formate dehydrogenase N complex

cellstructuremech:formate_dehydrogenase_n_complex · Energy complex · Multiprotein complex · Proposed

A nitrate-inducible, membrane-bound formate:quinone oxidoreductase complex whose FdnG, FdnH, and FdnI subunits oxidize formate and pass electrons to a membrane quinone during anaerobic respiration. [ComplexPortal:CPX-1975]

Synonyms: Formate dehydrogenase-N complex; FDH-N complex; FdnGHI complex; nitrate-inducible formate dehydrogenase complex; formate:quinone oxidoreductase

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Essential	Role
formate dehydrogenase-N alpha subunit	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	fdnG	ESSENTIAL	Mo-bisMGD catalytic alpha subunit of the nitrate-inducible formate dehydrogenase N complex. `ComplexPortal:CPX-1975` Complex Portal CPX-1975 curates three copies of P24183/FdnG in the E. coli K-12 formate dehydrogenase N complex.
formate dehydrogenase-N iron-sulfur subunit	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	fdnH	ESSENTIAL	Iron-sulfur electron-transfer subunit linking the FdnG catalytic subunit to the FdnI cytochrome b membrane subunit. `ComplexPortal:CPX-1975` Complex Portal CPX-1975 curates three copies of P0AAJ3/FdnH in the E. coli K-12 formate dehydrogenase N complex.
formate dehydrogenase-N cytochrome b556 subunit	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	fdnI	ESSENTIAL	Cytochrome b membrane subunit that carries the quinone-binding site. `ComplexPortal:CPX-1975` Complex Portal CPX-1975 curates three copies of P0AEK7/FdnI in the E. coli K-12 formate dehydrogenase N complex.

Organism-specific protein examples

Named proteins in which each component's role was established, with the organism the evidence comes from. The component above is the taxon-agnostic family; these are the specific entries behind it.

formate dehydrogenase-N alpha subunit

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P24183`	Formate dehydrogenase, nitrate-inducible, major subunit	fdnG	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) `UniProtKB:P24183` Reviewed Swiss-Prot entry FDNG_ECOLI is E. coli K-12 FdnG and cross-references GO:0009326 and ComplexPortal:CPX-1975.

formate dehydrogenase-N iron-sulfur subunit

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P0AAJ3`	Formate dehydrogenase, nitrate-inducible, iron-sulfur subunit	fdnH	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) `UniProtKB:P0AAJ3` Reviewed Swiss-Prot entry FDNH_ECOLI is E. coli K-12 FdnH and cross-references GO:0009326 and ComplexPortal:CPX-1975.

formate dehydrogenase-N cytochrome b556 subunit

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P0AEK7`	Formate dehydrogenase, nitrate-inducible, cytochrome b556(Fdn) subunit	fdnI	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) `UniProtKB:P0AEK7` Reviewed Swiss-Prot entry FDNI_ECOLI is E. coli K-12 FdnI and cross-references GO:0009326 and ComplexPortal:CPX-1975.

Source composition assertions

Formate dehydrogenase N complex (ComplexPortal:CPX-1975)

Escherichia coli (strain K12) (NCBITaxon:83333) · Heterononamer · ECO:0000353 · retrieved 2026-10-02

Participant	Source type	Source name	Stoichiometry
`UniProtKB:P0AEK7` — Formate dehydrogenase, nitrate-inducible, cytochrome b556(Fdn) subunit	protein	fdnI	3
`CHEBI:60539` — Mo(=O)-bis(molybdopterin guanine dinucleotide)(4-)	small molecule	mo(=o)-bis(molybdopterin guanine dinucleotide)(4-)	3
`CHEBI:16374` — menaquinone	small molecule	menaquinone	1
`UniProtKB:P24183` — Formate dehydrogenase, nitrate-inducible, major subunit	protein	fdnG	3
`UniProtKB:P0AAJ3` — Formate dehydrogenase, nitrate-inducible, iron-sulfur subunit	protein	fdnH	3
`CHEBI:30413` — heme	small molecule	heme	6
`CHEBI:33725` — tetra-mu3-sulfido-tetrairon	small molecule	fe4-s4	15

Curator-scoped import: E. coli K-12 CPX-1975 composition for the cellstructuremech:formate_dehydrogenase_n_complex formate dehydrogenase N complex. Source evidence: physical interaction evidence. The accession was resolved through the Complex Portal accession endpoint; no equivalence xref was inferred.

Canonical examples

NCBITaxon:83333 Escherichia coli K-12 — E. coli K-12 source of the CPX-1975 heterononameric FdnGHI composition with three FdnG, three FdnH, three FdnI, Mo-bisMGD, heme, 4Fe-4S, and menaquinone participants. [ComplexPortal:CPX-1975]

Functions

formate dehydrogenase (quinone) activity GO:0036397 — The FdnGHI complex oxidizes formate to carbon dioxide while reducing a membrane quinone to quinol.
- GO:0036397 GO:0036397 defines formate dehydrogenase (quinone) activity as formate plus quinone yielding CO2 plus quinol.
- PMID:11884747 Jormakka et al. 2002 solved the E. coli formate dehydrogenase-N structure and described its basis for proton-motive-force generation.

