CdvB (Saci_1373) is the founding ESCRT-III homolog of the Cdv cell division machinery of the crenarchaeon Sulfolobus acidocaldarius, encoded in the cdvA-cdvB-cdvC operon together with the membrane-binding CdvA and the Vps4-like AAA+ ATPase CdvC. It is a 261-residue protein with a canonical ESCRT-III core, a short N-terminal amphipathic helix, a C-terminal MIT-interacting motif (residues 183-193) that binds the MIT domain of CdvC/Vps4, and a C-terminal winged-helix-like domain that binds CdvA. CdvB is expressed at the onset of division and, recruited by CdvA, assembles into a single narrow polymeric ring at the mid-cell division plane between the segregated nucleoids. This ring acts as a template on which the ESCRT-III paralogs CdvB1 and CdvB2 assemble into a composite division ring, while holding that ring in a non-constricted state. Division is then triggered when CdvB is removed from the ring by Vps4/CdvC and degraded by the PAN-20S proteasome, a step that depends on its C-terminal broken-winged helix and lets the CdvB1:CdvB2 polymers constrict and cut the cell in two. CdvB is essential in S. acidocaldarius.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0009295 nucleoid | IEA GO_REF:0000044 | MODIFY | Summary: Electronic mapping of the UniProt subcellular-location line "Cytoplasm, nucleoid" (SL-0187) for CdvB. The experimental observations behind that line (PMID:18987308, PMID:19008417) place CdvB in a band or ring between the two segregating nucleoids at the site of membrane ingression, i.e. at the mid-cell division plane, not within the nucleoid. Reason: The localization claim is wrong as encoded. The UniProt note itself says CdvB forms band-like structures between segregating nucleoids and localizes to the mid-cell in dividing cells; the controlled SubCell value "nucleoid" mis-encodes "between nucleoids", and the GO_REF:0000044 mapping propagated that to GO:0009295. Immunostaining and super-resolution imaging show a single narrow CdvB ring at the cell centre, correlating with the site of membrane ingression (PMID:19008417, PMID:36921039). The correct location is the division plane, GO:0032153 cell division site. This is a lateral correction, not a refinement, so the replacement is not a descendant of nucleoid. Proposed replacements: cell division site Supporting Evidence: file:SULAC/cdvB/cdvB-uniprot.txt Forms, with CdvA, colocalized band-like structures between segregating nucleoids file:SULAC/cdvB/cdvB-uniprot.txt Localizes to the mid-cell in dividing cells PMID:19008417 a band or belt of Saci1373 (ESCRT-III) was detected between the two nucleoids, correlating with the site of membrane ingression PMID:36921039 CdvB was found to localize into a single narrow ring positioned at the center of control cells |
| GO:0061639 Cdv-dependent cytokinesis | IDA PMID:32764038 The proteasome controls ESCRT-III-mediated cell division in ... | NEW | Summary: CdvB is the first ESCRT-III protein to assemble at the division site, forms the ring that templates the assembly of the contractile CdvB1:CdvB2 copolymer, and its Vps4-dependent removal and proteasomal degradation trigger ring constriction and cell division. The gene is essential. Reason: GO:0061639 was created for exactly this machinery (its definition names the Cdv proteins), and the parent GO:0000910 cytokinesis states that prokaryotes should be annotated to FtsZ-dependent or Cdv-dependent cytokinesis rather than to the parent. Participation test: CdvB does part of the work of the process as the structural template/scaffold of the division ring (CdvB1 and CdvB2 do not form division polymers without it), not merely as a proteasome substrate. Comparator check (QuickGO, 2026-10-15): GO:0061639 has no annotations to any gene product, so no other Cdv protein (CdvA, CdvC, CdvB1, CdvB2) carries it either; since the term was coined for these proteins, the absence reflects missing experimental curation of archaeal Cdv proteins rather than a convention against annotating them. Evidence is direct: localization to the division ring, ring templating and the degradation-triggered constriction (PMID:32764038, PMID:36921039, PMID:19008417). Supporting Evidence: PMID:32764038 CdvB both templates the assembly of a contractile ESCRT-III copolymer, composed of the paralogs CdvB1 (Saci_0451) and CdvB2 (Saci_1416), and prevents their constriction PMID:32764038 The absence of large polymeric CdvB1:CdvB2 structures in these early G1 cells implies that CdvB1 and CdvB2 do not form de novo ESCRT-III filaments without a CdvB template. PMID:32764038 Previous studies have suggested that CdvB, an essential gene in S. acidocaldarius, is actively required for division PMID:19008417 The highly specific localisation of these proteins to the mid-cell in dividing cells suggested a role in cell division-related processes. PMID:41514146 The loss of CdvB from the division ring frees CdvB1/B2 polymers to constrict and drive cytokinesis |
