011) and pathway-scale genetics (Meeske 2016). (meeske2016highthroughputgeneticscreens pages 30-31)
Current applications and real-world implementations
- In research, SpoIIGA and its partners (SpoIIR, pro-σE) provide a tractable model of membrane-associated developmental proteolysis and intercellular signaling in bacteria. Reconstitution in Escherichia coli demonstrates that SpoIIR and SpoIIGA are necessary and sufficient for accurate pro-σE processing, enabling heterologous assays for mutational analysis and substrate mapping. URL: https://doi.org/10.1093/jb/mvr027. (imamura2011substratespecificityof pages 2-3)
- In developmental genetics of spore formation, spoIIGA and spoIIR mutants serve as canonical controls for loss of σE activation, supporting phenotypic assays (e.g., σE-dependent reporters, microscopy of septal localization, immunoblots of pro-σE processing). URL: https://doi.org/10.1371/journal.pbio.1002341. (meeske2016highthroughputgeneticscreens pages 18-20)
Expert opinions and analysis from authoritative sources
- Mechanism and uniqueness: SpoIIGA is an unusual, signal-transducing aspartic protease that couples extracellular (septal) signaling to cytosolic proteolytic activation of a transcription factor—a paradigm highlighted in mechanistic analyses and structural modeling. This distinguishes SpoIIGA from housekeeping proteases by its developmental regulation and intercompartmental control. URL: https://doi.org/10.1093/jb/mvr027. (imamura2011substratespecificityof pages 2-3, imamura2011substratespecificityof pages 5-7)
- Pathway logic: The σF→SpoIIR→SpoIIGA→σE cascade exemplifies spatial segregation of regulators across the forespore–mother-cell interface, with SpoIIGA positioned to receive SpoIIR in the septal environment. Identification of SpoIIT as an additional forespore factor underscores the complexity and robustness of σE activation. URL: https://doi.org/10.1371/journal.pbio.1002341. (meeske2016highthroughputgeneticscreens pages 30-31, meeske2016highthroughputgeneticscreens pages 18-20)
Relevant statistics and data from recent studies
- High-throughput transposon sequencing (Tn-seq) recovered 133 of 148 previously known sporulation genes and discovered 24 new genes impacting sporulation, including components influencing σE activation. This places spoIIGA and spoIIR within a broad, validated genetic framework controlling the progression of sporulation. URL: https://doi.org/10.1371/journal.pbio.1002341. (meeske2016highthroughputgeneticscreens pages 30-31)
- Phenotypic outcomes: Loss-of-function in spoIIGA or spoIIR prevents σE activation, leading to abortive sporulation and characteristic defects (e.g., disporic sporangia), validated by microscopy, reporter assays, and immunoblotting of pro-σE processing. URL: https://doi.org/10.1371/journal.pbio.1002341. (meeske2016highthroughputgeneticscreens pages 18-20)
Molecular function and substrate specificity
- Reaction catalyzed: Proteolytic removal of the N-terminal pro-sequence of pro-σE to generate active σE. The pro-sequence residues around ~22–33 contain critical determinants; specifically, charge-reversal substitutions at D24 and E25 in pro-σE prevent processing. URL: https://doi.org/10.1093/jb/mvr027. (imamura2011substratespecificityof pages 3-4)
- Enzyme–substrate recognition: SpoIIGA residues R245 and K284, located near the modeled flap/loop regions of the catalytic domain, are important for substrate recognition. Mutations R245D and K284D reduce or abolish cleavage; P259 is highly conserved and influences activity. URL: https://doi.org/10.1093/jb/mvr027. (imamura2011substratespecificityof pages 3-4, imamura2011substratespecificityof pages 4-5)
- Ortholog specificity: B. subtilis SpoIIGA can process pro-σE from B. licheniformis and B. halodurans, but not from B. cereus unless distal pro-sequence residues are engineered, indicating that both proximal and distal pro-sequence elements contribute to specificity and that orthologous SpoIIGA enzymes differ in breadth of specificity. URL: https://doi.org/10.1093/jb/mvr027. (imamura2011substratespecificityof pages 4-5, imamura2011substratespecificityof pages 5-7)
Cellular localization and topology
- Topology: N-terminal domain with multiple transmembrane segments embeds in the mother-cell septal membrane; C-terminal catalytic domain faces the mother-cell cytoplasm where σE is released. URL: https://doi.org/10.1093/jb/mvr027; https://doi.org/10.1371/journal.pbio.1002341. (imamura2011substratespecificityof pages 2-3, meeske2016highthroughputgeneticscreens pages 30-31)
- Septal positioning: SpoIIGA and pro-σE concentrate at the sporulation septum, coordinating processing with asymmetrical division. URL: https://doi.org/10.1371/journal.pbio.1002341. (meeske2016highthroughputgeneticscreens pages 30-31)
Pathway integration and regulation