Mechanism graphs

FdnGHI couples formate oxidation to quinone reduction (FUNCTION)

The formate dehydrogenase N heterononamer oxidizes formate and transfers electrons through FdnG, FdnH, and FdnI cofactors to a membrane quinone.

Subject	Predicate	Object	Evidence
formate dehydrogenase-N alpha subunit	contributes to	formate dehydrogenase N complex	`ComplexPortal:CPX-1975` CPX-1975 curates three P24183/FdnG copies in the E. coli K-12 formate dehydrogenase N complex.
formate dehydrogenase-N iron-sulfur subunit	contributes to	formate dehydrogenase N complex	`ComplexPortal:CPX-1975` CPX-1975 curates three P0AAJ3/FdnH copies in the E. coli K-12 formate dehydrogenase N complex.
formate dehydrogenase-N cytochrome b556 subunit	contributes to	formate dehydrogenase N complex	`ComplexPortal:CPX-1975` CPX-1975 curates three P0AEK7/FdnI copies in the E. coli K-12 formate dehydrogenase N complex.
formate dehydrogenase N complex	enables	formate dehydrogenase (quinone) activity	`GO:0036397` GO:0036397 defines formate-dependent reduction of quinone to quinol.
formate	donates electrons to	formate dehydrogenase (quinone) activity	`GO:0036397` GO:0036397 records formate as the electron donor.
quinone	accepts electrons in	formate dehydrogenase (quinone) activity	`GO:0036397` GO:0036397 records a quinone as the electron acceptor that is reduced to quinol.
formate dehydrogenase (quinone) activity	produces	CO2	`GO:0036397` GO:0036397 records CO2 production from formate.
formate dehydrogenase (quinone) activity	produces	quinol	`GO:0036397` GO:0036397 records quinol production from quinone.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral families for FdnG, FdnH, and FdnI before replacing reviewed-label-only component rows. The reviewed E. coli FdnG/FdnH/FdnI entries carry multiple InterPro domain or formate-dehydrogenase-family signatures, but this new record does not assert any family as an exact source-neutral equivalent of the nitrate-inducible FdnG, FdnH, or FdnI constituents.

Evidence

ComplexPortal:CPX-1975 Complex Portal entry for the E. coli K-12 formate dehydrogenase N heterononamer.
GO:0009326 Gene Ontology parent cellular-component term for formate dehydrogenase complexes.
GO:0098803 Gene Ontology cellular-component term for respiratory-chain protein complexes.
GO:0036397 Gene Ontology molecular-function term for formate dehydrogenase (quinone) activity.
UniProtKB:P24183 Reviewed E. coli K-12 FdnG UniProtKB entry.
UniProtKB:P0AAJ3 Reviewed E. coli K-12 FdnH UniProtKB entry.
UniProtKB:P0AEK7 Reviewed E. coli K-12 FdnI UniProtKB entry.
CHEBI:60539 ChEBI identifier for the Mo-bisMGD cofactor curated in CPX-1975.
CHEBI:16374 ChEBI identifier for the menaquinone electron acceptor curated in CPX-1975.
CHEBI:30413 ChEBI identifier for the heme cofactor curated in CPX-1975.
CHEBI:33725 ChEBI identifier for the 4Fe-4S cluster curated in CPX-1975.
PMID:11884747 Jormakka et al. 2002, Molecular basis of proton motive force generation: structure of formate dehydrogenase-N.
DOI:10.1126/science.1068186 DOI for the Jormakka et al. 2002 E. coli formate dehydrogenase-N paper.
PDB:1KQF Worldwide PDB entry cross-referenced by CPX-1975 for formate dehydrogenase N structural evidence.
PDB:1KQG Worldwide PDB entry cross-referenced by CPX-1975 for formate dehydrogenase N structural evidence.

Curation history

2026-10-02T05:42:04Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-02T05:43:41Z codex · EXPANDED_RECORD — Added GO parentage, CPX-1975 synonymy, reviewed-label-only FdnG/FdnH/FdnI component rows with E. coli K-12 UniProt examples, the CPX-1975 heterononamer composition with cofactors, formate dehydrogenase (quinone) activity, literature/database evidence, a compact function graph, and a component-family grounding TODO.
2026-10-05T00:17:05Z codex · CORRECTED_METADATA — Issue #2043: preserve 4 nonprotein Complex Portal source name(s) in source_name instead of gene_symbol; identities, labels, taxa, membership and stoichiometry unchanged.

Source: data/structures/energy_complex/formate_dehydrogenase_n_complex.yaml