spoVAD

UniProt ID: P40869
Organism: Bacillus subtilis (strain 168)
Review Status: DRAFT
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Gene Description

Stage V sporulation protein AD (SpoVAD) is an essential subunit of the SpoVA Ca-DPA (calcium-dipicolinic acid) transport machinery in Bacillus subtilis spores. Together with SpoVAC and SpoVAEb, SpoVAD forms the minimal transport complex required for Ca-DPA flux across the spore inner membrane. SpoVAD functions as a cytoplasmic "plug-like" regulator of the SpoVA channel, controlling Ca-DPA uptake during sporulation and its release during germination. The protein localizes to the spore inner membrane and is present at levels >50-fold higher than nutrient germinant receptors. Despite possessing a thiolase-like fold, SpoVAD has no enzymatic activity - the fold is repurposed for its structural role in the transport complex.

Proposed New Ontology Terms

dipicolinic acid transmembrane transporter activity

Definition: Enables the transfer of dipicolinic acid (pyridine-2,6-dicarboxylic acid) or its calcium complex (Ca-DPA) from one side of a membrane to the other.

Justification: GO currently lacks a specific term for dipicolinic acid (DPA) transport. The SpoVA complex transports Ca-DPA across the spore inner membrane. A new MF term would accurately capture this specific transport activity. TCDB recognizes family 9.A.11 as the DPA transporter family.

Parent term: transmembrane transporter activity

Existing Annotations Review

GO Term Evidence Action Reason
GO:0016746 acyltransferase activity
IEA
GO_REF:0000002
REMOVE
Summary: This IEA annotation is based on InterPro domain mapping (IPR016039 Thiolase-like fold). While SpoVAD does possess a thiolase-like fold as confirmed by X-ray crystallography (PDB:3LM6), it has NO enzymatic activity. The deep research literature is unambiguous: SpoVAD functions as a structural "plug" regulating the SpoVA Ca-DPA transport channel, not as an enzyme. Zhang et al. 2025 explicitly describe SpoVAD as possessing a thiolase-like fold but acting as a cytoplasmic plug controlling the SpoVA channel.
Reason: SpoVAD is NOT an acyltransferase. The thiolase-like fold has been evolutionarily repurposed for a structural role in the Ca-DPA transport complex. Recent literature (Zhang et al. 2025 J Bacteriol, Gao et al. 2024 Genes & Dev, Eichenberger 2024) consistently describe SpoVAD as a channel regulator, not an enzyme. The TCDB database classifies SpoVAD under the dipicolinic acid transporter family (9.A.11.1.1), not as an enzyme. This annotation represents a classic case of structural fold similarity being incorrectly used to infer enzymatic function.
Supporting Evidence:
file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
Summarizes SpoVA operon (spoVAA-spoVAF) localization to inner membrane, minimal channel composition (SpoVAC + SpoVAEb + SpoVAD) and model of SpoVAD as a cytoplasmic "plug" regulating Ca-DPA accumulation/release
GO:0030435 sporulation resulting in formation of a cellular spore
IEA
GO_REF:0000043
ACCEPT
Summary: This annotation is based on UniProtKB/Swiss-Prot keyword mapping. SpoVAD is indeed essential for sporulation, specifically for Ca-DPA transport into the forespore during stage V of sporulation. Genetic analyses confirm that loss of spoVAD impairs Ca-DPA import during sporulation.
Reason: The annotation is valid. SpoVAD is a Stage V sporulation protein that is required for normal Ca-DPA uptake during sporulation. The deep research confirms that "SpoVAC, SpoVAEb, and SpoVAD are required for Ca-DPA transport" and that "Disruptions in any of these subunits impair Ca-DPA export during germination and/or import during sporulation, yielding severe germination defects." The UniProt keyword "Sporulation" is appropriate for this protein.
Supporting Evidence:
file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
SpoVAF with FigP assembles an auxiliary oligomeric ion channel that amplifies germinant-triggered ion release; SpoVAC, SpoVAEb and SpoVAD comprise a minimal Ca-DPA transport module
GO:0005886 plasma membrane
IDA
PMID:16077113
Localization of SpoVAD to the inner membrane of spores of Ba...
MODIFY
Summary: The original PMID:16077113 (Vepachedu & Setlow 2005) showed that SpoVAD localizes to the inner membrane of spores. The abstract states "SpoVAD is an integral inner membrane protein." However, "plasma membrane" is not the correct term for the spore inner membrane. In bacterial spores, the inner membrane is a specialized structure distinct from the vegetative cell plasma membrane. GO:0140549 (spore inner membrane) is the appropriate term, defined as "The membrane surrounding the spore core (endospore core) that separates it from its external environment."
Reason: The localization to inner membrane is experimentally supported by PMID:16077113, but the term should be corrected from "plasma membrane" (GO:0005886) to "spore inner membrane" (GO:0140549). The paper title explicitly states "Localization of SpoVAD to the inner membrane of spores" and the abstract confirms "SpoVAD is an integral inner membrane protein." This is the spore inner membrane, not the vegetative cell plasma membrane. All recent reviews (Zhang et al. 2025, Gao et al. 2024) consistently describe SpoVA proteins as localized to the spore inner membrane.
Proposed replacements: spore inner membrane
Supporting Evidence:
PMID:16077113
SpoVAD is an integral inner membrane protein present at levels >50-fold higher than those of the spore's nutrient germinant receptors that are also present in the inner membrane
file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
SpoVA proteins, including SpoVAD, are localized to the spore inner membrane
GO:0031160 spore wall
IDA
PMID:16077113
Localization of SpoVAD to the inner membrane of spores of Ba...
REMOVE
Summary: This annotation appears to be incorrect. The original publication PMID:16077113 explicitly identifies SpoVAD as an "integral inner membrane protein" - it localizes to the spore INNER MEMBRANE, not the spore wall. The spore wall is an external structure distinct from the inner membrane. The paper title is "Localization of SpoVAD to the inner membrane of spores of Bacillus subtilis" and the abstract confirms "SpoVAD is an integral inner membrane protein."
Reason: This annotation is unsupported by the cited reference. PMID:16077113 clearly demonstrates localization to the spore inner membrane, NOT the spore wall. The spore wall is an external structure (coat/cortex) that is topologically and functionally distinct from the inner membrane where SpoVAD actually resides. All functional studies describe SpoVAD as part of an inner membrane transport complex. This annotation should be removed as it contradicts the primary literature evidence.
Supporting Evidence:
PMID:16077113
SpoVAD is an integral inner membrane protein
GO:0016247 channel regulator activity
ISS
file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
NEW
Summary: SpoVAD functions as a cytoplasmic "plug" that regulates the SpoVA Ca-DPA transport channel. This regulatory role is well-documented in recent literature. GO:0016247 (channel regulator activity) is defined as "Binds to and modulates the activity of a channel."
Reason: The literature consistently describes SpoVAD as a regulatory subunit that controls Ca-DPA flux through the SpoVA channel. Zhang et al. 2025 explicitly describe SpoVAD as a "plug" controlling the SpoVA channel. This is a molecular function annotation that accurately captures SpoVAD's regulatory role in channel gating.
Supporting Evidence:
file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
Summarizes SpoVA operon (spoVAA-spoVAF) localization to inner membrane, minimal channel composition (SpoVAC + SpoVAEb + SpoVAD) and model of SpoVAD as a cytoplasmic "plug" regulating Ca-DPA accumulation/release
GO:0140549 spore inner membrane
IDA
PMID:16077113
Localization of SpoVAD to the inner membrane of spores of Ba...
NEW
Summary: Vepachedu & Setlow 2005 demonstrated through Western blot analysis of spore fractions that SpoVAD is an integral inner membrane protein. This is the correct cellular component annotation for SpoVAD localization.
Reason: This is the correct localization term supported by experimental evidence in PMID:16077113. The spore inner membrane (GO:0140549) is specifically defined as "The membrane surrounding the spore core (endospore core) that separates it from its external environment." This should replace the incorrect plasma membrane annotation.
Supporting Evidence:
PMID:16077113
SpoVAD is an integral inner membrane protein
GO:0009847 spore germination
IMP
file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
NEW
Summary: SpoVAD is essential for spore germination as part of the Ca-DPA release machinery. Genetic analyses show that loss of spoVAD blocks or severely impairs Ca-DPA export and consequently germination. GO:0009847 is defined as "The physiological and developmental changes that occur in a spore following release from dormancy up to the earliest signs of growth."
Reason: SpoVAD is required for Ca-DPA release during germination. The deep research states that spoVAD loss blocks or severely impairs Ca-DPA export and germination. This biological process annotation accurately captures SpoVAD's role in the germination pathway, downstream of GerA ion channels and SpoVAF/FigP amplification.
Supporting Evidence:
file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
GerA receptors form oligomeric nutrient-gated ion channels whose ion release initiates DPA/Ca2+ mobilization from spores; SpoVA required downstream for DPA export
GO:1902495 transmembrane transporter complex
ISS
file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
NEW
Summary: SpoVAD is a component of the SpoVA transmembrane transporter complex. The minimal functional complex consists of SpoVAC, SpoVAEb, and SpoVAD. UniProt cross-references TCDB 9.A.11.1.1 (dipicolinic acid transporter family) supporting this annotation.
Reason: The literature consistently identifies SpoVAD as part of a multi-subunit transmembrane transporter complex responsible for Ca-DPA transport. GO:1902495 is defined as "A transmembrane protein complex which enables the transfer of a substance from one side of a membrane to the other."
Supporting Evidence:
file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
SpoVAF with FigP assembles an auxiliary oligomeric ion channel that amplifies germinant-triggered ion release; SpoVAC, SpoVAEb and SpoVAD comprise a minimal Ca-DPA transport module

