Msed_1695 encodes a 221-residue ESCRT-III-family (Snf7-domain) protein of the thermoacidophilic crenarchaeon Metallosphaera sedula. It is the ortholog of Sulfolobus acidocaldarius CdvB2 (Saci_1416): it belongs to the CdvB1/CdvB2 family of archaeal ESCRT-III proteins, is the reciprocal best hit of S. acidocaldarius CdvB2, and lies in the conserved cdvB2 gene neighbourhood, while its close paralog Msed_2179 is CdvB1. The protein has not been studied directly. By orthology it is expected to act in the Cdv cell-division machinery of the Sulfolobales. There, CdvB2 is recruited with CdvB1 onto a template ring of CdvB at mid-cell. After CdvB is degraded, CdvB2 forms part of the constricting ESCRT-III polymer that keeps the ring centred, coats the narrowing membrane bridge and, when disassembled by the AAA+ ATPase Vps4/CdvC, allows membrane scission between the daughter cells. In S. acidocaldarius, CdvB2 binds archaeal membranes through short N-terminal amphipathic helices and forms helical filaments.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0007034 vacuolar transport | IEA GO_REF:0000002 | REMOVE | Summary: Electronic InterPro2GO transfer from the Snf7 family (IPR005024, Pfam PF03357) to vacuolar transport. Msed_1695 is an archaeal ESCRT-III protein, the M. sedula ortholog of S. acidocaldarius CdvB2, whose known role is in Cdv-dependent cell division. Archaea have no vacuole. Reason: The mapping encodes the eukaryotic ESCRT-III role in multivesicular body sorting and transport to the vacuole/lysosome. M. sedula, like all archaea, has no vacuole or endosomal system, so the process cannot occur, and no data link this protein or any archaeal ESCRT-III protein to vacuolar transport. The archaeal ESCRT-III CdvB1/CdvB2 proteins act in cell division (PMID:32764038, PMID:32502411, PMID:36921039). This is not a MODIFY: transport into or within a vacuole is a different process from cytokinesis, not a less specific term for it, so the division process is proposed separately as a NEW row. The same InterPro2GO mapping puts GO:0007034 on 41 archaeal ESCRT-III homologs (QuickGO, 2026-10-15); in M. sedula it hits only Msed_1695 because only this paralog also matches the Pfam Snf7 model. Restricting the IPR005024 to GO:0007034 mapping to Eukaryota would fix the whole set. Supporting Evidence: file:METS5/Msed_1695/Msed_1695-uniprot.txt NCBIfam; NF041005; cell_div_CdvB1_B2; 1. 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 file:METS5/Msed_1695/Msed_1695-bioinformatics/RESULTS.md Msed_1695 is the CdvB2 ortholog of M. sedula |
| GO:0061639 Cdv-dependent cytokinesis | ISS PMID:32502411 Live Imaging of a Hyperthermophilic Archaeon Reveals Distinc... | NEW | Summary: Orthology-based inference from S. acidocaldarius CdvB2 (Saci_1416, Q4J8Y4), whose role as a subunit of the constricting ESCRT-III division ring is shown by deletion and rescue, imaging and structural work. Msed_1695 has not been tested directly. Reason: Orthology: Msed_1695 is in the CdvB1/CdvB2 family (NCBIfam NF041005), is 64.8% identical to and the reciprocal best hit of S. acidocaldarius CdvB2, and shares five neighbouring-gene arCOGs with the cdvB2 locus and none with cdvB1. Its sister paralog Msed_2179 has been independently named M. sedula CdvB1 (PMID:35238034). Participation: in S. acidocaldarius, CdvB2 does part of the work of the process. It is a structural subunit of the contractile ESCRT-III ring, keeps the ring centred during constriction, coats the membrane bridge, and its Vps4-dependent disassembly is linked to scission (PMID:32502411, PMID:36921039). It is not merely required or a substrate. GO:0061639 was coined for the Cdv machinery, and GO:0000910 cytokinesis directs prokaryotic annotation to it. Comparator check (QuickGO, 2026-10-15): GO:0061639 has no annotations on any gene product, including the experimentally studied S. acidocaldarius CdvB, CdvB1 and CdvB2. This reflects the lack of any GO curation of archaeal Cdv proteins, not a convention against annotating them. Evidence is ISS from Q4J8Y4. No M. sedula experiment exists for this protein. Supporting Evidence: PMID:32502411 These data suggested that CdvB2 is recruited (along with CdvB1) to the correct position at the cell center by the CdvB ring and functions, following the loss of CdvB, to prevent the division ring from slipping as it constricts. PMID:36921039 membrane scission depends on disassembly of polymeric CdvB2 from the cytokinetic bridge PMID:35238034 The gene for CdvB1 from Metallosphaera sedula (Msed_2179, UniProtID A4YIR6) was obtained from the Gen Bank database file:METS5/Msed_1695/Msed_1695-bioinformatics/RESULTS.md Msed_1695 is the CdvB2 ortholog of M. sedula |
Loading supporting content…
Download this section (compressed HTML)Q: Should the InterPro2GO mapping of IPR005024 (Snf7 family) to GO:0007034 vacuolar transport be restricted to Eukaryota? It currently places vacuolar transport on 41 archaeal ESCRT-III homologs, and within one genome it hits CdvB1/B2 paralogs inconsistently depending on whether the Pfam Snf7 model matches.
Q: Does M. sedula CdvB2 (Msed_1695) share the S. acidocaldarius CdvB2 role in keeping the division ring centred, or have the CdvB1 and CdvB2 roles been partitioned differently in Metallosphaera?
Experiment: Immunolocalize or tag Msed_1695 in M. sedula cells, together with CdvB (Msed_1671) and CdvB1 (Msed_2179), to test whether it forms a mid-cell ring that follows the CdvB template ring and persists during constriction.
Type: immunofluorescence microscopy
Experiment: Purify Msed_1695 and test liposome binding, filament formation and depolymerization by M. sedula CdvC, in parallel with the published M. sedula CdvB1 assays.
Type: in vitro reconstitution
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)