qmoB

UniProt ID: Q72DT0
Organism: Nitratidesulfovibrio vulgaris (Desulfovibrio vulgaris Hildenborough)
Review Status: COMPLETE
📝 Provide Detailed Feedback

Gene Description

QmoB (DVU_0849) is subunit B of the quinone-interacting membrane-bound oxidoreductase (QmoABC) complex of Desulfovibrio vulgaris Hildenborough, encoded in the aprBA-qmoABC gene cluster (DVU_0846-DVU_0850). It is a soluble iron-sulfur flavoprotein of the HdrA family that, with QmoA, forms the cytoplasmic part of the complex; the membrane subunit QmoC exchanges electrons with the menaquinone pool. Its HdrA-like region contains an FAD-binding domain and a ferredoxin-type insert with two 4Fe-4S cysteine motifs, and it carries a C-terminal MvhD/FlpD-like domain, homologous to the [2Fe-2S] subunit of methanogen Mvh hydrogenase. The QmoABC complex is required for growth with sulfate as terminal electron acceptor and is proposed to supply electrons to adenylylsulfate (APS) reductase AprAB in dissimilatory sulfate reduction, possibly by flavin-based electron confurcation. The specific partner and reaction of QmoB within this process are not yet established.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0016491 oxidoreductase activity
IEA
GO_REF:0000120 		ACCEPT
Summary: Automated oxidoreductase activity. QmoB is an HdrA-family iron-sulfur flavoprotein subunit of the QmoABC electron-transfer complex.
Reason: Supported by the FAD/NAD-binding domain (IPR023753) and HdrA-like architecture. The general term is accurate; the specific reaction of QmoB is unknown, so no more specific child term is justified.
Supporting Evidence:
DOI:10.3389/fmicb.2012.00137
QmoA and QmoB are both soluble iron–sulfur
DOI:10.3389/fmicb.2024.1336360
Quinone oxidoreductase, QmoABC complex, subunit B QmoB Q72DT0 DVU_0849
GO:0046872 metal ion binding
IEA
GO_REF:0000043 		ACCEPT
Summary: Keyword-mapped metal ion binding, reflecting the iron of the protein's iron-sulfur clusters.
Reason: Correct but less informative than the 4Fe-4S cluster binding annotation.
Supporting Evidence:
DOI:10.3389/fmicb.2012.00137
QmoA and QmoB are both soluble iron–sulfur
GO:0051536 iron-sulfur cluster binding
IEA
GO_REF:0000043 		ACCEPT
Summary: Keyword-mapped iron-sulfur cluster binding.
Reason: QmoB is an iron-sulfur flavoprotein; UniProt calls two PROSITE 4Fe-4S ferredoxin-type domains (542-571, 572-601) in its HdrA-like region.
Supporting Evidence:
DOI:10.3389/fmicb.2012.00137
QmoA and QmoB are both soluble iron–sulfur
GO:0051539 4 iron, 4 sulfur cluster binding
IEA
GO_REF:0000043 		ACCEPT
Summary: Keyword-mapped 4Fe-4S cluster binding (UniProt KW 4Fe-4S, ARBA rule), consistent with a ferredoxin-type dicluster motif pair in the HdrA-like region.
Reason: The cluster type rests on sequence motifs and family inference, not on a characterized site: the Qmo literature says only that the complex carries "several iron-sulfur centers". The motifs are nonetheless specific. InterPro places the two PS51379 domains (542-571, 572-601) and a Pfam Fer4_9 4Fe-4S dicluster domain (550-595) inside the HdrA-like region (IPR039650, 216-640), N-terminal to the MvhD/FlpD domain (PF02662, 626-747). Each domain carries a complete CxxCxxCxxxC motif matching the PS00198 4Fe-4S ferredoxin signature (C551/C554/C557/C561 and C581/C584/C587/C591), the ligand set of a bacterial 2x[4Fe-4S] ferredoxin. The MvhD-like domain, which Ramos et al. relate to the [2Fe-2S] subunit MvhD, is a separate segment. It may carry an additional [2Fe-2S] cluster, but none is annotated and no such term is proposed.
Supporting Evidence:
DOI:10.3389/fmicb.2012.00137
two FAD groups and several iron–sulfur centers
GO:0005515 protein binding
IPI
PMID:26873250
Bacterial Interactomes: Interacting Protein Partners Share S... 		MODIFY
Summary: AP-MS interactome of D. vulgaris; interaction of QmoB (DVU_0849) with Q72DS8 (DVU_0851), the small protein encoded immediately downstream of qmoC and referred to as QmoD.
