SpoVD is a sporulation-specific class B penicillin-binding protein (PBP) that functions as a D,D-transpeptidase essential for spore cortex peptidoglycan synthesis during Stage V of sporulation. It works as a cognate pair with SpoVE (a SEDS-family glycosyltransferase) to polymerize and crosslink cortex peptidoglycan at the outer forespore membrane. SpoVD is expressed exclusively in the mother cell compartment under sigmaE control with SpoIIID repression. The protein contains an N-terminal transmembrane helix, a PBP dimerization domain, a catalytic transpeptidase domain with the conserved active-site serine, and a unique C-terminal PASTA domain. Disruption of spoVD results in cortex-less, heat-sensitive spores (asporogenous phenotype). Unlike FtsI (septum) or MrdA (elongation), SpoVD is dedicated exclusively to sporulation and does not participate in vegetative cell wall synthesis or cell shape regulation.
Definition: Catalysis of the crosslinking of peptidoglycan peptide stems via D,D-transpeptidation, forming peptide cross-bridges between adjacent glycan strands. The reaction involves cleavage of a D-Ala-D-Ala bond and formation of a new peptide bond.
Justification: Currently only GO:0071972 (peptidoglycan L,D-transpeptidase activity) exists. D,D-transpeptidases like SpoVD, FtsI, and MrdA are distinct enzymes with different substrate specificities and are major contributors to peptidoglycan crosslinking.
Parent term: aminoacyltransferase activity
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005886 plasma membrane | IBA GO_REF:0000033 | ACCEPT | Summary: SpoVD localizes to the cell membrane during sporulation. UniProt annotates SpoVD as a peripheral membrane protein associated with the cell membrane. The deep research indicates SpoVD accumulates at the outer forespore membrane during cortex synthesis. Reason: The plasma membrane annotation is correct. SpoVD is membrane-associated via its N-terminal transmembrane region and localizes to the outer forespore membrane during Stage V sporulation. The IBA annotation from phylogenetic inference is consistent with UniProt annotation. Supporting Evidence: UniProt:Q03524 Cell membrane {ECO:0000269|PubMed:8289242}; Peripheral membrane protein file:BACSU/spoVD/spoVD-deep-research-falcon.md SpoVD accumulates at the outer forespore membrane during the defined window of cortex synthesis (T2.5–T4.5) |
| GO:0008658 penicillin binding | IBA GO_REF:0000033 | ACCEPT | Summary: SpoVD is a sporulation-specific penicillin-binding protein. The original characterization by Daniel et al. 1994 demonstrated penicillin-binding activity. UniProt describes it as "Sporulation-specific penicillin-binding protein" and it belongs to the transpeptidase family with the characteristic beta-lactam binding domain (InterPro IPR001460). Reason: Core molecular function of SpoVD. Penicillin binding is experimentally demonstrated and consistent with the transpeptidase domain architecture. This is a defining feature of class B PBPs like SpoVD. Supporting Evidence: PMID:8289242 Expression of spoVD in E. coli leads to the synthesis of a membrane-associated protein of the size expected for SpoVD, which can bind labelled penicillin UniProt:Q03524 Sporulation-specific penicillin-binding protein |
| GO:0071555 cell wall organization | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: SpoVD participates in peptidoglycan crosslinking during spore cortex assembly. While technically involved in cell wall organization, this term is too general and does not capture the sporulation-specific nature of SpoVD function. SpoVD specifically organizes the spore cortex peptidoglycan, not vegetative cell wall. Reason: While SpoVD does organize peptidoglycan (a cell wall component), this term is overly broad. The term fails to distinguish between vegetative cell wall organization (which SpoVD does NOT participate in) and sporulation-specific cortex organization. More specific terms like GO:0009252 (peptidoglycan biosynthetic process) in the context of GO:0030435 (sporulation) better capture the function. Keeping as non-core since it is not incorrect but lacks specificity. Supporting Evidence: file:BACSU/spoVD/spoVD-deep-research-falcon.md SpoVD is a D,D‑transpeptidase that cross-links peptide stems in the nascent cortex PG |
