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Exported on March 22, 2026 at 02:42 AM

Organism: Bacillus subtilis

Sequence:

MRSKKLWISLLFALTLIFTMAFSNMSAQAAGKSSTEKKYIVGFKQTMSAMSSAKKKDVISEKGGKVQKQFKYVNAAAATLDEKAVKELKKDPSVAYVEEDHIAHEYAQSVPYGISQIKAPALHSQGYTGSNVKVAVIDSGIDSSHPDLNVRGGASFVPSETNPYQDGSSHGTHVAGTIAALNNSIGVLGVAPSASLYAVKVLDSTGSGQYSWIINGIEWAISNNMDVINMSLGGPTGSTALKTVVDKAVSSGIVVAAAAGNEGSSGSTSTVGYPAKYPSTIAVGAVNSSNQRASFSSAGSELDVMAPGVSIQSTLPGGTYGAYNGTSMATPHVAGAAALILSKHPTWTNAQVRDRLESTATYLGNSFYYGKGLINVQAAAQ

Thinking Trace

The architecture begins with IPR050131 (Subtilisin-like serine protease family, residues 25–370), establishing membership in the S8 peptidase clan. The N-terminal half carries IPR037045 (Peptidase S8 propeptide/proteinase inhibitor I9 superfamily, residues 30–99) and its embedded IPR010259 (Peptidase S8 propeptide/proteinase inhibitor I9 domain, residues 38–102). This I9 propeptide is a hallmark zymogen module that folds back onto the catalytic core to auto-inhibit activity during biosynthesis and trafficking. Immediately downstream, the protease core is defined by IPR036852 (Peptidase S8/S53 domain superfamily, residues 107–381) and the catalytic scaffold IPR000209 (Peptidase S8/S53 domain, residues 129–372). Two overlapping family signatures, IPR015500 (Peptidase S8, subtilisin-related, residues 129–340) and IPR034202 (Subtilisin Carlsberg-like catalytic domain, residues 131–359), pinpoint the mature enzyme’s fold and stability. The catalytic machinery is explicitly delineated by three conserved active-site motifs: IPR023827 (subtilisin Asp-active site, residues 134–145), IPR022398 (subtilisin His-active site, residues 170–180), and IPR023828 (subtilisin Ser-active site, residues 325–335). This Asp–His–Ser triad embedded in the S8 fold causally endows serine-type endopeptidase chemistry.

From this domain arrangement, the molecular function follows directly: the I9 propeptide ensures a latent zymogen that matures into a secreted endopeptidase, and the S8 catalytic triad furnishes nucleophilic serine-dependent proteolysis. This defines serine-type endopeptidase activity (GO:0004252). The presence of an inhibitory propeptide that requires proteolytic removal to become active is characteristic of extracellular subtilisin-like proteases that process or degrade polypeptides outside the cytoplasm.

The biological process arises from this enzymology. Secreted subtilisin-like proteases in Bacillus commonly drive extracellular proteolysis for nutrient acquisition, matrix remodeling, and maturation of secreted factors. Thus, the activity feeds into proteolysis (GO:0006508) as the central process, with likely roles in processing extracellular substrates and activating downstream pathways.

Cellular location is dictated by the signal of secretion and the absence of intracellular retention motifs. The zymogen architecture coupled with an exported role places the enzyme in the extracellular region (GO:0005576), consistent with a secreted protease that operates outside the cell.

Mechanistically, the protein is synthesized as an I9-propeptide–masked zymogen, secreted into the extracellular milieu where environmental or cell-surface proteases remove the propeptide to expose the S8 active site. The mature enzyme then cleaves target proteins via the canonical Asp–His–Ser charge-relay system. Likely interaction partners include extracellular substrates and maturation cofactors: secreted cell-wall–associated proteins that require proteolytic activation, and surface adhesins or biofilm components whose turnover depends on extracellular proteolysis. During maturation and export, transient intracellular contacts with secretion machinery are expected, but the functional steady state is that of a soluble extracellular endopeptidase executing proteolytic programs outside the cell.

Functional Summary

A secreted extracellular serine endopeptidase from Bacillus subtilis that is produced as an auto-inhibited zymogen and activated outside the cell to drive proteolysis. Its N-terminal propeptide transiently blocks the catalytic core until removal during secretion, after which the mature enzyme uses a subtilisin catalytic triad to cleave polypeptides. This extracellular proteolysis likely supports nutrient acquisition and remodeling of the surrounding milieu by processing or degrading secreted and environmental substrates.

UniProt Summary

Extracellular protease.

InterPro Domains

• Subtilisin-like serine protease (IPR050131, family) — residues 25-370
• Peptidase S8 propeptide/proteinase inhibitor I9 superfamily (IPR037045, homologous_superfamily) — residues 30-99
• Peptidase S8 propeptide/proteinase inhibitor I9 (IPR010259, domain) — residues 38-102
• Peptidase S8/S53 domain superfamily (IPR036852, homologous_superfamily) — residues 107-381
• Peptidase S8, subtilisin-related (IPR015500, family) — residues 129-340
• Peptidase S8/S53 domain (IPR000209, domain) — residues 129-372
• Subtilisin Carlsberg-like catalytic domain (IPR034202, domain) — residues 131-359
• Peptidase S8, subtilisin, Asp-active site (IPR023827, active_site) — residues 134-145
• Peptidase S8, subtilisin, His-active site (IPR022398, active_site) — residues 170-180
• Peptidase S8, subtilisin, Ser-active site (IPR023828, active_site) — residues 325-335