- Signaling cascade: Forespore σF activates spoIIR expression; SpoIIR is secreted and interacts with SpoIIGA to trigger pro-σE processing in the mother-cell membrane. Processed σE engages RNA polymerase to activate the mother-cell transcriptional program. SpoIIT, a forespore factor, augments σE activation efficiency. URL: https://doi.org/10.1371/journal.pbio.1002341; https://doi.org/10.1093/jb/mvr027. (meeske2016highthroughputgeneticscreens pages 18-20, imamura2011substratespecificityof pages 2-3)
- Reconstitution and sufficiency: Co-expression in E. coli established that SpoIIR and SpoIIGA are necessary and sufficient to process pro-σE accurately, providing a powerful system for mechanistic dissection. URL: https://doi.org/10.1093/jb/mvr027. (imamura2011substratespecificityof pages 2-3)
Mutant phenotypes and genetic evidence
- spoIIGA and spoIIR mutants: Failure to activate σE, leading to defects in mother-cell gene expression and abortive sporulation; phenotypes visualized by σE-dependent reporters and septal localization markers. URL: https://doi.org/10.1371/journal.pbio.1002341. (meeske2016highthroughputgeneticscreens pages 18-20)
- Suppressor analysis: Specific spoIIGA mutations can modulate processing of defective pro-σE variants, indicating sensitivity of the protease–substrate interface to both enzyme and substrate side-chain chemistry. URL: https://doi.org/10.1093/jb/mvr027. (imamura2011substratespecificityof pages 4-5)
Limitations and open questions
- Structural gap: While modeling supports a dimeric aspartic protease fold, high-resolution experimental structures of SpoIIGA are not reported in the cited evidence; thus, the precise architecture of the active site and SpoIIR-binding interface remains inferred. URL: https://doi.org/10.1093/jb/mvr027. (imamura2011substratespecificityof pages 5-7)
- Recency: We found no new mechanistic studies since 2023 focused specifically on SpoIIGA; current understanding relies on established biochemical and genetic evidence. Continued advances may come from cryo-EM or in situ structural approaches targeting septal protein complexes during sporulation. (meeske2016highthroughputgeneticscreens pages 30-31)
Embedded summary table
| Aspect | Finding | Evidence/Notes | Key Source (with URL) |
|---|---|---|---|
| Identity & family | Sporulation sigma-E factor-processing peptidase (SpoIIGA); member of membrane-associated aspartic protease / peptidase U4 family | Described as a membrane-associated, signal-transducing aspartic protease that processes pro-σE (putative catalytic Asp, family U4 assignment). (imamura2011substratespecificityof pages 1-2, imamura2011substratespecificityof pages 2-3) | Imamura et al., 2011: https://doi.org/10.1093/jb/mvr027 |
| Cellular localization | Localized to the mother-cell side of the septal membrane (septal/membrane-associated) | Targeted to sites of spore septum formation; N-terminal TM segments anchor SpoIIGA in the mother-cell septal membrane. (meeske2016highthroughputgeneticscreens pages 30-31, imamura2011substratespecificityof pages 2-3) | Meeske et al., 2016: https://doi.org/10.1371/journal.pbio.1002341; Imamura 2011: https://doi.org/10.1093/jb/mvr027 |
| Primary function | Proteolytic processing of pro-σE (Pro-σE → σE) to activate mother-cell σE regulon during sporulation | Direct processing of Pro-σE required for release of mature σE and initiation of σE-dependent transcription in the mother cell. (imamura2011substratespecificityof pages 1-2, meeske2016highthroughputgeneticscreens pages 18-20) | Imamura 2011: https://doi.org/10.1093/jb/mvr027; Meeske 2016: https://doi.org/10.1371/journal.pbio.1002341 |
| Catalytic mechanism | Aspartic protease mechanism; essential catalytic Asp (D183) and likely dimeric active site (retroviral-like protease fold) | D183A catalytic mutant is inactive; structural modelling predicts dimerization and flap/loop substrate-interaction regions analogous to retroviral/aspartic proteases. (imamura2011substratespecificityof pages 2-3, imamura2011substratespecificityof pages 5-7) | Imamura 2011: https://doi.org/10.1093/jb/mvr027 |
| Required partners | Activation via forespore-secreted SpoIIR (and accessory SpoIIT) which signal across septum to stimulate SpoIIGA activity | SpoIIR produced in forespore and required to stimulate SpoIIGA-mediated cleavage; SpoIIT identified as an additional forespore-expressed factor aiding efficient processing. (imamura2011substratespecificityof pages 2-3, meeske2016highthroughputgeneticscreens pages 18-20) | Meeske 2016: https://doi.org/10.1371/journal.pbio.1002341; Imamura 2011: https://doi.org/10.1093/jb/mvr027 |