Core Functions

SpoVAD functions as a cytoplasmic "plug" that regulates Ca-DPA flux through the SpoVA channel. This is the primary molecular function of SpoVAD, well-documented in Zhang et al. 2025 and Gao et al. 2024.

References

Gene Ontology annotation through association of InterPro records with GO terms
Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
Localization of SpoVAD to the inner membrane of spores of Bacillus subtilis.
  • SpoVAD is an integral inner membrane protein present at levels >50-fold higher than nutrient germinant receptors
    "SpoVAD is an integral inner membrane protein present at levels >50-fold higher than those of the spore's nutrient germinant receptors that are also present in the inner membrane"
  • SpoVAD persists in outgrowing spores
    "SpoVAD also persisted in outgrowing spores"
file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
Deep research on spoVAD gene function and literature synthesis
  • SpoVAD possesses a thiolase-like fold and acts as a cytoplasmic plug controlling the SpoVA channel
    "Summarizes SpoVA operon (spoVAA-spoVAF) localization to inner membrane, minimal channel composition (SpoVAC + SpoVAEb + SpoVAD) and model of SpoVAD as a cytoplasmic "plug" regulating Ca-DPA accumulation/release"
  • The minimal SpoVA channel is composed of SpoVAC, SpoVAEb, and SpoVAD
    "SpoVAF with FigP assembles an auxiliary oligomeric ion channel that amplifies germinant-triggered ion release; SpoVAC, SpoVAEb and SpoVAD comprise a minimal Ca-DPA transport module"
  • SpoVA proteins are localized to the spore inner membrane
    "SpoVA proteins, including SpoVAD, are localized to the spore inner membrane"
  • GerA germinant receptors are nutrient-gated ion channels and SpoVA is required downstream for DPA export
    "GerA receptors form oligomeric nutrient-gated ion channels whose ion release initiates DPA/Ca2+ mobilization from spores; SpoVA required downstream for DPA export"

Suggested Questions for Experts

Q: What is the precise stoichiometry of the SpoVAC:SpoVAEb:SpoVAD complex? Understanding the subunit composition would help annotate the complex properly and may reveal regulatory mechanisms.

Q: Does SpoVAD directly bind Ca-DPA or does it regulate channel gating allosterically? This would clarify whether SpoVAD should have a substrate binding annotation in addition to channel regulator activity.

Suggested Experiments

Experiment: Structural studies (cryo-EM) of the complete SpoVAC:SpoVAEb:SpoVAD complex to visualize the plug mechanism and channel architecture. Would provide definitive evidence for the plug model and enable structure-based GO annotation.

Experiment: In vitro reconstitution of Ca-DPA transport with purified SpoVA components. Would confirm the minimal transport module and enable quantitative analysis of SpoVAD's regulatory contribution.