GO Terms

Molecular 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), serine hydrolase activity (GO:0017171), peptidase activity (GO:0008233), serine-type peptidase activity (GO:0008236), endopeptidase activity (GO:0004175), serine-type endopeptidase activity (GO:0004252)

Biological Process: biological_process (GO:0008150), metabolic process (GO:0008152), biological regulation (GO:0065007), regulation of biological process (GO:0050789), negative regulation of biological process (GO:0048519), regulation of response to stimulus (GO:0048583), negative regulation of hemostasis (GO:1900047), regulation of biological quality (GO:0065008), negative regulation of multicellular organismal process (GO:0051241), regulation of multicellular organismal process (GO:0051239), regulation of hemostasis (GO:1900046), organic substance metabolic process (GO:0071704), negative regulation of response to stimulus (GO:0048585), nitrogen compound metabolic process (GO:0006807), primary metabolic process (GO:0044238), regulation of coagulation (GO:0050818), negative regulation of blood coagulation (GO:0030195), regulation of response to external stimulus (GO:0032101), regulation of blood coagulation (GO:0030193), regulation of body fluid levels (GO:0050878), organonitrogen compound metabolic process (GO:1901564), protein metabolic process (GO:0019538), negative regulation of coagulation (GO:0050819), macromolecule metabolic process (GO:0043170), negative regulation of response to wounding (GO:1903035), regulation of response to stress (GO:0080134), negative regulation of response to external stimulus (GO:0032102), negative regulation of wound healing (GO:0061045), proteolysis (GO:0006508), regulation of response to wounding (GO:1903034), regulation of wound healing (GO:0061041)

Cellular Component: cellular_component (GO:0005575), cellular anatomical entity (GO:0110165), extracellular region (GO:0005576), extracellular space (GO:0005615)

Generated by BioReason

BioReason Chat Export

Exported on March 22, 2026 at 02:42 AM

Organism: Bacillus subtilis

Sequence:

MRSKKLWISLLFALTLIFTMAFSNMSAQAAGKSSTEKKYIVGFKQTMSAMSSAKKKDVISEKGGKVQKQFKYVNAAAATLDEKAVKELKKDPSVAYVEEDHIAHEYAQSVPYGISQIKAPALHSQGYTGSNVKVAVIDSGIDSSHPDLNVRGGASFVPSETNPYQDGSSHGTHVAGTIAALNNSIGVLGVAPSASLYAVKVLDSTGSGQYSWIINGIEWAISNNMDVINMSLGGPTGSTALKTVVDKAVSSGIVVAAAAGNEGSSGSTSTVGYPAKYPSTIAVGAVNSSNQRASFSSAGSELDVMAPGVSIQSTLPGGTYGAYNGTSMATPHVAGAAALILSKHPTWTNAQVRDRLESTATYLGNSFYYGKGLINVQAAAQ

Thinking Trace

The architecture begins with IPR050131 (Subtilisin-like serine protease family, residues 25–370), establishing membership in the S8 peptidase clan. The N-terminal half carries IPR037045 (Peptidase S8 propeptide/proteinase inhibitor I9 superfamily, residues 30–99) and its embedded IPR010259 (Peptidase S8 propeptide/proteinase inhibitor I9 domain, residues 38–102). This I9 propeptide is a hallmark zymogen module that folds back onto the catalytic core to auto-inhibit activity during biosynthesis and trafficking. Immediately downstream, the protease core is defined by IPR036852 (Peptidase S8/S53 domain superfamily, residues 107–381) and the catalytic scaffold IPR000209 (Peptidase S8/S53 domain, residues 129–372). Two overlapping family signatures, IPR015500 (Peptidase S8, subtilisin-related, residues 129–340) and IPR034202 (Subtilisin Carlsberg-like catalytic domain, residues 131–359), pinpoint the mature enzyme’s fold and stability. The catalytic machinery is explicitly delineated by three conserved active-site motifs: IPR023827 (subtilisin Asp-active site, residues 134–145), IPR022398 (subtilisin His-active site, residues 170–180), and IPR023828 (subtilisin Ser-active site, residues 325–335). This Asp–His–Ser triad embedded in the S8 fold causally endows serine-type endopeptidase chemistry.

From this domain arrangement, the molecular function follows directly: the I9 propeptide ensures a latent zymogen that matures into a secreted endopeptidase, and the S8 catalytic triad furnishes nucleophilic serine-dependent proteolysis. This defines serine-type endopeptidase activity (GO:0004252). The presence of an inhibitory propeptide that requires proteolytic removal to become active is characteristic of extracellular subtilisin-like proteases that process or degrade polypeptides outside the cytoplasm.

The biological process arises from this enzymology. Secreted subtilisin-like proteases in Bacillus commonly drive extracellular proteolysis for nutrient acquisition, matrix remodeling, and maturation of secreted factors. Thus, the activity feeds into proteolysis (GO:0006508) as the central process, with likely roles in processing extracellular substrates and activating downstream pathways.

Cellular location is dictated by the signal of secretion and the absence of intracellular retention motifs. The zymogen architecture coupled with an exported role places the enzyme in the extracellular region (GO:0005576), consistent with a secreted protease that operates outside the cell.

Mechanistically, the protein is synthesized as an I9-propeptide–masked zymogen, secreted into the extracellular milieu where environmental or cell-surface proteases remove the propeptide to expose the S8 active site. The mature enzyme then cleaves target proteins via the canonical Asp–His–Ser charge-relay system. Likely interaction partners include extracellular substrates and maturation cofactors: secreted cell-wall–associated proteins that require proteolytic activation, and surface adhesins or biofilm components whose turnover depends on extracellular proteolysis. During maturation and export, transient intracellular contacts with secretion machinery are expected, but the functional steady state is that of a soluble extracellular endopeptidase executing proteolytic programs outside the cell.