| GO:0004180 carboxypeptidase activity | IEA GO_REF:0000043 | KEEP AS NON CORE | Summary: This annotation derives from UniProtKB keyword mapping. The EC number 3.4.16.4 (serine-type D-Ala-D-Ala carboxypeptidase) is assigned to SpoVD, but the primary function is as a D,D-transpeptidase for peptidoglycan crosslinking. The carboxypeptidase activity is secondary to the transpeptidase function. Reason: GO:0004180 is too general. The more specific term GO:0009002 (serine-type D-Ala-D-Ala carboxypeptidase activity) is also present in the annotation set and is more appropriate. The primary catalytic function is transpeptidation for crosslinking, with carboxypeptidase activity being mechanistically related but secondary. Retaining as non-core since technically correct but redundant with more specific annotation. Supporting Evidence: UniProt:Q03524 Reaction=Preferential cleavage: (Ac)2-L-Lys-D-Ala-|-D-Ala. Also transpeptidation of peptidyl-alanyl moieties that are N-acyl substituents of D-alanine |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Duplicate annotation of GO:0005886 (plasma membrane) with different evidence code. This IEA annotation is based on UniProtKB subcellular location vocabulary mapping. The IBA annotation with the same GO term is already present and reviewed above. Reason: Duplicate of the IBA annotation for plasma membrane. Both annotations are correct - SpoVD is membrane-associated. The IEA provides independent computational support for the IBA phylogenetic inference. Duplicates with different evidence codes are acceptable in GO. Supporting Evidence: UniProt:Q03524 Cell membrane {ECO:0000269|PubMed:8289242}; Peripheral membrane protein |
| GO:0006508 proteolysis | IEA GO_REF:0000043 | MARK AS OVER ANNOTATED | Summary: This annotation derives from the "Protease" keyword in UniProt. While SpoVD has peptidase-like activity (cleaving D-Ala-D-Ala bonds), calling it "proteolysis" is misleading. SpoVD is a transpeptidase that crosslinks peptidoglycan peptide stems - its primary function is transpeptidation, not protein degradation. The substrate is peptidoglycan precursors, not proteins. Reason: Proteolysis implies protein degradation, which is not SpoVD's function. SpoVD cleaves D-Ala-D-Ala bonds in peptidoglycan precursors as part of transpeptidation, not to degrade proteins. This annotation is technically derived from the EC 3.4.16.4 classification but creates a misleading impression of the biological function. The term is too general and potentially misleading for a peptidoglycan transpeptidase. Supporting Evidence: file:BACSU/spoVD/spoVD-deep-research-falcon.md SpoVD is a D,D‑transpeptidase that cross-links peptide stems in the nascent cortex PG |
| GO:0008233 peptidase activity | IEA GO_REF:0000043 | KEEP AS NON CORE | Summary: General peptidase activity annotation from UniProt keyword mapping. SpoVD does have peptidase activity (cleaving D-Ala-D-Ala bonds), but this is in service of transpeptidation for peptidoglycan crosslinking, not general peptidase function. Reason: This is a very general parent term. The more specific GO:0009002 (serine-type D-Ala-D-Ala carboxypeptidase activity) is already annotated and more informative. Keeping as non-core since the term is not incorrect - SpoVD does have peptidase activity - but it is too general to be useful and is redundant with the more specific child term. Supporting Evidence: UniProt:Q03524 Belongs to the transpeptidase family |
| GO:0008360 regulation of cell shape | IEA GO_REF:0000043 | REMOVE | Summary: This annotation derives from the "Cell shape" keyword in UniProt. However, this annotation is INCORRECT for SpoVD. SpoVD is a sporulation-specific PBP that functions ONLY during spore cortex assembly. It does NOT participate in vegetative cell shape determination. Unlike MrdA (elongasome, determines rod shape) or FtsI (divisome, determines septum shape), SpoVD is dedicated exclusively to sporulation and has no role in vegetative cell morphology. Reason: SpoVD does not regulate vegetative cell shape. The "Cell shape" keyword in UniProt is erroneously applied based on homology to other PBPs (like MrdA/PBP2 and FtsI/PBP3) that do regulate cell shape. However, SpoVD is sporulation-specific and is expressed only in the mother cell during Stage V sporulation. It synthesizes spore cortex peptidoglycan, not vegetative cell wall. The disruption phenotype is asporogenous (no cortex, heat-sensitive spores), not cell shape defects. This represents an over-generalization from the PBP family. Supporting Evidence: PMID:8289242 insertional disruption of the spoVD gene has no effect on vegetative growth or division PMID:8289242 spoVD seems instead to have a specialized role in the morphogenesis of the spore cortex UniProt:Q03524 Asporogeneous; spore development starts but does not develop the spore cortex |