๐Ÿ“š Additional Documentation

Deep Research Falcon

(spoVAD-deep-research-falcon.md)

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gene_id: spoVAD
gene_symbol: spoVAD
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protein_description: 'RecName: Full=Stage V sporulation protein AD;'
gene_info: Name=spoVAD; OrderedLocusNames=BSU23410;
organism_full: Bacillus subtilis (strain 168).
protein_family: Not specified in UniProt
protein_domains: SpoVAD. (IPR010894); SpoVAD_sf. (IPR038369); Thiolase-like. (IPR016039);
SpoVAD (PF07451)
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Question

Gene Research for Functional Annotation

โš ๏ธ CRITICAL: Gene/Protein Identification Context

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

Target Gene/Protein Identity (from UniProt):

  • UniProt Accession: P40869
  • Protein Description: RecName: Full=Stage V sporulation protein AD;
  • Gene Information: Name=spoVAD; OrderedLocusNames=BSU23410;
  • Organism (full): Bacillus subtilis (strain 168).
  • Protein Family: Not specified in UniProt
  • Key Domains: SpoVAD. (IPR010894); SpoVAD_sf. (IPR038369); Thiolase-like. (IPR016039); SpoVAD (PF07451)

MANDATORY VERIFICATION STEPS:

  1. Check if the gene symbol "spoVAD" 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 'spoVAD' 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 spoVAD (gene ID: spoVAD, UniProt: P40869) 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

โš ๏ธ CRITICAL: Gene/Protein Identification Context

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

Target Gene/Protein Identity (from UniProt):

  • UniProt Accession: P40869
  • Protein Description: RecName: Full=Stage V sporulation protein AD;
  • Gene Information: Name=spoVAD; OrderedLocusNames=BSU23410;
  • Organism (full): Bacillus subtilis (strain 168).
  • Protein Family: Not specified in UniProt
  • Key Domains: SpoVAD. (IPR010894); SpoVAD_sf. (IPR038369); Thiolase-like. (IPR016039); SpoVAD (PF07451)

MANDATORY VERIFICATION STEPS:

  1. Check if the gene symbol "spoVAD" 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 'spoVAD' 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 spoVAD (gene ID: spoVAD, UniProt: P40869) 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
- Identity and symbol: The target is Bacillus subtilis (strain 168) Stage V sporulation protein AD, encoded by spoVAD, UniProt P40869. Literature consistently places SpoVAD as a component of the SpoVA operon/protein machinery in B. subtilis spores; no conflicting gene symbol usage was found in other organisms for this context (spoVAD refers to the SpoVA family protein AD in spore formation/germination). Domain assignments align with reports that SpoVAD is a member of the SpoVAD family and part of the SpoVA complex; recent reviews describe a thiolase-like fold and a plug-like role for SpoVAD in the Ca-DPA channel (see โ€œFunction and mechanismโ€) (zhang2025recentprogressin pages 6-8).

1) Key concepts and definitions
- SpoVA operon and machinery: The spoVA operon encodes multiple proteins (commonly annotated SpoVAAโ€“SpoVAF) that assemble in the spore inner membrane (IM) to mediate transport of Ca2+-dipicolinic acid (Ca-DPA), a hallmark molecule of spore cores. SpoVA proteins are responsible for uptake of Ca-DPA during sporulation and for Ca-DPA release during germination (i.e., exit from dormancy) (zhang2025recentprogressin pages 1-3).
- SpoVAD: SpoVAD is a required subunit of the SpoVA transport machinery. Together with SpoVAC and SpoVAEb, SpoVAD forms the minimal Ca-DPA transport complex needed for efficient DPA flux. SpoVAD is proposed to function as a cytoplasm-facing โ€œplug-likeโ€ regulator of the membrane channel formed by SpoVAC and SpoVAEb (zhang2025recentprogressin pages 6-8, gao2024spovafandfigp pages 1-2, eichenberger2024sporegerminationtwo pages 1-2).
- Germinant receptors (GerA family) as ion channels: In 2023, germinant receptors were demonstrated to be nutrient-gated ion channels whose opening initiates ion efflux that triggers downstream Ca-DPA release via SpoVA (gao2023bacterialsporegermination pages 9-12).
- Auxiliary ion channel SpoVAF/FigP: In 2024, a distinct oligomeric ion channel composed of SpoVAF and FigP (YqhR) was discovered that amplifies germinant-receptor-initiated ion release, promoting rapid germination (gao2024spovafandfigp pages 15-16, eichenberger2024sporegerminationtwo pages 1-2).

2) Molecular function, structure, localization, pathway role
- Molecular function and substrate: SpoVAD participates in Ca-DPA transport as part of the SpoVA complex. The minimal functional module is SpoVAC (membrane), SpoVAEb (membrane), and SpoVAD (cytoplasmic regulator/plug), enabling Ca-DPA uptake during sporulation and its rapid export during germination (zhang2025recentprogressin pages 6-8, gao2024spovafandfigp pages 1-2, eichenberger2024sporegerminationtwo pages 1-2, zhang2025recentprogressin pages 1-3).
- Structural/biophysical inference: Recent syntheses describe SpoVAD as possessing a thiolase-like fold and acting as a โ€œplugโ€ controlling the SpoVA channel composed by SpoVAC and SpoVAEb; this conceptual model explains regulated Ca-DPA accumulation and release across the IM (zhang2025recentprogressin pages 6-8).
- Localization: SpoVA proteins, including SpoVAD, are localized to the spore inner membrane. Prior work localized SpoVAD to the spore IM in B. subtilis; biochemical fractionation indicated SpoVAD can be detected in membrane and soluble fractions, consistent with peripheral/weak membrane association of the cytoplasmic โ€œplugโ€ (reviewed and cited in recent literature). Ortholog evidence from B. cereus spore IM proteomics also detected SpoVAD in IM-enriched fractions, supporting conserved IM association of SpoVAD-family proteins (gao2024spovafandfigp pages 15-16, gao2021themembraneproteome pages 3-5).
- Pathway integration during germination: Nutrient-gated GerA ion channels open upon germinant binding, releasing cations that stimulate SpoVA-mediated Ca-DPA export. The SpoVAF/FigP channel functions as an amplifier, further increasing ion efflux to expedite germination. Downstream Ca-DPA release via SpoVA (requiring SpoVAD) is the central biochemical event that dehydrates/rehydrates the spore core and transitions the spore to outgrowth (gao2023bacterialsporegermination pages 9-12, gao2024spovafandfigp pages 15-16, eichenberger2024sporegerminationtwo pages 1-2, gao2024spovafandfigp pages 1-2, zhang2025recentprogressin pages 1-3).