Reason: The interaction is consistent with Q72DS8 being a fourth Qmo-associated subunit: a blue-native PAGE band from D. vulgaris membranes contained all four Qmo subunits. "Protein binding" is uninformative; the functional content is QmoB's electron-transfer role within the Qmo complex.
Proposed replacements: electron transfer activity
Supporting Evidence:
PMID:26873250
459 high confidence PPIs from D. vulgaris
PMID:23842468
a unique band was observed that contained all four Qmo subunits
DOI:10.3389/fmicb.2024.1336360
Quinone oxidoreductase, QmoABC complex, hypothetical protein QmoD Q72DS8 DVU_0851
GO:0005515 protein binding
IPI
PMID:26873250
Bacterial Interactomes: Interacting Protein Partners Share S... 		MODIFY
Summary: AP-MS interactome of D. vulgaris; interaction of QmoB (DVU_0849) with QmoA (Q72DT1, DVU_0848).
Reason: QmoA and QmoB are the two cytoplasmic subunits of the QmoABC complex, so this interaction reflects complex membership. "Protein binding" is uninformative.
Proposed replacements: electron transfer activity
Supporting Evidence:
PMID:26873250
459 high confidence PPIs from D. vulgaris
DOI:10.3389/fmicb.2012.00137
The QmoABC complex has one membrane (QmoC) and two cytoplasmic subunits (QmoAB)
GO:0005515 protein binding
IPI
PMID:27099342
Quantitative Tagless Copurification: A Method to Validate an... 		MODIFY
Summary: Tagless copurification independently supports the QmoB - Q72DS8 (QmoD, DVU_0851) association.
Reason: Orthogonal support for Qmo complex membership; "protein binding" remains uninformative.
Proposed replacements: electron transfer activity
Supporting Evidence:
PMID:27099342
200 high confidence D. vulgaris PPIs based on tagless copurification and colocalization in the genome
PMID:23842468
a unique band was observed that contained all four Qmo subunits
GO:0005515 protein binding
IPI
PMID:27099342
Quantitative Tagless Copurification: A Method to Validate an... 		MODIFY
Summary: Tagless copurification independently supports the QmoB - QmoA association.
Reason: Orthogonal support for QmoABC complex membership; "protein binding" remains uninformative.
Proposed replacements: electron transfer activity
Supporting Evidence:
PMID:27099342
200 high confidence D. vulgaris PPIs based on tagless copurification and colocalization in the genome
PMID:23842468
co-purification of QmoA/B and AprA/B from affinity-tagged D. vulgaris Hildenborough strains (AprA, QmoA and QmoB)
GO:0050660 flavin adenine dinucleotide binding
TAS
DOI:10.3389/fmicb.2012.00137 		NEW
Summary: QmoB is an HdrA-family flavoprotein; UniProt lists FAD as cofactor (ARBA) and the QmoABC complex binds two FAD groups, carried by its two HdrA-like subunits.
Reason: FAD binding is not in GOA although UniProt assigns the FAD cofactor. The Qmo literature describes QmoB as a flavoprotein and the complex as containing two FAD groups. Evidence code TAS because this is an author statement in a primary Qmo paper rather than a QmoB-specific cofactor assay.
Supporting Evidence:
DOI:10.3389/fmicb.2012.00137
two FAD groups and several iron–sulfur centers
DOI:10.3389/fmicb.2012.00137
QmoA and QmoB are both soluble iron–sulfur
GO:0019420 dissimilatory sulfate reduction
TAS
DOI:10.3389/fmicb.2012.00137 		NEW
Summary: QmoB is a redox subunit of the QmoABC complex, which is required for growth with sulfate as electron acceptor and is proposed to supply electrons to APS reductase.
Reason: QmoB is a cofactor-carrying subunit of the complex that does the electron delivery step to AprAB, so this is participation rather than mere necessity. Earlier versions of this row cited a thesis about the FlxABCD-HdrABC complex (DVU_2399-DVU_2405), a different locus; that basis was invalid and has been replaced. TAS because the qmoABC deletion phenotype (Zane et al. 2010) is reported via Ramos et al. 2012.
Supporting Evidence:
DOI:10.3389/fmicb.2012.00137
In Desulfovibrio vulgaris Hildenborough a deletion mutant of the qmoABC genes could not grow with sulfate as electron acceptor
DOI:10.3389/fmicb.2012.00137
The QmoABC complex has one membrane (QmoC) and two cytoplasmic subunits (QmoAB)