| Substrate & specificity | Substrate = Pro-σE pro-sequence (N-terminal ~ residues ~22–33 determinants); specificity influenced by both Pro-σE and SpoIIGA residues; cross-species differences observed | Mutational analysis shows charged residues (e.g., D24/E25) in Pro-σE are critical; SpoIIGA residues (R245, K284, P259) affect recognition; B. subtilis SpoIIGA cleaves some orthologs but not B. cereus unless pro-sequence altered. (imamura2011substratespecificityof pages 3-4, imamura2011substratespecificityof pages 4-5) | Imamura 2011: https://doi.org/10.1093/jb/mvr027 |
| Regulation / pathway context | σF (forespore) → spoIIR secretion → SpoIIGA activation (mother cell) → pro-σE processing → σE regulon activation; SpoIIT as accessory forespore signal | Pathway places SpoIIGA as membrane protease transducing an intercellular signal from forespore to mother cell to control developmental transcription. (meeske2016highthroughputgeneticscreens pages 30-31, imamura2011substratespecificityof pages 2-3) | Meeske 2016: https://doi.org/10.1371/journal.pbio.1002341; Imamura 2011: https://doi.org/10.1093/jb/mvr027 |
| Mutant phenotype | spoIIGA or spoIIR loss-of-function prevents σE activation and causes abortive/defective sporulation | Loss of spoIIGA or spoIIR leads to failure to activate σE and results in abortive disporic sporangia or blocked mother-cell development. (meeske2016highthroughputgeneticscreens pages 18-20, meeske2016highthroughputgeneticscreens pages 30-31) | Meeske 2016: https://doi.org/10.1371/journal.pbio.1002341 |
| Experimental systems | Reconstitution in E. coli (co-expression of SpoIIGA + SpoIIR + Pro-σE) sufficient for accurate Pro-σE cleavage; mutagenesis and suppressor analysis used to map determinants | E. coli co-expression assays required SpoIIR to stimulate SpoIIGA cleavage; catalytic mutants and suppressor alleles characterized experimentally. (imamura2011substratespecificityof pages 2-3, imamura2011substratespecificityof pages 4-5) | Imamura 2011: https://doi.org/10.1093/jb/mvr027 |
| Recent developments note | Few SpoIIGA-specific publications in 2023–2024; broader sporulation / sporulation-gene discovery efforts continue (e.g., high-throughput screens reveal additional regulators) | Targeted SpoIIGA mechanistic work is primarily from prior studies (Imamura et al. 2008/2011); large-scale genetic screens (Meeske 2016) add context and identify accessory factors like SpoIIT. (meeske2016highthroughputgeneticscreens pages 30-31, imamura2011substratespecificityof pages 5-7) | Meeske 2016: https://doi.org/10.1371/journal.pbio.1002341; Imamura 2011: https://doi.org/10.1093/jb/mvr027 |
Table: Concise summary table of SpoIIGA (B. subtilis 168) covering identity, localization, mechanism, partners, substrate specificity, pathway context, phenotypes, experimental systems, and recent-update notes, with evidence citations to the primary sources used.
Conclusions
SpoIIGA (spoIIGA; UniProt P13801) in Bacillus subtilis 168 is a membrane-embedded, signal-transducing aspartic protease that processes pro-σE at the sporulation septum in response to the forespore-secreted signal SpoIIR, thereby activating the mother-cell σE regulon. Its catalytic activity requires a conserved aspartate (D183) and likely dimerization, with substrate recognition governed by acidic residues in the pro-σE pro-sequence (notably D24/E25) and complementary basic residues in SpoIIGA (e.g., R245, K284). Ortholog comparisons reveal species-specific substrate preferences, highlighting co-evolution within the σE activation module. Mutational and high-throughput genetic studies firmly place SpoIIGA at a critical checkpoint in spore development, with loss-of-function preventing σE activation and sporulation. URLs: Imamura 2011 (https://doi.org/10.1093/jb/mvr027), Meeske 2016 (https://doi.org/10.1371/journal.pbio.1002341). (imamura2011substratespecificityof pages 1-2, imamura2011substratespecificityof pages 2-3, imamura2011substratespecificityof pages 3-4, imamura2011substratespecificityof pages 4-5, imamura2011substratespecificityof pages 5-7, meeske2016highthroughputgeneticscreens pages 18-20, meeske2016highthroughputgeneticscreens pages 30-31)
References
(imamura2011substratespecificityof pages 1-2): Daisuke Imamura, Ritsuko Kuwana, Lee Kroos, Michael Feig, Hiromu Takamatsu, and Kazuhito Watabe. Substrate specificity of spoiiga, a signal-transducing aspartic protease in bacilli. Journal of biochemistry, 149 6:665-71, Jun 2011. URL: https://doi.org/10.1093/jb/mvr027, doi:10.1093/jb/mvr027. This article has 13 citations and is from a peer-reviewed journal.
(imamura2011substratespecificityof pages 2-3): Daisuke Imamura, Ritsuko Kuwana, Lee Kroos, Michael Feig, Hiromu Takamatsu, and Kazuhito Watabe. Substrate specificity of spoiiga, a signal-transducing aspartic protease in bacilli. Journal of biochemistry, 149 6:665-71, Jun 2011. URL: https://doi.org/10.1093/jb/mvr027, doi:10.1093/jb/mvr027. This article has 13 citations and is from a peer-reviewed journal.