Functional Summary

A secreted extracellular serine endopeptidase from Bacillus subtilis that is produced as an auto-inhibited zymogen and activated outside the cell to drive proteolysis. Its N-terminal propeptide transiently blocks the catalytic core until removal during secretion, after which the mature enzyme uses a subtilisin catalytic triad to cleave polypeptides. This extracellular proteolysis likely supports nutrient acquisition and remodeling of the surrounding milieu by processing or degrading secreted and environmental substrates.

UniProt Summary

Extracellular protease.

InterPro Domains

• Subtilisin-like serine protease (IPR050131, family) — residues 25-370
• Peptidase S8 propeptide/proteinase inhibitor I9 superfamily (IPR037045, homologous_superfamily) — residues 30-99
• Peptidase S8 propeptide/proteinase inhibitor I9 (IPR010259, domain) — residues 38-102
• Peptidase S8/S53 domain superfamily (IPR036852, homologous_superfamily) — residues 107-381
• Peptidase S8, subtilisin-related (IPR015500, family) — residues 129-340
• Peptidase S8/S53 domain (IPR000209, domain) — residues 129-372
• Subtilisin Carlsberg-like catalytic domain (IPR034202, domain) — residues 131-359
• Peptidase S8, subtilisin, Asp-active site (IPR023827, active_site) — residues 134-145
• Peptidase S8, subtilisin, His-active site (IPR022398, active_site) — residues 170-180
• Peptidase S8, subtilisin, Ser-active site (IPR023828, active_site) — residues 325-335

GO Terms

Molecular 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), serine hydrolase activity (GO:0017171), peptidase activity (GO:0008233), serine-type peptidase activity (GO:0008236), endopeptidase activity (GO:0004175), serine-type endopeptidase activity (GO:0004252)

Biological Process: biological_process (GO:0008150), metabolic process (GO:0008152), biological regulation (GO:0065007), regulation of biological process (GO:0050789), negative regulation of biological process (GO:0048519), regulation of response to stimulus (GO:0048583), negative regulation of hemostasis (GO:1900047), regulation of biological quality (GO:0065008), negative regulation of multicellular organismal process (GO:0051241), regulation of multicellular organismal process (GO:0051239), regulation of hemostasis (GO:1900046), organic substance metabolic process (GO:0071704), negative regulation of response to stimulus (GO:0048585), nitrogen compound metabolic process (GO:0006807), primary metabolic process (GO:0044238), regulation of coagulation (GO:0050818), negative regulation of blood coagulation (GO:0030195), regulation of response to external stimulus (GO:0032101), regulation of blood coagulation (GO:0030193), regulation of body fluid levels (GO:0050878), organonitrogen compound metabolic process (GO:1901564), protein metabolic process (GO:0019538), negative regulation of coagulation (GO:0050819), macromolecule metabolic process (GO:0043170), negative regulation of response to wounding (GO:1903035), regulation of response to stress (GO:0080134), negative regulation of response to external stimulus (GO:0032102), negative regulation of wound healing (GO:0061045), proteolysis (GO:0006508), regulation of response to wounding (GO:1903034), regulation of wound healing (GO:0061041)

Cellular Component: cellular_component (GO:0005575), cellular anatomical entity (GO:0110165), extracellular region (GO:0005576), extracellular space (GO:0005615)

Generated by BioReason

provider: falcon
model: Edison Scientific Literature
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start_time: '2025-12-17T23:25:25.365540'
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template_file: templates/gene_research_go_focused.md
template_variables:
organism: BACSU
gene_id: aprE
gene_symbol: aprE
uniprot_accession: P04189
protein_description: 'RecName: Full=Subtilisin E; EC=3.4.21.62 {ECO:0000269|PubMed:7589571};
Flags: Precursor;'
gene_info: Name=aprE {ECO:0000303|PubMed:9579061}; Synonyms=apr, aprA, sprE {ECO:0000303|PubMed:6322190};
OrderedLocusNames=BSU10300;
organism_full: Bacillus subtilis (strain 168).
protein_family: Belongs to the peptidase S8 family. .
protein_domains: Peptidase_S8/S53_dom. (IPR000209); Peptidase_S8/S53_dom_sf. (IPR036852);
Peptidase_S8_Asp-AS. (IPR023827); Peptidase_S8_His-AS. (IPR022398); Peptidase_S8_Ser-AS.
(IPR023828)
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Question

Gene Research for Functional Annotation

⚠️ CRITICAL: Gene/Protein Identification Context

BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.

Target Gene/Protein Identity (from UniProt):

• UniProt Accession: P04189
• Protein Description: RecName: Full=Subtilisin E; EC=3.4.21.62 {ECO:0000269|PubMed:7589571}; Flags: Precursor;
• Gene Information: Name=aprE {ECO:0000303|PubMed:9579061}; Synonyms=apr, aprA, sprE {ECO:0000303|PubMed:6322190}; OrderedLocusNames=BSU10300;
• Organism (full): Bacillus subtilis (strain 168).
• Protein Family: Belongs to the peptidase S8 family. .
• Key Domains: Peptidase_S8/S53_dom. (IPR000209); Peptidase_S8/S53_dom_sf. (IPR036852); Peptidase_S8_Asp-AS. (IPR023827); Peptidase_S8_His-AS. (IPR022398); Peptidase_S8_Ser-AS. (IPR023828)

MANDATORY VERIFICATION STEPS:

1. Check if the gene symbol "aprE" matches the protein description above
2. Verify the organism is correct: Bacillus subtilis (strain 168).
3. Check if protein family/domains align with what you find in literature
4. If you find literature for a DIFFERENT gene with the same or similar symbol, STOP

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'aprE' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information

Research Target:

Please provide a comprehensive research report on the gene aprE (gene ID: aprE, UniProt: P04189) 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.