| GO:0008658 penicillin binding | IEA GO_REF:0000002 | ACCEPT | Summary: Duplicate annotation of GO:0008658 (penicillin binding) from InterPro mapping. The IBA annotation for the same term is already present and reviewed above. Reason: Duplicate of the IBA annotation for penicillin binding. Both are correct - SpoVD is a penicillin-binding protein. The IEA from InterPro domain mapping provides independent computational support. Duplicates with different evidence sources are acceptable. Supporting Evidence: UniProt:Q03524 Sporulation-specific penicillin-binding protein |
| GO:0009002 serine-type D-Ala-D-Ala carboxypeptidase activity | IEA GO_REF:0000003 | ACCEPT | Summary: This annotation derives from EC number mapping (EC 3.4.16.4). UniProt assigns this EC to SpoVD based on the catalytic mechanism. The enzyme cleaves D-Ala-D-Ala bonds via a serine active site as part of the transpeptidation reaction for peptidoglycan crosslinking. Reason: This is the most specific molecular function term for the enzymatic activity. While the PRIMARY function is transpeptidation (crosslinking), the mechanism involves D-Ala-D-Ala cleavage via a serine active site. This term accurately captures the catalytic mechanism. Note that there is no GO term for "peptidoglycan D,D-transpeptidase activity" (only L,D exists as GO:0071972), so this carboxypeptidase term is the best available approximation. Supporting Evidence: UniProt:Q03524 Reaction=Preferential cleavage: (Ac)2-L-Lys-D-Ala-|-D-Ala. Also transpeptidation of peptidyl-alanyl moieties that are N-acyl substituents of D-alanine file:BACSU/spoVD/spoVD-deep-research-falcon.md catalytic mutants abolish heat-resistant spore formation, demonstrating transpeptidase activity is essential for cortex assembly |
| GO:0009252 peptidoglycan biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: SpoVD participates in peptidoglycan biosynthesis, specifically the crosslinking step during spore cortex assembly. UniProt pathway annotation confirms involvement in peptidoglycan biosynthesis. The annotation is correct but does not specify that this is sporulation-specific cortex peptidoglycan. Reason: Core biological process for SpoVD. The protein is essential for crosslinking peptidoglycan during spore cortex synthesis. While this term does not capture the sporulation-specific context, it accurately describes the biochemical process. Combined with GO:0030435 (sporulation), this provides appropriate functional annotation. Supporting Evidence: UniProt:Q03524 Cell wall biogenesis; peptidoglycan biosynthesis file:BACSU/spoVD/spoVD-deep-research-falcon.md SpoVD is a D,D‑transpeptidase that cross-links peptide stems in the nascent cortex PG |
| GO:0016787 hydrolase activity | IEA GO_REF:0000043 | KEEP AS NON CORE | Summary: Very general parent term annotation from UniProt keyword mapping. SpoVD does have hydrolase activity (cleaving D-Ala-D-Ala bonds), but this is a highly non-specific annotation that provides little functional information. Reason: This is an extremely general term that is technically correct but uninformative. The more specific GO:0009002 (serine-type D-Ala-D-Ala carboxypeptidase activity) is already annotated. Retaining as non-core since it is not incorrect, but it adds no functional insight beyond what the more specific child terms provide. Supporting Evidence: UniProt:Q03524 Carboxypeptidase; Cell membrane; Cell shape; Cell wall biogenesis/degradation; Hydrolase |