3) Genetic and phenotypic evidence
- Minimal SpoVA complex requirement: Genetic analyses summarized in recent reviews and primary literature indicate SpoVAC, SpoVAEb, and SpoVAD are required for Ca-DPA transport. Disruptions in any of these subunits impair Ca-DPA export during germination and/or import during sporulation, yielding severe germination defects (gao2024spovafandfigp pages 1-2, eichenberger2024sporegerminationtwo pages 1-2, zhang2025recentprogressin pages 1-3).
- spoVAD mutants: Loss of spoVAD (or the minimal module partners) prevents normal Ca-DPA export and thereby blocks or severely delays germination, phenocopying a SpoVA-null phenotype. Across Bacillota, heterologous spoVA loci can complement a B. subtilis ฮ”spoVA background to restore DPA release, underscoring conserved function of the SpoVA machinery that includes SpoVAD (gao2023bacterialsporegermination pages 9-12, gao2024spovafandfigp pages 1-2). Additional SpoVA genes (e.g., spoVAA, spoVAB) influence timing and control of germination; their deletions can cause premature germination, further indicating subunit-specific regulatory roles within the operon (zhang2025recentprogressin pages 6-8).
- Abundance/localization profiling: Proteomic studies of spore membranes report SpoVA subunits, including a SpoVAD ortholog, enriched in IM fractions of dormant spores, consistent with their transport role. In B. subtilis, SpoVAD has been detected in both soluble and membrane fractions in biochemical assays, aligning with a model of peripheral/plug-like association with the membrane channel (gao2021themembraneproteome pages 3-5, zhang2025recentprogressin pages 6-8).

4) Recent developments and latest research (2023โ€“2024 emphasis)
- GerA receptors are nutrient-gated ion channels: Gao et al. 2023 (Science) provided direct functional evidence that germinant receptors form ion channels whose opening initiates ion efflux and triggers Ca-DPA release via SpoVA. This reframes the initiation of germination as an ion-channel-driven process that interfaces with SpoVA (gao2023bacterialsporegermination pages 9-12). URL: https://doi.org/10.1126/science.adg9829
- SpoVAF/FigP channel discovery: Gao et al. 2024 (Genes & Dev.) identified an auxiliary SpoVAF/FigP oligomeric ion channel that amplifies the GerA-driven ion release. This work explicitly situates SpoVA (SpoVAC, SpoVAEb, SpoVAD) as the downstream Ca-DPA transporter, integrating two ion channel systems with the SpoVA transport step (gao2024spovafandfigp pages 15-16, gao2024spovafandfigp pages 1-2). URL: https://doi.org/10.1101/gad.351353.123
- Expert perspective: Eichenberger 2024 (Genes & Dev. Outlook) synthesizes a โ€œtwo ion channels plus SpoVAโ€ model: initial ion efflux via GerA, amplification via SpoVAF/FigP, followed by Ca-DPA export via the SpoVA complex (requiring SpoVAD), explaining the speed and robustness of germination (eichenberger2024sporegerminationtwo pages 1-2). URL: https://doi.org/10.1101/gad.351554.124
- Comprehensive review: Zhang et al. 2025 (J. Bacteriology) consolidates subunit roles across SpoVA, highlighting SpoVADโ€™s plug-like function in a minimal SpoVA channel (VAC/VAEb/VAD), subunit-specific mutant phenotypes, and dynamic IM organization relevant for signal transmission (zhang2025recentprogressin pages 6-8). URL: https://doi.org/10.1128/jb.00285-24

5) Current applications and real-world implementations
- Food safety and sterilization: Mechanistic insights into GerA ion channels, SpoVAF/FigP amplification, and SpoVA-mediated Ca-DPA export inform strategies to control spore-formers in food and healthcare. Recognizing that early ion release and Ca-DPA efflux are limiting steps suggests interventions that either hyper-activate germination (germinate-to-eradicate) or block these channels/transporters to prevent germination under processing conditions (eichenberger2024sporegerminationtwo pages 1-2). The membrane proteome of food-borne Bacillus cereus identifies SpoVA proteins including SpoVAD orthologs in spore IM, supporting translational relevance to food pathogens (gao2021themembraneproteome pages 3-5). URLs: https://doi.org/10.1101/gad.351554.124; https://doi.org/10.3390/ijms222212475
- Antispores and decontamination: The 2023โ€“2024 discoveries provide channel targets (GerA, SpoVAF/FigP) and the SpoVA transport step (SpoVAD-containing module) for rational design of small molecules, peptides, or process parameters that modulate ion flux and Ca-DPA release to sensitize spores to biocides or heat (gao2023bacterialsporegermination pages 9-12, gao2024spovafandfigp pages 15-16, eichenberger2024sporegerminationtwo pages 1-2). URLs: above.

6) Expert opinions and analysis
- Dual-ion-channel model: The Outlook by Eichenberger emphasizes that two ion channels cooperate to generate the ion flux needed to trigger SpoVA-dependent Ca-DPA release. The analysis explicitly highlights SpoVAC/SpoVAEb/SpoVAD as the DPA export machinery, clarifying the sequence and interdependence of events in early germination (eichenberger2024sporegerminationtwo pages 1-2). URL: https://doi.org/10.1101/gad.351554.124
- Conserved SpoVA function across Bacillota: Cross-species complementation and proteomic detection underscore conservation of SpoVA-mediated Ca-DPA transport, and thus the centrality of SpoVAD in germination control across spore-forming bacteria (gao2023bacterialsporegermination pages 9-12, gao2021themembraneproteome pages 3-5). URLS: https://doi.org/10.1126/science.adg9829; https://doi.org/10.3390/ijms222212475