(meeske2016highthroughputgeneticscreens pages 30-31): Alexander J. Meeske, Christopher D. A. Rodrigues, Jacqueline Brady, Hoong Chuin Lim, Thomas G. Bernhardt, and David Z. Rudner. High-throughput genetic screens identify a large and diverse collection of new sporulation genes in bacillus subtilis. PLOS Biology, 14:e1002341, Jan 2016. URL: https://doi.org/10.1371/journal.pbio.1002341, doi:10.1371/journal.pbio.1002341. This article has 125 citations and is from a highest quality peer-reviewed journal.
(imamura2011substratespecificityof pages 3-4): Daisuke Imamura, Ritsuko Kuwana, Lee Kroos, Michael Feig, Hiromu Takamatsu, and Kazuhito Watabe. Substrate specificity of spoiiga, a signal-transducing aspartic protease in bacilli. Journal of biochemistry, 149 6:665-71, Jun 2011. URL: https://doi.org/10.1093/jb/mvr027, doi:10.1093/jb/mvr027. This article has 13 citations and is from a peer-reviewed journal.
(imamura2011substratespecificityof pages 4-5): Daisuke Imamura, Ritsuko Kuwana, Lee Kroos, Michael Feig, Hiromu Takamatsu, and Kazuhito Watabe. Substrate specificity of spoiiga, a signal-transducing aspartic protease in bacilli. Journal of biochemistry, 149 6:665-71, Jun 2011. URL: https://doi.org/10.1093/jb/mvr027, doi:10.1093/jb/mvr027. This article has 13 citations and is from a peer-reviewed journal.
(imamura2011substratespecificityof pages 5-7): Daisuke Imamura, Ritsuko Kuwana, Lee Kroos, Michael Feig, Hiromu Takamatsu, and Kazuhito Watabe. Substrate specificity of spoiiga, a signal-transducing aspartic protease in bacilli. Journal of biochemistry, 149 6:665-71, Jun 2011. URL: https://doi.org/10.1093/jb/mvr027, doi:10.1093/jb/mvr027. This article has 13 citations and is from a peer-reviewed journal.
(meeske2016highthroughputgeneticscreens pages 18-20): Alexander J. Meeske, Christopher D. A. Rodrigues, Jacqueline Brady, Hoong Chuin Lim, Thomas G. Bernhardt, and David Z. Rudner. High-throughput genetic screens identify a large and diverse collection of new sporulation genes in bacillus subtilis. PLOS Biology, 14:e1002341, Jan 2016. URL: https://doi.org/10.1371/journal.pbio.1002341, doi:10.1371/journal.pbio.1002341. This article has 125 citations and is from a highest quality peer-reviewed journal.
Source: spoIIGA-deep-research-bioreason-rl.md
The BioReason functional summary reads:
A membrane-anchored processing endopeptidase in Bacillus subtilis that catalyzes the maturation of a sporulation transcriptional regulator by site-specific proteolysis of its precursor. By executing this activating cleavage at the membrane interface, it commits the developmental program toward spore formation and coordinates with membrane-tethered substrate recognition to drive the sporulation pathway.
This is a largely accurate summary. The description of SpoIIGA as a membrane-anchored processing endopeptidase that activates a sporulation sigma factor precursor matches the curated core function of aspartic-type endopeptidase activity (GO:0004190). The membrane localization (GO:0005886) is correct. The sporulation context is captured, though BioReason assigns the more general GO:0030435 rather than the curated preference for endospore formation (GO:0034301).
The key inaccuracy is in the molecular function specificity: BioReason identifies "endopeptidase activity" (GO:0004175) as the primary term, while the curated review establishes aspartic-type endopeptidase activity (GO:0004190) based on experimental evidence (PMID:18378688) showing D183 as the essential catalytic aspartate and a dimeric active site architecture similar to HIV-1 protease. BioReason's GO predictions do include aspartic-type endopeptidase activity and aspartic-type peptidase activity, so this information is present in the predictions but the narrative summary uses the less specific "processing endopeptidase" language.
Omissions:
Missing substrate identity: The summary refers to "a sporulation transcriptional regulator" but never names pro-sigmaE as the substrate or sigmaE as the product. The curated review clearly identifies the pro-sigmaE to sigmaE conversion.
Missing signaling mechanism: SpoIIGA is activated by the forespore-secreted protein SpoIIR, representing a key intercellular signaling mechanism coordinating forespore and mother cell gene expression. BioReason vaguely mentions "spatially restricted proteolysis" but does not capture this signaling axis.
Missing compartment specificity: SpoIIGA specifically localizes to the mother cell side of the sporulation septum. The curated review notes this mother cell specificity.