Core Functions

QmoB is a cytoplasmic HdrA-family iron-sulfur flavoprotein subunit of the QmoABC complex, which transfers electrons between the menaquinone pool and APS reductase during dissimilatory sulfate reduction. QmoB's own partner and reaction are not established; its HdrA and MvhD similarity suggests it engages an additional physiological partner, possibly in electron confurcation.

Molecular Function:
electron transfer activity
Directly Involved In:
dissimilatory sulfate reduction
Cellular Locations:
cytoplasmic side of plasma membrane
Supporting Evidence:
  • DOI:10.3389/fmicb.2012.00137
    The QmoABC complex has one membrane (QmoC) and two cytoplasmic subunits (QmoAB)
  • DOI:10.3389/fmicb.2012.00137
    In Desulfovibrio vulgaris Hildenborough a deletion mutant of the qmoABC genes could not grow with sulfate as electron acceptor

Two 4Fe-4S ferredoxin-type domains (UniProt features 542-571 and 572-601) with complete CxxCxxCxxxC ligand motifs, in the ferredoxin-type insert of the HdrA-like region rather than in the C-terminal MvhD-like domain (626-747). The cluster type is inferred from sequence, not measured.

Molecular Function:
4 iron, 4 sulfur cluster binding

HdrA-family flavoprotein; the QmoABC complex binds two FAD groups, carried by its HdrA-like subunits.

Molecular Function:
flavin adenine dinucleotide binding
Supporting Evidence:
  • DOI:10.3389/fmicb.2012.00137
    two FAD groups and several iron–sulfur centers

References

Loading supporting content…

Download this section (compressed HTML)

Suggested Questions for Experts

Q: What is the physiological partner of QmoB, suggested by its HdrA and MvhD similarity?

Q: Is QmoB (rather than QmoA) the site of flavin-based electron confurcation in the Qmo complex?

Q: What is the role of the fourth Qmo-associated protein QmoD (DVU_0851) that co-purifies with QmoB?

Q: Does the C-terminal MvhD-like domain of QmoB (residues 626-747) bind a [2Fe-2S] cluster, as its homolog MvhD does?

Suggested Experiments

Experiment: Reconstitute menaquinol-dependent APS reduction with purified QmoABC and AprAB plus candidate low-potential donors (e.g. reduced ferredoxin)

Hypothesis: APS reduction by QmoABC requires a second low-potential electron donor that interacts with QmoB

Experiment: Site-directed mutagenesis of the cysteine ligands of the two ferredoxin-type motifs of QmoB

Hypothesis: Loss of the QmoB [4Fe-4S] clusters abolishes sulfate-dependent growth without disrupting QmoABC assembly

Deep Research

Falcon

(Q72DT0-deep-research-falcon.md)

Loading supporting content…

Download this section (compressed HTML)

📄 View Raw YAML

Loading supporting content…

Download this section (compressed HTML)