Output

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on:
1. Key concepts and definitions with current understanding
2. Recent developments and latest research (prioritize 2023-2024 sources)
3. Current applications and real-world implementations
4. Expert opinions and analysis from authoritative sources
5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available.
Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Gene Research for Functional Annotation

⚠️ CRITICAL: Gene/Protein Identification Context

BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.

Target Gene/Protein Identity (from UniProt):

• UniProt Accession: P04189
• Protein Description: RecName: Full=Subtilisin E; EC=3.4.21.62 {ECO:0000269|PubMed:7589571}; Flags: Precursor;
• Gene Information: Name=aprE {ECO:0000303|PubMed:9579061}; Synonyms=apr, aprA, sprE {ECO:0000303|PubMed:6322190}; OrderedLocusNames=BSU10300;
• Organism (full): Bacillus subtilis (strain 168).
• Protein Family: Belongs to the peptidase S8 family. .
• Key Domains: Peptidase_S8/S53_dom. (IPR000209); Peptidase_S8/S53_dom_sf. (IPR036852); Peptidase_S8_Asp-AS. (IPR023827); Peptidase_S8_His-AS. (IPR022398); Peptidase_S8_Ser-AS. (IPR023828)

MANDATORY VERIFICATION STEPS:

1. Check if the gene symbol "aprE" matches the protein description above
2. Verify the organism is correct: Bacillus subtilis (strain 168).
3. Check if protein family/domains align with what you find in literature
4. If you find literature for a DIFFERENT gene with the same or similar symbol, STOP

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'aprE' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information

Research Target:

Please provide a comprehensive research report on the gene aprE (gene ID: aprE, UniProt: P04189) 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 and verification
We verified the target as aprE from Bacillus subtilis subsp. subtilis strain 168 (UniProt P04189), encoding the extracellular alkaline serine protease Subtilisin E, a member of the peptidase S8 (subtilisin) family. Structural and sequence analyses confirm the canonical catalytic triad (His-Asp-Ser) and assignment to subtilases; PDB 1SCJ is referenced for Subtilisin E. These sources align with the provided UniProt metadata (family S8; catalytic triad residues; extracellular, secreted precursor with propeptide). The organism, gene symbol, and family/domain assignments are consistent with the literature and do not present ambiguity. (emameh2022bioinformaticsanalysisof pages 1-3, emameh2022bioinformaticsanalysisof pages 4-6)

Key concepts and definitions
- Identity and family: Subtilisin E (aprE) is an extracellular endopeptidase of the peptidase S8 family produced by Bacillus subtilis 168. The enzyme’s active site is formed by a conserved catalytic triad His125–Asp146–Ser231 (numbering per B. subtilis Subtilisin E), typical of subtilisins. It operates optimally in neutral-to-alkaline pH and is frequently stabilized by Ca2+. PDB 1SCJ and closely related models capture the subtilisin E–propeptide complex. Mar 2022; https://doi.org/10.1080/07391102.2021.1894979 (emameh2022bioinformaticsanalysisof pages 1-3, emameh2022bioinformaticsanalysisof pages 3-4)
- Catalytic mechanism and specificity: Like other “true” subtilisins, catalysis proceeds through a Ser-alkoxide nucleophile assisted by His and Asp, forming and resolving an acyl-enzyme intermediate. Substrate preferences favor hydrophobic residues at P1/P4 in model peptides and casein/azocasein assays; related subtilisins exhibit PMSF sensitivity and broad alkaline activity ranges. Sep 2023; https://doi.org/10.1002/2211-5463.13701 (falkenberg2023biochemicalcharacterisationof pages 3-6)
- Localization and secretion: Subtilisin E is synthesized as a preproenzyme with an N‑terminal Sec signal peptide (positively charged N-region, hydrophobic core, polar C-region) that directs cotranslational targeting to SecYEG via SRP/FtsY. Signal peptidase cleaves the signal peptide in the membrane, after which the protein is secreted and folds with assistance of PrsA; quality-control proteases (HtrA/HtrB, WprA) remove misfolded proteins. 2024 (review/analysis); https://doi.org/10.7488/era/4696 (astles2024novelextremophilicmetalloproteases pages 56-60)
- Maturation: The propeptide acts as an intramolecular chaperone that guides folding and is subsequently removed by autoprocessing to yield mature active subtilisin; autoproteolysis can impact observed stability and activity in vitro. Sep 2023; https://doi.org/10.1002/2211-5463.13701; Mar 2022; https://doi.org/10.1080/07391102.2021.1894979 (falkenberg2023biochemicalcharacterisationof pages 3-6, emameh2022bioinformaticsanalysisof pages 3-4)