Missing protease mechanism details: The curated review describes the novel dimeric aspartic protease architecture (peptidase U4 family, HIV-1 protease-like dimer). BioReason does not specify the aspartic mechanism in its narrative.
Comparison with interpro2go:
The interpro2go annotation for spoIIGA is based on the single IPR005081 (SpoIIGA family) domain. The curated review's GO_REF:0000002 annotations include asexual sporulation (GO:0030436), which is flagged for modification to the more specific endospore formation (GO:0034301). BioReason's GO predictions include aspartic-type endopeptidase activity and proteolysis terms that match interpro2go outputs. BioReason adds meaningful context by describing the sigma factor precursor processing role and membrane anchor, going beyond what interpro2go alone provides.
The trace correctly identifies the SpoIIGA family signature and infers a membrane-tethered processing endopeptidase function. The reasoning about intramembrane proteolysis and sigma factor maturation is appropriate. The trace does not identify the specific aspartic protease mechanism, instead using the broader "endopeptidase" classification.
id: P13801
gene_symbol: spoIIGA
product_type: PROTEIN
status: COMPLETE
taxon:
id: NCBITaxon:224308
label: Bacillus subtilis (strain 168)
description: >-
SpoIIGA is a membrane-embedded, signal-transducing aspartic protease essential for sporulation
in Bacillus subtilis. It is responsible for proteolytic processing of the inactive pro-sigma-E
(pro-sigmaE/P31) to generate the active sigma factor sigmaE in the mother cell during endospore
formation. SpoIIGA contains an N-terminal multi-pass transmembrane domain that anchors it to
the mother cell side of the sporulation septum, and a C-terminal catalytic domain that faces
the mother cell cytoplasm. The enzyme is activated by interaction with the forespore-secreted
signaling protein SpoIIR, representing a key intercellular signaling mechanism that coordinates
gene expression between the forespore and mother cell compartments. SpoIIGA belongs to the
peptidase U4 family and functions as a novel type of aspartic protease with a dimeric active
site architecture similar to retroviral proteases. The catalytic mechanism requires the
conserved aspartate residue D183. Upon activation, SpoIIGA cleaves the N-terminal pro-sequence
from pro-sigmaE, releasing mature sigmaE to associate with RNA polymerase and activate the
mother cell transcriptional program required for spore development.
existing_annotations:
- term:
id: GO:0004190
label: aspartic-type endopeptidase activity
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: >-
This IEA annotation correctly identifies SpoIIGA as an aspartic-type endopeptidase.
Experimental studies have demonstrated that SpoIIGA functions as a signal-transducing
aspartic protease, with the catalytic aspartate D183 being essential for activity.
The annotation is well-supported by biochemical and mutational evidence from PMID:18378688
and PMID:21362630.
action: ACCEPT
reason: >-
This annotation accurately reflects the core molecular function of SpoIIGA. The protein
has been experimentally characterized as an aspartic protease that cleaves pro-sigmaE.
Mutation of the catalytic aspartate D183 abolishes protease activity. While SpoIIGA
belongs to the peptidase U4 family rather than typical pepsin-like aspartic proteases,
it functions via an aspartic protease mechanism with a dimeric active site.
supported_by:
- reference_id: PMID:18378688
supporting_text: >-
Modeling and mutational analyses provide evidence that SpoIIGA is a novel type of
aspartic protease whose C-terminal half forms a dimer similar to the human
immunodeficiency virus type 1 protease.
- reference_id: PMID:21362630
supporting_text: >-
SpoIIGA is a novel type of membrane-associated aspartic protease that responds to
a signal from the forespore by cleaving Pro-σ(E) in the mother cell during
sporulation of Bacillus subtilis.
- reference_id: file:BACSU/spoIIGA/spoIIGA-deep-research-falcon.md
supporting_text: See deep research file for comprehensive analysis
- term:
id: GO:0005886
label: plasma membrane
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: >-
This IEA annotation indicates plasma membrane localization for SpoIIGA. This is
correct but lacks specificity. SpoIIGA is specifically localized to the sporulation
septum on the mother cell side. The protein is an integral membrane protein with
multiple transmembrane segments.
action: ACCEPT
reason: >-
While 'plasma membrane' is technically correct, SpoIIGA is more specifically localized
to the sporulation septum. However, GO does not have a more specific term for bacterial
sporulation septum membrane. The annotation correctly captures that SpoIIGA is
membrane-associated as demonstrated by experimental evidence.
supported_by:
- reference_id: PMID:18378688
supporting_text: >-
We found that SpoIIGA expressed in E. coli is membrane-associated and that after
detergent treatment SpoIIGA was self-associated.
- term:
id: GO:0006508
label: proteolysis
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: >-
This IEA annotation to 'proteolysis' is a general biological process term. SpoIIGA
does perform proteolysis, specifically cleaving pro-sigmaE to generate active sigmaE.