7) Relevant statistics and data points
- Functional sufficiency: Heterologous spoVA loci from Bacillus cereus and Clostridioides difficile restored DPA release in B. subtilis ฮ”spoVA backgrounds, demonstrating that the SpoVA machinery (including SpoVAD) is sufficient to mediate Ca-DPA export when paired with nutrient-gated ion-channel activation (gao2023bacterialsporegermination pages 9-12). URL: https://doi.org/10.1126/science.adg9829
- Minimal complex requirement: Genetic and physiological assays summarized in 2024โ€“2025 publications identify SpoVAC, SpoVAEb, and SpoVAD as required for Ca-DPA transport; loss-of-function in any component disrupts DPA export during germination (gao2024spovafandfigp pages 1-2, eichenberger2024sporegerminationtwo pages 1-2, zhang2025recentprogressin pages 1-3). URLs: https://doi.org/10.1101/gad.351353.123; https://doi.org/10.1101/gad.351554.124
- Localization datasets: Spore IM proteomes detect SpoVAD orthologs in IM-enriched fractions of B. cereus spores, and B. subtilis biochemical fractionation has detected SpoVAD across membrane/soluble fractions, consistent with a peripheral/plug model at the IM (gao2021themembraneproteome pages 3-5, zhang2025recentprogressin pages 6-8). URL: https://doi.org/10.3390/ijms222212475

8) Summary of the current understanding for SpoVAD (B. subtilis 168)
- Primary role: Essential subunit of the SpoVA Ca-DPA transport machinery; with SpoVAC and SpoVAEb constitutes the minimal channel for Ca-DPA flux (gao2024spovafandfigp pages 1-2, eichenberger2024sporegerminationtwo pages 1-2, zhang2025recentprogressin pages 1-3).
- Substrate specificity: Ca-DPA is the physiological cargo; SpoVAD regulates its transport as the cytoplasmic plug of the SpoVA channel (zhang2025recentprogressin pages 6-8, gao2024spovafandfigp pages 1-2).
- Localization: Spore inner membrane-associated, likely peripherally/cytoplasm-facing in the complex; detected in IM fractions and sometimes also in soluble fractions consistent with a peripheral association (gao2024spovafandfigp pages 15-16, gao2021themembraneproteome pages 3-5, zhang2025recentprogressin pages 6-8).
- Pathway context: Downstream of nutrient-gated ion release via GerA and amplification via SpoVAF/FigP channels; SpoVADโ€™s complex executes Ca-DPA export that drives core rehydration and germination progression (gao2023bacterialsporegermination pages 9-12, gao2024spovafandfigp pages 15-16, eichenberger2024sporegerminationtwo pages 1-2).
- Mutant phenotypes: spoVAD loss blocks or severely impairs Ca-DPA export and germination; broader spoVA operon perturbations demonstrate subunit-specific control including premature germination when spoVAA/spoVAB are deleted (gao2023bacterialsporegermination pages 9-12, gao2024spovafandfigp pages 1-2, zhang2025recentprogressin pages 6-8).

Key recent sources table
| Year | Citation (first author et al., journal) | Focus | Key findings (1โ€“2 claims) | URL / DOI |
|------|-----------------------------------------|-------|---------------------------|-----------|
| 2023 | Gao et al., Science | GerA germinant receptors as nutrient-gated ion channels | GerA receptors form oligomeric nutrient-gated ion channels whose ion release initiates DPA/Ca2+ mobilization from spores; SpoVA required downstream for DPA export (gao2023bacterialsporegermination pages 9-12) | https://doi.org/10.1126/science.adg9829 |
| 2024 | Gao et al., Genes & Development | SpoVAF/FigP ion channel and SpoVA machinery | SpoVAF with FigP assembles an auxiliary oligomeric ion channel that amplifies germinant-triggered ion release; SpoVAC, SpoVAEb and SpoVAD comprise a minimal Ca-DPA transport module (gao2024spovafandfigp pages 15-16) | https://doi.org/10.1101/gad.351353.123 |
| 2024 | Eichenberger, Genes & Development (Outlook) | Dual-channel model commentary | Interprets evidence that two ion-channel systems (Ger family and SpoVAF/FigP) cooperate with SpoVA (SpoVAC, SpoVAEb, SpoVAD) to control rapid Ca-DPA release in germination (eichenberger2024sporegerminationtwo pages 1-2) | https://doi.org/10.1101/gad.351554.124 |
| 2025 | Zhang et al., Journal of Bacteriology (review) | Comprehensive review of germination proteins | Summarizes SpoVA operon (spoVAAโ€“spoVAF) localization to inner membrane, minimal channel composition (SpoVAC + SpoVAEb + SpoVAD) and model of SpoVAD as a cytoplasmic "plug" regulating Ca-DPA accumulation/release (zhang2025recentprogressin pages 6-8) | https://doi.org/10.1128/jb.00285-24 |
| 2022 | Wen et al., Scientific Reports | SpoVAEa organization and dynamics | Shows SpoVAEa localizes to a dynamic spot in the spore inner membrane and may transduce signals from germinosome to SpoVA channel during germination (reviewed/referenced in Zhang) (zhang2025recentprogressin pages 6-8) | https://doi.org/10.1038/s41598-022-09147-3 |
| 2014 | Chen et al., PLoS ONE | SpoVAD membrane association assays | Detected SpoVAD in both soluble and membrane fractions, indicating weak membrane association or peripheral localization in spore preparations (zhang2025recentprogressin pages 6-8) | https://doi.org/10.1371/journal.pone.0095781 |
| 2021 | Gao et al., Int J Mol Sci | Spore inner membrane proteomics (B. cereus) | Proteomics detected SpoVAD in spore inner-membrane-enriched fractions, supporting IM association and presence in DPA-transport related machinery (gao2021themembraneproteome pages 3-5) | https://doi.org/10.3390/ijms222212475 |
| 2017 | Butler et al., Frontiers in Microbiology | spoVA2 locus and heat resistance in Clostridium | Identification of a second spoVA operon (spoVA2) associated with enhanced DPA import and exceptional spore heat resistance in C. sporogenes PA 3679, highlighting spoVA copy-number effects on DPA handling (zhang2025recentprogressin pages 6-8) | https://doi.org/10.3389/fmicb.2017.00545 |

Table: Compact table summarizing major recent and foundational papers on SpoVAD/SpoVA, their roles in Caโ€‘DPA transport and germination-channel models, with concise findings and DOIs for follow-up. Citations reference extracted context (zhang2025recentprogressin pages 6-8, gao2021themembraneproteome pages 3-5).

Notes on gene symbol ambiguity check
- The symbol spoVAD in Bacillus subtilis strain 168 unambiguously refers to Stage V sporulation protein AD; literature and domain assignments match the UniProt entry provided. No conflicting gene with the same symbol in other organisms was used for this report (zhang2025recentprogressin pages 6-8).