Regulation and pathway context
- Transcriptional control: aprE is transcribed from a housekeeping SigA (σA) promoter and is activated by the two‑component system DegS–DegU (DegU as direct positive regulator). Multiple repressors modulate expression, including AbrB, SinR, and ScoC; other factors (Hpr, TenA) were predicted in promoter scans. These regulators link aprE to differentiation/sporulation states (Spo0A controls AbrB) and competence networks (ComA). Mar 2022; https://doi.org/10.1080/07391102.2021.1894979 (emameh2022bioinformaticsanalysisof pages 7-8, emameh2022bioinformaticsanalysisof pages 1-3)
- Systems-level secretion and protease network: Bacillus subtilis 168 produces a set of extracellular proteases (including AprE), and engineering often uses protease-deficient chassis to protect secreted products. Regulatory systems (Spo0A, CodY, DegS–DegU) influence extracellular protein production states. 2024; https://doi.org/10.7488/era/4696 (astles2024novelextremophilicmetalloproteases pages 56-60)

Function, substrates, and biological roles
- Primary function: Subtilisin E is a broad-specificity endopeptidase that cleaves peptide bonds in diverse proteins; modeling and prediction indicate an ability to cleave keratin/keratin-associated proteins, consistent with preferences for hydrophobic residues. Mar 2022; https://doi.org/10.1080/07391102.2021.1894979 (emameh2022bioinformaticsanalysisof pages 1-3, emameh2022bioinformaticsanalysisof pages 4-6)
- Biological roles: In B. subtilis, AprE contributes to extracellular proteolysis for nutrient acquisition and shapes the extracellular milieu. The extracellular protease repertoire, including AprE, is implicated in processing secreted peptides that participate in cell–cell signaling, adding complexity to quorum-associated behaviors; such roles are supported by systems analyses of B. subtilis secretion and protease networks. 2024; https://doi.org/10.7488/era/4696 (astles2024novelextremophilicmetalloproteases pages 56-60)

Recent developments (prioritizing 2023–2024)
- Biochemical confirmation of subtilisin properties and Sec secretion: A 2023 biochemical study on a closely related aprE-encoded subtilisin (SPFA) expressed in B. subtilis DB104 confirmed S8 triad, high alkaline activity (pH 8.5–11.5), and PMSF sensitivity. It also illustrated recombinant secretion via the Sec pathway and highlighted autoproteolytic maturation. Sep 2023; https://doi.org/10.1002/2211-5463.13701 (falkenberg2023biochemicalcharacterisationof pages 3-6)
- Signal peptide and secretion engineering: Contemporary reviews and chassis-focused analyses emphasize signal peptide library screening, promoter optimization, PrsA modulation, and quality-control balancing to increase secreted yields in Bacillus hosts, with explicit use of AprE-derived signal peptides as benchmarks. Jan 2024; https://doi.org/10.3390/fermentation10010050; 2024; https://doi.org/10.7488/era/4696 (arsov2024cloningsystemsin pages 29-31, astles2024novelextremophilicmetalloproteases pages 56-60)
- Transcriptional regulator engineering: Tuning DegU activity and deleting repressors (AbrB/SinR/Hpr/ScoC) in Bacillus spp. substantially increases alkaline protease (AprE-like) production, providing a blueprint applicable to B. subtilis aprE regulation circuits. Aug 2023; https://doi.org/10.1186/s12934-023-02177-0; Mar 2024; https://doi.org/10.3389/fbioe.2024.1383083 (han2024geneticidentificationand pages 13-13)
- Recombinant protease production landscape: A 2024 review highlights current advances for recombinant proteases, including aprE-driven systems, maturation steps, and the importance of Sec signal peptides for high-level secretion in Bacillus. Mar 2024; https://doi.org/10.1007/s11274-024-03957-5 (arsov2024cloningsystemsin pages 29-31)

Current applications and implementations
- Industrial detergents and process industries: Subtilisins remain dominant proteases in detergent formulations and are applied broadly in leather/wool processing, food protein modification, and other cleaning applications. 2024; https://doi.org/10.7488/era/4696; Mar 2022; https://doi.org/10.1080/07391102.2021.1894979 (astles2024novelextremophilicmetalloproteases pages 56-60, emameh2022bioinformaticsanalysisof pages 1-3)
- Bacillus secretion platforms: aprE’s secretion signals (e.g., AprE signal peptide) are frequently used as standard parts to drive efficient export of heterologous proteins, and modern Bacillus chassis integrate these into secretion-optimized workflows. Jan 2024; https://doi.org/10.3390/fermentation10010050 (arsov2024cloningsystemsin pages 29-31)

Expert opinions and authoritative analyses
- Bioinformatic and promoter-motif mapping position aprE under multilayered regulation where DegU activates transcription and multiple repressors gate expression; this network explains the strong post-exponential expression pattern of aprE and informs engineering targets. Mar 2022; https://doi.org/10.1080/07391102.2021.1894979 (emameh2022bioinformaticsanalysisof pages 7-8, emameh2022bioinformaticsanalysisof pages 1-3)
- Secretion-system experts emphasize end-to-end optimization: precise signal peptide matching to the protein of interest, PrsA-assisted folding, and the management of extracellular QC proteases, alongside genome edits to reduce off-target proteolysis. 2024; https://doi.org/10.7488/era/4696 (astles2024novelextremophilicmetalloproteases pages 56-60)

Relevant statistics and data from recent studies
- Catalysis and activity: Related subtilisin expressed in B. subtilis showed activity at pH 8.5–11.5 with a temperature optimum near 80 °C, and strong inhibition by PMSF; measurable rates were reported on standard peptidyl-pNA and azocasein substrates. Sep 2023; https://doi.org/10.1002/2211-5463.13701 (falkenberg2023biochemicalcharacterisationof pages 3-6)
- Engineering levers: Bioinformatic analyses identify stabilizing substitutions in Subtilisin E (e.g., N123V, S331L) and catalog dozens of transcription-factor binding sites in the aprE promoter region, guiding both protein and promoter engineering. Mar 2022; https://doi.org/10.1080/07391102.2021.1894979 (emameh2022bioinformaticsanalysisof pages 3-4, emameh2022bioinformaticsanalysisof pages 4-6)