| GO:0000815 ESCRT III complex | IDA PMID:36921039 The patterned assembly and stepwise Vps4-mediated disassembl... | NEW | Summary: CdvB is a bona fide ESCRT-III fold protein that co-assembles with its paralogs CdvB1 and CdvB2 into a patterned composite ESCRT-III division ring, which is disassembled stepwise by Vps4/CdvC. Reason: The GO:0000815 definition is not endosome-specific: it describes a membrane remodelling/scission complex acting in several processes including cytokinetic abscission, so it applies to the archaeal ESCRT-III division polymer without importing eukaryotic compartment semantics. Structural (PMID:41543908) and imaging (PMID:36921039, PMID:32764038) data show CdvB is an ESCRT-III protein that forms a composite polymer with CdvB1 and CdvB2 and is a Vps4 substrate within it. This is a component annotation, distinct from the endosome/MVB/vacuole process terms that should not be transferred to archaea. Supporting Evidence: PMID:36921039 CdvB, CdvB1, and CdvB2 assemble at spatially distinct positions relative to one another at the cell midzone to generate a prepatterned composite division ring PMID:36921039 This is consistent with the notion that MIM2-dependent removal of CdvB from the ESCRT-III copolymer ring by Vps4 is a prerequisite for its subsequent proteasomal degradation PMID:41543908 Monomeric CdvB adopts the canonical ESCRT-III fold in both a closed and a distinct |
| GO:0005198 structural molecule activity | IDA PMID:32764038 The proteasome controls ESCRT-III-mediated cell division in ... | NEW | Summary: CdvB polymerizes into the ring that serves as the structural template for assembly of the CdvB1:CdvB2 contractile copolymer. Reason: CdvB has no enzymatic activity; its molecular contribution is structural. It forms the first ESCRT-III polymer at the division site and CdvB1/CdvB2 do not form division polymers without it (PMID:32764038). No more specific GO molecular function captures "template for a contractile polymer" (GO:0140489 molecular template activity refers to copying shape or sequence and does not fit). GO:0180020 membrane bending activity is not proposed because CdvB alone did not deform liposomes (PMID:21255729) and constriction in vivo is performed by CdvB1 and CdvB2. Supporting Evidence: PMID:32764038 The absence of large polymeric CdvB1:CdvB2 structures in these early G1 cells implies that CdvB1 and CdvB2 do not form de novo ESCRT-III filaments without a CdvB template. PMID:21255729 In contrast, when ESCRT-III is added on its own, no substantial deformation of the liposomes is observed. |
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Download this section (compressed HTML)Q: Does CdvB bind archaeal membranes on its own (N-terminal amphipathic helix, PMID:41543908) or only when recruited by CdvA (PMID:21255729), and does the answer differ between monomer and polymer?
Q: Should GO capture CdvB's role of holding the CdvB1:CdvB2 ring in a non-constricted state until its degradation (a negative regulatory role within Cdv-dependent cytokinesis), or is it adequately covered by participation in the process?
Q: Should the InterPro2GO mapping of IPR005024 (Snf7 family) to GO:0007034 vacuolar transport be taxon-restricted to Eukaryota, given that it is applied to dozens of archaeal ESCRT-III/CdvB homologs in cells with no vacuole?
Experiment: Liposome co-sedimentation of CdvB and CdvB lacking its N-terminal amphipathic helix, with and without CdvA, in the same buffer and lipid conditions, to resolve the conflicting membrane-binding results.
Type: in vitro reconstitution
Experiment: Express a non-degradable but Vps4-extractable CdvB variant in S. acidocaldarius and image the CdvB1/CdvB2 rings, to separate the roles of Vps4 extraction and proteasomal degradation in triggering constriction.
Type: live-cell imaging of mutant strains
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