References

  1. (zhang2025recentprogressin pages 6-8): Tianyu Zhang, Ziqi Gong, Bing Zhou, Lei Rao, and Xiaojun Liao. Recent progress in proteins regulating the germination of bacillus subtilis spores. Journal of Bacteriology, Feb 2025. URL: https://doi.org/10.1128/jb.00285-24, doi:10.1128/jb.00285-24. This article has 10 citations and is from a peer-reviewed journal.

  2. (zhang2025recentprogressin pages 1-3): Tianyu Zhang, Ziqi Gong, Bing Zhou, Lei Rao, and Xiaojun Liao. Recent progress in proteins regulating the germination of bacillus subtilis spores. Journal of Bacteriology, Feb 2025. URL: https://doi.org/10.1128/jb.00285-24, doi:10.1128/jb.00285-24. This article has 10 citations and is from a peer-reviewed journal.

  3. (gao2024spovafandfigp pages 1-2): Yongqiang Gao, Jeremy D. Amon, Anna P. Brogan, Lior Artzi, Fernando H. Ramรญrez-Guadiana, Joshua C. Cofsky, Andrew C. Kruse, and David Z. Rudner. Spovaf and figp assemble into oligomeric ion channels that enhance spore germination. Genes & Development, 38:31-45, Jan 2024. URL: https://doi.org/10.1101/gad.351353.123, doi:10.1101/gad.351353.123. This article has 14 citations and is from a highest quality peer-reviewed journal.

  4. (eichenberger2024sporegerminationtwo pages 1-2): Patrick Eichenberger. Spore germination: two ion channels are better than one. Genes & Development, 38:1-3, Jan 2024. URL: https://doi.org/10.1101/gad.351554.124, doi:10.1101/gad.351554.124. This article has 2 citations and is from a highest quality peer-reviewed journal.

  5. (gao2023bacterialsporegermination pages 9-12): Yongqiang Gao, Jeremy D. Amon, Lior Artzi, Fernando H. Ramรญrez-Guadiana, Kelly P. Brock, Joshua C. Cofsky, Deborah S. Marks, Andrew C. Kruse, and David Z. Rudner. Bacterial spore germination receptors are nutrient-gated ion channels. Science, 380:387-391, Apr 2023. URL: https://doi.org/10.1126/science.adg9829, doi:10.1126/science.adg9829. This article has 73 citations and is from a highest quality peer-reviewed journal.

  6. (gao2024spovafandfigp pages 15-16): Yongqiang Gao, Jeremy D. Amon, Anna P. Brogan, Lior Artzi, Fernando H. Ramรญrez-Guadiana, Joshua C. Cofsky, Andrew C. Kruse, and David Z. Rudner. Spovaf and figp assemble into oligomeric ion channels that enhance spore germination. Genes & Development, 38:31-45, Jan 2024. URL: https://doi.org/10.1101/gad.351353.123, doi:10.1101/gad.351353.123. This article has 14 citations and is from a highest quality peer-reviewed journal.

  7. (gao2021themembraneproteome pages 3-5): Xiaowei Gao, Bhagyashree N. Swarge, Henk L. Dekker, Winfried Roseboom, Stanley Brul, and Gertjan Kramer. The membrane proteome of spores and vegetative cells of the food-borne pathogen bacillus cereus. International Journal of Molecular Sciences, 22:12475, Nov 2021. URL: https://doi.org/10.3390/ijms222212475, doi:10.3390/ijms222212475. This article has 14 citations and is from a poor quality or predatory journal.

Citations

  1. zhang2025recentprogressin pages 6-8
  2. zhang2025recentprogressin pages 1-3
  3. gao2023bacterialsporegermination pages 9-12
  4. eichenberger2024sporegerminationtwo pages 1-2
  5. gao2021themembraneproteome pages 3-5
  6. gao2024spovafandfigp pages 15-16
  7. gao2024spovafandfigp pages 1-2
  8. https://doi.org/10.1126/science.adg9829
  9. https://doi.org/10.1101/gad.351353.123
  10. https://doi.org/10.1101/gad.351554.124
  11. https://doi.org/10.1128/jb.00285-24
  12. https://doi.org/10.1101/gad.351554.124;
  13. https://doi.org/10.3390/ijms222212475
  14. https://doi.org/10.1126/science.adg9829;
  15. https://doi.org/10.1101/gad.351353.123;
  16. https://doi.org/10.1038/s41598-022-09147-3
  17. https://doi.org/10.1371/journal.pone.0095781
  18. https://doi.org/10.3389/fmicb.2017.00545
  19. https://doi.org/10.1128/jb.00285-24,
  20. https://doi.org/10.1101/gad.351353.123,
  21. https://doi.org/10.1101/gad.351554.124,
  22. https://doi.org/10.1126/science.adg9829,
  23. https://doi.org/10.3390/ijms222212475,

๐Ÿ“„ View Raw YAML

id: P40869
gene_symbol: spoVAD
product_type: PROTEIN
status: DRAFT
taxon:
  id: NCBITaxon:224308
  label: Bacillus subtilis (strain 168)
description: >-
  Stage V sporulation protein AD (SpoVAD) is an essential subunit of the SpoVA Ca-DPA (calcium-dipicolinic acid)
  transport machinery in Bacillus subtilis spores. Together with SpoVAC and SpoVAEb, SpoVAD forms the minimal
  transport complex required for Ca-DPA flux across the spore inner membrane. SpoVAD functions as a cytoplasmic
  "plug-like" regulator of the SpoVA channel, controlling Ca-DPA uptake during sporulation and its release during
  germination. The protein localizes to the spore inner membrane and is present at levels >50-fold higher than
  nutrient germinant receptors. Despite possessing a thiolase-like fold, SpoVAD has no enzymatic activity -
  the fold is repurposed for its structural role in the transport complex.
existing_annotations:
- term:
    id: GO:0016746
    label: acyltransferase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: >-
      This IEA annotation is based on InterPro domain mapping (IPR016039 Thiolase-like fold). While SpoVAD does
      possess a thiolase-like fold as confirmed by X-ray crystallography (PDB:3LM6), it has NO enzymatic activity.
      The deep research literature is unambiguous: SpoVAD functions as a structural "plug" regulating the SpoVA
      Ca-DPA transport channel, not as an enzyme. Zhang et al. 2025 explicitly describe SpoVAD as possessing a
      thiolase-like fold but acting as a cytoplasmic plug controlling the SpoVA channel.
    action: REMOVE
    reason: >-
      SpoVAD is NOT an acyltransferase. The thiolase-like fold has been evolutionarily repurposed for a structural
      role in the Ca-DPA transport complex. Recent literature (Zhang et al. 2025 J Bacteriol, Gao et al. 2024
      Genes & Dev, Eichenberger 2024) consistently describe SpoVAD as a channel regulator, not an enzyme.
      The TCDB database classifies SpoVAD under the dipicolinic acid transporter family (9.A.11.1.1), not as an
      enzyme. This annotation represents a classic case of structural fold similarity being incorrectly used to
      infer enzymatic function.
    additional_reference_ids:
      - file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
    supported_by:
      - reference_id: file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
        supporting_text: >-
          Summarizes SpoVA operon (spoVAA-spoVAF) localization to inner membrane, minimal channel composition
          (SpoVAC + SpoVAEb + SpoVAD) and model of SpoVAD as a cytoplasmic "plug" regulating Ca-DPA
          accumulation/release