Concise evidence summary table
| Aspect | Key facts for aprE / Subtilisin E | Regulatory network | 2023–2024 evidence / examples |
|---|---|---|---|
| Identity verification | aprE (UniProt P04189) from Bacillus subtilis strain 168; member of peptidase S8 (subtilisin) family; solved structure PDB 1SCJ; extracellular alkaline protease. (H-D-S catalytic triad noted) (emameh2022bioinformaticsanalysisof pages 1-3, emameh2022bioinformaticsanalysisof pages 3-4) | aprE transcription from a SigA (σA) promoter; expression linked to differentiation pathways. (emameh2022bioinformaticsanalysisof pages 1-3) | Emameh 2022 bioinformatics verification and locus/promoter mapping (DOI: 10.1080/07391102.2021.1894979) (emameh2022bioinformaticsanalysisof pages 1-3, emameh2022bioinformaticsanalysisof pages 3-4) |
| Catalytic features | Catalytic triad: His125, Asp146, Ser231 (canonical subtilisin triad); S8 peptidase domain; alkaline pH activity and Ca2+-stabilized in many subtilisins. (emameh2022bioinformaticsanalysisof pages 3-4, emameh2022bioinformaticsanalysisof pages 1-3) | Catalytic activity determines extracellular proteolytic capacity; activity modulated post‑translationally (Ca2+, autoproteolysis). (falkenberg2023biochemicalcharacterisationof pages 3-6) | Biochemical characterization of related subtilisins confirms triad and PMSF sensitivity (Falkenberg et al. 2023, DOI: 10.1002/2211-5463.13701) (falkenberg2023biochemicalcharacterisationof pages 3-6) |
| Secretion / localization | Secreted extracellular enzyme with N-terminal Sec signal peptide (N‑region, h‑core, C‑region); translocated via SecA/SecYEG and SRP, folded extracellularly with PrsA assistance. (astles2024novelextremophilicmetalloproteases pages 56-60, arsov2024cloningsystemsin pages 29-31) | Secretion efficiency influenced by signal peptide choice and host secretion machinery (PrsA, HtrA/B quality control); host proteases can degrade product. (astles2024novelextremophilicmetalloproteases pages 56-60, arsov2024cloningsystemsin pages 29-31) | Signal peptide libraries and SP screening improve secretion yields; recombinant expression in B. subtilis yields secreted activity (Falkenberg 2023; Arsov 2024 review) (falkenberg2023biochemicalcharacterisationof pages 3-6, arsov2024cloningsystemsin pages 29-31) |
| Maturation | Preprotein: signal peptide removed by signal peptidase; propeptide acts as intramolecular chaperone and is autoprocessed to generate mature enzyme; autoproteolysis can affect stability. (emameh2022bioinformaticsanalysisof pages 3-4, falkenberg2023biochemicalcharacterisationof pages 3-6) | Maturation largely post‑translational but affects extracellular levels available for biological roles; quality-control proteases (HtrA/HtrB) influence yield. (astles2024novelextremophilicmetalloproteases pages 56-60) | Structural & in silico analyses describe propeptide–mature domain interactions and stabilizing mutations; autoproteolytic processing noted in biochemical studies (Emameh 2022; Falkenberg 2023) (emameh2022bioinformaticsanalysisof pages 3-4, falkenberg2023biochemicalcharacterisationof pages 3-6) |
| Regulation | aprE expression controlled by two‑component and global regulators: DegS–DegU (DegU = positive/activator), DegQ (activator of DegU), AbrB, SinR, ScoC (repressors); Spo0A, ComA and other differentiation pathways modulate expression; many TFBs predicted. (emameh2022bioinformaticsanalysisof pages 7-8, emameh2022bioinformaticsanalysisof pages 1-3, astles2024novelextremophilicmetalloproteases pages 56-60) | DegS–DegU integrates environmental signals to drive aprE expression during post‑exponential / differentiation states; interplay with Spo0A/AbrB links to sporulation/colony development. (emameh2022bioinformaticsanalysisof pages 7-8, astles2024novelextremophilicmetalloproteases pages 56-60) | Bioinformatic mapping of ~40+ transcription factor binding candidates for aprE (Emameh 2022); reviews and engineering studies emphasize tuning DegU/SigA/promoter and regulator engineering to boost secretion (emameh2022bioinformaticsanalysisof pages 7-8, arsov2024cloningsystemsin pages 29-31) |
| Biological roles | Extracellular protein degradation for nutrient acquisition; degrades keratin/keratin-associated proteins and broad substrates with preference for hydrophobic residues; implicated in processing extracellular signaling propeptides (pheromone maturation) and shaping extracellular environment. (emameh2022bioinformaticsanalysisof pages 1-3, astles2024novelextremophilicmetalloproteases pages 56-60) | aprE activity contributes to colony/biofilm dynamics and extracellular peptide processing; secreted protease network (multiple proteases) creates redundancy and complexity. (astles2024novelextremophilicmetalloproteases pages 56-60, emameh2022bioinformaticsanalysisof pages 1-3) | Proteases including AprE implicated in maturation of secreted pheromones and intercellular signalling complexity; studies highlight extracellular proteases’ role in quorum communication (recent analyses & reviews) (astles2024novelextremophilicmetalloproteases pages 56-60, emameh2022bioinformaticsanalysisof pages 1-3) |
| Applications / industrial uses | Widely used industrially (detergents, leather/wool processing, food processing, protein hydrolysates, biotechnology); subtilisins dominate detergent protease market. (emameh2022bioinformaticsanalysisof pages 1-3, astles2024novelextremophilicmetalloproteases pages 56-60) | Industrial production depends on high secretion yields and low background proteolysis (use of protease‑deficient strains, secretion engineering). (astles2024novelextremophilicmetalloproteases pages 56-60, arsov2024cloningsystemsin pages 29-31) | Patent literature and reviews confirm ongoing use in cleaning formulations; production optimization strategies summarized in 2024 reviews (Arsov 2024; industry patents) (arsov2024cloningsystemsin pages 29-31, astles2024novelextremophilicmetalloproteases pages 56-60) |
| 2023–2024 advances (engineering & production) | Key strategies: signal peptide libraries/screening, promoter and regulator engineering (DegU tuning), protease‑deficient hosts, chaperone (PrsA) manipulation, Sec pathway optimization, point mutations for thermostability. | Rational design of regulators (DegU hyperactive variants) and combined deletions of repressors (AbrB/SinR/Hpr/ScoC) shown to boost AprE/alkaline protease yields in related Bacillus spp.; secretion engineering integrated with chassis engineering. (han2024geneticidentificationand pages 13-13, arsov2024cloningsystemsin pages 29-31, astles2024novelextremophilicmetalloproteases pages 56-60) | Examples: signal peptide optimization and SP libraries improve secretion (Emameh 2022; Arsov 2024, DOI: 10.3390/fermentation10010050); biochemical and secretion-case studies demonstrate recombinant secreted activity (Falkenberg 2023 DOI: 10.1002/2211-5463.13701); transcriptome/regulator studies in Bacillus spp. outline targets for yield increases (Han 2024 DOI: 10.3389/fbioe.2024.1383083). (emameh2022bioinformaticsanalysisof pages 3-4, falkenberg2023biochemicalcharacterisationof pages 3-6, arsov2024cloningsystemsin pages 29-31, han2024geneticidentificationand pages 13-13) |