The term is accurate but lacks specificity about the biological context.
action: KEEP_AS_NON_CORE
reason: >-
While accurate, 'proteolysis' is a very general term. The more informative annotation
would be to a sporulation-specific process. This annotation should be kept as it
correctly identifies the general process, but the core function is better captured
by the endospore formation annotation.
supported_by:
- reference_id: PMID:18378688
supporting_text: >-
We report that expression of SpoIIR, a putative signaling protein normally made
in the forespore, and SpoIIGA, a putative protease, is necessary and sufficient
for accurate, rapid, and abundant processing of pro-sigma(E) to sigma(E) in
Escherichia coli.
- term:
id: GO:0008233
label: peptidase activity
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >-
This annotation to 'peptidase activity' is correct but redundant with the more
specific 'aspartic-type endopeptidase activity' annotation. SpoIIGA is indeed
a peptidase, but the more specific term better captures its mechanism.
action: KEEP_AS_NON_CORE
reason: >-
This annotation is accurate but less informative than the aspartic-type endopeptidase
annotation. It should be kept for compatibility with keyword-based annotations but
is not the core function term. The more specific aspartic-type endopeptidase term
should be preferred.
supported_by:
- reference_id: PMID:21362630
supporting_text: >-
SpoIIGA is a novel type of membrane-associated aspartic protease that responds to
a signal from the forespore by cleaving Pro-σ(E) in the mother cell during
sporulation of Bacillus subtilis.
- term:
id: GO:0016787
label: hydrolase activity
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >-
This annotation to 'hydrolase activity' is a very high-level molecular function
term. While technically correct since peptidases are hydrolases, this term is
too general to be informative about SpoIIGA function.
action: MARK_AS_OVER_ANNOTATED
reason: >-
This is a very general parent term. Since more specific terms (aspartic-type
endopeptidase activity, peptidase activity) are already annotated, this high-level
term adds no informational value and represents over-annotation. It is implied
by the more specific terms.
supported_by:
- reference_id: PMID:18378688
supporting_text: >-
Modeling and mutational analyses provide evidence that SpoIIGA is a novel type of
aspartic protease whose C-terminal half forms a dimer similar to the human
immunodeficiency virus type 1 protease.
- term:
id: GO:0030435
label: sporulation resulting in formation of a cellular spore
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >-
This annotation correctly identifies SpoIIGA involvement in sporulation. However,
a more specific term exists: 'endospore formation' (GO:0034301) which better
describes the bacterial endospore formation process in which SpoIIGA functions.
action: MODIFY
reason: >-
While SpoIIGA is involved in sporulation, the term 'endospore formation' (GO:0034301)
is more precise for Bacillus subtilis. SpoIIGA specifically functions in the process
of bacterial endospore formation by activating sigmaE in the mother cell.
proposed_replacement_terms:
- id: GO:0034301
label: endospore formation
supported_by:
- reference_id: PMID:18378688
supporting_text: >-
The bacterium Bacillus subtilis undergoes endospore formation in response to
starvation.
- term:
id: GO:0030436
label: asexual sporulation
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >-
This annotation from InterPro correctly identifies involvement in asexual sporulation.
Bacterial endospore formation is indeed a form of asexual sporulation. However,
the more specific term 'endospore formation' better captures the specific process.
action: MODIFY
reason: >-
While 'asexual sporulation' is correct, 'endospore formation' (GO:0034301) is more
specific and appropriate for the bacterial context. Endospore formation is the
relevant biological process in Bacillus subtilis.
proposed_replacement_terms:
- id: GO:0034301
label: endospore formation
supported_by:
- reference_id: PMID:18378688
supporting_text: >-
The bacterium Bacillus subtilis undergoes endospore formation in response to
starvation.
- term:
id: GO:0004190
label: aspartic-type endopeptidase activity
evidence_type: IMP
original_reference_id: PMID:18378688
review:
summary: >-
This experimental (IMP) annotation provides direct evidence for aspartic-type
endopeptidase activity. The study demonstrated that SpoIIGA processes pro-sigmaE
via an aspartic protease mechanism, with the catalytic aspartate D183 being
essential for activity.
action: ACCEPT
reason: >-
This is a high-quality experimental annotation based on mutational analysis.
The study showed that D183A mutation abolishes protease activity, consistent
with an aspartic protease mechanism. The modeling and biochemical data strongly
support this annotation.
supported_by:
- reference_id: PMID:18378688
supporting_text: >-
Modeling and mutational analyses provide evidence that SpoIIGA is a novel type of
aspartic protease whose C-terminal half forms a dimer similar to the human
immunodeficiency virus type 1 protease.
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:18378688
review:
summary: >-
This annotation indicates protein binding based on physical interaction evidence.