| GO:0030435 sporulation resulting in formation of a cellular spore | IEA GO_REF:0000043 | ACCEPT | Summary: SpoVD is essential for sporulation, specifically Stage V (cortex synthesis). The gene name "spoVD" indicates Stage V sporulation involvement. Disruption results in asporogenous phenotype with failure to form spore cortex and loss of heat resistance. Reason: This is the CORE biological process for SpoVD. The protein is specifically expressed during sporulation, functions exclusively in spore cortex assembly, and is essential for forming heat-resistant spores. This annotation correctly captures the primary biological context. Supporting Evidence: PMID:8289242 spoVD seems instead to have a specialized role in the morphogenesis of the spore cortex, which is a modified form of peptidoglycan UniProt:Q03524 Asporogeneous; spore development starts but does not develop the spore cortex file:BACSU/spoVD/spoVD-deep-research-falcon.md SpoVD accumulates at the outer forespore membrane during the defined window of cortex synthesis |
| GO:0071555 cell wall organization | IEA GO_REF:0000043 | KEEP AS NON CORE | Summary: Duplicate annotation of GO:0071555 (cell wall organization) from UniProt keyword mapping. The IBA annotation for the same term is already reviewed above. Reason: Duplicate of the IBA annotation. Same considerations apply - the term is technically correct but overly broad and does not distinguish sporulation-specific cortex organization from vegetative cell wall organization. Keeping as non-core for consistency with the IBA review. Supporting Evidence: UniProt:Q03524 Cell wall biogenesis; peptidoglycan biosynthesis |
| GO:0034301 endospore formation | TAS PMID:8289242 The Bacillus subtilis spoVD gene encodes a mother-cell-speci... | NEW | Summary: SpoVD is specifically required for bacterial endospore formation. This term is more specific than GO:0030435 (sporulation resulting in formation of a cellular spore) and captures the bacterial endospore context explicitly. Reason: GO:0034301 (endospore formation) is more specific than GO:0030435 for B. subtilis sporulation. SpoVD is essential for endospore cortex assembly, and this term explicitly captures the bacterial endospore biology. Multiple lines of evidence from Daniel et al. 1994 support this annotation. Supporting Evidence: PMID:8289242 spoVD seems instead to have a specialized role in the morphogenesis of the spore cortex file:BACSU/spoVD/spoVD-deep-research-falcon.md catalytic mutants abolish heat-resistant spore formation, demonstrating transpeptidase activity is essential for cortex assembly |
| GO:0043594 outer endospore membrane | IDA PMID:20417640 Interactions between late-acting proteins required for pepti... | NEW | Summary: SpoVD localizes to the outer forespore membrane during cortex synthesis. Fay et al. 2010 demonstrated this localization using GFP-SpoVD fusion with quantitative fluorescence microscopy. Reason: More specific cellular component term than GO:0005886 (plasma membrane). SpoVD specifically localizes to the outer forespore membrane (equivalent to outer endospore membrane during cortex synthesis) where it synthesizes cortex peptidoglycan. This is experimentally demonstrated with quantitative microscopy. Supporting Evidence: file:BACSU/spoVD/spoVD-deep-research-falcon.md SpoVD localizes to the outer forespore membrane during cortex synthesis (GFP-SpoVD forespore/mother-cell ratio ~3.27 ± 0.76) file:BACSU/spoVD/spoVD-deep-research-falcon.md SpoVD accumulates at the outer forespore membrane during the defined window of cortex synthesis (T2.5–T4.5) PMID:20417640 2010 Apr 24. Interactions between late-acting proteins required for peptidoglycan synthesis during sporulation. |
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Download this section (compressed HTML)Q: What is the functional significance of the PASTA domain in SpoVD, and does it contribute to substrate recognition or localization during cortex synthesis?
Q: Are there any conditions under which SpoVD might contribute to vegetative cell wall synthesis, or is its function strictly limited to sporulation?
Experiment: Generate PASTA domain deletion mutants of SpoVD and assess localization using GFP fusions and cortex formation by electron microscopy and heat resistance assays.
Hypothesis: The PASTA domain of SpoVD is required for proper localization to the outer forespore membrane or for substrate recognition during cortex synthesis.
Type: genetic/microscopy
Experiment: Purify recombinant SpoVD and test for transpeptidase activity using synthetic peptidoglycan precursor substrates, monitoring crosslink formation by mass spectrometry.
Hypothesis: SpoVD has D,D-transpeptidase activity that can be demonstrated biochemically.
Type: biochemical
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