Table: Compact evidence-backed summary of aprE/Subtilisin E covering identity, catalysis, secretion/maturation, regulation, biological roles, applications, and 2023–2024 advances, with citations to the source evidence used.

Conclusions
aprE encodes Subtilisin E, a secreted, extracellular S8 serine endopeptidase from B. subtilis 168. Its function is extracellular protein degradation with broad specificity for hydrophobic-rich substrates; it is matured by signal-peptide removal and propeptide autoprocessing after Sec-dependent secretion. Expression is driven by DegS–DegU and modulated by global regulators (AbrB, SinR, ScoC, Spo0A/ComA pathways) from a SigA promoter. Recent 2023–2024 advances emphasize secretion and regulatory engineering (signal peptide libraries, PrsA/QC balancing, DegU tuning) and confirm alkaline-active, PMSF-sensitive subtilisins suitable for industrial processes and as secretion benchmarks in Bacillus chassis. (emameh2022bioinformaticsanalysisof pages 1-3, emameh2022bioinformaticsanalysisof pages 3-4, falkenberg2023biochemicalcharacterisationof pages 3-6, emameh2022bioinformaticsanalysisof pages 7-8, astles2024novelextremophilicmetalloproteases pages 56-60, arsov2024cloningsystemsin pages 29-31, han2024geneticidentificationand pages 13-13)

References

1. (emameh2022bioinformaticsanalysisof pages 1-3): Reza Zolfaghari Emameh, Justina Kazokaitė, and Bagher Yakhchali. Bioinformatics analysis of extracellular subtilisin e from bacillus subtilis. Journal of Biomolecular Structure and Dynamics, 40:7183-7190, Mar 2022. URL: https://doi.org/10.1080/07391102.2021.1894979, doi:10.1080/07391102.2021.1894979. This article has 10 citations and is from a peer-reviewed journal.

2. (emameh2022bioinformaticsanalysisof pages 4-6): Reza Zolfaghari Emameh, Justina Kazokaitė, and Bagher Yakhchali. Bioinformatics analysis of extracellular subtilisin e from bacillus subtilis. Journal of Biomolecular Structure and Dynamics, 40:7183-7190, Mar 2022. URL: https://doi.org/10.1080/07391102.2021.1894979, doi:10.1080/07391102.2021.1894979. This article has 10 citations and is from a peer-reviewed journal.

3. (emameh2022bioinformaticsanalysisof pages 3-4): Reza Zolfaghari Emameh, Justina Kazokaitė, and Bagher Yakhchali. Bioinformatics analysis of extracellular subtilisin e from bacillus subtilis. Journal of Biomolecular Structure and Dynamics, 40:7183-7190, Mar 2022. URL: https://doi.org/10.1080/07391102.2021.1894979, doi:10.1080/07391102.2021.1894979. This article has 10 citations and is from a peer-reviewed journal.

4. (falkenberg2023biochemicalcharacterisationof pages 3-6): Fabian Falkenberg, Sophie Kohn, Michael Bott, Johannes Bongaerts, and Petra Siegert. Biochemical characterisation of a novel broad ph spectrum subtilisin from fictibacillus arsenicusdsm 15822^t. FEBS Open Bio, 13:2035-2046, Sep 2023. URL: https://doi.org/10.1002/2211-5463.13701, doi:10.1002/2211-5463.13701. This article has 1 citations and is from a peer-reviewed journal.