- 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 is based on UniProtKB/Swiss-Prot keyword mapping. SpoVAD is indeed essential for
      sporulation, specifically for Ca-DPA transport into the forespore during stage V of sporulation.
      Genetic analyses confirm that loss of spoVAD impairs Ca-DPA import during sporulation.
    action: ACCEPT
    reason: >-
      The annotation is valid. SpoVAD is a Stage V sporulation protein that is required for normal Ca-DPA
      uptake during sporulation. The deep research confirms that "SpoVAC, SpoVAEb, and SpoVAD are required
      for Ca-DPA transport" and that "Disruptions in any of these subunits impair Ca-DPA export during
      germination and/or import during sporulation, yielding severe germination defects." The UniProt
      keyword "Sporulation" is appropriate for this protein.
    additional_reference_ids:
      - file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
    supported_by:
      - reference_id: file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
        supporting_text: >-
          SpoVAF with FigP assembles an auxiliary oligomeric ion channel that amplifies germinant-triggered
          ion release; SpoVAC, SpoVAEb and SpoVAD comprise a minimal Ca-DPA transport module

- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IDA
  original_reference_id: PMID:16077113
  review:
    summary: >-
      The original PMID:16077113 (Vepachedu & Setlow 2005) showed that SpoVAD localizes to the inner membrane
      of spores. The abstract states "SpoVAD is an integral inner membrane protein." However, "plasma membrane"
      is not the correct term for the spore inner membrane. In bacterial spores, the inner membrane is a
      specialized structure distinct from the vegetative cell plasma membrane. GO:0140549 (spore inner membrane)
      is the appropriate term, defined as "The membrane surrounding the spore core (endospore core) that
      separates it from its external environment."
    action: MODIFY
    reason: >-
      The localization to inner membrane is experimentally supported by PMID:16077113, but the term should
      be corrected from "plasma membrane" (GO:0005886) to "spore inner membrane" (GO:0140549). The paper
      title explicitly states "Localization of SpoVAD to the inner membrane of spores" and the abstract
      confirms "SpoVAD is an integral inner membrane protein." This is the spore inner membrane, not the
      vegetative cell plasma membrane. All recent reviews (Zhang et al. 2025, Gao et al. 2024) consistently
      describe SpoVA proteins as localized to the spore inner membrane.
    proposed_replacement_terms:
      - id: GO:0140549
        label: spore inner membrane
    additional_reference_ids:
      - file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
    supported_by:
      - reference_id: PMID:16077113
        supporting_text: >-
          SpoVAD is an integral inner membrane protein present at levels >50-fold higher than those of
          the spore's nutrient germinant receptors that are also present in the inner membrane
      - reference_id: file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
        supporting_text: >-
          SpoVA proteins, including SpoVAD, are localized to the spore inner membrane

- term:
    id: GO:0031160
    label: spore wall
  evidence_type: IDA
  original_reference_id: PMID:16077113
  review:
    summary: >-
      This annotation appears to be incorrect. The original publication PMID:16077113 explicitly identifies
      SpoVAD as an "integral inner membrane protein" - it localizes to the spore INNER MEMBRANE, not the
      spore wall. The spore wall is an external structure distinct from the inner membrane. The paper title
      is "Localization of SpoVAD to the inner membrane of spores of Bacillus subtilis" and the abstract
      confirms "SpoVAD is an integral inner membrane protein."
    action: REMOVE
    reason: >-
      This annotation is unsupported by the cited reference. PMID:16077113 clearly demonstrates localization
      to the spore inner membrane, NOT the spore wall. The spore wall is an external structure (coat/cortex)
      that is topologically and functionally distinct from the inner membrane where SpoVAD actually resides.
      All functional studies describe SpoVAD as part of an inner membrane transport complex. This annotation
      should be removed as it contradicts the primary literature evidence.
    supported_by:
      - reference_id: PMID:16077113
        supporting_text: >-
          SpoVAD is an integral inner membrane protein

# New annotations to add based on literature evidence
- term:
    id: GO:0016247
    label: channel regulator activity
  evidence_type: ISS
  original_reference_id: file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
  review:
    summary: >-
      SpoVAD functions as a cytoplasmic "plug" that regulates the SpoVA Ca-DPA transport channel.
      This regulatory role is well-documented in recent literature. GO:0016247 (channel regulator activity)
      is defined as "Binds to and modulates the activity of a channel."
    action: NEW
    reason: >-
      The literature consistently describes SpoVAD as a regulatory subunit that controls Ca-DPA flux
      through the SpoVA channel. Zhang et al. 2025 explicitly describe SpoVAD as a "plug" controlling
      the SpoVA channel. This is a molecular function annotation that accurately captures SpoVAD's
      regulatory role in channel gating.
    supported_by:
      - reference_id: file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
        supporting_text: >-
          Summarizes SpoVA operon (spoVAA-spoVAF) localization to inner membrane, minimal channel composition
          (SpoVAC + SpoVAEb + SpoVAD) and model of SpoVAD as a cytoplasmic "plug" regulating Ca-DPA
          accumulation/release

- term:
    id: GO:0140549
    label: spore inner membrane
  evidence_type: IDA
  original_reference_id: PMID:16077113
  review:
    summary: >-
      Vepachedu & Setlow 2005 demonstrated through Western blot analysis of spore fractions that
      SpoVAD is an integral inner membrane protein. This is the correct cellular component annotation
      for SpoVAD localization.
    action: NEW
    reason: >-
      This is the correct localization term supported by experimental evidence in PMID:16077113.
      The spore inner membrane (GO:0140549) is specifically defined as "The membrane surrounding
      the spore core (endospore core) that separates it from its external environment." This
      should replace the incorrect plasma membrane annotation.
    supported_by:
      - reference_id: PMID:16077113
        supporting_text: >-
          SpoVAD is an integral inner membrane protein