SpoIIGA has been shown to interact with SpoIIR (the signaling protein from the
forespore) and with SigE (the substrate pro-sigmaE). However, 'protein binding'
is uninformative.
action: MODIFY
reason: >-
The generic 'protein binding' term does not capture the functional significance
of the interactions. SpoIIGA interacts with SpoIIR as part of signal transduction,
and with pro-sigmaE as its substrate. A more specific term would be preferable,
but since GO lacks a term for 'aspartic protease substrate binding', this
annotation should be removed in favor of more informative terms.
proposed_replacement_terms:
- id: GO:0004190
label: aspartic-type endopeptidase activity
supported_by:
- reference_id: PMID:18378688
supporting_text: >-
Also, SpoIIGA interacts with SpoIIR.
- term:
id: GO:0005886
label: plasma membrane
evidence_type: IDA
original_reference_id: PMID:18378688
review:
summary: >-
This experimental (IDA) annotation provides direct evidence for plasma membrane
localization. The study demonstrated that SpoIIGA is membrane-associated when
expressed in E. coli.
action: ACCEPT
reason: >-
This is a high-quality experimental annotation demonstrating membrane association.
While SpoIIGA is more specifically localized to the sporulation septum in
B. subtilis, GO lacks a more specific term for this location, so plasma membrane
is the appropriate term.
supported_by:
- reference_id: PMID:18378688
supporting_text: >-
We found that SpoIIGA expressed in E. coli is membrane-associated and that after
detergent treatment SpoIIGA was self-associated.
- term:
id: GO:0006508
label: proteolysis
evidence_type: IMP
original_reference_id: PMID:18378688
review:
summary: >-
This experimental (IMP) annotation indicates proteolysis based on mutant phenotype
evidence. The study demonstrated pro-sigmaE processing to sigmaE by SpoIIGA.
action: KEEP_AS_NON_CORE
reason: >-
This annotation is accurate but general. The more informative biological process
annotation would be to endospore formation. However, this annotation correctly
captures the general biochemical activity demonstrated in the study.
supported_by:
- reference_id: PMID:18378688
supporting_text: >-
We report that expression of SpoIIR, a putative signaling protein normally made
in the forespore, and SpoIIGA, a putative protease, is necessary and sufficient
for accurate, rapid, and abundant processing of pro-sigma(E) to sigma(E) in
Escherichia coli.
- term:
id: GO:0006508
label: proteolysis
evidence_type: IMP
original_reference_id: PMID:21362630
review:
summary: >-
This experimental (IMP) annotation from a second study confirms proteolytic
activity through substrate specificity analysis. The study examined cleavage
of pro-sigmaE orthologs by SpoIIGA.
action: KEEP_AS_NON_CORE
reason: >-
This annotation provides additional experimental support for proteolytic activity.
The study extended understanding of substrate specificity but the term remains
general. Both proteolysis annotations should be kept as they come from different
studies with complementary evidence.
supported_by:
- reference_id: PMID:21362630
supporting_text: >-
SpoIIGA is a novel type of membrane-associated aspartic protease that responds to
a signal from the forespore by cleaving Pro-σ(E) in the mother cell during
sporulation of Bacillus subtilis.
- term:
id: GO:0008233
label: peptidase activity
evidence_type: IMP
original_reference_id: PMID:21362630
review:
summary: >-
This experimental (IMP) annotation indicates peptidase activity based on the
substrate specificity study. The annotation is correct but less specific than
the aspartic-type endopeptidase term.
action: KEEP_AS_NON_CORE
reason: >-
This annotation is accurate and experimentally supported. While the aspartic-type
endopeptidase term is more informative, this annotation correctly captures the
general peptidase function demonstrated in the study examining substrate
recognition and cleavage.
supported_by:
- reference_id: PMID:21362630
supporting_text: >-
By co-expressing proteins in Escherichia coli, it was shown that charge reversal
substitutions for acidic residues 24 and 25 of Pro-σ(E), and for basic residues
245 and 284 of SpoIIGA, impaired cleavage.
references:
- id: GO_REF:0000002
title: Gene Ontology annotation through association of InterPro records with GO terms
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:18378688
title: Evidence that the Bacillus subtilis SpoIIGA protein is a novel type of
signal-transducing aspartic protease.
findings:
- statement: SpoIIGA is a membrane-associated aspartic protease
supporting_text: >-
Modeling and mutational analyses provide evidence that SpoIIGA is a novel type of
aspartic protease whose C-terminal half forms a dimer similar to the human
immunodeficiency virus type 1 protease.
- statement: SpoIIGA C-terminal domain forms a dimer similar to HIV-1 protease
supporting_text: >-
SpoIIGA is a novel type of aspartic protease whose C-terminal half forms a dimer
similar to the human immunodeficiency virus type 1 protease.
- statement: SpoIIR and SpoIIGA are necessary and sufficient for pro-sigmaE processing
supporting_text: >-
We report that expression of SpoIIR, a putative signaling protein normally made
in the forespore, and SpoIIGA, a putative protease, is necessary and sufficient
for accurate, rapid, and abundant processing of pro-sigma(E) to sigma(E) in
Escherichia coli.
- statement: SpoIIGA interacts with SpoIIR signaling protein
supporting_text: >-
Also, SpoIIGA interacts with SpoIIR.