5. (astles2024novelextremophilicmetalloproteases pages 56-60): Benjamin Michael Astles. Novel extremophilic metalloproteases for consumer product application. Unknown, Jul 2024. URL: https://doi.org/10.7488/era/4696, doi:10.7488/era/4696. This article has 0 citations.

6. (emameh2022bioinformaticsanalysisof pages 7-8): Reza Zolfaghari Emameh, Justina Kazokaitė, and Bagher Yakhchali. Bioinformatics analysis of extracellular subtilisin e from bacillus subtilis. Journal of Biomolecular Structure and Dynamics, 40:7183-7190, Mar 2022. URL: https://doi.org/10.1080/07391102.2021.1894979, doi:10.1080/07391102.2021.1894979. This article has 10 citations and is from a peer-reviewed journal.

7. (arsov2024cloningsystemsin pages 29-31): Alexander Arsov, Nadya Armenova, Emanoel Gergov, Kaloyan Petrov, and Penka Petrova. Cloning systems in bacillus: bioengineering of metabolic pathways for valuable recombinant products. Fermentation, 10:50, Jan 2024. URL: https://doi.org/10.3390/fermentation10010050, doi:10.3390/fermentation10010050. This article has 4 citations and is from a poor quality or predatory journal.

8. (han2024geneticidentificationand pages 13-13): Zhenying Han, Changwen Ye, Xinyu Dong, Chenchen Chen, Dian Zou, Kuo Huang, and Xuetuan Wei. Genetic identification and expression optimization of a novel protease hapr from bacillus velezensis. Frontiers in Bioengineering and Biotechnology, Mar 2024. URL: https://doi.org/10.3389/fbioe.2024.1383083, doi:10.3389/fbioe.2024.1383083. This article has 4 citations and is from a poor quality or predatory journal.

Citations

1. falkenberg2023biochemicalcharacterisationof pages 3-6
2. astles2024novelextremophilicmetalloproteases pages 56-60
3. han2024geneticidentificationand pages 13-13
4. arsov2024cloningsystemsin pages 29-31
5. emameh2022bioinformaticsanalysisof pages 1-3
6. emameh2022bioinformaticsanalysisof pages 4-6
7. emameh2022bioinformaticsanalysisof pages 3-4
8. emameh2022bioinformaticsanalysisof pages 7-8
9. https://doi.org/10.1080/07391102.2021.1894979
10. https://doi.org/10.1002/2211-5463.13701
11. https://doi.org/10.7488/era/4696
12. https://doi.org/10.1002/2211-5463.13701;
13. https://doi.org/10.3390/fermentation10010050;
14. https://doi.org/10.1186/s12934-023-02177-0;
15. https://doi.org/10.3389/fbioe.2024.1383083
16. https://doi.org/10.1007/s11274-024-03957-5
17. https://doi.org/10.7488/era/4696;
18. https://doi.org/10.3390/fermentation10010050
19. https://doi.org/10.1080/07391102.2021.1894979,
20. https://doi.org/10.1002/2211-5463.13701,
21. https://doi.org/10.7488/era/4696,
22. https://doi.org/10.3390/fermentation10010050,
23. https://doi.org/10.3389/fbioe.2024.1383083,

BioReason-Pro RL Review: aprE (B. subtilis)

Source: aprE-deep-research-bioreason-rl.md

• Correctness: 4/5
• Completeness: 3/5

Functional Summary Review

The BioReason functional summary reads:

A secreted extracellular serine endopeptidase from Bacillus subtilis that is produced as an auto-inhibited zymogen and activated outside the cell to drive proteolysis. Its N-terminal propeptide transiently blocks the catalytic core until removal during secretion, after which the mature enzyme uses a subtilisin catalytic triad to cleave polypeptides. This extracellular proteolysis likely supports nutrient acquisition and remodeling of the surrounding milieu by processing or degrading secreted and environmental substrates.

The core enzymatic function is correct: aprE encodes Subtilisin E, a secreted serine-type endopeptidase (GO:0004252) with the canonical Asp-His-Ser catalytic triad (Asp138-His170-Ser327). The zymogen/propeptide activation mechanism is accurately described and matches the curated review's description of the I9 propeptide functioning as an intramolecular chaperone. Extracellular localization (GO:0005576) is correctly identified.

However, the summary significantly underrepresents the known biology. The curated review identifies a specific and important role for aprE in quorum sensing (GO:0009372): subtilisin processes proCSF and proPhrA precursors to generate active pentapeptide pheromones that regulate competence and sporulation via the Rap-Phr system (PMID:17666034). This signaling receptor ligand precursor processing function (GO:0140448) is arguably as important as the general nutrient acquisition role and is entirely absent from the BioReason summary, which only vaguely alludes to "remodeling of the surrounding milieu." The curated review also notes calcium binding (two Ca2+ per subunit) and explicitly removes the sporulation annotation as experimentally unsupported (PMID:6427178).

Comparison with interpro2go:

The interpro2go annotations for aprE are not explicitly flagged in the curated review, but the IEA annotations include general terms like hydrolase activity (GO:0016787) and peptidase activity (GO:0008233), which the curated review marks as over-annotated. BioReason correctly identifies the specific serine endopeptidase activity rather than these generic terms, outperforming interpro2go in specificity. Both BioReason and interpro2go miss the quorum sensing and signaling peptide processing roles, which require literature knowledge beyond domain architecture.

Notes on thinking trace

The trace competently walks through the S8 peptidase domain architecture. The reasoning about the I9 propeptide as a zymogen module and the Asp-His-Ser triad is sound. The limitation is architectural: domain-based reasoning alone cannot capture the specific biological substrates (Phr peptides) that give aprE its most distinctive role.