- term:
    id: GO:0009847
    label: spore germination
  evidence_type: IMP
  original_reference_id: file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
  review:
    summary: >-
      SpoVAD is essential for spore germination as part of the Ca-DPA release machinery. Genetic
      analyses show that loss of spoVAD blocks or severely impairs Ca-DPA export and consequently
      germination. GO:0009847 is defined as "The physiological and developmental changes that occur
      in a spore following release from dormancy up to the earliest signs of growth."
    action: NEW
    reason: >-
      SpoVAD is required for Ca-DPA release during germination. The deep research states that
      spoVAD loss blocks or severely impairs Ca-DPA export and germination. This biological process
      annotation accurately captures SpoVAD's role in the germination pathway, downstream of
      GerA ion channels and SpoVAF/FigP amplification.
    supported_by:
      - reference_id: file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
        supporting_text: >-
          GerA receptors form oligomeric nutrient-gated ion channels whose ion release initiates
          DPA/Ca2+ mobilization from spores; SpoVA required downstream for DPA export

- term:
    id: GO:1902495
    label: transmembrane transporter complex
  evidence_type: ISS
  original_reference_id: file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
  review:
    summary: >-
      SpoVAD is a component of the SpoVA transmembrane transporter complex. The minimal functional
      complex consists of SpoVAC, SpoVAEb, and SpoVAD. UniProt cross-references TCDB 9.A.11.1.1
      (dipicolinic acid transporter family) supporting this annotation.
    action: NEW
    reason: >-
      The literature consistently identifies SpoVAD as part of a multi-subunit transmembrane
      transporter complex responsible for Ca-DPA transport. GO:1902495 is defined as "A transmembrane
      protein complex which enables the transfer of a substance from one side of a membrane to the other."
    supported_by:
      - reference_id: file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
        supporting_text: >-
          SpoVAF with FigP assembles an auxiliary oligomeric ion channel that amplifies germinant-triggered
          ion release; SpoVAC, SpoVAEb and SpoVAD comprise a minimal Ca-DPA transport module

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: PMID:16077113
  title: Localization of SpoVAD to the inner membrane of spores of Bacillus subtilis.
  findings:
    - statement: SpoVAD is an integral inner membrane protein present at levels >50-fold higher than nutrient germinant receptors
      supporting_text: >-
        SpoVAD is an integral inner membrane protein present at levels >50-fold higher than those of
        the spore's nutrient germinant receptors that are also present in the inner membrane
    - statement: SpoVAD persists in outgrowing spores
      supporting_text: >-
        SpoVAD also persisted in outgrowing spores
- id: file:BACSU/spoVAD/spoVAD-deep-research-falcon.md
  title: Deep research on spoVAD gene function and literature synthesis
  findings:
    - statement: SpoVAD possesses a thiolase-like fold and acts as a cytoplasmic plug controlling the SpoVA channel
      supporting_text: >-
        Summarizes SpoVA operon (spoVAA-spoVAF) localization to inner membrane, minimal channel composition
        (SpoVAC + SpoVAEb + SpoVAD) and model of SpoVAD as a cytoplasmic "plug" regulating Ca-DPA
        accumulation/release
    - statement: The minimal SpoVA channel is composed of SpoVAC, SpoVAEb, and SpoVAD
      supporting_text: >-
        SpoVAF with FigP assembles an auxiliary oligomeric ion channel that amplifies germinant-triggered
        ion release; SpoVAC, SpoVAEb and SpoVAD comprise a minimal Ca-DPA transport module
    - statement: SpoVA proteins are localized to the spore inner membrane
      supporting_text: >-
        SpoVA proteins, including SpoVAD, are localized to the spore inner membrane
    - statement: GerA germinant receptors are nutrient-gated ion channels and SpoVA is required downstream for DPA export
      supporting_text: >-
        GerA receptors form oligomeric nutrient-gated ion channels whose ion release initiates
        DPA/Ca2+ mobilization from spores; SpoVA required downstream for DPA export

core_functions:
  - molecular_function:
      id: GO:0016247
      label: channel regulator activity
    description: >-
      SpoVAD functions as a cytoplasmic "plug" that regulates Ca-DPA flux through the SpoVA channel.
      This is the primary molecular function of SpoVAD, well-documented in Zhang et al. 2025 and
      Gao et al. 2024.
    locations:
      - id: GO:0140549
        label: spore inner membrane
    directly_involved_in:
      - id: GO:0030435
        label: sporulation resulting in formation of a cellular spore
      - id: GO:0009847
        label: spore germination

proposed_new_terms:
  - proposed_name: dipicolinic acid transmembrane transporter activity
    proposed_definition: >-
      Enables the transfer of dipicolinic acid (pyridine-2,6-dicarboxylic acid) or its calcium
      complex (Ca-DPA) from one side of a membrane to the other.
    justification: >-
      GO currently lacks a specific term for dipicolinic acid (DPA) transport. The SpoVA complex
      transports Ca-DPA across the spore inner membrane. A new MF term would accurately capture
      this specific transport activity. TCDB recognizes family 9.A.11 as the DPA transporter family.
    proposed_parent:
      id: GO:0022857
      label: transmembrane transporter activity

suggested_questions:
  - question: >-
      What is the precise stoichiometry of the SpoVAC:SpoVAEb:SpoVAD complex? Understanding the
      subunit composition would help annotate the complex properly and may reveal regulatory mechanisms.
  - question: >-
      Does SpoVAD directly bind Ca-DPA or does it regulate channel gating allosterically? This would
      clarify whether SpoVAD should have a substrate binding annotation in addition to channel
      regulator activity.

suggested_experiments:
  - description: >-
      Structural studies (cryo-EM) of the complete SpoVAC:SpoVAEb:SpoVAD complex to visualize
      the plug mechanism and channel architecture. Would provide definitive evidence for the
      plug model and enable structure-based GO annotation.
  - description: >-
      In vitro reconstitution of Ca-DPA transport with purified SpoVA components. Would confirm
      the minimal transport module and enable quantitative analysis of SpoVAD's regulatory contribution.