- statement: SpoIIGA self-associates when membrane-associated
supporting_text: >-
We found that SpoIIGA expressed in E. coli is membrane-associated and that after
detergent treatment SpoIIGA was self-associated.
- statement: Catalytic aspartate D183 is essential for activity
supporting_text: >-
Modeling and mutational analyses provide evidence that SpoIIGA is a novel type of
aspartic protease whose C-terminal half forms a dimer similar to the human
immunodeficiency virus type 1 protease.
- id: PMID:21362630
title: Substrate specificity of SpoIIGA, a signal-transducing aspartic protease in Bacilli.
findings:
- statement: Residues D24 and E25 of pro-sigmaE are critical for cleavage
supporting_text: >-
By co-expressing proteins in Escherichia coli, it was shown that charge reversal
substitutions for acidic residues 24 and 25 of Pro-σ(E), and for basic residues
245 and 284 of SpoIIGA, impaired cleavage.
- statement: Residues R245 and K284 of SpoIIGA are important for substrate recognition
supporting_text: >-
By co-expressing proteins in Escherichia coli, it was shown that charge reversal
substitutions for acidic residues 24 and 25 of Pro-σ(E), and for basic residues
245 and 284 of SpoIIGA, impaired cleavage.
- statement: B. subtilis SpoIIGA can cleave pro-sigmaE from B. licheniformis and B. halodurans
supporting_text: >-
Bacillus subtilis SpoIIGA cleaved Pro-σ(E) orthologs from Bacillus licheniformis
and Bacillus halodurans, but not from Bacillus cereus.
- statement: B. cereus pro-sigmaE is not cleaved unless distal pro-sequence is modified
supporting_text: >-
A triple substitution in the pro-sequence of B. cereus Pro-σ(E) allowed cleavage
by B. subtilis SpoIIGA, indicating that residues distal from the cleavage site
contribute to substrate specificity.
- statement: Cross-species differences in substrate specificity exist among Bacillus SpoIIGA orthologs
supporting_text: >-
Co-expression of SpoIIGA and Pro-σ(E) orthologs in different combinations
suggested that B. licheniformis SpoIIGA has a relatively narrow substrate specificity
as compared with B. subtilis SpoIIGA, whereas B. cereus SpoIIGA and B. halodurans
SpoIIGA appear to have broader substrate specificity.
- id: file:BACSU/spoIIGA/spoIIGA-deep-research-falcon.md
title: Deep research review of SpoIIGA function
findings:
- statement: SpoIIGA is the dedicated processing protease that converts pro-sigmaE to active sigmaE
supporting_text: >-
SpoIIGA is the dedicated processing protease that converts pro-σE (Pro-σE) to active σE
in the mother cell, initiating the σE transcriptional program required for early
mother-cell development during sporulation.
core_functions:
- molecular_function:
id: GO:0004190
label: aspartic-type endopeptidase activity
directly_involved_in:
- id: GO:0034301
label: endospore formation
locations:
- id: GO:0005886
label: plasma membrane
description: >-
SpoIIGA is a signal-transducing aspartic protease that specifically cleaves
pro-sigmaE to activate the sigmaE transcription factor. The enzyme has a
unique membrane-associated architecture with an N-terminal transmembrane
domain and C-terminal catalytic domain.
supported_by:
- reference_id: PMID:18378688
supporting_text: >-
Modeling and mutational analyses provide evidence that SpoIIGA is a novel type of
aspartic protease whose C-terminal half forms a dimer similar to the human
immunodeficiency virus type 1 protease.
- reference_id: PMID:21362630
supporting_text: >-
SpoIIGA is a novel type of membrane-associated aspartic protease that responds to
a signal from the forespore by cleaving Pro-σ(E) in the mother cell during
sporulation of Bacillus subtilis.
proposed_new_terms: []
suggested_questions:
- question: What is the structural basis for SpoIIR-mediated activation of SpoIIGA protease activity?
- question: How does SpoIIGA achieve specificity for pro-sigmaE over other cellular substrates?
- question: What determines the species-specific differences in SpoIIGA substrate recognition among Bacillus species?
suggested_experiments:
- description: Cryo-EM structure determination of SpoIIGA alone and in complex with SpoIIR
hypothesis: >-
Determining the structure of SpoIIGA will reveal the mechanism of SpoIIR-mediated
activation and the architecture of the substrate binding site.
experiment_type: structural biology
- description: In vivo crosslinking studies to map the SpoIIR-SpoIIGA interaction interface at the septum
hypothesis: >-
Crosslinking will identify specific residues involved in the SpoIIR-SpoIIGA interaction
and validate the predicted interaction model.
experiment_type: biochemistry
- description: Quantitative proteomics to determine if SpoIIGA has additional substrates beyond pro-sigmaE
hypothesis: >-
SpoIIGA may have additional substrates that contribute to mother cell development
beyond the known pro-sigmaE substrate.
experiment_type: proteomics